Improvement of early developmental competence of postovulatory-aged oocytes using metaphase II spindle injection in mice.

ABSTRACT

PURPOSE: Assisted reproductive technology (ART) is a widely applied fertility treatment. However, the developmental competence of aged oocytes from women of a late reproductive age is seriously reduced and the aged oocytes often fail in fertilization even when ART is used. To resolve this problem, we examined usefulness of a new method "the metaphase II spindle transfer (MESI)" as ART using mouse oocytes. METHODS: This work was composed of two experiments. First, 24 hours after collection, embryos from oocytes (1-day-old oocytes, called postovulatory-aged oocytes), were observed, after intracytoplasmic sperm injection (ICSI), and it was found that they were not able to reach the blastocyst stage. Next, the metaphase II chromosome-spindle complexes from 1-day-old oocytes were injected into cytoplasts from oocytes just collected, using piezo pulses to generate reconstructed oocytes. This procedure was named metaphase II spindle injection (MESI). RESULTS: After ICSI, embryos from the reconstructed oocytes (32/105), which contained the genes of 1-day-old oocytes, were able to develop into the blastocyst stage. The fragmentation rate after ICSI was 28.6%. Thus, the developmental competence of 1-day-old oocytes was improved by MESI. CONCLUSIONS: The MESI method has the potential to improve the success rate of infertility treatments for women of a late reproductive age.