Germline mutation rates at tandem repeat loci in DNA-repair deficient mice

Mutation rates at two expanded simple tandem repeat (ESTR) loci were studied in the germline of non-exposed and irradiated severe combined immunodeficient (scid) and poly(ADP-ribose) polymerase (PARP-1(-/-)) deficient male mice. Non-exposed scid and PARP(-/-) male mice showed considerably elevated ESTR mutation rates, far higher than those in wild-type isogenic mice and other inbred strains. The irradiated scid and PARP-1(-/-) male mice did not show any detectable increases in their mutation rate, whereas significant ESTR mutation induction was observed in the irradiated wild-type isogenic males. ESTR mutation spectra in the scid and PARP-1(-/-) strains did not differ from those in the isogenic wild-type strains. Considering these data and the results of previous studies, we propose that a delay in repair of DNA damage in scid and PARP-1(-/-) mice could result in replication fork pausing which, in turn, may affect ESTR mutation rate in the non-irradiated males. The lack of mutation induction in irradiated scid and PARP-1(-/-) can be explained by the high cell killing effects of irradiation on the,germline of deficient mice. (C) 2004 Elsevier B.V. All rights reserved.