Incorporation of Tritiated Thymidine of High Specific Activity into DNA of the Mouse Oocyte

Summary

C57/B10 mice aged between 2 days and 23 months were injected with ³H-thymidine (³H-Tdr) of high specific activity and killed 4 hours later.

Autoradiographs of ovarian tissue exposed for 90 days revealed low levels of ³H-Tdr incorporation into less than 1 per cent of oocyte nuclear DNA in some mice. The frequency of labelling declined after 12 months old. A pulsechase experiment on 10-week-old animals suggested some stability of incorporated label, at least until 34 days after injection. No reduction in reproductive performance was found when ³H-Tdr injected females were mated and their litter-size compared with controls injected with saline. The possible significance of ‘unscheduled’ DNA synthesis in mouse oocytes is discussed.