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Molecular and Cellular Biology, November 2002, p. 7572-7580, Vol. 22, No. 21
0270-7306/02/$04.00+0     DOI: 10.1128/MCB.22.21.7572-7580.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

DNA Methylation Density Influences the Stability of an Epigenetic Imprint and Dnmt3a/b-Independent De Novo Methylation

Matthew C. Lorincz,1 Dirk Schübeler,1 Shauna R. Hutchinson,2 David R. Dickerson,1 and Mark Groudine1,3*

Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109,1 Department of Radiation Oncology, University of Washington School of Medicine, Seattle, Washington 98195,3 Department of Biological Sciences, Hunter College, City University of New York, New York, New York 100212

Received 13 June 2002/ Accepted 31 July 2002

DNA methylation plays an important role in transcriptional repression. To gain insight into the dynamics of demethylation and de novo methylation, we introduced a proviral reporter, premethylated at different densities, into a defined chromosomal site in murine erythroleukemia cells and monitored the stability of the introduced methylation and reporter gene expression. A high density of methylation was faithfully propagated in vivo. In contrast, a low level of methylation was not stable, with complete demethylation and associated transcriptional activation or maintenance-coupled de novo methylation and associated silencing occurring with equal probability. Deletion of the proviral enhancer increased the probability of maintenance-coupled de novo methylation, suggesting that this enhancer functions in part to antagonize such methylation. The DNA methyltransferases (MTases) Dnmt3a and Dnmt3b are thought to be the sole de novo MTases in the mammalian genome. To determine whether these enzymes are responsible for maintenance-coupled de novo methylation, the unmethylated or premethylated proviral reporter was introduced into DNA MTase-deficient embryonic stem cells. These studies revealed the presence of a Dnmt3a/Dnmt3b-independent de novo methyltransferase activity that is stimulated by the presence of preexisting methylation.

* Corresponding author. Mailing address: Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. N, A3-025, Seattle, WA 98109-1024. Phone: (206) 667-4497. Fax: (206) 667-5894. E-mail: markg{at}fhcrc.org.

Molecular and Cellular Biology, November 2002, p. 7572-7580, Vol. 22, No. 21
0022-538X/02/$04.00+0     DOI: 10.1128/MCB.22.21.7572-7580.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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