ESTROGEN-RECEPTOR PROTEIN AND MESSENGER-RNA EXPRESSION IN THE OVARY OF SHEEP

Using immunohistochemistry and in situ hybridization, we attempted to identify the estrogen receptor (ER) protein and messenger RNA (mRNA) i n sheep ovaries during the follicular phase of the estrous cycle. Mono clonal anti-ER antibodies H222 and 1D5 were used for localizing estrog en receptor on ovarian cryo-sections. Labeling for ER was found over t he nuclei of surface epithelium, interstitial tissue, and granulosa ce lls of small as well as large ovarian follicles. In the preantral and small antral follicles, intense nuclear ER labeling was observed in mu ral granulosa cells and particularly in cumulus/granulosa cells surrou nding the oocyte. In the large healthy looking follicles, greater dive rsity in labeling for ER was observed, which is characterized by mixed populations of granulosa cells expressing positive and more or less n egative nuclear labeling. Such a pattern of labeling was particularly evident in follicles showing the signs of atresia. Generally, more int ense nuclear staining was localized in granulosa cells proximal to bas al membrane. In situ hybridization studies revealed the presence of ER mRNA in ovarian tissue. Autoradiographic visualization localized ER m RNA expression over the granulosa cells of healthy follicles of all si zes. Level of hybridization signal was comparable in mural and cumulus granulosa cells. In atretic follicles, the level of hybridization sig nal in granulosa cells was comparable to that of healthy follicles. A relatively weaker level of labeling was observed in granulosa cells di spersed in follicular antrum in follicles with advanced atretic lesion s. Theca cells expressed a lower level of labeling than granulosa cell s. Specificity of labeling for both ER protein and mRNA in ovary was p roved by parallel probing the ovine uterus. Ovine ER recognition by bo th H222 and 1D5 antibodies was also proved by immunoblotting. These st udies demonstrate the presence of the estrogen receptor and its messen ger RNA in the sheep ovary and suggest an autocrine/paracrine role of estradiol and its receptor in the regulation of ovarian follicle devel opment in sheep. (C) 1997 Wiley-Liss, Inc.