Abstract
PURPOSE: Cytogenetic risk of intracytoplasmic sperm injection (ICSI) after artificial oocyte activation (post-activation ICSI) was evaluated in the mouse. METHODS: Mouse zygotes were produced by ICSI into eggs at various intervals after parthenogenetic exposure to strontium (Sr) for 30 min. Male pronucleus formation and the chromosome constitution were studied. RESULTS: Sperm nuclei injected into oocytes within 1 h after Sr exposure (from early through mid-telophase) transformed normally into male pronuclei, and the number of chromosome aberrations did not significantly increase in the resultant zygotes. When sperm nuclei were injected into eggs at intervals beyond 1 h after Sr exposure (from late telophase through the G1 pronuclear stage), the rate of male pronucleus formation was significantly reduced. The incidence of chromosome aberrations increased with time between oocyte activation and ICSI. CONCLUSIONS: ICSI into oocytes within 1 h after parthenogenetic activation produces cytogenetically competent embryos in the mouse.