Proliferation of epidermal melanocytes during the healing of skin wounds in newborn mice.

A full-thickness cut 7 mm long was made on the middorsal skin of C57BL/10J mice using fine iridectomy scissors. Specimens from the wounded skins were fixed at various days after wounding and were subjected to the dopa reaction and to the combined dopa-premelanin reaction. In the epidermis within 1 mm from the wound edge, the melanocyte population positive to the dopa reaction as well as the melanoblast-melanocyte population positive to the combined dopa-premelanin reaction increased dramatically until the third day, then gradually decreased. In contrast, both populations in the regenerating wound epidermis appeared on the third day and increased until the seventh day, then gradually decreased. However, the maximal population density in the regenerating epidermis did not exceed the initial density. The size of the melanocyte population in both the epidermis within 1 mm from the wound edge and the regenerating epidermis did not differ from that of the melanoblast-melanocyte population in all stages of wound healing. Moreover, pigment-producing melanocytes in mitosis were found immediately after wounding in the epidermis within 1 mm from the wound edge, but not in the regenerating epidermis and control epidermis. These results indicate that the epidermal melanocytes in neonatal mouse skin can be stimulated to undergo mitosis immediately adjacent to a skin wound and, thereafter, to migrate into the regenerating epidermis.