At fertilization periodic Ca²⁺ oscillations release oocytes from meiotic 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 parthenotes and embryos generated by in vitro fertilization. After embryo culture, blastocysts were differentially stained for the inner cell mass and 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. Postimplantation development was also modestly improved by extending the time of exposure to Sr²⁺-containing medium. Together these data suggest that Ca²⁺ oscillations have a role in long-term embryonic events and that they provide more than merely a stimulus for meiotic resumption.
Developmental Biology Vol. 182, Issue 1, p. 172-179