Effects of actinomycin D and cycloheximide on the differentiation of epidermal melanocytes of newborn mice

Control of melanocyte proliferation and differentiation in the mouse epidermis

Melanocyte-stimulating hormone plays an important role in the regulation of melanocyte differentiation in the mouse epidermis by inducing tyrosinase activity, melanosome formation, translocation of melanosomes, and increased dendritogenesis. The proliferative activity of differentiating epidermal melanocytes of newborn mice during the healing of skin wounds is regulated by semi-dominant genes, suggesting that the genes are involved in regulating the proliferative activity of epidermal melanocytes during differentiation. From the results of serum-free culture of epidermal cell suspensions from neonatal mouse skin, basic fibroblast growth factor is shown to stimulate the sustained proliferation of melanoblasts in the presence of dibutyryl adenosine 3',5'-cyclic monophosphate and keratinocyte-derived factors. Moreover, each step of melanocyte differentiation is controlled by numerous coat color genes. These genes control melanocyte differentiation by regulating the differentiation of neural crest cells into melanoblasts in embryonic skin, or by regulating the differentiation of neural crest cells into melanoblasts in embryonic skin, or by regulating transcription and/or translation of the tyrosinase gene in the differentiating melanocytes. These results suggest that melanocyte proliferation and differentiation in the mouse epidermis are controlled by both genetic factors and local tissue environment.

Histochemical survey of the distribution of the epidermal melanoblasts and melanocytes in the mouse during fetal and postnatal periods

In order to clarify the time of onset of the differentiation of epidermal melanoblasts and melanocytes in C57BL/ 10J mice, pieces of skin were excised on various days after gestation and subjected to the dopa reaction and to the combined dopa- premelanin reaction. Cells positive to the combined dopa- premelanin reaction ( melanoblast -melanocyte population) were first identified on prenatal day 14 in the dorsal and ventral skin, and increased in number until day 17. The population remained constant (about 140 cells/0.1 mm2 for the dorsal skin and about 65 cells/0.1 mm2 for the ventral skin) until postnatal day 4, and then decreased. However, cells positive to the dopa reaction (melanocyte population) were first identified on prenatal day 16 in the dorsal and ventral skin, and increased until postnatal day 4 (about 95 cells/0.1 mm2 for the dorsal skin and about 25 cells/0.1 mm2 for the ventral skin), then gradually decreased and disappeared by day 30. These results indicate that mouse epidermal melanoblasts begin to differentiate on prenatal day 14, and 2 days later tyrosinase activity is induced within the cells.