Differential expression of estrogen receptor-beta and estrogen receptor-alpha in the rat ovary

Immunohistochemical localization of two estrogen receptor (ER) subtypes, ER beta and ER alpha, was performed in neonatal, early postnatal, immature, a nd adult rats to determine whether ER alpha and ER beta are differentially expressed in the ovary. ER beta and ER alpha were visualized using a polycl onal anti-ER beta antibody and a monoclonal ER alpha (ID5) antibody, respec tively. Postfixed frozen sections and antigen-retrieved paraffin sections o f the ovary revealed nuclear ER beta immunoreactivity (IR) in granulosa cel ls, which was prevented when peptide-adsorbed antibody was used instead. In immature and adult rat ovaries, ER beta was expressed exclusively in nucle i of granulosa cells of primary, secondary, and mature follicles. Atretic f ollicle granulosa cells showed only weak or no staining. No specific nuclea r ER beta IR was detected in thecal cells, luteal cells, interstitial cells , germinal epithelium, or oocytes. In neonatal rat ovary, no ER beta expres sion was found. In ovaries of 5- and 10-day-old rats, weak ER beta IR was o bserved in granulosa cells of primary and secondary follicles, but no stain ing was detected in the primordial follicles. ER alpha protein exhibited a differential distribution in the ovary with no detectable expression in the granulosa cells but evidence of ER alpha IR in germinal epithelium, inters titial cells, and thecal cells. In the oviduct and uterus, IR for ER alpha, but not ER beta, was found in luminal epithelium, stromal cells, muscle ce lls, and gland cells. Our present study demonstrates that ER beta and ER al pha proteins are expressed in distinctly different cell types in the ovary. The exclusive presence of ER beta in granulosa cells implies that this spe cific new subtype of ER beta mediates some effects of estrogen action in th e regulation of growth and maturation of ovarian follicles.