A glimpse into the epigenetic landscape of gene regulation.

Post-translational modifications to histone proteins and methylation of DNA comprise the epigenome of a cell. The epigenome, which changes through development, controls access to our genes. Recent advances in DNA sequencing technology has led to genome-wide distribution data for a limited number of histone modifications in mammalian stem cells and some differentiated lineages. These studies reveal predictive correlations between histone modifications, different classes of gene and chromosomal features. Moreover, this glimpse into our epigenome challenges current ideas about regulation of gene expression. Many genes in stem cells are poised for expression with initiated RNA polymerase II at the promoter. This state is maintained by an epigenetic mark through multiple lineages until the gene is expressed.