Four mechanisms by which eRNAs can functionWIKIMEDIA, PCLERMONTThere’s a lot that scientists don’t yet know about enhancers, genetic elements first described almost 35 years ago that, unlike promoters, can upregulate genes from some distance. That distance, while generally under 100 kilobases, can vary greatly. Usually, enhancers regulate the genes closest to them, but not always; the enhancer for the developmental gene Sonic hedgehog is a megabase away from its promoter in the human genome. What scientists do know is that enhancers seem to play key roles in human biology. One recently published atlas of enhancer expression in the human genome suggested that enhancers, which are expressed differently across cell types, could help explain how one genome encodes so many different kinds of cells. The same paper reported that single-nucleotide changes associated with human diseases are over-represented in enhancers and promoters relative to exons.
In a 2010 Nature paper, researchers in the lab of neurobiologist Michael Greenberg at Harvard Medical School reported that enhancers can produce RNA. Working with cultured mouse neurons, the scientists found that enhancers activated by neuron depolarization were transcribed all over the genome and that levels of enhancer RNAs (eRNAs) correlated with the production of messenger RNA (mRNA) from genes near the enhancers. Researchers had observed enhancer RNAs before, but this was the first evidence of widespread enhancer transcription. In the years since, several other groups have reported finding eRNAs in various biological systems. While eRNAs promise to help researchers understand how enhancers work, they also raise many questions of their own.
ERNAs are fairly short, ranging in length from 500 basepairs to 5 kilobases. ...
