The melanocortin receptor-1 gene but not the proopiomelanocortin gene is expressed in melanoblasts and contributes their differentiation in the mouse skin

Alpha-melanocyte stimulating hormone (α-MSH) added to serum-free primary culture of melanoblasts derived from epidermal cell suspensions of 0.5 d old C57BL/10JHir mice induced their differentiation. Analysis using the reverse transcription-polymerase chain reaction showed that the expression of the melanocyte-specific α-MSH receptor gene, melanocortin receptor-1 (MC1-R), had already been initiated before addition of ot-MSH, and, in addition, no up-regulation of the MC1-R gene was observed after addition of at-MSH. However, no expression of the proopiomelanocortin (POMC) gene was observed before or after the addition of at-MSH. The expression of the MC1-R and POMC genes in the epidermis and dermis of the dorsal skin was surveyed from 13 d old embryos to 5.5 d old neonates. The expression of the MC1-R gene was first observed in the epidermis of 13 d old embryos, and gradually increased up to 0.5 d after birth, and thereafter remained constant. By contrast, the expression of the MC1-R gene in the dermis was first observed in 16 d old embryos, and gradually increased up to 3.5 d after birth, and thereafter remained constant. However, no expression of the POMC gene was observed in the epidermis or dermis of the dorsal skin at any age of mice tested. These results suggest that the expression of the MC1-R gene, but not of the POMC gene, plays an important role in the regulation of melanocyte differentiation in mouse skin.