Stimulation of dendritogenesis in the epidermal melanocytes of newborn mice by melanocyte-stimulating hormone.

The number of dendrites and the total length of dendrites in the epidermal melanocytes positive for the dopa reaction were shown to increase when newborn mice were injected with alpha-MSH or DBc-AMP. Moreover, both indices of the degree of dendritogenesis increased when skin explants of newborn mice were cultured in medium containing alpha-MSH or DBc-AMP. Electron-microscopic observation showed that the number of melanosomes was also increased by alpha-MSH treatment. Many mature melanosomes were observed in the dendrites of the epidermal melanocytes of alpha-MSH-injected mice. Highly dendritic melanocytes seem to be the cells stimulated by MSH to form melanosomes and translocate them to dendrites. Dendritogenesis stimulated by the hormone was suppressed by actinomycin D or cycloheximide, suggesting that the dendritogenesis in the epidermal melanocytes requires de novo transcription and translation.