Effects of 17β-estradiol and xenoestrogens on mouse embryonic stem cells

Xenoestrogens such as 4-tert-octylphenol (OP) and 4-nonylphenol (NP) can adversely affect the reproductive and immune systems from their estrogenic effects in target cells. In this study, we investigated the effects of xenoestrogens on the expression of undifferentiation markers in mouse embryonic stem (ES) cells and of cardiomyocyte differentiation markers in mouse embryoid body (EB) cells induced to differentiate into cardiomyocytes from ES cells. The expressions of undifferentiation markers (Oct4, Sox2, Zfp206, and Rex-1) and cardiomyocyte differentiation markers (α-MHC, β-MHC, ANF, and MLC-2V) were determined by semi- and quantitative real-time PCR. Treatment with E2 or OP and NP induced an increase in Oct4 expression at the transcriptional level in a dose- and time-dependent manner. However, no difference was observed in the expression of Sox2, Zfp206 or Rex-1 genes in ES cells, suggesting that E2 may be an Oct4 enhancer in ES cells. Induction of Oct4 expression by E2 and xenoestrogens (OP and NP) did not change the methylation pattern of the Oct4-promoter and was not affected by treatment with a demethylating agent, 5-azacytidine. Taken together, these results suggest that E2 and xenoestrogens may impact on the undifferentiation process of ES and EB cells, and retain ES cells in an undifferentiated state.