Nucleotide excision repair in rat male germ cells: low level of repair in intact cells contrasts with high dual incision activity in vitro

The acquisition of genotoxin-induced mutations in the mammalian germline is detrimental to the stable transfer of genomic information. in somatic cell s, nucleotide excision repair (MER) is a major pathway to counteract the mu tagenic effects of DNA damage. Two NER subpathways have been identified, gl obal genome repair (GGR) and transcription-coupled repair (TCR). In contras t to somatic cells, little is known regarding the expression of these pathw ays in germ cells. To address this basic question, we have studied NER in r at spermatogenic cells in crude cell suspension, in enriched cell stages an d within seminiferous tubules after exposure to UV or N-acetoxy-2-acetylami nofluorene. Surprisingly, repair in spermatogenic cells was inefficient in the genome overall and in transcriptionally active genes indicating non-fun ctional GGR and TCR, In contrast, extracts from early/mid pachytene cells d isplayed dual incision activity in vitro as high as extracts from somatic c ells, demonstrating that the proteins involved in incision are present and functional in premeiotic cells, However, incision activities of extracts fr om diplotene cells and round spermatids were low, indicating a stage-depend ent expression of incision activity. We hypothesize that sequestering of NE R proteins by mispaired regions in DNA involved in synapsis and recombinati on may underlie the lack of NER activity in premeiotic cells.