43 Actions of colony-stimulating factor 3 on the maturing oocyte and developing embryo in cattle

Colony-stimulating factor 3 (CSF3), also known as granulocyte colony-stimulating factor, has been reported to improve blastocyst yield when administered during oocyte maturation in the pig and to increase pregnancy outcomes in specific IVF patient populations when infused transvaginally. Here, we tested whether recombinant bovine CSF3 can act on the bovine oocyte during maturation or on the developing embryo to modify competence for development to the blastocyst stage. For Experiment 1, oocytes were matured with 0, 1, 10, or 100ngmL−1 of CSF3. Oocytes were then fertilised and embryos were cultured in serum-free medium for 7.5 days. There was no effect of CSF3 on cleavage rate or on development to the blastocyst stage except that 100ngmL−1 reduced (P=0.0366) the percentage of putative zygotes (P=0.0366) and cleaved embryos (P=0.0254) becoming blastocysts. Expression of transcripts for 93 genes in blastocysts was evaluated by RT-PCR using the Fluidigm platform. Transcript abundance was affected (P<0.05) by one or more concentrations of CSF3 for 4 genes only (CYP11A1, NOTCH2, RAC1, and YAP1). For Experiment 2, cumulus-oocyte complexes were fertilised with either X- or Y-sorted semen for 18-22h. Putative zygotes were cultured in medium containing 0, 1, 10, or 100ngmL−1 of CSF3. There was no effect of CSF3, sex, or the interaction on the percentage of putative zygotes that cleaved or on the percentage of putative zygotes or cleaved embryos becoming blastocysts. Gene expression was not determined. For Experiment 3, CSF3 (0, 1, 10, and 100ngmL−1) was added from Day 4 to 7.5 of development. Again, there was no effect of CSF3 on development to the blastocyst stage. Transcript abundance for a total of 10 genes was increased (P<0.05) by 100ngmL−1 of CSF3, including markers of epiblast (NANOG, SOX2), hypoblast (ALPL, FN1, KDM2B, and PDGFRA), both epiblast and hypoblast (HNF4A), and trophectoderm (TJAP1). Results are indicative that high concentrations of CSF2 can reduce oocyte competence and act on the embryo to affect characteristics of the blastocyst. Support was provided by the Elanco and Larson Endowment Fund.