Transcriptional activity of sex chromosomes in the oocytes of the B6.Y(TIR) sex-reversed female mouse

In the B6.YTIR mouse strain, half of the XY progeny develop bilateral ovaries and the female phenotype. These XY females are infertile mainly due to the death of their embryos. This developmental failure has been attributed to a defect intrinsic to the XY oocyte.;The present study examined the transcriptional activity of the X and Y chromosomes in these oocytes. RT-PCR results show that the Ube1y gene is transcribed in the XY ovary at all stages examined and also in growing XY oocytes. The Sry gene was transcribed only at the onset of ovarian differentiation whereas the Zfy gene was undetectable at all stages during fetal life. The Xist gene, which is involved in X inactivation, was not expressed in XY oocytes. We speculate that expression of Y-encoded genes may have a deleterious effect on the quality of the oocytes and thus renders them incompetent for post-fertilization development.