neural crest

Neural crest
Two stages in the development of the neural crest in the human embryo.
Gray's	subject #184 736
Carnegie stage	9
Days	24
Precursor	ectoderm
MeSH	Neural+Crest

The neural crest, a transient component of the ectoderm, is located in between the neural tube and the epidermis (or the free margins of the neural folds) of an embryo during neural tube formation. Neural crest cells quickly migrate during or shortly after neurulation, an embryological event marked by neural tube closure.

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 autonomic nervous system (ANS); some skeletal elements, tendons and smooth muscle; chondrocytes, osteocytes, melanocytes, chromaffin cells, and supporting cells and hormone producing cells in certain organs.

Clinical significance

Diseases due to defects in the neural crest induction, formation or migration are referred to as neurocristopathies, and genes that cause some of these like piebaldism and Hirschprung's disease have been cloned in mice models.

History and Nomenclature

In 1868 Wilhelm His described Neural Crest as "zwischenstrang"- a strip of cells lying between the dorsal ectoderm and the neural tube.^[1]

From this time until the 1950s, most of the work on this structure was done on amphibian embryos, as in a 1950 comprehensive review in a monograph by the Swedish embryologist Sven Hörstadius.^[2] Newth (who also studied it in fishes)^[3] in 1951 described it as "a remarkable embryonic structure".

In 1960s with the invention of cell labeling with tritiated thymidine by Chibon^[4] and Weston^[5] gave rise to a major breakthrough in this field through amphibian and avian studies. But this was a transient method of cell labeling and the field had to wait for the chick-quail transfer studies for a definitive confirmation of those results. These extensive works in 1970s was reviewed extensively in "the Neural Crest" by Nicole Le Douarin, first published in 1982.^[6]

The nomenclature of these cells derives from amphibian and avian studies which demonstrate migration from the neural crest which forms on the rostral region of the neurulating 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.

Induction

Cells fated to become neural crest tissue are induced by BMP, Wnt and FGF signaling to express the proteins FoxD3, RhoB and Snail, and to lose expression of E-cadherin.

• RhoB is likely to signal cytoskeletal changes required for migration. ^[7]
• Snail is a repressor^[8] that leads to an activation of factors that dissociate tight junctions.

Categories

There are several main categories of neural crest based upon function:^[9]

Some sources group it into two main categories, "cranial" and "trunk", with "cardiac" being a subcategory of cranial that migrates.^[10] Other sources include a category "vagal and sacral".^[11]

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.

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.

Trunk neural crest

The trunk neural crest lies between the vagal and sacral neural crest.

Cardiac neural crest

The cardiac neural crest develops from the dorsal neural tube.

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.

Plasticity

Neural crest cells show varying degrees of plasticity. Cranial neural crest cells can give rise to trunk neural crest derivatives if transplanted. However, heart neural crest cells are committed before migration.

See also

• Neural plate
• DGCR2 - may control neural crest cell migration

References

External links

• Embryology at UNSW Notes/ncrest
• NeuroNames ancil-445
• Diagram at University of Michigan
• Hox domains in chicks