In this study, we have analyzed the melanogenic potential of Schwann cells using 
in vitro cell cultures of embryonic quail peripheral nerves. It is shown that in 
Schwann cells, two factors, 12-O-tetradecanoylphorbol-13 acetate (TPA) and 
endothelin 3, trigger a differentiation pathway toward melanocytes, and that 
Steel factor has no effect on these cells unless treated simultaneously with 
TPA. In these cultures, TPA induces the expression of c-kit, whereas Steel 
factor enhances the development of melanocytes. In the assay system we employed, 
neither neuronal nor catecholaminergic phenotypes were obtained, regardless of 
various combinations of related factors added to the culture medium. These data 
support our previous observations indicating the existence of bipotent 
progenitors that are capable of differentiating into Schwann cells or into 
melanocytes, and the regulatory role of endothelin 3 on those precursors, as 
revealed by the clonal culture of neural crest cells.