BMP, Kit and Mitf on melanocytes and melanoma cells

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We previously established three distinct cell populations of mouse neural crest (NC) cells, NCCmelb4, NCCmelb4M5 and NCCmelan5. BMP4 is activated and is involved in the regulation of Kit expression on most immature melanocyte precursors. We further investigated the influence of BMP4 in vitro using primary NC cells cultured from wild-type mice. Addition of BMP4 to the medium increased the number of Kit-positive cells compared to untreated controls. We have identified BMP4 as an important factor for prepubertal Kit-negative melanoblasts just prior to entering the Kit-dependent cycle of melanogenesis. Western blotting revealed expression of the Ret protein in NCCmelb4M5 and in Mel-Ret cells, but in contrast, there was no expression of the Ret protein in NCCmelb4 or NCCmelan5 cells. Immunostaining revealed that NCCmelb4M5 and Mel-Ret cells are positive for Ret, but NCCmelb4 and NCCmelan5 cells are negative for Ret. Thus, Ret protein is expressed in most immature melanoblasts, while melanocytes are negative for Ret. Based on these findings, the combined effects of Ret and BMP4 might provide important clues towards understanding the roles and working mechanisms in melanocyte development.