Regulation of expression of microvillus membrane proteins by estrogen in baboon fetal ovarian oocytes.

We previously demonstrated that the number and height of oocyte microvilli were reduced in baboon fetuses deprived of estrogen in utero and restored to normal in animals supplemented with estradiol. Phosphorylated ezrin and Na+/H+ exchange regulatory factor 1 (NHERF, now termed SLC9A3R1) link f-actin bundles to the membrane, whereas alpha-actinin cross-links f-actin to form microvilli. Therefore, we determined whether these proteins were expressed in oocytes of the fetal baboon ovary and whether expression and/or localization were altered between mid and late gestation in association with an increase in estrogen and in late gestation in animals in which estrogen was suppressed (>95%) or restored by treatment with an aromatase inhibitor with or without estradiol. Expression of alpha-actinin was low at mid gestation, increased on the surface of oocytes of primordial follicles in late gestation, and was negligible in the ovaries of estrogen-suppressed fetuses and normal in animals treated with estrogen. Ezrin (total and phosphorylated) and SLC9A3R1 expression was localized to the surface of oocytes at mid and late gestation in estrogen-replete baboons and to the cytoplasm in late gestation after estrogen suppression. These results are the first to show that the fetal baboon oocyte expressed ezrin, SLC9A3R1, and alpha-actinin, and that these proteins were localized to the oocyte surface consistent with their role in microvilli development in epithelial cells. The current study also showed that the developmental increase in oocyte expression of alpha-actinin is regulated by estrogen and correlated with the estrogen-dependent increase in oocyte microvilli demonstrated previously. Therefore, we propose that development of oocyte microvilli requires expression of alpha-actinin and that expression of alpha-actinin and localization of ezrin-phosphate and SLC9A3R1 to the oocyte membrane are regulated by estrogen.