Introduction

The neural crest segregates from the tips of the neural folds just before or shortly after they fuse to give rise to the neural tube. Prior to their migration, neural crest cells are an integral part of the neuroepithelium. Thanks to a morphogenetic conversion that causes these epithelial progenitors to become mesenchymal, the neural crest cells become motile and engage in migration. This process, which is highly complex both in space and time, leads the cells through defined pathways until reaching their final homing sites.

Research during the past years has made use of sensitive techniques (described in Chapter 1) to track the movements of these progenitors in relation to the equally dynamic neighboring structures. These studies have clarified the timing and pathways of migration of neural crest cells and related these parameters with their ultimate fate. At the same time, they raised fundamental questions as to the molecular mechanisms that regulate migration. Some examples are the as yet uncovered molecular cascade leading to the detachment of neural crest cells from the neuroepithelium and the factors that control the onset and arrest of migration, respectively.

A general problem about the mechanisms that control the migration of neural crest cells concerns the relationship that may exist between the directionality of migration and the degree of cell specification.