The incidence of aneuploidy after single pulse electroactivation of mouse oocytes

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Abstract
A brief electric pulse often produces a high rate of activation of recently ovulated oocytes. Some other efficient parthenogenetic stimuli, such as alcohol, however, disrupt the spindle apparatus and increase the incidence of aneuploidy. In this paper, we have determined whether electroactivation per se increases the incidence of chromosomal segregation errors in haploid parthenogenones as evidenced at first cleavage mitosis. Superovulated F1 hybrid female mice were killed at 15.5, 18.5, 22.5, and 25 h after the HCG injection. Batches of 10–12 cumulus-denuded oocytes were transferred to an electroactivation chamber containing mannitol which was connected to a high voltage pulse stimulator and the pulse was triggered once. A high proportion of oocytes activated following this treatment, but only the single-pronuclear haploid parthenogenones were incubated overnight in medium containing colcemid, to determine the incidence of aneuploidy as evidenced at first cleavage mitosis. “Sham” electroactivation groups were also examined for evidence of activation and aneuploidy as described above. In these cases, cumulus-denuded oocytes were put through the electroactivation chamber but the pulse was not triggered. A further group of oocytes was studied to determine the effect of handling and exposure to hyaluronidase on activation frequency and parthenogenetic pathways. Finally, the spontaneous rate of aneuploidy was examined in fertilised embryos of F1 hybrid female mice × Rb(1.3)1Bnr male mice at first cleavage mitosis. The results show that single pulse electroactivation does not increase the level of aneuploidy in single-pronuclear parthenogenones compared to the “sham” group or the spontaneous rate observed in 1-cell fertilised embryos, nor does aneuploidy appear to increase with postovulatory age. The developmental pathways observed in the electroactivation group are significantly different to those observed in the “sham” group, and the level of activation observed in both groups is increased through handling of oocytes and their exposure to hyaluronidase.