Oocyte in-vitro maturation: BCL2 mRNA content in cumulus cells reflects oocyte competency

BCL2-associated X protein (BAX) and B-cell leukaemia/lymphoma gene-2 (BCL2), which are, respectively, pro- and anti-apoptotic proteins of the BCL2 gene family, participate in the mitochondria-dependent apoptosis pathway. A correlation between low incidence of apoptosis in cumulus cells and oocyte maturation has previously been suggested in ovarian stimulation. However, little is known in unprimed ovaries. These authors have investigated whether BAX and BCL2 expression in cumulus cells affects the competency of in-vitro matured oocytes. We have studied 100 cumulus–oocyte–complexes (COC) recovered from unprimed ovaries of 13 women diagnosed with polycystic ovary syndrome (PCOS) and undergoing in-vitro maturation (IVM) with their informed consent. COC were matured for 24 h in a specific maturation medium and the cumulus was stripped from the oocyte. BAX and BCL2 mRNA content was measured in each COC using real-time polymerase chain reaction. We found that BCL2 mRNA expression was significantly higher in cumulus cells associated with mature oocytes than those associated with immature oocytes while BAX mRNA concentrations did not vary in cumulus cells. Regarding fertilization, higher BCL2 mRNA content was found in cumulus cells enclosing fertilized oocytes (0.140 versus 0.075; P = 0.03). These results suggest that BCL2 expression is strongly associated with the ability of oocytes to complete nuclear maturation and to be fertilized