Parthenogenetic activation of mouse oocytes by strontium

The purposes of this study were to determine the optimal conditions for inducing parthenogenetic activation by strontium and to evaluate the developmental ability of the activated oocytes in mice. MII oocytes collected from B6CBF1 and CD-1 mice were cultured for 2-60 min in medium containing 1.7 mM strontium. The proportion of oocytes activated increased in a time-dependent manner, with an apparent difference between the B6CBF1 and CD-1 strains in sensitivity to strontium. In oocytes derived from B6CBF1 mice more than 90% of oocytes were activated by the treatment with strontium for 30 min, whereas more than 80% of the oocytes from CD-1 mice were activated by the treatment for 5 min. The majority of oocytes formed the second polar body and a single pronucleus in both cases. Of the parthenogenetically activated 1-cell embryos with the haploid genome, around 39% developed to the blastocyst stage in the B6CBF1, and in contrast the developmental ability was low (11%) in the CD-1 strain. The ability to develop to blastocysts was significantly improved in diploid parthenogenetic embryos of both the strains; 93% and 58% were developed to the blastocyst stage, respectively. After transfer of the diploid parthenogenetic embryos to recipient mice, 11% of the embryos developed to day 10 of gestation. The record of intracytoplasmic Ca ²⁺ concentrations showed that the exposure of oocytes to medium containing 1.7 mM strontium induced repetitive intracellular Ca ²⁺ transients. These data clearly showed that strontium is a potent stimulus for inducing parthenogenetic activation and supporting in vitro and in vivo development in mouse oocytes.