Cell-adhesion and substrate-adhesion molecules: their instructive roles in neural crest cell migration.

The individualization of crest cells from the neural folds and neural tube involves distinct mechanisms affecting both the tissue shape and the cell environment. Though these mechanisms are not fully understood at the molecular level, the analysis of the distribution of several molecules reported to promote intercellular contacts indicates a correlation between cell detachment from the neurepithelium and the decrease of cell adhesion molecule expression. During the following phase of migration, the mode of adhesion of crest cells switches preferentially to the cell-to-substratum type. Various experiments showed that among the major extracellular matrix components, fibronectins were decisive in promoting cell attachment, spreading and motility. Additional studies on receptors for fibronectins gave new insights on the differences between a motile and a stationary cell. These results will be discussed with particular reference to the migration at the cephalic level where most perturbation experiments were performed. The molecular biology of fibronectins provided a finer understanding of the interactions between a cell and these molecules. The tools derived from this technique will open new areas of investigation hopefully leading to a better understanding of (i) the regulation of the cell-fibronectins interaction and (ii) the specificity of the pathways of migration followed by migrating cells, like the descendants of the neural crest.