Progesterone receptor membrane component 1 (PGRMC1) action during bovine oocyte meiosis: a functional study

Progesterone Receptor Membrane Component 1 (PGRMC1) localizes to the centromeres at metaphase-I and II stages of bovine oocyte meiotic division, while it concentrates between the separating chromosomes at ana/telophase-I stages. This localization suggests an essential role for PGRMC1 during meiosis. The aim of the present study is to expand these morphological observations by using small-interfering RNA (RNAi) mediated gene silencing.Cumulus-Oocytes Complexes were collected from ovarian follicles and microinjected to deliver PGRMC1 or CTRL-RNAi into the oocytes cytoplasm, kept in meiotic arrest for 18h then in vitro-matured (IVM) for 24h. After IVM, efficacy in depleting PGRMC1 expression was assessed by quantitative RT-PCR and western blotting. These analysis revealed a significant 30% reduction of both mRNA and protein expression. After treatment, the oocyte capability to extrude the first polar body (PBI) and the morphology of the MII plates were considered as biological end-points. Our data indicated that PGRMC1`s down regulation determines a significant impairment of the oocyte`s capability to complete meiotic division. In fact, we observed a 22% reduction of the oocytes that extruded the PBI (p<0.05), which was accompanied by altered chromosomes segregation and increase in chromosomal scattering. These results are consistent with PGRMC1 localization and with a putative role during both chromosome segregation and cytokinesis. We hypothesize that altering PGRMC1 function impairs the process of chromosome separation and/or PBI formation that can result in genetic instability.