News media always seem to focus on the negative . . . war, violence, men wearing kilts sans underwear through airport security lines on National Opt-Out Day. The same can be said about genetic elements that regulate transcription: the repressors seem to get all of the attention.
Part of the reason is that enhancers are trickier to study. Not only can they reside thousands of base pairs from a target gene, but also nobody knew how to distinguish active enhancers from those that are inactive or gearing up for activation. Now a team of researchers led by Rudy Jaenisch at the Whitehead Institute has found that the histone mark H3K27ac identifies active enhancers and predicts a cell’s developmental state.
Previously, researchers used the histone mark H3K4me1 to identify many cell type-specific enhancers. But Jaenisch and colleagues showed that only a subset of enhancers containing H3K4me1 actively promote gene expression, and those active enhancers bear the H3K27ac mark. Enhancers bearing H3K4me1 alone are merely poised for activation in response to external stimuli. Different mouse cell types had diverse H3K4me1 and H3K27ac patterns.
This paper’s more revealing than a full-body scanner, so take a look at PNAS, November 2010