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Poly (ADP‐ribose) polymerase‐1 deficiency does not affect ethylnitrosourea mutagenicity in liver and testis of lacZ transgenic mice

Poly (ADP‐ribose) polymerase‐1 (Parp1) has been implicated in DNA base excision repair, single‐ and double‐strand break repair pathways, as well as in cell death by apoptosis or necrosis. We used Parp1−/− lacZ plasmid‐based transgenic mice to investigate whether Parp1 deficiency influences the in vivo mutagenic and clastogenic response to the alkylating agent N‐ethyl‐N‐Nitrosourea (ENU) in somatic and germ‐cell tissues. The comparison of the lacZ mutant frequencies (MFs) between Parp1+/+ and Parp1−/− mice showed that the ablation of Parp1 does not affect the spontaneous or ENU‐induced MFs in liver and testis. In addition, the spectrum of the ENU‐induced mutations was not dependent on the Parp1 status, given that similar spectra, consisting mostly of point mutations and a small fraction of deletions/insertions, wereobserved in organs of both Parp1−/− and Parp1+/+ mice. Sequencing of point mutations revealed a consistent significant increase in A:T → T:A base substitutions, typically induced by ENU. Overall, we observed that neither the frequency nor the spectrum of ENU‐induced mutations demonstrated a specificity that could be attributed to the Parp1 impairment in mice organs. The analysis of micronucleus frequency in peripheral blood reticulocytes showed that ENU was clastogenic in both Parp1−/− and Parp1+/+ mice and had a strong cytotoxic effect in Parp1−/− mice only. The present data suggest that, at a whole‐organism level, Parp1‐independent repair mechanisms may be operative in the removal of ENU‐induced DNA lesions or that highly damaged cells may be preferentially committed to death when Parp1 is inactivated. Environ. Mol. Mutagen. 2010. © 2010 Wiley‐Liss, Inc.