Progesterone receptors: expression and regulation in the mammalian ovary.

The authors have briefly discussed the molecular structure, regulation, and function of progesterone receptors in the mammalian ovary. Particularly important is the contrast in the regulatory mechanisms of PR induction in the ovary (gonadotropins/membrane receptor mediated) and other well-known progesterone target tissues, such as the uterus and mammary gland (estrogen/nuclear receptor mediated). Future research will focus on how the PR gene responds to these hormonal regulatory signals in this cell-specific manner. Equally important in this discussion has been the mounting evidence indicating that PRs are an essential component of the ovulatory process. The observation that PR-/- knockout mice are incapable of undergoing ovulation, even in response to gonadotropin challenge, further supports the previous physiological evidence indicating that PRs in preovulatory follicles are induced before, and are necessary for, ovulation. Further studies are required to determine the identity of PR-regulated target genes during the periovulatory period. Although our knowledge of PR structure, regulation, and function has increased dramatically during the past decade, many exciting questions remain related to the regulation and function(s) of PRs in the ovary and other tissues.