2016 Group Project 2: Difference between revisions

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'''Trabeculation'''
'''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 and colleagues (2015). <ref name=PMID26641715><pubmed>26641715</pubmed></ref>


'''Development of the Outflow Tract'''
'''Development of the Outflow Tract'''

Revision as of 13:15, 21 September 2016

2016 Student Projects 
Signalling: 1 Wnt | 2 Notch | 3 FGF Receptor | 4 Hedgehog | 5 T-box | 6 TGF-Beta
2016 Group Project Topic - Signaling in Development

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Notch signalling pathway

Introduction

The Notch signalling pathway is critical 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.[1][2]

History

1914 First description of a "notch" defect (loss of tissue in the wing) in Drosophila by John S. Dexter, giving the gene its name
1917 First allele of Notch is identified by Thomas Hunt Morgan
1930s Donald F. Poulson conducts research into the involvement of Notch in development

Overview of Molecular Mechanisms

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.[3]

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.[3] 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.[1] Cell-cell interaction is therefore critical in the process of triggering Notch signalling. The NICD enters the nucleus and interacts with the Suppressor of Hairless DNA-binding protein (Su(H)) to promote transcription of Notch target genes.[2] 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.[3]

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. [4] The following subsections will further elucidate the vital roles of Notch signalling during normal embryonic development.

Cardiovascular

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. [5] 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. [6]

On the other hand, studies such as that by Boni and colleagues (2008) have found that Notch signalling may also promote myogenesis from cardiac progenitor cells. [4] Cardiogenesis has also been promoted by downregulating Notch-1 activity in stem cells of embryos (Nemir et al., 2006).[7]

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. [8]

Development of the Atrioventricular Canal

A study by Rutenberg and colleagues (2006) and another by Kokubo and colleagues (2007) implicate a role for Notch signaling in the region between the atria and the ventricles of the heart (the atrioventricular canal, or AVC).[9] [10] 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.[11]

See the summary diagram below for a schematic representation of this molecular interaction during AVC development.

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. [12]

A more recent paper by Wang and colleagues (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. [13]

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. [14] Furthermore, the important process of trabeculation has recently been shown to be controlled by sequential Notch activation by an investigation by D’Amato and colleagues (2015). [15]

Development of the Outflow Tract


Summary of Notch Signalling in Cardiac Development
Summary of Notch Signalling in Cardiac Development[16]

Central Nervous System

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. [17]

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. [18]

Other Systems


Roles in Animal Development

Drosophila melanogaster

Unlike the four Notch paralogs in humans, only one Notch homolog is present in Drosophila.[3]

Research has 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. They also 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.[19]

Zebrafish

Abnormalities in Notch signalling

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.[20] 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.[21]


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%).[22][23] 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.[23][24] 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.[22] There is currently no effective treatment available for CADASIL.



Current Areas of Research



Glossary

References

  1. 1.0 1.1 Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.
  2. 2.0 2.1 <pubmed>10075488</pubmed>
  3. 3.0 3.1 3.2 3.3 Yamamoto, S., Schulze, K.L. & Bellen, H.J. (2014). Introduction to Notch Signalling. Notch Signaling: Methods and Protocols. Methods in Molecular Biology: 1187
  4. 4.0 4.1 <pubmed>18832173</pubmed>
  5. <pubmed>19580804</pubmed>
  6. <pubmed>10934030</pubmed>
  7. <pubmed>16690879</pubmed>
  8. <pubmed>19917614</pubmed>
  9. <pubmed>17021042</pubmed>
  10. <pubmed>17259303</pubmed>
  11. <pubmed>16554359</pubmed>
  12. <pubmed>14701881</pubmed>
  13. <pubmed>23560082</pubmed>
  14. <pubmed>17336907</pubmed>
  15. <pubmed>26641715</pubmed>
  16. <pubmed>24345875</pubmed>
  17. <pubmed>16594731</pubmed>
  18. <pubmed>20887720</pubmed>
  19. <pubmed>21447553</pubmed>
  20. <pubmed>26548814</pubmed>
  21. <pubmed>16773578</pubmed>
  22. 22.0 22.1 <pubmed>21045164</pubmed>
  23. 23.0 23.1 <pubmed>20301673</pubmed>
  24. <pubmed>24579972</pubmed>