Effect of different culture media on the temporal gene expression in the bovine developing embryos.

We have previously shown that the in vitro embryonic development and the yield of viable calves were increased by using a two-step chemically defined medium for post-fertilization culture of bovine embryos. In this study, we explored the embryonic development and the temporal behavioral interaction of the genes involved in IFNτ gene expression and how they behave in an orchestrated manner to increase the developmental competence of IVF produced embryos by culturing in the chemically defined medium. Behavior of genes included ETS2, CDX2, GATA2, GATA3, OCT4 and NANOG was analyzed in early bovine IVF produced embryos, (from compact morulae to the blastocyst hatching stages), by semi- and relative quantitative PCR and compared between two in vitro culture (IVC) systems, two-step chemically defined medium and modified synthetic oviductal fluid (mSOF) containing 8 mg/mL, BSA. Early embryonic development was found to be better in two-step chemically defined culture system than that of mSOF as indicated by the increment of blastocyst yield, 33.1% in two-step culture system vs 18.8% in mSOF medium, and the blastocyst hatching, 52.3% in two-step culture system vs 33.5% in mSOF medium. Relative quantitative gene expression showed harmonic behavior in the two-step culture system rather than the culture in mSOF, IFNτ showed even increase throughout the embryonic development in the two-step culture medium while it decreased with blastocyst hatching in mSOF culture condition. Temporal dominance of OCT4 over all the transcription factors was found in regulation of IFNτ expression (the major factor of expression regulation but in inverse manner). However, ETS2, CDX2, GATA2 and GATA3 are potent IFNτ stimulator in cumulative manner but in case of OCT4 decrement. CDX2 directly related with IFNτ, but still under OCT4 dominance and also regulated by the subservient of OCT4 which is NANOG. In conclusion, this study confirmed our previous results about the usefulness of using the two-step chemically defined culture medium for increasing the developmental competence of IVF produced embryos and elucidated the dominance of OCT4 over the other genes implicated in regulation of IFNτ expression.