Control of the oocyte population in mouse ovaries

Oocyte loss and meiotic prophase progression was studied in XY sex-reversed and XO female mice, two mouse models that lack pairing between their sex chromosomes. An arrest at the pachytene stage of meiosis was not observed, nor was a significant loss of oocytes at this stage compared to normal XX control mice. Thus, it was concluded that a pairing checkpoint either does not exist in oocytes or is not as stringent as the one observed in males.The effect of mutating the pro-apoptotic Bax molecule was studied at three distinct ages corresponding to the time when female germ cells are premeiotic, in meiotic prophase, and arrested in dictyotene. Although it appeared that more germ cells were retained in the Bax homozygous mutant compared to the wild-type and heterozygous mice at 18.5 dpc, by 24.5 dpc all of the mice possessed similar numbers of germ cells. These results indicate a role for Bax in germ cell death but also support the idea that an alternative pathway can compensate for the elimination of this molecule