Corporate Banner
Satellite Banner
Scientific Community
Become a Member | Sign in
Home>News>This Article

Unanticipated Consequences of DNA Hypomethylation; Loss and Gain of Polycomb Mediated Transcription Repression in Somatic Cells

Published: Monday, April 01, 2013
Last Updated: Monday, April 01, 2013
Bookmark and Share
By genome-wide mapping of the Polycomb Repressive Complex 2 (PRC2)-signature histone mark, H3K27me3, in DNA methylation-deficient mouse somatic cells, the Meehan lab shows that loss of DNA methylation is coincident with widespread H3K27me3 redistribution.

Unanticipated consequences of DNA hypomethylation; loss and gain of Polycomb mediated transcription repression in somatic cells.

Text book DNA biology describes a genetic code comprising of four DNA bases (A,C,T,G ) and a 5th chemically modified (methylated) base 5-methylcytosine (5mC). The presence of the 5mC base at cytosine rich gene promoters (CpG islands) is highly correlated with transcriptional silencing. Non-methylated CpG island genes are usually highly expressed in cells, but a fraction of these genes can be regulated by a separate regulatory system that does not involve 5mC, termed Polycomb. In this case instead of adding a modification to DNA, it can add methyl groups to a protein closely associated with DNA that also results in gene silencing. Specifically lysine 27 (K27) on histone H3 becomes tri-methylated resulting in H3K27me3 at silenced CpG islands. Polycomb and DNA methylation have always been thought to work independently at CpG islands. However a genome wide study by Reddington, Meehan and co-authors suggests that these mechanisms are more closely linked than previously appreciated. Meehan and co-authors examined the 5mC and histone H3K27me3 profile in cells that have reduced levels of DNA methylation. Essentially they observed many normally non-5mC marked CpG island genes loose Polycomb marks in hypomethylated cells; leading to gene activation without changes in DNA methylation. This accounts for around a third of the increased expression observed in hypomethylated cells, suggesting that participating in Polycomb mediated repression is also a major function for DNA methylation in gene regulation. They hypothesise that loss of methylation throughout the genome creates new, more attractive, ‘landing sites’ for Polycomb. They show that in the hypomethylated cells the Polycomb repression machinery migrates to these new landing sites and can cause de novo silencing of adjacent genes. Frequent observations in cancers are DNA hypomethylation of large genomic domains and hypermethylation of CpG islands. It will be intriguing to investigate the effect of DNA methylation redistribution on Polycomb targeting in cancer cells, and its downstream effect on gene expression. Indeed, new domains of H3K27me3 have been observed in breast cancer cell lines in regions that become DNA hypomethylated.

 A systems level understanding of chromatin structure requires a detailed comprehension of the functional relationships between epigenetic mechanisms, in addition to the roles of the individual mechanisms themselves. The Meehan lab undertook a systematic genomics approach to investigate the emerging functional relationships between DNA methylation and the Polycomb repressor system; two essential epigenetic mechanisms involved in the gene silencing. By genome-wide mapping of the Polycomb Repressive Complex 2 (PRC2)-signature histone mark, H3K27me3, in DNA methylation-deficient mouse somatic cells, James Reddington and colleagues show that loss of DNA methylation leads to widespread H3K27me3 redistribution, consistent with the DNA methylome being an important factor in the targeting of the PRC2 complex throughout the genome. Unexpectedly, in addition to increased H3K27me3 at previously highly DNA methylated genomic regions, they observe a striking loss of H3K27me3 and PRC2 from its normal target gene promoters, including Hox gene clusters. Importantly, we show that many of these genes become ectopically expressed in DNA methylation-deficient cells, consistent with loss of Polycomb-mediated gene repression. They propose that an intact DNA methylome is required for appropriate Polycomb-mediated gene repression by constraining PRC2 targeting. These observations identify a novel functional relationship between DNA methylation and the Polycomb system in gene regulation and will influence our understanding of how these epigenetic mechanisms contribute to normal development and disease.

This study was funded by the Medical Research Council (UK) at the MRC Human Genetics Unit at the IGMM in at Edinburgh University.


Author list
James P. Reddington, Sara M. Perricone, Colm E. Nestor, Judith Reichmann, Neil A. Youngson, Masako Suzuki, Diana Reinhardt, Donncha S. Dunican, James G. Prendergast, Heidi Mjoseng, Bernard H. Ramsahoye, Emma Whitelaw, John M. Greally, Ian R. Adams, Wendy A. Bickmore and Richard R Meehan* Title : Redistribution of H3K27me3 upon DNA hypomethylation results in de-repression of polycomb-target genes.

Further Information

Join For Free

Access to this exclusive content is for Technology Networks Premium members only.

Join Technology Networks Premium for free access to:

  • Exclusive articles
  • Presentations from international conferences
  • Over 3,500+ scientific posters on ePosters
  • More than 5,100+ scientific videos on LabTube
  • 35 community eNewsletters

Sign In

Forgotten your details? Click Here
If you are not a member you can join here

*Please note: By logging into you agree to accept the use of cookies. To find out more about the cookies we use and how to delete them, see our privacy policy.

Related Content

Tissue of Origin Determines Cancer-associated CpG Island Promoter Hypermethylation Patterns
Meehan, Sproul and co-workers conclude that general aberrant promoter hypermethylation in cancer does not promote tumorigenesis, but instead reinforces transcription repression inherited from pre-cancerous tissue.
Friday, October 05, 2012
Non-Genotoxic Carcinogen Exposure Induces Defined Changes in the 5-Hydroxymethylome
In a genome wide study Meehan, Moggs and MARCAR co-authors examined 5mC and 5hmC profiles of liver in control and phenobarbital treated mice. They observe dynamic and reciprocal changes in the 5mC/5hmC patterns over genes promoters that are transcriptionally up-regulated.
Friday, October 05, 2012
Scientific News
Integrated Omics Analysis
Studying multi-omics promises to give a more holistic picture of the organism and its place in its ecosystem, however despite the complexities involved those within the field are optimistic.
Salford Lung Study - The First Real World Clinical Trial
In this podcast, we learn about the Salford Lung Study and its potential to revolutionize the way we assess new drugs and treatments around the world.
Supercomputers Could Improve Cancer Diagnostics
Researchers push the boundaries of cancer research through high-performance computing to map the human immunone.
Systems Medicine – The Future Approach to Diseases
Review give insight into the future of understanding the body and its mechanisms through systems medicine.
Genetic Signature Linked to Cancer Prognosis Identified
The results of the analysis of 8,161 tissue samples could in the future help clinicians decide how best to treat a patient as well as aid the development of new targeted treatments.
Microsatellites Linked to Cancer
DNA repeat stretches, called microsatellites, play a greater role in cancer progression and survival that previously thought.
Mapping the Human Immune System
Researchers try to harness supercomputers to create the first map of the human immune system.
Universal Flu Vaccine Designed by Scientists
An international team of scientists have designed a new generation of universal flu vaccines to protect against future global pandemics that could kill millions.
Faecal Bacteria Linked to Body Fat
Researchers at King’s College London have found a new link between the diversity of bacteria in human poo – known as the human faecal microbiome - and levels of abdominal body fat.
Ancient Eggshell Protein Breaks Through DNA Time Barrier
Fossil proteins from a 3.8million year-old eggshell have been identifed, suggests proteins could give insight into evolutionary tree.
Scroll Up
Scroll Down

SELECTBIO Market Reports
Go to LabTube
Go to eposters
Access to the latest scientific news
Exclusive articles
Upload and share your posters on ePosters
Latest presentations and webinars
View a library of 1,800+ scientific and medical posters
3,500+ scientific and medical posters
A library of 2,500+ scientific videos on LabTube
5,100+ scientific videos