Neural crest

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Neural crest
Two stages in the development of the neural crest in the human embryo.
Gray's	subject #184 736
Carnegie stage	9
Precursor	ectoderm
MeSH	Neural+Crest

The neural crest, a component of the ectoderm, is found in between the neural tube and the epidermis of an embryo. Neural crest cells quickly leave this during or shortly after neurulation

It has been referred to as the fourth germ layer, due to its great importance. The neural crest can give rise to neurons and glia of the peripheral nervous system (PNS), skeletal and smooth muscle, chondrocytes, osteocytes, melanocytes, chromaffin cells, and supporting cells and hormone producing cells in certain organs.

Contents 1 Nomenclature 2 Induction 3 Categories 3.1 Cranial neural crest 3.2 Vagal and sacral neural crest 3.3 Trunk neural crest 3.4 Cardiac neural crest 4 Migration 5 Plasticity 6 See also 7 External links

[edit] Nomenclature

The nomenclature of these cells derives from avian studies which demonstrate migration from the neural crest which forms on the rostral region of the ectoderm in the trilaminar disc.

In humans, the cells actually migrate from the lateral margins of the neural tube however the use of 'crest cells' in this regard is retained.

[edit] Induction

Cells fated to become neural crest tissue are induced by BMP, Wnt and FGF signaling to express the proteins Fox3D, RhoB and Slug, and to lose expression of E-cadherin.

• RhoB is likely to signal cytoskeletal changes required for migration.
• Slug is a repressor that leads to an activation of factors that dissociate tight junctions.

[edit] Categories

There are four main categories of neural crest based upon function:

[edit] Cranial neural crest

• The cranial neural crest arises in the anterior and populates the face and the pharyngeal arches giving rise to bones, cartilage, nerves and connective tissue.

Other Migration Locations:

• Into the pharyngeal arches and play an inductive in thymus development.
• Into the pharyngeal arches and form the parafollicular cell or ultimobranchial bodies of the thyroid gland.
• Into the pharyngeal arches and play an inductive role in parathyroid gland development.
• Facial ectomesenchyme of the pharyngeal arches forming skeletal muscle, bone, and cartilage in the face.
• Odontoblasts (dentin-producing cells) of the teeth.
• Into the optic vesicle and the developing eye and contributes to many anterior eye elements such the cornea, sclera, and ciliary muscle. It also contributes to the attaching skeletal muscles of the eye.
• Into the otic placode and participates in the inner ear development.
• Sensory ganglia of the fifth, seventh, ninth and tenth cranial nerves.

[edit] Vagal and sacral neural crest

• The vagal and sacral neural crest arises in the neck and tail and populates the gut, forming the parasympathetic neurons that regulates peristalsis and control blood vessel dilation.

Other Migration Locations:

• Walls of the viscera to become enteric ganglia.

[edit] Trunk neural crest

• The trunk neural crest lies between the vagal and sacral neural crest and gives rise to two groups of cells. One group migrates dorsolateral and populates the skin, forming pigment cells and the other migrates ventrolateral through the anterior sclerotome to become the epinephrine-producing cells of the adrenal gland and the neurons of the sympathetic nervous system. Some cells remain in the sclerotome to form the dorsal root ganglia

Other Migration Locations:

• Proximal to the spinal cord and line up symmetrically to form the dorsal root ganglia.
• Into the skin to form melanocytes and Merkel cells.
• Chromaffin cells of the adrenal medulla.
• Near the vertebral column and become sympathetic chain ganglia.

[edit] Cardiac neural crest

• The cardiac neural crest overlaps the vagal neural crest and migrates to populate the pharyngeal arches 3, 4 and 6 (producing structures in the head) and to the heart, forming connective tissue that separates the great vessels of the heart.

Other Migration Locations:

• Into the pharyngeal arches and Truncus arteriosus (embryology), forming the aorticopulmonary septum and the smooth muscle of great arteries.
• Anterior of the aorta to become the four pre-aortic ganglia (celiac ganglion, superior mesenteric ganglion, inferior mesenteric ganglion and aortical renal ganglia)

[edit] Migration

Neural crest cells require extracellular matrix to migrate through interactions between integrins and fibronectin and laminin. Migration is directed by inhibitory and attractive signals from cells. Ephrin is an inhibitory ligand in posterior sclerotome that affects ventral pathway trunk neural crest cells and causes them to migrate through the anterior sclerotome instead. Thrombospondin promotes migration through the anterior sclerotome. Another signal, stem cell factor is involved in specifying the destination of migration. If expressed in the wrong locations, pigment cells migrate to that site and proliferate there.

[edit] Plasticity

Neural crest cells show varying degrees of plasticity. Some trunk neural crest cells are pluripotent. Cranial neural crest cells can give rise to trunk neural crest cells if transplanted. However, heart neural crest cells are committed before migration. Individual neural crest cells can take on a new fate, however groups of neural crest cells cannot.

[edit] See also

• Neural plate

[edit] External links

• Embryology at UNSW Notes/ncrest
• NeuroNames ancil-445
• Diagram at umich.edu
• Hox domains in chicks