Low oxygen tension during IVM improves bovine oocyte competence and enhances anaerobic glycolysis

This study evaluated the effect of two oxygen concentrations (20 and 5%) on bovine embryo development (kinetics of first cleavage and blastocyst development) during maturation (M) and fertilization (F) and analysed differences in gene expression between cumulus-oocyte complexes (COC) matured at 5 or 20% oxygen and the resulting blastocysts. A total of 1179 COC were divided into four groups according to the oxygen tension used (M5F5, M5F20, M20F5 and M20F20). Relative poly(A) mRNA abundance of GLUT1, GAPDH, LDHA, G6PD, MNSOD, GPX1, IGFR2, BAX, CCNB1, PTGS2 and GREM1 was analysed in COC, whereas 10 quality-related genes were analysed in blastocysts. M20F5 group developmental rates were significantly lower than all other groups (one-way ANOVA, P < or = 0.05). Two-way ANOVA showed a beneficial effect of low oxygen tension during in-vitro maturation on developmental rates, whereas the opposite situation was obtained in fertilization (P < or = 0.05). GAPDH, IGFR2, CCNB1, and GREM1 were up-regulated in the oocytes matured in low oxygen, whereas GLUT1, GAPDH, LDHA and GREM1 were up-regulated and PTGS2 down-regulated in the cumulus cells from the M5 group (P < or = 0.05). No differences were observed in blastocysts. Low oxygen tension during maturation alters the expression of genes related to oocyte competence and glucose metabolism and significantly (P < or = 0.05) improves embryo development, but not blastocyst quality.