Involvement of Mouse Rev3 in Tolerance of Endogenous and Exogenous DNA Damage

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Abstract
The Rev3 gene of Saccharomyces cerevisiae encodes the catalytic subunit of DNA polymerase ζ that is implicated in mutagenic translesion synthesis of damaged DNA. To investigate the function of its mouse homologue, we have generated mouse embryonic stem cells and mice carrying a targeted disruption of Rev3. Although some strain-dependent variation was observed, Rev3−/− embryos died around midgestation, displaying retarded growth in the absence of consistent developmental abnormalities. Rev3−/− cell lines could not be established, indicating a cell-autonomous requirement of Rev3 for long-term viability. Histochemical analysis of Rev3−/− embryos did not reveal aberrant replication or cellular proliferation but demonstrated massive apoptosis in all embryonic lineages. Although increased levels of p53 are detected in Rev3−/− embryos, the embryonic phenotype was not rescued by the absence of p53. A significant increase in double-stranded DNA breaks as well as chromatid and chromosome aberrations was observed in cells from Rev3−/− embryos. The inner cell mass of cultured Rev3−/− blastocysts dies of a delayed apoptotic response after exposure to a low dose of N-acetoxy-2-acetylaminofluorene. These combined data are compatible with a model in which, in the absence of polymerase ζ, double-stranded DNA breaks accumulate at sites of unreplicated DNA damage, eliciting a p53-independent apoptotic response. Together, these data are consistent with involvement of polymerase ζ in translesion synthesis of endogenously and exogenously induced DNA lesions.