Embryo response to different progesterone concentrations during superovulation of Holstein heifers
Greater progesterone (P4) concentrations during the follicular growth have been associated with greater quality of embryos produced by superovulated cows and heifers. However, it is yet to be determined the mechanisms by which oocyte exposure to greater P4 concentrations improves early embryo quality. The objective of this study was to evaluate the impact of different P4 concentrations during superovulation on the transcriptome profile of early bovine embryos. A total of 63 post-puberty Holstein heifers were randomly assigned into two experimental groups: High P4 (n = 31) and Low P4 (n = 32). Heifers received a pre-synchronization protocol followed by a protocol of superovulation that included the allocated P4 treatment. Embryo collection was performed 7 days post artificial insemination and embryos were evaluated for stage of embryonic development and grades of quality. Embryos graded as good/excellent quality (High P4: n = 27; Low P4: n = 27) were randomly allocated in 3 biological replicates per treatment group, balanced for stage of embryonic development. Transcriptome analysis suggested that exposure to different concentrations of P4 during superovulation promote changes in gene expression of 7 days old embryos that may be related to their developmental competence. These modifications are associated with downregulation of beta-estradiol pathway, upregulation of trophoblast-related genes and downregulation of WNT signalling pathway. Our results suggest a potential sensitivity of future embryos to follicular P4 levels but do not allow to conclude if the effect is from the oocyte, the oviduct, or the uterus response to P4. Overall design: Heifers underwent to a pre-synchronization protocol followed by a protocol of superovulation that included the allocated P4 treatment. Embryos were collected 7 d post-artificial insemination (AI) and were evaluated for fertilization, stage of embryonic development, and grades of quality. Embryos were randomly allocated in 3 biological replicates per treatment group on which we performed gene expression profiling using RNAseq. Finally, we identified differential expression of genes between treatment groups.