Local DNA demethylation in vertebrates: how could it be performed and targeted

In vertebrates, cytosine methylation is an epigenetic DNA modification that participates in genome stability and gene repression. Methylation patterns are either maintained throughout cell division, or modified by global or l ocal de novo methylation and demethylation, Site-specific demethylation is a rather elusive process that occurs mainly in parallel to gene activation during development. In light of our studies of the glucocorticoid-dependent DNA demethylation of the tyrosine aminotransferase gene, we discuss the po tential biochemical mechanisms allowing DNA demethylation and its targeting to specific sequences by transcription factors as well as possible links t o DNA replication and chromatin remodelling. (C) 2001 Federation of Europea n Biochemical Societies, Published by Elsevier Science B.V. All rights rese rved.