(359) Progesterone Receptor Component (PGRMC) 1 and 2 Regulate Primordial Follicle Formation

Progesterone Receptor Component (PGRMC) 1 and 2 Regulate Primordial Follicle Formation

Agnes A. Asubonteng¹; Melissa Pepling²

< ![if !supportLists] >1.       < ![endif] >Department of Biology, Syracuse University, Syracuse, New York

< ![if !supportLists] >2.       < ![endif] >Department of Biology, Syracuse University, Syracuse, New York

Primordial follicles consist of single oocyte, each surrounded by a layer of granulosa cells. The pool of these follicles at the time of birth serves as the ovarian reserve that defines fertility in most female mammals. Oocytes start off as primordial germ cells which divide mitotically but with incomplete cytokinesis so that cells are connected by intercellular bridges, forming cysts. The germ cells enter meiosis and progress through prophase 1 to the diplotene substage. Next, cysts break apart, releasing individual oocytes which are each then surrounded by a layer of granulosa cells forming a primordial follicle containing a diplotene arrested oocyte. The mechanisms controlling these processes remain unclear. Our model is that normally maternal progesterone (P4) prevents premature cyst breakdown and primordial follicle formation. Yet, how the developing ovary receives the P4 signals is unknown. Studies have demonstrated active P4-membrane signaling during cyst breakdown. In this work, we explore whether progesterone receptor membrane components (PGRMC) 1 and 2 play a role in primordial follicle formation dependent or independent of P4 signaling in the developing ovary. Here we used antibodies against PGRMC1 and 2 in whole mount immunohistochemistry to determine if both receptors are present prior to and during primordial follicle formation in harvested ovaries at 15.5 days post coitum (dpc) through to Postnatal day (PND) 5. Our results show PGRMC1 and 2 expression in both oocytes and somatic cells before birth and gradually becoming localized in the cytoplasm of oocytes over time. Furthermore, we used an ovary organ culture system to directly observe the roles of PGRMC1 and 2 during primordial follicle formation similar to in vivo. Ovaries were collected at either 17.5 dpc or PND 1, placed in culture, and treated with control media, media supplemented with IgG, a 2.5ug/ml PGRMC1, or 20ug/ml of PGRMC1 and 2 function blocking antibodies for 5 days. Our results showed a significant reduction of about 10% and 4% in the percent single oocytes, our measure of primordial follicle formation in ovaries cultured starting at 17.5dpc with PGRMC1 or PGRMC2 blocking antibodies respectively compared to the controls. There was no significant change in the number of oocytes in ovaries starting at 17.5 dpc between cultured ovaries of both experimental groups and controls. When cultured, starting at PND1, the significant change remained at 4% between ovaries cultured with PGRMC2 function blocking antibody and control but changed to 14% in ovaries cultured with PGRMC1 function blocking antibody compared to the control. Again, there was no change in the number of oocytes at PND1. Also, when treated with PGRMC1 and 2 function blocking antibody together, there was an additive effect with a significant reduction of about 24% in the percent single oocytes compared to the control. These results suggest PGRMC1 and 2 promote cyst breakdown. Our findings suggest a role for PGRMC1 and 2 in the establishment of the ovarian reserve.