Somatic cell mutation and photoproduct formation in Drosophila induced by monochromatic UV light in sunlight

We recently reported that natural sunlight can induce somatic mutation and chromosomal recombination in Drosophila, as detected by the wing spot test. Simultaneously, cyclobutane thymine dimers (CTDs) and (6-4)photoproducts [(6-4)PPs] are formed in the DNA. In the present work, we have performed monochromatic UV irradiation for evaluating the action spectrum of sunlight in genotoxicity. Third instar larvae in petri dishes were irradiated by monochromatic UV light at a wavelength between 310 and 360 nm. The mutant spots induced by the irradiation of 310, 320, 330, and 340 nm light were (4.4 ± 1.0) x 10^-1, (1.1 ± 0.2) x 10^-2, (2.5 ± 0.7) x 10^-3, and (2.0 ± 0.7) x 10^-3 spots/wing/kJ/m², respectively. The mutagenicity at 360 nm irradiation was not significant. The amounts of photoproducts in irradiated larval DNA were measured by an enzyme-linked immunosorbent assay (ELISA) using the monoclonal antibodies against CTDs and (6-4)PPs. CTDs were found in the DNA from all of these irradiated larvae, and their amounts increased with the UV dose: the longer the wavelength, the lower the CTD formation and the mutagenesis. These data suggest that, in the sunlight, the component around 310-340 nm causes the somatic cell mutation by forming thymine dimers as main lesions. (C) 2000 by John Wiley and Sons, Inc.