Mouse Mos protooncogene product is present and functions during oogenesis.

We have identified the mouse Mos-encoded protein product, p39mos, in maturing mouse oocytes and have shown that it is indistinguishable from the product expressed in Mos-transformed NIH 3T3 cells. p39mos is detected in oocytes arrested in the first meiotic prophase, during germinal-vesicle breakdown, metaphase I, anaphase I, and in ovulated eggs. We show that microinjection of three different Mos antisense (but not sense) oligodeoxyribonucleotides into germinal vesicle-stage oocytes prevents first polar-body emission and therefore interrupted the normal progression of meiosis. These results show that in mouse oocytes, as in the amphibian Xenopus [Sagata, N., Oskarsson, M., Copeland, T., Brumbaugh, J. & Vande Woude, G.F. (1988) Nature (London) 335, 519-525], the product of Mos is necessary for normal meiotic maturation.