Embryology - User contributions [en-gb]

2018 Group Project 4

2018-10-16T10:21:04Z

Z5229281: /* Time Course of Neural Crest Cardiac Development */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

== Introduction ==
----
The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

== Development of the Cardiovascular System==
----
Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

=== Timeline of Development of the Cardiovascular System===

(Timeline of embryonic origins)

{| class = "pretty table"
|-
| Week 2 - 3
|
* Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac neural crest cells ==
----
Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}. CNCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Studies have shown that cardiac neural crest cells play a role in the development of:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===
----
Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===
----
After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===
----
The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the respective pharyngeal arches. Slit proteins, a family of secreted extracellular matrix proteins, can target cells to migrate to arch 3. Fibroblast growth factor 8 (FGF-8) targets migration towards the arch 4. EphA, a subclass of receptor tyrosine kinase which responds to Ephrins, targets for arch 6. Ras-related C3 botulinum toxin substrate 1 (Rac1) and Stromal cell-derived factor 1 (Sdf1) are both expressed in the cells, causing them to condensate around the arch arteries.

Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
----
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===
----
The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===
----
The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into cardiac chambers and arterial trunks subsequently. {{#pmid:12807866|PMID12807866}}

====Formation and Developement of Primary Myocardial Heart Tube====
The embryo undergoes gastrulation and mesodermal layer tissues give rise to the heart.The cells form a crescent virtually at the cranial border of the disc, and then the central region of ectoderm shapes itself into the neural plate. {{#pmid:12807866|PMID12807866}} The The structure eventually folds and is known as neural folds. The developing heart in humans is initially cranial within the disc relative to the neural folds. The developing heart is also shaped by a plate of promyocardial cells, which helps the folding and positioning of the developing heart comapred to the neural structures.

====Formation of Cardiac Chambers====
By looping, the primary heart tube inside the pericardial cavity can be separated into atrial and ventricular parts by the atrioventricular canal, along with an outflow tract. {{#pmid:12807866|PMID12807866}} The constriction which is at the site of the primary interventricular foramen will eventually become the left and right ventricles. The primary myocardium is then formed by the myocardial walls of the heart tube. {{#pmid:10882515|PMID10882515}}

====Formation of Arterial Trunks====
During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}} The most important part of the outflow tract is that it breaks up by the merging of the cushions within it, causing new myocardium to form within the cushions to produce the medial part of the subpulmonary infundibulum. This retains its origin from the right ventricle.{{#pmid:10433836|PMID10433836}} Concurrently, the subaortic part of the outflow segment is positioned to the left ventricle by the merging of the cushions to the crest of the muscular ventricular septum. The myocardium of the initial inner heart curvature then disintegrates to allow fibrous continuity between the leaflets of the aortic and mitral valves in the ventricular roof. {{#pmid:12807866|PMID12807866}}

=== Formation of the Cardiac Ganglia ===
----
The cardiac crest is made up completely by the cardiac ganglia. Both the neuronal cell bodies and supporting cells originate from the cardiac crest.{{#pmid:6844926|PMID6844926}} The factors that affect how the cardiac crest segregates and form the aorticopulmonary septum or their condensation as ganglia is not known. Cardiac crest cells do contribute to the forming of nodose ganglion, which is the distal sensory ganglion of the vagus nerve. The neurons that originated from the nodose placode located dorsal to pharyngeal arches, forms the nodose ganglion as well. The process works by having the neuron cells migrate from this placode to combine with cardiac crest to form the nodose ganglion. The condensation process of this ganglion have several factors such as the molecule N-cadherin and signaling by Slit/Robo signaling. In the cranial crest, both N-cadherin and Slit1/Robo signaling is crucial for the merging of crest cells and placode-derived neurons into ganglia. Placodal neurons expresses N-cadherin and Robo2, while neural crest cells expresses Slit1{{#pmid:PMC3011257|PMC3011257}} N-Cadherin and Robo2 are the most important signaling molecules. If either of them are not expressed, the ganglia cannot combine and form properly.{{#pmid:PMC2781051|PMC2781051}}

Neural crest cells play a important role in structuring placodal neurons during early ganglion assembly. The orientation and shape of the cranial ganglia greatly resembles the shifting and moving patterns of the cranial neural crest. Furthermore, ablation of the dorsal midbrain neural folds results in abnormalities in trigeminal ganglion assembly, showing that neural crest cells are needed for the proper organization and integration of placodal neurons into the ganglion.{{#pmid:18278043|PMID18278043}} The neural crest migration will have defects and result in neuronal cell bodies and axons being wrongly positioned if there is a loss of receptor neuropilin 2 which is expressed by neural crest cells, and/or loss of semaphorin ligands which are expressed by the adjacent mesenchyme. This will cause abnormal interlinked trigeminal and facial ganglia.{{#pmid:17443771|PMID17443771}} Cell-cell signaling between neural crest and placodes is most possible to trigger their coordinated and cooperative interactions in shaping the cranial ganglia. For example, Robo2 is expressed by trigeminal placode cells, but ligand Slit1 is expressed by neural crest cells. If either the receptor or the function is blocked, the ligand will have severe deformities like abnormal of diffusely condensed ganglia.{{#pmid:18278043|PMID18278043}}

== Signalling Molecules ==
----

Many signalling pathways are involved in the proper development of the cardiovascular system, however most of the mechanisms remain unknown to date. Some of the studied signalling molecules that play a role in the proper development of the cardiovascular system in an embryo are described briefly below:

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
# '''Meis2''': Transcription factor that directly binds to Pbx proteins. The Meis2/Pbx protein complex binds to DNA and regulates their transcription, playing important roles during the development of the heart. One of the target genes controlled by Meis-Pbx expression is the Hox gene. {{#pmid: PMC4636814 | PMC4636814}}

== Time Course of Neural Crest Cardiac Development ==
----

(Timeline of the Outflow Tract)

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
----
[[File:Heart Defects.png|400px|thumb|right|]]

Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

=== Disruptions to outflow tract septation ===
----
In the human, at Carnegie stage 14, the myocardial wall of the outflow tract extends to the border of the pericardial cavity where it joins the aortic sac, giving rise to the arteries that feed the pharyngeal arches <ref name="PMID12739611" />.OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as well as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus. Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot. Anomalies involving the outflow tract and its valves make up a significant proportion of congenital cardiac defects, with a prevalence of at least 4 per 10,000 births {{#pmid:12739611|PMID12739611}}.

=== DiGeorge Syndrome ===
----
[[File:TBX1 factor figure.jpg|400px|thumb|right|]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (Tbx1). Tbx1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor Tbx1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}. (The figure to the right shows Tbx1 colored in red affecting the cardiac cushions).

==Models and Research==

=== Animal Models ===
----
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
----
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

[[File:Outlfow tract.png|450px|thumb|right|Reconstructed aspects of the outflow tract of a developing mouse at E11.5]]

==== Mouse ====
----
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of the proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow tract development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}} Mouse models also allow for the digital reconstruction of the aspects of the outflow tract in a developing embryo as shown in the figure on the right.

==== Zebrafish model ====
----
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors are known to interact with HOX and Pre-B cell leukemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor. {{#pmid:3462257|PMC3462257}}

=== Current Research ===

==== Importance of Semaphorin 3c in the proper septation of OFT ====
----
Semaphorin 3c (Sema3c) is a neurovascular signalling guide factor which is necessary for the proper development of the OFT. Recent studies have shown that Sema3c mediates the interaction between cNCCs and the SHF during the development of the OFT to allow proper septation of the OFT and establish the separate systemic and pulmonary circulation systems.{{#pmid:5533775|PMC5533775}} During the initial stages of heart development, Sema3c is expressed in the OFT as well as in the pharyngeal arch region which also contains cardiac progenitor niches composed of SHF progenitor cells and CNCCs.{{#pmid:5533775|PMC5533775}} Sema3c expression can be regulated positively and negatively by Foxc1/Foxc2 and Tbx1-Fgf8 signalling respectively. Changes in expression levels of Sema3c can alter the development and migration of CNCCs for OFT formation during embryogenesis. For example, the inhibition of Sema3c expression in mouse models have caused disruption in the aortic arch and also led to persistent truncus arteriosus. {{#pmid:5533775|PMC5533775}}

==== Defective Parasympathetic Innervation in Tbx1 Mutant Hearts ====
----
Previous studies have shown that T-box transcription factor (Tbx1) is expressed dynamically in the pharyngeal during the development of mouse and that Tbx1 homozygous mutants display various neural crest cell defects. This led to further investigations on whether parasympathetic (vagal) innervation of the heart will be affected by mutations in Tbx1. Recent studies have shown that Tbx1 plays a role in regulating epibranchial ganglion positioning, migratory paths of CNCCs and subsequent vagal nerve projections to the heart. Tbx1 mutants show reduced expression of Sema3c which results in a disrupted CNCC migration pattern. Sema3C mutant embryos display a cardiac innervation phenotype similar to those observed in Tbx1 mutant embryos.{{#pmid:30249045|PMID30249045}}

==Glossary==
----

Bulbus cordis - Bulb of the heart that lies ventrally to the primitive ventricle. Gives rise to the ventricles of the formed heart together with the primitive ventricle.

Cardiac outflow tract - Transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac

DiGeorge Syndrome - 22q11.2 deletion syndrome which can lead to symptoms such as delayed developmental progress, congenital heart problems, specific facial features, etc.

Induction - Process where progenitor cells begin to differentiate

Infundibulum - conical pouch formed from the upper and left angle of the right ventricle in the chordate heart, from which the pulmonary trunk arises.

Persistent Truncus Arteriosus - Occurs when the embryological structure known as the truncus arteriosus fails to properly divide into the pulmonary trunk and aorta.

Valvulogenesis - Complicated process involving the formation and morphogenesis of the atrioventricular and semilunar valves.

Promyocardial cells - helps the folding and positioning of the developing heart.

Semaphorins - class of secreted and membrane proteins that were originally identified as axonal growth cone guidance molecules.

== List of Abbreviations ==
----
* '''Aortopulmonary''' - (AP)
* '''Bone morphogenetic protein''' - (BMP)
* '''Cardiac neural crest cells''' - (CNCCs)
* '''DiGeorge syndrome''' - (DGS)
* '''Dominant-negative Notch inhibitor''' - (DN-MAML)
* '''Endothelial cells''' - (ECs)
* '''Fibroblast growth factor''' - (FGF)
* '''Myeloid ecotropic viral integration site 2 homolog''' - (MEIS2)
* '''Outflow tract septation''' - (OFT)
* '''Pre-B cell leukemia transcription factors''' - (PBX)
* '''Persistent Truncus Arteriosus''' - (PTA)
* '''Ras-related C3 botulinum toxin substrate 1''' - (Rac1)
* '''Stromal cell-derived factor 1''' - (Sdf1)
* '''Semaphorin 3c''' - (Sema3c)
* '''Second heart field-derived''' - (SHF-derived)
* '''T-box transcription factor''' - (Tbx1)

==References==

2018 Group Project 4

2018-10-16T10:20:03Z

Z5229281: /* Timeline of Development of the Cardiovascular System */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

== Introduction ==
----
The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

== Development of the Cardiovascular System==
----
Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

=== Timeline of Development of the Cardiovascular System===

(Timeline of embryonic origins)

{| class = "pretty table"
|-
| Week 2 - 3
|
* Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac neural crest cells ==
----
Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}. CNCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Studies have shown that cardiac neural crest cells play a role in the development of:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===
----
Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===
----
After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===
----
The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the respective pharyngeal arches. Slit proteins, a family of secreted extracellular matrix proteins, can target cells to migrate to arch 3. Fibroblast growth factor 8 (FGF-8) targets migration towards the arch 4. EphA, a subclass of receptor tyrosine kinase which responds to Ephrins, targets for arch 6. Ras-related C3 botulinum toxin substrate 1 (Rac1) and Stromal cell-derived factor 1 (Sdf1) are both expressed in the cells, causing them to condensate around the arch arteries.

Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
----
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===
----
The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===
----
The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into cardiac chambers and arterial trunks subsequently. {{#pmid:12807866|PMID12807866}}

====Formation and Developement of Primary Myocardial Heart Tube====
The embryo undergoes gastrulation and mesodermal layer tissues give rise to the heart.The cells form a crescent virtually at the cranial border of the disc, and then the central region of ectoderm shapes itself into the neural plate. {{#pmid:12807866|PMID12807866}} The The structure eventually folds and is known as neural folds. The developing heart in humans is initially cranial within the disc relative to the neural folds. The developing heart is also shaped by a plate of promyocardial cells, which helps the folding and positioning of the developing heart comapred to the neural structures.

====Formation of Cardiac Chambers====
By looping, the primary heart tube inside the pericardial cavity can be separated into atrial and ventricular parts by the atrioventricular canal, along with an outflow tract. {{#pmid:12807866|PMID12807866}} The constriction which is at the site of the primary interventricular foramen will eventually become the left and right ventricles. The primary myocardium is then formed by the myocardial walls of the heart tube. {{#pmid:10882515|PMID10882515}}

====Formation of Arterial Trunks====
During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}} The most important part of the outflow tract is that it breaks up by the merging of the cushions within it, causing new myocardium to form within the cushions to produce the medial part of the subpulmonary infundibulum. This retains its origin from the right ventricle.{{#pmid:10433836|PMID10433836}} Concurrently, the subaortic part of the outflow segment is positioned to the left ventricle by the merging of the cushions to the crest of the muscular ventricular septum. The myocardium of the initial inner heart curvature then disintegrates to allow fibrous continuity between the leaflets of the aortic and mitral valves in the ventricular roof. {{#pmid:12807866|PMID12807866}}

=== Formation of the Cardiac Ganglia ===
----
The cardiac crest is made up completely by the cardiac ganglia. Both the neuronal cell bodies and supporting cells originate from the cardiac crest.{{#pmid:6844926|PMID6844926}} The factors that affect how the cardiac crest segregates and form the aorticopulmonary septum or their condensation as ganglia is not known. Cardiac crest cells do contribute to the forming of nodose ganglion, which is the distal sensory ganglion of the vagus nerve. The neurons that originated from the nodose placode located dorsal to pharyngeal arches, forms the nodose ganglion as well. The process works by having the neuron cells migrate from this placode to combine with cardiac crest to form the nodose ganglion. The condensation process of this ganglion have several factors such as the molecule N-cadherin and signaling by Slit/Robo signaling. In the cranial crest, both N-cadherin and Slit1/Robo signaling is crucial for the merging of crest cells and placode-derived neurons into ganglia. Placodal neurons expresses N-cadherin and Robo2, while neural crest cells expresses Slit1{{#pmid:PMC3011257|PMC3011257}} N-Cadherin and Robo2 are the most important signaling molecules. If either of them are not expressed, the ganglia cannot combine and form properly.{{#pmid:PMC2781051|PMC2781051}}

Neural crest cells play a important role in structuring placodal neurons during early ganglion assembly. The orientation and shape of the cranial ganglia greatly resembles the shifting and moving patterns of the cranial neural crest. Furthermore, ablation of the dorsal midbrain neural folds results in abnormalities in trigeminal ganglion assembly, showing that neural crest cells are needed for the proper organization and integration of placodal neurons into the ganglion.{{#pmid:18278043|PMID18278043}} The neural crest migration will have defects and result in neuronal cell bodies and axons being wrongly positioned if there is a loss of receptor neuropilin 2 which is expressed by neural crest cells, and/or loss of semaphorin ligands which are expressed by the adjacent mesenchyme. This will cause abnormal interlinked trigeminal and facial ganglia.{{#pmid:17443771|PMID17443771}} Cell-cell signaling between neural crest and placodes is most possible to trigger their coordinated and cooperative interactions in shaping the cranial ganglia. For example, Robo2 is expressed by trigeminal placode cells, but ligand Slit1 is expressed by neural crest cells. If either the receptor or the function is blocked, the ligand will have severe deformities like abnormal of diffusely condensed ganglia.{{#pmid:18278043|PMID18278043}}

== Signalling Molecules ==
----

Many signalling pathways are involved in the proper development of the cardiovascular system, however most of the mechanisms remain unknown to date. Some of the studied signalling molecules that play a role in the proper development of the cardiovascular system in an embryo are described briefly below:

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
# '''Meis2''': Transcription factor that directly binds to Pbx proteins. The Meis2/Pbx protein complex binds to DNA and regulates their transcription, playing important roles during the development of the heart. One of the target genes controlled by Meis-Pbx expression is the Hox gene. {{#pmid: PMC4636814 | PMC4636814}}

== Time Course of Neural Crest Cardiac Development ==
----

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
----
[[File:Heart Defects.png|400px|thumb|right|]]

Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

=== Disruptions to outflow tract septation ===
----
In the human, at Carnegie stage 14, the myocardial wall of the outflow tract extends to the border of the pericardial cavity where it joins the aortic sac, giving rise to the arteries that feed the pharyngeal arches <ref name="PMID12739611" />.OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as well as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus. Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot. Anomalies involving the outflow tract and its valves make up a significant proportion of congenital cardiac defects, with a prevalence of at least 4 per 10,000 births {{#pmid:12739611|PMID12739611}}.

=== DiGeorge Syndrome ===
----
[[File:TBX1 factor figure.jpg|400px|thumb|right|]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (Tbx1). Tbx1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor Tbx1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}. (The figure to the right shows Tbx1 colored in red affecting the cardiac cushions).

==Models and Research==

=== Animal Models ===
----
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
----
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

[[File:Outlfow tract.png|450px|thumb|right|Reconstructed aspects of the outflow tract of a developing mouse at E11.5]]

==== Mouse ====
----
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of the proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow tract development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}} Mouse models also allow for the digital reconstruction of the aspects of the outflow tract in a developing embryo as shown in the figure on the right.

==== Zebrafish model ====
----
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors are known to interact with HOX and Pre-B cell leukemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor. {{#pmid:3462257|PMC3462257}}

=== Current Research ===

==== Importance of Semaphorin 3c in the proper septation of OFT ====
----
Semaphorin 3c (Sema3c) is a neurovascular signalling guide factor which is necessary for the proper development of the OFT. Recent studies have shown that Sema3c mediates the interaction between cNCCs and the SHF during the development of the OFT to allow proper septation of the OFT and establish the separate systemic and pulmonary circulation systems.{{#pmid:5533775|PMC5533775}} During the initial stages of heart development, Sema3c is expressed in the OFT as well as in the pharyngeal arch region which also contains cardiac progenitor niches composed of SHF progenitor cells and CNCCs.{{#pmid:5533775|PMC5533775}} Sema3c expression can be regulated positively and negatively by Foxc1/Foxc2 and Tbx1-Fgf8 signalling respectively. Changes in expression levels of Sema3c can alter the development and migration of CNCCs for OFT formation during embryogenesis. For example, the inhibition of Sema3c expression in mouse models have caused disruption in the aortic arch and also led to persistent truncus arteriosus. {{#pmid:5533775|PMC5533775}}

==== Defective Parasympathetic Innervation in Tbx1 Mutant Hearts ====
----
Previous studies have shown that T-box transcription factor (Tbx1) is expressed dynamically in the pharyngeal during the development of mouse and that Tbx1 homozygous mutants display various neural crest cell defects. This led to further investigations on whether parasympathetic (vagal) innervation of the heart will be affected by mutations in Tbx1. Recent studies have shown that Tbx1 plays a role in regulating epibranchial ganglion positioning, migratory paths of CNCCs and subsequent vagal nerve projections to the heart. Tbx1 mutants show reduced expression of Sema3c which results in a disrupted CNCC migration pattern. Sema3C mutant embryos display a cardiac innervation phenotype similar to those observed in Tbx1 mutant embryos.{{#pmid:30249045|PMID30249045}}

==Glossary==
----

Bulbus cordis - Bulb of the heart that lies ventrally to the primitive ventricle. Gives rise to the ventricles of the formed heart together with the primitive ventricle.

Cardiac outflow tract - Transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac

DiGeorge Syndrome - 22q11.2 deletion syndrome which can lead to symptoms such as delayed developmental progress, congenital heart problems, specific facial features, etc.

Induction - Process where progenitor cells begin to differentiate

Infundibulum - conical pouch formed from the upper and left angle of the right ventricle in the chordate heart, from which the pulmonary trunk arises.

Persistent Truncus Arteriosus - Occurs when the embryological structure known as the truncus arteriosus fails to properly divide into the pulmonary trunk and aorta.

Valvulogenesis - Complicated process involving the formation and morphogenesis of the atrioventricular and semilunar valves.

Promyocardial cells - helps the folding and positioning of the developing heart.

Semaphorins - class of secreted and membrane proteins that were originally identified as axonal growth cone guidance molecules.

== List of Abbreviations ==
----
* '''Aortopulmonary''' - (AP)
* '''Bone morphogenetic protein''' - (BMP)
* '''Cardiac neural crest cells''' - (CNCCs)
* '''DiGeorge syndrome''' - (DGS)
* '''Dominant-negative Notch inhibitor''' - (DN-MAML)
* '''Endothelial cells''' - (ECs)
* '''Fibroblast growth factor''' - (FGF)
* '''Myeloid ecotropic viral integration site 2 homolog''' - (MEIS2)
* '''Outflow tract septation''' - (OFT)
* '''Pre-B cell leukemia transcription factors''' - (PBX)
* '''Persistent Truncus Arteriosus''' - (PTA)
* '''Ras-related C3 botulinum toxin substrate 1''' - (Rac1)
* '''Stromal cell-derived factor 1''' - (Sdf1)
* '''Semaphorin 3c''' - (Sema3c)
* '''Second heart field-derived''' - (SHF-derived)
* '''T-box transcription factor''' - (Tbx1)

==References==

File:Outlfow tract.png

2018-10-16T10:01:25Z

Z5229281:

The images show reconstructed aspects of the outflow tract of a developing mouse at E11.5. The reconstructions were segmented so that all myocardium, determined using a myocardial-specific marker, was shown in silver, and non-myocardial tissues, lacking the marker, were shown in green (Details provided in Reference [7]). The septal outflow cushion was shown in brown, and the parietal cushion in yellow. Panel (A) shows a superior view of the distal margins of the muscular outflow tract having digitally removed the non-myocardial distal outflow tract. The distal myocardial border has an obvious fishmouth appearance, with the distal margins of the major outflow cushions confluent with the muscular margins. Panel (B) shows the non-myocardial walls of the distal outflow tract viewed from the front. The two non-myocardial tongues fill the spaces formed by the angles of the jaws of the muscular fishmouth. They will become the parietal walls of the aorta and the pulmonary trunk.

z5229281

==Reference==

Anderson, R.H.; Mohun, T.J.; Spicer, D.E.; Bamforth, S.D.; Brown, N.A.; Chaudhry, B.; Henderson, D.J. Myths and Realities Relating to Development of the Arterial Valves. J. Cardiovasc. Dev. Dis. 2014, 1, 177-200.

https://www.mdpi.com/2308-3425/1/3/177

==Copyright==
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

{{Template:2018 Student Image}}

File:TBX1 factor figure.jpg

2018-10-16T10:00:46Z

Z5229281:

Cardiac neural crest cell defects in Tbx1 mutant embryos. (A) E9.5 Tbx1CRE-RosaYFP embryos were stained for the cNCC marker AP2α together with YFP as a marker for the Tbx1-lineage. cNCCs and Tbx1 do not colocalize (arrowheads). (B) E12.5 Tbx1+/+, Tbx1+/− and Tbx1neo2/− outflow tracts were stained for the cNCC marker Sema3C. cNCCs have migrated into the outflow tract cushions in Tbx1+/+ and Tbx1+/− but not in Tbx1neo2/− embryos. White arrowheads and arrows indicate Sema3C expression in myocardial cuff cells and the septal bridge area, respectively. Asterisk indicates absent Sema3C in the outflow tract right cushion. Yellow arrow marks residual Sema3C-positive cNCCs in the outflow tract left cushion. Scale Bars are in μm.

===Reference===

Calmont, A.; Anderson, N.; Suntharalingham, J.P.; Ang, R.; Tinker, A.; Scambler, P.J. Defective Vagal Innervation in Murine Tbx1 Mutant Hearts. J. Cardiovasc. Dev. Dis. 2018, 5, 49.

Illustration obtained from
https://www.mdpi.com/2308-3425/5/4/49

===Copyright===
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

{{Template:2018 Student Image}}

z5229281

File:TBX1 factor figure.jpg

2018-10-16T10:00:19Z

Z5229281:

2018 Group Project 4

2018-10-16T09:44:34Z

Z5229281: /* Human Congenital Heart Diseases associated with Neural Crest Cells */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

== Introduction ==
----
The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

== Development of the Cardiovascular System==
----
Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

=== Timeline of Development of the Cardiovascular System===
{| class = "pretty table"
|-
| Week 2 - 3
|
* Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac neural crest cells ==
----
Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}. CNCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Studies have shown that cardiac neural crest cells play a role in the development of:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===
----
Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===
----
After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===
----
The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the respective pharyngeal arches. Slit proteins, a family of secreted extracellular matrix proteins, can target cells to migrate to arch 3. Fibroblast growth factor 8 (FGF-8) targets migration towards the arch 4. EphA, a subclass of receptor tyrosine kinase which responds to Ephrins, targets for arch 6. Ras-related C3 botulinum toxin substrate 1 (Rac1) and Stromal cell-derived factor 1 (Sdf1) are both expressed in the cells, causing them to condensate around the arch arteries.

Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
----
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===
----
The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===
----
The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into cardiac chambers and arterial trunks subsequently. {{#pmid:12807866|PMID12807866}}

====Formation and Developement of Primary Myocardial Heart Tube====
The embryo undergoes gastrulation and mesodermal layer tissues give rise to the heart.The cells form a crescent virtually at the cranial border of the disc, and then the central region of ectoderm shapes itself into the neural plate. {{#pmid:12807866|PMID12807866}} The The structure eventually folds and is known as neural folds. The developing heart in humans is initially cranial within the disc relative to the neural folds. The developing heart is also shaped by a plate of promyocardial cells, which helps the folding and positioning of the developing heart comapred to the neural structures.

====Formation of Cardiac Chambers====
By looping, the primary heart tube inside the pericardial cavity can be separated into atrial and ventricular parts by the atrioventricular canal, along with an outflow tract. {{#pmid:12807866|PMID12807866}} The constriction which is at the site of the primary interventricular foramen will eventually become the left and right ventricles. The primary myocardium is then formed by the myocardial walls of the heart tube. {{#pmid:10882515|PMID10882515}}

====Formation of Arterial Trunks====
During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}} The most important part of the outflow tract is that it breaks up by the merging of the cushions within it, causing new myocardium to form within the cushions to produce the medial part of the subpulmonary infundibulum. This retains its origin from the right ventricle.{{#pmid:10433836|PMID10433836}} Concurrently, the subaortic part of the outflow segment is positioned to the left ventricle by the merging of the cushions to the crest of the muscular ventricular septum. The myocardium of the initial inner heart curvature then disintegrates to allow fibrous continuity between the leaflets of the aortic and mitral valves in the ventricular roof. {{#pmid:12807866|PMID12807866}}

=== Formation of the Cardiac Ganglia ===
----
The cardiac crest is made up completely by the cardiac ganglia. Both the neuronal cell bodies and supporting cells originate from the cardiac crest.{{#pmid:6844926|PMID6844926}} The factors that affect how the cardiac crest segregates and form the aorticopulmonary septum or their condensation as ganglia is not known. Cardiac crest cells do contribute to the forming of nodose ganglion, which is the distal sensory ganglion of the vagus nerve. The neurons that originated from the nodose placode located dorsal to pharyngeal arches, forms the nodose ganglion as well. The process works by having the neuron cells migrate from this placode to combine with cardiac crest to form the nodose ganglion. The condensation process of this ganglion have several factors such as the molecule N-cadherin and signaling by Slit/Robo signaling. In the cranial crest, both N-cadherin and Slit1/Robo signaling is crucial for the merging of crest cells and placode-derived neurons into ganglia. Placodal neurons expresses N-cadherin and Robo2, while neural crest cells expresses Slit1{{#pmid:PMC3011257|PMC3011257}} N-Cadherin and Robo2 are the most important signaling molecules. If either of them are not expressed, the ganglia cannot combine and form properly.{{#pmid:PMC2781051|PMC2781051}}

Neural crest cells play a important role in structuring placodal neurons during early ganglion assembly. The orientation and shape of the cranial ganglia greatly resembles the shifting and moving patterns of the cranial neural crest. Furthermore, ablation of the dorsal midbrain neural folds results in abnormalities in trigeminal ganglion assembly, showing that neural crest cells are needed for the proper organization and integration of placodal neurons into the ganglion.{{#pmid:18278043|PMID18278043}} The neural crest migration will have defects and result in neuronal cell bodies and axons being wrongly positioned if there is a loss of receptor neuropilin 2 which is expressed by neural crest cells, and/or loss of semaphorin ligands which are expressed by the adjacent mesenchyme. This will cause abnormal interlinked trigeminal and facial ganglia.{{#pmid:17443771|PMID17443771}} Cell-cell signaling between neural crest and placodes is most possible to trigger their coordinated and cooperative interactions in shaping the cranial ganglia. For example, Robo2 is expressed by trigeminal placode cells, but ligand Slit1 is expressed by neural crest cells. If either the receptor or the function is blocked, the ligand will have severe deformities like abnormal of diffusely condensed ganglia.{{#pmid:18278043|PMID18278043}}

== Signalling Molecules ==
----

Many signalling pathways are involved in the proper development of the cardiovascular system, however most of the mechanisms remain unknown to date. Some of the studied signalling molecules that play a role in the proper development of the cardiovascular system in an embryo are described briefly below:

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
# '''Meis2''': Transcription factor that directly binds to Pbx proteins. The Meis2/Pbx protein complex binds to DNA and regulates their transcription, playing important roles during the development of the heart. One of the target genes controlled by Meis-Pbx expression is the Hox gene. {{#pmid: PMC4636814 | PMC4636814}}

== Time Course of Neural Crest Cardiac Development ==
----

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
----
[[File:Heart Defects.png|400px|thumb|right|]]

Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

=== Disruptions to outflow tract septation ===
----
In the human, at Carnegie stage 14, the myocardial wall of the outflow tract extends to the border of the pericardial cavity where it joins the aortic sac, giving rise to the arteries that feed the pharyngeal arches <ref name="PMID12739611" />.OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as well as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus. Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot. Anomalies involving the outflow tract and its valves make up a significant proportion of congenital cardiac defects, with a prevalence of at least 4 per 10,000 births {{#pmid:12739611|PMID12739611}}.

=== DiGeorge Syndrome ===
----
[[File:TBX1 factor figure.jpg|400px|thumb|right|]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (Tbx1). Tbx1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor Tbx1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}. (The figure to the right shows Tbx1 colored in red affecting the cardiac cushions).

==Models and Research==

=== Animal Models ===
----
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
----
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

[[File:Outlfow tract.png|450px|thumb|right|Reconstructed aspects of the outflow tract of a developing mouse at E11.5]]

==== Mouse ====
----
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of the proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow tract development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}} Mouse models also allow for the digital reconstruction of the aspects of the outflow tract in a developing embryo as shown in the figure on the right.

==== Zebrafish model ====
----
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors are known to interact with HOX and Pre-B cell leukemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor. {{#pmid:3462257|PMC3462257}}

=== Current Research ===

==== Importance of Semaphorin 3c in the proper septation of OFT ====
----
Semaphorin 3c (Sema3c) is a neurovascular signalling guide factor which is necessary for the proper development of the OFT. Recent studies have shown that Sema3c mediates the interaction between cNCCs and the SHF during the development of the OFT to allow proper septation of the OFT and establish the separate systemic and pulmonary circulation systems.{{#pmid:5533775|PMC5533775}} During the initial stages of heart development, Sema3c is expressed in the OFT as well as in the pharyngeal arch region which also contains cardiac progenitor niches composed of SHF progenitor cells and CNCCs.{{#pmid:5533775|PMC5533775}} Sema3c expression can be regulated positively and negatively by Foxc1/Foxc2 and Tbx1-Fgf8 signalling respectively. Changes in expression levels of Sema3c can alter the development and migration of CNCCs for OFT formation during embryogenesis. For example, the inhibition of Sema3c expression in mouse models have caused disruption in the aortic arch and also led to persistent truncus arteriosus. {{#pmid:5533775|PMC5533775}}

==== Defective Parasympathetic Innervation in Tbx1 Mutant Hearts ====
----
Previous studies have shown that T-box transcription factor (Tbx1) is expressed dynamically in the pharyngeal during the development of mouse and that Tbx1 homozygous mutants display various neural crest cell defects. This led to further investigations on whether parasympathetic (vagal) innervation of the heart will be affected by mutations in Tbx1. Recent studies have shown that Tbx1 plays a role in regulating epibranchial ganglion positioning, migratory paths of CNCCs and subsequent vagal nerve projections to the heart. Tbx1 mutants show reduced expression of Sema3c which results in a disrupted CNCC migration pattern. Sema3C mutant embryos display a cardiac innervation phenotype similar to those observed in Tbx1 mutant embryos.{{#pmid:30249045|PMID30249045}}

==Glossary==
----

Bulbus cordis - Bulb of the heart that lies ventrally to the primitive ventricle. Gives rise to the ventricles of the formed heart together with the primitive ventricle.

Cardiac outflow tract - Transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac

DiGeorge Syndrome - 22q11.2 deletion syndrome which can lead to symptoms such as delayed developmental progress, congenital heart problems, specific facial features, etc.

Induction - Process where progenitor cells begin to differentiate

Infundibulum - conical pouch formed from the upper and left angle of the right ventricle in the chordate heart, from which the pulmonary trunk arises.

Persistent Truncus Arteriosus - Occurs when the embryological structure known as the truncus arteriosus fails to properly divide into the pulmonary trunk and aorta.

Valvulogenesis - Complicated process involving the formation and morphogenesis of the atrioventricular and semilunar valves.

Promyocardial cells - helps the folding and positioning of the developing heart.

Semaphorins - class of secreted and membrane proteins that were originally identified as axonal growth cone guidance molecules.

== List of Abbreviations ==
----
* '''Aortopulmonary''' - (AP)
* '''Bone morphogenetic protein''' - (BMP)
* '''Cardiac neural crest cells''' - (CNCCs)
* '''DiGeorge syndrome''' - (DGS)
* '''Dominant-negative Notch inhibitor''' - (DN-MAML)
* '''Endothelial cells''' - (ECs)
* '''Fibroblast growth factor''' - (FGF)
* '''Myeloid ecotropic viral integration site 2 homolog''' - (MEIS2)
* '''Outflow tract septation''' - (OFT)
* '''Pre-B cell leukemia transcription factors''' - (PBX)
* '''Persistent Truncus Arteriosus''' - (PTA)
* '''Ras-related C3 botulinum toxin substrate 1''' - (Rac1)
* '''Stromal cell-derived factor 1''' - (Sdf1)
* '''Semaphorin 3c''' - (Sema3c)
* '''Second heart field-derived''' - (SHF-derived)
* '''T-box transcription factor''' - (Tbx1)

==References==

2018 Group Project 4

2018-10-16T09:43:24Z

Z5229281: /* Human Congenital Heart Diseases associated with Neural Crest Cells */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

== Introduction ==
----
The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

== Development of the Cardiovascular System==
----
Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

=== Timeline of Development of the Cardiovascular System===
{| class = "pretty table"
|-
| Week 2 - 3
|
* Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac neural crest cells ==
----
Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}. CNCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Studies have shown that cardiac neural crest cells play a role in the development of:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===
----
Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===
----
After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===
----
The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the respective pharyngeal arches. Slit proteins, a family of secreted extracellular matrix proteins, can target cells to migrate to arch 3. Fibroblast growth factor 8 (FGF-8) targets migration towards the arch 4. EphA, a subclass of receptor tyrosine kinase which responds to Ephrins, targets for arch 6. Ras-related C3 botulinum toxin substrate 1 (Rac1) and Stromal cell-derived factor 1 (Sdf1) are both expressed in the cells, causing them to condensate around the arch arteries.

Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
----
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===
----
The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===
----
The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into cardiac chambers and arterial trunks subsequently. {{#pmid:12807866|PMID12807866}}

====Formation and Developement of Primary Myocardial Heart Tube====
The embryo undergoes gastrulation and mesodermal layer tissues give rise to the heart.The cells form a crescent virtually at the cranial border of the disc, and then the central region of ectoderm shapes itself into the neural plate. {{#pmid:12807866|PMID12807866}} The The structure eventually folds and is known as neural folds. The developing heart in humans is initially cranial within the disc relative to the neural folds. The developing heart is also shaped by a plate of promyocardial cells, which helps the folding and positioning of the developing heart comapred to the neural structures.

====Formation of Cardiac Chambers====
By looping, the primary heart tube inside the pericardial cavity can be separated into atrial and ventricular parts by the atrioventricular canal, along with an outflow tract. {{#pmid:12807866|PMID12807866}} The constriction which is at the site of the primary interventricular foramen will eventually become the left and right ventricles. The primary myocardium is then formed by the myocardial walls of the heart tube. {{#pmid:10882515|PMID10882515}}

====Formation of Arterial Trunks====
During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}} The most important part of the outflow tract is that it breaks up by the merging of the cushions within it, causing new myocardium to form within the cushions to produce the medial part of the subpulmonary infundibulum. This retains its origin from the right ventricle.{{#pmid:10433836|PMID10433836}} Concurrently, the subaortic part of the outflow segment is positioned to the left ventricle by the merging of the cushions to the crest of the muscular ventricular septum. The myocardium of the initial inner heart curvature then disintegrates to allow fibrous continuity between the leaflets of the aortic and mitral valves in the ventricular roof. {{#pmid:12807866|PMID12807866}}

=== Formation of the Cardiac Ganglia ===
----
The cardiac crest is made up completely by the cardiac ganglia. Both the neuronal cell bodies and supporting cells originate from the cardiac crest.{{#pmid:6844926|PMID6844926}} The factors that affect how the cardiac crest segregates and form the aorticopulmonary septum or their condensation as ganglia is not known. Cardiac crest cells do contribute to the forming of nodose ganglion, which is the distal sensory ganglion of the vagus nerve. The neurons that originated from the nodose placode located dorsal to pharyngeal arches, forms the nodose ganglion as well. The process works by having the neuron cells migrate from this placode to combine with cardiac crest to form the nodose ganglion. The condensation process of this ganglion have several factors such as the molecule N-cadherin and signaling by Slit/Robo signaling. In the cranial crest, both N-cadherin and Slit1/Robo signaling is crucial for the merging of crest cells and placode-derived neurons into ganglia. Placodal neurons expresses N-cadherin and Robo2, while neural crest cells expresses Slit1{{#pmid:PMC3011257|PMC3011257}} N-Cadherin and Robo2 are the most important signaling molecules. If either of them are not expressed, the ganglia cannot combine and form properly.{{#pmid:PMC2781051|PMC2781051}}

Neural crest cells play a important role in structuring placodal neurons during early ganglion assembly. The orientation and shape of the cranial ganglia greatly resembles the shifting and moving patterns of the cranial neural crest. Furthermore, ablation of the dorsal midbrain neural folds results in abnormalities in trigeminal ganglion assembly, showing that neural crest cells are needed for the proper organization and integration of placodal neurons into the ganglion.{{#pmid:18278043|PMID18278043}} The neural crest migration will have defects and result in neuronal cell bodies and axons being wrongly positioned if there is a loss of receptor neuropilin 2 which is expressed by neural crest cells, and/or loss of semaphorin ligands which are expressed by the adjacent mesenchyme. This will cause abnormal interlinked trigeminal and facial ganglia.{{#pmid:17443771|PMID17443771}} Cell-cell signaling between neural crest and placodes is most possible to trigger their coordinated and cooperative interactions in shaping the cranial ganglia. For example, Robo2 is expressed by trigeminal placode cells, but ligand Slit1 is expressed by neural crest cells. If either the receptor or the function is blocked, the ligand will have severe deformities like abnormal of diffusely condensed ganglia.{{#pmid:18278043|PMID18278043}}

== Signalling Molecules ==
----

Many signalling pathways are involved in the proper development of the cardiovascular system, however most of the mechanisms remain unknown to date. Some of the studied signalling molecules that play a role in the proper development of the cardiovascular system in an embryo are described briefly below:

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
# '''Meis2''': Transcription factor that directly binds to Pbx proteins. The Meis2/Pbx protein complex binds to DNA and regulates their transcription, playing important roles during the development of the heart. One of the target genes controlled by Meis-Pbx expression is the Hox gene. {{#pmid: PMC4636814 | PMC4636814}}

== Time Course of Neural Crest Cardiac Development ==
----

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
----
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

[[File:File:Heart Defects.png|400px|thumb|right|]]

=== Disruptions to outflow tract septation ===
----
In the human, at Carnegie stage 14, the myocardial wall of the outflow tract extends to the border of the pericardial cavity where it joins the aortic sac, giving rise to the arteries that feed the pharyngeal arches <ref name="PMID12739611" />.OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as well as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus. Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot. Anomalies involving the outflow tract and its valves make up a significant proportion of congenital cardiac defects, with a prevalence of at least 4 per 10,000 births {{#pmid:12739611|PMID12739611}}.

=== DiGeorge Syndrome ===
----
[[File:TBX1 factor figure.jpg|400px|thumb|right|]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (Tbx1). Tbx1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor Tbx1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}. (The figure to the right shows Tbx1 colored in red affecting the cardiac cushions).

==Models and Research==

=== Animal Models ===
----
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
----
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

[[File:Outlfow tract.png|450px|thumb|right|Reconstructed aspects of the outflow tract of a developing mouse at E11.5]]

==== Mouse ====
----
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of the proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow tract development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}} Mouse models also allow for the digital reconstruction of the aspects of the outflow tract in a developing embryo as shown in the figure on the right.

==== Zebrafish model ====
----
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors are known to interact with HOX and Pre-B cell leukemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor. {{#pmid:3462257|PMC3462257}}

=== Current Research ===

==== Importance of Semaphorin 3c in the proper septation of OFT ====
----
Semaphorin 3c (Sema3c) is a neurovascular signalling guide factor which is necessary for the proper development of the OFT. Recent studies have shown that Sema3c mediates the interaction between cNCCs and the SHF during the development of the OFT to allow proper septation of the OFT and establish the separate systemic and pulmonary circulation systems.{{#pmid:5533775|PMC5533775}} During the initial stages of heart development, Sema3c is expressed in the OFT as well as in the pharyngeal arch region which also contains cardiac progenitor niches composed of SHF progenitor cells and CNCCs.{{#pmid:5533775|PMC5533775}} Sema3c expression can be regulated positively and negatively by Foxc1/Foxc2 and Tbx1-Fgf8 signalling respectively. Changes in expression levels of Sema3c can alter the development and migration of CNCCs for OFT formation during embryogenesis. For example, the inhibition of Sema3c expression in mouse models have caused disruption in the aortic arch and also led to persistent truncus arteriosus. {{#pmid:5533775|PMC5533775}}

==== Defective Parasympathetic Innervation in Tbx1 Mutant Hearts ====
----
Previous studies have shown that T-box transcription factor (Tbx1) is expressed dynamically in the pharyngeal during the development of mouse and that Tbx1 homozygous mutants display various neural crest cell defects. This led to further investigations on whether parasympathetic (vagal) innervation of the heart will be affected by mutations in Tbx1. Recent studies have shown that Tbx1 plays a role in regulating epibranchial ganglion positioning, migratory paths of CNCCs and subsequent vagal nerve projections to the heart. Tbx1 mutants show reduced expression of Sema3c which results in a disrupted CNCC migration pattern. Sema3C mutant embryos display a cardiac innervation phenotype similar to those observed in Tbx1 mutant embryos.{{#pmid:30249045|PMID30249045}}

==Glossary==
----

Bulbus cordis - Bulb of the heart that lies ventrally to the primitive ventricle. Gives rise to the ventricles of the formed heart together with the primitive ventricle.

Cardiac outflow tract - Transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac

DiGeorge Syndrome - 22q11.2 deletion syndrome which can lead to symptoms such as delayed developmental progress, congenital heart problems, specific facial features, etc.

Induction - Process where progenitor cells begin to differentiate

Infundibulum - conical pouch formed from the upper and left angle of the right ventricle in the chordate heart, from which the pulmonary trunk arises.

Persistent Truncus Arteriosus - Occurs when the embryological structure known as the truncus arteriosus fails to properly divide into the pulmonary trunk and aorta.

Valvulogenesis - Complicated process involving the formation and morphogenesis of the atrioventricular and semilunar valves.

Promyocardial cells - helps the folding and positioning of the developing heart.

Semaphorins - class of secreted and membrane proteins that were originally identified as axonal growth cone guidance molecules.

== List of Abbreviations ==
----
* '''Aortopulmonary''' - (AP)
* '''Bone morphogenetic protein''' - (BMP)
* '''Cardiac neural crest cells''' - (CNCCs)
* '''DiGeorge syndrome''' - (DGS)
* '''Dominant-negative Notch inhibitor''' - (DN-MAML)
* '''Endothelial cells''' - (ECs)
* '''Fibroblast growth factor''' - (FGF)
* '''Myeloid ecotropic viral integration site 2 homolog''' - (MEIS2)
* '''Outflow tract septation''' - (OFT)
* '''Pre-B cell leukemia transcription factors''' - (PBX)
* '''Persistent Truncus Arteriosus''' - (PTA)
* '''Ras-related C3 botulinum toxin substrate 1''' - (Rac1)
* '''Stromal cell-derived factor 1''' - (Sdf1)
* '''Semaphorin 3c''' - (Sema3c)
* '''Second heart field-derived''' - (SHF-derived)
* '''T-box transcription factor''' - (Tbx1)

==References==

File:Heart Defects.png

2018-10-16T09:40:07Z

Z5229281:

Fig. 26.2 Cellular interaction of the second heart field (SHF) and cardiac neural crest (CNC) for the outflow tract (OFT) development and diseases. Progenitor cells derived from the SHF and the CNC give rise to the OFT myocardium and septum, respectively. TBX1 is exclusively expressed in the SHF cells. TBX1 deletion in 22q11DS may affect not only the SHF cells but also the interaction between the SHF cells and CNC, resulting in OFT defects ranging from TOF, which is characterized by malalignment of the OFT septum, to PTA, which results from aplasia of the OFT septum. GATA6-SEMA3C (ligand)-PLXNA2 (receptor) pathway also plays a role in interaction between the SHF and CNC during the OFT development (Modified from [36])

==Reference==

The Author(s) 2016T. Nakanishi et al. (eds.),Etiology and Morphogenesis of Congenital Heart Disease,DOI 10.1007/978-4-431-54628-3_26

==Copyright==

Available via license: CC BY-NC 2.5

LicenseCC BY-NC 2.5

https://creativecommons.org/licenses/by-nc/2.5/

{{Template:2018 Student Image}}

z5229281

File:Heart Defects.png

2018-10-16T09:34:52Z

Z5229281: Fig. 26.2 Cellular interaction of the second heart field (SHF) and cardiac neural crest (CNC) for the outflow tract (OFT) development and diseases. Progenitor cells derived from the SHF and the CNC give rise to the OFT myocardium and septum, respective...

User:Z5229281

2018-10-16T01:47:27Z

Z5229281: /* Reference */

hello
{{Editing Links}}

==Reference==
PMID: 30056110

{{#pmid:30056110}}

[[File:Neuropore cell shape changes.png|400px]]

Neuropore cell shape changes{{#pmid:30064364|PMID30064364}}

<references/>

PubMed Reference Search - [https://www.ncbi.nlm.nih.gov/search/?term=neural+crest neural crest]

[[User:Z5229281|Z5229281]] ([[User talk:Z5229281|talk]]) 11:37, 14 August 2018 (AEST)Alex Herald[[User:Z5229281|Z5229281]] ([[User talk:Z5229281|talk]]) 11:37, 14 August 2018 (AEST)

[[User:Z5229281|Z5229281]] ([[User talk:Z5229281|talk]]) 11:38, 14 August 2018 (AEST)Alex Herald[[User:Z5229281|Z5229281]] ([[User talk:Z5229281|talk]]) 11:38, 14 August 2018 (AEST)

[[User:Z5229281|Z5229281]] ([[User talk:Z5229281|talk]]) 11:39, 14 August 2018 (AEST)z5229281[[User:Z5229281|Z5229281]] ([[User talk:Z5229281|talk]]) 11:39, 14 August 2018 (AEST)

[[User:Z5229281|Z5229281]] ([[User talk:Z5229281|talk]]) 11:39, 14 August 2018 (AEST)

adrenal medulla group review
The beginning introduction is good and very detailed which is excellent as it shows adequate research has been applied but it may be too in depth as the project pertains to the adrenal medulla. But after reading it all it transitions nicely into the project so I don't mind all of the details that much. The information is organized and is well constructed in the first section of this project I like the time frames and each description under each, maybe use more than one reference for the intro so it is not all from one source. other than that the intro is really good.

For the developmental adult section, it is either not researched or not started, I would just remove it as the rest of the project is put together and the adult function is not super important. Also, the developmental time course would be really cool to have to see the steps involved in the creation of the medulla, if not added not a big deal.

The hand drawn figures are really nice add a certain flare to the project which i think is sweet.

Other than that minor edits need to be made and this project is polished, some sections need to be researched more as there are still two weeks left until it is assessed, so plenty of time to polish.

Melanocyte Group
Wow, I can tell all of you have put in a lot of time researching this project has loads of information and all of the sections that are filled transition well. Other than what I assume you already know as some sections are missing information an I'm sure your group will have those filled out as the semester ends. Melanocyte group I have small changes to make. One this is just personal opinion I feel that for the figures under sections eyes and heart should be right justified and the wording should be on the left instead of the pictures being in the middle of the page. Also more photos as it seems very content heavy. Sections such as developmental time course and mechanisms will have information in the future I assume, the project is well put together without those sections included. The current research section about pluripotent stem cells could be researched a bit more as I feel it is lacking infromation. Maybe give details on how the process is actually done and how pluripotent stem cells are obtained or more infromation on the overiview of the topic that goes a little more in depth analysis. other than those small edits your group is doing an outstanding job this semester.

Dorsal root ganglia group
The references and images are great. I would like more of a description on the image in the neural crest migration to the DRG section as it seems brief and I am a little lost, maybe add information on what the colors are specifically so I know what I am looking at. That section is extremely well written with loads of information which is great. In the section glial development, the descriptions of the proteins and what they do would help me understand such as proteins SOX10 and P2x3 in the section there is information on the proteins but not specifically where they are form and what functions they have. The last thing is just fix up the glossary and history section and the project is complete and nicely done dorsal root ganglia group.

2018 Group Project 4

2018-10-16T01:30:43Z

Z5229281: /* DiGeorge Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

== Introduction ==
----
The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

== Development of the Cardiovascular System==
----
Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

=== Timeline of Development of the Cardiovascular System===
{| class = "pretty table"
|-
| Week 2 - 3
|
* Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac neural crest cells ==
----
Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}. CNCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Studies have shown that cardiac neural crest cells play a role in the development of:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===
----
Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===
----
After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===
----
The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the respective pharyngeal arches. Slit proteins, a family of secreted extracellular matrix proteins, can target cells to migrate to arch 3. Fibroblast growth factor 8 (FGF-8) targets migration towards the arch 4. EphA, a subclass of receptor tyrosine kinase which responds to Ephrins, targets for arch 6. Ras-related C3 botulinum toxin substrate 1 (Rac1) and Stromal cell-derived factor 1 (Sdf1) are both expressed in the cells, causing them to condensate around the arch arteries.

Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
----
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===
----
The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===
----
The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into cardiac chambers and arterial trunks subsequently. {{#pmid:12807866|PMID12807866}}

====Formation and Developement of Primary Myocardial Heart Tube====
The embryo undergoes gastrulation and mesodermal layer tissues give rise to the heart.The cells form a crescent virtually at the cranial border of the disc, and then the central region of ectoderm shapes itself into the neural plate. {{#pmid:12807866|PMID12807866}} The The structure eventually folds and is known as neural folds. The developing heart in humans is initially cranial within the disc relative to the neural folds. The developing heart is also shaped by a plate of promyocardial cells, which helps the folding and positioning of the developing heart comapred to the neural structures.

====Formation of Cardiac Chambers====
By looping, the primary heart tube inside the pericardial cavity can be separated into atrial and ventricular parts by the atrioventricular canal, along with an outflow tract. {{#pmid:12807866|PMID12807866}} The constriction which is at the site of the primary interventricular foramen will eventually become the left and right ventricles. The primary myocardium is then formed by the myocardial walls of the heart tube. {{#pmid:10882515|PMID10882515}}

====Formation of Arterial Trunks====
During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}} The most important part of the outflow tract is that it breaks up by the merging of the cushions within it, causing new myocardium to form within the cushions to produce the medial part of the subpulmonary infundibulum. This retains its origin from the right ventricle.{{#pmid:10433836|PMID10433836}} Concurrently, the subaortic part of the outflow segment is positioned to the left ventricle by the merging of the cushions to the crest of the muscular ventricular septum. The myocardium of the initial inner heart curvature then disintegrates to allow fibrous continuity between the leaflets of the aortic and mitral valves in the ventricular roof. {{#pmid:12807866|PMID12807866}}

=== Formation of the Cardiac Ganglia ===
----
The cardiac crest is made up completely by the cardiac ganglia. Both the neuronal cell bodies and supporting cells originate from the cardiac crest.{{#pmid:6844926|PMID6844926}} The factors that affect how the cardiac crest segregates and form the aorticopulmonary septum or their condensation as ganglia is not known. Cardiac crest cells do contribute to the forming of nodose ganglion, which is the distal sensory ganglion of the vagus nerve. The neurons that originated from the nodose placode located dorsal to pharyngeal arches, forms the nodose ganglion as well. The process works by having the neuron cells migrate from this placode to combine with cardiac crest to form the nodose ganglion. The condensation process of this ganglion have several factors such as the molecule N-cadherin and signaling by Slit/Robo signaling. In the cranial crest, both N-cadherin and Slit1/Robo signaling is crucial for the merging of crest cells and placode-derived neurons into ganglia. Placodal neurons expresses N-cadherin and Robo2, while neural crest cells expresses Slit1{{#pmid:PMC3011257|PMC3011257}} N-Cadherin and Robo2 are the most important signaling molecules. If either of them are not expressed, the ganglia cannot combine and form properly.{{#pmid:PMC2781051|PMC2781051}}

Neural crest cells play a important role in structuring placodal neurons during early ganglion assembly. The orientation and shape of the cranial ganglia greatly resembles the shifting and moving patterns of the cranial neural crest. Furthermore, ablation of the dorsal midbrain neural folds results in abnormalities in trigeminal ganglion assembly, showing that neural crest cells are needed for the proper organization and integration of placodal neurons into the ganglion.{{#pmid:18278043|PMID18278043}} The neural crest migration will have defects and result in neuronal cell bodies and axons being wrongly positioned if there is a loss of receptor neuropilin 2 which is expressed by neural crest cells, and/or loss of semaphorin ligands which are expressed by the adjacent mesenchyme. This will cause abnormal interlinked trigeminal and facial ganglia.{{#pmid:17443771|PMID17443771}} Cell-cell signaling between neural crest and placodes is most possible to trigger their coordinated and cooperative interactions in shaping the cranial ganglia. For example, Robo2 is expressed by trigeminal placode cells, but ligand Slit1 is expressed by neural crest cells. If either the receptor or the function is blocked, the ligand will have severe deformities like abnormal of diffusely condensed ganglia.{{#pmid:18278043|PMID18278043}}

== Signalling Molecules ==
----

Many signalling pathways are involved in the proper development of the cardiovascular system, however most of the mechanisms remain unknown to date. Some of the studied signalling molecules that play a role in the proper development of the cardiovascular system in an embryo are described briefly below:

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
# '''Meis2''': Transcription factor that directly binds to Pbx proteins. The Meis2/Pbx protein complex binds to DNA and regulates their transcription, playing important roles during the development of the heart. One of the target genes controlled by Meis-Pbx expression is the Hox gene. {{#pmid: PMC4636814 | PMC4636814}}

== Time Course of Neural Crest Cardiac Development ==
----

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
----
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

=== Disruptions to outflow tract septation ===
----
In the human, at Carnegie stage 14, the myocardial wall of the outflow tract extends to the border of the pericardial cavity where it joins the aortic sac, giving rise to the arteries that feed the pharyngeal arches <ref name="PMID12739611" />.OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as well as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus. Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot. Anomalies involving the outflow tract and its valves make up a significant proportion of congenital cardiac defects, with a prevalence of at least 4 per 10,000 births {{#pmid:12739611|PMID12739611}}.

=== DiGeorge Syndrome ===
----
[[File:TBX1 factor figure.jpg|400px|thumb|right|]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (Tbx1). Tbx1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor Tbx1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}. (The figure to the right shows Tbx1 colored in red affecting the cardiac cushions).

==Models and Research==

=== Animal Models ===
----
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
----
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

[[File:Outlfow tract.png|450px|thumb|right|Reconstructed aspects of the outflow tract of a developing mouse at E11.5]]

==== Mouse ====
----
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of the proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow tract development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}} Mouse models also allow for the digital reconstruction of the aspects of the outflow tract in a developing embryo as shown in the figure on the right.

==== Zebrafish model ====
----
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors are known to interact with HOX and Pre-B cell leukemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor. {{#pmid:3462257|PMC3462257}}

=== Current Research ===

==== Importance of Semaphorin 3c in the proper septation of OFT ====
----
Semaphorin 3c (Sema3c) is a neurovascular signalling guide factor which is necessary for the proper development of the OFT. Recent studies have shown that Sema3c mediates the interaction between cNCCs and the SHF during the development of the OFT to allow proper septation of the OFT and establish the separate systemic and pulmonary circulation systems.{{#pmid:5533775|PMC5533775}} During the initial stages of heart development, Sema3c is expressed in the OFT as well as in the pharyngeal arch region which also contains cardiac progenitor niches composed of SHF progenitor cells and CNCCs.{{#pmid:5533775|PMC5533775}} Sema3c expression can be regulated positively and negatively by Foxc1/Foxc2 and Tbx1-Fgf8 signalling respectively. Changes in expression levels of Sema3c can alter the development and migration of CNCCs for OFT formation during embryogenesis. For example, the inhibition of Sema3c expression in mouse models have caused disruption in the aortic arch and also led to persistent truncus arteriosus. {{#pmid:5533775|PMC5533775}}

==== Defective Parasympathetic Innervation in Tbx1 Mutant Hearts ====
----
Previous studies have shown that T-box transcription factor (Tbx1) is expressed dynamically in the pharyngeal during the development of mouse and that Tbx1 homozygous mutants display various neural crest cell defects. This led to further investigations on whether parasympathetic (vagal) innervation of the heart will be affected by mutations in Tbx1. Recent studies have shown that Tbx1 plays a role in regulating epibranchial ganglion positioning, migratory paths of CNCCs and subsequent vagal nerve projections to the heart. Tbx1 mutants show reduced expression of Sema3c which results in a disrupted CNCC migration pattern. Sema3C mutant embryos display a cardiac innervation phenotype similar to those observed in Tbx1 mutant embryos.{{#pmid:30249045|PMID30249045}}

==Glossary==
----

Bulbus cordis - Bulb of the heart that lies ventrally to the primitive ventricle. Gives rise to the ventricles of the formed heart together with the primitive ventricle.

DiGeorge Syndrome - 22q11.2 deletion syndrome which can lead to symptoms such as delayed developmental progress, congenital heart problems, specific facial features, etc.

Persistent Truncus Arteriosus - Occurs when the embryological structure known as the truncus arteriosus fails to properly divide into the pulmonary trunk and aorta.

Valvulogenesis - Complicated process involving the formation and morphogenesis of the atrioventricular and semilunar valves.

== List of Abbreviations ==

*Aortopulmonary - (AP)
*Bone morphogenetic protein - (BMP)
*Cardiac neural crest cells - (CNCCs)
*DiGeorge syndrome (DGS)
*Dominant-negative Notch inhibitor - (DN-MAML)
*Endothelial cells - (ECs)
*Fibroblast growth factor - (FGF)
*MEIS2 (myeloid ecotropic viral integration site 2 homolog)
*Outflow tract septation - (OFT)
*Pre-B cell leukemia transcription factors (PBX)
*Persistent Truncus Arteriosus (PTA)
*Ras-related C3 botulinum toxin substrate 1 - (Rac1)
*Stromal cell-derived factor 1 - (Sdf1)
*Semaphorin 3c (Sema3c)
*Second heart field-derived - (SHF-derived)
*T-box transcription factor (Tbx1)

==References==

2018 Group Project 4

2018-10-16T00:45:59Z

Z5229281: /* DiGeorge Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

== Introduction ==
----
The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

== Development of the Cardiovascular System==
----
Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

=== Timeline of Development of the Cardiovascular System===
{| class = "pretty table"
|-
| Week 2 - 3
|
* Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac neural crest cells ==
----
Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}. CNCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Studies have shown that cardiac neural crest cells play a role in the development of:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===
----
Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===
----
After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===
----
The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the respective pharyngeal arches. Slit proteins, a family of secreted extracellular matrix proteins, can target cells to migrate to arch 3. Fibroblast growth factor 8 (FGF-8) targets migration towards the arch 4. EphA, a subclass of receptor tyrosine kinase which responds to Ephrins, targets for arch 6. Ras-related C3 botulinum toxin substrate 1 (Rac1) and Stromal cell-derived factor 1 (Sdf1) are both expressed in the cells, causing them to condensate around the arch arteries.

Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
----
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===
----
The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===
----
The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into cardiac chambers and arterial trunks subsequently. {{#pmid:12807866|PMID12807866}}

====Formation and Developement of Primary Myocardial Heart Tube====
The embryo undergoes gastrulation and mesodermal layer tissues give rise to the heart.The cells form a crescent virtually at the cranial border of the disc, and then the central region of ectoderm shapes itself into the neural plate. {{#pmid:12807866|PMID12807866}} The The structure eventually folds and is known as neural folds. The developing heart in humans is initially cranial within the disc relative to the neural folds. The developing heart is also shaped by a plate of promyocardial cells, which helps the folding and positioning of the developing heart comapred to the neural structures.

====Formation of Cardiac Chambers====
By looping, the primary heart tube inside the pericardial cavity can be separated into atrial and ventricular parts by the atrioventricular canal, along with an outflow tract. {{#pmid:12807866|PMID12807866}} The constriction which is at the site of the primary interventricular foramen will eventually become the left and right ventricles. The primary myocardium is then formed by the myocardial walls of the heart tube. {{#pmid:10882515|PMID10882515}}

====Formation of Arterial Trunks====
During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}} The most important part of the outflow tract is that it breaks up by the merging of the cushions within it, causing new myocardium to form within the cushions to produce the medial part of the subpulmonary infundibulum. This retains its origin from the right ventricle.{{#pmid:10433836|PMID10433836}} Concurrently, the subaortic part of the outflow segment is positioned to the left ventricle by the merging of the cushions to the crest of the muscular ventricular septum. The myocardium of the initial inner heart curvature then disintegrates to allow fibrous continuity between the leaflets of the aortic and mitral valves in the ventricular roof. {{#pmid:12807866|PMID12807866}}

=== Formation of the Cardiac Ganglia ===
----
The cardiac crest is made up completely by the cardiac ganglia. Both the neuronal cell bodies and supporting cells originate from the cardiac crest.{{#pmid:6844926|PMID6844926}} The factors that affect how the cardiac crest segregates and form the aorticopulmonary septum or their condensation as ganglia is not known. Cardiac crest cells do contribute to the forming of nodose ganglion, which is the distal sensory ganglion of the vagus nerve. The neurons that originated from the nodose placode located dorsal to pharyngeal arches, forms the nodose ganglion as well. The process works by having the neuron cells migrate from this placode to combine with cardiac crest to form the nodose ganglion. The condensation process of this ganglion have several factors such as the molecule N-cadherin and signaling by Slit/Robo signaling. In the cranial crest, both N-cadherin and Slit1/Robo signaling is crucial for the merging of crest cells and placode-derived neurons into ganglia. Placodal neurons expresses N-cadherin and Robo2, while neural crest cells expresses Slit1{{#pmid:PMC3011257|PMC3011257}} N-Cadherin and Robo2 are the most important signaling molecules. If either of them are not expressed, the ganglia cannot combine and form properly.{{#pmid:PMC2781051|PMC2781051}}

Neural crest cells play a important role in structuring placodal neurons during early ganglion assembly. The orientation and shape of the cranial ganglia greatly resembles the shifting and moving patterns of the cranial neural crest. Furthermore, ablation of the dorsal midbrain neural folds results in abnormalities in trigeminal ganglion assembly, showing that neural crest cells are needed for the proper organization and integration of placodal neurons into the ganglion.{{#pmid:18278043|PMID18278043}} The neural crest migration will have defects and result in neuronal cell bodies and axons being wrongly positioned if there is a loss of receptor neuropilin 2 which is expressed by neural crest cells, and/or loss of semaphorin ligands which are expressed by the adjacent mesenchyme. This will cause abnormal interlinked trigeminal and facial ganglia.{{#pmid:17443771|PMID17443771}} Cell-cell signaling between neural crest and placodes is most possible to trigger their coordinated and cooperative interactions in shaping the cranial ganglia. For example, Robo2 is expressed by trigeminal placode cells, but ligand Slit1 is expressed by neural crest cells. If either the receptor or the function is blocked, the ligand will have severe deformities like abnormal of diffusely condensed ganglia.{{#pmid:18278043|PMID18278043}}

== Signalling Molecules ==
----

Many signalling pathways are involved in the proper development of the cardiovascular system, however most of the mechanisms remain unknown to date. Some of the studied signalling molecules that play a role in the proper development of the cardiovascular system in an embryo are described briefly below:

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
# '''Meis2''': Transcription factor that directly binds to Pbx proteins. The Meis2/Pbx protein complex binds to DNA and regulates their transcription, playing important roles during the development of the heart. One of the target genes controlled by Meis-Pbx expression is the Hox gene. {{#pmid: PMC4636814 | PMC4636814}}

== Time Course of Neural Crest Cardiac Development ==
----

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
----
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

=== Disruptions to outflow tract septation ===
----
In the human, at Carnegie stage 14, the myocardial wall of the outflow tract extends to the border of the pericardial cavity where it joins the aortic sac, giving rise to the arteries that feed the pharyngeal arches <ref name="PMID12739611" />.OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as well as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus. Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot. Anomalies involving the outflow tract and its valves make up a significant proportion of congenital cardiac defects, with a prevalence of at least 4 per 10,000 births {{#pmid:12739611|PMID12739611}}.

=== DiGeorge Syndrome ===
----
[[File:TBX1 factor figure.jpg|400px|thumb|right|alt text]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}. (The figure to the right shows TBX1 colored in red affecting the cardiac cushions).

==Models and Research==

=== Animal Models ===
----
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
----
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

[[File:Outlfow tract.png|450px|thumb|right|Reconstructed aspects of the outflow tract of a developing mouse at E11.5]]

==== Mouse ====
----
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of the proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow tract development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}} Mouse models also allow for the digital reconstruction of the aspects of the outflow tract in a developing embryo as shown in the figure on the right.

==== Zebrafish model ====
----
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors are known to interact with HOX and Pre-B cell leukemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor. {{#pmid:3462257|PMC3462257}}

=== Current Research ===

==== Importance of Semaphorin 3c in the proper septation of OFT ====
----
Semaphorin 3c (Sema3c) is a neurovascular signalling guide factor which is necessary for the proper development of the OFT. Recent studies have shown that Sema3c mediates the interaction between cNCCs and the SHF during the development of the OFT to allow proper septation of the OFT and establish the separate systemic and pulmonary circulation systems.{{#pmid:5533775|PMC5533775}} During the initial stages of heart development, Sema3c is expressed in the OFT as well as in the pharyngeal arch region which also contains cardiac progenitor niches composed of SHF progenitor cells and CNCCs.{{#pmid:5533775|PMC5533775}} Sema3c expression can be regulated positively and negatively by Foxc1/Foxc2 and Tbx1-Fgf8 signalling respectively. Changes in expression levels of Sema3c can alter the development and migration of CNCCs for OFT formation during embryogenesis. For example, the inhibition of Sema3c expression in mouse models have caused disruption in the aortic arch and also led to persistent truncus arteriosus. {{#pmid:5533775|PMC5533775}}

==== Defective Parasympathetic Innervation in Tbx1 Mutant Hearts ====
----
Previous studies have shown that T-box transcription factor (Tbx1) is expressed dynamically in the pharyngeal during the development of mouse and that Tbx1 homozygous mutants display various neural crest cell defects. This led to further investigations on whether parasympathetic (vagal) innervation of the heart will be affected by mutations in Tbx1. Recent studies have shown that Tbx1 plays a role in regulating epibranchial ganglion positioning, migratory paths of CNCCs and subsequent vagal nerve projections to the heart. Tbx1 mutants show reduced expression of Sema3c which results in a disrupted CNCC migration pattern. Sema3C mutant embryos display a cardiac innervation phenotype similar to those observed in Tbx1 mutant embryos.{{#pmid:30249045|PMID30249045}}

==Glossary==
----

:'''[[#Number|Number]] | [[#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]]'''

Bulbus cordis - Bulb of the heart that lies ventrally to the primitive ventricle. Gives rise to the ventricles of the formed heart together with the primitive ventricle.

DiGeorge Syndrome - 22q11.2 deletion syndrome which can lead to symptoms such as delayed developmental progress, congenital heart problems, specific facial features, etc.

Persistent Truncus Arteriosus - Occurs when the embryological structure known as the truncus arteriosus fails to properly divide into the pulmonary trunk and aorta.

Valvulogenesis - Complicated process involving the formation and morphogenesis of the atrioventricular and semilunar valves.

==References==

2018 Group Project 4

2018-10-14T09:08:33Z

Z5229281: /* Human Congenital Heart Diseases associated with Neural Crest Cells */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

== Introduction ==
----
The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

== Development of the Cardiovascular System==
----
Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==
----
Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===
----
Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===
----
After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===
----
The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
----
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===
----
The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===
----
The heart first transforms from the embryo into four parts:
The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into cardiac chambers and arterial trunks subsequently. {{#pmid:12807866|PMID12807866}}

Formation and Developement of Primary Myocardial Heart Tube:
The embryo undergoes gastrulation and mesodermal layer tissues give rise to the heart.The cells form a crescent virtually at the cranial border of the disc, and then the central region of ectoderm shapes itself into the neural plate. {{#pmid:12807866|PMID12807866}} The The structure eventually folds and is known as neural folds. The developing heart in humans is initially cranial within the disc relative to the neural folds. The developing heart is also shaped by a plate of promyocardial cells, which helps the folding and positioning of the developing heart comapred to the neural structures.

Formation of Cardiac Chambers:
By looping, the primary heart tube inside the pericardial cavity can be separated into atrial and ventricular parts by the atrioventricular canal, along with an outflow tract. {{#pmid:12807866|PMID12807866}} The constriction which is at the site of the primary interventricular foramen will eventually become the left and right ventricles. The primary myocardium is then formed by the myocardial walls of the heart tube. {{#pmid:10882515|PMID10882515}}

Formation of Arterial Trunks:
During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}} The most important part of the outflow tract is that it breaks up by the merging of the cushions within it, causing new myocardium to form within the cushions to produce the medial part of the subpulmonary infundibulum. This retains its origin from the right ventricle.{{#pmid:10433836|PMID10433836}} Concurrently, the subaortic part of the outflow segment is positioned to the left ventricle by the merging of the cushions to the crest of the muscular ventricular septum. The myocardium of the initial inner heart curvature then disintegrates to allow fibrous continuity between the leaflets of the aortic and mitral valves in the ventricular roof. {{#pmid:12807866|PMID12807866}}

=== Formation of the Cardiac Ganglia ===
----
Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==
----
# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==
----

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
----
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

=== Disruptions to outflow tract septation ===
----
In the human, at Carnegie stage 14, the myocardial wall of the outflow tract extends to the border of the pericardial cavity where it joins the aortic sac, giving rise to the arteries that feed the pharyngeal arches <ref name="PMID12739611" />.OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as well as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus. Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot. Anomalies involving the outflow tract and its valves make up a significant proportion of congenital cardiac defects, with a prevalence of at least 4 per 10,000 births {{#pmid:12739611|PMID12739611}}.

=== DiGeorge Syndrome ===
----
[[File:TBX1 factor figure.jpg|400px|thumb|right|alt text]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

==Models and Research==

=== Animal Models ===
----
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
----
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

[[File:Outlfow tract.png|450px|thumb|right|Reconstructed aspects of the outflow tract of a developing mouse at E11.5]]

==== Mouse ====
----
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of the proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow tract development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}} Mouse models also allow for the digital reconstruction of the aspects of the outflow tract in a developing embryo as shown in the figure on the right.

==== Zebrafish model ====
----
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors are known to interact with HOX and Pre-B cell leukemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor. {{#pmid:3462257|PMC3462257}}

=== Current Research ===

==== Importance of Semaphorin 3c in the proper septation of OFT ====
----
Semaphorin 3c (Sema3c) is a neurovascular signalling guide factor which is necessary for the proper development of the OFT. Recent studies have shown that Sema3c mediates the interaction between cNCCs and the SHF during the development of the OFT to allow proper septation of the OFT and establish the separate systemic and pulmonary circulation systems.{{#pmid:5533775|PMC5533775}} During the initial stages of heart development, Sema3c is expressed in the OFT as well as in the pharyngeal arch region which also contains cardiac progenitor niches composed of SHF progenitor cells and CNCCs.{{#pmid:5533775|PMC5533775}} Sema3c expression can be regulated positively and negatively by Foxc1/Foxc2 and Tbx1-Fgf8 signalling respectively. Changes in expression levels of Sema3c can alter the development and migration of CNCCs for OFT formation during embryogenesis. For example, the inhibition of Sema3c expression in mouse models have caused disruption in the aortic arch and also led to persistent truncus arteriosus. {{#pmid:5533775|PMC5533775}}

==== Defective Parasympathetic Innervation in Tbx1 Mutant Hearts ====
----
Previous studies have shown that T-box transcription factor (Tbx1) is expressed dynamically in the pharyngeal during the development of mouse and that Tbx1 homozygous mutants display various neural crest cell defects. This led to further investigations on whether parasympathetic (vagal) innervation of the heart will be affected by mutations in Tbx1. Recent studies have shown that Tbx1 plays a role in regulating epibranchial ganglion positioning, migratory paths of CNCCs and subsequent vagal nerve projections to the heart. Tbx1 mutants show reduced expression of Sema3c which results in a disrupted CNCC migration pattern. Sema3C mutant embryos display a cardiac innervation phenotype similar to those observed in Tbx1 mutant embryos.{{#pmid:30249045|PMID30249045}}

==Glossary==
----

:'''[[#Number|Number]] | [[#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]]'''

Bulbus cordis - Bulb of the heart that lies ventrally to the primitive ventricle. Gives rise to the ventricles of the formed heart together with the primitive ventricle.

DiGeorge Syndrome - 22q11.2 deletion syndrome which can lead to symptoms such as delayed developmental progress, congenital heart problems, specific facial features, etc.

Primitive atrium

Primitive ventricle

Persistent Truncus Arteriosus - Occurs when the embryological structure known as the truncus arteriosus fails to properly divide into the pulmonary trunk and aorta.

RhoA/B

Sinus venosus

Snail2

Valvulogenesis - Complicated process involving the formation and morphogenesis of the atrioventricular and semilunar valves.

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-12T00:23:56Z

Z5229281: /* Disruptions to outflow tract septation */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

In the human, at Carnegie stage 14, the myocardial wall of the outflow tract extends to the border of the pericardial cavity where it joins the aortic sac, giving rise to the arteries that feed the pharyngeal arches <ref name="PMID12739611" />.OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as well as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus. Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot. Anomalies involving the outflow tract and its valves make up a significant proportion of congenital cardiac defects, with a prevalence of at least 4 per 10,000 births {{#pmid:12739611|PMID12739611}}.

=== DiGeorge Syndrome ===

[[File:TBX1 factor figure.jpg|400px|thumb|right|alt text]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of the proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow tract development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}}

[[File:Outlfow tract.png|350px|thumb|right|alt text]]

==== Zebrafish model ====

[[File:Zebra Fish Animal model.jpg|350px|thumb|right|alt text]]

Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors are known to interact with HOX and Pre-B cell leukemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor. {{#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-12T00:12:15Z

Z5229281: /* Zebrafish model */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as well as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus. Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

[[File:TBX1 factor figure.jpg|400px|thumb|right|alt text]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of the proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow tract development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}}

[[File:Outlfow tract.png|350px|thumb|right|alt text]]

==== Zebrafish model ====

[[File:Zebra Fish Animal model.jpg|350px|thumb|right|alt text]]

Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors are known to interact with HOX and Pre-B cell leukemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor. {{#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-12T00:04:21Z

Z5229281: /* Mouse */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as well as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus. Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

[[File:TBX1 factor figure.jpg|400px|thumb|right|alt text]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of the proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow tract development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}}

[[File:Outlfow tract.png|350px|thumb|right|alt text]]

==== Zebrafish model ====

[[File:Zebra Fish Animal model.jpg|350px|thumb|right|alt text]]

Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors is known to interact with HOX and Pre-B cell leukaemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor.{{#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-12T00:02:40Z

Z5229281: /* Disruptions to outflow tract septation */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as well as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus. Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

[[File:TBX1 factor figure.jpg|400px|thumb|right|alt text]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}}

==== Zebrafish model ====

[[File:Zebra Fish Animal model.jpg|350px|thumb|right|alt text]]

Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors is known to interact with HOX and Pre-B cell leukaemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor.{{#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

File:Outlfow tract.png

2018-10-12T00:00:55Z

Z5229281: /* Reference */

File:Outlfow tract.png

2018-10-12T00:00:15Z

Z5229281: /* Copyright */

The images show reconstructed aspects of the outflow tract of a developing mouse at E11.5. The reconstructions were segmented so that all myocardium, determined using a myocardial-specific marker, was shown in silver, and non-myocardial tissues, lacking the marker, were shown in green (Details provided in Reference [7]). The septal outflow cushion was shown in brown, and the parietal cushion in yellow. Panel (A) shows a superior view of the distal margins of the muscular outflow tract having digitally removed the non-myocardial distal outflow tract. The distal myocardial border has an obvious fishmouth appearance, with the distal margins of the major outflow cushions confluent with the muscular margins. Panel (B) shows the non-myocardial walls of the distal outflow tract viewed from the front. The two non-myocardial tongues fill the spaces formed by the angles of the jaws of the muscular fishmouth. They will become the parietal walls of the aorta and the pulmonary trunk.

z5229281

==Reference==

==Copyright==
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

This image was originally uploaded as part of an undergraduate science student project and may contain inaccuracies in either description or acknowledgements. Students have been advised in writing concerning the reuse of content and may accidentally have misunderstood the original terms of use. If image reuse on this non-commercial educational site infringes your existing copyright, please contact the site editor for immediate removal.

File:Outlfow tract.png

2018-10-11T23:59:44Z

Z5229281: /* Copyright */

File:Outlfow tract.png

2018-10-11T23:59:21Z

Z5229281:

File:Outlfow tract.png

2018-10-11T23:58:33Z

Z5229281: The images show reconstructed aspects of the outflow tract of a developing mouse at E11.5. The reconstructions were segmented so that all myocardium, determined using a myocardial-specific marker, was shown in silver, and non-myocardial tissues, lackin...

2018 Group Project 4

2018-10-11T23:55:01Z

Z5229281: /* Zebrafish model */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

[[File:TBX1 factor figure.jpg|400px|thumb|right|alt text]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}}

==== Zebrafish model ====

[[File:Zebra Fish Animal model.jpg|350px|thumb|right|alt text]]

Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors is known to interact with HOX and Pre-B cell leukaemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor.{{#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-11T23:54:11Z

Z5229281: /* Zebrafish model */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

[[File:TBX1 factor figure.jpg|400px|thumb|right|alt text]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}}

==== Zebrafish model ====

[[File:Zebra Fish Animal model.jpg|400px|thumb|right|alt text]]

Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors is known to interact with HOX and Pre-B cell leukaemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor.{{#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

File:Zebra Fish Animal model.jpg

2018-10-11T23:53:04Z

Z5229281:

Forskolin increases expression of the mitfa transcriptional repressor foxd3. (A–C) 10× magnification of Bacfoxd3::GFP transgenic larvae at 2 dpf. Transgenic zebrafish express GFP in foxd3-dependent cells including the pineal gland (arrowhead) and presumptive iridophores (arrows). Scale bar in panel C = 200 um and applies to panels A–C. (D–E) 20× magnification of BACfoxd3::GFP zebrafish. Arrows indicate cells co-expressing GFP and iridescence typically observed in iridophores. The scale bar in panel E = 100 um and applies to panels D and E. (F,G) 20× magnification of 25 hpf 0.1% DMSO or 5 µM forskolin-treated BACfoxd3::GFP transgenic fish processed for immunocytochemistry using anti-GFP and anti-beta catenin antibodies (red). Forskolin treatment leads to an increase in GFP (arrowheads indicate pharyngeal arches), indicating expanded domains of foxd3 expression. Scale bar in panel F = 100 um and applies to panels F and G. (H,I) 0.1% DMSO and 5 µM forskolin-treated wildtype embryos processed for in situ hybridization using the foxd3 probe. Forskolin expands the areas of foxd3 expression, notably in the dorsal head and trunk regions (arrows) which are locations of presumptive iridophores, and in pharyngeal arch neural crest streams (arrowheads). Scale bar in panel H = 100 um and applies to panels H and I.

z5229281

==Reference==
Cooper, C.D.; Erickson, S.D.; Yin, S.; Moravec, T.; Peh, B.; Curran, K. Protein Kinase A Signaling Inhibits Iridophore Differentiation in Zebrafish. J. Dev. Biol. 2018, 6, 23.

https://www.mdpi.com/2221-3759/6/4/23

==Copyright==
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

This image was originally uploaded as part of an undergraduate science student project and may contain inaccuracies in either description or acknowledgements. Students have been advised in writing concerning the reuse of content and may accidentally have misunderstood the original terms of use. If image reuse on this non-commercial educational site infringes your existing copyright, please contact the site editor for immediate removal.

2018 Group Project 4

2018-10-11T23:49:46Z

Z5229281: /* Zebrafish model */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

[[File:TBX1 factor figure.jpg|400px|thumb|right|alt text]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}}

==== Zebrafish model ====
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors is known to interact with HOX and Pre-B cell leukaemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor.{{#pmid:3462257|PMC3462257}}

[[File:Zebra Fish Animal model.jpg|450px|thumb|right|alt text]]

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-11T23:47:51Z

Z5229281: /* Zebrafish model */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

[[File:TBX1 factor figure.jpg|400px|thumb|right|alt text]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, where premigratory presumptive arch neural crest cells from quail embryos were grafted onto early chick embryos.{{#pmid:1858673|PMC1858673}} Majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the Quail-Chick Chimeras. For example, ablation studies on quail-chick chimeras have shown that CNCCs are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of proper development of neural crest cells. For example, knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.{{#pmid:3986121|PMC3986121}}

==== Zebrafish model ====
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors is known to interact with HOX and Pre-B cell leukaemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor.{{#pmid:3462257|PMC3462257}}

File:Zebra Fish Animal model.jpg

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

File:Zebra Fish Animal model.jpg

2018-10-11T23:46:12Z

Z5229281:

File:Zebra Fish Animal model.jpg

2018-10-11T23:45:23Z

Z5229281: Forskolin increases expression of the mitfa transcriptional repressor foxd3. (A–C) 10× magnification of Bacfoxd3::GFP transgenic larvae at 2 dpf. Transgenic zebrafish express GFP in foxd3-dependent cells including the pineal gland (arrowhead) and pr...

File:TBX1 factor figure.jpg

2018-10-11T23:39:40Z

Z5229281: /* Reference */

File:TBX1 factor figure.jpg

2018-10-11T09:58:26Z

Z5229281: /* Copyright */

Cardiac neural crest cell defects in Tbx1 mutant embryos. (A) E9.5 Tbx1CRE-RosaYFP embryos were stained for the cNCC marker AP2α together with YFP as a marker for the Tbx1-lineage. cNCCs and Tbx1 do not colocalize (arrowheads). (B) E12.5 Tbx1+/+, Tbx1+/− and Tbx1neo2/− outflow tracts were stained for the cNCC marker Sema3C. cNCCs have migrated into the outflow tract cushions in Tbx1+/+ and Tbx1+/− but not in Tbx1neo2/− embryos. White arrowheads and arrows indicate Sema3C expression in myocardial cuff cells and the septal bridge area, respectively. Asterisk indicates absent Sema3C in the outflow tract right cushion. Yellow arrow marks residual Sema3C-positive cNCCs in the outflow tract left cushion. Scale Bars are in μm.

===Reference===

Illustration obtained from

===Copyright===
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

z5229281

This image was originally uploaded as part of an undergraduate science student project and may contain inaccuracies in either description or acknowledgements. Students have been advised in writing concerning the reuse of content and may accidentally have misunderstood the original terms of use. If image reuse on this non-commercial educational site infringes your existing copyright, please contact the site editor for immediate removal.

2018 Group Project 4

2018-10-11T09:34:52Z

Z5229281: /* DiGeorge Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

[[File:TBX1 factor figure.jpg|400px|thumb|right|alt text]]

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, and majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the chick embryo. {{#pmid:1858673|PMC1858673 }} Ablation studies on quail-chick chimeras have shown that CNCC are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of proper development of neural crest cells. Knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.

http://www.pnas.org/content/111/14/E1374

==== Zebrafish model ====
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors is known to interact with HOX and Pre-B cell leukaemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor.{{#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-11T09:32:39Z

Z5229281: /* DiGeorge Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

[[File:TBX1 factor figure.jpg|300px|thumb|right|alt text]]

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}} It is important to note that the absence of an obvious phenotype in an animal model does not necessarily mean that the gene of interest is not normally involved in the process for humans. Rather, it could be that the gene has a redundant function in the animal model, which could differ amongst species.

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, and majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the chick embryo. {{#pmid:1858673|PMC1858673 }} Ablation studies on quail-chick chimeras have shown that CNCC are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of proper development of neural crest cells. Knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.

http://www.pnas.org/content/111/14/E1374

==== Zebrafish model ====
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors is known to interact with HOX and Pre-B cell leukaemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor.{{#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-11T09:30:31Z

Z5229281: /* DiGeorge Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

[[File:TBX1 factor figure.jpg|200px|thumb|left|alt text]]

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}}

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, and majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the chick embryo. {{#pmid:1858673|PMC1858673 }} Ablation studies on quail-chick chimeras have shown that CNCC are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. The mouse offers a powerful genetic model for as many mouse mutants exhibit various neural crest phenotypes that lead on to important discoveries related to the importance of proper development of neural crest cells. Knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.

http://www.pnas.org/content/111/14/E1374

==== Zebrafish model ====
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors is known to interact with HOX and Pre-B cell leukaemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor.{{#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

File:TBX1 factor figure.jpg

2018-10-11T09:29:23Z

Z5229281: Cardiac neural crest cell defects in Tbx1 mutant embryos. (A) E9.5 Tbx1CRE-RosaYFP embryos were stained for the cNCC marker AP2α together with YFP as a marker for the Tbx1-lineage. cNCCs and Tbx1 do not colocalize (arrowheads). (B) E12.5 Tbx1+/+, Tbx1...

2018 Group Project 4

2018-10-11T09:23:08Z

Z5229281: /* DiGeorge Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion {{#pmid:30249045|PMID:30249045}}.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}}

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, and majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the chick embryo. {{#pmid:1858673|PMC1858673 }} Ablation studies on quail-chick chimeras have shown that CNCC are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. Knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.

http://www.pnas.org/content/111/14/E1374

==== Zebrafish model ====
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors is known to interact with HOX and Pre-B cell leukaemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor.{{#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-11T09:22:03Z

Z5229281: /* DiGeorge Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

DiGeorge syndrome (DGS), also known as Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion <ref name="PMID30249045" />

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}}

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, and majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the chick embryo. {{#pmid:1858673|PMC1858673 }} Ablation studies on quail-chick chimeras have shown that CNCC are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. Knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.

http://www.pnas.org/content/111/14/E1374

==== Zebrafish model ====
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) is critical for the proper development of the heart and cardiac looping. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {{#pmid:3462257|PMC3462257}} MEIS transcription factors is known to interact with HOX and Pre-B cell leukaemia transcription factors (PBX) to regulate downstream targets in multiple cellular processes. In situ time course experiments in developing zebrafish embryos have shown that MEIS2b expression in the heart field resembled that of Gata4, a known cardiac transcription factor.{{#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-11T09:19:26Z

Z5229281: /* DiGeorge Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

DiGeorge syndrome (DGS), aka Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion <ref name="PMID30249045" />.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}}

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, and majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the chick embryo. {{#pmid:1858673|PMC1858673 }} Ablation studies on quail-chick chimeras have shown that CNCC are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. Knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.

http://www.pnas.org/content/111/14/E1374

==== Zebrafish model ====
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) genes are critical for cardiac development. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-11T09:18:09Z

Z5229281: /* DiGeorge Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

DiGeorge syndrome (DGS), aka Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

Research in the pathway/mechanism of why chromosome 22q11.2 deletion occurs happens due to a recent discovery in T-Box transcription factor (TBX1). TBX1 is involved in the regulation of neural crest cell migratory pathways. Haploinsufficiency of the T-box transcription factor TBX1 is responsible for the many features of 22q11.2 deletion syndrome. {{#pmid:30249045|PMID:30249045}}. Tbx1 controls cardiac innervation by modulating NCC and nerve migratory pathways in a non-cell autonomous fashion. <ref name="PMID30249045" />.

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}}

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, and majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the chick embryo. {{#pmid:1858673|PMC1858673 }} Ablation studies on quail-chick chimeras have shown that CNCC are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse ====
Another key animal model that is commonly used for CNCC studies is the mouse. Knockout studies on mouse models have shown the importance of a ubiquitously expressed nonreceptor tyrosine phosphatase, known as SHP-2 which plays a role in the cardiac outflow track development and semilunar valvulogenesis.

http://www.pnas.org/content/111/14/E1374

==== Zebrafish model ====
Using the zebrafish model, studies have demonstrated that MEIS2 (myeloid ecotropic viral integration site 2 homolog) genes are critical for cardiac development. Embryos that received splice-blocking morpholino oligonucleotide directed against meis2b were shown to have defective cardiac morphogenesis. {#pmid:3462257|PMC3462257}}

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-11T09:01:39Z

Z5229281: /* DiGeorge Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

DiGeorge syndrome (DGS), aka Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}}

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, and majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the chick embryo. {{#pmid:1858673|PMC1858673 }} Ablation studies on quail-chick chimeras have shown that CNCC are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse =====
Another key animal model that is commonly used for CNCC studies is the mouse

however, several conditional knockout (cKO) mouse models have investigated the embryonic in vivo requirement of SHP-2 using various Cre recombinase drivers. These models, although primarily embryonically lethal, have demonstrated that SHP-2 can play a role in NC-mediated events such as cardiac outflow track development, semilunar valvulogenesis
http://www.pnas.org/content/111/14/E1374

Mouse models:

Quail-chick chimeras: most of our knowledge of the distribution of cardiac neural crest cells in the heart comes from quail-chick chimeras.

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-11T09:00:15Z

Z5229281: /* DiGeorge Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The very first major system to develop its function within a vertebrate embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself.
The four major embryonic regions that are involved in the process of vertebrate heart development are the primary heart field, secondary heart field, cardiac neural crest, and proepicardium. Each region have important contributions to the overall cardiac development, which occurs with complex and precise developmental timing and regulation. Neural crests are a population of multipotent cells which arises during embryonic development at the dorsal neural tube and were first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan. {{#pmid:29787146|PMID29787146}}. The first study showing the relationship of neural crest cells with heart development was published in 1983 where a specific subgroup of neural crest cells, known as cardiac neural crest cells, have been shown to be essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. Since then, the role of cardiac neural crest cells in the development of heart have been explored extensively in various studies which allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube during weeks 3–4 {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart that functions initially as a conduit for the blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

[[Image:hannelore1.jpg|thumb]]

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==

=== Outflow Septation ===
The septation of the outflow tract is tightly coordinated with the septation of both the ventricles and atria. After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.

Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> .

Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks.

Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}.

The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

The outflow septum has three main components:
# Aortico-Pulmonary Septum - The most cranial portion of the septum and forms in the aortic sac:
# Truncus Septum - Caudal of the aorticopulmonary septum and forms partition between aortic and pulmonary semilunar valves
# Conus Septum - Inferior portion of the outflow septum and is needed for the closure of the ventricular septum {{#pmid:9558464|PMID9558464}}

Failure of proper OFT septation during embryogenesis will result in inappropriate mixing of oxygenated and deoxygenated blood at birth and this may cause an unfavourable clinical prognosis.

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development. The OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

The heart first transforms from the embryo into four parts: The atrial chamber, ventricular chamber, arterial trunks and great veins. The first part of cardiac development involves the separation into phases of formation of the primary myocardial tube, looping of the tube, additional parts for future topography compartments, and assembly of the components into arterial trunks and cardiac chambers subsequently. {{#pmid:12807866|PMID12807866}}

During the formation of the two arterial trunks, the cushions that divided them disintegrates. The parts that possess their own distinct walls, separated by extra-cardiac space are the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum.{{#pmid:12860885|PMID12860885}}

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that turn on intracellular signalling pathways. The Wnt pathway is needed to stabilize the expression of B-catenin by hindering proteasome degradation. If the Wnt pathway is inhibited, the decrease in B-catenin can result in a reduced proliferation of CNCCs which may result in the hindered development of the OFT. {{#pmid:20651295 |PMID20651295}}
# '''Notch''': a transmembrane protein whose signalling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes. Inhibition of the Notch pathway in neural crest cells via dominant-negative Notch inhibitor (DN-MAML) have been shown to cause various defects in outflow tract, cardiac and aortic arch defects. Neural crest cell migration, survival and contribution to the branchial arches are not affected by Notch inhibition thus suggesting that Notch signalling is essential for post-migratory differentiation of cardiac neural crest into smooth muscle.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''GATA''': Transcription factors which are key factors in the restriction of cell lineage differentiation during the development of the heart. One important member of GATA is the GATA6 which regulates the morphogenetic patterning of the outflow tract and aortic arch. If GATA6 is inactivated in CNCCs, defects in the development of the cardiovascular system such as persistent truncus arteriorus would occur
* Meis2 {{#pmid: PMC4636814 | PMC4636814}}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==
Cardiac neural crest ablation experiments in vertebrate models have demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced such as:
# Defective development of the cardiac outflow tract;
# Abnormal myocardial function;
# Defective development of the derivatives of the caudal pharynx including arch arteries, pharyngeal glands and the secondary heart field.

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but can also be involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

Even though there are various cardiac dysmorphologies caused by cardiac neural crest ablation, only those involving outflow or conotruncal defects are commonly seen, thus the majority of the studies have been focused on these cardiac defects which can include:
# Complete absence of outflow septation,
# Persistent truncus arteriosus,
# Overriding aorta

---- not yet edited----

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

=== Disruptions to outflow tract septation ===

OFT remodeling is a process whereby the embryonic outﬂow tract undergoes a series of developmental transitions that involves extra cardiac cells recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus (PTA), a rare congenital heart anomaly in humans. <ref name="PMID29920846" />. PTA occurs when there is a deficiency in the number of neural crest cells that reach the cardiac outflow tract, thus the truncus arteriosus will not be developed properly and will not be able to properly divide the common truncal outflow vessel into the pulmonary trunk and aorta, resulting in only a single arterial trunk arising from the heart {{#pmid:3791607|PMID3791607}}. This will cause the oxygenated and deoxygenated blood to be mixed and the mixed blood will be pumped through the coronary and pulmonary arteries as wel as the systemic circulation. This can result in various defects such as cyanosis at birth, cardiomegaly and even heart failure in the fetus.

Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot.

=== DiGeorge Syndrome ===

DiGeorge syndrome (DGS), aka Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produces cardio-craniofacial anomalies which can be found in DGS patients. {{#pmid:26755698|PMID26755698}}

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

==Models and Research==

=== Animal Models ===
In the past century, various vertebrates have been utilised for the study of neural crest biology, such as: amphibians, fish, avians, mice, lamprey and even hagfish. {{#pmid:12100892|PMID12100892}}{{#pmid:16043371|PMID16043371}}{{#pmid:17765683|PMID17765683}} Interestingly enough, Zebrafish, Xenopus and chick embryos largely display consistent requirements for specific genes in early steps of neural crest development. However, knockout of homologous genes in the mouse often do not exhibit comparable early neural crest phenotypes, suggesting that there might be major differences between vertebrate species.{{#pmid:25922521|PMID25922521}}

==== Quail-Chick Chimeras ====
For CNCCs, the main experimental animal model is the chick embryo, specifically quail-chick chimeras, and majority of what was learnt about the importance of CNCCs in cardiovascular development were derived from studies done on the chick embryo. {{#pmid:1858673|PMC1858673 }} Ablation studies on quail-chick chimeras have shown that CNCC are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

==== Mouse =====
Another key animal model that is commonly used for CNCC studies is the mouse

however, several conditional knockout (cKO) mouse models have investigated the embryonic in vivo requirement of SHP-2 using various Cre recombinase drivers. These models, although primarily embryonically lethal, have demonstrated that SHP-2 can play a role in NC-mediated events such as cardiac outflow track development, semilunar valvulogenesis
http://www.pnas.org/content/111/14/E1374

Mouse models:

Quail-chick chimeras: most of our knowledge of the distribution of cardiac neural crest cells in the heart comes from quail-chick chimeras.

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-06T10:20:22Z

Z5229281: /* References */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The neural crest (NC) was first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan.{{#pmid:29787146|PMID29787146}}The very first major system to develop its function within an embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself. Studies done in avian and fish embryos have shown that a specific subgroup of neural crest cells, known as cardiac neural crest cells are essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. The studies have allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart which initially functions as a conduit for blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]
=== Outflow Septation ===
After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.
Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> . Currently, not much is known about which factors are responsible for attracting neural crest cells into the outflow tract cushions. Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks. Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}. The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

three components are responsible for forming the septa in the outflow tract:
# Conus Septum
# truncus Septum
# Aorto-Pulmonary Septum

--> https://www.sciencedirect.com/science/article/pii/B9780124017306000120
PMID: 26053665

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development.T he OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

that subsequent to the formation of the two arterial trunks, there was disappearance of the cushions that initially divided them. Thus, in the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum, possess their own discrete walls, separated by extra-cardiac space.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767797/

<<not edited>>

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that activate intracellular signaling pathways. The decrease of B-catenin results in a reduction in the proliferation of cardiac neural crest cells.
# '''Notch''': a transmembrane protein whose signaling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''FGF8'''(fibroblast growth factor 8): Transcription factors that are essential for regulating the addition of secondary heart field cells into the cardiac outflow tract.
# '''GATA''': Transcription factors which play a critical role in cell lineage differentiation restriction during cardiac development.

* Meis2 {{#pmid: PMC4636814 | PMC4636814 }}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but are involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

---- not yet edited----

Cardiac neural crest ablation experiments demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced.

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

===Conotruncal Heart Malformations ===

OFT remodeling is a process whereby the embryonic outﬂowtract undergoes a series of developmental transitions that involves extra cardiac cell recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus <ref name="PMID29920846" /> : if the cardiac neural crest is removed before it begins to migrate, the conotruncal septa completely fails to develop, and blood leaves both the ventricles through what is termed a persistent truncus arteriosus, a rare congenital heart anomaly in humans. (Martinson)
Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot (Martinson).

This is a defect on the NKX2 gene/locus

=== DiGeorge Syndrome ===

DiGeorge syndrome (DGS), aka Velocardiofacial Syndrome, is a congenital condition which affects the development of many tissues that are patterned by or derived from NCCs. People suffering from DGS display symptoms such as craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, mental disorders and cardiovascular defects. <ref name="PMID29787146" />. DGS results primarily due to defective development of cranial and cardiac NCCs which invades the first four pharyngeal arches that contribute to the development of the lower jaw, neck and cardiac structures. Studies have shown in chicks that the ablation of the pharyngeal NCCs population produce cardiocraniofacial anomalies which can be found in DGS patients.
(how to cite this?: http://dev.biologists.org/content/143/4/582)

DGS
* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

(to edit)
The DiGeorge syndrome consists of a PTA, type B interrupted aortic arch, absent or hypoplastic thymus, craniofacial dysmorphology and cognitive or behavioral disorders. (ref) It can also include absent or hypoplastic parathyroid and thyroid glands.

https://www.ncbi.nlm.nih.gov/pubmed/9514586
https://www.ncbi.nlm.nih.gov/pubmed/3728313

A variant of the DiGeorge phenotype, called Sprintzen or Velocardiofacial syndrome, also includes cleft palate.
https://www.ncbi.nlm.nih.gov/pubmed/272242

=== C.H.A.R.G.E Syndrome ===

*'''C'''oloboma
*'''H'''eart anomaly
*'''A'''tresia of choanae
*'''R'''etardation of physical and mental development
*'''G'''enital hypoplasia
*'''E'''ar anomalies and/or deafness

{{#pmid: PMC3389200|PMC3389200}}

The link between the chromatin-remodeling protein CHD7 with cardiac NCC-associated defects suggests that epigenetic regulation is important for genes controlling NCC function.

--> https://pdfs.semanticscholar.org/42cc/ee7fbb545ea6752e1c126cc2769e8e33e7b7.pdf

Neural crest cells contribute to these deformations and abnormalities of the tissues. How is because NC development involves many convoluted steps such as specification, delamination, migration, induction, and differentiation <ref name="PMID29082625" />. These processes are controlled by regulatory gene networks. If certain genes are disrupted affecting the neural crest cells then a variety of human diseases arise categorized as neurocristopathies. CHARGE is an acronym for a collection of symptoms including, heart defects, retarded growth, and development, genital hypoplasia, ear anomalies, and deafness. CHARGE syndrome is a sporadic, autosomal dominant malformation disorder diagnosed in 1/8,500-1/10,000 live births <ref name="PMID29082625" />. In addition, malformations of the foregut, kidneys, limbs, lung, and liver have been described in infants with CHARGE syndrome. The gene most commonly affected in patients with CHARGE syndrome is CHD7, which encodes a DNA binding protein involved in chromatin remodeling <ref name="PMID29082625" />.Mutations in the chromatin helicase DNA-binding protein 7(CHD7) gene are causative of CHARGE syndrome and the loss-of-function.

==Models and Research==

=== Animal Models ===

* Main animal models are chicken, fish, and mice.

Chick embryo models: (to edit)

the chick embryo using quail-chick chimeras to study neural crest migration and derivatives as well as using ablation of premigratory neural crest cells to study their function. These studies show that cardiac neural crest cells are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

https://www.ncbi.nlm.nih.gov/pubmed/17224285

These studies show that after the cardiac neural crest cells migrate into pharyngeal arches 3, 4 and 6, a subset of the cells continue migrating into the cardiac outflow cushions.

<<insert image>>

https://www.ncbi.nlm.nih.gov/pubmed/3568286

Mouse models:

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}
{{#pmid:29082625}}

2018 Group Project 4

2018-10-06T10:18:12Z

Z5229281: /* C.H.A.R.G.E Syndrome */

2018 Group Project 4

2018-10-05T23:58:02Z

Z5229281: /* C.H.A.R.G.E Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The neural crest (NC) was first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan.{{#pmid:29787146|PMID29787146}}The very first major system to develop its function within an embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself. Studies done in avian and fish embryos have shown that a specific subgroup of neural crest cells, known as cardiac neural crest cells are essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. The studies have allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart which initially functions as a conduit for blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]
=== Outflow Septation ===
After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.
Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> . Currently, not much is known about which factors are responsible for attracting neural crest cells into the outflow tract cushions. Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks. Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}. The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

three components are responsible for forming the septa in the outflow tract:
# Conus Septum
# truncus Septum
# Aorto-Pulmonary Septum

--> https://www.sciencedirect.com/science/article/pii/B9780124017306000120
PMID: 26053665

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development.T he OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

that subsequent to the formation of the two arterial trunks, there was disappearance of the cushions that initially divided them. Thus, in the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum, possess their own discrete walls, separated by extra-cardiac space.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767797/

<<not edited>>

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that activate intracellular signaling pathways. The decrease of B-catenin results in a reduction in the proliferation of cardiac neural crest cells.
# '''Notch''': a transmembrane protein whose signaling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''FGF8'''(fibroblast growth factor 8): Transcription factors that are essential for regulating the addition of secondary heart field cells into the cardiac outflow tract.
# '''GATA''': Transcription factors which play a critical role in cell lineage differentiation restriction during cardiac development.

* Meis2 {{#pmid: PMC4636814 | PMC4636814 }}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but are involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

---- not yet edited----

Cardiac neural crest ablation experiments demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced.

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

===Conotruncal Heart Malformations ===

OFT remodeling is a process whereby the embryonic outﬂowtract undergoes a series of developmental transitions that involves extra cardiac cell recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus <ref name="PMID29920846" /> : if the cardiac neural crest is removed before it begins to migrate, the conotruncal septa completely fails to develop, and blood leaves both the ventricles through what is termed a persistent truncus arteriosus, a rare congenital heart anomaly in humans. (Martinson)
Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot (Martinson).

This is a defect on the NKX2 gene/locus

=== DiGeorge Syndrome and Velocardiofacial Syndrome ===

DiGeorge syndrome (DGS) is a condition that affects the development of many tissues that are patterned by or derived from NCCs. Thus, patients have variable types of craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, and OFT and aortic arch defects. Also known as velocardiofacial (Shprintzen) syndrome and conotruncal anomaly face (Takao) syndrome.<ref name="PMID29787146" />

* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

(to edit)
The DiGeorge syndrome consists of a PTA, type B interrupted aortic arch, absent or hypoplastic thymus, craniofacial dysmorphology and cognitive or behavioral disorders. (ref) It can also include absent or hypoplastic parathyroid and thyroid glands.

https://www.ncbi.nlm.nih.gov/pubmed/9514586
https://www.ncbi.nlm.nih.gov/pubmed/3728313

A variant of the DiGeorge phenotype, called Sprintzen or Velocardiofacial syndrome, also includes cleft palate.
https://www.ncbi.nlm.nih.gov/pubmed/272242

=== C.H.A.R.G.E Syndrome ===

*'''C'''oloboma
*'''H'''eart anomaly
*'''A'''tresia of choanae
*'''R'''etardation of physical and mental development
*'''G'''enital hypoplasia
*'''E'''ar anomalies and/or deafness

{{#pmid: PMC3389200|PMC3389200}}

The link between the chromatin-remodeling protein CHD7 with cardiac NCC-associated defects suggests that epigenetic regulation is important for genes controlling NCC function.

--> https://pdfs.semanticscholar.org/42cc/ee7fbb545ea6752e1c126cc2769e8e33e7b7.pdf

Mutations in the chromatin helicase DNA-binding protein 7(CHD7) gene are causative of CHARGE syndrome and loss-of-function

Neural crest cells contribute to these deformations and abnormalities of the tissues. How is because NC development involves many convoluted steps such as specification, delamination, migration, induction, and differentiation <ref name="PMID29082625" />. These processes are controlled by regulatory gene networks. If certain genes are disrupted affecting the neural crest cells then a variety of human diseases arise categorized as neurocristopathies. CHARGE is an acronym for a collection of symptoms including, heart defects, retarded growth, and development, genital hypoplasia, ear anomalies, and deafness. CHARGE syndrome is a sporadic, autosomal dominant malformation disorder diagnosed in 1/8,500-1/10,000 live births <ref name="PMID29082625" />. In addition, malformations of the foregut, kidneys, limbs, lung, and liver have been described in infants with CHARGE syndrome. The gene most commonly affected in patients with CHARGE syndrome is CHD7, which encodes a DNA binding protein involved in chromatin remodeling <ref name="PMID29082625" />.

==Models and Research==

=== Animal Models ===

* Main animal models are chicken, fish, and mice.

Chick embryo models: (to edit)

the chick embryo using quail-chick chimeras to study neural crest migration and derivatives as well as using ablation of premigratory neural crest cells to study their function. These studies show that cardiac neural crest cells are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

https://www.ncbi.nlm.nih.gov/pubmed/17224285

These studies show that after the cardiac neural crest cells migrate into pharyngeal arches 3, 4 and 6, a subset of the cells continue migrating into the cardiac outflow cushions.

<<insert image>>

https://www.ncbi.nlm.nih.gov/pubmed/3568286

Mouse models:

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}

2018 Group Project 4

2018-10-05T23:56:43Z

Z5229281: /* C.H.A.R.G.E Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The neural crest (NC) was first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan.{{#pmid:29787146|PMID29787146}}The very first major system to develop its function within an embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself. Studies done in avian and fish embryos have shown that a specific subgroup of neural crest cells, known as cardiac neural crest cells are essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. The studies have allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart which initially functions as a conduit for blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]
=== Outflow Septation ===
After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.
Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> . Currently, not much is known about which factors are responsible for attracting neural crest cells into the outflow tract cushions. Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks. Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}. The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

three components are responsible for forming the septa in the outflow tract:
# Conus Septum
# truncus Septum
# Aorto-Pulmonary Septum

--> https://www.sciencedirect.com/science/article/pii/B9780124017306000120
PMID: 26053665

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development.T he OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

that subsequent to the formation of the two arterial trunks, there was disappearance of the cushions that initially divided them. Thus, in the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum, possess their own discrete walls, separated by extra-cardiac space.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767797/

<<not edited>>

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that activate intracellular signaling pathways. The decrease of B-catenin results in a reduction in the proliferation of cardiac neural crest cells.
# '''Notch''': a transmembrane protein whose signaling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''FGF8'''(fibroblast growth factor 8): Transcription factors that are essential for regulating the addition of secondary heart field cells into the cardiac outflow tract.
# '''GATA''': Transcription factors which play a critical role in cell lineage differentiation restriction during cardiac development.

* Meis2 {{#pmid: PMC4636814 | PMC4636814 }}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but are involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

---- not yet edited----

Cardiac neural crest ablation experiments demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced.

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

===Conotruncal Heart Malformations ===

OFT remodeling is a process whereby the embryonic outﬂowtract undergoes a series of developmental transitions that involves extra cardiac cell recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus <ref name="PMID29920846" /> : if the cardiac neural crest is removed before it begins to migrate, the conotruncal septa completely fails to develop, and blood leaves both the ventricles through what is termed a persistent truncus arteriosus, a rare congenital heart anomaly in humans. (Martinson)
Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot (Martinson).

This is a defect on the NKX2 gene/locus

=== DiGeorge Syndrome and Velocardiofacial Syndrome ===

DiGeorge syndrome (DGS) is a condition that affects the development of many tissues that are patterned by or derived from NCCs. Thus, patients have variable types of craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, and OFT and aortic arch defects. Also known as velocardiofacial (Shprintzen) syndrome and conotruncal anomaly face (Takao) syndrome.<ref name="PMID29787146" />

* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

(to edit)
The DiGeorge syndrome consists of a PTA, type B interrupted aortic arch, absent or hypoplastic thymus, craniofacial dysmorphology and cognitive or behavioral disorders. (ref) It can also include absent or hypoplastic parathyroid and thyroid glands.

https://www.ncbi.nlm.nih.gov/pubmed/9514586
https://www.ncbi.nlm.nih.gov/pubmed/3728313

A variant of the DiGeorge phenotype, called Sprintzen or Velocardiofacial syndrome, also includes cleft palate.
https://www.ncbi.nlm.nih.gov/pubmed/272242

=== C.H.A.R.G.E Syndrome ===

*'''C'''oloboma
*'''H'''eart anomaly
*'''A'''tresia of choanae
*'''R'''etardation of physical and mental development
*'''G'''enital hypoplasia
*'''E'''ar anomalies and/or deafness

{{#pmid: PMC3389200|PMC3389200}}

The link between the chromatin-remodeling protein CHD7 with cardiac NCC-associated defects suggests that epigenetic regulation is important for genes controlling NCC function.

--> https://pdfs.semanticscholar.org/42cc/ee7fbb545ea6752e1c126cc2769e8e33e7b7.pdf

Mutations in the chromatin helicase DNA-binding protein 7(CHD7) gene are causative of CHARGE syndrome and loss-of-function

Neural crest cells contribute to these deformations and abnormalities of the tissues. How is because NC development involves many convoluted steps such as specification, delamination, migration, induction, and differentiation <ref name="PMID29082625" />. These processes are controlled by regulatory gene networks. If certain genes are disrupted affecting the neural crest cells then a variety of human diseases arise categorized as neurocristopathies. CHARGE is an acronym for a collection of symptoms including, heart defects, retarded growth, and development, genital hypoplasia, ear anomalies, and deafness. CHARGE syndrome is a sporadic, autosomal dominant malformation disorder diagnosed in 1/8,500-1/10,000 live births {{#pmid:29082625|29082625}}. In addition, malformations of the foregut, kidneys, limbs, lung, and liver have been described in infants with CHARGE syndrome. The gene most commonly affected in patients with CHARGE syndrome is CHD7, which encodes a DNA binding protein involved in chromatin remodeling <ref name="PMID29082625" />.
PMID: 29082625
--> https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajmg.c.31584

==Models and Research==

=== Animal Models ===

* Main animal models are chicken, fish, and mice.

Chick embryo models: (to edit)

the chick embryo using quail-chick chimeras to study neural crest migration and derivatives as well as using ablation of premigratory neural crest cells to study their function. These studies show that cardiac neural crest cells are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

https://www.ncbi.nlm.nih.gov/pubmed/17224285

These studies show that after the cardiac neural crest cells migrate into pharyngeal arches 3, 4 and 6, a subset of the cells continue migrating into the cardiac outflow cushions.

<<insert image>>

https://www.ncbi.nlm.nih.gov/pubmed/3568286

Mouse models:

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}

2018 Group Project 4

2018-10-05T23:55:19Z

Z5229281: /* C.H.A.R.G.E Syndrome */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The neural crest (NC) was first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan.{{#pmid:29787146|PMID29787146}}The very first major system to develop its function within an embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself. Studies done in avian and fish embryos have shown that a specific subgroup of neural crest cells, known as cardiac neural crest cells are essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. The studies have allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart which initially functions as a conduit for blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]
=== Outflow Septation ===
After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.
Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> . Currently, not much is known about which factors are responsible for attracting neural crest cells into the outflow tract cushions. Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks. Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}. The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

three components are responsible for forming the septa in the outflow tract:
# Conus Septum
# truncus Septum
# Aorto-Pulmonary Septum

--> https://www.sciencedirect.com/science/article/pii/B9780124017306000120
PMID: 26053665

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development.T he OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

that subsequent to the formation of the two arterial trunks, there was disappearance of the cushions that initially divided them. Thus, in the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum, possess their own discrete walls, separated by extra-cardiac space.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767797/

<<not edited>>

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that activate intracellular signaling pathways. The decrease of B-catenin results in a reduction in the proliferation of cardiac neural crest cells.
# '''Notch''': a transmembrane protein whose signaling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''FGF8'''(fibroblast growth factor 8): Transcription factors that are essential for regulating the addition of secondary heart field cells into the cardiac outflow tract.
# '''GATA''': Transcription factors which play a critical role in cell lineage differentiation restriction during cardiac development.

* Meis2 {{#pmid: PMC4636814 | PMC4636814 }}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but are involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

---- not yet edited----

Cardiac neural crest ablation experiments demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced.

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

===Conotruncal Heart Malformations ===

OFT remodeling is a process whereby the embryonic outﬂowtract undergoes a series of developmental transitions that involves extra cardiac cell recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus <ref name="PMID29920846" /> : if the cardiac neural crest is removed before it begins to migrate, the conotruncal septa completely fails to develop, and blood leaves both the ventricles through what is termed a persistent truncus arteriosus, a rare congenital heart anomaly in humans. (Martinson)
Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot (Martinson).

This is a defect on the NKX2 gene/locus

=== DiGeorge Syndrome and Velocardiofacial Syndrome ===

DiGeorge syndrome (DGS) is a condition that affects the development of many tissues that are patterned by or derived from NCCs. Thus, patients have variable types of craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, and OFT and aortic arch defects. Also known as velocardiofacial (Shprintzen) syndrome and conotruncal anomaly face (Takao) syndrome.<ref name="PMID29787146" />

* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

(to edit)
The DiGeorge syndrome consists of a PTA, type B interrupted aortic arch, absent or hypoplastic thymus, craniofacial dysmorphology and cognitive or behavioral disorders. (ref) It can also include absent or hypoplastic parathyroid and thyroid glands.

https://www.ncbi.nlm.nih.gov/pubmed/9514586
https://www.ncbi.nlm.nih.gov/pubmed/3728313

A variant of the DiGeorge phenotype, called Sprintzen or Velocardiofacial syndrome, also includes cleft palate.
https://www.ncbi.nlm.nih.gov/pubmed/272242

=== C.H.A.R.G.E Syndrome ===

*'''C'''oloboma
*'''H'''eart anomaly
*'''A'''tresia of choanae
*'''R'''etardation of physical and mental development
*'''G'''enital hypoplasia
*'''E'''ar anomalies and/or deafness

{{#pmid: PMC3389200|PMC3389200}}

The link between the chromatin-remodeling protein CHD7 with cardiac NCC-associated defects suggests that epigenetic regulation is important for genes controlling NCC function.

--> https://pdfs.semanticscholar.org/42cc/ee7fbb545ea6752e1c126cc2769e8e33e7b7.pdf

Mutations in the chromatin helicase DNA-binding protein 7(CHD7) gene are causative of CHARGE syndrome and loss-of-function

Neural crest cells contribute to these deformations and abnormalities of the tissues. How is because NC development involves many convoluted steps such as specification, delamination, migration, induction, and differentiation <ref name="PMID29082625" />. These processes are controlled by regulatory gene networks. If certain genes are disrupted affecting the neural crest cells then a variety of human diseases arise categorized as neurocristopathies. CHARGE is an acronym for a collection of symptoms including, heart defects, retarded growth, and development, genital hypoplasia, ear anomalies, and deafness. CHARGE syndrome is a sporadic, autosomal dominant malformation disorder diagnosed in 1/8,500-1/10,000 live births{{#pmid:2908265|2908265}}. In addition, malformations of the foregut, kidneys, limbs, lung, and liver have been described in infants with CHARGE syndrome. The gene most commonly affected in patients with CHARGE syndrome is CHD7, which encodes a DNA binding protein involved in chromatin remodeling <ref name="PMID29082625" />.
PMID: 29082625
--> https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajmg.c.31584

==Models and Research==

=== Animal Models ===

* Main animal models are chicken, fish, and mice.

Chick embryo models: (to edit)

the chick embryo using quail-chick chimeras to study neural crest migration and derivatives as well as using ablation of premigratory neural crest cells to study their function. These studies show that cardiac neural crest cells are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

https://www.ncbi.nlm.nih.gov/pubmed/17224285

These studies show that after the cardiac neural crest cells migrate into pharyngeal arches 3, 4 and 6, a subset of the cells continue migrating into the cardiac outflow cushions.

<<insert image>>

https://www.ncbi.nlm.nih.gov/pubmed/3568286

Mouse models:

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}

2018 Group Project 4

2018-10-05T23:43:04Z

Z5229281: /* Neural Crest and Cardiac Development */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The neural crest (NC) was first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan.{{#pmid:29787146|PMID29787146}}The very first major system to develop its function within an embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself. Studies done in avian and fish embryos have shown that a specific subgroup of neural crest cells, known as cardiac neural crest cells are essential for the septation of the cardiac outflow track as well as the development of aortic arch artery. The studies have allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others{{#pmid:29802835|PMID29802835}}. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart which initially functions as a conduit for blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]
=== Outflow Septation ===
After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.
Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> . Currently, not much is known about which factors are responsible for attracting neural crest cells into the outflow tract cushions. Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks. Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}. The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

three components are responsible for forming the septa in the outflow tract:
# Conus Septum
# truncus Septum
# Aorto-Pulmonary Septum

--> https://www.sciencedirect.com/science/article/pii/B9780124017306000120
PMID: 26053665

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development.T he OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

that subsequent to the formation of the two arterial trunks, there was disappearance of the cushions that initially divided them. Thus, in the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum, possess their own discrete walls, separated by extra-cardiac space.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767797/

<<not edited>>

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that activate intracellular signaling pathways. The decrease of B-catenin results in a reduction in the proliferation of cardiac neural crest cells.
# '''Notch''': a transmembrane protein whose signaling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''FGF8'''(fibroblast growth factor 8): Transcription factors that are essential for regulating the addition of secondary heart field cells into the cardiac outflow tract.
# '''GATA''': Transcription factors which play a critical role in cell lineage differentiation restriction during cardiac development.

* Meis2 {{#pmid: PMC4636814 | PMC4636814 }}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but are involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

---- not yet edited----

Cardiac neural crest ablation experiments demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced.

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

===Conotruncal Heart Malformations ===

OFT remodeling is a process whereby the embryonic outﬂowtract undergoes a series of developmental transitions that involves extra cardiac cell recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus <ref name="PMID29920846" /> : if the cardiac neural crest is removed before it begins to migrate, the conotruncal septa completely fails to develop, and blood leaves both the ventricles through what is termed a persistent truncus arteriosus, a rare congenital heart anomaly in humans. (Martinson)
Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot (Martinson).

This is a defect on the NKX2 gene/locus

=== DiGeorge Syndrome and Velocardiofacial Syndrome ===

DiGeorge syndrome (DGS) is a condition that affects the development of many tissues that are patterned by or derived from NCCs. Thus, patients have variable types of craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, and OFT and aortic arch defects. Also known as velocardiofacial (Shprintzen) syndrome and conotruncal anomaly face (Takao) syndrome.<ref name="PMID29787146" />

* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

(to edit)
The DiGeorge syndrome consists of a PTA, type B interrupted aortic arch, absent or hypoplastic thymus, craniofacial dysmorphology and cognitive or behavioral disorders. (ref) It can also include absent or hypoplastic parathyroid and thyroid glands.

https://www.ncbi.nlm.nih.gov/pubmed/9514586
https://www.ncbi.nlm.nih.gov/pubmed/3728313

A variant of the DiGeorge phenotype, called Sprintzen or Velocardiofacial syndrome, also includes cleft palate.
https://www.ncbi.nlm.nih.gov/pubmed/272242

=== C.H.A.R.G.E Syndrome ===

*'''C'''oloboma
*'''H'''eart anomaly
*'''A'''tresia of choanae
*'''R'''etardation of physical and mental development
*'''G'''enital hypoplasia
*'''E'''ar anomalies and/or deafness

{{#pmid: PMC3389200|PMC3389200}}

The link between the chromatin-remodeling protein CHD7 with cardiac NCC-associated defects suggests that epigenetic regulation is important for genes controlling NCC function.

--> https://pdfs.semanticscholar.org/42cc/ee7fbb545ea6752e1c126cc2769e8e33e7b7.pdf

Mutations in the chromatin helicase DNA-binding protein 7(CHD7) gene are causative of CHARGE syndrome and loss-of-function

Neural crest cells contribute to these deformations and abnormalities of the tissues. How is because NC development involves many convoluted steps such as specification, delamination, migration, induction, and differentiation. These processes are controlled by regulatory gene networks. If certain genes are disrupted affecting the neural crest cells then a variety of human diseases arise categorized as neurocristopathies. CHARGE is an acronym for a collection of symptoms including, heart defects, retarded growth, and development, genital hypoplasia, ear anomalies, and deafness. CHARGE syndrome is a sporadic, autosomal dominant malformation disorder diagnosed in 1/8,500-1/10,000 live births. In addition, malformations of the foregut, kidneys, limbs, lung, and liver have been described in infants with CHARGE syndrome. The gene most commonly affected in patients with CHARGE syndrome is CHD7, which encodes a DNA binding protein involved in chromatin remodeling(reference here).

--> https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajmg.c.31584

==Models and Research==

=== Animal Models ===

* Main animal models are chicken, fish, and mice.

Chick embryo models: (to edit)

the chick embryo using quail-chick chimeras to study neural crest migration and derivatives as well as using ablation of premigratory neural crest cells to study their function. These studies show that cardiac neural crest cells are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

https://www.ncbi.nlm.nih.gov/pubmed/17224285

These studies show that after the cardiac neural crest cells migrate into pharyngeal arches 3, 4 and 6, a subset of the cells continue migrating into the cardiac outflow cushions.

<<insert image>>

https://www.ncbi.nlm.nih.gov/pubmed/3568286

Mouse models:

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}

2018 Group Project 4

2018-10-05T22:30:42Z

Z5229281: /* Cardiac Neural Crest Cells */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The neural crest (NC) was first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan.{{#pmid:29787146|PMID29787146}}The very first major system to develop its function within an embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself. Studies done in avian and fish embryos have shown that a specific subgroup of neural crest cells, known as cardiac neural crests, is essential for the septation of cardiac outflow track as well as the development of aortic arch artery. The studies have allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus <ref name="PMID29158447" />

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart which initially functions as a conduit for blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]
=== Outflow Septation ===
After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.
Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> . Currently, not much is known about which factors are responsible for attracting neural crest cells into the outflow tract cushions. Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks. Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}. The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

three components are responsible for forming the septa in the outflow tract:
# Conus Septum
# truncus Septum
# Aorto-Pulmonary Septum

--> https://www.sciencedirect.com/science/article/pii/B9780124017306000120
PMID: 26053665

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development.T he OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

that subsequent to the formation of the two arterial trunks, there was disappearance of the cushions that initially divided them. Thus, in the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum, possess their own discrete walls, separated by extra-cardiac space.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767797/

<<not edited>>

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that activate intracellular signaling pathways. The decrease of B-catenin results in a reduction in the proliferation of cardiac neural crest cells.
# '''Notch''': a transmembrane protein whose signaling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''FGF8'''(fibroblast growth factor 8): Transcription factors that are essential for regulating the addition of secondary heart field cells into the cardiac outflow tract.
# '''GATA''': Transcription factors which play a critical role in cell lineage differentiation restriction during cardiac development.

* Meis2 {{#pmid: PMC4636814 | PMC4636814 }}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but are involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

---- not yet edited----

Cardiac neural crest ablation experiments demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced.

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

===Conotruncal Heart Malformations ===

OFT remodeling is a process whereby the embryonic outﬂowtract undergoes a series of developmental transitions that involves extra cardiac cell recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus <ref name="PMID29920846" /> : if the cardiac neural crest is removed before it begins to migrate, the conotruncal septa completely fails to develop, and blood leaves both the ventricles through what is termed a persistent truncus arteriosus, a rare congenital heart anomaly in humans. (Martinson)
Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot (Martinson).

This is a defect on the NKX2 gene/locus

=== DiGeorge Syndrome and Velocardiofacial Syndrome ===

DiGeorge syndrome (DGS) is a condition that affects the development of many tissues that are patterned by or derived from NCCs. Thus, patients have variable types of craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, and OFT and aortic arch defects. Also known as velocardiofacial (Shprintzen) syndrome and conotruncal anomaly face (Takao) syndrome.<ref name="PMID29787146" />

* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

(to edit)
The DiGeorge syndrome consists of a PTA, type B interrupted aortic arch, absent or hypoplastic thymus, craniofacial dysmorphology and cognitive or behavioral disorders. (ref) It can also include absent or hypoplastic parathyroid and thyroid glands.

https://www.ncbi.nlm.nih.gov/pubmed/9514586
https://www.ncbi.nlm.nih.gov/pubmed/3728313

A variant of the DiGeorge phenotype, called Sprintzen or Velocardiofacial syndrome, also includes cleft palate.
https://www.ncbi.nlm.nih.gov/pubmed/272242

=== C.H.A.R.G.E Syndrome ===

*'''C'''oloboma
*'''H'''eart anomaly
*'''A'''tresia of choanae
*'''R'''etardation of physical and mental development
*'''G'''enital hypoplasia
*'''E'''ar anomalies and/or deafness

{{#pmid: PMC3389200|PMC3389200}}

The link between the chromatin-remodeling protein CHD7 with cardiac NCC-associated defects suggests that epigenetic regulation is important for genes controlling NCC function.

--> https://pdfs.semanticscholar.org/42cc/ee7fbb545ea6752e1c126cc2769e8e33e7b7.pdf

Mutations in the chromatin helicase DNA-binding protein 7(CHD7) gene are causative of CHARGE syndrome and loss-of-function

Neural crest cells contribute to these deformations and abnormalities of the tissues. How is because NC development involves many convoluted steps such as specification, delamination, migration, induction, and differentiation. These processes are controlled by regulatory gene networks. If certain genes are disrupted affecting the neural crest cells then a variety of human diseases arise categorized as neurocristopathies. CHARGE is an acronym for a collection of symptoms including, heart defects, retarded growth, and development, genital hypoplasia, ear anomalies, and deafness. CHARGE syndrome is a sporadic, autosomal dominant malformation disorder diagnosed in 1/8,500-1/10,000 live births. In addition, malformations of the foregut, kidneys, limbs, lung, and liver have been described in infants with CHARGE syndrome. The gene most commonly affected in patients with CHARGE syndrome is CHD7, which encodes a DNA binding protein involved in chromatin remodeling(reference here).

--> https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajmg.c.31584

==Models and Research==

=== Animal Models ===

* Main animal models are chicken, fish, and mice.

Chick embryo models: (to edit)

the chick embryo using quail-chick chimeras to study neural crest migration and derivatives as well as using ablation of premigratory neural crest cells to study their function. These studies show that cardiac neural crest cells are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

https://www.ncbi.nlm.nih.gov/pubmed/17224285

These studies show that after the cardiac neural crest cells migrate into pharyngeal arches 3, 4 and 6, a subset of the cells continue migrating into the cardiac outflow cushions.

<<insert image>>

https://www.ncbi.nlm.nih.gov/pubmed/3568286

Mouse models:

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}

2018 Group Project 4

2018-10-05T06:41:34Z

Z5229281: /* Outflow Septation */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The neural crest (NC) was first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan.{{#pmid:29787146|PMID29787146}}The very first major system to develop its function within an embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself. Studies done in avian and fish embryos have shown that a specific subgroup of neural crest cells, known as cardiac neural crests, is essential for the septation of cardiac outflow track as well as the development of aortic arch artery. The studies have allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}
{{#pmid:23481200}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus
{{#pmid:29158447}}

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart which initially functions as a conduit for blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]
=== Outflow Septation ===
After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}.
Cushion formation and septation rely on the interaction of 3 distinct cell types, cardiac neural crest cells (NCCs), second heart field-derived (SHF-derived) cells, and endothelial cells (ECs) <ref name="PMID26053665" /> . Currently, not much is known about which factors are responsible for attracting neural crest cells into the outflow tract cushions. Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks. Studies have shown that the TGFbeta/BMP signaling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}. The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

three components are responsible for forming the septa in the outflow tract:
# Conus Septum
# truncus Septum
# Aorto-Pulmonary Septum

--> https://www.sciencedirect.com/science/article/pii/B9780124017306000120
PMID: 26053665

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development.T he OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

that subsequent to the formation of the two arterial trunks, there was disappearance of the cushions that initially divided them. Thus, in the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum, possess their own discrete walls, separated by extra-cardiac space.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767797/

<<not edited>>

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that activate intracellular signaling pathways. The decrease of B-catenin results in a reduction in the proliferation of cardiac neural crest cells.
# '''Notch''': a transmembrane protein whose signaling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''FGF8'''(fibroblast growth factor 8): Transcription factors that are essential for regulating the addition of secondary heart field cells into the cardiac outflow tract.
# '''GATA''': Transcription factors which play a critical role in cell lineage differentiation restriction during cardiac development.

* Meis2 {{#pmid: PMC4636814 | PMC4636814 }}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but are involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

---- not yet edited----

Cardiac neural crest ablation experiments demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced.

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

===Conotruncal Heart Malformations ===

OFT remodeling is a process whereby the embryonic outﬂowtract undergoes a series of developmental transitions that involves extra cardiac cell recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus <ref name="PMID29920846" /> : if the cardiac neural crest is removed before it begins to migrate, the conotruncal septa completely fails to develop, and blood leaves both the ventricles through what is termed a persistent truncus arteriosus, a rare congenital heart anomaly in humans. (Martinson)
Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot (Martinson).

This is a defect on the NKX2 gene/locus

=== DiGeorge Syndrome and Velocardiofacial Syndrome ===

DiGeorge syndrome (DGS) is a condition that affects the development of many tissues that are patterned by or derived from NCCs. Thus, patients have variable types of craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, and OFT and aortic arch defects. Also known as velocardiofacial (Shprintzen) syndrome and conotruncal anomaly face (Takao) syndrome.<ref name="PMID29787146" />

* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

(to edit)
The DiGeorge syndrome consists of a PTA, type B interrupted aortic arch, absent or hypoplastic thymus, craniofacial dysmorphology and cognitive or behavioral disorders. (ref) It can also include absent or hypoplastic parathyroid and thyroid glands.

https://www.ncbi.nlm.nih.gov/pubmed/9514586
https://www.ncbi.nlm.nih.gov/pubmed/3728313

A variant of the DiGeorge phenotype, called Sprintzen or Velocardiofacial syndrome, also includes cleft palate.
https://www.ncbi.nlm.nih.gov/pubmed/272242

=== C.H.A.R.G.E Syndrome ===

*'''C'''oloboma
*'''H'''eart anomaly
*'''A'''tresia of choanae
*'''R'''etardation of physical and mental development
*'''G'''enital hypoplasia
*'''E'''ar anomalies and/or deafness

{{#pmid: PMC3389200|PMC3389200}}

The link between the chromatin-remodeling protein CHD7 with cardiac NCC-associated defects suggests that epigenetic regulation is important for genes controlling NCC function.

--> https://pdfs.semanticscholar.org/42cc/ee7fbb545ea6752e1c126cc2769e8e33e7b7.pdf

Mutations in the chromatin helicase DNA-binding protein 7(CHD7) gene are causative of CHARGE syndrome and loss-of-function

Neural crest cells contribute to these deformations and abnormalities of the tissues. How is because NC development involves many convoluted steps such as specification, delamination, migration, induction, and differentiation. These processes are controlled by regulatory gene networks. If certain genes are disrupted affecting the neural crest cells then a variety of human diseases arise categorized as neurocristopathies. CHARGE is an acronym for a collection of symptoms including, heart defects, retarded growth, and development, genital hypoplasia, ear anomalies, and deafness. CHARGE syndrome is a sporadic, autosomal dominant malformation disorder diagnosed in 1/8,500-1/10,000 live births. In addition, malformations of the foregut, kidneys, limbs, lung, and liver have been described in infants with CHARGE syndrome. The gene most commonly affected in patients with CHARGE syndrome is CHD7, which encodes a DNA binding protein involved in chromatin remodeling(reference here).

--> https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajmg.c.31584

==Models and Research==

=== Animal Models ===

* Main animal models are chicken, fish, and mice.

Chick embryo models: (to edit)

the chick embryo using quail-chick chimeras to study neural crest migration and derivatives as well as using ablation of premigratory neural crest cells to study their function. These studies show that cardiac neural crest cells are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

https://www.ncbi.nlm.nih.gov/pubmed/17224285

These studies show that after the cardiac neural crest cells migrate into pharyngeal arches 3, 4 and 6, a subset of the cells continue migrating into the cardiac outflow cushions.

<<insert image>>

https://www.ncbi.nlm.nih.gov/pubmed/3568286

Mouse models:

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}

2018 Group Project 4

2018-10-05T06:36:10Z

Z5229281: /* Formation of Pharyngeal Arches and Cardiac Outflow Tract */

{{2018ANAT2341ProjectHeader}}

=Neural Crest and Cardiac Development=

'' Introduction ''

The neural crest (NC) was first identified by Wilhelm His as “Zwischenstrang,” the intermediate cord, in 1868, the year of Meiji Ishin, the westernizing revolution of Japan.{{#pmid:29787146|PMID29787146}}The very first major system to develop its function within an embryo is the cardiovascular system with the heart becoming active from the fourth week of development when the placenta is no longer able to sustain the requirements of the growing embryo by itself. Studies done in avian and fish embryos have shown that a specific subgroup of neural crest cells, known as cardiac neural crests, is essential for the septation of cardiac outflow track as well as the development of aortic arch artery. The studies have allowed for the classification of neural crest associated human cardiac defects such as DiGeorge syndrome.

''Development of the Cardiovascular System''

Development of the cardiovascular system begins with the formation of two endocardial tubes that merge together to form the tubular heart. These loop together and separate into the four chambers and paired arterial trunks form the adult heart. The tubular heart differentiates into the truncus arterioles, bulbus cordis, primitive ventricle, primitive atrium and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation. Septa form within the atria and ventricles to separate the left and right sides of the heart.

<html5media width="480" height="358">https://www.youtube.com/embed/5DIUk9IXUaI</html5media>

{| class = "pretty table"
|-
| Week 2 - 3
|*Bilateral cardiogenic areas form
|-
| Week 3 - 4
|
*Mesoderm splitting
* Folding brings heart tubes into the ventral midline
* Heart tube fusion
* Heart tube begins to beat
|-
| Week 4 - 5
|
* Heart looping
* Neural crest migration starts
* Dorsal and ventral endocardial cushions fused
* Foramen premium closed, septum secundum begins to develop
|-
| Week 5-6
|
* Deep, muscular interventricular septum
* Bulbar ridges and trabeculations evident
|-
| Week 7
|
* Aortic and pulmonary trunks cleave
* Valves developed
|}

== Cardiac Neural Crest Cells ==

Neural crest cells are a population of multipotent cells which arises during embryonic development at the dorsal neural tube. Neural crest cells originate from the dorsal-most region of the neural tube. These cells are capable of migrating and differentiating throughout the body to give rise to many different cell types. Cardiac neural crest cells (CNCCs) are a subpopulation of the cranial neural crest cells and migrate ventrally from the dorsal neural tube {{#pmid:PMC4288758|PMC4288758}}. CNCCs will then proceed and fall in place into third, fourth and the sixth caudal pharyngeal arches as they develop during their migration to the cardiac outflow tract. They will form condensed mesenchymal cells of the aorticopulmonary septation complex and also differentiate into cardiac ganglia{{#pmid:23481200|PMID:23481200}}.NCCs are necessary for aortic arch artery remodeling and outflow tract septation (OFT). {{#pmid:29158447|PMID29158447}}
{{#pmid:23481200}}

Cardiac neural Cells can develop into:
* Melanocytes near the heart region
* neurons associated with cardiac innervation
* cartilage
* connective tissue (they form the connective tissue wall of the large arteries from the heart, as well as the septum between the branches in the heart)
* provide signals required for the maintenance and differentiation of the other cell layers in the pharyngeal apparatus
{{#pmid:29158447}}

==Early Development ==

=== Induction ===

Initially, NCCs are morphologically similar to other neuroepithelial cells and cannot be differentiated from them. With contact-mediated inductive signals from the surface ectoderm and underlying mesoderm through a process known as Induction where progenitor cells begin to differentiate {{#pmid:PMC3552505|PMC3552505}}. Progenitor cells are found in the epiblast around Henson's node and are brought into the neural folds where signalling molecules will induce the progenitor cells to turn into CNCCs {{#pmid:PMC3552505|PMC3552505}}. While key signalling regulators of neural crest cell formation such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) have been identified in species such as fish and avians, there is currently no evidence that suggests the same factors play a role in mammalian neural crest cell induction, thus more studies have to be carried out to identify the signaling pathway for mammalian neural crest cell formation {{#pmid:PMC3552505|PMC3552505}}. Studies have also shown that if BMP levels are too high or low, the progenitor cells will not be able to migrate, thus an intermediate level of BMP is ideal for the induction process.{{#pmid:PMC3011257|PMC3011257}} As for the other signaling cascades involved, little information is known.

=== Migration From Neural Crest to Circumpharyngeal Ridge ===

After the Induction process, cranial neural crest cells undergo an epithelial-to-mesenchymal transition and emigrate from the neural tube to the circumpharyngeal ridge which is an arc-shaped ridge structure that is found dorsal to developing caudal pharyngeal arches {{#pmid:PMC3011257|PMC3011257}}. In higher vertebrates, cranial neural crest cells will migrate in three clusters (cranial, middle and caudal) and eventually develop cranial nerve ganglia at even-numbered rhombomeres proximally and populate pharyngeal arches distally. The caudal stream comprises most of the CNCCs.

There are multiple signaling factors which control the migration of CNCCs.
*Snail2 inhibits the expression of cadherins and studies on avians and fish have shown that the presence of Snail2 helps to facilitate cell migration {{#pmid:PMC2595139|PMC2595139}}. However, the expression of Snail does not seem to be needed for the neural crest induction in mammals {{#pmid:PMC3552505|PMC3552505}}.
*RhoA/B, a GTPase protein, regulates and remodels the actin cytoskeleton of the cells to alter the planar cell polarity to allow neural crest migration {{#pmid:PMC3011257|PMC3011257}}.
*CNCC expresses integrin receptors and MMP-2 to allow them to migrate on fibronectin in extracellular matrix which is believed to provide a permissive environment to allow the migration of crest cells to the circumpharyngeal ridge {{#pmid:PMC3011257|PMC3011257}}.

=== Formation of Pharyngeal Arches and Cardiac Outflow Tract ===

The Cardiac Outflow Tract (OFT) is a transient embryonic structure located at the arterial pole of the heart which initially functions as a conduit for blood flowing from the right ventricle into the aortic sac.{{#pmid:26053665|PMID26053665}}.

CNCCs will initially pause their migration at the circumpharyngeal ridge as their destined pharyngeal arches have not been developed. The pericardial cavity will regress caudally, allowing pharyngeal pouches to indent the body wall and delineate the pharyngeal arches from the cranial to the caudal direction and generate arches (3, 4 and 6). As the arches develop, they will be populated by cardiac neural crest cells which migrates from the circumpharyngeal ridge.

CNCCs express different factors that target the cells to the pharyngeal arches. Slit cells can target cells to migrate to arch 3. FGF-8 targets for arch 4. EphA targets for arch 6. Rac1 and Sdf1 are both expressed in the cells, causing them to condensate around the arch arteries.
Semaphorin is expressed and causes the cells to migrate further to the cardiac outflow tract. Notch and BMP are then expressed condensing the cells, forming the semilunar valve and aorticopulmonary septum.
* The 3rd arch is dedicated in the formation of the carotid system. It forms the left and right common carotid arteries which will sprout into internal and external carotid arteries by angiogenesis {{#pmid:PMC4199908|PMC4199908}}.
* The 4th arch gives rise to the definitive aortic arch along with the pulmonary artery.
* The 6th arch initially develops into the pulmonary trunk that emerges from the right ventricles, but this structure will be remodeled asymmetrically and gives rise to the ductus arteriosus which is a crucial embryonic structure that connects the pulmonary artery with the descending aorta for blood circulation in the fetus. This shunt allows blood from the right ventricle to bypass the lungs because the fetal blood is oxygenated through the placenta. At birth, as the lungs start their function, the ductus arteriosus closes allowing circulation through to the lungs to oxygenate the blood that subsequently reaches the systemic circulation of the newborn {{#pmid:PMC4199908|PMC4199908}}.

Ectomesenchyme that is derived from CNCCs in pharyngeal arches 3, 4 and 6 are critical for the repatterning of the bilaterally symmetrical pharyngeal arch arteries to form the asymmetric great arteries of the thorax.

Migration of cardiac neural crest cells from the neuroectoderm into the outflow tract cushions
induces the formation of the aortopulmonary (AP) septum, which divides the common outflow tract
at the cardiac to vascular border into an aortic and pulmonary orifice and more proximally
intracardiac into a right and left ventricular outflow tract. {{#pmid:30242109|PMID:30242109}}

==Later Development==
[[File:Progressive development of the Embryonic Heart.jpeg|thumb|Development of the heart in the fetus and partitioning of the heart into four chambers]]
=== Outflow Septation ===
After migrating into the pharynx, some CNCCs will remain in the pharyngeal arches while the rest would continue and migrate into cardiac outflow cushions which converges to separate blood flow from the embryonic left and right ventricles {{#pmid:PMC4288758|PMC4288758}}. Currently, not much is known about which factors are responsible for attracting neural crest cells into the outflow tract cushions. Within the cushions, the CNCCs will condense and form the aorticopulmonary septation complex which is essentially two centrally placed columns and divides the common arterial outflow into the aorta and pulmonary trunks. Studies have shown that the TGFbeta/BMP signalling family is involved in this condensation process{{#pmid:PMC3011257|PMC3011257}}. The cushions will be populated with three main types of mesenchymal cells, depending on their proximal-distal location in the outflow tract {{#pmid:PMC4288758|PMC4288758}}.

three components are responsible for forming the septa in the outflow tract:
# conus septum
# truncus septum
# aorto-pulmonary septum

--> https://www.sciencedirect.com/science/article/pii/B9780124017306000120

===Valvulogenesis ===

The majority of heart defects in live births arise from disruption of cardiac outﬂow tract development.T he OFT is an embryonic structure that gives rise to the ascending aortic and pulmonary arteries as well as their respective tricuspid aortic (AV) and pulmonary (PV) valves.{{#pmid:29920846|PMID29920846}}.The cNCC also contribute to the aortic and pulmonary valves, thereby connecting the heart to the vascular system. OFT endothelial cells that have undergone endoMT are thought to give rise to the bulk of the semilunar valves, which form within the aorta and pulmonary artery, to prevent the backflow of blood into the ventricles. In addition, cardiac NCCs also colonize the semilunar valves, where they mainly contribute to the two leaflets adjacent to the aorticopulmonary septum. Cells of the NCC have also been found to contribute to the atrioventricular valves, consisting of the bicuspid (mitral) valve and tricuspid valve, which is located between the upper atria and the lower ventricles.

===Atrial and Ventricular Separation===

that subsequent to the formation of the two arterial trunks, there was disappearance of the cushions that initially divided them. Thus, in the definitive heart, the proximal parts of the aorta and pulmonary trunk, along with the sinuses of the arterial roots and the subpulmonary infundibulum, possess their own discrete walls, separated by extra-cardiac space.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767797/

<<not edited>>

=== Formation of the Cardiac Ganglia ===

Cardiac ganglia are made entirely from cardiac crest cells.

"Virtually nothing is known about the factors that control their separation from the cardiac crest forming the aorticopulmonary septum or their condensation as ganglia. However, cardiac crest cells also participate in the formation of the nodose ganglion. This is the distal sensory ganglion of the vagus nerve. The nodose ganglion is formed from neurons derived from the nodose placode located dorsal to pharyngeal arches 4/6. Cells migrate from this placode to coalesce with cardiac crest to form the nodose ganglion. Condensation of this ganglion depends on N-cadherin and signaling by Slit/Robo signaling. In cranial crest Slit1/Robo signaling in conjunction with N-cadherin is important for coalescence of crest cells and placode-derived neurons into ganglia. N-cadherin and Robo2 are expressed by placodal neurons and Slit1 is on neural crest cells. If either N-cadherin or Robo2 is knocked down, the ganglia do not coalesce properly.115"

{{#pmid:PMC3011257|PMC3011257}}

== Signaling Molecules ==

# '''Wnt''': extracellular growth factors that activate intracellular signaling pathways. The decrease of B-catenin results in a reduction in the proliferation of cardiac neural crest cells.
# '''Notch''': a transmembrane protein whose signaling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes.
# '''BMP''' (bone morphogenetic proteins): they are required for neural crest cell migration into the cardiac cushions (=precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries.
# '''FGF8'''(fibroblast growth factor 8): Transcription factors that are essential for regulating the addition of secondary heart field cells into the cardiac outflow tract.
# '''GATA''': Transcription factors which play a critical role in cell lineage differentiation restriction during cardiac development.

* Meis2 {{#pmid: PMC4636814 | PMC4636814 }}

== Developmental Time Course ==

{| class = "pretty table"
|-
| Week 3-4
| Day 22-28
| Neural crest migration starts
|-
| Week 5-6
| Day 32-37
| Cardiac neural crest migrates through the aortic arches and enters the outflow tract of the heart
|-
| Week 9
| Day 57+
| Outflow tract and ventricular septation complete
|}

==Human Congenital Heart Diseases associated with Neural Crest Cells==

The loss of neural crest cells or their dysfunction may not always directly cause abnormal cardiovascular development, but are involved secondarily because crest cells represent a major component in the complex tissue interactions in the head, pharynx and outflow tract. {{#pmid:22595346|PMID22595346}}

---- not yet edited----

Cardiac neural crest ablation experiments demonstrated that upon removal of the pre-migratory cardiac neural crest cardiovascular abnormalities are induced.

that the quantity rather than the quality of neural crest cells is important in OFT septation.

Furthermore, cardiac malformations associated with partial ablation of the cardiac neural crest, show normal formation of the aorticopulmonary septum and as a result an aorta and a pulmonary trunk. However, the aorta and pulmonary trunk are malaligned with respect to the ventricles. One might argue that the neural crest-derived cells are not only crucial in the regulation of septation but also in the alignment of the great arteries with respect to the ventricles. On the other hand, one might argue that the malalignment is due to an indirect effect of neural crest ablation.
https://academic.oup.com/cardiovascres/article/47/2/212/363634
----End of unedited part----

===Conotruncal Heart Malformations ===

OFT remodeling is a process whereby the embryonic outﬂowtract undergoes a series of developmental transitions that involves extra cardiac cell recruitment and transformations that when disrupted, can result in Persistent Truncus Arteriosus <ref name="PMID29920846" /> : if the cardiac neural crest is removed before it begins to migrate, the conotruncal septa completely fails to develop, and blood leaves both the ventricles through what is termed a persistent truncus arteriosus, a rare congenital heart anomaly in humans. (Martinson)
Failure of outflow tract septation may also be responsible for other forms of congenital heart disease, including transposition of the great vessels, high ventricular septal defects, and tetralogy of Fallot (Martinson).

This is a defect on the NKX2 gene/locus

=== DiGeorge Syndrome and Velocardiofacial Syndrome ===

DiGeorge syndrome (DGS) is a condition that affects the development of many tissues that are patterned by or derived from NCCs. Thus, patients have variable types of craniofacial defects, aplasia or hypoplasia of the thymus and parathyroid glands, and OFT and aortic arch defects. Also known as velocardiofacial (Shprintzen) syndrome and conotruncal anomaly face (Takao) syndrome.<ref name="PMID29787146" />

* Caused by a chromosomal 22q11.2 deletion.
* a hemizygous deletion within chromosome band 22q11.2 has been found in 25% of DGS patients.
* Characterized by interrupted aortic arch type B, outflow tract malformations that include xxx

<ref name="PMID22595346" />

(to edit)
The DiGeorge syndrome consists of a PTA, type B interrupted aortic arch, absent or hypoplastic thymus, craniofacial dysmorphology and cognitive or behavioral disorders. (ref) It can also include absent or hypoplastic parathyroid and thyroid glands.

https://www.ncbi.nlm.nih.gov/pubmed/9514586
https://www.ncbi.nlm.nih.gov/pubmed/3728313

A variant of the DiGeorge phenotype, called Sprintzen or Velocardiofacial syndrome, also includes cleft palate.
https://www.ncbi.nlm.nih.gov/pubmed/272242

=== C.H.A.R.G.E Syndrome ===

*'''C'''oloboma
*'''H'''eart anomaly
*'''A'''tresia of choanae
*'''R'''etardation of physical and mental development
*'''G'''enital hypoplasia
*'''E'''ar anomalies and/or deafness

{{#pmid: PMC3389200|PMC3389200}}

The link between the chromatin-remodeling protein CHD7 with cardiac NCC-associated defects suggests that epigenetic regulation is important for genes controlling NCC function.

--> https://pdfs.semanticscholar.org/42cc/ee7fbb545ea6752e1c126cc2769e8e33e7b7.pdf

Mutations in the chromatin helicase DNA-binding protein 7(CHD7) gene are causative of CHARGE syndrome and loss-of-function

Neural crest cells contribute to these deformations and abnormalities of the tissues. How is because NC development involves many convoluted steps such as specification, delamination, migration, induction, and differentiation. These processes are controlled by regulatory gene networks. If certain genes are disrupted affecting the neural crest cells then a variety of human diseases arise categorized as neurocristopathies. CHARGE is an acronym for a collection of symptoms including, heart defects, retarded growth, and development, genital hypoplasia, ear anomalies, and deafness. CHARGE syndrome is a sporadic, autosomal dominant malformation disorder diagnosed in 1/8,500-1/10,000 live births. In addition, malformations of the foregut, kidneys, limbs, lung, and liver have been described in infants with CHARGE syndrome. The gene most commonly affected in patients with CHARGE syndrome is CHD7, which encodes a DNA binding protein involved in chromatin remodeling(reference here).

--> https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajmg.c.31584

==Models and Research==

=== Animal Models ===

* Main animal models are chicken, fish, and mice.

Chick embryo models: (to edit)

the chick embryo using quail-chick chimeras to study neural crest migration and derivatives as well as using ablation of premigratory neural crest cells to study their function. These studies show that cardiac neural crest cells are absolutely required to form the aorticopulmonary septum dividing the cardiac arterial pole into systemic and pulmonary circulations. They support the normal development and patterning of derivatives of the caudal pharyngeal arches and pouches, including the great arteries and the thymus, thyroid and parathyroids.

https://www.ncbi.nlm.nih.gov/pubmed/17224285

These studies show that after the cardiac neural crest cells migrate into pharyngeal arches 3, 4 and 6, a subset of the cells continue migrating into the cardiac outflow cushions.

<<insert image>>

https://www.ncbi.nlm.nih.gov/pubmed/3568286

Mouse models:

=== Research ===
* Can cardiac neural crest cells be used to repair human heart tissue? They are basically neural crest stem cells. In 2005, Tomita transplanted neural crest cells from mammal hearts to the neural crest of chick embryos --> find more research for this
* What is the contribution of the cardiac NCCs to the myocardium and conduction system of the heart.

==Glossary==

:'''[[#Number|Number]] | [[#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]]'''

==References==

{{#pmid:29787146}}
{{#pmid:29158447}}