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This study examined the effects of O2 concentration (5% vs 20%) during in vitro maturation (IVM), fertilization (IVF) and culture (IVC) or supplementation of IVM and IVC media with cysteamine (50 and 100 μm, respectively; IVM, IVF and IVC carried out in 20% O2), on blastocyst rate and relative mRNA abundance of some apoptosis-related genes measured by real-time qPCR in immature and in vitro-matured buffalo oocytes and in embryos at 2-, 4-, 8- to 16-cell, morula and blastocyst stages. The blastocyst rate was significantly higher (p < 0.05) while the percentage of TUNEL-positive cells was significantly lower (p < 0.05) under 5% O2 than that under 20% O2. The mRNA expression of anti-apoptotic genes BCL-2 and MCL-1 was significantly higher (p < 0.05) and that of pro-apoptotic genes BAX and BID was lower (p < 0.05) under 5% O2 than that under 20% O2 concentration at many embryonic stages. Following cysteamine supplementation, the blastocyst rate and the relative mRNA abundance of BCL-XL and MCL-1 was significantly higher (p < 0.05) and that of BAX but not BID was lower (p < 0.05) at many stages of embryonic development, although it did not affect the percentage of TUNEL positive cells in the blastocysts significantly. The mRNA expression pattern of these genes during embryonic development was different in 5% vs 20% O2 groups and in cysteamine supplemented vs controls. At the 8- to 16-cell stage, where developmental block occurs in buffalo, the relative mRNA abundance of BCL-2 and MCL-1 was highest under 5% O2 concentration and that of BAX and BID was highest (p < 0.05) under 20% O2 concentration. These results suggest that one of the mechanisms through which beneficial effects of low O2 concentration and cysteamine supplementation are mediated during in vitro embryo production is through an increase in the expression of anti-apoptotic and a decrease in the expression of pro-apoptotic genes.