Expression pattern of oxygen and stress-responsive gene transcripts at various developmental stages of in vitro and in vivo preimplantation bovine embryos

The present study examined the expression pattern of oxygen (O2) and stress-responsive gene transcripts at various preimplantation developmental stages of in vitro produced (IVP) and in vivo derived (IVD) bovine embryos. Embryos were produced in vitro from oocytes matured, fertilized and cultured in synthetic oviductal fluid (SOF) medium under low (5%) and high (20%) O2 concentrations. In vivo embryos were derived from 18 superovulated and artificially inseminated cows. In IVP and IVD groups, embryos were collected at 2-, 4-, 8-, 16-cell morula and blastocyst stages at specific time points for gene expression analysis. The cleavage rates (69.8 ± 4.8%) did not differ significantly, but blastocyst rates were significantly higher (28.5 ± 3.7%) in low O2 than those in high O2 group (18.7 ± 3.9%). Mean cell number in low O2 (145 ± 12) and high O2 (121 ± 73) IVP blastocyst were lower (P < 0.05) than those of IVD blastocyst (223 ± 25). The ICM ratio of IVD blastocyst (26 ± 4) was lower (P < 0.05) than that of IVP embryos under 5% O2 (33 ± 5) and 20% O2 (34 ± 4) concentrations, respectively. Using real time PCR, for the set of target transcripts (Glut1, Glut5, Sox, G6PD, MnSOD, PRDX5, NADH and Hsp 70.1) analyzed, there were differences in the mRNA expression pattern at 2-, 4-, 8-, 16-cell morula and Day 7 blastocyst stages between the two embryo sources. It can be concluded that, although in vitro bovine embryo culture in SOF medium under low (5%) O2 concentration provided a more conducive environment in terms of blastocyst formation; differences in the total cell number and gene expression pattern between the IVP and IVD embryos reflected the effect of O2 concentration.