A team from the US, France, and Australia investigates chromatin sites carrying histone modification marks linked to both transcriptional activation and repression "bivalent chromatin" sites with potential roles in development and cancer. "Most gene promoters DNA-hypermethylated in adult human cancer are bivalently marked in [embryonic stem cells]," the researchers write. Based on available epigenetic data and their own experiments in pluripotent human and mouse embryonic stem cells, they suggest that promoters with both the H3K4me3 transcriptional activation and the repressed chromatin-related H3K27me3 marks may be protected against de novo DNA methylation
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