121 DIFFERENTIAL mRNA EXPRESSION BETWEEN IN VIVO AND IN VITRO-DERIVED BOS INDICUS AND BOS TAURUS EMBRYOS

Abstract

Brazil is a leading country in the world of commercial use of in vitro-produced bovine embryos with 200 000 transfers per year. The majority of in vitro-produced embryos are pure breed Nelore and are transferred fresh with 40% pregnancy rate. However, pregnancies are drastically reduced with frozen in vitro embryos. This experiment is part of our effort to learn more about molecular composition and morphology of in vitro-derived embryos that may be responsible for such discrepancy. We examined molecular expression of mRNA transcripts of 6 selected genes; apoptosis Bax,TP53(p53), SHC1SHC(p66), insulin growth factor receptor (IGF2R), stabilization of the plasma membrane PLAC8 and glucose conversion H6PD in in-vivo (control) and in-vitro Nelore and Bos taurus embryos. In vivo embryos were collected from superovulated cows at Day 7. In vitro embryo was produced from oocytes aspirated from live cows. A total of 284 oocytes (4 replicates) were matured and fertilized by standard IVF procedures. Presumptive zygotes were cultured in CR2 medium with 5% BSA in 50 μL drops (25 zygotes per drop) at 39°C under paraffin oil and 5% CO₂ in humidified air. Embryos that developed on Days 7 to blastocyst were transferred to recipients, and 10 blastocysts from each replicate were frozen for evaluation of gene expression patterns. Poly(A) mRNA was prepared from 3 groups of pools of 10 in vitro embryos and 10 of control in vivo-derived embryos. The quantification of all gene transcripts was carried out by real-time quantitative RT-PCR using the comparative CT method. Data on mRNA expression were normalized to the endogenous H2a.z and was analyzed by one-way repeated-measures ANOVA. The cleavage rates at Day 2 and number of blastocysts developed at Day 7 were 80.3 ± 3.2 and 42.2 ± 6.4, respectively. The level of expression of IGF2R was significantly (P < 0.05) higher in in vivo-derived embryos than in both groups of in vitro embryos. The expression of all 3 apoptosis genes were lower (P < 0.05) in in vivo than in vitro embryos with exception of p53 gene that was not different between Nelore in vitro and in vivo embryos but was significantly higher (P < 0.05) in Bos taurus in vitro embryos. There was no difference in expression of PLAC8 gene among any tested group of embryos and in expression of H6PD gene between Nelore in vitro and in vivo embryos. We concluded that significant differences in molecular makeup between in vitro and in vivo-derived Nelore embryos exist. Of particular importance seems to be pattern of expression of IGF2R receptor gene known as a good indicator of embryo quality, which promotes proliferation and differentiation. Similarly, higher expression of 2 BAX and p66 genes of apoptosis in in vitro embryos seems to be a further indication of inferior quality of Nelore in vitro-derived embryos that showed to be more profound in Bos taurus in vitro-derived embryos.