General Introduction

Summary

Although the neural crest is a discrete structure which comprises only a few cells and exists transiently in the early embryo, it embodies most of the crucial issues of developmental biology. Its highly pluripotent component cells yield an astonishing variety of cell types: from bones, tendons, connective and adipose tissues, and dermis to melanocytes, neurons of many kinds, glial, and endocrine cells. The neural crest forms according to a rostrocaudal gradient along the body axis and releases free-moving mesenchymal-like cells that follow definite migration routes at precise times of development, finally reaching target embryonic sites where they settle and differentiate. What triggers this migratory behavior? Which signals do these cells require to move along these definite pathways and what causes them to stop and accumulate? These are among the most puzzling problems raised by morphogenesis, problems that go beyond embryology and concern the stability of the histiotypic state and its disruption in metastasis.

The neural crest was first described in the chick embryo by His (1868) as a “Zwisehenstrang,” a strip of cells lying between the dorsal ectoderm and the neural tube. This observation prompted a number of studies, essentially performed in the amphibian embryo, which provided the grounds for the first recognition of the neural crest as a “remarkable embryonic structure” designated as such by Newth (1951).