Bleomycin-induced DNA damage and repair in Xenopus laevis and Xenopus tropicalis

Microgel cell electrophoresis has been used with various species to measure breakage of DNA and DNA repair following exposure to the radiomimetic antibiotic, bleomycin. With humans, a high degree of DNA damage is considered to be predictive of cancer susceptibility. Non-isogeneic Xenopus laevis, the South African clawed toad, rarely develop spontaneous or induced cancers. Here, we investigate bleomycin-induced DNA damage and repair in splenic lymphocytes of this species to test consistency with cancer predictability. As X laevis is pseudotetraploid in nature, while Xenopus tropicalis is diploid, we additionally explore the effect of polyploidy on DNA damage and repair in these vertebrates. The results show that higher doses of bleomycin are required to induce comparable levels of DNA damage in both Xenopus species, than in humans. X tropicalis, the diploid, is more bleomycin-sensitive than is X laevis. Additionally, repair rates of damaged DNA of X laevis lymphocytes are more rapid than those of X tropicalis, although both are hours slower than human leukocytes. While no data exist on cancer susceptibility in X tropicalis, the results suggest greater susceptibility to cancer than X laevis, but less than in humans. Thus, polyploidy serves as a protection against DNA damage and allows more rapid repair.