Significant embryo mortality occurs at or around the time of implantation or attachment in virtually all mammalian species studied to date, even in naturally conceived embryos. Embryos resulting from assisted reproductive technologies (ART) are even more susceptible to peri-implantation failure. Herein we describe our effort to characterise the transcriptomes of embryonic disc (ED) and trophoblast (TE) cells from porcine embryos derived from AI, IVF, parthenogenetic oocyte activation (PA) and somatic cell nuclear transfer (NT) on Days 10, 12 and 14 of gestation. The IVF, PA and somatic cell NT embryos were generated using in vitro–matured oocytes, cultured overnight in vitro and then transferred at the 1- to 2-cell stage into appropriately synchronized recipient gilts. On the appropriate collection day, embryos were flushed from the uterus and ED was separated from TE by mechanical dissection. Double-stranded cDNA from the collected samples was sequenced using the GAII platform from Illumina (San Diego, CA, USA). The resulting sequencing reads were aligned to a custom swine transcriptome database (see Isom et al. 2010). A generalized linear model was fit for each of 41 693 genomic regions, for ED and TE samples separately, accounting for embryo type, gestation day and their interaction and using total lane read count as a normalizing offset. Genes with significant embryo type differences (controlling the false discovery rate at 0.10) were subsequently tested for differences between IVF and each of AI, PA and NT. Those genes with significant post hoc differences (either up- or down-regulated compared with IVF) were characterised in terms of gene ontologies and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways using a gene set enrichment test. Bone morphogenetic protein signalling was down-regulated (KEGG; P = 0.0099; adjusted to control for FDR at 0.05) in the ED of IVF embryos when compared with AI embryos. In TE cells from IVF embryos, ubiquitin-mediated proteolysis and ErbB signalling (adj P = 0.031 for both pathways) were aberrantly regulated when compared with AI embryos. Of particular interest is the observation that expression of genes involved in chromatin modification (GO:BiologicalProcess; q-value = 0.00005) and epigenetic regulation of transcription (q = 0.00007) was very significantly disrupted in inner cell mass cells from NT embryos compared with IVF embryos. Surprisingly, no such disruption of the epigenetic machinery was observed in the TE cells from NT embryos. In summary, we have used high-throughput sequencing technologies to compare gene expression profiles of various ART embryo types during peri-implantation development. We expect that these data will provide important insight into the root causes of (and possible opportunities for mitigation of) suboptimal development of embryos derived from ART.
Funding was received from NIH R01 RR013438 and Food for the 21st Century (RSP) and the Utah Agricultural Experiment Station (UTA00151 and UTA00560 for S. C. Isom and J. R. Stevens, respectively).