LINKING TERATOGENESIS, GROWTH, AND DNA PHOTODAMAGE TO ARTIFICIAL ULTRAVIOLET-B RADIATION IN XENOPUS-LAEVIS LARVAE

The frog embryo teratogenesis assay-Xenopus (FETAX) was used to illust rate sublethal endpoints indicative of ultraviolet B (UV-B) radiation exposure in Xenopus laevis larvae. Xenopus laevis embryos were covered with plastic cutoff filters to manipulate UV dose, and irradiated und er a light carriage consisting of two UV-B and three W-A bulbs. At the end of day 2, 20% of the tadpoles from all treatments were removed, a nd DNA was extracted. Frequency of pyrimidine dimers was estimated by quantifying single-strand breaks after incubating DNA with an endonucl ease specific for cyclobutane pyrimidine dimers. Remaining tadpoles we re sacrificed on day 5, and mortality, malformations, and growth data were recorded. Teratogenesis and growth inhibition were positively cor related with increasing UV-B dose in all tests. Photodamage to DNA in experiment 1 increased with higher UV-B doses. Teratogenesis positivel y correlated with the frequency of pyrimidine dimers. In experiment 2, significant variation with DNA photodamage in egg clutches was observ ed and no treatment effect was found. Usage of these sublethal endpoin ts in the field or laboratory would be helpful in discerning adaptatio nal responses of developing amphibians to UV-B radiation, and interact ive effects between UV and photosensitive chemicals.