Effects of genic substitution at the agouti, brown, albino, dilute, and pink-eyed dilution loci on the proliferation and differentiation of mouse epidermal melanocytes in serum-free culture

To examine the effects of coat-color genes on the proliferation and differentiation of mouse epidermal melanocytes, we cultured epidermal cell suspensions derived from neonatal skins of C57BL/10JHir (black) and its congenic mice carrying agouti, brown, albino, dilute, and pink-eyed dilution genes in a serum-free medium supplemented with dibutyryl adenosine 3',5'-cyclic monophosphate. The proliferative rates of agouti, brown and dilute black melanocytes were similar to that of black melanocytes, while those of albino and pink-eyed black melanocytes were about one-half of that of black melanocytes. The morphology of albino and pink-eyed black melanocytes, though nonpigmented, was similar to black melanocytes; namely, dendritic, polygonal or epithelioid. Dilute black melanocytes also possessed the similar morphology, whereas their melanosomes w ere accumulated in the perinuclear region. Dopa-melanin depositions after dopa reaction in brown and dilute black melanocytes were greater than in black and agouti melanocytes. Although dopa-melanin depositions were not observed in albino melanocytes, about 8 % of pink-eyed black melanocytes were positive to dopa reaction; Silver depositions after combined dopa-premelanin reaction in agouti, brown and dilute black melanocytes were similar to that in black melanocytes. Although albino melanocytes were devoid of silver depositions, about 25 % of pink-eyed black melanocytes were positive to the reaction. Pyrrole-2,3,5-tricarboxylic acid (PTCA, degradation product of eumelanin) contents in agouti and dilute black melanocytes were slightly lower than in black melanocytes, while that in brown melanocytes was reduced to one-third. in contrast, PTCA contents in albino and pink-eyed black melanocytes were reduced to less than 0.5 %. Aminohydroxyphenylalanine (AHP, degradation product of pheomelanin) contents did not differ among these melanocytes. These results suggest that the coat-color genes exert their influences on the proliferation and differentiation of mouse epidermal melanocytes by affecting tyrosinase activity, melanosome maturation and transport, and eumelanin synthesis.