Low oxygen tension improves developmental competence and reduces apoptosis in hand-made cloned buffalo (Bubalus bubalis) embryos

This study compared the effects of oxygen tension on the developmental competence, quality and expression level of some important genes in somatic cell nuclear transfer (SCNT) buffalo embryos produced through hand-made cloning. Following in vitro culture (IVC) of reconstructed embryos under 5% and 20% oxygen tension, the blastocyst rate (72.0±4.78 vs. 58.0±4.61%) and total cell number (413.5±66.7 vs. 265.4±29.8) were higher (P<0.01), and the apoptotic index (2.46±0.71 vs. 11.13±1.52) was lower (P<0.01), respectively, although there was no effect on the cleavage rate. The relative mRNA abundance of hypoxia inducible factors (HIF1α and HIF2α), was higher (P<0.01) whereas that of oxidative stress - (SOD-2, PRDX1 and GPX-1) and apoptosis-related genes (CASPASE3 and P53) was lower (P<0.05) in reconstructed embryos cultured under 5% oxygen than in those cultured under 20% oxygen tension. In conclusion, these results indicate that lowering the oxygen tension during IVC of SCNT embryos from 20 to 5% improves their developmental competence and quality, reduces the apoptosis level and that many of these effects may be elicited through altering the expression of transcription factors.