Sequencing An Epigenetic Mark
Because access to DNA is tightly controlled, hair doesn’t grow on bone and toenails don’t appear in the spleen. Control comes from a system that includes chemical modifications to DNA bases, or epigenetic marks, that ensure the right genes are expressed in the right place at the right time. Two widely known chemical modifications are 5-hydroxymethyl­cytosine (5hmC) and 5-methylcytosine (5mC). What they do can now be better understood with the first tool to measure, with single-base resolution, their relative amounts (Science, DOI: 10.1126/science.1220671). Researchers have known that when cytosine bases are methylated, the gene is silenced. The precise role of 5hmC is still debated, but it’s clear it has enormous biological importance, says Shankar Balasubramanian, a chemical biologist at Cambridge University. Most researchers believe that 5hmC marks are an epigenetic “on” switch for genes. Others think that 5hmC is an intermediate in so-called active demethylation, which occurs in the first ...