DNA repair synthesis-related enzymes during spermatogenesis in the mouse

To assess whether uracil DNA glycosylase and dUTP nucleotidohydrolase (dUTPase) can be involved in repair-type DNA synthesis associated to crossing-over or induced by UV and X-ray treatments, we have studied these enzyme activities in male mouse germ cells at specific stages of differentiation. Although the highest uracil DNA glycosylase activity was observed in dividing germ cells (spermatogonia and preleptotene spermatocytes), some activity was also detected in meiotic (3.5%) and post-meiotic (1.0%) cells with a relative maximum of activity at pachytene stage (4.7%) when meiotic crossing-over takes place. These findings suggest that uracil DNA glycosylase is involved, in this biological system, in DNA replication and in repair-type DNA synthesis. dUTPase is present at all the stages of spermatogenesis studied but, unlike thymidylate synthetase which is mainly associated with replicating germ cells, dUTPase activity is maximal in spermatocytes at pachytene stages. The data reported suggest that, in this biological system, the main role of dUTPase is to degrade dUTP to prevent misincorporation of uracil into DNA during crossing-over, rather than to participate in the biosynthetic pathway of dTTP.