An explanation for the mysterious distribution of melanin in human skin: a rare example of asymmetric (melanin) organelle distribution during mitosis of basal layer progenitor keratinocytes.

In this preliminary report, we provide a plausible and histologically supported explanation for how human skin pigmentation is efficiently organized in the epidermis. Steady-state epidermis pigmentation may involve much less redox-sensitive melanogenesis than previously thought, and at least some premade melanin may be available for reuse. The epidermal melanin unit may be an excellent example with which to study organelle distribution via asymmetric or symmetric inheritance in response to microenvironment and tissue demands.