Distribution of thymine dimers induced in mouse skin by ultraviolet radiation

The cellular and tissue distributions of thymine dimers induced in mouse skin by UV radiation were compared in 3 haired mouse strains: Sencar, BALB/c, and C3H. These strains differ markedly in their overall susceptibility to photocarcinogenesis, and they develop UV-induced skin tumors of different histological types and in different anatomical locations. The purpose of this study was to determine whether the differences in strain and site susceptibility are due to inequalities in the distribution of UV radiation-induced DNA damage in the target tissues. An indirect immuno-fluorescence assay was used to examine the location of thymine dimers induced by 254-nm UV radiation (UVC) or 280-400 nm UV radiation (UVAB) in ears and dorsal skin. No differences in the distribution of dimers in skin cells or tissues were found among mouse strains or between anatomical sites (ear vs. dorsum). Thus, these results do not support the hypothesis that differences in the optical properties of skin, which govern penetration and absorption of UV radiation, contribute to site or strain susceptibility in photocarcinogenesis. However, two distinct differences in the cellular and tissue distribution of dimers were found when UVC and UVAB-treated tissues were compared: a) UVAB produced dimers in both dermal and epidermal cells, whereas UVC induced a detectable number of dimers only in epidermal cells; b) UVAB-induced dimers were observed in both the nuclei and cytoplasm of affected cells, whereas dimers induced by UVC were confined to nuclei.