EFFECTS OF GENIC SUBSTITUTION AT THE AGOUTI, BROWN, ALBINO, DILUTE, AND PINK-EYED DILUTION LOCI ON THE PROLIFERATION AND DIFFERENTIATION OFMOUSE EPIDERMAL MELANOCYTES IN SERUM-FREE CULTURE

To examine the effects of coat-color genes on the proliferation and di fferentiation of mouse epidermal melanocytes, we cultured epidermal ce ll suspensions derived from neonatal skins of C57BL/10JHir (black) and its congenic mice carrying agouti, brown, albino, dilute, and pink-ey ed dilution genes in a serum-free medium supplemented with dibutyryl a denosine 3',5'-cyclic monophosphate. The proliferative rates of agouti , brown and dilute black melanocytes were similar to that of black mel anocytes, while those of albino and pink-eyed black melanocytes were a bout one-half of that of black melanocytes. The morphology of albino a nd pink-eyed black melanocytes, though nonpigmented, was similar to bl ack melanocytes; namely, dendritic, polygonal or epithelioid. Dilute b lack 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-melan in depositions were not observed in albino melanocytes, about 8 % of p ink-eyed black melanocytes were positive to dopa reaction; Silver depo sitions after combined dopa-premelanin reaction in agouti, brown and d ilute black melanocytes were similar to that in black melanocytes. Alt hough 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) con tents in agouti and dilute black melanocytes were slightly lower than in black melanocytes, while that in brown melanocytes was reduced to o ne-third. in contrast, PTCA contents in albino and pink-eyed black mel anocytes were reduced to less than 0.5 %. Aminohydroxyphenylalanine (A HP, degradation product of pheomelanin) contents did not differ among these melanocytes. These results suggest that the coat-color genes exe rt their influences on the proliferation and differentiation of mouse epidermal melanocytes by affecting tyrosinase activity, melanosome mat uration and transport, and eumelanin synthesis.