Insight into Progesterone Receptor Membrane Component 1 (PGRMC1) action during bovine oocyte meiosis by means of small-interfering RNA mediated gene silencing

Introduction Previous studies suggest that Progesterone Receptor Membrane Component 1 (PGRMC1) plays an essential role during bovine oocyte meiosis, since it 1) localizes to the centromeres at metaphase-I and II and 2) concentrates between the separating chromosomes at ana/telophase-I. Moreover, injection of an antibody to PGRMC1 significantly impairs completion of meiosis. The aim of the present study is to expand these findings by using small-interfering RNA (RNAi) mediated gene silencing. Methods Cumulus-Oocytes Complexs were microinjected to deliver PGRMC1 or CTRL-RNAi into the cytoplasm of oocytes, kept in meiotic arrest for 18h with 10µM cilostamide and then in vitro-matured for 24h (IVM). After IVM, efficacy in depleting PGRMC1 expression was assessed by quantitative RT-PCR. Finally, the oocyte capability to extrude the first polar body (PBI) and the morphology of the MII plates were assessed. Results and Discussion PGRMC1 expression following PGRMC1-RNAi treatment was significantly reduced by 30%. This was accompanied by a 22% reduction of the oocytes that extruded the PBI (p<0.05). Surprisingly, PGRMC1-RNAi treatment did not affect MII plate formation or morphology. However, a significantly higher proportion of PGRMC1-RNAi injected oocytes possessed clumps of DNA scattered throughout the ooplasm in addition to the MII plate (p<0.05). This is consistent with PGRMC1 localization at the midbody and with a putative role in cytokinesis. We hypothesize that lower PGRMC1 expression impairs the process of PBI formation. As a consequence, DNA that should be extruded with the PBI is retained in the cytoplasm and degraded. Funding: FP7-PEOPLE-2011-CIG, contract n.:303640-Pro-Ovum.