Action spectrum of UV-induced mutation in skin

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It is important to determine the action spectrum of ultraviolet light (UV)-induced mutation in skin for risk evaluation of sunlightinduced skin cancer in human population because the recent increase of the UV component of sunlight has caused significant induction of human skin carcinoma. Utilizing a bacterial lacZ gene-introduced transgenic mouse Muta^<TM>, which has been widely used for in vivo assay of induced mutations in an animal body exposed to various mutagens, we studied the induced mutations in mouse dorsal skin irradiated with monochromatic UV light at various wavelengths ranging around UVB and UVA regions. We showed the UV lights less than or equal to 334 nm could increase dose-dependently the frequency of the lacZ mutants in skin epidermis genome. The obtained action spectrum of mutation induction in UV-irradiated skin epidermis showed the maximum efficiency of mutation induction at the wavelengths shorter than or equal to 295 nm and 10,000-fold differences between the maximum and that at 334 nm. These results indicate the major contribution of UVB to skin cancer with the sunlight exposure of human skin and enable an quantitative evaluation of the risk of skin cancer in human population exposed to sunlight of known dose.