Cell fate and gene expression in the developing neural crest

Our laboratory has been interested in the cellular and molecular mechanisms that govern the way cells choose their developmental fates during embryonic neurogenesis. We have focused on the differentiation of a subset of neural crest derivatives: the endocrine (chromaffin) cells of the adrenal medulla, and the principal noradrenergic neurons of the sympathetic ganglia (LeDouarin, 1982). Previous studies have suggested that environmental signals, such as Nerve Growth Factor (NGF) and glucocorticoids (GC), may play an important role in the development of these two cell types (Aloe and Levi-Montalcini, 1979). In particular, apparently mature chromaffin cells are able to convert into cells phenotypically indistinguishable from sympathetic neurons, when cultured in the presence of NGF and absence of GC (Unsicker et al., 1978; Ogawa et al., 1984; Lillien and Claude, 1985; Doupe et al., 1985a,b). We now wish to account for this plasticity in terms of the developmental history of these cells. Do sympathetic neurons and chromaffin cells in fact share a common embryonic progenitor? What is the phenotype of this progenitor? How much of this progenitor's ultimate fate is controlled by its earlier history, and how much by its immediate environment? What environmental factors control this decision, and how do they work?