Enhancer function: new insights into the regulation of tissue-specific gene expression.

Enhancer function underlies regulatory processes by which cells establish patterns of gene expression. Recent results suggest that many enhancers are specified by particular chromatin marks in pluripotent cells, which may be modified later in development to alter patterns of gene expression and cell differentiation choices. These marks may contribute to the repertoire of epigenetic mechanisms responsible for cellular memory and determine the timing of transcription factor accessibility to the enhancer. Mechanistically, cohesin and non-coding RNAs are emerging as crucial players responsible for facilitating enhancer-promoter interactions at some genes. Surprisingly, these interactions may be required not only to facilitate initiation of transcription but also to activate the release of RNA polymerase II (RNAPII) from promoter-proximal pausing.