ROLE OF DEOXYRIBONUCLEIC-ACID POLYMERASE IN SPERMATOGENESIS IN MICE

Previous studies on DNA polymerase epsilon indicate that this enzyme i s involved in replication of chromosomal DNA. In this study, we examin ed the expression of DNA polymerases alpha, delta, and epsilon during mouse testis development and germ cell differentiation. The steady-sta te levels of mRNAs encoding DNA polymerase epsilon and the recombinati on enzyme Rad51 remained constant during testis development, whereas t he mRNA levels of DNA polymerases alpha and delta declined from birth until sexual maturity. Immunohistochemical staining methods, using a s tage-specific model of the seminiferous epithelium, revealed dramatic differences between DNA polymerase alpha and epsilon distribution. As expected, DNA polymerase alpha and proliferating cell nuclear antigen showed relatively strong immunostaining in mitotically proliferating s permatogonia and even stronger staining in preleptotene cells undergoi ng meiotic DNA replication. The distribution of Rad51 was similar, but there was a dramatic peak in late pachytene cells. In contrast, DNA p olymerase epsilon was detectable in mitotically proliferating spermato gonia but not in the early stages of meiotic prophase. However, DNA po lymerase epsilon reappeared in tate pachytene cells and remained throu gh the two meiotic divisions, and was present in haploid spermatids up to the stage at which the flagellum starts developing. Overall, the r esults suggest that DNA polymerase epsilon functions in mitotic replic ation, in the completion of recombination in late pachytene cells, and in repair of DNA damage in round spermatids. In contrast, DNA polymer ases alpha and delta appear to be involved in meiotic DNA synthesis, w hich occurs early in meiotic prophase, in addition to functioning in D NA replication in proliferating spermatogonia.