Removal of stem cell factor or addition of monoclonal anti-c-KIT antibody induces apoptosis in murine melanocyte precursors

Previous findings indicate that the protein c-KIT and its ligand, stem cell factor (SCF) play a crucial role in the development of melanocytes from their precursors in the embryonic neural crest cells. Using a monoclonal anti-c-KIT antibody, ACK2, which is an antagonistic blocker of c-KIT function, we and others demonstrated that mouse melanocytes disappeared with the injection of ACK2 during certain periods of embryonic and postnatal life. The precise mechanisms of this disappearance, however, remain unclear. Because melanocytes disappeared without any inflammation in these in vivo studies, we suspect that apoptosis was a main cause of their disappearance. In this study, to clarify the underlying mechanism, we studied whether ACK2 induces apoptosis in c-KIT-positive melanoblasts, which appear in mouse neural crest cells cultured with SCF from 9.5 d old mouse embryos. With an in situ apoptosis detection kit, a significant increase in apoptosis was detected after the removal of SCF, which further increased with the addition of ACK2 during SCF-dependent periods. The occurrence of apoptosis in the cultured cells was also demonstrated by a DNA analysis and electron microscopy. Immunohistochemical double staining confirmed that the apoptotic cells were c-KIT positive, and the electron microscopy showed that these apoptotic cells were melanocyte precursors. It was therefore demonstrated that apoptosis was induced in the SCF-dependent c-KIT-positive melanocytes in vitro when the SCF/c-KIT interaction was obstructed. These findings elucidate the mechanism of the regulation of melanocyte development, and the survival and proliferation of these precursor cells, by SCF/c-KIT interaction.