The neural crest (NC) yields pluripotent cells endowed with migratory properties. They give rise to neurons, glia, melanocytes and endocrine cells,and to diverse `mesenchymal' derivatives. Experiments in avian embryos have revealed that the differentiation of the NC `neural' precursors is strongly influenced by environmental cues. The reversibility of differentiated cells(such as melanocytes or glia) to a pluripotent precursor state can even be induced in vitro by a cytokine, endothelin 3. The fate of `mesenchymal' NC precursors is strongly restricted by Hox gene expression. In this context,however, facial skeleton morphogenesis is under the control of a multistep crosstalk between the epithelia (endoderm and ectoderm) and NC cells.
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