A new kind of methylation

By now we're all aware of epigenetics and the role of cytosine methylation in gene expression, imprinting and retrotransposon silencing. We may however, have been fooling ourselves, since there may exist another type of methylated cytosine: 5-hydroxymethylcytosine. The journal Science will unveil 2 papers next week describing this novel modification. How could we have missed it for so long? :

"The reason that this nucleotide had not been seen before, the researchers say, is because of the methodologies used in most epigenetic experiments. Typically, scientists use a procedure called bisulfite sequencing to identify the sites of DNA methylation. But this test cannot distinguish between 5-hydroxymethylcytosine and 5-methylcytosine, a shortcoming that has kept the newly discovered nucleotide hidden for years, the researchers say. Its discovery may force investigators to revisit earlier work. The Human Epigenome Project, for example, is in the process of mapping all of the sites of methylation using bisulfite sequencing. "If it turns out in the future that (5-hydroxymethylcytosine and 5-methylcytosine) have different stable biological meanings, which we believe very likely, then epigenome mapping experiments will have to be repeated with the help of new tools that would distinguish the two," says Kriaucionis."

This is exciting, can't wait to read up on it. It seems very abundant, stable and well conserved too...