The role of DNA demethylation during development.

The somatic genomic methylation pattern which plays a role in the suppression of basal gene activity is established anew in each generation through developmentally regulated de novo and demethylation steps. Demethylation appears to be carried out by a nucleotide exchange reaction which may involve RNA molecules, and is directed to specific loci in the genome through interactions between cis acting elements and trans acting factors.