On the persistence of oocyte nuclei from fetus to maturity in the laboratory mouse.

Tritiated thymidine injected intraperitoneally into female mice midway through the gestation period was demonstrated by autoradiographic methods to be incorporated into the nuclei of oocytes of female embryos, observed at the pachytene stage of meiosis 2 to 4 days after the injection. The tritium label was also demonstrated in the oocyte nuclei of the daughters of similarly treated females at maturity (6 weeks post partum). It was also found that some follicle cells, likewise labeled with H(3)-thymidine in mid-fetal life, persisted to maturity with few or no intervening mitoses. The observations are presented in support of the prevailing view that individual oocytes which arise from germ cell primordia in fetal stages become the egg cells of the adult female mammal.