DNA methylation is a process that has proved difficult to observe but is thought to occur mainly in parallel with gene activation during development. A role for DNA demethylation in the regulation of genes expressed in differentiated somatic cells remains controversial. In the January 27 Nature Immunology, Denis Bruniquel and Ronald H. Schwartz at the National Institutes of Health, Bethesda, USA, show that selective and stable demethylation of the interleukin-2 (Il2) gene is an active process that enhances transcription in T cells (Nature Immunology, doi:10.1038/ni887, January 27, 2003).

Bruniquel and Schwartz used bisulfite genomic sequencing and examined every CpG site in the Il2 promoter. They observed that a rapid, highly specific demethylation event occurred following T cell activation, both in vitro and in vivo. In addition, they observed that this epigenetic change was stable and causally affected the transcription level of Il2.

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