Cellular and Molecular Mechanisms of Mammalian Ovulation

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DESCRIPTION (provided by applicant): The long-term goal of our research is to elucidate the molecular cascades of LH-induced signals within preovulatory follicles, leading to ovulation. The LH surge stimulates the synthesis of progesterone and its intracellular receptors, progesterone receptors (PRs), in the granulosa cells of preovulatory follicles. Interaction between progesterone and PRs in an autocrine/paracrine fashion is essential for ovulation. However, the exact mechanisms by which ligand-dependent activation of PRs controls ovulation and thus normal reproductive cyclicity and fecundity are unknown. To gain insight into the molecular mechanisms underlying PR-mediated ovarian functions, we initiated cloning of PR downstream genes in luteinizing granulosa cells. The two genes we have characterized as PR-downstream are the ligand-receptor system for pituitary adenylate cyclase activating polypeptide (PACAP): PACAP and its receptor type 1 (PAC1). The temporal and spatial pattern of expression and secretion of the ligand PACAP along with the cellular localization of the receptor PAC1 in the ovary advocates the potential significance of this ligand-receptor system for ovulatory processes. Indeed, pharmacological blockade of ligand-dependent activation of PAC1 appears to interfere with the efficacy of LH and progesterone in bringing about ovulatory processes. Thus, our working hypothesis is that PACAP-induced activation of PAC1 mediates, at least in part, PR function critical for follicular rupture with release of a meiotically mature oocyte. The immediate goal of this application is to determine the functional importance of PACAP within preovulatory follicles during the periovulatory period, using in vivo and in vitro approaches. In Aim 1, we will test whether PR-induced PACAP is critical for follicular rupture and for expression of ovulation-related genes, including proteolytic enzymes. In addition, we will identify PAC1-downstream genes that may play an important role in follicular rupture. In Aim 2, we will determine the initial death/survival pathway(s) that is modulated by PR-induced PACAP in luteinizing granulosa cells. In Aim 3, we will test whether PR-induced PACAP regulates the polyadenylation/translation capacity of meiotically maturing oocytes. The proposed studies are designed to provide functional endpoint(s) of interaction between PR-induced PACAP and PAC1 in preovulatory follicles during the periovulatory period. Information derived from our results will allow us to better manage fertility, infertility, and endocrine-based disorders.