PARTHENOGENETIC DEVELOPMENT OF MOS-DEFICIENT MOUSE OOCYTES

Ovarian teratomas develop in Mos(-/-) mutant mice produced by homologo us recombination. These teratomas are probably derived from oocytes th at undergo spontaneous parthenogenetic activation within the ovaries. However, it is not clear how the activated eggs develop into teratomas since embryonic development beyond the four-cell stage was not observ ed either in vitro or in vivo. In this study, Mos(-/-) parthenotes der ived from in vitro-matured oocytes were cultured using a recently deve loped medium, KSOM/AA, which promotes a high frequency of preimplantat ion development by normal embryos. In total, 5% of the Mos(-/-) oocyte s developed to the blastocyst stage. Preimplantation-like and early po stimplantation-like embryos were observed in the ovaries of 60-63-day- old Mos(-/-) mice. These observations support the hypothesis that Mos( -/-) teratomas are derived from parthenogenetically activated oocytes that undergo early embryonic development up to early postimplantation- like stages within the ovaries. Aberrant meiotic divisions commonly ob served in Mos(-/-) oocytes in vitro may adversely affect preimplantati on development and reduce the frequency of blastocyst formation even u nder the best culture conditions. (C) 1997 Wiley-Liss, Inc.