Epidermal growth factor enhances the developmental competence of yak (Bos grunniens) preimplantation embryos by modulating the expression of survivin and HSP70

- EGF significantly enhances the yak blastocyst formation and the cell numbers.
- The expression of HSP70 and survivin was increased by EGF.
- The optimum concentration of EGF on yak embryos was 100 ng/mL.

Culture conditions can affect cleavage, zygotic genome activation, embryonic development, and blastocyst quality. Epidermal growth factor (EGF) has important autocrine and/or paracrine effects during early embryonic development. However, few studies of the effect of EGF on yak embryos have been reported. The aim of this study was to determine the effects of exogenous EGF on yak embryonic development in vitro, as well as the correlation between HSP70 and survivin expression patterns, blastocyst quality and EGF concentration. The in vitro matured cumulus-oocyte complexes (COCs) were fertilized with frozen-thawed semen, and the zygotes were incubated in culture media supplemented with different concentrations of EGF. During in vitro culture, the embryos were analyzed for development to the 4-cell, 8-cell, 16-cell, and blastocyst stages. The variation in total blastocyst cell numbers and their allocation to the inner cell mass (ICM) and trophectoderm (TE) lineages were determined by differential CDX2 staining. Relative HSP70 and survivin mRNA expression was examined by qPCR at the blastocyst stage. Compared to the control, EGF treatment (100 ng/mL) significantly increased the blastocyst formation rate but had no significant effect at other stages. The total number of cells per blastocyst increased with 100 ng/mL of EGF. HSP70 and survivin expression was higher in the EGF treatment groups than in the control group and highest with 100 ng/mL EGF. From the present study, we conclude that EGF significantly enhances yak blastocyst formation and cell numbers, which might be associated with the increased expression of HSP70 and survivin after EGF treatment.