MEIOTIC AND MITOTIC CA2+ OSCILLATIONS AFFECT CELL COMPOSITION IN RESULTING BLASTOCYSTS

At fertilization periodic Ca2+ oscillations release oocytes from meiot ic arrest. The present study examined whether these oscillations have a long-term role in pre- and postimplantation development, independent of their immediate effect, Sr2+-containing medium was used to induce oscillations during exit from meiosis and first embryonic mitosis and Sr2+-activated parthenotes were compared to ethanol-activated partheno tes and embryos generated by in vitro fertilization. After embryo cult ure, blastocysts were differentially stained for the inner cell mass a nd trophectoderm. It was found that oscillations both during exit from meiosis and during mitosis acted to increase the number of inner cell mass cells. In contrast, the trophectoderm cell number was largest in ethanol-activated parthenotes and smallest in fertilized embryos. Pos timplantation development was also modestly improved by extending the time of exposure to Sr2+-containing medium. Together these data sugges t that Ca2+ oscillations have a role in long-term embryonic events and that they provide more than merely a stimulus for meiotic resumption. (C) 1997 Academic Press.