Influence of α-melanocyte-stimulating hormone and ultraviolet radiation on the transfer of melanosomes to keratinocytes

SPECIFIC AIMSMelanocytes manufacture melanin-loaded organelles called melanosomes and distribute them to neighboring keratinocytes where their presence confers to the skin its color and photoprotective properties. In this study, we used murine melan-a melanocytes and murine SP-1 keratinocytes alone and in coculture to characterize the processes involved in melanosome transfer. We also sought to determine whether two physiological stimulators of mammalian pigmentation—ultraviolet radiation (UV) and α-melanocyte-stimulating hormone (MSH)—stimulated melanosome transfer by melanocytes and/or by keratinocytes.PRINCIPAL FINDINGS1. Melanosome transfer in cocultures of melanocytes and keratinocytesWe studied melanosome transfer in cocultures of melanocytes and keratinocytes using time-lapse microphotography. During our many hours of observations (not shown), we saw melanocyte dendrite tips frequently and actively contact keratinocytes for several minutes, but they would eventually retract, leaving nothing behind....