ABLATION OF BCL-2 GENE-EXPRESSION DECREASES THE NUMBERS OF OOCYTES AND PRIMORDIAL FOLLICLES ESTABLISHED IN THE POSTNATAL FEMALE MOUSE GONAD

Oocyte loss, either directly through attrition (germ cell death) or in directly through follicular atresia (somatic or granulosa cell death), is a fundamental event associated with defining the time of normal or premature reproductive senescence in females. Although apoptosis has been reported to function as the underlying mechanism responsible for death of both germ cells and somatic cells in the ovary, the final mol ecular steps which commit ovarian cells to death have not been fully e lucidated. To examine if death repressor activity of the bcl-2 gene pr oduct is important for germ cell survival, we conducted studies using a Bcl-2 loss-of-function (bcl-2 -/-) transgenic mouse model. Histologi cal analyses revealed that ovaries collected from bcl-2 -/- mice posse ssed numerous aberrantly formed primordial follicle-like structures co ntaining a single layer of granulosa cells without an oocyte. Addition ally, the total number of primordial follicles present which contained a healthy oocyte was markedly reduced in bcl-2 -/- mice as compared t o heterozygote (bcl-2 -/+) or wild-type (bcl-2 +/+) mice, suggesting t hat expression of the bcl-2 death repressor gene is critical for endow ment of a normal complement of germ cells and primordial follicles in the mammalian ovary.