Immunohistochemical localization of the avian progesterone receptor and its candidate receptor binding factor (RBF‐1)

An avian oviduct nuclear matrix protein in the 6–10 kDa size range has been implicated to function in the cell‐free nuclear binding of the avian oviduct progesterone receptor (PR). This protein, termed the receptor binding factor‐1 (RBF‐1), has been purified and partially characterized [Schuchard et al.: Biochemistry 30:4535–4542, 1991]. This paper describes the immunohistochemical co‐localization of the RBF‐1 and PR in the avian oviduct cell nuclei and rat reproductive cell nuclei using antibodies directed specifically against the RBF‐1 and activated PR. In the undifferentiated oviduct, the immunoreactivities for both PR and RBF‐1 were co‐localized in the nuclei of only epithelial cells, but not the stromal cells or smooth muscle cells. In the partially differentiated oviduct of estrogen treated chicks, the immunoreactivity co‐localized in the nuclei of not only epithelial but also glandular and stromal cells. Staining for the PR, but not RBF‐1, was detected in the smooth muscle cells. The intensity of the PR but not the RBF‐1 staining was markedly down‐regulated in these cells at 2 and 6 h after treatment of the animals with progesterone (P). However, the band patterns for RBF‐1 in the Western blots did show qualitative changes which may reflect P‐induced post‐translational modifications which alter the epitope on the RBF‐1. Interestingly, immunohistochemical analysis of several reproductive tissues of the rat showed that certain cell types in the uterus, ovary, and prostate displayed strong positive nuclear staining for an RBF‐1–like antigen(s). Western blot analyses of the rat reproductive tissues showed that the immunoreactive component was a 15 kDa antigenically related RBF‐1 which was only present in the uterus.