Kenneth Y. Tsai, MD, PhD

After injury, melanocyte stem cells migrate from the follicle to the wound site and regenerate epidermal melanocytes.

Melanocytes migrate long distances from the neural crest to peripheral tissues in the course of development, but how this process is affected by the responses to injury has been unknown. The follicular pattern of repigmentation following recovery from vitiligo is consistent with the idea that the hair follicle contains a reserve of melanocyte stem cells (McSCs) capable of regenerating epidermal melanocytes in humans.

Unlike humans, adult mice have only follicular (and not epidermal) melanocytes. Using a genetically engineered mouse in which melanocytes and their progeny could be tracked over time, Chou and colleagues found that McSCs migrate from the follicular bulge and secondary hair-germ stem-cell niches following excisional wounding or ultraviolet B (UVB) exposure. This migration was also observable in denuded human skin explants devoid of epidermal melanocytes, occurring during reepithelialization. The researchers found unpigmented follicles in the wound periphery and discovered that McSCs migrate without proliferating, thus causing the peripheral depletion. By way of contrast, UVB exposure caused similar migration but incomplete depletion. Finally, the researchers showed that Mc1r, the receptor for melanin-stimulating hormone (MSH), is important for the epidermal migration of McSCs.

Citation(s):

Chou WC et al. Direct migration of follicular melanocyte stem cells to the epidermis after wounding or UVB irradiation is dependent on Mc1r signaling. Nat Med 2013 Jun 9; [e-pub ahead of print].