Mapping Genome Occupancy in Embryonic Stem Cells

• Growth Conditions
• Human ES Cell Quality Control
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• Data Analysis

Polycomb group proteins are essential for early development in metazoans but their contributions to human development are not yet well understood. We have mapped the Polycomb Repressive Complex 2 (PRC2) subunit Suz12 across the entire non-repeat portion of the genome in human embryonic stem (ES) cells. We found that Suz12 is distributed across large portions of over two hundred genes encoding key developmental regulators. These genes are occupied by nucleosomes trimethylated at histone H3K27, are transcriptionally repressed, and contain some of the most highly conserved non-coding elements in the vertebrate genome. We found that preferential activation of PRC2 target genes occurs during differentiation of ES cells into other cell types. The ES cell transcriptional regulators Oct4, Sox2 and Nanog co-occupied a significant subset of these genes, further supporting a link between repression of developmental regulators and stem cell pluripotency. These results indicate that PRC2 occupies a special set of developmental genes in ES cells that must be repressed to maintain pluripotency and that are poised for activation during ES cell differentiation.