Neural Crest  - Development and Stem Cells

Embryonic and Postnatal Development of the Neural Crest:

Mammalian neural crest cells are a multipotent migratory stem cell population that generates an impressively broad array of cell and tissue types during development. Neural crest cells are of ectodermal origin and only exist in vertebrates. Because of their significant contribution to the cellular diversity in vertebrates and their unique features, some view the neural crest as a fourth germ layer (in addition to the ectoderm, mesoderm and endoderm).

Murine neural crest cells are transiently generated along almost the entire vertebrate axis at neural plate border, which is the interface between the surface ectoderm and the neural plate of the embryo. During this induction process, neuroepithelial cells undergo an epithelial-to-mesenchymal transformation (EMT), at which point they delaminate and begin to migrate from the neural tube to the periphery.  During a narrow time window after migration, the four rostro-caudal axial level populations are induced: cranial (head), cardiac, vagal and trunk neural crest cells.  Each population later contributes to specific cells and tissue types. Most of the neural crest cell progenitors differentiate to the various tissues during the early postnatal period of the organism. In adults, only some neural crest stem cells will persists to function and replenish associated tissues. 

Murine neural crest cell migration commences at the ~4–5 somite stage, in the region of the caudal midbrain and rostral hindbrain and proceeds as a rostral- caudal wave. In mammalian embryos, neural crest cell migration begins well before neural tube closure, while in avian embryos, it commences only after its closure (HH stage 8-9). Usually, there is a narrow time window within which neural crest cells are induced to delaminate and emigrate from the dorsal neural tube; in mice this process typically persists 7–9 hours for each of the four rostro-caudal axial level populations.

Functions of the Neural Crest:

Multiple types of neural tissues arise from the neural crest, including sympathetic ganglia, parasympathetic ganglia, spinal ganglia and the enteric nervous system. Non-neural cells derived from the neural crest include melanocytes, satellite cells of ganglia, Schwann cells and the adrenal medulla.

The cranial neural crest (CNC) differs from trunk neural crest in their potential to differentiate into craniofacial cartilage and bone elements (bones of the skull vault and cartilage of the cranial base), along with their ability to give rise to dermis, fat, smooth muscle of skin, dental papilla and meninges. The cardiac neural crest  contribute to smooth muscle cells of the heart outflow tract and its septum, walls of aortic and arch-derived arteries, all of the parasympathetic innervation of the heart and the connective tissue of the glands in the head and neck regions.