Embryology - User contributions [en-gb]

User:Z5015014

2016-10-28T02:06:10Z

Z5015014: /* Lab Attendance */

{{ANAT2341Student2016}}

==Lab Attendance==
[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 14:35, 5 August 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 14:40, 12 August 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:13, 19 August 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:03, 26 August 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 2 September 2016 (AEST) 

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:07, 9 September 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:03, 16 September 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:03, 7 October 2016 (AEDT)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 14 October 2016 (AEST) 

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:05, 21 October 2016 (AEDT)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:06, 28 October 2016 (AEDT)
 

==Week 1 Homework==
===Team Role===
I studied the Belbin Team Roles in a previous course and identified myself as a Teamworker, which I still definitely agree with, but I'd probably also add that I have the tendencies of a Complete Finisher. In group assignments I always prefer not to take charge and rather to provide support by facilitating discussions and encouraging good communication within the group. In the past, I've often mediated between my real life friends when conflict happens so I'm comfortable in doing that for any group situation I find myself in. I'm also very indecisive as a person and I know this reflects into any group work that I do because I find it difficult if I have to lead or make choices for the rest of the team. I would also say that because I don't particularly look forward to group assignments in the first place, because I'd much rather complete a task by myself, I can sometimes be a Complete Finisher. I know that I hesitate having to rely on other people because I worry that they won't do something the way I would have chosen to do it.

===Lecture 1: Fertilisation (2/8/16)===
I've always found fertilisation to be an exciting and interesting topic. Even though I've studied it before in previous courses I still find it so fascinating just how much goes into the 'simple' union of a sperm and an egg cell. The way that so many processes and reactions and biological design come together to allow fertilisation to happen really amazes me. But I think the most interesting thing I heard in today's lecture was about the zona pellucida and the ZP2 protein, and how it's used as a signal to attract the sperm to bind to the ovum, and then modified to prevent polyspermy by stopping additional sperm from binding. I'd never learnt about this before so it was really interesting to understand the mechanism involved.

{|
|-bgcolor="FAF5FF"
| [[User:Z8600021|Mark Hill]] ([[User talk:Z8600021|talk]]) 12:36, 5 August 2016 (AEST) Very good. maybe a little to many sub-sub-sub- headings, this will get messy. I will discuss in today's lab online formatting etc.
|}

==Lab 1 Assessment==
'''IVF culture medium affects post-natal weight in humans during the first 2 years of life.'''<ref><pubmed>24549211</pubmed></ref> 
''Sander H.M. Kleijkers, Aafke P.A. van Montfoort, Luc J.M. Smits, Wolfgang Viechtbauer, Tessa J. Roseboom, Ewka C.M. Nelissen, Edith Coonen, Josien G. Derhaag, Lobke Bastings, Inge E.L. Schreurs, Johannes L.H. Evers & John C.M. Dumoulin'' 
:In this study, Kleijkers et al. investigated the relationship between the culture media used for embryos during the process of IVF and the subsequent development of the IVF children in early life. This followed on from previous research in which it was observed that the choice of culture medium had an impact on birthweight as well as development of the fetus during pregnancy. 1432 IVF treatments were initially involved and each was randomly allocated to either grow in Cook medium or Vitrolife medium. From this, 126 embryos from the Cook group and 168 embryos from the Vitrolife group were successfully birthed and used for further study. Kleijkers et al. contacted all of the parents two years after the initial birth for records of the postnatal weight, height, and head circumference of their child over the two year period. Statistical analysis and different analytical models were used to compare the collected data. It was observed that the weight of singletons whose embryos had been cultured in Cook medium was consistently lower than that of the Vitrolife group; this confirms that the effect of culture media on fetal growth, as had been previously researched, persists in early postnatal development. Kleijkers et al. propose that these results show the sensitivity of the human embryo to its environment, whether ''in vivo'' or ''in vitro''. Hence because the chosen media for the embryo is the environment it grows in before implantation, the adaptation of this embryo to the media, possibly by epigenetic modification, is seen to have consequences for later development. This emphasises the need for further research into the growth media used for IVF treatment to ensure an optimal environment for the preimplantation growth of the embryo, and therefore both prenatal and postnatal development of an IVF child.

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 18 August 2016 - You have added the citation correctly and written a good brief summary of the article findings. You also seem to have practiced using some of the Wiki formatting tools. So the very conditions of initial growth may have long-term developmental ramifications. You can see why research in this area is important. These days we have a reasonably large IVF cohort to begin to get some useful data.

You have to be careful though when commercial products are being compared. [https://www.cookmedical.com/products/wh_sibm_webds Cook medium] | [http://www.vitrolife.com/en/Products/G-SeriesTM-media/G-IVF Vitrolife medium]
| width=100px| Assessment 5/5
|}

==Lab 2 Assessment==
[[File:Human Blastocyst with Decidualized Endometrial Stromal Cells.png|400px]] 
Human blastocyst attached to decidualized human endometrial stromal cells after 72 hours of co-culture.<ref><pubmed>22412909</pubmed></ref>

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 29 August 2016 - All information Reference, Copyright and Student Image template correctly included with the file and referenced on your page here.
| Assessment 5/5
|}

== Lab 3 Assessment ==

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 31 August 2016 - Lab 3 Assessment Quiz - [[Lecture_-_Mesoderm_Development|Mesoderm]] and [[Lecture_-_Ectoderm_Development|Ectoderm]] development. All correct, well done!

| Assessment 5/5
|}

==Lab 4 Assessment==
===Gastrointestinal Development Quiz===
<quiz display=simple>
{1. The splanchnic mesoderm does '''not''' contribute to:
|type="()"}
+ epithelium
- mesentery
- blood vessels
- smooth muscle
||The splanchnic mesoderm is involved in the development of mesentery, connective tissue, smooth muscle, and blood vessels. The endoderm contributes to development of epithelium.

{2. The correct order of blood supply for the foregut, midgut, and hindgut is:
|type="()"}
- inferior mesenteric artery, celiac artery, superior mesenteric artery
- superior mesenteric artery, inferior mesenteric artery, celiac artery
+ celiac artery, superior mesenteric artery, inferior mesenteric artery
- celiac artery, inferior mesenteric artery, superior mesenteric artery
||The foregut is supplied by the celiac artery, the midgut is supplied by the superior mesenteric artery, and the hindgut is supplied by the inferior mesenteric artery.

{3. Which of these statements is '''false'''?
|type="()"}
- The right hepatic bud will eventually form the right lobe of the liver.
- The cloaca initially forms a common urogenital and gastrointestinal space.
- Meckel's diverticulum is a common abnormality caused by failed degeneration of the vitelline duct during development.
+ The ventral mesentery is completely lost during development.
||The ventral mesentery is lost except at the level of the stomach and the liver, and will eventually contribute to the development of the lesser omentum and the falciform ligament.

{4. Which abnormality involves narrowing of the gastrointestinal tract lumen?
|type="()"}
+ stenosis
- atresia
- duplication
- gastroschisis
||Stenosis is narrowing of the GIT lumen. Atresia is interruption of the lumen, duplication is incomplete recanalisation leading to the formation of parallel lumens, and gastroschisis is an abdominal wall defect that results in herniation of the abdominal viscera into the amniotic cavity.
</quiz>

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 17 October 2016 - GIT Quiz covers a range of related topics. Question 1 identifies difference between endoderm and mesoderm origins. Question 2 is about blood supply, not a testing question as the 3 options are given in several options. Question 3 and 4 are good testing questions.
| Assessment 5/5
|}

==Lab 5 Assessment==
I completed the course review questionnaire!

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 17 October 2016 - course review questionnaire.
| Assessment 5/5
|}

==Lab 6 Assessment==
'''Meta-analysis Reveals Genome-Wide Significance at 15q13 for Nonsyndromic Clefting of Both the Lip and the Palate, and Functional Analyses Implicate GREM1 As a Plausible Causative Gene.'''<ref><pubmed>26968009</pubmed></ref> 
''Kerstin U Ludwig, Syeda Tasnim Ahmed, Anne C Böhmer, Nasim Bahram Sangani, Sheryil Varghese, Johanna Klamt, Hannah Schuenke, Pinar Gültepe, Andrea Hofmann, Michele Rubini, Khalid Ahmed Aldhorae, Regine P Steegers-Theunissen, Augusto Rojas-Martinez, Rudolf Reiter, Guntram Borck, Michael Knapp, Mitsushiro Nakatomi, Daniel Graf, Elisabeth Mangold & Heiko Peters''
:In their research, Ludwig et al. looked at findings from previous studies and confirmed that the 15q13 region is a risk locus for developing nonsyndromic cleft lip and palate (nsCL/P) but not nonsyndromic cleft lip only (nsCLO). By experimenting on mice, they also associated genetic variation in a 5 kb region downstream from the ''Gremlin-1'' (''Grem1'') transcription start site with developing nsCL/P. They observed localised expression of ''Grem1'' in the soft palate and in the processes forming the lip during mouse embryogenesis. While ''Grem1''-deficient mice did not develop lip or palate defects, the addition of ectopic Grem1 was shown to have a pathogenic effect on the morphogenesis of the palatal shelves during secondary palate development. ''Grem1'' is known to be critical for limb bud development, but not lip and palate development. Its role in limb bud development is to establish a positive feedback loop between Shh and Fgf via inhibition of Bmp signalling (a negative regulator of SHH expression in limb mesenchyme). However, previous research determined that Bmp signalling is a positive regulator of Shh expression in the palatal shelf epithelium and cell proliferation in the anterior palatal shelf mesenchyme. Bmp4 and Bmp2 are involved in the normal development of the anterior palate and Bmp4 and Bmp7 are expressed in the posterior palatal shelves. Therefore, it was concluded that an abnormality in ''Grem1'' expression could interrupt normal development of the secondary palate due to the inhibition of Bmp signalling.

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 17 October 2016 - [http://www.omim.org/entry/603054 GREM1] is a novel factor and your summary is useful and you have good to also included the signaling pathway involved.
| Assessment 5/5
|}

==Lab 7 Assessment==
Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy, affecting 1 in 3,500-5,000 newborn males globally. It is caused by recessive loss-of-function mutations in the dystrophin gene on the X chromosome.<ref name="PMID26140716"><pubmed>26140716</pubmed></ref> Frame-shift mutations in the gene lead to failed expression of the dystrophin mutation and hence the manifestation of DMD. One-third of DMD cases can occur by spontaneous mutation, meaning that a positive family history is not required for diagnosis. Physical examinations, molecular biopsies, genetic testing, and review of clinical history are all involved when diagnosing DMD. Serum creatine kinase (CK) is used as an initial diagnostic tool to measure the levels of muscle enzymes.<ref name="PMID27524897"><pubmed>27524897</pubmed></ref> DMD is defined at the molecular level as producing no dystrophin and clinically as the loss of ambulation at 12 years of age or younger.<ref name="PMID26140716"/> A less severe mutation of the dystrophin gene, such as an in-frame deletion, can instead produce a truncated version of the protein which results in Becker muscular dystrophy (BMD), a milder form of DMD.<ref name="PMID25740330"><pubmed>25740330</pubmed></ref>

Dystrophin is a major muscle protein which connects the cytoskeleton (cytoskeletal actin, microtubules, and intermediate filaments) and the extracellular matrix (ECM).<ref name="PMID25740330"/><ref name="PMID26295289"><pubmed>26295289</pubmed></ref> Dystrophin is anchored to the plasma membrane by phospholipids and β-dystroglycan. The dystrophin complex is found in costameres of skeletal and heart muscle, which are located at the periphery of the muscle fibers. Costameres are involved in transmitting forces from the cytosol to the ECM and therefore prevent the collapse of the cell membrane during muscle contraction. Hence, in DMD and BMD the impaired function of dystrophin results in frequent cell damage when the muscle contracts. The rupture of the plasma membrane causes leakage of the intracellular components; for example, creatine kinase can be released from the damaged cell which explains the high concentrations of serum creatine kinase in DMD patients.<ref name="PMID26295289"/>

The most common mutation implicated in DMD and BMD is a deletion of one or more exons, accounting for 60-70% of DMD cases and 80-85% of BMD cases. Point mutations are have been found in approxiamtely 26% of DMD cases and 13% of BMD cases, while exonic duplications are involved in 10-15% of DMD cases and 5-10% of BMD cases. Other possible mutations include subexonic insertions, deletions, splice mutations, and missense mutations.<ref name="PMID26140716"/>

Animal models used to investigate DMD and BMD include the ''mdx'' mouse and the ''grmd'' dog.<ref name="PMID26295289"/><ref name="PMID25740330"/> Due to the size of the dystrophin gene, it is difficult to treat DMD or BMD with gene therapy.<ref name="PMID27594988"><pubmed>27594988</pubmed></ref> The idea of producing a smaller version of the protein, micro-dystrophin, has been attempted, but due to its smaller size it cannot act as a perfect functional substitute for dystrophin. In the case of DMD, exon skipping therapy has been investigated as a way of altering the mutation of the dystrophin gene. Instead of the frame-shift mutation which results in no functional dystrophin being produced, the splicing of the mRNA can be modified to exclude one or more additional exons which therefore restores the reading frame and results in production of a BMD-like dystrophin (truncated, but still partly functional). This has been accomplished by introducing small antisense oligonucleotides (AONs) sequences, which bind to exon splice junctions and inhibit the action of the spliceosome.<ref name="PMID26295289"/> However, this ultimately only lessens the severity of the disease and still presents the problem of treating the BMD-like symptoms. There is still no effective cure for either DMD or BMD. Most available treatments are focused on slowing the progression of the diseases and continued research is being done into ways of converting a severe phenotype of disease to a more mild phenotype.<ref name="PMID27594988"/><ref name="PMID26140716"/>
 

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 17 October 2016 - You have answered all questions and also included the source references, well done.
| Assessment 5/5
|}

==Lab 9 Assessment==
====Group 1 Peer Review====
Great job on all the content you’ve produced as a group so far. It’s clear you guys have done a lot of research into the topic and you’ve identified key aspects of Wnt signalling. The information you have is all relevant, everything is referenced, and all your abbreviations are defined. It’s really good that you have included some specific studies and explained the findings and what they discovered about Wnt signalling. It’s great you’ve also started to look into the abnormalities so if you put some more info into that I think it presents a really interesting topic for the reader to read about.

The first things I would point out is mostly for the structure/layout of your page. Make sure you use the correct wiki formatting so the page looks uniform and clean. You should separate your references out from the main body of info and collate them properly at the end of the page. Also make sure that you have in-text referencing so the reader knows exactly where the information is from. And for your content, I think it would look more professional to present it in structured paragraphs instead of bullet points. I would suggest having a proper introduction paragraph so that the reader gets an immediate overview of Wnt signalling and which aspects you’ll be exploring, rather than going straight into explanation of the pathway. Also, while you do have good headings for each section I think putting in more specific subheadings will help both you and the reader to organise the information better. In terms of the info you have so far, I would just make a point that you should try and get most of the content from primary sources instead of review articles. Additionally, because you are focusing on Wnt signalling in skin development I don’t think you have enough explanation in that area. Since it’s your focal aspect then I think you should explore a lot more of the research and the related abnormalities that have been found. You could also just include some links to papers that describe Wnt signalling in other embryonic roles since you aren’t investigating those. Finally I would suggest making the page more interesting by including images, diagrams, tables, timeline, etc. so it’s not just paragraphs of text one after the other (and to fulfill the assessment criteria). But overall you guys have made great progress - I hope these comments will help you improve!

====Group 3 Peer Review====
At first glance, your page looks well structured with lots of information present so well done! Your introduction is concise but effective and it provides a good outline of the topic. It’s also good that you’ve started to explain the history - I think the timeline will be really helpful once it’s finished. All your referencing looks to be correct and most of the abbreviations are all defined. The table of subtypes of FGFR is a great way to present this info briefly and clearly, and I really like that you’ve also listed the associated abnormalities. Also, your hand-drawn image is a great effort but it would be better to clearly explain all the abbreviations (at least on the actual image summary page, or maybe in the glossary) since it’s not all defined in the text. You guys have done a really great job so far in explaining the different roles in embryonic development and it’s especially good that you’ve included descriptions of primary research. And your image for bone development is a really helpful addition to your info.

Obviously your group still has some research and info to fill out in your sections but you’ve done really well so far. For your abnormalities section, I think it would be good if you can find some related pictures to include. In general I think you should add more content and explain your sections in some more detail - particularly the overview of the pathway and the signal transduction section. At the moment it’s more of a description/listing of the components and factors, rather than a full explanation of how they interact and the responses they induce. So as long as you guys get fill out your content a bit more and make sure to finish off your quiz, history, animal models, and new/current research sections then I think you will have a great page by the end.

====Group 4 Peer Review====
First off you guys have chosen great headings and subheadings! It’s really helpful in breaking down your information to be better understood and I like all the aspects you’ve chosen to explore. Your content so far is clear and concise and most of it is correctly referenced - well done particularly on the info for animal models. The examples of primary research you’ve included are also a great addition. The information you’ve presented is also written well and in a way that’s not too scientific so it’s easy to understand.

It would be great if you included an introduction paragraph to just give a brief overview of Hedgehog signalling. While your animal model content is good, I think you need a lot more info for human embryonic development (considering that it should be the focus of the project) - you’ve mentioned organogenesis very briefly, but I think if you explored each of the systems in greater detail then it would really improve your page. I would strongly recommend including a glossary as well. Make sure you have captions for your images so the reader understands why the image is relevant to your text. Also you should fully define all the abbreviations somewhere (either in your glossary on the image’s page) for the reader’s benefit. If you have some more images in the signalling/animal model sections I think that would break up the paragraphs a bit more and make it easier to read. And you might want to include a summary table, maybe of the molecular pathway factors, somewhere. But overall you’ve started off really well as a team - keep working hard to finish off/improve each section.

====Group 5 Peer Review====
Congrats Group 5 on producing a really great looking page so far! Straightaway I like that you have an introduction paragraph and that I can immediately see inclusion of tables, images, and some correct referencing. Explaining the origin of the T-box name is a great piece of background info to include (maybe make it a proper subheading though?). You’ve also touched on some of the history of the gene/signalling pathway in your paragraphs but it might be good to also present that in a brief timeline/table. Your table for T-box family features is really great - especially because of inclusion of main expression sites and the related abnormalities. Also, you have references to primary research articles so it’s good to see you’re backing up your content with accurate and relevant sources. You’ve done a really great job on exploring the animal models as well.

Ultimately you guys have done great work so my suggestions for improving your page are mostly minor! You have a lot of PMID links just left at the end of some paragraphs so make sure you get those properly listed at the end in your reference section. If you change your pictures to thumbnails then I think they would integrate into your text better (because at the moment where they are placed breaks up the text). Also, I’m not sure if there’s a particular reason why you did this in the first place but I wouldn’t capitalise all the subheadings in the abnormalities section. And I suggest moving the ‘Ancient origins and evolution of the T-box gene family’ near the top of your page, because at the moment it seems out of place and doesn’t really flow on from discussing the abnormalities. The other thing I would say is that - if it’s possible - it would be great if you could explain more about the actual molecular pathway and include a picture of the molecules/factors involved, because at the moment you’ve only described it in the context of different TBX genes being expressed in each developmental role. I think especially if you have an image of the structure of some of the different proteins, transcription factors, etc. then it would really help to visualise the molecular aspects of the pathway. Hope my comments are helpful!

====Group 6 Peer Review====
Group 6 - it looks like you’ve started off well and from the headings/subheadings you’ve chosen, I think you’ve chosen some great aspects to explore. The content you have so far is relevant and written in a way that’s easy to understand. Your explanation of the signalling pathway is good and you’ve included some pictures, but I think more work still has to be done.

Your page is clearly still being worked on but here are my suggestions. Firstly your page really needs a lot more content. You haven’t explained anything about the involvement of TGF-beta in embryonic development yet and that’s supposed to be the key point of this project, so you should really focus on finding some info about that. Your referencing as well is really poor. Make sure you have in-text referencing so that the reader knows exactly where each part of your content has come from - at the moment there are no clear references for anything you have written. You should especially be referencing your images (in the image caption). You should also edit the formatting of your headings because at the moment they are all considered subheadings of ‘Introduction’. I would suggest moving the history section to the beginning of your page and presenting the info in a table. And it would be really great if you had a section on ‘Animal Models’ and ‘Abnormalities’, like most of the other pages have done. Your references section is also not formatted correctly so you need to fix that. As long as you work hard from now on I think you can still put up a great project!
 

{{Stem Cell Presentations 2016}}

==Lab 11 Assessment==
'''Distinct phases of cardiomyocyte differentiation regulate growth of the zebrafish heart.'''<ref><pubmed>19395641</pubmed></ref> 
''Emma de Pater, Linda Clijsters, Sara R. Marques, Yi-Fan Lin, Zayra V. Garavito-Aguilar, Deborah Yelon & Jeroen Bakkers''
:In this study, de Pater et al. investigated the regulation of development of the zebrafish heart. Although the process of heart development (e.g. elongation, septation, heart looping) of vertebrates is well known, the regulatory mechanisms are less understood. De Pater et al. performed their research with the aim of looking into cardiomyocyte differentiation during cardiac development. By counting the number of differentiated cardiomyocytes of the linear zebrafish heart tube vs. the looped chambers, they found that the cardiomyocytes in the heart tube were increased during the process of looping. They also stained cells with BrdU to detect proliferating cells, then used protein expression detection and a timing assay to discover that there were distinct phases of proliferation and differentiation among different cell populations. It was seen that cardiomyocyte differentiation began in the ventricle and continued along the atrium, which also allowed new cardiomyocytes to be added at the venous pole of the heart tube. De Pater et al. also observed a subsequent second phase of differentiation located at the arterial pole. In conclusion, the first phase of differentiation (which produced the cardiomyocytes that formed the ventricle and atrium) was completely separate from the second phase (addition of cells to the arterial pole). They also found that different signalling mechanisms were involved in the different phases. Therefore the temporal regulation ''and'' the signalling regulation of the phases of differentiation at each pole were different.
:This research was referred to in the 2016 review article, 'Building and re-building the heart by cardiomyocyte proliferation<ref><pubmed>26932668</pubmed></ref>', by Foglia & Poss. De Pater et al.'s findings were mentioned as evidence for cardiac growth in zebrafish occurring specifically through the proliferation of existing cardiomyocytes.
 

==References==
<references/>

2016 Group Project 2

2016-10-27T09:42:57Z

Z5015014: /* Non-canonical pathway */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development.<ref><pubmed>16588136</pubmed></ref>
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.<ref><pubmed>6403942</pubmed></ref>
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.<ref><pubmed>2338245</pubmed></ref>
|-
| 2012
| The Notch ligand Jag1 was expressed in PA6 cells and showed demonstrated that the ability for the cells to differentiate was interrupted by the Notch signalling inhibition pathway. <ref><pubmed>22558462</pubmed></ref>
|-bgcolor="FAF5FF"
| 2014
| Breakthrough in the applications of the Notch signalling pathway. Evidence emerged showing an association between the Notch signalling pathway and gastric cancer and found that Notch1 and Notch2 pathways have been activated in gastric cancer.<ref><pubmed>25083094</pubmed></ref>
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

{| class="pretty table"
|-
| colspan="5" align="center" | <big>Examples of Non-Canonical Notch Signalling</big> (adapted from Table 1<ref name="PMID22397947"/>)
|- align="center"
| width="75" | '''Species'''
| width="300" | '''Cell type'''
| '''Independent of'''
| '''Function'''
| '''Interacting molecule/signalling pathway'''
|-
| Human
| Human embryonic stem cells (''in vitro'')
| Ligand, CSL
| Negative regulation of Wnt signalling
| Active β-catenin/Wnt signalling
|-
| rowspan="4" | Rodent
| Mouse embryonic stem cells, neural stem cells, mesenchymal stem cells, cardiac progenitor cells
| Ligand, CSL
| Negative regulation of Wnt signalling
| Active β-catenin/Wnt signalling
|-
| T-cells
| CSL
| Notch1 stimulates NF-ϰb
| NF-ϰb pathway
|-
| Primary embryonic cells
| Presenilin, Ligand
| HES1 activation and MCK inhibition
| HES1 and MCK
|-
| Skin progenitor cells
| CSL
| Leukocytosis, longetivity
|
|-
| Avian
| Neural crest (stem cells)
| CSL
| Slug expression
| Slug
|-
| Frog
| Embryo
| CSL
| Negative regulation of Wnt signalling
| β-catenin/Wnt signalling
|-
| rowspan="5" | Fly
| rowspan="2" | Wing primordium
| Ligand, CSL
| Negative regulation of Wnt signalling
| Active β-catenin/Wnt signalling
|-
| CSL
| Inhibition of ligand function
| Serrate
|-
| Muscle progenitor cells
| Ligand, CSL
| Muscle precursor selection
| Wnt signalling
|-
| Embryo
| CSL
| Dorsal epidermis patterning (closure)
| JNK pathway
|-
| Neural precursors
| CSL
| Repression of neural fate
| Wnt signalling
|}
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===
The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.
 

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref name="PMID23840804"><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"/>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref name="PMID23840804"/>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886">As reviewed by <pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref>As reviewed by <pubmed>26548814</pubmed></ref> Two variants of AGS, type 1 and type 2, have been identified, and each is related to different defects in the Notch pathway. In clinically diagnosed cases of AGS type 1 (which accounts for approximately 97% of all cases of AGS), a mutation in the gene encoding the Notch ligand Jagged1 (Jag1) has been identified as a contributing factor.<ref>As reviewed by <pubmed>11745040</pubmed></ref> In the much rarer AGS type 2, a mutation in the NOTCH2 gene has been implicated in the manifestation of AGS. The mechanisms by which mutations in JAG1 and NOTCH2 lead to pathogenesis of AGS are not well understood, but it is known that normal Notch signalling is important in angiogenesis. Therefore, it is thought that abnormal JAG1 or NOTCH2 will cause disruptions to the pathway that leads to the vascular disorders present in AGS. This is also evidenced by research that JAG1 knockout mice suffer premature death due to vascular defects.<ref>As reviewed by <pubmed>21934706</pubmed></ref> It is possible that AGS caused by a mutation in NOTCH2 alone will lead to a different presentation than AGS patients with mutated JAG1; however, this is still undergoing further research. It is also unclear why AGS type 2 occurs at a significantly lower incidence than AGS type 1.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example. 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516>As reviewed by <pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch modulation for therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy: 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees! 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch signalling is involved in embryo implantation!</big>
|-
| Notch is essential for many developmental embryonic processes, as described in our [[#Roles in Embryonic Development|Roles in Embryonic Development]] section. Interestingly, research has shown that Notch signalling also has an important role in the initial process of establishing a successful pregnancy. Specifically, normal Notch signalling has been seen to be a critical factor in fetal-maternal communication during implantation and placentation. (To read more about these processes, go to these pages on [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development Weeks 1-2] and [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_3_Development Week 3] of development.) 

[https://www.ncbi.nlm.nih.gov/pubmed/24357662 '''Fetal-maternal communication: the role of Notch signalling in embryo implantation.''']<ref>As reviewed by <pubmed>24357662</pubmed></ref>

This review describes both human and animal studies of Notch signalling during pregnancy. It explains research of Notch signalling at the human blastocyst-maternal interface, and that Notch signalling has been observed in both the maternal endometrium and the blastocyst. Furthermore, Notch signalling is also important for the processes of implantation and placentation. Overall, the review summarises findings of Notch signalling in endometrial-trophectoderm interactions during the implantation, regulation of extravillous trophoblast invasion and spiral artery remodelling in the decidua, and angiogenesis in the placenta, as well as how abnormal Notch signalling is related with impaired placentation and pre-eclampsia.
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T09:37:45Z

Z5015014: /* History */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development.<ref><pubmed>16588136</pubmed></ref>
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.<ref><pubmed>6403942</pubmed></ref>
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.<ref><pubmed>2338245</pubmed></ref>
|-
| 2012
| The Notch ligand Jag1 was expressed in PA6 cells and showed demonstrated that the ability for the cells to differentiate was interrupted by the Notch signalling inhibition pathway. <ref><pubmed>22558462</pubmed></ref>
|-bgcolor="FAF5FF"
| 2014
| Breakthrough in the applications of the Notch signalling pathway. Evidence emerged showing an association between the Notch signalling pathway and gastric cancer and found that Notch1 and Notch2 pathways have been activated in gastric cancer.<ref><pubmed>25083094</pubmed></ref>
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

{| class="pretty table"
|-
| colspan="5" align="center" | <big>Examples of Non-Canonical Notch Signalling</big> (adapted from Table 1<ref name="PMID22397947"/>)
|- align="center"
| width="75" | '''Species'''
| width="300" | '''Cell type'''
| '''Independent of'''
| '''Function'''
| '''Interacting molecule/signalling pathway'''
|-
| Human
| Human embryonic stem cells (''in vitro'')
| Ligand, CSL
| Negative regulation of Wnt signalling
| Active β-catenin/Wnt signalling
|-
| rowspan="4" | Rodent
| Mouse embryonic stem cells, neural stem cells, mesenchymal stem cells, cardiac progenitor cells
| Ligand, CSL
| Negative regulation of Wnt signalling
| Active β-catenin/Wnt signalling
|-
| T-cells
| CSL
| Notch1 stimulates NF-ϰb
| NF-ϰb pathway
|-
| Primary embryonic cells
| Presenilin, Ligand
| HES1 activation and MCK inhibition
| HES1 and MCK
|-
| Skin progenitor cells
| CSL
| Leukocytosis, longetivity
|
|-
| Avian
| Neural crest (stem cells)
| CSL
| Slug expression
| Slug
|-
| Frog
| Embryo
| CSL
| Negative regulation of Wnt signalling
| β-catenin/Wnt signalling
|-
| rowspan="4" | Fly
| Wing primordium
| Ligand, CSL CSL
| Negative regulation of Wnt signalling Inhibition of ligand function
| Active β-catenin/Wnt signalling Serrate
|-
| Muscle progenitor cells
| Ligand, CSL
| Muscle precursor selection
| Wnt signalling
|-
| Embryo
| CSL
| Dorsal epidermis patterning (closure)
| JNK pathway
|-
| Neural precursors
| CSL
| Repression of neural fate
| Wnt signalling
|}
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===
The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.
 

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref name="PMID23840804"><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"/>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref name="PMID23840804"/>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886">As reviewed by <pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref>As reviewed by <pubmed>26548814</pubmed></ref> Two variants of AGS, type 1 and type 2, have been identified, and each is related to different defects in the Notch pathway. In clinically diagnosed cases of AGS type 1 (which accounts for approximately 97% of all cases of AGS), a mutation in the gene encoding the Notch ligand Jagged1 (Jag1) has been identified as a contributing factor.<ref>As reviewed by <pubmed>11745040</pubmed></ref> In the much rarer AGS type 2, a mutation in the NOTCH2 gene has been implicated in the manifestation of AGS. The mechanisms by which mutations in JAG1 and NOTCH2 lead to pathogenesis of AGS are not well understood, but it is known that normal Notch signalling is important in angiogenesis. Therefore, it is thought that abnormal JAG1 or NOTCH2 will cause disruptions to the pathway that leads to the vascular disorders present in AGS. This is also evidenced by research that JAG1 knockout mice suffer premature death due to vascular defects.<ref>As reviewed by <pubmed>21934706</pubmed></ref> It is possible that AGS caused by a mutation in NOTCH2 alone will lead to a different presentation than AGS patients with mutated JAG1; however, this is still undergoing further research. It is also unclear why AGS type 2 occurs at a significantly lower incidence than AGS type 1.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example. 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516>As reviewed by <pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy: 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees! 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch signalling is involved in embryo implantation!</big>
|-
| Notch is essential for many developmental embryonic processes, as described in our [[#Roles in Embryonic Development|Roles in Embryonic Development]] section. Interestingly, research has shown that Notch signalling also has an important role in the initial process of establishing a successful pregnancy. Specifically, normal Notch signalling has been seen to be a critical factor in fetal-maternal communication during implantation and placentation. (To read more about these processes, go to these pages on [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development Weeks 1-2] and [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_3_Development Week 3] of development.) 

[https://www.ncbi.nlm.nih.gov/pubmed/24357662 '''Fetal-maternal communication: the role of Notch signalling in embryo implantation.''']<ref>As reviewed by <pubmed>24357662</pubmed></ref>

This review describes both human and animal studies of Notch signalling during pregnancy. It explains research of Notch signalling at the human blastocyst-maternal interface, and that Notch signalling has been observed in both the maternal endometrium and the blastocyst. Furthermore, Notch signalling is also important for the processes of implantation and placentation. Overall, the review summarises findings of Notch signalling in endometrial-trophectoderm interactions during the implantation, regulation of extravillous trophoblast invasion and spiral artery remodelling in the decidua, and angiogenesis in the placenta, as well as how abnormal Notch signalling is related with impaired placentation and pre-eclampsia.
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T09:34:32Z

Z5015014: /* Non-canonical pathway */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
|-
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development.<ref><pubmed>16588136</pubmed></ref>
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
|-
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.<ref><pubmed>6403942</pubmed></ref>
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
|-
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.<ref><pubmed>2338245</pubmed></ref>
|-
| 2012
| The Notch ligand Jag1 was expressed in PA6 cells and showed demonstrated that the ability for the cells to differentiate was interrupted by the Notch signalling inhibition pathway. <ref><pubmed>22558462</pubmed></ref>
|-
| 2014
| Breakthrough in the applications of the Notch signalling pathway. Evidence emerged showing an association between the Notch signalling pathway and gastric cancer and found that Notch1 and Notch2 pathways have been activated in gastric cancer.<ref><pubmed>25083094</pubmed></ref>
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

{| class="pretty table"
|-
| colspan="5" align="center" | <big>Examples of Non-Canonical Notch Signalling</big> (adapted from Table 1<ref name="PMID22397947"/>)
|- align="center"
| width="75" | '''Species'''
| width="300" | '''Cell type'''
| '''Independent of'''
| '''Function'''
| '''Interacting molecule/signalling pathway'''
|-
| Human
| Human embryonic stem cells (''in vitro'')
| Ligand, CSL
| Negative regulation of Wnt signalling
| Active β-catenin/Wnt signalling
|-
| rowspan="4" | Rodent
| Mouse embryonic stem cells, neural stem cells, mesenchymal stem cells, cardiac progenitor cells
| Ligand, CSL
| Negative regulation of Wnt signalling
| Active β-catenin/Wnt signalling
|-
| T-cells
| CSL
| Notch1 stimulates NF-ϰb
| NF-ϰb pathway
|-
| Primary embryonic cells
| Presenilin, Ligand
| HES1 activation and MCK inhibition
| HES1 and MCK
|-
| Skin progenitor cells
| CSL
| Leukocytosis, longetivity
|
|-
| Avian
| Neural crest (stem cells)
| CSL
| Slug expression
| Slug
|-
| Frog
| Embryo
| CSL
| Negative regulation of Wnt signalling
| β-catenin/Wnt signalling
|-
| rowspan="4" | Fly
| Wing primordium
| Ligand, CSL CSL
| Negative regulation of Wnt signalling Inhibition of ligand function
| Active β-catenin/Wnt signalling Serrate
|-
| Muscle progenitor cells
| Ligand, CSL
| Muscle precursor selection
| Wnt signalling
|-
| Embryo
| CSL
| Dorsal epidermis patterning (closure)
| JNK pathway
|-
| Neural precursors
| CSL
| Repression of neural fate
| Wnt signalling
|}
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===
The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.
 

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref name="PMID23840804"><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"/>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref name="PMID23840804"/>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886">As reviewed by <pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref>As reviewed by <pubmed>26548814</pubmed></ref> Two variants of AGS, type 1 and type 2, have been identified, and each is related to different defects in the Notch pathway. In clinically diagnosed cases of AGS type 1 (which accounts for approximately 97% of all cases of AGS), a mutation in the gene encoding the Notch ligand Jagged1 (Jag1) has been identified as a contributing factor.<ref>As reviewed by <pubmed>11745040</pubmed></ref> In the much rarer AGS type 2, a mutation in the NOTCH2 gene has been implicated in the manifestation of AGS. The mechanisms by which mutations in JAG1 and NOTCH2 lead to pathogenesis of AGS are not well understood, but it is known that normal Notch signalling is important in angiogenesis. Therefore, it is thought that abnormal JAG1 or NOTCH2 will cause disruptions to the pathway that leads to the vascular disorders present in AGS. This is also evidenced by research that JAG1 knockout mice suffer premature death due to vascular defects.<ref>As reviewed by <pubmed>21934706</pubmed></ref> It is possible that AGS caused by a mutation in NOTCH2 alone will lead to a different presentation than AGS patients with mutated JAG1; however, this is still undergoing further research. It is also unclear why AGS type 2 occurs at a significantly lower incidence than AGS type 1.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example. 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516>As reviewed by <pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy: 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees! 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch signalling is involved in embryo implantation!</big>
|-
| Notch is essential for many developmental embryonic processes, as described in our [[#Roles in Embryonic Development|Roles in Embryonic Development]] section. Interestingly, research has shown that Notch signalling also has an important role in the initial process of establishing a successful pregnancy. Specifically, normal Notch signalling has been seen to be a critical factor in fetal-maternal communication during implantation and placentation. (To read more about these processes, go to these pages on [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development Weeks 1-2] and [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_3_Development Week 3] of development.) 

[https://www.ncbi.nlm.nih.gov/pubmed/24357662 '''Fetal-maternal communication: the role of Notch signalling in embryo implantation.''']<ref>As reviewed by <pubmed>24357662</pubmed></ref>

This review describes both human and animal studies of Notch signalling during pregnancy. It explains research of Notch signalling at the human blastocyst-maternal interface, and that Notch signalling has been observed in both the maternal endometrium and the blastocyst. Furthermore, Notch signalling is also important for the processes of implantation and placentation. Overall, the review summarises findings of Notch signalling in endometrial-trophectoderm interactions during the implantation, regulation of extravillous trophoblast invasion and spiral artery remodelling in the decidua, and angiogenesis in the placenta, as well as how abnormal Notch signalling is related with impaired placentation and pre-eclampsia.
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T09:00:10Z

Z5015014: /* Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 117761886) */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
|-
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development.<ref><pubmed>16588136</pubmed></ref>
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
|-
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.<ref><pubmed>6403942</pubmed></ref>
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
|-
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.<ref><pubmed>2338245</pubmed></ref>
|-
| 2012
| The Notch ligand Jag1 was expressed in PA6 cells and showed demonstrated that the ability for the cells to differentiate was interrupted by the Notch signalling inhibition pathway. <ref><pubmed>22558462</pubmed></ref>
|-
| 2014
| Breakthrough in the applications of the Notch signalling pathway. Evidence emerged showing an association between the Notch signalling pathway and gastric cancer and found that Notch1 and Notch2 pathways have been activated in gastric cancer.<ref><pubmed>25083094</pubmed></ref>
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===
The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.
 

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref name="PMID23840804"><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"/>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref name="PMID23840804"/>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886">As reviewed by <pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref>As reviewed by <pubmed>26548814</pubmed></ref> Two variants of AGS, type 1 and type 2, have been identified, and each is related to different defects in the Notch pathway. In clinically diagnosed cases of AGS type 1 (which accounts for approximately 97% of all cases of AGS), a mutation in the gene encoding the Notch ligand Jagged1 (Jag1) has been identified as a contributing factor.<ref>As reviewed by <pubmed>11745040</pubmed></ref> In the much rarer AGS type 2, a mutation in the NOTCH2 gene has been implicated in the manifestation of AGS. The mechanisms by which mutations in JAG1 and NOTCH2 lead to pathogenesis of AGS are not well understood, but it is known that normal Notch signalling is important in angiogenesis. Therefore, it is thought that abnormal JAG1 or NOTCH2 will cause disruptions to the pathway that leads to the vascular disorders present in AGS. This is also evidenced by research that JAG1 knockout mice suffer premature death due to vascular defects.<ref>As reviewed by <pubmed>21934706</pubmed></ref> It is possible that AGS caused by a mutation in NOTCH2 alone will lead to a different presentation than AGS patients with mutated JAG1; however, this is still undergoing further research. It is also unclear why AGS type 2 occurs at a significantly lower incidence than AGS type 1.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example. 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516>As reviewed by <pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy: 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees! 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch signalling is involved in embryo implantation!</big>
|-
| Notch is essential for many developmental embryonic processes, as described in our [[#Roles in Embryonic Development|Roles in Embryonic Development]] section. Interestingly, research has shown that Notch signalling also has an important role in the initial process of establishing a successful pregnancy. Specifically, normal Notch signalling has been seen to be a critical factor in fetal-maternal communication during implantation and placentation. (To read more about these processes, go to these pages on [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development Weeks 1-2] and [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_3_Development Week 3] of development.) 

[https://www.ncbi.nlm.nih.gov/pubmed/24357662 '''Fetal-maternal communication: the role of Notch signalling in embryo implantation.''']<ref>As reviewed by <pubmed>24357662</pubmed></ref>

This review describes both human and animal studies of Notch signalling during pregnancy. It explains research of Notch signalling at the human blastocyst-maternal interface, and that Notch signalling has been observed in both the maternal endometrium and the blastocyst. Furthermore, Notch signalling is also important for the processes of implantation and placentation. Overall, the review summarises findings of Notch signalling in endometrial-trophectoderm interactions during the implantation, regulation of extravillous trophoblast invasion and spiral artery remodelling in the decidua, and angiogenesis in the placenta, as well as how abnormal Notch signalling is related with impaired placentation and pre-eclampsia.
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T08:56:52Z

Z5015014: fixed a duplicate reference

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
|-
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development.<ref><pubmed>16588136</pubmed></ref>
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
|-
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.<ref><pubmed>6403942</pubmed></ref>
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
|-
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.<ref><pubmed>2338245</pubmed></ref>
|-
| 2012
| The Notch ligand Jag1 was expressed in PA6 cells and showed demonstrated that the ability for the cells to differentiate was interrupted by the Notch signalling inhibition pathway. <ref><pubmed>22558462</pubmed></ref>
|-
| 2014
| Breakthrough in the applications of the Notch signalling pathway. Evidence emerged showing an association between the Notch signalling pathway and gastric cancer and found that Notch1 and Notch2 pathways have been activated in gastric cancer.<ref><pubmed>25083094</pubmed></ref>
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===
The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.
 

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref name="PMID23840804"><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"/>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref name="PMID23840804"/>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref>As reviewed by <pubmed>26548814</pubmed></ref> Two variants of AGS, type 1 and type 2, have been identified, and each is related to different defects in the Notch pathway. In clinically diagnosed cases of AGS type 1 (which accounts for approximately 97% of all cases of AGS), a mutation in the gene encoding the Notch ligand Jagged1 (Jag1) has been identified as a contributing factor.<ref>As reviewed by <pubmed>11745040</pubmed></ref> In the much rarer AGS type 2, a mutation in the NOTCH2 gene has been implicated in the manifestation of AGS. The mechanisms by which mutations in JAG1 and NOTCH2 lead to pathogenesis of AGS are not well understood, but it is known that normal Notch signalling is important in angiogenesis. Therefore, it is thought that abnormal JAG1 or NOTCH2 will cause disruptions to the pathway that leads to the vascular disorders present in AGS. This is also evidenced by research that JAG1 knockout mice suffer premature death due to vascular defects.<ref>As reviewed by <pubmed>21934706</pubmed></ref> It is possible that AGS caused by a mutation in NOTCH2 alone will lead to a different presentation than AGS patients with mutated JAG1; however, this is still undergoing further research. It is also unclear why AGS type 2 occurs at a significantly lower incidence than AGS type 1.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example. 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516>As reviewed by <pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy: 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees! 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch signalling is involved in embryo implantation!</big>
|-
| Notch is essential for many developmental embryonic processes, as described in our [[#Roles in Embryonic Development|Roles in Embryonic Development]] section. Interestingly, research has shown that Notch signalling also has an important role in the initial process of establishing a successful pregnancy. Specifically, normal Notch signalling has been seen to be a critical factor in fetal-maternal communication during implantation and placentation. (To read more about these processes, go to these pages on [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development Weeks 1-2] and [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_3_Development Week 3] of development.) 

[https://www.ncbi.nlm.nih.gov/pubmed/24357662 '''Fetal-maternal communication: the role of Notch signalling in embryo implantation.''']<ref>As reviewed by <pubmed>24357662</pubmed></ref>

This review describes both human and animal studies of Notch signalling during pregnancy. It explains research of Notch signalling at the human blastocyst-maternal interface, and that Notch signalling has been observed in both the maternal endometrium and the blastocyst. Furthermore, Notch signalling is also important for the processes of implantation and placentation. Overall, the review summarises findings of Notch signalling in endometrial-trophectoderm interactions during the implantation, regulation of extravillous trophoblast invasion and spiral artery remodelling in the decidua, and angiogenesis in the placenta, as well as how abnormal Notch signalling is related with impaired placentation and pre-eclampsia.
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T06:46:20Z

Z5015014: /* Want to Read More About Notch? */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===
The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.
 

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"><pubmed>23840804</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref><pubmed>23840804</pubmed></ref>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref>As reviewed by <pubmed>26548814</pubmed></ref> Two variants of AGS, type 1 and type 2, have been identified, and each is related to different defects in the Notch pathway. In clinically diagnosed cases of AGS type 1 (which accounts for approximately 97% of all cases of AGS), a mutation in the gene encoding the Notch ligand Jagged1 (Jag1) has been identified as a contributing factor.<ref>As reviewed by <pubmed>11745040</pubmed></ref> In the much rarer AGS type 2, a mutation in the NOTCH2 gene has been implicated in the manifestation of AGS. The mechanisms by which mutations in JAG1 and NOTCH2 lead to pathogenesis of AGS are not well understood, but it is known that normal Notch signalling is important in angiogenesis. Therefore, it is thought that abnormal JAG1 or NOTCH2 will cause disruptions to the pathway that leads to the vascular disorders present in AGS. This is also evidenced by research that JAG1 knockout mice suffer premature death due to vascular defects.<ref>As reviewed by <pubmed>21934706</pubmed></ref> It is possible that AGS caused by a mutation in NOTCH2 alone will lead to a different presentation than AGS patients with mutated JAG1; however, this is still undergoing further research. It is also unclear why AGS type 2 occurs at a significantly lower incidence than AGS type 1.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example. 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516><pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy: 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees! 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch signalling is involved in embryo implantation!</big>
|-
| Notch is essential for many developmental embryonic processes, as described in our [[#Roles in Embryonic Development|Roles in Embryonic Development]] section. Interestingly, research has shown that Notch signalling also has an important role in the initial process of establishing a successful pregnancy. Specifically, normal Notch signalling has been seen to be a critical factor in fetal-maternal communication during implantation and placentation. (To read more about these processes, go to these pages on [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development Weeks 1-2] and [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_3_Development Week 3] of development.) 

[https://www.ncbi.nlm.nih.gov/pubmed/24357662 '''Fetal-maternal communication: the role of Notch signalling in embryo implantation.''']<ref>As reviewed by <pubmed>24357662</pubmed></ref>

This review describes both human and animal studies of Notch signalling during pregnancy. It explains research of Notch signalling at the human blastocyst-maternal interface, and that Notch signalling has been observed in both the maternal endometrium and the blastocyst. Furthermore, Notch signalling is also important for the processes of implantation and placentation. Overall, the review summarises findings of Notch signalling in endometrial-trophectoderm interactions during the implantation, regulation of extravillous trophoblast invasion and spiral artery remodelling in the decidua, and angiogenesis in the placenta, as well as how abnormal Notch signalling is related with impaired placentation and pre-eclampsia.
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T06:42:45Z

Z5015014: /* Alagille Syndrome */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===
The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.
 

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"><pubmed>23840804</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref><pubmed>23840804</pubmed></ref>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref>As reviewed by <pubmed>26548814</pubmed></ref> Two variants of AGS, type 1 and type 2, have been identified, and each is related to different defects in the Notch pathway. In clinically diagnosed cases of AGS type 1 (which accounts for approximately 97% of all cases of AGS), a mutation in the gene encoding the Notch ligand Jagged1 (Jag1) has been identified as a contributing factor.<ref>As reviewed by <pubmed>11745040</pubmed></ref> In the much rarer AGS type 2, a mutation in the NOTCH2 gene has been implicated in the manifestation of AGS. The mechanisms by which mutations in JAG1 and NOTCH2 lead to pathogenesis of AGS are not well understood, but it is known that normal Notch signalling is important in angiogenesis. Therefore, it is thought that abnormal JAG1 or NOTCH2 will cause disruptions to the pathway that leads to the vascular disorders present in AGS. This is also evidenced by research that JAG1 knockout mice suffer premature death due to vascular defects.<ref>As reviewed by <pubmed>21934706</pubmed></ref> It is possible that AGS caused by a mutation in NOTCH2 alone will lead to a different presentation than AGS patients with mutated JAG1; however, this is still undergoing further research. It is also unclear why AGS type 2 occurs at a significantly lower incidence than AGS type 1.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example. 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516><pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy: 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees! 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch signalling is involved in embryo implantation!</big>
|-
| Notch is essential for many developmental embryonic processes, as described in our [[#Roles in Embryonic Development|Roles in Embryonic Development]] section. Interestingly, research has shown that Notch signalling also has an important role in the initial process of establishing a successful pregnancy. Specifically, normal Notch signalling has been seen to be a critical factor in fetal-maternal communication during implantation and placentation. (To read more about these processes, go to these pages on [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development Weeks 1-2] and [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_3_Development Week 3] of development.) 

[https://www.ncbi.nlm.nih.gov/pubmed/24357662 '''Fetal-maternal communication: the role of Notch signalling in embryo implantation.''']<ref><pubmed>24357662</pubmed></ref>

This review describes both human and animal studies of Notch signalling during pregnancy. It explains research of Notch signalling at the human blastocyst-maternal interface, and that Notch signalling has been observed in both the maternal endometrium and the blastocyst. Furthermore, Notch signalling is also important for the processes of implantation and placentation. Overall, the review summarises findings of Notch signalling in endometrial-trophectoderm interactions during the implantation, regulation of extravillous trophoblast invasion and spiral artery remodelling in the decidua, and angiogenesis in the placenta, as well as how abnormal Notch signalling is related with impaired placentation and pre-eclampsia.
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T06:35:51Z

Z5015014: /* Alagille Syndrome */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===
The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.
 

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"><pubmed>23840804</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref><pubmed>23840804</pubmed></ref>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref><pubmed>26548814</pubmed></ref> Two variants of AGS, type 1 and type 2, have been identified, and each is related to different defects in the Notch pathway. In clinically diagnosed cases of AGS type 1 (which accounts for approximately 97% of all cases of AGS), a mutation in the gene encoding the Notch ligand Jagged1 (Jag1) has been identified as a contributing factor. In the much rarer AGS type 2, a mutation in the NOTCH2 gene has been implicated in the manifestation of AGS. The mechanisms by which mutations in JAG1 and NOTCH2 lead to pathogenesis of AGS are not well understood, but it is known that normal Notch signalling is important in angiogenesis. Therefore, it is thought that abnormal JAG1 or NOTCH2 will cause disruptions to the pathway that leads to the vascular disorders present in AGS. This is also evidenced by research that JAG1 knockout mice suffer premature death due to vascular defects. It is possible that AGS caused by a mutation in NOTCH2 alone will lead to a different presentation than AGS patients with mutated JAG1; however, this is still undergoing further research. It is also unclear why AGS type 2 occurs at a significantly lower incidence than AGS type 1.<ref name="PMID21934706">As reviewed by <pubmed>21934706</pubmed></ref><ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example. 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516><pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy: 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees! 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch signalling is involved in embryo implantation!</big>
|-
| Notch is essential for many developmental embryonic processes, as described in our [[#Roles in Embryonic Development|Roles in Embryonic Development]] section. Interestingly, research has shown that Notch signalling also has an important role in the initial process of establishing a successful pregnancy. Specifically, normal Notch signalling has been seen to be a critical factor in fetal-maternal communication during implantation and placentation. (To read more about these processes, go to these pages on [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development Weeks 1-2] and [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_3_Development Week 3] of development.) 

[https://www.ncbi.nlm.nih.gov/pubmed/24357662 '''Fetal-maternal communication: the role of Notch signalling in embryo implantation.''']<ref><pubmed>24357662</pubmed></ref>

This review describes both human and animal studies of Notch signalling during pregnancy. It explains research of Notch signalling at the human blastocyst-maternal interface, and that Notch signalling has been observed in both the maternal endometrium and the blastocyst. Furthermore, Notch signalling is also important for the processes of implantation and placentation. Overall, the review summarises findings of Notch signalling in endometrial-trophectoderm interactions during the implantation, regulation of extravillous trophoblast invasion and spiral artery remodelling in the decidua, and angiogenesis in the placenta, as well as how abnormal Notch signalling is related with impaired placentation and pre-eclampsia.
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T06:11:40Z

Z5015014: /* Roles in Animal Development */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===
The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.
 

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"><pubmed>23840804</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref><pubmed>23840804</pubmed></ref>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref><pubmed>26548814</pubmed></ref> In 94% of clinically diagnosed cases, a mutation in the gene encoding the Notch ligand JAG1 has been identified as a contributing factor. In combination with this, a mutation in the NOTCH2 gene has also been implicated in the manifestation of AGS in some patients.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example. 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516><pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy: 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees! 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch signalling is involved in embryo implantation!</big>
|-
| Notch is essential for many developmental embryonic processes, as described in our [[#Roles in Embryonic Development|Roles in Embryonic Development]] section. Interestingly, research has shown that Notch signalling also has an important role in the initial process of establishing a successful pregnancy. Specifically, normal Notch signalling has been seen to be a critical factor in fetal-maternal communication during implantation and placentation. (To read more about these processes, go to these pages on [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development Weeks 1-2] and [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_3_Development Week 3] of development.) 

[https://www.ncbi.nlm.nih.gov/pubmed/24357662 '''Fetal-maternal communication: the role of Notch signalling in embryo implantation.''']<ref><pubmed>24357662</pubmed></ref>

This review describes both human and animal studies of Notch signalling during pregnancy. It explains research of Notch signalling at the human blastocyst-maternal interface, and that Notch signalling has been observed in both the maternal endometrium and the blastocyst. Furthermore, Notch signalling is also important for the processes of implantation and placentation. Overall, the review summarises findings of Notch signalling in endometrial-trophectoderm interactions during the implantation, regulation of extravillous trophoblast invasion and spiral artery remodelling in the decidua, and angiogenesis in the placenta, as well as how abnormal Notch signalling is related with impaired placentation and pre-eclampsia.
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T06:07:51Z

Z5015014: /* Current Areas of Research and Future Directions */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===

The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"><pubmed>23840804</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref><pubmed>23840804</pubmed></ref>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref><pubmed>26548814</pubmed></ref> In 94% of clinically diagnosed cases, a mutation in the gene encoding the Notch ligand JAG1 has been identified as a contributing factor. In combination with this, a mutation in the NOTCH2 gene has also been implicated in the manifestation of AGS in some patients.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example. 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516><pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy: 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees! 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch signalling is involved in embryo implantation!</big>
|-
| Notch is essential for many developmental embryonic processes, as described in our [[#Roles in Embryonic Development|Roles in Embryonic Development]] section. Interestingly, research has shown that Notch signalling also has an important role in the initial process of establishing a successful pregnancy. Specifically, normal Notch signalling has been seen to be a critical factor in fetal-maternal communication during implantation and placentation. (To read more about these processes, go to these pages on [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development Weeks 1-2] and [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_3_Development Week 3] of development.) 

[https://www.ncbi.nlm.nih.gov/pubmed/24357662 '''Fetal-maternal communication: the role of Notch signalling in embryo implantation.''']<ref><pubmed>24357662</pubmed></ref>

This review describes both human and animal studies of Notch signalling during pregnancy. It explains research of Notch signalling at the human blastocyst-maternal interface, and that Notch signalling has been observed in both the maternal endometrium and the blastocyst. Furthermore, Notch signalling is also important for the processes of implantation and placentation. Overall, the review summarises findings of Notch signalling in endometrial-trophectoderm interactions during the implantation, regulation of extravillous trophoblast invasion and spiral artery remodelling in the decidua, and angiogenesis in the placenta, as well as how abnormal Notch signalling is related with impaired placentation and pre-eclampsia.
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T06:05:30Z

Z5015014: /* Want to Read More About Notch? */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===

The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"><pubmed>23840804</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref><pubmed>23840804</pubmed></ref>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref><pubmed>26548814</pubmed></ref> In 94% of clinically diagnosed cases, a mutation in the gene encoding the Notch ligand JAG1 has been identified as a contributing factor. In combination with this, a mutation in the NOTCH2 gene has also been implicated in the manifestation of AGS in some patients.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
 
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example. 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516><pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy: 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees! 

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch signalling is involved in embryo implantation!</big>
|-
| Notch is essential for many developmental embryonic processes, as described in our [[#Roles in Embryonic Development|Roles in Embryonic Development]] section. Interestingly, research has shown that Notch signalling also has an important role in the initial process of establishing a successful pregnancy. Specifically, normal Notch signalling has been seen to be a critical factor in fetal-maternal communication during implantation and placentation. (To read more about these processes, go to these pages on [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development Weeks 1-2] and [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_3_Development Week 3] of development.) 

[https://www.ncbi.nlm.nih.gov/pubmed/24357662 '''Fetal-maternal communication: the role of Notch signalling in embryo implantation.''']<ref><pubmed>24357662</pubmed></ref>

This review describes both human and animal studies of Notch signalling during pregnancy. It explains research of Notch signalling at the human blastocyst-maternal interface, and that Notch signalling has been observed in both the maternal endometrium and the blastocyst. Furthermore, Notch signalling is also important for the processes of implantation and placentation. Overall, the review summarises findings of Notch signalling in endometrial-trophectoderm interactions during the implantation, regulation of extravillous trophoblast invasion and spiral artery remodelling in the decidua, and angiogenesis in the placenta, as well as how abnormal Notch signalling is related with impaired placentation and pre-eclampsia.
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T05:42:08Z

Z5015014: /* Want to Read More About Notch? */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===

The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"><pubmed>23840804</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref><pubmed>23840804</pubmed></ref>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref><pubmed>26548814</pubmed></ref> In 94% of clinically diagnosed cases, a mutation in the gene encoding the Notch ligand JAG1 has been identified as a contributing factor. In combination with this, a mutation in the NOTCH2 gene has also been implicated in the manifestation of AGS in some patients.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
 
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===
The [http://www.omim.org/ OMIM (Online Mendelian Inheritance in Man) database] contains extensive information about the Notch genes and associated proteins and is a great place to go if you want to find out more about the Notch pathway in humans! Click on these links to learn more about the Notch genes that encode the human receptors and ligands:
<li>[http://www.omim.org/entry/190198 NOTCH1] | [http://www.omim.org/entry/600275 NOTCH2] | [http://www.omim.org/entry/600276 NOTCH3] | [http://www.omim.org/entry/164951 NOTCH4]
<li>[http://www.omim.org/entry/601920 JAG1] | [http://www.omim.org/entry/602570 JAG2]
<li>[http://www.omim.org/entry/606582 DLL1] | [http://www.omim.org/entry/602768 DLL3] | [http://www.omim.org/entry/605185 DLL4]
 

You can also look at these papers for examples of reviews and research papers that reinforce the diversity of how the Notch pathway functions in organisms.
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example.

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516><pubmed>21505516</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy:

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees!

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T05:19:19Z

Z5015014: /* Abnormalities in Notch Signalling */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===

The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"><pubmed>23840804</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref><pubmed>23840804</pubmed></ref>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref> The diseases listed in this summary table are only a few examples and are described in more detail below.
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref><pubmed>26548814</pubmed></ref> In 94% of clinically diagnosed cases, a mutation in the gene encoding the Notch ligand JAG1 has been identified as a contributing factor. In combination with this, a mutation in the NOTCH2 gene has also been implicated in the manifestation of AGS in some patients.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>
 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>
{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
 
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example.

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516><pubmed>21505516</pubmed></ref>
|}
 
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy:

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
 
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees!

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-27T05:05:34Z

Z5015014: /* Tumourigenesis */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

About one third of congenital heart defects include malformations in the outflow tract which include the aorta, pulmonary arteries, aortic arch and ductus arteriosus. During cardiogenesis, neural crest cells interact with second heart field myocardium and endocardial mesenchyme. <ref><pubmed>20201902</pubmed></ref>
Studies involving neurogenesis demonstrated the sensitivity of Notch signaling to temporal and spatial cues and showed the early Notch signaling initially controls the number of cells with a neurogenic fate and later dictates the lineage decision of neural versus glial cell fate. <ref><pubmed>16429119</pubmed></ref>
Neural crest precursors for ideal patterning of the outflow tract are required in the Notch signaling pathway. The use of a dominant negative form of a master mind like protein (MAML) which has shown to be a pan Notch inhibitor in neural crest cells inactivates Notch signaling. This results in congenital heart defects like pulmonary artery stenosis and aortic arch patterning defects associated with defects in smooth muscle formation. <ref><pubmed> 17273555 </pubmed></ref>
Part of the phenotype in defective neural crest cells is attributed to loss of Notch2 signalling as Notch2 inactivation in these cells produces small caliber aortas and pulmonary arteries because of defects in smooth muscle. <ref><pubmed> 18330927 </pubmed></ref>
Jagged1 is the ligand involved which signals to Notch on neural crest cell surfaces to induce vascular smooth muscle cell differentiation. <ref><pubmed> 18245384 </pubmed></ref>
Mutations in both JAGGED1 and NOTCH2 genes have been known to cause Alagille syndrome, further substantiating the importance of this pathway in proper formation of the outflow tract. <ref><pubmed> 16575836 </pubmed></ref>

Another study by Garg stresses the importance of Notch signaling in the outflow tract region. NOTCH1 mutations were seen in patients with aortic stenosis. Aortic stenosis results from the calcification of the aortic valve and is quite common in adults. However, in children, this may result in failure of the left ventricle to develop properly. NOTCH1 haploinsufficiency is also linked to early calcification and bicuspid aortic valve disease. This could be due to an early induction of Runx2 through the HRT genes.
<ref><pubmed> 16025100 </pubmed></ref>

 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===

The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"><pubmed>23840804</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref><pubmed>23840804</pubmed></ref>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref>
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref><pubmed>26548814</pubmed></ref> In 94% of clinically diagnosed cases, a mutation in the gene encoding the Notch ligand JAG1 has been identified as a contributing factor. In combination with this, a mutation in the NOTCH2 gene has also been implicated in the manifestation of AGS in some patients.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>

 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour suppressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/> Defective Notch signalling has been implicated in the pathogenesis of several human cancers, such as acute myelogenous leukemia (overexpression of Jagged1 and Notch1), multiple myeloma (overexpression of Jagged1/2 and Notch1/2), and B-cell–derived Hodgkin lymphoma (overexpression of Jagged1 and Notch1).<ref name="PMID16291593">As reviewed by <pubmed>16291593</pubmed></ref>

Elevated levels of Notch ligand proteins and/or mRNA have been observed in several cancers. Upregulated Jagged1 mRNA has been seen in human pancreatic cancer; Jagged1 protein overexpression has also been studied in prostate, cervix, and brain cancers. Cervical cancers have shown upregulated Jagged2 mRNA. Additionally, elevated Dll1 mRNA has been observed in cervical cancers, as well as in human brain cancers at both Dll1 mRNA and protein levels. Additionally, defective Notch receptor expression has been implicated in cancer as well. For example, elevated Notch1 protein expression has been found in cervical, colon, lung, pancreas, skin, and brain cancers. Protein overexpression of Notch3 and Notch4 has also been seen in malignant melanoma and pancreatic cancer.<ref name="PMID16291593"/>

Interestingly, research has shown that Notch signalling can also have a tumour-suppressive effect. Studies have indicated that Notch signalling can inhibit proliferation and even stimulate apoptosis in malignant B-cells. Furthermore, the Notch1 intracellular domain has also shown the ability to induce growth arrest and apoptosis in Hodgkin lymphoma and multiple myeloma cells.<ref name="PMID16291593"/>
 

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an example of how abnormal Notch signalling can lead to the development of cancer. T-ALL is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch1 receptor, which is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of Notch1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>
 

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>

{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
 
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example.

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516><pubmed>21505516</pubmed></ref>
|}
 
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy:

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
 
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees!

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Calcification'''
| The accumulation of calcium salts in body tissue. It normally occurs in the formation of bone, but abnormally calcium can be deposited in soft tissue causing it to harden.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Haploinsufficiency'''
| When a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation), and so the total level of a gene product (a particular protein) produced by the cell is about half of the normal level.
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Runx2'''
| Runt-related transcription factor 2 is a protein that in humans is encoded by the ''RUNX2'' gene ([http://omim.org/entry/600211 OMIM600211]). RUNX2 is an important transcription factor associated with osteoblast (bone substance-secreting cells) differentiation.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

User talk:Z5015014

2016-10-26T08:44:44Z

Z5015014:

http://www.ncbi.nlm.nih.gov/pubmed/27203305

http://cshperspectives.cshlp.org/content/4/8/a005975.full

http://www.omim.org/entry/606582

<pubmed>16291593</pubmed>
<pubmed>10531053</pubmed>
<pubmed>14712268</pubmed>
<pubmed>16869730</pubmed>
<pubmed>25003789</pubmed>
<pubmed>23560082</pubmed>

2016 Group Project 2

2016-10-26T07:31:35Z

Z5015014: /* Non-canonical pathway */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

TBC
 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===

The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"><pubmed>23840804</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref><pubmed>23840804</pubmed></ref>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref>
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref><pubmed>26548814</pubmed></ref> In 94% of clinically diagnosed cases, a mutation in the gene encoding the Notch ligand JAG1 has been identified as a contributing factor. In combination with this, a mutation in the NOTCH2 gene has also been implicated in the manifestation of AGS in some patients.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>

 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour supressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/>

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch receptor that is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of NOTCH1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>

{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
 
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example.

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516><pubmed>21505516</pubmed></ref>
|}
 
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy:

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
 
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees!

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

2016 Group Project 2

2016-10-26T07:30:02Z

Z5015014: /* Non-canonical pathway */

{{ANAT2341Project2016header}}
{{Group Assessment Criteria table}}

=The Notch Signalling Pathway=
===Introduction===
The Notch signalling pathway is the most prevalent form of intracellular communication in multicellular organisms. It is a critical pathway for cell differentiation, proliferation, and apoptosis. It is involved in embryonic organ development through the regulation of cell-cell signalling; specifically lateral inhibition, formation of boundaries, and cell lineage assignation.<ref name="The Developing Human">Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.</ref><ref name="PMID10075488">As reviewed by <pubmed>10075488</pubmed></ref> This pathway is also actively involved in adjacent cell communication, developmental process such as adult homeostasis, and stem cell maintenance. Since this pathway is an intricate and crucial aspect of an organism's development and cell signalling, a mutation in the functional components of this pathway can cause a myriad of diseases such as congenital disorders, cancers, strokes, Alagille syndrome, and leukoencephalopathy.<ref name="PMID19255248">As reviewed by <pubmed>19255248</pubmed></ref> The process of Notch signalling primarily utilises a ligand-receptor interaction to release protein fragments at the cellular membrane, which then provide signals to the internal environment of the cell and to adjacent cells. In mammals, the Notch signalling pathway is comprised of four receptors (Notch 1-4) which interact with Delta or Jagged ligands to bring about the activation of this pathway. Homologous Notch genes have been identified in other animals, such as ''Drosophila melanogaster'' (fruit fly) and ''Danio rerio'' (zebrafish).
 

<big>What will you find on this wiki page?</big>

This page is designed to provide an overview of such features of the Notch signalling pathway, but is in no way a complete resource for all Notch-related information (especially since this signalling pathway has such a wide array of activities in many organisms and the scientific understanding of it is continuously updating!). By reading this page you should come to a better understanding of Notch in regards to: general molecular mechanisms; embryonic development by systems; examples of animal development; abnormalities and disease; current and potential future research; as well as a couple of links to interesting articles for those who want to read more. There is a [[#Glossary| Glossary]] at the bottom of the page for better understanding of scientific terms used throughout this page, and readers are encouraged to 'expand' any collapsed information on the page to optimise their experience in reading about Notch.
 
<div align="center"><html5media width="560" height="315">https://www.youtube.com/embed/axkDX0XZyN0</html5media></div>
 

===History===
{| class="pretty table"
|-bgcolor="FAF5FF"
| 1914
| First description of a "notch" defect (loss of tissue in the wing) in ''Drosophila'' by John S. Dexter, giving the gene its name<ref>Dexter, J. (1914). The Analysis of a Case of Continuous Variation in Drosophila by a Study of Its Linkage Relations. ''The American Naturalist'', 48(576), 712-758. Retrieved from http://www.jstor.org/stable/2455888</ref>
|-
| 1917
| First allele of ''Notch'' is identified by Thomas Hunt Morgan<ref>Morgan, T. H. (1917). The theory of the gene. ''The American Naturalist'', 51(609), 513-544.</ref>
|-bgcolor="FAF5FF"
| 1930s
| Donald F. Poulson conducts research into the involvement of ''Notch'' in development
|-
| 1958
| An investigation by W.J. Welshons confirmed that the locus of Notch is contained within the 3C7 band of the X chromosome.<ref><pubmed>13635554</pubmed></ref>
|-bgcolor="FAF5FF"
| 1983
| DNA sequences belonging to the Notch locus cloned and determined that RNA is required for the function of the wild type Notch. Further insight developed into the function of Notch and its role in differentiation and regeneration.
|-
| 1986
| The molecular analysis and sequence of the Notch locus was determined by Michael W. Young and his team. A relationship was identified between the protein encoded by the major Notch transcript and mammalian clotting and growth factors.<ref><pubmed>3097517</pubmed></ref>
|-bgcolor="FAF5FF"
| 1989
| Neurogenic loci "Delta" and "Mastermind" identified and research conducted to search for genes which may have an interaction with the Notch protein. It was confirmed that mutations in these loci will affect neurogenesis.
|}

===Overview of Molecular Mechanisms===
Mammals possess a total of four ''Notch'' genes, with five genes for encoding the associated ligands, Delta-like and Jagged. The ''Notch'' genes each code for a single transmembrane receptor. Extracellularly, it contains epidermal growth factor (EGF)-like repeats for ligand interaction and Lin-12-Notch (LN) repeats for regulating the interactions between the extracellular and intracellular regions. Intracellularly, Notch has seven ankyrin (ANK) repeats and a transactivation domain (TAD), as well as a proline, glutamine, serine, threonine-rich (PEST) domain for degradation of Notch.
 
[[File:Notch structure cartoon.jpg|thumb|700px|center|'''The structure of the Notch receptor.'''<ref name="PMID19255248"/> Extracellularly there are epidermal growth factor (EGF)-like repeats and Lin-12-Notch repeats (LNRs). The Notch intracellular domain (NICD) is made up of a rRBP-Jkappa-associated module (RAM) domain, ankyrin (ANK) repeats, and a proline, glutamine, serine, threonine-rich (PEST) domain. There are three sites for cleavage by enzymes: S1, S2, and S3/S4.]]

====Canonical pathway====
[[File:Overview of Notch signalling.png|thumb|500px|'''Summary of canonical Notch signalling.''' The interaction between Delta-like or Serrate ligands (DSL) and the Notch receptor on an adjacent cell initiates proteolytic cleavage of Notch and the release of the Notch intracellular domain (NICD). The NICD is then transported to the nucleus where it can induce transcription of Notch target genes by binding to specific proteins (MAM, CSL).<ref><pubmed>27404588</pubmed></ref>]]
The canonical Notch pathway is unique in that it involves direct interaction between adjacent cells, as opposed to paracrine signalling, because both the Notch ligands and Notch receptors are transmembrane proteins found in the cell membrane. Furthermore, the lack of a secondary messenger or amplification process means that the Notch pathway has limited opportunities for regulation and must therefore be tightly controlled. Depending on its developmental and cellular context, activation or inhibition of the pathway can result in a variety of cellular responses, including cell death, proliferation, or differentiation.<ref name="Introduction to Notch Signalling">Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. ''Notch Signaling: Methods and Protocols''. Methods in Molecular Biology: 1187</ref>
 
Four Notch proteins are involved in the canonical pathway. NOTCH1 to NOTCH4 are single transmembrane receptors and can interact with a variety of ligands, including NOTCH ligands (e.g. Delta ligands) and Serrate ligands. There are three Delta ligands (Dll1, Dll3, and Dll4) and two Serrate ligands (Jagged1 and Jagged2) present in mammals.<ref name="Introduction to Notch Signalling"/> The binding between the Notch receptor and the ligand on the adjacent cell induces the release of the Notch intracellular domain (NICD) via a sequence of proteolytic reactions.<ref name="The Developing Human"/> Cell-cell interaction is therefore critical in the process of triggering Notch signalling.
 
The interaction on the cell surface between Notch and its ligand on an adjacent cell causes the extracellular metalloprotease site (S2 site) to be exposed. The S2 site is then cleaved by transmembrane proteases belonging to the a disintegrin and metalloproteinase/tumour necrosis factor α converting enzyme (ADAM/TACE) family. The remaining Notch fragment subsequently undergoes two more intramembranous cleavages at the S3/S4 sites by the γ-secretase complex. Finally, the NICD is released and enters the nucleus to interact with CSL (CBF1, Suppressor of Hairless, Lag-1) and Mastermind-like proteins (MAMLs). CSL is a DNA-binding protein that acts as a transcription factor by forming repressor or activator complexes; in the absence of the NCID, CSL is bound to corepressor proteins (CoR) that prevent transcription of Notch target genes. MAMLs are transcriptional co-activators that are required for transcription of the target genes, hence they are involved in the regulation of the pathway.<ref name=PMID10075488/><ref name="Introduction to Notch Signalling"/> To stop signalling, the NICD is phosphorylated by kinases and ubiquitinated by E3 ubiquitin ligases, which results in proteasome mediated degradation and subsequent termination of the signal.<ref name="Introduction to Notch Signalling"/>
 

====Non-canonical pathway====
Immense research has been carried out on the canonical Notch pathway and its members are well known. While canonical notch ligands control most of the known Notch signalling, a group of structurally distinct non-canonical ligands exist which activate Notch and its pleiotropic effects. Notch can non-canonically carry out its functions by post-translationally targeting Wnt/β-catenin signalling. This type of signalling is CSL-independent and can also work independently of ligands. Some genes are affected by the non-canonical Notch signalling, however their mediators in most cases are unknown. Notch binds and titrates levels of active β-catenin. Therefore, active β-catenin activity may serve as a useful readout for non-canonical Notch signals.<ref name="PMID22397947">As reviewed by <pubmed>22397947</pubmed></ref>

Recent research has shown that Notch signalling plays crucial roles for cellular differentiation during development through γ-secretase-dependent intramembrane proteolysis followed by transcription of target genes. Hayashi et al. (2016) uncovered a ligand-dependent but γ-secretase-independent, non-canonical Notch signalling involved in presynaptic protein expression in postmitotic neurons.<ref name="PMID27040987"><pubmed>27040987</pubmed></ref>
 

====Transcriptional regulation of Notch signalling====
A number of genes have been found to act as modulators of Notch signalling by modifying the ability of Notch to interact with its ligands. These include proteins acting extracellularly (Fringe, Brainiac, Egghead, Scabrous, Wingless), proteins acting at the cell membrane (Big brain), proteins acting intracellularly (Numb, Sanpodo, Disabled, Deltex, Dishevelled), and proteins acting within the nucleus (Hairless, EMB-5, Strawberry notch).<ref name="PMID9892565">As reviewed by <pubmed>9892565</pubmed></ref>

In ''Drosophila melanogaster'', it has been seen that ''fringe'' is able to affect the ability of Notch to be activated by the Serrate and Delta ligands. Specifically in the ''Drosophila'' wing, it was observed that Serrate did not interact with Notch in specific areas due to the action of ''fringe''<ref><pubmed>9247339</pubmed></ref>. Fringe is not required for initial Notch signalling, but is thought to be important for signalling processes when Notch activation occurs along the borders between distinct cell populations. Research suggests that Fringe specifically affects the binding between Notch and its ligands, rather than an activation step separate or subsequent to ligand binding. The ''brainiac'' and ''egghead'' genes are thought to either influence the production of a Notch ligand or act as substitute ligands themselves.<ref name="PMID9892565"/>
 

====Examples of Proteins Involved in Interaction with the Notch Intracellular Domain (adapted from Table 3<ref name="PMID21828089"/>)====
{| class="pretty table"
|-bgcolor="A3BFB1"
| '''Protein'''
| '''Interaction with NICD'''
|-bgcolor="F5FFFA"
| Adenamatous polyposis coli (Apc)
| Controls Notch trafficking
|-
| Cyclin-dependant kinase 8 (CDK8)
| Phosphorylates NICD to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| CBF1, Su(H) and LAG-1/Recombination signal binding protein for immunoglobulin kappa J region (CSL/RBP-J)
| Main canonical transcriptional co-factor for NICD
|-
| Cyclin C (CycC)
| Targets NICD for phosphorylation to make it a substrate for ubiquitylation and degradation
|-bgcolor="F5FFFA"
| Dishevelled (Dsh/Dvl)
| Controls ligand-independent Notch trafficking; inhibits canonical Notch signalling
|-
| Deltex-1-4 (Dtx1-4)
| Controls Notch ubiquitylation, processing, and internalisation
|-bgcolor="F5FFFA"
| Itchy, E3 ubiquitin protein ligase (Itch)
| Promotes ubiquitylation of NICD
|-
| Mastermind-like 1/2 (Maml1/2)
| Co-activator for NICD/CSL
|-bgcolor="F5FFFA"
| Nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NF-ϰb)
| NICD blocks NF-ϰb transcription of NF-ϰb target genes through binding to p50/cRel NICD enhances NF-ϰb transcription of target genes by retaining NF-ϰb in the nucleus
|-
| Numb homolog (Numb)
| Suppresses Notch signaling by recruiting E3 ubiquitin ligases to ubiquitylate Notch Controls Notch trafficking during asymmetric cell division
|-bgcolor="F5FFFA"
| Smad family members (SMAD)
| Smads enhance Notch signalling; Notch fine-tunes signalling through Smads
|}
 

===Roles in Embryonic Development===
The phylogenetically conserved Notch signalling pathway plays a crucial role in the development of multiple organ systems, and is a major regulator of stem cell fate. It is responsible for the regulation of the transcription of a number of signalling molecules, such as ''MyoD'', ''Mash1'' and ''GATA2'', which are genes controlling the fate of myogenic, neurogenic and haematopoietic stem cells, respectively. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development. If you would like to better understand human embryonic development before reading this section, [https://embryology.med.unsw.edu.au/embryology/index.php/Embryonic_Development| this page] serves as a great resource.
 

====Cardiovascular====

If you would like to generally learn about and become familiar with cardiac development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_11_-_Heart here]!

'''Cardiomyocyte Specification and Differentiation'''

Expression during the appropriate window of the timeline of embryogenesis of Notch receptors, ligands and downstream effector molecules elucidates a role for the Notch pathway in the earliest stages of cardiac development. It has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification as early as during gastrulation. <ref name=PMID19580804><pubmed>19580804</pubmed></ref> Interestingly, Notch has been found to play both suppressive and promoting roles in cardiogenesis.

For example, it has been shown that Notch suppresses cardiomyocyte cell fate specification during early cardiogenesis. This has been demonstrated through studies such as that carried out by Rones and colleagues (2000), which used activation and inhibition of Notch signaling in Xenopus. <ref name=PMID10934030><pubmed>10934030</pubmed></ref>

On the other hand, studies such as that by Boni et al. (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. <ref name=PMID18832173><pubmed>18832173</pubmed></ref> Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).<ref name=PMID16690879><pubmed>16690879</pubmed></ref>

Despite the understanding that Notch signalling is crucial to embryonic myogenesis, the exact molecular mechanism remains elusive. Research by Buas and colleagues (2010) has explored such mechanisms by studying the Notch target, Hey1, which is known to suppress myogenic differentiation. They concluded that this inhibitory function of Hey1 is primarily mediated through binding near to myogenin and Mef2C promoters, which leads to cessation of target gene expression. <ref name=PMID19917614><pubmed>19917614</pubmed></ref>

[[File:Notch CVS simple diagram.png|thumb|500px|right|alt=Simplified Scheme of the Roles of Notch in Cardiac Development|'''Simplified Scheme of the Roles of Notch in Cardiac Development.''' Notch has been found to restrict the expression of specific cardiogenic genes in a spatiotemporal manner and regulate cardiac field specification early in development. Further after cardiac differentiation, Notch influences development of the AVC (atrioventricular canal), cardiac valves, ventricular trabeculae and the cardiac outflow tract. (This student-drawn image is based upon Figure 2 in the 2014 review by Zhou and Liu: [https://www.ncbi.nlm.nih.gov/pubmed/24345875 ''Role of Notch signaling in the mammalian heart.'']<ref name=PMID24345875><pubmed>24345875</pubmed></ref>)]]

'''Development of the Atrioventricular Canal'''

A study by Rutenberg et al. (2006) and another by Kokubo et al. (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).<ref name=PMID17021042><pubmed>17021042</pubmed></ref> <ref name=PMID17259303><pubmed>17259303</pubmed></ref> They used chicken and mouse models, respectively, to show that other signalling factors, ''Bmp2'' and ''Tbx2'', are restricted to the AVC region by Notch signalling during development.

Furthermore, Watanabe and colleagues (2006) showed that deletion of Notch targets increases ''Bmp2'' expression and expansion of the AVC tissue, however other, non-Notch restrictive factors involved in AVC development are likely to exist.<ref name=PMID16554359><pubmed>16554359</pubmed></ref>

'''Heart Valve Development'''

In order for the heart valve to properly form in the embryo, endocardial to mesenchymal transformation (EMT) must occur. The Notch pathway, alongside Wnt and Bmp, has been found to regulate the process of EMT, defects in which can lead to congenital heart valve disease. Interestingly, Timmerman and colleagues (2004) demonstrated that this role of Notch may also promote oncogenic transformation. This team also showed that embryos exhibited abortive endocardial EMT if they were deficient in Notch signalling components in vivo and in vitro. <ref name=PMID14701881><pubmed>14701881</pubmed></ref>

A more recent paper by Wang et al. (2013) further explored the underlying signalling processes and interrelationships of molecules that impact EMT. They found that Jagged1-Notch1 signalling in cells of the endocardium potentiates expression of Wnt4, which in turn carries out paracrine action on adjacent AVC tissue to upregulate Bmp2 expression and thus signal EMT. <ref name=PMID23560082><pubmed>23560082</pubmed></ref>

'''Trabeculation'''

Trabeculation is the initial process of ventricular chamber development that forms a series of cardiomyocyte projections within the lumens of the ventricles of the heart (called trabeculae). Grego-Bessa and colleagues (2007) addressed the roles Notch plays in trabeculation through ''RBPJk'' (the gene product of which interacts with Notch) and ''Notch1'' gene manipulation. Mutants of these two genes showed perturbed expression and signalling of ''EphrinB2'', ''NRG1'' and ''BMP10'', alongside reduced proliferation of myocardiocytes. This research ultimately suggested that ''EphrinB2'' is a direct target of Notch in the endocardium that simultaneously requires the Notch-dependent action of BMP10 and NRG1 in order for ventricular myocardium proliferation and differentiation to occur normally. <ref name=PMID17336907><pubmed>17336907</pubmed></ref> Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato et al. (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>

'''Development of the Outflow Tract'''

TBC
 

====Central Nervous System====

If you would like to generally learn about and become familiar with neural development in the embryo before reading this section, click [https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development here]!

[[File:Notch CNS simple diagram.png|thumb|450px|right|alt=Simplified Diagram of Roles of Notch in Neuronal Differentiation|'''Simplified Diagram of Roles of Notch in Neuronal Differentiation'''. Notch influences the differentiation of embryonic stem cells into neural cells via signalling with RBP (recombining binding protein), cyclin D1 and Hes1. (This student-drawn image is based upon Figure 1 from Chuang, Tung and Lin's 2015 review: [https://www.ncbi.nlm.nih.gov/pubmed/25815127 ''Neural differentiation from embryonic stem cells in vitro: An overview of the signaling pathways'']<ref name="PMID25815127"><pubmed>25815127</pubmed></ref>)]]
'''Early Neural Differentiation'''

Notch plays a major role in promoting neural commitment of cells. Lowell and colleagues (2011) used genetic manipulation to discover that the phenotype of stem cells is not affected by constitutively activated Notch in mouse embryonic stem cells (mESCs), however, interfering with Notch signalling -for example by pharmacological means- did impede neural fate determination. This role required Notch signalling via fibroblast growth factor (FGF) receptors. Furthermore, the conservation of the Notch signalling pathway within pluripotent stem cells is implied due to the existence of Notch ligands in stromal cells in human embryonic stem cells (hESCs) that induce neural differentiation. <ref name=PMID16594731><pubmed>16594731</pubmed></ref>

Das and colleagues (2010) manipulated Notch protein levels during specific stages of neural differentiation and found that if Notch signalling pathways were activated during day 3 of neural development for 6 hours, cell proliferation was dramatically enhanced. This was attributed to the induction by Notch of cyclin D1 expression. Without Notch signalling during neural development, there was reduced cyclin D1 levels. Manipulation of mESCs to express a dominant negative form of cyclin D1 resulted in abrogation of cell proliferation stimulated by Notch. Overall these results imply a temporally-specific role for Notch in CNS development, and that it requires cyclin D1 as a signalling molecule.<ref name=PMID20887720><pubmed>20887720</pubmed></ref>

Hes1 has also been shown to play a Notch-mediated role in neural progenitor maintenance, which is essential for proper development since cells need to proliferate only during specific periods in the embryo for the correct number, cell type and function to result. Shimojo, Ohtsuka and Kageyama (2008) used real time imaging in mice to show that Notch induces oscillatory expression of ''Hes1'' and other Notch target genes to maintain the complex temporal organisation of events in neural development. They concluded that further research could elucidate more about Hes1 oscillations in regards to neural progenitor maintenance, proliferation and differentiation <ref name=PMID18400163><pubmed>18400163</pubmed></ref>.

Lastly, as well as influencing neural progenitor differentiation, it has been found that Notch also impacts the development and maintenance of polarised neural structures in the embryo. This was concluded from a knockout study in mice that elucidated a role for RBP (recombining binding protein), downstream of Notch, in modulating neural differentiation and maintaining rosette structure (an experimental ''in vitro'' correlate used for neural tube development) <ref name=PMID23675446><pubmed>23675446</pubmed></ref>. The researchers concluded that RBP knockouts lacked canonical Notch signalling and as a result showed multiple neurulation defects.
 

====Other Systems====

As aforementioned, Notch plays a wide array of roles in embryonic development, the follow table summarises these roles by each organ system:

<big>Summary Table of Examples of Notch Signalling in Developmental Processes</big> (adapted from Table 1<ref name="PMID21828089">As reviewed by <pubmed>21828089</pubmed></ref>)
{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Organ/Tissue'''
| '''Processes regulated by Notch'''
|-bgcolor="F5FAFF"
| Brain
| Controls the balance between gliogenesis and neurogenesis; stem cell maintenance<ref><pubmed>21262462</pubmed></ref><ref>As reviewed by <pubmed>20816397</pubmed></ref>; organisation and maintenance of polarity during early development<ref name="PMID23675446"/>
|-
| Craniofacial structures
| Palate morphogenesis: loss of Notch signalling results in cleft palate, fusion of the tongue with the palatal shelves, and other craniofacial defects; also involved in tooth development
|-bgcolor="F5FAFF"
| Ear
| Defines the presumptive sensory epithelium; determines hair cell and supporting cell fates
|-
| Esophagus
| Regulates esophageal epithelial homeostasis
|-bgcolor="F5FAFF"
| Heart
| Cardiac patterning, cardiomyocyte differentiation, valve development, ventricular trabeculation, outflow tract development
|-
| Intestine
| Controls proliferation and differentiation, including absorptive vs. secretory cell fates
|-bgcolor="F5FAFF"
| Limbs
| Apical ectodermal ridge (AER) formation and digit morphogenesis, especially regulation of apoptosis
|-
| Lungs
| Lateral inhibition between tracheal cells prevents extra cells from assuming the lead position during tracheal branching morphogenesis
|-bgcolor="F5FAFF"
| Neural crest
| Controls patterning of neural crest precursors for the outflow tract region of the heart; regulates the transition from Schwann cell precursor to Schwann cell, controls Schwann cell proliferation and inhibits myelination; controls melanocyte stem cell maintenance
|-
| Pancreas
| Specifies endocrine cell differentiation through lateral inhibition: endocrine lineage cells inhibit endocrine differentiation of their neighboring cells; maintains pancreatic endocrine precursor cells, inhibits terminal acinar cell differentiation; controls pancreatic epithelium branching and bud size
|-bgcolor="F5FAFF"
| Skin
| Regulates cell adhesion, control of proliferation, hair follicle or feather papillae differentiation and homeostasis
|-
| Thyroid
| Regulates the numbers of thyrocyte and C-cell progenitors and regulates differentiation and endocrine function of thyrocytes and C-cells<ref><pubmed>21364918</pubmed></ref>
|-bgcolor="F5FAFF"
| Vasculature
| Regulates arteriovenous specification and differentiation in endothelial cells and vascular smooth muscle cells; regulates blood vessel sprouting and branching
|}

====Quiz Your Notch-Knowledge on Embryonic Development!====

<quiz display=simple>

{ In the development of which organ does Notch exert lateral inhibition to differentiate endocrine cells?
|type="()"}
-   The heart
-   The central nervous system
-   The skin
+   The pancreas
|| Remember, Notch signals endocrine lineage cells of the developing pancreas to inhibit endocrine differentiation of their neighbouring cells, known as lateral inhibition. Notch plays various roles in the heart, central nervous system and skin, but not in this way.
</quiz>
 

===Roles in Animal Development===

The Notch signalling pathway doesn't just play a significant role in human development, but also affects events such as neurogenesis and myogenesis in some animals (thus why these animals are often used as models for human development in research!). Read below for information on some of these roles for Notch.

[[File:Notch animals.png|thumb|450px|right|alt=Animals Whose Developmental Processes are Affected by Notch.|'''Animals Whose Developmental Processes are Affected by Notch.''' This is a simplified representation of a few examples of the animals (Drosophila flies<ref name=PMID21447553><pubmed>21447553</pubmed></ref>, C. elegans<ref name=PMID18599512><pubmed>18599512</pubmed></ref>, and the zebrafish<ref><pubmed>23840804</pubmed></ref>) in which development is influenced by the Notch signalling pathway, and their scientific names.]]

====''Drosophila melanogaster''====

'''(The Fly)'''

Unlike the four Notch paralogs in humans, only one Notch homolog is present in ''Drosophila''.<ref name="Introduction to Notch Signalling"/>

Both canonical and non-canonical Notch signalling are involved in the structural and physiological responses and functional plasticity of olfactory receptor neurons in reaction to prolonged odour exposure.<ref><pubmed>26986723</pubmed></ref><ref><pubmed>26011623</pubmed></ref> Research has also shown that Notch is crucial for the formation of longitudinal connections in the Drosophila CNS. Kuzina, Song, and Giniger (2011) created temperature-sensitive mutations of Notch genes that prevented the development of mature longitudinal axon tracts. Additionally, it was found that the Notch phenotype appears at the earliest stages of the development of longitudinal connections in the CNS by observing early stage 13 embryos.<ref name=PMID21447553><pubmed>21447553</pubmed></ref>
 

====''Caenorhabditis elegans''====

'''(The Worm)'''

The Notch pathway in ''C. elegans'' occurs throughout development in populations of equipotent cells for neuronal function in postmitotic differentiated neurons. In these postmitotic neurons, there is a specialised post-embryonic development stage knows as 'dauer'. The Notch pathway is activated when cell signalling downstream of the developmental decision enter dauer. The Notch receptor glp-1 and the ligand lag-2 are expressed in the dauer stage and aid in maintaining this stage. Another Notch receptor, lin-12, functions upstream of insulin signalling components to promote conditions for growth and enhance dauer recovery. <ref name=PMID18599512><pubmed>18599512</pubmed></ref>
 

====''Danio rerio''====

'''(The Zebrafish)'''

The expression of Notch in the myogenic region and apical ectodermal ridge (AER) of the developing zebrafish fin is similar to what has been observed in developing chicken and mouse limbs, which shows how highly conserved the role of Notch signalling is in the development of appendages in vertebrates. During zebrafish embryogenesis, the timing and positioning of fin formation are dependent on Notch signalling. Notch is also involved in the actual processes of fin formation, such as AER signalling, chondrogenic differentiation, and myogenesis. In zebrafish embryos with defective Notch signalling, it was observed that the skeletal muscle fibres were thin and fragmented and the structure of the sarcomeres was significantly compromised. <ref name="PMID23840804"><pubmed>23840804</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Expand this for an image from this research study</big>
|-
|[[File:Abnormal pectoral fins are formed in Notch signalling disrupted larvae.jpg|thumb|450px|right|alt=Abnormal pectoral fins are formed in Notch signalling disrupted larvae|'''Abnormal pectoral fins are formed in Notch signalling disrupted larvae.''' (A–F) Live pictures of 5 dpf larvae. (A’) A pectoral fin from a sibling embryo showing the cartilaginous endoskeletal disc with individualized cells surrounded by thin matrix deposits, the fin fold and the chleitrum (n = 17) (E, E’). A similar pectoral fin was found in a DMSO-treated embryo (n = 9). Pectoral fins of Notch signalling disrupted embryos such as mibta52b (n = 18) (B, B’), jagged2 (n = 10) (C, C’) and Su(H)1+2 (n = 12) (D, D’) morphants and DAPT-treated embryos (n = 10) (F, F’) showing disorganized endoskeletal disc cells. cl, chleitrum; ed, endoskeletal disc; ff, fin fold.<ref name="PMID23840804"/>]]
|}
 

====Quiz Your Notch-Knowledge on Animal Development!====

<quiz display=simple>

{In which animal (as described in this section) has it been shown that defective notch signalling leads to thinning and fragmentation of skeletal muscle fibres?
|type="()"}
-   Drosophila melanogaster
-   I don't know!
-   Caenorhabditis elegans
+   Danio rerio
|| Remember, it was observed in one study that the skeletal muscle fibres of zebrafish (Danio rerio) were thin and fragmented and the structure of their sarcomeres were significantly compromised.<ref><pubmed>23840804</pubmed></ref>
</quiz>

===Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 1<ref name="PMID17761886"><pubmed>17761886</pubmed></ref>)===
{| class="pretty table"
|-bgcolor="a3bfb1"
| '''Mammals'''
| '''''Drosophila'''''
| '''''C.elegans'''''
| '''Function'''
|-bgcolor="F5FFFA"
| Notch 1-4
| Notch
| Lin-12, Glp-1
| Single transmembrane receptor and transcription factor
|-
| Delta 1, Delta3-4, Jagged1-2
| Delta, Serrate
| APX-1, LAG-2, ARG-1, DSL-1
| Single transmembrane ligands of the Notch receptor
|-bgcolor="F5FFFA"
| CBF1/RBPJK Mastermind1-3
| Su(H) Mastermind
| Lag-1 Lag-3
| DNA-binding transcription factor Transcriptional co-activator
|-
| Lunatic, manic, and radical Fringe
| Fringe
|
| Modifies both Notch and its ligands
|-bgcolor="F5FFFA"
| ADAM10, ADAM17
| Kuzbanian, Kuzbanian-like, TACE
| SUP-17, ADM-4
| Metalloproteases targeting S2 Notch cleavage sites
|-
| Presenilin 1-2, nicastrin, APH1, PEN2
| Presenilin, nicastrin, APH1, PEN2
| SEL-12, APH-1, APH-2, PEN2
| Proteins of the γ-secretase complex, which targets Notch S3 and S4 cleavage sites
|-bgcolor="F5FFFA"
| Mind bomb, skeletrophin, neuralized 1-2
| Mind bomb 1-2, neuralized
| Y47D3A.22
| E3 ubiquitin-protein ligases that targets Delta and Jagged/Serrate and regulate their endocytosis
|}
 

===Abnormalities in Notch Signalling===
Mutations in Notch genes and hence defects in Notch signalling have been implicated in the pathogenesis of several inherited diseases in humans.<ref name="PMID23729744">As reviewed by <pubmed>23729744</pubmed></ref><ref name="PMID22306179">As reviewed by <pubmed>22306179</pubmed></ref>
 

{| class="pretty table"
|-bgcolor="CEDFF2"
| '''Disease'''
| '''Gene'''
| '''Phenotype'''
|-bgcolor="F5FAFF"
| Alagille syndrome ([http://omim.org/entry/118450 OMIM118450], [http://omim.org/entry/610205 OMIM610205])
| ''JAG1'', ''NOTCH2''
| Developmental abnormalities of the heart, liver, eye, and skeleton. Neonatal jaundice and cholestasis are early symptoms.
|-
| CADASIL ([http://omim.org/entry/125310 OMIM125310])
| ''NOTCH3''
| Autosomal vascular disorders linked to ischemic strokes, dementia, and premature death.
|-bgcolor="F5FAFF"
| T-cell acute lymphoblastic leukaemia ([http://omim.org/entry/613065 OMIM613065])
| ''NOTCH1'' (mutation in heterodimerization domain or PEST domain)
| Tumour derived from T-cell progenitors. Symptoms include anaemia and enlargement of lymph nodes in the liver and/or spleen.
|-
| Spondylocostal dysostosis ([http://omim.org/entry/122600 OMIM122600])
| ''DLL3'', Lunatic fringe
| Vertebral segmentation defects as well as rib abnormalities.
|}

====Alagille Syndrome====
Alagille syndrome (AGS) is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. Diagnostic characteristics of the disease include liver disease, cardiac disease, vertebral defects, eye conditions, and facial features, as well as renal and vascular abnormalities.<ref><pubmed>26548814</pubmed></ref> In 94% of clinically diagnosed cases, a mutation in the gene encoding the Notch ligand JAG1 has been identified as a contributing factor. In combination with this, a mutation in the NOTCH2 gene has also been implicated in the manifestation of AGS in some patients.<ref><pubmed>16773578</pubmed></ref>
 

====Spondylocostal Dysostosis====
Spondylocostal Dysostosis (SD) is a collective term for conditions characterised by anomalies relating to rib and spine. The vertebrae are fused and shaped abnormally which can result in scoliosis. Similarly, the ribs may also be fused together or in some cases completely missing. As a result, people with this condition have short trunk dwarfism where their bodies are short in stature but have normal length limbs. Genetic changes are known to cause SD. SD Type 1 is the most prevalent form of this disease which is caused by the mutation in the delta like canonical Notch ligand 3 (DLL3 gene).<ref><pubmed>10742114</pubmed></ref> DLL3 provides the information for making a protein that regulates the Notch signalling pathway. The DLL3 protein in conjunction with the Notch pathway is primarily responsible for preventing the fusion of future vertebrae in a process known as somite segmentation.<ref><pubmed>11236715</pubmed></ref> An interruption in the Notch pathway inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine as seen in SD. 25 percent of SD arise from mutations in the identified genes and further research suggest that other genes involved in the Notch signalling pathway may also be related to SD.
 

====Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)====
CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life. The symptoms, age of onset, and prognosis are variable. Distinguishing symptoms include subcortical ischemic events (60-80% of cases), cognitive impairment (60% of late stage disease), migraines (30-40%), mood disturbances (30%), and apathy (40%).<ref name="PMID21045164"><pubmed>21045164</pubmed></ref><ref name="PMID20301673"><pubmed>20301673</pubmed></ref> Approximately 5-10% of CADASIL patients also experience seizures. The mean age of onset is 45 years of age and the disease duration is between 10–40 years. More than 95% of CADASIL cases present with pathogenic mutations in NOTCH3 (located on chromosome 19p13), specifically the epidermal growth factor-like repeat domain.<ref name="PMID20301673"/><ref><pubmed>24579972</pubmed></ref> The NOTCH3 gene is involved in the normal development of blood vessels in both fetal and adult brains. In adults, NOTCH3 is expressed in the smooth muscle cells of arteries.<ref name="PMID21045164"/> There is currently no effective treatment available for CADASIL.
 

====Congenital Heart Defects====

'''Aortic Valve Disease'''

[[File:Aortic valve disease.jpg|thumb|450px|right|alt=Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves|'''Loss of NOTCH1 expression in proximity to calcific nodules in human aortic valves.''' (A) Representative sections from control (A,B) and diseased (C-F) aortic valve cusps. (B) is high magnification image of boxed area in (A) and (D,E) are higher magnification of region in (C) while image in (F) shows another calcified aortic valve. Expression of Notch1 intracellular domain (NICD) is found in the thickened fibrosa of diseased aortic valve (C,E) as compared to the acellular fibrosa of control valves (A,B). However, there is significant loss of NICD expression in cells residing adjacent to calcific nodules (D,F). The fibrosa is oriented upward in all panels, and scale bars equal 100 microns (B,D,E,F are at same magnification). Brown signal represents NICD expression while nuclei are counterstained in blue.<ref name="PMID22110751"><pubmed>22110751</pubmed></ref>]]

Calcification of the aortic valve is a leading cause of adult heart disease. Mutations in NOTCH1 have been found to cause various aortic valve abnormalities, including the development of a bicuspid aortic valve (as opposed to tricuspid) and valve calcification.

&emsp;&emsp;A study by Garg et al. (2005) looked at mouse embryos and the expression of ''Notch1'' during development. It was found that during normal embryonic development, ''Notch1'' was abundantly expressed in the outflow tract mesenchyme (which develops into the heart valves) and the endocardium, as well as in the endothelial layer and mesenchyme of the aortic valve leaflets at the time of arterial trunk septation. Abnormal ''Notch1'' led to the death of mice from vascular endothelial defects. Garg et al. then investigated whether NOTCH1 was involved in calcium deposition and therefore valve calcification. This is thought to be due to differentiation of valve cells into osteoblast-like cells. This leads to the upregulation of osteopontin, osteocalcin, and other osteoblast-specific genes, which is normally regulated by the transcription factor Runx2. Runx2 is known to be upregulated in animal models of valve calcification. Garg et al. found that Notch1 was capable of repressing Runx2 activation. Heart tissue and vasculature are normally abundant with the hairy-related transcriptional repressors Hrt1 and Hrt2 (also called Hey1 and Hey2), which are normally activated by Notch and are key mediators of the Notch pathway. Hrt1 and Hrt2 were both expressed in the endothelium of the mice aortic valve leaflets, the endocardium, and the vascular endothelium. They were found to inhibit the activation of osteoblast-specific genes by Runx2. It was thought that Hrt proteins can repress Runx2 by physical interaction as well as mediate Notch1 repression of Runx2. Therefore, a defect in Notch will cause upregulation of Runx2, due to the lack of repressor activity by Notch itself and the activation of the repressors Hrt1 and Hrt2. This leads to the expression of osteoblast genes that results in the differentiation of valvular cells into osteoblast-like cells and ultimately causes aortic valve calficiation.<ref><pubmed>16025100</pubmed></ref>

The picture to the right is a histological image of aortic valve disease from a study performed in rats investigating molecular changes that occurred when Notch signalling was suppressed in the aortic valve.<ref name="PMID22110751"/>

 

====Tumourigenesis====
Notch has been shown to be involved in cancer development and can act as both an oncogene and a tumour supressor gene.<ref>As reviewed by <pubmed>14570040</pubmed></ref><ref name="PMID23729744"/>

'''T-Cell Acute Lymphoblastic Leukaemia''' 
T-cell acute lymphoblastic leukaemia (T-ALL) is an aggressive childhood cancer of the immune system's T-cells. The NOTCH1 gene encodes the Notch receptor that is involved in the determination of pluripotent cell progenitors to T-cells and the organisation of these cells in the developing thymus. Activating mutations in the extracellular domain and/or the C-terminal PEST domain of NOTCH1 have been identified in more than half of all cases of T-ALL.<ref><pubmed>15472075</pubmed></ref>

{| class="wikitable mw-collapsible mw-collapsed"
! Other Examples of Roles of Notch in Cancer (adapted from ''Notch in disease''<ref name="PMID23729744"/>)
|-
|-bgcolor="a3bfb1"
| '''Gene'''
| '''Role of Notch'''
| '''Disease'''
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2''
| Oncogene Tumour suppressor
| Pancreatic ductal adenocarcinoma
|-
| ''NCSTN'' ''MAML1'' ''APH1A'' ''NOTCH2''
| Tumour suppressor
| Chronic myelomonocytic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Chronic lymphocytic leukaemia
|-
| Activated NOTCH
| Tumour suppressor
| Hepatocellular carcinoma
|-bgcolor="F5FFFA"
| ''NOTCH1'' ''NOTCH2'' ''NOTCH3''
| Tumour suppressor
| Head and neck squamous cell carcinoma
|-
| NOTCH
| Tumour suppressor
| B-cell acute lymphoblastic leukaemia
|-bgcolor="F5FFFA"
| ''NOTCH1''
| Oncogene
| Non-small-cell lung cancer
|-
| ''NOTCH1''
| Oncogene
| T-cell acute lymphoblastic leukaemia
|}
 

====Quiz Your Notch-Knowledge on Abnormalities in Notch Signalling!====

<quiz display=simple>

{ What is the name for the collection of rib and spine abnormalities that result from interruption in the Notch pathway that leads to inhibition of somite segmentation in the embryo?
|type="()"}
-   Alagille Syndrome
-   T-cell acute lymphoblastic leukaemia
+   Spondylocostal Dysostosis
-   CADASIL
|| Remember, Spondylocostal Dysostosis is a collective term for conditions characterised by anomalies relating to rib and spine. Genetic changes lead to an interruption in the Notch pathway that inhibits the somite segmentation resulting in abnormalities relating to the ribs and spine. Alagille syndrome is an autosomal dominant, multisystem disorder that mainly affects the liver, heart, and kidney. T-cell acute lymphoblastic leukaemia is an aggressive childhood cancer of the immune system's T-cells. CADASIL is an autosomal-dominant disease of the small to medium-sized arteries, mainly in the brain, that leads to dementia and disability in mid-life.
</quiz>

===Current Areas of Research and Future Directions===
 
Notch has been identified as having a role in the development of several cancers, and therefore research has recently begun investigating the use of Notch inhibitors in cancer treatment.<ref>As reviewed by <pubmed>27732970</pubmed></ref> γ-secretase inhibitors (GSIs), which inhibit the normal cleavage of Notch at the cell membrane and hence NICD release, have been a popular area of research. In the specific case of desmoid tumours, it was observed that treatment GSIs resulted in decreases in NICD and Hes1 expression in the tumour cells. Overall, tumour cell migration and invasion were decreased and cell growth was also inhibited.<ref><pubmed>26349011</pubmed></ref> GSIs have also been shown to have an inhibitory growth effect on pancreatic, breast, and lung cancers, but unfortunately they also produce side effects ''in vivo''.<ref>As reviewed by <pubmed>27688721</pubmed></ref> Therefore continued study into GSIs is required to make them safe for human treatment. Ultimately, with ongoing research, it is possible that the Notch pathway will eventually become an effective therapeutic target for cancers.
 

<big>To search and read recent PubMed research and review articles on Notch, click [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Notch here]!</big>
 

===Want to Read More About Notch?===

{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences adult development as well!</big>
|-
|Interestingly, Notch does not only play a role in human embryonic development, but has also been found to influence developmental processes after birth. One of these processes is neurogenesis, for example.

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159580/ '''Not(ch) just development: Notch signalling in the adult brain.''']

This review explains that the Notch signalling pathway, which is so often regarded as a major molecular player in development, actually has important functions related to neural cells in the adult. As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch abnormalities are involved in a number of diseases, which underlines its importance in maintaining adult brain function. Some highlights of this review are: Figure 2 provides a schematic representation of precise roles Notch activation can play in the adult brain; explanations of the ways that Notch influences brain plasticity; and the discussion of conflicting results of studies exploring the role of Notch in stroke recovery.<ref name=PMID21505516><pubmed>21505516</pubmed></ref>
|}
 
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch Modulation for Therapy</big>
|-
|As you would have read in the [[#Abnormalities in Notch signalling| Abnormalities in Notch Signalling]] section, Notch can play different roles in cancer development. An interesting review further elucidates that modulation of Notch signalling is actually being investigated as a potential target for cancer therapy:

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704338/ '''Targeting the Notch signaling pathway in cancer therapeutics''']

This articles focuses on reviewing data emerging from recent research, explaining how Notch contributes to the development of a number of cancers, and then outlining the current focuses of investigations into how to therapeutically manipulate the Notch pathway. Some highlights from this review are: the detailed description of how Notch interacts with other signalling pathways such as Wnt and the signalling cytokine Interleukin-6; explanations of the seemingly conflicting roles of Notch as a tumour promoter and suppressor; and discussion of the findings of various Notch-related studies in cancer stem cells.<ref name=PMID26767041><pubmed>26767041</pubmed></ref>
|}
 
{| class="wikitable mw-collapsible mw-collapsed"
! <big>Notch influences reproduction in worker honey bees!</big>
|-
| In our [[#Roles in Animal Development| Roles in Animal Development]] section we discussed Notch in relation to a number of animals, however one that we did not cover was the worker honey bee, or ''Apis mellifera''. A recent study shows that Notch also plays a role in these honeybees!

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976197/ '''Notch signalling mediates reproductive constraint in the adult worker honeybee.''']

This research paper essentially concludes that in the worker honeybee Notch signalling constrains reproduction between males and females; they were the first team to elucidate a molecular mechanism underlying the link between adult ovary activity in bees and the presence of the queen bee. Some highlights from this unique and interesting study are: the background explanation that female worker bees have suppressed activity due to pheromones produced by the queen; the finding that Notch plays a part in this inactivation of reproductivity; and the discussion about social control of reproduction and evolution.<ref name=PMID27485026><pubmed>27485026</pubmed></ref>
|}
 

===Glossary===
{| class="pretty table"
|-
| '''AER'''
| 'Apical Ectodermal Ridge' is a structure that forms from the ectodermal cells at the distal end of each limb bud. The AER acts as a major signalling centre in order to ensure proper limb development.
|-
| '''Apoptosis'''
| Programmed cell death which occurs in the development of many systems.
|-
| '''Cardiogenic'''
| From cardiogenesis - meaning formation of the heart.
|-
| '''Cardiomyocyte'''
| The muscle cells (myocytes) that make up the cardiac muscle
|-
| '''Congenital'''
| (Of a disease or physical abnormality) present from birth.
|-
| '''Craniofacial'''
| Meaning relating to the cranium and the face.
|-
| '''Cyclin D1'''
| A protein required for progression through the G1 phase of the cell cycle. Read more about it [https://en.wikipedia.org/wiki/Cyclin_D1 here], or see information on its encoding gene here: [http://omim.org/entry/168461 OMIM168461].
|-
| '''Endocardial'''
| From endocardium - meaning the thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves.
|-
| '''Endocrine'''
| As in the endocrine system, refers to glands that secrete hormones or other substances directly into the blood.
|-
| '''Epithelium'''
| The thin tissue that forms the outer layer of a body's surface and also lines the alimentary canal and other hollow structures.
|-
| '''Gastrulation'''
| Describes the formative process of the formation of the trilaminar embryo containing the three germ layers.
|-
| '''Gliogenesis'''
| The formation and development of glial cells (astrocytes, oligodendrocytes, Schwann cells, microglia).
|-
| '''Haematopoietic'''
| From haematopoiesis - meaning the formation of blood cellular components
|-
| '''Homeostasis'''
| The ability to maintain a constant internal environment in response to environmental changes.
|-
| '''Ligand'''
| A molecule that binds to a specific binding site on a protein (receptor).
|-
| '''Mef2C promoters'''
| Myocyte-specific enhancer factor 2C is a transcription factor in the Mef2 family that is encoded by the gene ''MEF2C'' in humans ([https://omim.org/entry/600662 OMIM 600662]). This gene is involved in cardiac morphogenesis and myogenesis, as well as vascular development. It is thought to also possibly play a role in neurogenesis.
|-
| '''Mesenchymal'''
| From mesenchyme - meaning a loosely organised, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
|-
| '''Morphogenesis'''
| Refers to the origin and development of morphological characteristics.
|-
| '''Myogenic'''
| From myogenesis - meaning formation of muscle.
|-
| '''Myogenin'''
| Also known as myogenic factor 4, this is a muscle-specific basic-helix-loop-helix transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair.
|-
| '''Neural Crest'''
| In vertebrate embryos, this is a transient structure that gives rise to most of the peripheral nervous system and to a number of non-neural cell types such as the smooth muscle cells of the cardiovascular system.
|-
| '''Neurogenic'''
| From neurogenesis - meaning the formation of nervous tissue.
|-
| '''Neurulation'''
| The folding process in vertebrate embryos whereby the neural plate transforms into the neural tube.
|-
| '''NICD'''
| Notch intracellular domain
|-
| '''Oncogenic'''
| From oncogenesis, also known as tumorigenesis or carcinogenesis - meaning the formation of a cancer, whereby normal cells are transformed into cancer cells.
|-
| '''Paracrine'''
| A hormone that exerts an effect only in the vicinity of the gland secreting it.
|-
| '''Protease'''
| An enzyme which breaks down proteins and peptides.
|-
| '''Stromal cells'''
| The connective tissue cells of any organ. They support the function of the parenchymal cells of that organ. Fibroblasts and pericytes are among the most common types of stromal cells.
|-
|}

====Further Glossary Links====
[[A|A]] | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]] | [[Numbers|#]]

===References===
<references/>

Talk:2016 Group Project 2

2016-10-25T05:24:54Z

Z5015014:

{{ANAT2341Project2016discussionheader}}

===Tips from Mark Hill about our wiki pages===

*in the introduction:
**Describe what the signaling pathway does,
**what the project page is going to talk about
**Make limitations as to what you will cover and what you will not cover
**Describe the importance of that signaling
*don't need to reference glossary
*quiz is a very useful resource
*make sure the reference list is sorted properly so no multiple entries for same reference
*if you use any complicated terms/acronyms in a diagram make sure the acronyms are listed below the picture on the page so it is easier for the reader to understand
*videos are a good extra to have on the page (make sure they can play on the page)
*include what is still unknown about the signalling pathway - read the discussions of recent papers to see what is still unknown/future directions of research

'''comments specific to our page:'''
*the history timeline needs to be referenced at each point (there should be a research paper referenced for each point)
*if table is based upon a review say that at the top with a link to the reference
*link to embryology pages for background information for readers (e.g. i linked the cardiac development page at the top of the section about notch in cardio development)
*make sure the quiz answers have descriptions as to why the correct answer is true and why the others are wrong
*OMIM links are good
*make sure further reading section links to well-explained, current articles

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 16:24, 25 October 2016 (AEDT) hey pals, I think the main sections we need to fill out a bit more content on are Notch in embryonic development of CNS + other systems, animal models of Notch (especially knock-out models), and history/timeline. so if you could focus on adding stuff there then I think our page will be great! and I'll finish off the molecular pathway part.

[[User:Z3462474|Z3462474]] ([[User talk:Z3462474|talk]]) 08:21, 12 October 2016 (AEDT) Hey everyone i have an idea based on some of the feedback we got from the peer reviews saying to make our page more 'student friendly' and maybe incorporate a quiz, I was thinking at the end of each subsection we could have 1 or 2 quiz questions for people to test themselves on. I thought this might be better than just one big quiz at the bottom since it'll keep people involved as they read through the page. Let me know what you think!

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 12:31, 21 October 2016 (AEDT) I changed some of the formatting of the images but if you don't like the placement then we can change it back! also I've put in a lot of tables, I don't think all of them will be necessary so let me know what you think or if we should keep them all.

===To do before Friday===

[[User:Z3462474|Z3462474]] ([[User talk:Z3462474|talk]]) 14:48, 14 October 2016 (AEDT) hey guys please read through this and indicate what you are able to work on before the due date next Friday (i think its friday but am now having trouble finding any solid info on the wiki page, i had this friday written in my diary as the due date)! Let me know if I've forgotten anything we need to cover :)

'''For Everyone to do:'''
*Drawings to support explanations (I'm happy to do ones for the different development systems since I've been working on these areas)
*Glossary for any words in your section that aren't common knowledge
*One quiz question for the end of each of the content sections -Present under a subheading ‘Test Your Knowledge on (Section)’
*Fix anything you see needs fixing from the feedback I posted that refers to your section

'''Subheadings to fill in:'''

we could put our names under each one we will do
*Extend the history timeline
*Receptor subtypes summarised in a table (see feedback) - '''Lydia'''
** This textbook chapter looks like it has a good diagram (figure 8.1) summarising the Notch targets [http://www.sciencedirect.com.wwwproxy0.library.unsw.edu.au/science/article/pii/S0070215310920085 Chapter Eight - Notch Targets and Their Regulation]
*After non-canonical section: Video/simplified representation (maybe a table or a simple drawn diagram?) comparing canonical and non canonical - '''Lydia''' (I'll try!)
*Neuro development - '''Elisa''', '''Lydia'''
*Other development -
*Introductory sentence under Animal models heading - '''Elisa'''
*Current Research and Future Directions
*Further Reading (maybe just linking and displaying some interesting resources for notch, student friendly ones) - '''Lydia''' (I'll link some good review articles I've found) - '''Elisa''' (I've got a couple too I'll add!)

===things we can improve===

[[User:Z3462474|Z3462474]] ([[User talk:Z3462474|talk]]) 08:15, 12 October 2016 (AEDT) hey guys I've read through the peer reviews and have jotted down the main aspects that other students have suggested we improve so thought I'd post them here so we don't all have to read through all the reviews: (my notes are not in any order of importance)

[[User:Z3491219|Z3491219]] hey sounds good .. i'll try and find a good video on non canonical pathway and once again i've done the parts but i have to reference them and put it up. i have a group presentation tomorrow so i'll try and finish my part by wednesday :)
* add more info under CNS
* better summarise/explain the differences between canonical and non canonical pathways especially in terms of embryology, perhaps using a video
* add more terms to glossary, a number of terms throughout our page were unfamiliar to readers
* add more interactive and engaging features such as a quiz or video
* investigate more organ systems and how notch plays a role in their development
* draw pictures ourselves instead of using other people's, then we can emphasise the more relevant parts
* stop saying ‘and colleagues’ so much (this is my section haha i will fix it!)
* extend the history section past 1989
* expand on how the canonical pathway is tightly controlled, is it through transcriptional regulation or other mechanisms?
* Alagille Syndrome - how is the mutation brought about?
* Add a ‘Further Reading’ section linking interesting articles or facts
* Add references to the history section
* Change the images to have their descriptions/captions on the page so its easier to understand
* Add other forms of media such as videos
* Canonical pathway: mention specific gene targets of Notch
* try to see if we can add information on how Notch’s receptors come about (what genes transcribe the receptors, how the protein is processed or expressed before the pathway can start to work)
* summarise receptor subtypes involved in different pathways, their role in embryonic development and abnormalities related to embryonic development, in a table
* Make introduction a bit easier to understand with a hand-drawn diagram supporting the information

===Group Presentation===

[[User:Z3491219|Z3491219]] hey guys I've done non canonical pathway , transcriptional regulation of NOTCH signalling, congenital heart defects
and development of the outflow rate. i just need to figure out how to upload it :P

Bystander Effect Fuels Human Induced Pluripotent Stem Cell-Derived Neural Stem Cells to Quickly Attenuate Early Stage Neurological Deficits After Stroke

'''Google Slides Document for making our presentation'''

https://docs.google.com/presentation/d/1weuOzJTEpbmh0JoW2-OGV6j8plIkDh4SxwZ_AasdkBA/edit?usp=sharing

=Peer Review=
 
 
Group 2:
 
 
Positive aspects of the project and suggested improvements: 
Group 2 has provided a variety of different topics related to the Notch receptor, such as its molecular pathway, its role in embryonic developing both in humans and animals as well as abnormalities caused by disruption in the receptor’s normal function (criteria 6). This variety is excellent, as it informs the audience of various aspects of the Notch receptor ranging from normal to abnormal development as well as newly emerging research (criteria 1.). Group 2 has also utilised both tables and diagrams to represent Notch receptor’s history and signalling pathway respectively (criteria 2). The use of diagrams is a great idea as it allows peers to understand the complexity of the signalling pathway in a much simpler manner (criteria 4).
 
 
In addition, the authors have correctly utilised in text citations when referencing all sources and have created a list of references at the conclusion of the page (criteria 3). Group 2 also investigated specific components of organ development which was another magnificent feature of their page, such that they divided cardiovascular development into different stages including “heart valve development” and “trabeculation” for example. This allows for an in-depth understanding of organ development with respect to the Notch receptor, rather than a general overview of the receptor’s involvement (criteria 5 and 6). The authors also have extended beyond Notch’s involvement in human embryonic development by exploring its role in animal embryonic development (criteria 5).
 
 
Although there are many positives, a possible improvement to this outstanding wiki would be to include a table of the different types of Notch receptors that exist and their different roles in embryonic development. This will allow the audience to understand that there is not just a single receptor playing a role in embryonic development but multiple. Another suggestion would be to add more subheadings under the “Central nervous system” development, as this subheading appears to have a lot less information compared to others. Also, it is obvious that there are different pathways for this receptor such as “Canonical” and “Non-canonical”, therefore it would be a great idea to include a youtube video to summarise these pathways and reinforce the in-depth description already provided on the page.
 
 

Negative aspects of the project and suggested improvements:
 
 

It was also noticed that a variety of terms were utilised which were not defined in the glossary such as “cyclins”, “pluripotent stem cells” and “ligands” for example. It is important to consider that the wiki should be able to teach at a peer level (criteria 4), as some students may not understand these terms. Therefore it is important to define them so audiences can develop a coherent understanding of the information. Another negative feature of the page was that it lacked interactivity. Indeed the page is very informative, however to further engage the audience, a suggestion would be to include a set of multiple choice questions at the end of the page which tests peers about the content covered.
 
 
It was also noticed that the page had a very limited number of subheadings regarding Notch’s involvement in embryonic development. A possible improvement would be to investigate Notch’s involvement in organ systems other than Cardiovascular and central nervous system. This will add a greater variety to the page and provide a greater depth of understanding regarding the role of the Notch signalling pathway in embryonic development.

 
 

===Group 2 Peer Review===
Really well organised structures! Nice and clear. The history part is really good. It makes your project both educative and attractive. After the history, the molecular background has been well explained. You guys have really looked into this pathway in depth and understood it clearly. I'm really looking forward to reading the non-canonical and the regulation part of the molecular basis. As ANAT2341 is an anatomy course, you guys have perfectly caught the main point of this project. Most of your following paragraphs focus on the anatomical aspect related to Notch signalling pathway. Moreover, you have also identified some abnormalities associated with Notch which makes your page look really good (almost like a lecture note page)!

Just a few points about your page. Firstly, I think it might be better if you guys can find another or draw a picture yourselves showing important components of this pathway. The one that you guys have now looks a little bit massy. I think you guys can photoshop the picture a little bit, just to make the important components more obvious. Moreover, I believe that the differences between canonical pathway and non-canonical pathway are more than component differences. Maybe address more about what does the canonical pathway do and what does the non-canonical pathway do, so that those pathways can be differentiated better. However, since you haven't pasted you non-canonical part yet, it hard to judge whether or not my comment is appropriate.

Overall, I think this page is really good, for it has a lot of attractive contents and well structured which makes us easy to follow. What you guys need is just to complete it. Great job!

===Group 2 Peer Review===
At first glance, I was blown away by your team's page. Definitely very impressive and understandable. The key points relating to the Notch signalling process are definitely clearly described however I may recall Dr Hill requesting that teams steer clear of clinical effects of genes(citation needed!). The choice of headings, sub-headings and diagrams show more than a good understanding of the topic area, it may be useful to include a table that summarises the various aspects of the Notch pathway so that readers realise there are different receptors. The content is cited correctly, however, I would not mind reading 'et al' instead of 'and colleagues' more often, I got sick of reading 'and colleagues'.

The information presented is mostly peer friendly in the context of a simple introduction but your glossary certainly needs updating, there are a lot of terms that a lot of students would not understand and a comprehensive checking of your page will offer you a list of words that you need to define. Also lacking are sketches presented in your own hands, instead of reusing published images. There is plenty of evidence that suggests your team has went beyond the formal teaching activities. In the context of the aims of the embryology course, you guys have emphasised the embryonic role of Notch but the aspect of developing technologies appears to have been ignored to an extent.

Overall, you guys have done a very impressive job that only requires minor tweaking, namely slight editing in the context of in text referencing, more comprehensive glossary as well as checking the course aims of embryology to incorporate the second criterion regarding technology. Excellent work!
===Group 2===

Well done on the progress you have made thus far! You guys have chosen appropriate headings and subheadings that effectively break down the Notch signalling pathway. A coherent introduction has been provided, giving a taste of what is to be expected in this project. The use of a table to explore the history of this signalling pathway was particularly useful in making the information understandable and relevant. Though you have done an excellent job, was there any reason you stopped at 1989? It may even be useful to create a brief timeline of events, thus allowing you to better explore current areas of research by considering past studies that have been performed.

You’ve provided a good overview of the canonical pathway with the appropriate use of a diagram which aids reader’s understanding of the information provided. In saying this, I think it would be useful to expand on how this pathway is tightly controlled, is it through transcriptional regulation or through other means? In addition, it may be useful to explain the differences in the non-canonical and canonical pathways in terms of their significance and role in embryonic development. I’ve noticed that you have provided a general overview of the role of Notch signalling pathway in embryonic development, do these roles differ between the canonical and non-canonical pathways?

In addition, it’s good that you have included the role of the Notch signalling pathway in animal development as it explores the scope of this pathway beyond human embryology but it may also be useful to explore animal models in research, especially considering that the ‘first description of a “notch” defect’ was discovered in Drosophila. By combining the role of animal models in expanding our knowledge of the Notch signalling pathway with the effect of this pathway in animals, it provides a more rounded approach to explaining and discussing this signalling pathway.

I particularly like how you have included statistics in the ‘Abnormalities of Notch signalling’ section as it provides insight into the importance of this pathway in embryological development. You have successfully described the type of mutation that results in the particularly disease in most cases except for Alagille syndrome. More detail in how the mutation causes the syndrome would be useful with an explanation of how the mutation is brought about.

Overall, you guys have done a fantastic job! You have appropriately referenced and cited all the information provided and have included useful flowcharts, tables and diagrams that aid understanding of the text provided. Providing more detail to each of the sections and communicating with all your team members in the discussion page will ensure that you produce an excellent project! Good luck!

===Group 2 Critical Assessment===

A job well done with the introduction! The introduction is brief however manages to link the topic to embryonic development, different medical conditions, whilst also outlining the function and elements of the pathway. Being brief and succinct, it allows the viewer to continue exploring the page without experiencing confusion at the first lot of information. Further to this, the history of the pathway is formatted well and is not too overwhelming or boring. It is evident you have decided ‘Current Areas of Research’ will also be included in your page which is a great idea as you have included a section on History. This would ensure your Wiki flows well, and covers the pathway from start to finish.

Images have been included to visually represent the elements of the general pathway, as well as the elements specific to the pathway in cardiac development, which forms a great aid for viewers in understanding the content. Videos explaining the different canonical and non- canonical pathways could also be included for viewers with a video learning preference.

Use of in text citations neatens the layout of information and enables viewers to access the article should they find the point interesting. Numerous subheadings have been included which further break down the page into small sections of information. This is a fantastic positive as viewers can locate information in which they are interested in easily instead of having to read through long paragraphs of text. I feel as if linking the topic clinically is extremely important which you have done a great job in! Along with the text explaining the disease, you could possibly include a table stating the disease, the mutation, and the symptoms for viewers after a more easy, accessible format.

Throughout the topics covered, a lot of jargon is utilized, however a full glossary has not been provided. A glossary should definitely be included for terms such as ‘gastrulation’, ‘kinases’ or ‘cardiogenesis’ in order to satisfy criteria 4. Additionally, the page does not cater for viewers interested in further reading up on the topic. To ensure criteria’s 4 and 5 are met, links to interesting facts or articles could be provided so the audience has access to more information if they would like to further their understanding. With a few improvements this Wiki page can definitely prove helpful in understanding the pathway!

===Group 2 Peer Assessment===

Your project is quite good and seems to be on the right track. All your references have been done in-text and have made it really easy to make one’s way to the research article to read more about certain points. Not only that, you have appropriately abbreviated your terms by using the full name initially, and I can see that you have a glossary section which should be beneficial in the future when more terms are added. Your history section is well presented but, it might be important to add references to the papers of the main points of discovery in your history section as to allow people to easily access and find the full article regarding the discovery.

The fact that you have added pictures is quite handy when it comes to using it as an aid to accompanying passage. With regards to the image legend, maybe add more information to it or transfer the description of the image present when clicking into the image onto the legend as to better represent what the image is about while having the passage right next to it. Furthermore, maybe it would be beneficial to add other forms of media such as videos to compliment the passages as well, and help better engage the reader in the topic.

With regards to your section on the canonical pathway, I’ve noticed that the specific genes that are targeted by Notch have been left out and I feel that it is important to mention those genes targets explicitly there as well. That being said, they are mentioned in the proceeding section so it isn’t imperative that you do this. Maybe also try seeing if there is any literature on how the NOTCH receptors come about, such as what genes transcribe it and how the protein is processed and expressed before signalling in the pathway can occur.

I think for the most part there is very little to improve with your wiki page given the quality of it albeit a few minor corrections that I have mentioned above. It is very concise and at no times do I feel that I am reading a wall of text that is disengaging. Thus I feel that as long as such quality is maintained then your wiki page will be quite good when finished.

===Group 2 – Notch Signaling Pathway ===
First impressions of Group 2’s page on the notch-signaling pathway are all positive. Subheadings are very well defined. They have chosen to include a brief yet informative introduction on the pathway, a simple table outlining the major scientific developments over the last 100 years, the molecular mechanisms of the pathway, its specific role in embryonic development (which they have further defined as cardiovascular and CNS), role in animal development, abnormalities relating to this pathway and a glossary. I think another positive aspect of this project, is that they have identified additional subheadings for which they are still to do research on; a particularly important one is current areas of research which not many groups have included. Furthermore, additional positive aspects of this project include the addition of images on the canonical notch signaling pathway and its role in cardiovascular development (which both appear also to be appropriately added to the website), which support the text nicely. It might also be useful to find a relevant video to include just to break up some of the text, and help make the page more interactive. It appears this group has widely researched their topic using both primary and review articles, which are all appropriately referenced using in-text citations. All of these aspects help to clearly convey the necessary information to the reader, and fulfill much of the required criteria of this project. In terms of their written information, Group 2 has included really detailed information on its role in embryonic cardiovascular development, as well as identifying some of the major research articles that have lead to these discoveries and a little bit about them (which then the reader if they are interested it can go read thanks to the inclusion of the in-text citations.) They do include a section of the roles of this pathway in animal development, which is really interesting and goes beyond the normal scope of this course.

Some negative aspects of the project include that, as part of the criteria being that the project has an “element of teaching at a peer level using the student's own innovative diagrams, tables or figures and/or using interesting examples or explanations” perhaps it would be useful to consider including a hand drawn image when researching the non-canonical pathway or transcriptional regulation of notch signaling, or even of some of the receptor/ligands involved in this signaling pathway. Furthermore, on a similar note it may be important to summarise the receptor subtypes involved in the different pathways, their role in embryonic development and abnormalities of the receptor subtype specifically relating to embryonic development in a table or dot point format. Additionally perhaps more information on its role in the CNS (or other systems during embryonic development) even if its not as detailed as cardiovascular, may help to inform the reader of all of its various roles.

In conclusion, it appears that this project is one of the strongest, it has very clear and informative subheadings separating well researched written material, supported by images sourced from the Internet. The main criticisms were just including your own innovative diagrams or explanations, videos to help make it more interactive and table or dot points summarizing the different receptor subtypes involved in each pathway. Following the completion of this, and the subheadings yet to be researched (and glossary) it appears that this project is going to be very successful in informing peers about the said pathway.

===Group 2 Peer Assessment===

Positive Assessment:

So far this page looks great and very organised. I am really impressed by the set out of the information and the way the headings are arranged. It made it really easy for me to navigate around for particular information and not have to look for around aimlessly when I was looking for something in particular. Furthermore I think that the actual categories/sub headings used so far are very concise and effective. For example, I appreciate the brief introduction along with an overview of the molecular mechanisms involved in notch signalling before introducing its roles in embryonic development. This way I was able to have a understanding of what is really involved before understanding how it is important in embryonic development.

The references are also very neatly and correctly done and many times when I did not fully understand a concept I clicked on the citations which took me to the relevant articles and my understanding was clarified. I also really enjoyed the commentary on the specific research papers, for example cardiomyocyte specification and differentiation where you guys actually compared information from separate studies to make the information more whole and relevant.

In the abnormalities section, I think it was really awesome you guys included so many statistics and symptoms and not just a description of the abnormality.

Critical Assessment:

Although everything looks really amazing a couple of improvements that I personally think could be made would make this page really useful to students.

The introduction, although very informative can be simplified a bit more to address criteria 4 and make it a bit easier to understand. This can be done through including an interesting or very simplified diagram to engage the student from the beginning. I would also generally include more diagrams and drawings that are personally drawn as the pictures used although effective, can be difficult to understand when you are learning for the first time. It would also be nice if more words are included in the glossary because there was a quite few words I did not know the meaning of.
Lastly I think it would be a great addition to your page to include another subheading which outlines how the abnormalities are treated as this is something that I was intrigued to discover.

Overall I think your page is going great guys keep it going !

===Project 2: Notch signalling pathway===
====1. The key points relating to the topic are clearly described.====
There are headings for key points and the information for these key points has clearly described. This information is laid out in a clear way beginning with an introduction, historical aspect of the topic and continues to more specific information (e.g. animal models) related to the overall topic.

====2.The choice of content, headings and sub-headings, diagrams, tables, graphs show a good understanding of the topic area.====
The Notch singalling pathway has a very clear contents list. This demonstrates that a lot of thought and research has gone into the topic. There are two figures which are very neat and well set out. These are referenced. There is one table which described the historical aspect of this topic and this is very clear and beneficial as it summerises a lot of information in a clear manner.

====3. Content correctly cited.====
The content is cited correctly. If the refernces are used more than twice this has been cited in following the Wiki guidelines and the reference is not repeated in the list.

====4. The wiki has an element of teaching at a peer level using the student's own innovative diagrams, tables or figures and/or using interesting examples or explanations.====
This wiki does have an element of teaching: It is clearly laid out, it is easy to read and the information is set up in a correct manner with a general overview, historical aspects and then more precise information is given. There is some interesting examples given which describes abnormalities in this pathway.

====5. Evidence of significant research relating to basic and applied sciences that goes beyond the formal teaching activities. ====
This is very much evident. There is evidence that research has been undertaken as the topic has been divided into sub topics and there is a lot of interesting clear information to educate the reader.

====6.Relates the topic and content of the Wiki entry to learning aims of embryology. ====
Yes the topic does related to the learning aims of embryology and how Notch signalling pathway is involved in embryonic organ development through the regulation of cell-cell signalling

====7. Clearly reflects on editing/feedback from group peers and articulates how the Wiki could be improved (or not) based on peer comments/feedback. Demonstrates an ability to review own work when criticised in an open edited wiki format. Reflects on what was learned from the process of editing a peer's wiki.====
This is still not as evident as there is no comments or feedback observed. There are still some sections that have information missing and perhaps comment or feedback could have been given here to ensure that the students fill in this missing information or remove the subheadings all together.

====8. Evaluates own performance and that of group peers to give a rounded summary of this wiki process in terms of group effort and achievement.====
The way this Wiki is laid out clearly demonstrates that there has been some feedback and communication between the group. It seems that each member of the group did write a section, yet the sections do come together and do not seem out of place. However there are sections with information missing and this needs to be addressed.

====9. The content of the wiki should demonstrate to the reader that your group has researched adequately on this topic and covered the key areas necessary to inform your peers in their learning. ====
Yes the Wiki content does demonstrate that the group has researched adqueately in this area.

====10. Develops and edits the wiki entries in accordance with the above guidelines. ====
This has been achieved. This wiki entry does seem to be in accordance with the guidelines provided.

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:17, 7 October 2016 (AEDT) here's the article for our Lab 10 presentation: PMID26025980

[[User:Z3462474|Z3462474]] ([[User talk:Z3462474|talk]]) 07:15, 23 September 2016 (AEST) Hey no worries I hope you feel better soon! I won't be able to do as much during the midsem break which is why I've been doing lots this week. I'll have a look at that link thanks! Also I tried to make a Glossary but am having trouble with the coding side of it but I'll try fix it later to make it a proper glossary :)

 
[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 21:00, 22 September 2016 (AEST) I'm so sorry I've been terrible with putting stuff on our page!! I know I said I would get some done this week but I've been sick these past few days and still recovering so I probably won't make it to the lab tomorrow. I'm having some trouble finding an image that summarises Notch signalling that we can use (most of the good ones I've found don't allow reuse) but I'll keep looking. I'll definitely do a lot more during the midsem break. sorry again! I also found this link: http://www.omim.org/entry/190198 that looks like it has some really good references for different roles in development.

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 14:27, 16 September 2016 (AEST) looks like a great picture so I think we can leave it. I just altered the formatting of the image a little bit, but feel free to change it back if you prefer the previous placement! also I think having the copyright info on the file page is enough. thanks for doing that, I'm still hunting out pictures as well. I've been busy this week with another group project but now that it's out of the way I should be able to do a lot more here. :)

[[User:Z3462474|Z3462474]] ([[User talk:Z3462474|talk]]) 09:21, 16 September 2016 (AEST) I found one that didnt look too complicated and also found that it allowed unrestricted use so I've added it into the cardio section of our page (we can always delete it later if need be), not 100% about my formatting though and whether I should include the legend/copyright notice directly on our page? If you click the image though its all there :)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 23:08, 12 September 2016 (AEST) I've been looking around and found some images, but most of the time they involve a lot more detail than we need and I don't want to overcomplicate it. will keep researching this week and see if I can find some simpler diagrams. :) The images in that book look really good but yeah I'm not sure what the copyright details for that are. if it comes to it I think if we reproduce it by hand and credit the source then it's fine!

[[User:Z3462474|Z3462474]] ([[User talk:Z3462474|talk]]) 13:50, 12 September 2016 (AEST) Has anyone found any good images to use for our page? I have found a couple of diagrams on cardiac development and Notch in this book chapter: http://www.sciencedirect.com.wwwproxy0.library.unsw.edu.au/science/article/pii/S0070215310920115 but am still looking to the copyright restrictions etc and thought I'd check everyone's opinion

[[User:Z3462474|Z3462474]] ([[User talk:Z3462474|talk]]) 09:22, 9 September 2016 (AEST) Hey everyone, I have added some of my notes to the main page, they are still a work in progress though! I'll continue to research the roles of Notch in the development of the different systems

[[User:Z3462474|Z3462474]] ([[User talk:Z3462474|talk]]) 10:04, 2 September 2016 (AEST) Just found this online textbook titled 'Notch Signaling : Methods and Protocols' http://www.springerprotocols.com.wwwproxy0.library.unsw.edu.au/BookToc/doi/10.1007/978-1-4939-1139-4

This one also looks like it might be helpful: http://www.sciencedirect.com.wwwproxy0.library.unsw.edu.au/science/bookseries/00702153/92

[[User:Z3462474|Z3462474]] ([[User talk:Z3462474|talk]]) 14:27, 26 August 2016 (AEST) Here are some reviews I have found that could be a helpful starting point:

Notch signalling at a glance: http://jcs.biologists.org/content/joces/126/10/2135.full.pdf

Signalling pathways for neural development: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4369499/pdf/WJSC-7-437.pdf

Notch's role in diabetic neuropathy https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3677813/pdf/nihms473246.pdf

Notch in cardio development and disease http://circres.ahajournals.org/content/118/1/e1.full

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 14:28, 26 August 2016 (AEST) here's the embryology site page for [[Developmental Signals - Notch|Notch signalling]]!

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 14:31, 26 August 2016 (AEST) I also found a review article for Notch signalling in the common fruit fly, which could be a good idea for a subsection: PMID 12369105 ''General outlines of the molecular genetics of the Notch signalling pathway in Drosophila melanogaster: a review''.

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 14:44, 26 August 2016 (AEST) and here's some more reviews: PMID 22397947 ''Non-canonical Notch signaling: emerging role and mechanism'' and PMID 21828089 ''Notch signaling: simplicity in design, versatility in function''.

[[User:Z5014803|Z5014803]] ([[User talk:Z5014803|talk]])
https://www.researchgate.net/publication/264164124_Introduction_to_Notch_Signaling This seems like a good link for the history and discovery of the pathway

[[User:Z5014803|Z5014803]] ([[User talk:Z5014803|talk]])
https://embryo.asu.edu/pages/notch-signaling-pathway-embryogenesis Can be used for introduction

[[User:Z3462474|Z3462474]] ([[User talk:Z3462474|talk]]) 12:41, 19 August 2016 (AEST) Signalling in neural embryonic development looks interesting! Particularly the paper about NSCs and psychiatric disorders.

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 21:59, 18 August 2016 (AEST): Hedgehog signalling (specifically SHH signalling) sounds really interesting!

[[User:Z5014803|Z5014803]] ([[User talk:Z5014803|talk]]) 22:39, 18 August 2016 (AEST): Bone Morphogenetic Proteins (BMP) signalling in development looks interesting

[[User:Z3491219|Z3491219]] ([[User talk:Z3491219|talk]]) I think looking at how in utero exposure to cigarette smoke affects fetal ovarian development signalling would be interesting.

===Group 2===
This web page is developing very well, with comprehensive information and textual information. Relevant images and diagrams have been included and accurately referenced, which is to be commended. Student produced images, diagrams and flowcharts should also be included to reflect depth of knowledge on this topic. More images would enhance the readers’ understanding of topics like the development of the Atrioventricular Canal, heart valve and outflow tract, all of which are subheadings. Short movies and animations should also be included to assist the readers in visualising these signalling pathways and embryological developments being discussed. An interesting and potentially humorous image could also be included at the beginning of the web page to attract the reader’s attention and add interest to the page, such as an image of an ordinary notch at the top of the page.

The subheadings included in this web page are appropriate and have been well organised, ensuring consistency and cohesiveness in this project. The introduction is well written, as it covers a range of topics including an overview of the role of the Notch signalling pathway as well as an introduction to the abnormalities associated with mutations in the functional components of the pathway. The timeline could also be improved by including developments in research over the last 20 years, as well as the direction current research is moving in and where future research could be headed. An elaboration on 1914 by further explaining why this is called the “Notch signalling pathway” with the aid of an image would also be useful. More information on John S. Dexter and his research process, his team and initial findings would also add depth and interest to the web page. Another table could be included in this web page to help the readers differentiate between the four Notch genes in Mammals, including further information on each gene, their respective locations on chromosomes, functions and an image of each if possible. The location of the locus of the Notch gene on the 3C7 band of the X chromosome is included, as well as the NOTCH3 located on chromosome 19p13, showing detailed knowledge and extensive research by the group. Images, potentially student drawn, of where these locations physically are would also reflect a deeper understanding.

The ‘Roles in Embryonic Development’ section and its respective subheadings have also been well organised and structured. There are several headings in this web page that require completion before the submission date, including the ‘non-canonical pathway’ and ‘transcriptional regulation of notch signalling’ headings. More animal models can also be included, with the subheadings in this section also requiring completion. An abnormalities section has also begun well and is detailed and well referenced. It still requires completion as some of the sub-headings are still empty. Images of symptoms of these abnormalities such as the rib and spine abnormalities associated with Spondylocostal Dysostosis, and the eye conditions and facial features associated with Alagille syndrome would add depth to this section. A glossary section has also been started, but can definitely be added to to improve the understanding of the readers. Terms to be added could include proteolytic reactions, ligands and descriptions of signalling molecules such as MyoD, Mash1 and GATA2.

Referencing has been carried out well, with in-text referencing throughout the web page. The introduction was well referenced, as well as the “Roles in Embryonic development”, “Animal Models” and “Abnormalities” sections. However, no in-text referencing has been carried out for the “Overview of Molecular Mechanisms” section and the timeline. This should be resolved as soon as possible so that external links are easily accessed by the readers should they want to seek further information. Complete and proper referencing would also satisfy one of the criteria of this assessment, that the content is correctly cited and referenced.

GROUP 2
Moving the the 2nd group I can see that their topic is mainly about the Notch receptor. They seem to elucidate upon different aspects of the receptor, like it’s role in embryonic development and molecular pathways. The aspect done especially well in this group is the vastness and breadth of their information. They explore numerous aspects of the Notch receptor, including the abnormalities that can arise in development. By showing such a vastness and clarity in their research they successfully achieve criteria 1. Furthermore, Group 2 has a phenomenal amount of tables, diagrams and figures describing canonical Notch signalling and the history of the discoveries for these receptors. This qualifies criteria 2 very well as they have included all these as well as headings and sub headings in a succinct manner. Moving onto referencing, this group has done a fantastic job in that aspect as they have a separate section for references, which is clear and easy to understand, fulfilling criteria 3. Overall, I have been able to learn from this group’s project and thus I believe that they fulfil an aspect of criteria 4, in that they have an element of teaching for peers. Improvements I might suggest would be having an even larger array of different learning outlets or media types. Examples could include maybe having a video included in your group project. In terms of improvements to specific information, maybe quickly glance over the different types of receptors and the different pathways they have.

===Group 2 Peer Review===
Upon first look this group’s project is very well laid out, each heading and subheading fall under each other perfectly and the overall formatting is very appealing. In conjunction with this the group has made efforts to use flowcharts and diagrams which is again another positive aspect, however they should aim to also include a student made figure as is indicated in the marking criteria.

In regards to the content of the page, the Notch signaling pathway is well introduced and the history section gives a good overview of steps taken to build up to our current knowledge of the Notch system. The referencing for this page has been done in different formats, i.e there are multiple types of intext citation, in some instances a superscript number is provided with a link where as in other cases there are author names provided, in order to increase the readability and flow of the article I recommend sticking to a single format.

The group has provided a more than substantial amount of information for a draft version of their page however in some areas it is difficult to follow along due to the presence of undefined or newly introduced terms. This problem may be alleviated by adding the more technical terms to the glossary section they have created.

===Peer Review===
The page has a proper introduction stating the critical functions of Notch signalling, examples of diseases associated with Notch mutations as well as a brief description of the mechanism of Notch signalling. There is also a timeline on the page which none of the other groups have managed to do so good job!

Some headings are missing text but those with content (e.g. canonical pathway section) are covered in extensive detail. The subheadings and headings chosen for the page indicate the group’s in depth understanding of the key components of the Notch signalling pathway. Furthermore, the page contains correct referencing and citation of text and images.

The page also discusses Notch signalling in animal models as well. A recent study was included for Drosophila. What about the other two?

Overall, Group 2 has made excellent progress. Well done!

Wow! Group 2, I was very impressed with your page. The information is organized and clearly presented under relevant headings and subheadings, with the amount of content demonstrating that you have done your research. The ‘Introduction’ at the start of your page was well written – it was short but included everything necessary, such as the processes that involve the Notch signaling pathway, how it is activated and how it is a part of the process of embryology. The history of the pathway, formatted in a timeline, could not have been done any better! I found it very easy to understand because it was presented so clearly. If it is possible to add a few more points, I think that will enhance that section even more.
The content is correctly citied in this page. I was very impressed with the use of in-text references, as it enables students like me to easily access the article they have used. In addition, the complete reference list at the bottom of the page showed a large number of articles, which demonstrates that this group has done significant research relating to basic and applied sciences that goes beyond the formal teaching activities.
Another positive aspect of the project is how well they have explored the Notch signalling pathway’s roles in embryonic development, which they further split into the Cardiovascular section and the Central Nervous system. Under the Cardiovascular system are numerous subheadings that further delve into how different parts of the system, such as the heart valve and atrioventricular canal, are developed. This fulfils the criteria of showing the specific role in embryonic development. I would suggest that the group add more information under Central Nervous system to balance out the content (though I am aware this is an unfinished project).

Overall, it is evident that Group 2 has diligently and consistently worked on this project. They have done an amazing job so far, and the project will become even better once more things are added and everything is finalised. Great job!

===Group 2 Peer Review===

Well done on the presentation and content of your topic, everything is set out very clearly and you have covered quite a lot of content. The history timeline is a great addition to the page as it outlines clearly and simply the progression through time of what new information had been learnt. The use of both tables and images assists the understanding of the individual in a simple manner. The in text citations are quite useful and extensive, it allows the reader to further their own research on a particular area of the topic. The introduction was quite detailed yet simple to understand and gave a great overall understanding of what will be included in the page. The cardiovascular information on the page related to embryonic development is a major highlight. You have covered quite a significant amount of information and yet you have distributed the information into sub-headings that allow an easier understanding of the topic.

You have also included on your page animal models and studies in relation to the Notch signalling pathway. It is quite interesting to see what the role of the pathway is in each of the models. Also, the addition of the abnormalities is quite interesting to read, and you have covered several abnormalities that can occur.

One thing I must point out is maybe you should include a more detailed glossary section, as you have used a few terms that may be hard to understand for some people, or better explain them within the paragraph. You have also included some pictures on your page, however, you do not link them to your explanation very well, maybe you should explain in detail what is exactly going on in the image. For example, it seems as if your explanation and terms used for the canonical pathway does not match those of the image for that section. Also, that particular image is not of the best quality and any writing present cannot be clearly and easily read. There are also several sub-headings that are missing information, I do, however, look forward to read what you will include

You have put together quite an impressive page with lots of information that is divided clearly into many sub-headings. It was fairly simple to understand the content, only minor changes should be made to your page.

===GP2 peer review===

Things are worth to be learnt:

-Formatted reference part.

-Used time line about the history the notch signalling findings.

-Suitable length for each section and informative.

Things needed to be improved:

-Pictures are assists, could be attached more.

Overall group 2 had a good progress of their project, use the history of the notch signalling as part of introduction, clear content. Only needs to fill the gaps in the page and try to add more pictures to help the audience understand the topic, especially for the abnormality of this signalling.

2016 Group Project 2

2016-10-25T05:19:15Z

Z5015014: /* To search and read recent PubMed research and review articles on Notch, click here! */

2016 Group Project 2

2016-10-25T05:13:55Z

Z5015014: /* Summary of Functions of Proteins Involved in Notch Signalling (adapted from Table 117761886) */

2016 Group Project 2

2016-10-25T03:49:54Z

Z5015014: /* Current Areas of Research and Future Directions */

2016 Group Project 2

2016-10-25T03:28:13Z

Z5015014:

2016 Group Project 2

2016-10-25T03:24:16Z

Z5015014: /* Abnormalities in Notch signalling */

2016 Group Project 2

2016-10-25T03:03:00Z

Z5015014: /* Congenital Heart Defects */

2016 Group Project 2

2016-10-25T02:58:42Z

Z5015014: /* Overview of Molecular Mechanisms */

2016 Group Project 2

2016-10-25T02:57:34Z

Z5015014: /* Transcriptional regulation of Notch signalling */

2016 Group Project 2

2016-10-25T02:38:33Z

Z5015014: /* Summary of Functions of Proteins Involved in Notch Signalling17761886 */

2016 Group Project 2

2016-10-25T02:35:55Z

Z5015014: /* Examples of Proteins Involved in Interaction with the Notch Intracellular Domain */

2016 Group Project 2

2016-10-25T02:32:56Z

Z5015014: /* Introduction */

2016 Group Project 2

2016-10-25T02:29:06Z

Z5015014: /* Summary Table of Examples of Notch Signalling in Developmental Processes21828089 */

2016 Group Project 2

2016-10-25T02:22:45Z

Z5015014: /* History */

2016 Group Project 2

2016-10-25T02:06:35Z

Z5015014: /* Introduction */

2016 Group Project 2

2016-10-25T02:01:16Z

Z5015014: /* History */

User:Z5015014

2016-10-24T06:51:40Z

Z5015014:

{{ANAT2341Student2016}}

==Lab Attendance==
[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 14:35, 5 August 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 14:40, 12 August 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:13, 19 August 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:03, 26 August 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 2 September 2016 (AEST) 

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:07, 9 September 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:03, 16 September 2016 (AEST)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:03, 7 October 2016 (AEDT)

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 14 October 2016 (AEST) 

[[User:Z5015014|Z5015014]] ([[User talk:Z5015014|talk]]) 13:05, 21 October 2016 (AEDT)
 

==Week 1 Homework==
===Team Role===
I studied the Belbin Team Roles in a previous course and identified myself as a Teamworker, which I still definitely agree with, but I'd probably also add that I have the tendencies of a Complete Finisher. In group assignments I always prefer not to take charge and rather to provide support by facilitating discussions and encouraging good communication within the group. In the past, I've often mediated between my real life friends when conflict happens so I'm comfortable in doing that for any group situation I find myself in. I'm also very indecisive as a person and I know this reflects into any group work that I do because I find it difficult if I have to lead or make choices for the rest of the team. I would also say that because I don't particularly look forward to group assignments in the first place, because I'd much rather complete a task by myself, I can sometimes be a Complete Finisher. I know that I hesitate having to rely on other people because I worry that they won't do something the way I would have chosen to do it.

===Lecture 1: Fertilisation (2/8/16)===
I've always found fertilisation to be an exciting and interesting topic. Even though I've studied it before in previous courses I still find it so fascinating just how much goes into the 'simple' union of a sperm and an egg cell. The way that so many processes and reactions and biological design come together to allow fertilisation to happen really amazes me. But I think the most interesting thing I heard in today's lecture was about the zona pellucida and the ZP2 protein, and how it's used as a signal to attract the sperm to bind to the ovum, and then modified to prevent polyspermy by stopping additional sperm from binding. I'd never learnt about this before so it was really interesting to understand the mechanism involved.

{|
|-bgcolor="FAF5FF"
| [[User:Z8600021|Mark Hill]] ([[User talk:Z8600021|talk]]) 12:36, 5 August 2016 (AEST) Very good. maybe a little to many sub-sub-sub- headings, this will get messy. I will discuss in today's lab online formatting etc.
|}

==Lab 1 Assessment==
'''IVF culture medium affects post-natal weight in humans during the first 2 years of life.'''<ref><pubmed>24549211</pubmed></ref> 
''Sander H.M. Kleijkers, Aafke P.A. van Montfoort, Luc J.M. Smits, Wolfgang Viechtbauer, Tessa J. Roseboom, Ewka C.M. Nelissen, Edith Coonen, Josien G. Derhaag, Lobke Bastings, Inge E.L. Schreurs, Johannes L.H. Evers & John C.M. Dumoulin'' 
:In this study, Kleijkers et al. investigated the relationship between the culture media used for embryos during the process of IVF and the subsequent development of the IVF children in early life. This followed on from previous research in which it was observed that the choice of culture medium had an impact on birthweight as well as development of the fetus during pregnancy. 1432 IVF treatments were initially involved and each was randomly allocated to either grow in Cook medium or Vitrolife medium. From this, 126 embryos from the Cook group and 168 embryos from the Vitrolife group were successfully birthed and used for further study. Kleijkers et al. contacted all of the parents two years after the initial birth for records of the postnatal weight, height, and head circumference of their child over the two year period. Statistical analysis and different analytical models were used to compare the collected data. It was observed that the weight of singletons whose embryos had been cultured in Cook medium was consistently lower than that of the Vitrolife group; this confirms that the effect of culture media on fetal growth, as had been previously researched, persists in early postnatal development. Kleijkers et al. propose that these results show the sensitivity of the human embryo to its environment, whether ''in vivo'' or ''in vitro''. Hence because the chosen media for the embryo is the environment it grows in before implantation, the adaptation of this embryo to the media, possibly by epigenetic modification, is seen to have consequences for later development. This emphasises the need for further research into the growth media used for IVF treatment to ensure an optimal environment for the preimplantation growth of the embryo, and therefore both prenatal and postnatal development of an IVF child.

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 18 August 2016 - You have added the citation correctly and written a good brief summary of the article findings. You also seem to have practiced using some of the Wiki formatting tools. So the very conditions of initial growth may have long-term developmental ramifications. You can see why research in this area is important. These days we have a reasonably large IVF cohort to begin to get some useful data.

You have to be careful though when commercial products are being compared. [https://www.cookmedical.com/products/wh_sibm_webds Cook medium] | [http://www.vitrolife.com/en/Products/G-SeriesTM-media/G-IVF Vitrolife medium]
| width=100px| Assessment 5/5
|}

==Lab 2 Assessment==
[[File:Human Blastocyst with Decidualized Endometrial Stromal Cells.png|400px]] 
Human blastocyst attached to decidualized human endometrial stromal cells after 72 hours of co-culture.<ref><pubmed>22412909</pubmed></ref>

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 29 August 2016 - All information Reference, Copyright and Student Image template correctly included with the file and referenced on your page here.
| Assessment 5/5
|}

== Lab 3 Assessment ==

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 31 August 2016 - Lab 3 Assessment Quiz - [[Lecture_-_Mesoderm_Development|Mesoderm]] and [[Lecture_-_Ectoderm_Development|Ectoderm]] development. All correct, well done!

| Assessment 5/5
|}

==Lab 4 Assessment==
===Gastrointestinal Development Quiz===
<quiz display=simple>
{1. The splanchnic mesoderm does '''not''' contribute to:
|type="()"}
+ epithelium
- mesentery
- blood vessels
- smooth muscle
||The splanchnic mesoderm is involved in the development of mesentery, connective tissue, smooth muscle, and blood vessels. The endoderm contributes to development of epithelium.

{2. The correct order of blood supply for the foregut, midgut, and hindgut is:
|type="()"}
- inferior mesenteric artery, celiac artery, superior mesenteric artery
- superior mesenteric artery, inferior mesenteric artery, celiac artery
+ celiac artery, superior mesenteric artery, inferior mesenteric artery
- celiac artery, inferior mesenteric artery, superior mesenteric artery
||The foregut is supplied by the celiac artery, the midgut is supplied by the superior mesenteric artery, and the hindgut is supplied by the inferior mesenteric artery.

{3. Which of these statements is '''false'''?
|type="()"}
- The right hepatic bud will eventually form the right lobe of the liver.
- The cloaca initially forms a common urogenital and gastrointestinal space.
- Meckel's diverticulum is a common abnormality caused by failed degeneration of the vitelline duct during development.
+ The ventral mesentery is completely lost during development.
||The ventral mesentery is lost except at the level of the stomach and the liver, and will eventually contribute to the development of the lesser omentum and the falciform ligament.

{4. Which abnormality involves narrowing of the gastrointestinal tract lumen?
|type="()"}
+ stenosis
- atresia
- duplication
- gastroschisis
||Stenosis is narrowing of the GIT lumen. Atresia is interruption of the lumen, duplication is incomplete recanalisation leading to the formation of parallel lumens, and gastroschisis is an abdominal wall defect that results in herniation of the abdominal viscera into the amniotic cavity.
</quiz>

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 17 October 2016 - GIT Quiz covers a range of related topics. Question 1 identifies difference between endoderm and mesoderm origins. Question 2 is about blood supply, not a testing question as the 3 options are given in several options. Question 3 and 4 are good testing questions.
| Assessment 5/5
|}

==Lab 5 Assessment==
I completed the course review questionnaire!

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 17 October 2016 - course review questionnaire.
| Assessment 5/5
|}

==Lab 6 Assessment==
'''Meta-analysis Reveals Genome-Wide Significance at 15q13 for Nonsyndromic Clefting of Both the Lip and the Palate, and Functional Analyses Implicate GREM1 As a Plausible Causative Gene.'''<ref><pubmed>26968009</pubmed></ref> 
''Kerstin U Ludwig, Syeda Tasnim Ahmed, Anne C Böhmer, Nasim Bahram Sangani, Sheryil Varghese, Johanna Klamt, Hannah Schuenke, Pinar Gültepe, Andrea Hofmann, Michele Rubini, Khalid Ahmed Aldhorae, Regine P Steegers-Theunissen, Augusto Rojas-Martinez, Rudolf Reiter, Guntram Borck, Michael Knapp, Mitsushiro Nakatomi, Daniel Graf, Elisabeth Mangold & Heiko Peters''
:In their research, Ludwig et al. looked at findings from previous studies and confirmed that the 15q13 region is a risk locus for developing nonsyndromic cleft lip and palate (nsCL/P) but not nonsyndromic cleft lip only (nsCLO). By experimenting on mice, they also associated genetic variation in a 5 kb region downstream from the ''Gremlin-1'' (''Grem1'') transcription start site with developing nsCL/P. They observed localised expression of ''Grem1'' in the soft palate and in the processes forming the lip during mouse embryogenesis. While ''Grem1''-deficient mice did not develop lip or palate defects, the addition of ectopic Grem1 was shown to have a pathogenic effect on the morphogenesis of the palatal shelves during secondary palate development. ''Grem1'' is known to be critical for limb bud development, but not lip and palate development. Its role in limb bud development is to establish a positive feedback loop between Shh and Fgf via inhibition of Bmp signalling (a negative regulator of SHH expression in limb mesenchyme). However, previous research determined that Bmp signalling is a positive regulator of Shh expression in the palatal shelf epithelium and cell proliferation in the anterior palatal shelf mesenchyme. Bmp4 and Bmp2 are involved in the normal development of the anterior palate and Bmp4 and Bmp7 are expressed in the posterior palatal shelves. Therefore, it was concluded that an abnormality in ''Grem1'' expression could interrupt normal development of the secondary palate due to the inhibition of Bmp signalling.

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 17 October 2016 - [http://www.omim.org/entry/603054 GREM1] is a novel factor and your summary is useful and you have good to also included the signaling pathway involved.
| Assessment 5/5
|}

==Lab 7 Assessment==
Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy, affecting 1 in 3,500-5,000 newborn males globally. It is caused by recessive loss-of-function mutations in the dystrophin gene on the X chromosome.<ref name="PMID26140716"><pubmed>26140716</pubmed></ref> Frame-shift mutations in the gene lead to failed expression of the dystrophin mutation and hence the manifestation of DMD. One-third of DMD cases can occur by spontaneous mutation, meaning that a positive family history is not required for diagnosis. Physical examinations, molecular biopsies, genetic testing, and review of clinical history are all involved when diagnosing DMD. Serum creatine kinase (CK) is used as an initial diagnostic tool to measure the levels of muscle enzymes.<ref name="PMID27524897"><pubmed>27524897</pubmed></ref> DMD is defined at the molecular level as producing no dystrophin and clinically as the loss of ambulation at 12 years of age or younger.<ref name="PMID26140716"/> A less severe mutation of the dystrophin gene, such as an in-frame deletion, can instead produce a truncated version of the protein which results in Becker muscular dystrophy (BMD), a milder form of DMD.<ref name="PMID25740330"><pubmed>25740330</pubmed></ref>

Dystrophin is a major muscle protein which connects the cytoskeleton (cytoskeletal actin, microtubules, and intermediate filaments) and the extracellular matrix (ECM).<ref name="PMID25740330"/><ref name="PMID26295289"><pubmed>26295289</pubmed></ref> Dystrophin is anchored to the plasma membrane by phospholipids and β-dystroglycan. The dystrophin complex is found in costameres of skeletal and heart muscle, which are located at the periphery of the muscle fibers. Costameres are involved in transmitting forces from the cytosol to the ECM and therefore prevent the collapse of the cell membrane during muscle contraction. Hence, in DMD and BMD the impaired function of dystrophin results in frequent cell damage when the muscle contracts. The rupture of the plasma membrane causes leakage of the intracellular components; for example, creatine kinase can be released from the damaged cell which explains the high concentrations of serum creatine kinase in DMD patients.<ref name="PMID26295289"/>

The most common mutation implicated in DMD and BMD is a deletion of one or more exons, accounting for 60-70% of DMD cases and 80-85% of BMD cases. Point mutations are have been found in approxiamtely 26% of DMD cases and 13% of BMD cases, while exonic duplications are involved in 10-15% of DMD cases and 5-10% of BMD cases. Other possible mutations include subexonic insertions, deletions, splice mutations, and missense mutations.<ref name="PMID26140716"/>

Animal models used to investigate DMD and BMD include the ''mdx'' mouse and the ''grmd'' dog.<ref name="PMID26295289"/><ref name="PMID25740330"/> Due to the size of the dystrophin gene, it is difficult to treat DMD or BMD with gene therapy.<ref name="PMID27594988"><pubmed>27594988</pubmed></ref> The idea of producing a smaller version of the protein, micro-dystrophin, has been attempted, but due to its smaller size it cannot act as a perfect functional substitute for dystrophin. In the case of DMD, exon skipping therapy has been investigated as a way of altering the mutation of the dystrophin gene. Instead of the frame-shift mutation which results in no functional dystrophin being produced, the splicing of the mRNA can be modified to exclude one or more additional exons which therefore restores the reading frame and results in production of a BMD-like dystrophin (truncated, but still partly functional). This has been accomplished by introducing small antisense oligonucleotides (AONs) sequences, which bind to exon splice junctions and inhibit the action of the spliceosome.<ref name="PMID26295289"/> However, this ultimately only lessens the severity of the disease and still presents the problem of treating the BMD-like symptoms. There is still no effective cure for either DMD or BMD. Most available treatments are focused on slowing the progression of the diseases and continued research is being done into ways of converting a severe phenotype of disease to a more mild phenotype.<ref name="PMID27594988"/><ref name="PMID26140716"/>
 

{| width=95%
|-bgcolor="FAF5FF"
| [mailto:m.hill@unsw.edu.au Mark Hill] 17 October 2016 - You have answered all questions and also included the source references, well done.
| Assessment 5/5
|}

==Lab 9 Assessment==
====Group 1 Peer Review====
Great job on all the content you’ve produced as a group so far. It’s clear you guys have done a lot of research into the topic and you’ve identified key aspects of Wnt signalling. The information you have is all relevant, everything is referenced, and all your abbreviations are defined. It’s really good that you have included some specific studies and explained the findings and what they discovered about Wnt signalling. It’s great you’ve also started to look into the abnormalities so if you put some more info into that I think it presents a really interesting topic for the reader to read about.

The first things I would point out is mostly for the structure/layout of your page. Make sure you use the correct wiki formatting so the page looks uniform and clean. You should separate your references out from the main body of info and collate them properly at the end of the page. Also make sure that you have in-text referencing so the reader knows exactly where the information is from. And for your content, I think it would look more professional to present it in structured paragraphs instead of bullet points. I would suggest having a proper introduction paragraph so that the reader gets an immediate overview of Wnt signalling and which aspects you’ll be exploring, rather than going straight into explanation of the pathway. Also, while you do have good headings for each section I think putting in more specific subheadings will help both you and the reader to organise the information better. In terms of the info you have so far, I would just make a point that you should try and get most of the content from primary sources instead of review articles. Additionally, because you are focusing on Wnt signalling in skin development I don’t think you have enough explanation in that area. Since it’s your focal aspect then I think you should explore a lot more of the research and the related abnormalities that have been found. You could also just include some links to papers that describe Wnt signalling in other embryonic roles since you aren’t investigating those. Finally I would suggest making the page more interesting by including images, diagrams, tables, timeline, etc. so it’s not just paragraphs of text one after the other (and to fulfill the assessment criteria). But overall you guys have made great progress - I hope these comments will help you improve!

====Group 3 Peer Review====
At first glance, your page looks well structured with lots of information present so well done! Your introduction is concise but effective and it provides a good outline of the topic. It’s also good that you’ve started to explain the history - I think the timeline will be really helpful once it’s finished. All your referencing looks to be correct and most of the abbreviations are all defined. The table of subtypes of FGFR is a great way to present this info briefly and clearly, and I really like that you’ve also listed the associated abnormalities. Also, your hand-drawn image is a great effort but it would be better to clearly explain all the abbreviations (at least on the actual image summary page, or maybe in the glossary) since it’s not all defined in the text. You guys have done a really great job so far in explaining the different roles in embryonic development and it’s especially good that you’ve included descriptions of primary research. And your image for bone development is a really helpful addition to your info.

Obviously your group still has some research and info to fill out in your sections but you’ve done really well so far. For your abnormalities section, I think it would be good if you can find some related pictures to include. In general I think you should add more content and explain your sections in some more detail - particularly the overview of the pathway and the signal transduction section. At the moment it’s more of a description/listing of the components and factors, rather than a full explanation of how they interact and the responses they induce. So as long as you guys get fill out your content a bit more and make sure to finish off your quiz, history, animal models, and new/current research sections then I think you will have a great page by the end.

====Group 4 Peer Review====
First off you guys have chosen great headings and subheadings! It’s really helpful in breaking down your information to be better understood and I like all the aspects you’ve chosen to explore. Your content so far is clear and concise and most of it is correctly referenced - well done particularly on the info for animal models. The examples of primary research you’ve included are also a great addition. The information you’ve presented is also written well and in a way that’s not too scientific so it’s easy to understand.

It would be great if you included an introduction paragraph to just give a brief overview of Hedgehog signalling. While your animal model content is good, I think you need a lot more info for human embryonic development (considering that it should be the focus of the project) - you’ve mentioned organogenesis very briefly, but I think if you explored each of the systems in greater detail then it would really improve your page. I would strongly recommend including a glossary as well. Make sure you have captions for your images so the reader understands why the image is relevant to your text. Also you should fully define all the abbreviations somewhere (either in your glossary on the image’s page) for the reader’s benefit. If you have some more images in the signalling/animal model sections I think that would break up the paragraphs a bit more and make it easier to read. And you might want to include a summary table, maybe of the molecular pathway factors, somewhere. But overall you’ve started off really well as a team - keep working hard to finish off/improve each section.

====Group 5 Peer Review====
Congrats Group 5 on producing a really great looking page so far! Straightaway I like that you have an introduction paragraph and that I can immediately see inclusion of tables, images, and some correct referencing. Explaining the origin of the T-box name is a great piece of background info to include (maybe make it a proper subheading though?). You’ve also touched on some of the history of the gene/signalling pathway in your paragraphs but it might be good to also present that in a brief timeline/table. Your table for T-box family features is really great - especially because of inclusion of main expression sites and the related abnormalities. Also, you have references to primary research articles so it’s good to see you’re backing up your content with accurate and relevant sources. You’ve done a really great job on exploring the animal models as well.

Ultimately you guys have done great work so my suggestions for improving your page are mostly minor! You have a lot of PMID links just left at the end of some paragraphs so make sure you get those properly listed at the end in your reference section. If you change your pictures to thumbnails then I think they would integrate into your text better (because at the moment where they are placed breaks up the text). Also, I’m not sure if there’s a particular reason why you did this in the first place but I wouldn’t capitalise all the subheadings in the abnormalities section. And I suggest moving the ‘Ancient origins and evolution of the T-box gene family’ near the top of your page, because at the moment it seems out of place and doesn’t really flow on from discussing the abnormalities. The other thing I would say is that - if it’s possible - it would be great if you could explain more about the actual molecular pathway and include a picture of the molecules/factors involved, because at the moment you’ve only described it in the context of different TBX genes being expressed in each developmental role. I think especially if you have an image of the structure of some of the different proteins, transcription factors, etc. then it would really help to visualise the molecular aspects of the pathway. Hope my comments are helpful!

====Group 6 Peer Review====
Group 6 - it looks like you’ve started off well and from the headings/subheadings you’ve chosen, I think you’ve chosen some great aspects to explore. The content you have so far is relevant and written in a way that’s easy to understand. Your explanation of the signalling pathway is good and you’ve included some pictures, but I think more work still has to be done.

Your page is clearly still being worked on but here are my suggestions. Firstly your page really needs a lot more content. You haven’t explained anything about the involvement of TGF-beta in embryonic development yet and that’s supposed to be the key point of this project, so you should really focus on finding some info about that. Your referencing as well is really poor. Make sure you have in-text referencing so that the reader knows exactly where each part of your content has come from - at the moment there are no clear references for anything you have written. You should especially be referencing your images (in the image caption). You should also edit the formatting of your headings because at the moment they are all considered subheadings of ‘Introduction’. I would suggest moving the history section to the beginning of your page and presenting the info in a table. And it would be really great if you had a section on ‘Animal Models’ and ‘Abnormalities’, like most of the other pages have done. Your references section is also not formatted correctly so you need to fix that. As long as you work hard from now on I think you can still put up a great project!
 

{{Stem Cell Presentations 2016}}

==Lab 11 Assessment==
'''Distinct phases of cardiomyocyte differentiation regulate growth of the zebrafish heart.'''<ref><pubmed>19395641</pubmed></ref> 
''Emma de Pater, Linda Clijsters, Sara R. Marques, Yi-Fan Lin, Zayra V. Garavito-Aguilar, Deborah Yelon & Jeroen Bakkers''
:In this study, de Pater et al. investigated the regulation of development of the zebrafish heart. Although the process of heart development (e.g. elongation, septation, heart looping) of vertebrates is well known, the regulatory mechanisms are less understood. De Pater et al. performed their research with the aim of looking into cardiomyocyte differentiation during cardiac development. By counting the number of differentiated cardiomyocytes of the linear zebrafish heart tube vs. the looped chambers, they found that the cardiomyocytes in the heart tube were increased during the process of looping. They also stained cells with BrdU to detect proliferating cells, then used protein expression detection and a timing assay to discover that there were distinct phases of proliferation and differentiation among different cell populations. It was seen that cardiomyocyte differentiation began in the ventricle and continued along the atrium, which also allowed new cardiomyocytes to be added at the venous pole of the heart tube. De Pater et al. also observed a subsequent second phase of differentiation located at the arterial pole. In conclusion, the first phase of differentiation (which produced the cardiomyocytes that formed the ventricle and atrium) was completely separate from the second phase (addition of cells to the arterial pole). They also found that different signalling mechanisms were involved in the different phases. Therefore the temporal regulation ''and'' the signalling regulation of the phases of differentiation at each pole were different.
:This research was referred to in the 2016 review article, 'Building and re-building the heart by cardiomyocyte proliferation<ref><pubmed>26932668</pubmed></ref>', by Foglia & Poss. De Pater et al.'s findings were mentioned as evidence for cardiac growth in zebrafish occurring specifically through the proliferation of existing cardiomyocytes.
 

==References==
<references/>

2016 Group Project 2

2016-10-21T03:30:56Z

Z5015014: /* Glossary */

2016 Group Project 2

2016-10-21T03:18:24Z

Z5015014: /* Glossary */