Mechanisms of early neural crest development: from cell specification to migration.

The neural crest is a group of embryonic progenitors that forms during the process of neurulation by interactions that take place between the prospective epidermis and the specified neuroectoderm. Although initially an integral part of the neuroepithelium, neural crest cells separate from the central nervous system primordium by a process of epitheliomesenchymal transition and become a motile cell population. These mesenchymal cells then migrate through stereotypic pathways, some of which are common and others unique to various vertebrate species. Furthermore, the availability of distinct migratory pathways also differs according to embryonic stage and axial level. Studies have begun to address the molecular basis of neural crest specification, delamination, and migration. The present review summarizes some major advances in our understanding of the nature of the intercellular interactions and the molecules that mediate them during early phases of neural crest ontogeny.