Molecular regulation of neural crest development.

The neural crest is a transient embryonic structure that gives rise to a multitude of different cell types in the vertebrate. As such, it is an ideal model to study the processes of vertebrate differentiation and development. This review focuses on two major questions related to neural crest development. The first question concerns the degree and time of commitment of the neural crest cells to different cell lineages and the emerging role of the homeobox containing genes in regulating this process. Evidence from the cephalic crest suggests that the commitment process does start before the neural crest cells migrate away from the neural tube and gene ablation experiments suggest that different homeobox genes are required for the development of neural and mesenchymal tissue derivatives. However, clonal analysis of neural crest cells before migration suggests that many of the cells remain multi-potential indicating that the final determinative steps occur progressively during migration and in association with environmental influences. The second question concerns the nature of the environmental factors that determine the differentiation of neural crest cells into discrete lineages. Evidence is provided, mainly from in vitro experiments, that purified growth factors selectively promote the differentiation of neural crest cells down either sympathetic, adrenal, sensory, or melanocytic cell lineages.