Dynamics of DNA methylation pattern.

Methylation patterns are the result of de novo methylation, demethylation, and the maintenance of existing methylation. Although the existence and identity of an active demethylase remain in doubt, recent evidence suggests that protein binding can specify sites of demethylation through a replication-dependent pathway. By using a stable episomal system in human cells, plus the Drosophila system, and mouse embryonic stem cells, we are beginning to understand the function and targets of de novo methyltransferases in murine and human cells.