53 Transcriptomic profiles of uniform populations of invivo-produced spherical, ovoid, or tubular porcine embryos during the initiation of elongation

Signalling interactions among littermate porcine conceptuses during embryo elongation can alter the expression of genes that are essential in promoting successful embryo elongation. Understanding the differential expression of critical genes from uniform littermate conceptuses as they undergo the initiation of elongation can help identify critical pathways and genes to facilitate improved synchronization of embryo elongation and birthweight uniformity. The objective of this study was to identify differential gene expression from uniform porcine conceptuses as they transition through spherical (S), ovoid (O), and tubular (T) morphologies during the initiation of elongation invivo. White crossbred gilts (n=22) were bred at oestrus (designated as Day 0 of gestation) and harvested at Day 9, 10, or 11 of gestation to obtain corresponding uniform populations of each embryo morphology. Reproductive tracts were immediately collected and flushed with 40mL of RPMI-1640 medium. Based on morphology, embryos were assigned to one of three treatment groups: (1) uniform S (n=8); (2) uniform O (n=8); or (3) uniform T (n=6) in which at least 80% of the embryos within each litter corresponded to the latest stage morphology. RNA-Seq was performed from 22 libraries constructed from a single invivo-produced embryo from the uniform populations of S, O, or T embryos. Differentially expressed genes (DEG) and pathway analysis were evaluated using DESEqn 2 and iPathwayGuide, respectively. For the S vs. O comparison, 5726 DEG and 7 pathways were significantly enriched, including ribosome biogenesis, spliceosome, pyrimidine metabolism, RNA polymerase, one carbon pool by folate, ECM-receptor interaction, and MAPK signaling pathways. For the S vs. T comparison, 5914 DEG and 7 pathways were significantly enriched, including ribosome biogenesis, DNA replication, pyrimidine metabolism, cell cycle, mismatch repair, spliceosome, and one carbon pool by folate pathways. Interestingly, most of the transcripts in pathways involving DNA processing, nucleotide metabolism, transcription, and post-transcriptional modifications were upregulated in S embryos compared with O and T embryos. For the O vs. T comparison, only 20 DEG were identified and no pathways were found to be significant after FDR adjustment. These data illustrate dramatic changes in the transcriptomes from pre-elongation stage S embryos compared with transitional stage O and T embryos, and provide putative genes and pathways involved in internal signals for the initiation of embryo elongation in pigs. The USDA is an equal opportunity provider and employer. Funding was provided by USDA-NIFA-AFRI grant no. 2017-67015-26456.