DNA-REPAIR IN A SHORT-LIVED AND A LONG-LIVED RODENT SPECIES

Previous studies have reported a direct correlation between the rate of UV-induced unscheduled DNA synthesis and the maximum lifespan for seven mammalian species drawn from five different orders. We now examine this correlation in laboratory populations of two rodent species, the house mouse, Mus musculus, and the white-footed mouse, Peromyscus leucopus, both in the superfamily Muroidea. These species are similar in body size but Peromyscus exceeds Mus in lifespan by a factor of 2.5, as determined by life table studies in the same laboratory environment. The extent of UV-induced unscheduled DNA synthesis by third-passage primary fibroblast cell cultures was measured for these two subjects, and the rate of DNA synthesis was 2.5 times greater for the Peromyscus cells, consistent with the greater lifespan of Peromyscus and with the relationship of repair of UV damage to lifespan found previously among representatives of five orders of mammals. A determination of patch size (size of the repair regions) by bromouracil photolysis following ultraviolet irradiation revealed that the patch sizes were the same for the two species, and that the number of repaired sites was 2.2 times greater for Peromyscus than for Mus, in agreement with the ratio found by measurement of unscheduled DNA synthesis. The number of single-strand breaks induced by gamma rays, and the rate of rejoining of these breaks, as measured on alkaline sucrose gradients, were not significantly different in the two species.