Multiple actions of stem cell factor in neural crest cell differentiation in vitro

The neural crest is a transient tissue of the vertebrate embryo that gives rise to most primary sensory neurons and pigment cells in the adult organism, among other cell types and tissues. Many neural crest cells are pluripotent in the sense that their progeny can generate more than one phenotype. The presence of pluripotent neural crest cell-derived cells at sites of terminal differentiation suggests that location-specific cues from the embryonic environment, such as growth factors, are involved in directing their survival, proliferation, and cell type specification. We have therefore examined the influences of one pertinent growth factor, stem cell factor (SCF), on neural crest cell development by in vitro colony assay in a serum-free culture medium. SCF showed three major effects. (1) SCF is trophic for early neural crest cells, that is, either pluripotent cells and/or their more mature progeny. This effect occurs only if SCF is present throughout the culture period, and it is not observed when a neurotrophin is present in addition to SCF. (2) More colonies contain sensory neuron precursors in the presence of SCF. This effect is neutralized by NGF and neurotrophin-3 (NT-3), but not by brain-derived neurotrophic factor (BDNF). (3) The combination of SCF and any neurotrophin tested (NGF, BDNF, NT-3) is trophic for melanogenic cells, whereas SCF alone does not detectably affect melanogenesis. This suggests either that both types of factor are required for melanotrophic action or that melanogenic cells become dependent on neurotrophins after exposure to SCF. Our observation that SCF is required during the first half of the culture period only, and NGF during the second half only, indicates the latter possibility. Whereas coat color changes in the mouse mutants W (c-kit defect) and Steel (SCF defect) and several in vivo and in vitro studies by other investigators have shown previously that SCF is melanotrophic, they also indicated the requirement of an additional factor, or factors, in melanogenesis. Our data suggest that SCF affects neural crest cell development at multiple levels and that survival of melanogenic cells is mediated by a combination of SCF and a neurotropin, rather than by SCF alone.