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Histone methylation plays an important role in regulating chromatin structure and gene expression. Methylation of the lysine residue 27 of histone H3 (H3K27) is an epigenetic mark that is closely linked with transcriptional repression; global patterns of H3K27 methylation undergo dramatic changes during cleavage development in the mouse. The aim of this study was to characterize the H3K27 methylation pattern in cleavage stage porcine embryos obtained either by in vivo or in vitro fertilization or parthenogenetic activation and to determine the expression patterns of EED, EZH2, and SUZ12 (regulators of H3K27 methylation). We found that monomethylated H3K27 was detectable in the nuclei of oocytes and pronuclear, 2-cell, 4-cell, 8-cell, and blastocyst stage embryos. Trimethylated H3K27 was detectable in the nuclei of GV stage oocytes, the chromosome of MII stage oocytes and a single pronucleus of the pronuclear stage embryos produced by fertilization; the signals were faint or absent in nuclei of two-cell through blastocyst stage embryos. In addition, EED transcripts were increased from the four-cell stage (P |
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