Adult wild-type mice are not supposed to be proper models for ultraviolet radiation (UVR)-induced melanoma since melanocytes are confined to hair follicles and cannot be sufficiently reached by UVR. On the other hand, in mutated mouse models used for melanoma research limitations, including an altered immune system and selection of affected pathways, lead to tumors phenotypically quite different from naturally occurring melanomas. We compared the distribution of epidermal melanocytes in UVR and not-UVR-exposed wild-type C57BL/6 mice. Starting at the age of 8 weeks, mice were exposed to physiologic doses of UVR three times weekly over 16 weeks. Back skin biopsies were taken 4, 8, 12 and 16 weeks after initiation of exposure, and stained for Melan-A, representing a highly selective marker for melanocytes. Surprisingly, after exposure to UVR, Melan-A positive cells were detected also in the interfollicular epidermis of C57BL/6 mice. We conclude that UVR is capable of inducing interfollicular epidermal melanocytes in wild-type mice.
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