Immunohistochemical localization of progesterone receptor isoforms in the chick pre-follicular ovary

The distribution of progesterone receptor A and B isoforms in different cell types of the chick pre-follicular ovary was studied by immunohistochemistry. Newly hatched chicks were killed and the left ovary was removed, fixed and embedded in paraplast. Sections (5 microns thick) were made for the detection of progesterone receptor isoforms, using a technique of indirect immunoperoxidase. The results indicate that progesterone receptors were localized in the nuclei of germinal epithelium and germ cells of the ovarian cortex and in the interstitial and epithelial cells of the lacunar channels of the ovarian medulla. Undifferentiated cells did not present progesterone receptors. In all cell subpopulations progesterone receptor B was the predominantly expressed isoform. These data suggest that progesterone receptor isoforms are differentially expressed in the chick pre-follicular ovary and that progesterone effects in this tissue are mediated by the progesterone receptor B isoform.