Gamete Biology

Nucleotide Excision Repair Activity Varies among Murine Spermatogenic Cell Types

Abstract
Germ cells perform a unique and critical biological function; they propogate the DNA that will be used to direct development of the next generation. Genetic integrity of germ cell DNA is essential to produce healthy and reproductively fit offspring, and yet, germ cell DNA is damaged by endogenous and exogenous agents. Nucleotide excision repair (NER) is an important mechanism to cope with a variety of DNA lesions. Little is known about NER activity in spermatogenic cells. We expected that germ cells would be more efficient at DNA repair than somatic cells, and that this efficiency may be reduced with age when the prevalence of spontaneous mutations increases. In the present study NER was measured in defined spermatogenic cell types, including premeiotic cells (types A and B spermatogonia), meiotic cells (pachytene spermatocytes) and postmeiotic haploid cells (round spermatids) and compared to that in keratinocytes. Global genome repair and transcription-coupled repair subpathways of NER were examined. All spermatogenic cell types from young mice displayed good repair of (6-4) pyrimidone photoproducts, although the repair rate was slower than in primary keratinocytes. In aged mice, repair of 6-4 phyrimidone photoproducts was depressed in postmeiotic cells. While repair of cyclobutane pyrimidine dimers was not detected in spermatogenic cells or in keratinocytes, the transcribed strands of active genes were repaired with greater efficiency than nontranscribed strands or inactive genes in keratinocytes and in meiotic and postmeiotic cells; spermatogonia displayed low to moderate repair of cyclobutane pyrimidine dimers on both DNA strands regardless of transcriptional status. Overall, the data suggest cell type-specific NER activity during murine spermatogenesis and our results have possible implications for germ cell aging.

Key words: Gamete Biology • Aging • Gametogenesis • Spermatogenesis

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