Immunocytochemical localization of progesterone receptor in the chick ovary

The distribution of progesterone receptor (PR) in the chick ovary was studied using light- and electron-microscopic immunocytochemical methods. With the light microscopic technique, PR was observed in the germinal epithelium cells of estrogen-treated and estrogen-untreated immature chicks. With the preembedding immunocytochemical technique, which proved to be more sensitive than immunohistochemistry using paraffin sections, the germinal epithelium and also part of the thecal and stromal cells were stained when immature chicks were not treated with estrogen. After estrogen treatment, the number of PR-positive stromal and thecal cells increased, as did the immunostaining intensity in their nuclei. The granulosa cells were PR-positive only after estrogen treatment. In the ovary of laying hens, the most intense staining for PR was localized in the germinal epithelium. PR was also present in the thecal, stromal, and granulosa cells. At the subcellular level, PR was detected only in the cell nuclei, indicating that ovarian PR is intranuclear independent of the presence of progesterone. In conclusion, immunocytochemical methods proved to be suitable for studying steroid hormone receptors in steroid-producing tissues (e.g. the ovary), because excess endogenous hormones do not affect detection of the receptor with the antibody as they do detection with labeled ligands. Immunocytochemically, the germinal epithelium, stromal, thecal, and granulosa cells of the laying hen ovary were shown to be target cells for progesterone. The inducibility of PR by estrogen in the thecal, stromal, and granulosa cells suggests that these cell types are also sensitive to estrogen.