Differential immunolocalization of estrogen receptor α and β in rat ovary and uterus

In order to investigate the localization of estrogen receptor (ER) alpha and ER beta in the reproductive organs in the rat, polyclonal antibodies were raised to each specific amino acid sequence. The Western blot with anti-ER alpha antibody showed a 66 kDa band in rat ovary and uterus, while that with anti-ER beta antibody detected a 55 kDa band in rat ovary, uterus and prostate. The ligand-independent nuclear localization of the two receptors was verified by immunocytochemistry. By immunohistochemistry, the nuclei of glandular and luminal epithelial cells in the uterus were stained with anti-ER alpha antibody, whereas only the nuclei of glandular epithelium cells were stained with anti-ER beta antibody. In rat ovary, positive signals were shown with anti-ER beta antibody in the nuclei of granulosa cells. No specific immunostaining was observed with anti-ER alpha antibody. Although ER beta was immunostained at the proestrous, metestrous and diestrous stages, the immunoreactivity of ER beta was hardly detected at the estrous stage in rat ovary. Thus, we show differential expression of ER alpha and ER beta in rat uterus and ovary at the protein level, which may provide a clue for understanding the roles of the two receptors in reproductive organs.