replication independent, active demethylation hours after fertilization, well before the initiation of replication. Demethylation at very early stages in development has been relatively accepted, but the possibility of postnatal demethylation, especially in fully differentiated somatic cells, has been hotly disputed. However, active replication demethylation was demonstrated in Epstein-Barr virus (EB V)-infected B cells and in HEK293 cells. The HEK293 studies suggest that active replication-independent demethylation takes place in differentiated somatic cells and that it is dependent on alterations in chromatin structure.
