ADHESION MOLECULES IN NEURAL CREST DEVELOPMENT

Peripheral nerve cells, various endocrine and pigment cells and crania l connective tissue cells of vertebrates stem mainly from the embryoni c neural crest. This originates with the central nervous system, but t he crest cells detach from this tissue, via a decrease of cell-cell ad hesion involving, particularly, a reduction of the adherens junction c ell adhesive molecule A-CAM, This epithelio-mesenchymal transformation allows crest cells to migrate along pathways that are defined partly by the distribution of substrate adhesion molecules, the archetype bei ng fibronectin, an extracellular matrix molecule recognized by integri n receptors on crest cells. Many other molecules, however, may act in the same way. In contrast, some molecules may define migration pathway s by reducing adhesion; chondroitin sulfate proteoglycan is a candidat e for this role. Pathway selection is most likely achieved by balanced combinations of molecules that promote and reduce adhesion. Cessation of migration, in the case of the nervous ganglia, correlated with re- expression of cell-cell adhesion molecules like A-CAM and others, cons istent with an adhesive basis, although functional tests have not yet been performed. The development of the neural crest system provides a useful model that emphasizes the role of adhesion in morphogenesis.