[Effects of cigarette smoke on chromatin configuration, DNA methylation and expression of related genes in mice oocytes].

Objective: To study the effect of cigarette smoke on chromatin configuration, DNA methylation and expression of related genes in mice oocytes.

Methods: The clean grade ICR female mice were divided into 3 groups, control group, low dose group and high dose group. Animals were placed inside a perspex chamber( 18L) filled up with the smoke produced by 0, 1, 2 cigarettes, one hour a time, twice daily for 4weeks. Nuclear staining with Hoechst 33342, to observe the quality of oocyte and chromatin configuration. Analysis of the DNA methylation patterns by indirect immunofluorescence. The expressions of DNA methyltransferases( DNMT) 1, DNMT3a and DNMT3b mRNA were detected by quantitative real time PCR.

Results: With the increase of smoke concentration, the diameter of oocytes was significantly decreased( P <0. 05), the percentage of non surrounded nucleolus( NSN) chromatin configuration was significantly increased( P < 0. 05). In high dose group, the level of DNA methylation wassignificantly lower than that of control group( P < 0. 05). The expression of DNMT1 decreased with the increase of smoke concentration, but the expression level of DNMT3b was significantly decreased( P < 0. 05).

Conclusion: Cigarette smoke exposure may alter oocyte chromatin configuration, decrease the expression level of DNMTs, resulted in oocytes DNA methylation decreased, so as to decrease the quality of oocytes.