Cumulus-oocyte interactions and programmed cell death in bovine embryos produced in vitro

This study investigated the interactions between cumulus cells (CCs) and oocytes and programmed cell death in bovine cumulus-oocyte complexes (COCs) with different morphological characteristics. DNA fragmentation was assessed in CCs at 0 and 24 h of maturation, as well as parthenogenetic developmental competence on the 9th day post-activation, blastocyst quality and BCL-2 and BAX transcript levels in matured CCs. Most immature oocytes in the COC-A group (full cumulus and several compact layers) were in the initial germinal vesicle (iGV) stage, exhibiting minimal or no DNA damage. In contrast, after follicle removal, the COC-B (partial cumulus and one or two cell layers) and -C (expanded cumulus) groups presented in more advanced GV stages and exhibited DNA fragmentation. After maturation, significant increases in fragmented nuclei were noted in COC-C and COC-B groups. Embryos resulting from the COC-A developed more rapidly and had increased competence compared to embryos resulting from groups COC-B and COC-C. The COC-B group exhibited the highest BAX protein levels and a reduced BCL-2/BAX protein ratio. The results show a negative correlation between nuclear fragmentation and embryonic development potential in COCs with different morphologies. In addition, a low BCL-2/ BAX protein ratio might be associated with an increase in nuclear fragmentation in CCs. (C) 2018 Elsevier Inc. All rights reserved.