Transcription regulation by distal enhancers Who's in the loop?

Genome-wide chromatin profiling efforts have shown that enhancers are often located at large distances from gene promoters within the non-coding genome. Whereas enhancers can stimulate transcription initiation by communicating with promoters via chromatin looping mechanisms, we propose that enhancers may also stimulate transcription elongation by physical interactions with intronic elements. We review here recent findings derived from the study of the hematopoietic system.