Project description:Dynamic changes in DNA methylation are crucial in the epigenetic regulation of mammalian embryogenesis. Global DNA methylation studies in the bovine, however, remain mostly at the immunostaining level. We adopted the single-cell whole genome bisulfite sequencing (scWGBS) method to characterize stage-specific genome-wide DNA methylation in bovine sperm, individual oocytes derived in vivo and in vitro, as well as in vivo developed embryos at the 2-, 4-, 8- and 16-cell stages. This method allowed us to theoretically cover all CpG sites in the genome using single oocytes or embryos. We found that the major wave of genome-wide DNA demethylation was complete at the 8-cell stage when de novo methylation became prominent. Sperm and oocytes were differentially methylated in numerous regions (DMRs) which were enriched in intergenic regions, indicating these noncoding regions play important roles in gamete specification. DMRs were also identified between in vivo and in vitro matured oocytes. Moreover, X chromosome methylation followed the global dynamic patterns. Virtually no (less than 1.5%) DNA methylation was found in mitochondrial DNA. Finally, using our RNA-seq data generated from the same developmental stages, we revealed an inverse correlation between gene expression and promoter methylation. Our study provides the first fully comprehensive analysis of the global dynamics of DNA methylation in bovine gametes and single early embryos using scWGBS. These data provide insights into the critical features of the methylome of bovine embryos, and serve as an important reference for embryos produced by assisted reproduction, such as in vitro fertilization and cloning, and a model for human early embryo epigenetic regulation.
Project description:DNA methylation is an important epigenetic modification that undergoes dynamic changes in mammalian embryogenesis, during which both parental genomes are reprogrammed. Despite the many immunostaining studies that have assessed global methylation, the gene-specific DNA methylation patterns in bovine preimplantation embryos are unknown. Using reduced representation bisulfite sequencing, we determined genome-scale DNA methylation patterns of bovine sperm and individual in vivo developed oocytes and preimplantation embryos. We show that: 1) the major wave of genome-wide demethylation was completed by the 8-cell stage; 2) promoter methylation was significantly and inversely correlated with gene expression at the 8-cell and blastocyst stages; 3) sperm and oocytes have numerous differentially methylated regions (DMRs) - DMRs specific for sperm were strongly enriched in long terminal repeats (LTRs) and rapidly lost methylation in embryos, while the oocyte-specific DMRs were more frequently localized in exons and CpG islands (CGIs) and demethylated gradually across cleavage stages; 4) a unique set of DMRs were found between in vivo and in vitro matured oocytes; and 5) differential methylation between bovine gametes was confirmed in some but not all known imprinted genes. Our data provide insights into deciphering the complex epigenetic reprogramming of bovine early embryos and will serve as an important model for investigating human development and the evolutionary and regulatory roles of DNA methylation.
Project description:Oviductal extracellular vesicles (oEVs) are emerging as key players in gamete/embryo-oviduct interactions contributing to successful pregnancy. Various positive effects of oEVs on gametes and early embryos have been found in vitro. To find out if these effects are associated with changes of embryonic gene expression, the embryonic transcriptome was analyzed after supplementation of bovine embryos with bovine oEVs during in vitro culture (IVC) in comparison to corresponding controls without oEVs. Embryos were cultured during 7 days of IVC with fresh oEVs, oEVs frozen after isolation from oviductal fluid or without oEVs (control), since a previous study showed different effects of fresh and frozen oEVs. Five pools of 10-14 embryos were analyzed for each group by low-input Illumina RNA-sequencing. Analysis of differential gene expression revealed 221 differentially expressed genes (DEGs) for the comparison of frozen oEVs vs control, 67 DEGs for fresh vs frozen oEVs, and only minor differences for the comparison fresh oEVs vs control (28 DEGs). An integrative analysis with the previously studied mRNA and small ncRNA content of bovine oEVs suggested direct effects of oEVs content on the embryonic transcriptome for the supplementation with frozen oEVs, i.e., increase of transcripts found in higher concentrations in oEVs and decrease of transcripts which are potential targets of miRNAs found in oEVs.
Project description:Affymetrix Human GeneChips are used to profile gene expression of bovine tissues and embryos to identify uniquely expressed genes in bovine in-vitro fertilized embryos by comparing with seven bovine adult tissues through gene clustering Keywords: other
Project description:Pre-implantation embryos derived by in vitro fertilization differ in their developmental potential from embryos obtained in vivo. In order to characterize changes in gene expression profiles caused by in vitro culture environment, we employed microarray constructed from bovine embryo-specific cDNAs (BlueChip v., Université Laval, Québec) to compare in vitro cultured and in vivo derived bovine embryos at 4-cell and 8-cell stage.
Project description:Profiles of H3K4me3, H3K27ac, H3K27me3 and H3K9me3 in bovine GV oocytes and preimplantation embryos, and the characterization of chromatin accessibility in bovine blastocyst, inner cell mass and trophectoderm.
Project description:Early embryo development is a dynamic process involving important molecular and structural changes leading to the embryonic genome activation (EGA) and first cell lineage differentiation. Our aim was to elucidate proteomic changes in bovine embryos developed in vivo. Eleven Holstein females were used as embryo donors and pools of embryos at the 4-6 cell, 8-12 cell, morula, compact morula and blastocyst stages were analyzed by nanoliquid chromatography coupled with tandem MS (nanoLC-MS/MS). A total of 2757 proteins were identified, of which 1950 were quantitatively analyzed. Principal component analysis of data showed a separation of embryo pools according to their developmental stage. Differentially abundant proteins (DAPs) between stages were clustered into 626 upregulated and 400 downregulated proteins with most significant changes at the time of EGA and blastocyst formation. The main pathways and processes overrepresented among upregulated proteins were RNA metabolism, protein translation and ribosome biogenesis whereas Golgi vesicle transport and protein processing in endoplasmic reticulum were overrepresented among downregulated proteins. This is the first comprehensive study of proteome dynamics in non-rodent mammalian embryos developed in vivo. These data provide a number of functional protein candidates and will be useful to evaluate the impact of in vitro conditions on embryo quality.