Respiration rates correlate with mRNA expression of G6PD and GLUT1 genes in individual bovine in vitro-produced blastocysts

Quantification of embryo respiration is a promising procedure to assess embryonic metabolism and possibly select viable embryos. At the blastocyst stage, ATP is produced by glycolysis and oxidative phosphorylation, processes that require uptake of oxygen and glucose, which is regulated by the expression of GLUT1 and G6PD. The purpose of the present study was to investigate the relationship between respiration rates and relative abundances of G6PD and GLUT1 transcripts in individual bovine blastocysts produced in vitro. Respiration rates of 104 bovine in vitro-produced blastocysts were measured individually using the nanorespirometer technology. Real-time RT-PCR was employed to determine the relative abundance of G6PD and GLUT1 mRNA in individual embryos. The mean respiration rates were similar for male and female blastocysts of the same developmental stage, but the sex ratio was skewed towards males. GLUT1 expression was down-regulated in female versus male embryos. In contrast, a ∼1.8-fold increase in the expression of G6PD mRNA was observed in female blastocysts when compared to male blastocysts, indicating that dosage compensation for this gene had not yet occurred. Both GLUT1 and G6PD expression levels were affected by morphological quality and stage of development. Expression of GLUT1 and G6PD mRNAs was correlated with respiration rates, indicating that, in metabolically active blastocysts, uptake of oxygen and glucose are jointly increased. These findings suggest that expression of genes for oxidative phosphorylation and glycolysis are both involved in oxygen demanding ATP production.