LIVE-BORNS FROM XX BUT NOT XY OOCYTES IN THE CHIMERIC MOUSE OVARY COMPOSED OF B6.Y-TIR AND XX CELLS

When the Y chromosome of some Mus musculus domesticus subspecies is pl aced onto a C57BL/6J mouse background, the XY (B6.Y-TIR) progeny devel op only ovaries or ovotestes during fetal life, The XY sex-reversed fe male is infertile mainly because of death of embryos during preimplant ation development, In the present study, we constructed female mouse c himera composed of B6.Y-TIR and XX BALB/c cells to determine whether d evelopmental incompetence of XY oocytes san be attributed to defects i n the oocytes themselves or in the surrounding XY somatic cells. Distr ibution of XY cells in chimeric ovaries was examined by in situ hybrid ization. Of nine XX <-> XY chimeric females born, eight were composed of B6.Y-TIR and XX BALB/c cells with a wide range of XY contribution ( 16-95%), whereas one had 12% XY components of the BALB/c strain, All t hese females produced progeny exclusively derived from XX oocytes, By comparison, most XX <-> XX chimeric females produced progeny derived f rom oocytes of either strain. Two XY <-> XY males also produced progen y of both strains. In conclusion, the XY chromosomal composition in th e oocyte appears to be responsible for programming its incompetence fo r postfertilization development, On the other hand, the presence of XY somatic cells in the chimeric ovary allows development of fertile XX oocytes.