The influence of postovulatory ageing on the retardation of mouse oocyte maturation and chromosome segregation induced by vinblastine

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Abstract
Certain compounds can induce ovulated metaphase I (MI) oocytes. To study if these MI oocytes can overcome this blockage, ICR mice were given human chorionic gonadotrophin and 0.6 mg/kg vinblastine sulfate (VBS). Their ovulated oocytes were collected at 17, 19, 21, 23 and 25 h later. The results showed that the frequencies of MI oocytes decreased, the proportions of diploid metaphase II (MII) oocytes increased and the frequencies of hyperploid MII oocytes did not significantly differ (P > 0.05) among the five harvest or postovulatory times. We also found that the proportions of MII oocytes exhibiting premature anaphase II and premature centromere separation increased with postovulatory ageing, and that these frequencies were consistently higher in controls than in the VBS groups. These findings indicate that some of the oocytes blocked in MI can overcome this inhibition and produce primarily diploid MII oocytes. The ultimate fate of ovulated MI and diploid oocytes on aneuploid production hinges upon the formation of a functioning meiotic spindle, which is affected by both dosage and the specific chemical.

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