REPLICATING DNA DOES NOT BLOCK GERMINAL VESICLE BREAKDOWN IN MOUSE OOCYTES

Mouse germinal vesicle GV-G2 stage oocytes were fused to very early S- phase blastomeres from four cell stage embryos to test whether oocytes have a mechanism which detects replicating DNA and thereafter arrests meiosis at the GV stage. Our results show that oocytes are unable to recognize replicating DNA in transplanted nuclei and undergo germinal vesicle breakdown (GVBD). GVBD and blastomere nucleus breakdown are on ly blocked by inhibitors of both oocyte maturation and DNA synthesis. These results show that mouse immature oocytes do not possess a feedba ck control capable of detecting replicating DNA. (C) 1995 Wiley-Liss, inc.