Abstract: Objective: To explore the effects of bisphenol A （bisphenol A, BPA） on the oocyte chromosome non-disjunction in iNos-/- mice. Methods：Female iNos+/+ mice and iNos-/- mice, aged 20-22 days, were treated with BPA （100 or 200 μg/kg body weight per day） by intragastric administration for 13 days. The isopyknic corn oil was used as control. Results：In the iNos+/+ mice groups, the numbers of aneuploidy oocytes at metaphase MⅡ were not increased by BPA treatment. Interestingly, the numbers of those oocytes with the error-prone chromosome segregation and the precocious chromatid separation in the iNos-/- mice groups were significantly increased by BPA treatment. Meanwhile, the expressions of polo-like kinase-1（PLK1） and RAN GTPase（RAN） in oocytes of the iNos-/- mice were significantly down-regulated by BPA treatment. Conclusions：iNos has a direct or indirect protection against the faithful chromosome segregation during meiosis, possibly by maintaining stable expression of PLK1 and RAN in mammalian oocytes. BPA exposure at low level may induce chromosomal aberrations in those oocytes of iNos-/- mice.

Key words: Nitric oxide synthase, Meiosis, Aneuploidy, Oocytes, Mitotic spindle apparatus, Bisphenol A