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      5-Hydroxymethylcytosine localizes to enhancer elements and is associated with survival in glioblastoma patients

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          Abstract

          Glioblastomas exhibit widespread molecular alterations including a highly distorted epigenome. Here, we resolve genome-wide 5-methylcytosine and 5-hydroxymethylcytosine in glioblastoma through parallel processing of DNA with bisulfite and oxidative bisulfite treatments. We apply a statistical algorithm to estimate 5-methylcytosine, 5-hydroxymethylcytosine and unmethylated proportions from methylation array data. We show that 5-hydroxymethylcytosine is depleted in glioblastoma compared with prefrontal cortex tissue. In addition, the genomic localization of 5-hydroxymethylcytosine in glioblastoma is associated with features of dynamic cell-identity regulation such as tissue-specific transcription and super-enhancers. Annotation of 5-hydroxymethylcytosine genomic distribution reveal significant associations with RNA regulatory processes, immune function, stem cell maintenance and binding sites of transcription factors that drive cellular proliferation. In addition, model-based clustering results indicate that patients with low-5-hydroxymethylcytosine patterns have significantly poorer overall survival. Our results demonstrate that 5-hydroxymethylcytosine patterns are strongly related with transcription, localizes to disease-critical genes and are associated with patient prognosis.

          Abstract

          Glioblastomas have distorted epigenomes. Here, the authors compare the genome-wide profiles of 5-methylcytosine and 5- hydroxymethylcytosine in glioblastoma and prefrontal cortex tissue reporting a correlation between these profiles and patients' prognosis.

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          Most cited references38

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          Reconstructing and reprogramming the tumor-propagating potential of glioblastoma stem-like cells.

          Developmental fate decisions are dictated by master transcription factors (TFs) that interact with cis-regulatory elements to direct transcriptional programs. Certain malignant tumors may also depend on cellular hierarchies reminiscent of normal development but superimposed on underlying genetic aberrations. In glioblastoma (GBM), a subset of stem-like tumor-propagating cells (TPCs) appears to drive tumor progression and underlie therapeutic resistance yet remain poorly understood. Here, we identify a core set of neurodevelopmental TFs (POU3F2, SOX2, SALL2, and OLIG2) essential for GBM propagation. These TFs coordinately bind and activate TPC-specific regulatory elements and are sufficient to fully reprogram differentiated GBM cells to "induced" TPCs, recapitulating the epigenetic landscape and phenotype of native TPCs. We reconstruct a network model that highlights critical interactions and identifies candidate therapeutic targets for eliminating TPCs. Our study establishes the epigenetic basis of a developmental hierarchy in GBM, provides detailed insight into underlying gene regulatory programs, and suggests attendant therapeutic strategies. PAPERCLIP: Copyright © 2014 Elsevier Inc. All rights reserved.
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            Base-resolution analysis of 5-hydroxymethylcytosine in the mammalian genome.

            The study of 5-hydroxylmethylcytosines (5hmC) has been hampered by the lack of a method to map it at single-base resolution on a genome-wide scale. Affinity purification-based methods cannot precisely locate 5hmC nor accurately determine its relative abundance at each modified site. We here present a genome-wide approach, Tet-assisted bisulfite sequencing (TAB-Seq), that when combined with traditional bisulfite sequencing can be used for mapping 5hmC at base resolution and quantifying the relative abundance of 5hmC as well as 5mC. Application of this method to embryonic stem cells not only confirms widespread distribution of 5hmC in the mammalian genome but also reveals sequence bias and strand asymmetry at 5hmC sites. We observe high levels of 5hmC and reciprocally low levels of 5mC near but not on transcription factor-binding sites. Additionally, the relative abundance of 5hmC varies significantly among distinct functional sequence elements, suggesting different mechanisms for 5hmC deposition and maintenance. Copyright © 2012 Elsevier Inc. All rights reserved.
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              Quantitative sequencing of 5-methylcytosine and 5-hydroxymethylcytosine at single-base resolution.

              5-Methylcytosine can be converted to 5-hydroxymethylcytosine (5hmC) in mammalian DNA by the ten-eleven translocation (TET) enzymes. We introduce oxidative bisulfite sequencing (oxBS-Seq), the first method for quantitative mapping of 5hmC in genomic DNA at single-nucleotide resolution. Selective chemical oxidation of 5hmC to 5-formylcytosine (5fC) enables bisulfite conversion of 5fC to uracil. We demonstrate the utility of oxBS-Seq to map and quantify 5hmC at CpG islands (CGIs) in mouse embryonic stem (ES) cells and identify 800 5hmC-containing CGIs that have on average 3.3% hydroxymethylation. High levels of 5hmC were found in CGIs associated with transcriptional regulators and in long interspersed nuclear elements, suggesting that these regions might undergo epigenetic reprogramming in ES cells. Our results open new questions on 5hmC dynamics and sequence-specific targeting by TETs.
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                Author and article information

                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group
                2041-1723
                25 November 2016
                2016
                : 7
                : 13177
                Affiliations
                [1 ]Department of Pharmacology and Toxicology, Geisel School of Medicine at Dartmouth , Lebanon, New Hampshire 03756, USA
                [2 ]Department of Epidemiology, Geisel School of Medicine at Dartmouth , Lebanon, New Hampshire 03756, USA
                [3 ]Department of Biostatistics, College of Public Health and Human Sciences, Oregon State University , Corvallis, Oregon 97331, USA
                [4 ]Department of Neurology, University of Virginia , Charlottesville, Virginia 22908, USA
                Author notes
                Article
                ncomms13177
                10.1038/ncomms13177
                5133638
                27886174
                277ad76b-c4f1-46cd-a325-13479c7eafbc
                Copyright © 2016, The Author(s)

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                History
                : 04 April 2016
                : 09 September 2016
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