SummaryTo investigate the effects of physiologically relevant heat shock during oocyte maturation, buffalo cumulus-oocyte complexes (COCs) were cultured at 38.5°C (control) or were exposed to 39.5°C (T1) or 40.5°C (T2) for the first 6 h of in vitro maturation (IVM), followed by 38.5°C through the next 18 h/IVM and early embryonic development up to the blastocyst stage. Gene expression analysis was performed on selected target genes (HSF-1, HSF-2, HSP-70, HSP-90, BAX, p53, SOD1, COX1, MAPK14) in denuded oocytes and their isolated cumulus cells resulting from control COCs as well as from COCs exposed to a temperature of 39.5°C (T1). The results indicated that heat shock significantly (P < 0.01) decreased the maturation rate in T1 and T2 cells compared with the control. After in vitro fertilization (IVF), cleavage rate was lower (P < 0.01) for oocytes exposed to heat stress, and the percentage of oocytes arrested at the 2- or 4-cell stage was higher (P < 0.01) than that of the control. The percentage of oocytes that developed to the 8-cell, 16-cell or blastocyst stage was lower (P < 0.01) in both T1 and T2 groups compared with the control group. mRNA expression levels for the studied genes were decreased (P < 0.05) in treated oocytes (T1) except for HSP-90 and HSF-1, which were increased. In cumulus cells isolated from COCs (T1), the expression for the target genes was upregulated except for BAX, which was downregulated. The results of this study demonstrated that exposure of buffalo oocytes to elevated temperatures for 6 h severely compromised their developmental competence and gene expression.
Keywords: Cumulus cells; Embryo; Gene expression; Heat stress; Oocyte.