Loss of ERalpha-Mediated Estrogen Signaling Resulted in the Ovarian Expression of Male-Specific Gene.

Abstract

Sex hormones play a critical role in the development as well as maintenance of reproductive organs and their reproductive characteristics. While it is well established that estrogen plays a critical regulatory role in the developing gonads, whether it has a sex-specific functional role in sustaining the gonadal functions is not well known. Recent gene knockout approach has found that loss of estrogen signaling by knocking either aromatase or estrogen receptors resulted in the formation of somniferous tubule-like structure in the ovary. This surprising finding led us to hypothesize that estrogen suppresses the genes that confer male-specific characteristics. To test the hypothesis, we examined whether deletion of ER gene induced male-reproductive track-specific gene expression in the ovary. For this purpose, we compared gene expression profiles in the presence or absence of ERα-mediated estrogen signaling using DNA microarray. Briefly, total RNA extracted from wild-type (WT) and ERα knockout (ERαKO) mouse ovaries was subjected to microarray, which identified a number of differentially expressed genes. Among those genes are epididymal protease inhibitor (Eppin), seminal vesicle secretion protein (SVS) 5, and SVS6, which are all known to be specifically expressed in male reproductive track. The expression of Eppin mRNA was 10 folds higher in ERαKO than the baseline Eppin mRNA content in the WT ovary, while SVS5 and SVS6 mRNA showed 60 and 80 folds higher in the ER αKO, respectively. Expression of Eppin is well documented in male reproductive system (testis, epididymis, and spermatozoa) and is currently being studied as a potential target of male contraceptives. SVS proteins are semen coagulating factors and are known to enhance sperm motility. As was expected, no expression of Eppin or SVS has been reported in female reproductive tissues. To detect protein expression in the ERαKO ovary, we employed immunohistochemistry. Interestingly, however, unlike the above-mentioned strong Eppin mRNA expression in the ERαKO ovary, the protein expression level was very low compared to the strong expression in the epididymal epithelial cells, testis Sertoli cells, and spermatozoa. We are currently investigating the potential damaging effect of Eppin expression in the ovary. In conclusion, this novel finding suggests that estrogen may contribute to the maintenance of functional and potentially structural integrity of female gonad by suppressing the expression of genes that induce male specific phenotypes if expressed. Supported by a COBRE grant from NIH NCRR: P20 RR15592. (poster)