PPARG is dispensable for bovine embryo development up to tubular stages†

Following blastocyst hatching, ungulate embryos undergo a prolonged preimplantation period termed conceptus elongation. Conceptus elongation constitutes a highly susceptible period for embryonic loss, and the embryonic requirements during this process are largely unknown, but multiple lipid compounds have been identified in the fluid nourishing the elongating conceptuses. Peroxisome proliferator-activated receptors mediate the signaling actions of prostaglandins and other lipids, and, between them, PPARG has been pointed out to play a relevant role in conceptus elongation by a functional study that depleted PPARG in both uterus and conceptus. The objective of this study has been to determine if embryonic PPARG is required for bovine embryo development. To that aim, we have generated bovine PPARG knock-out embryos in vitro using two independent gene ablation strategies and assessed their developmental ability. In vitro development to Day 8 blastocyst was unaffected by PPARG ablation, as total, inner cell mass, and trophectoderm cell numbers were similar between wild-type and knock-out D8 embryos. In vitro post-hatching development to D12 was also comparable between different genotypes, as embryo diameter, epiblast cell number, embryonic disk formation, and hypoblast migration rates were unaffected by the ablation. The development of tubular stages equivalent to E14 was assessed in vivo, following a heterologous embryo transfer experiment, observing that the development of extra-embryonic membranes and of the embryonic disk was not altered by PPARG ablation. In conclusion, PPARG ablation did not impaired bovine embryo development up to tubular stages.