Transient steel factor dependence by neural crest-derived melanocyte precursors.

Growth/trophic factors, encountered by dispersing neural crest cells, affect the development of different crest-derived subpopulations. Here, we address the dependence by cells of the crest-derived melanogenic lineage on Steel factor (SLF). Specifically, we have asked when SLF-responsive cells first appear in cultured neural crest cell populations and whether there is a defined period during which this melanogenic subpopulation requires the presence of the SLF. We demonstrate that survival of a melanogenic subpopulation of cultured murine crest cells requires SLF for a critical period, which begins only after the second day of dispersal in vitro. We also conclude that the critical period of SLF dependence lasts about 4 days, ending about the time that melanocytes differentiate, as indicated by the presence of functional melanosomes, but before their overt melanization. Finally, we demonstrate that although the final stages of melanogenesis (i.e., melanization) do not appear to require SLF, this process may be enhanced by extended exposure to high levels of SLF in vitro.