The expression level of SOX2 at the blastocyst stage regulates the developmental capacity of bovine embryos up to day-13 of in vitro culture

Quality of in vitro-produced embryos is influenced by changes in gene expression in response to adverse conditions. Gene markers for predicting 'good embryos' do not exist at present. We propose that the expression of pluripotency markers OCT4-SOX2-NANOG in D9 (day 9) bovine demi-embryos correlated with development at D13 (day 13). Day 8 in vitro-produced blastocysts were split in two cloned halves, one half (D9) was subjected to analysis of pluripotency markers and the other was kept in culture until D13 of development. Embryo development was scored and correlated with its own status at D9 and assigned to one of two categories: G1, arrested/dead; or G2, development up to D13. SOX2 and NANOG expression levels were significantly higher in embryos from G1 and there was also negative correlation between SOX2 and embryo survival to D13 (G3; r = -0.37; P = 0.03). We observed a significant reduction in the expression of the three studied genes fromD9 to D13. Furthermore, there was a correlation between the expression of pluripotency markers at D9 and embryo diameter and the expression of trophoblasticmarkers at D13 (TP1-EOMES-FGF4-CDX2-TKDP1). Finally, the quotient between the relative expression of SOX2 and OCT4 in the D9 blastocysts from G1 and G2 showed that embryos that were considered as competent (G2) had a quotient close to one, while the other group had a quotient of 2.3 due to a higher expression of SOX2. These results might indicate that overexpression of SOX2 at the blastocyst stage had a negative effect on the control of embryonic developmental potential.