Effect of cigarette smoke exposure during pregnancy on offspring of ovarian development and oocyte DNA methylation in female mice

Abstract

Objective: To explore the effects of cigarette smoke exposure during pregnancy on the quality of oocytes and the whole genome DNA methylation in the offspring of female mice during the period of germinal vesicle (GV) . Methods: The pregnant 7 d mice were divided into 3 groups, exposure on the 0, 0.5, 1 lit cigarettes cabinet (volume 18 L) , at 9 am and 3 pm for 1 h twice daily, until delivery. When the mice were 6 weeks old, the organ index and the number of follicles in the ovary were detected by weighing and making HE stained sections. GV stage oocytes were obtained by Hoechst 33342 staining and indirect immunofluorescence to detect the quality of oocytes, chromatin configuration and whole genome DNA methylation level. Results: Compared with the control group and low dose group, the offspring ovarian organ index of female mice in the high dose group decreased, the difference was statistically significant (P<0.05) . Compared with the control group, the number of follicular oocytes in low dose group and high dose group female mice offspring decreased, the zona pellucida oocytes diameter decreased, and the zona pellucida thickness increased, the differences were statistical significance (P<0.05) . Compared with control group and low dose group, in the high dose group, the oocytes nucleus diameter of the female mice offspring decreased, the proportion of nucleolus surrounded type chromatin configuration (SN) decreased, and the proportion of nucleoil not surrounded type (NSN) increased, the relative fluorescence intensity of 5MeC decreased, the differences were statistically significant (P<0.05) . Conclusion: Exposure to cigarette smoke during pregnancy may reduce indicators of offspring ovarian organ index, female rat follicle number and oocyte quality change, the high dose group can lead to oocyte chromatin structure and DNA methylation level anomaly.