Sexual dimorphism in the regulation of meiotic process in the rabbit.

Meiosis, mitosis, and apoptosis during fetal and postnatal periods were investigated in order to explore mechanisms of sexual dimorphism in initiation of germ cell meiosis. Gonads were obtained from Japanese white rabbits from 23 to 51 days postcoitum (dpc). Gonadal thin sections were stained with hematoxylin and eosin. Germ cell alkaline phosphatase and apoptosis were detected with histochemical and immunohistochemical methods, respectively. In the ovary, meiotic germ cells were initially recognized at 29 dpc and arrested after enclosure within follicles. Similarly, meiotic germ cells were recognized outside seminiferous tubules at 29 dpc, but no meiotic figures were identified in intratubular spaces. Apoptotic germ cells were not recognized in the intratubular spaces before 35 dpc, and no apoptotic figures were recognized in the ovary during the period studied. In conclusion, the initiation of meiosis in testicular interstitial tissue at the time comparable to that in the ovary indicates that germ cells of both sexes have the ability to enter meiosis during the same stage of fetal development; and it appears most likely that delayed initiation of meiosis in the intratubular space is attributable to meiosis-inhibiting substance(s) present in seminiferous tubules.