Functional assessment of Progesterone Receptor Membrane Component 1 (PGRMC1) activity during bovine oocyte meiosis

Previous studies suggest that PGRMC1 plays essential roles dur- ing bovine oocyte meiosis since it localizes to the centromeres at metaphase-I and II and concentrates between the separating chromosomes at ana/telophase-I. To confirm this hypothesis, we conducted a series of functional studies in which PGRMC1 activity was disturbed by using several experimental approaches and the effect on meiosis-I was assessed. In a first set of experiments, treat- ment with the PGRMC1 inhibitor (AG205) significantly affected oocyte meiosis in a dose dependent manner by: (1) decreasing the % of oocytes that extruded the first polar body (PB-I); (2) affecting meiotic progression by decreasing the % of oocytes that reached MII-stage and increasing the % of oocytes showing aberration of chromosome segregation that often resulted in the formation of scattered DNA within the cytoplasm. In a second set of experiments, a siRNA-mediated gene silencing approach was used to reduce oocytes PGRMC1 expression. Overall, PGRMC1 down-regulation mirrored AG205 effects, by (1) significantly reducing the % of oocytes extruding PB-I; (2) increasing the % of oocytes showing aberrant meiotic figures and DNA scattering. Finally in a third set of experiments, injection of an antibody to PGRMC1 had a more pro- nounced effect. In fact, this treatment significantly impaired the formation of MI plates and completion of meiosis-I. The present findings are consistent with PGRMC1 localization and with a puta- tive role in both chromosomes separation and cytokinesis.