Mitotic activity of epidermal melanocytes in UV-irradiated mouse skin.

The role of mitosis in the increase in the epidermal melanocyte population following repeated ultraviolet (UV) irradiation has been studied in C57B1 mice. Cumulative labeling with 3H-methyl-thymidine (3HTdr) was used in combination with autoradiography. A 4-6 fold increase in the melanocyte population was associated with an isotope labeling of 65-80% of the melanocytes. This indicates that cell division during the irradiation period can account for the total increase in the number of melanocytes. Labeled melanocytes were also found in the epidermis from unirradiated skin. Thus, the epidermal melanocytes seem to constitute a dynamic cell population under continuous renewal.