27 Growth factor receptors in in vitro-produced bison and bovine embryos

In vitro embryo production (IVP) is a viable approach for genetic exchange between bison herds that eliminates the need to transport live animals and minimizes stress and biosecurity risks. Although IVP systems have been successfully employed in cattle, the same protocols are less efficient when applied to bison. We hypothesise that supplementation of IVP media with growth factors specific to stage of embryo development will improve the number and quality of bison embryos produced. The objective was to screen bison embryos for 13 growth factor receptors (GFR) observed in embryos from other species at various stages of development. Abattoir-sourced oocytes from bovine and bison were used to generate embryos using a standard IVP procedure (4 replicates). Embryos were collected as follows: zygotes ~21 h after fertilization and dependent upon the presence of 2 polar bodies (n = 200), 8–16 cell embryos 56 h postinsemination (p.i.; n = 120), morulae 6 days p.i. (n = 80), blastocysts (n = 20), and expanded blastocysts 7 days p.i. (n = 20). All embryos were washed in Dulbecco’s phosphate-buffered saline and polyvinyl alcohol and frozen at −80°C. Primer efficiencies were tested with bison and bovine granulosa cells on real-time quantitative polymerase chain reaction using standard curves, and only values between 90–110% were accepted for both species. The expression of IGF-R2, IL6-R, BMP-R2, FGF-R1, EGF-R, and IGF-R1 was quantified and normalized to the reference genes β-actin and GAPDH. Data were analysed using the ^ΔΔCT method, for statistical comparisons between species (bison vs bovine) and embryo stages within species, two-way ANOVA followed by Tukey’s post hoc test was employed. Bovine embryos served as the control for species comparisons. In bison embryos, higher fold changes were observed in BMP-R2 in 8- to 16-cell embryos (P < 0.05) and morulae[MOU1] (P < 0.00001); FGF-R1 in 8- to 16-cell embryos (P < 0.00001); EGF-R in 8- to 16-cell embryos (P < 0.001) and blastocysts (P < 0.00001); and IGF-R in 8- to 16-cell embryos (P < 0.001), morulae (P < 0.00001), blastocysts (P < 0.05), and expanded blastocysts (P < 0.001). There was no significant difference in the expression of IL6-R between the two species. The fold change in IGF-R2 was significantly lower in bison embryos at all stages. Embryo stage analysis within each species, using zygote as the control, revealed that in bison embryos, the expression of IGF-R2, BMP-R2, FGF-R1, EGF-R, and IGF-R1 was highest at the zygote and 8- to 16-cell embryo stages. The morula-stage embryos displayed significantly higher expression of IL6 in bison embryos. In bovine embryos, the expression of BMP-R2, EGF-R, and IGF-R1 was highest in zygote and 8- to 16-cell embryos. Moreover, zygotes exhibited significantly higher expression of FGF-R1 and IGF-R2, while 8- to 16-cell embryos displayed significantly higher expression in IL6. These differences in GFR expression between bison and cattle embryos will be used to develop supplementation strategies for a bison-specific IVP media system.