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LATE-REPLICATING HETEROCHROMATIN IS CHARACTERISED BY DECREASED CYTOSINE METHYLATION IN THE HUMAN GENOME (HELP assay)

ABSTRACT: Heterochromatin is believed to be associated with increased levels of cytosine methylation. With the recent availability of genome-wide, high-resolution molecular data reflecting cytosine methylation or heterochromatic organization, such relationships can be explored systematically. As a well-defined surrogate for heterochromatin, we tested the relationship between DNA replication timing and cytosine methylation in two human cell types, unexpectedly finding that the later-replicating, more heterochromatic regions to be less methylated than early-replicating regions. When we integrated gene expression data into the study, we found that regions of increased gene expression were earlier replicating, as previously identified, and that transcription-targeted cytosine methylation (TTCM) in gene bodies accounts for the positive correlation with early replication. A Self-Organising Map (SOM) approach was able to identify genomic regions with early replication and increased methylation but lacking annotated transcripts, which would have been missed in simple two variable analyses and may encode unrecognized intergenic transcripts. We conclude that the relationship of cytosine methylation with heterochromatin is not simple, and depends on whether the genomic context is tandemly-repetitive sequences often found near centromeres, which are known to be heterochromatic and methylated, or the remaining majority of the genome, where cytosine methylation is targeted preferentially to the transcriptionally-active, euchromatic compartment of the genome.

ORGANISM(S): Homo sapiens

PROVIDER: GSE27537 | GEO | 2011/08/06

SECONDARY ACCESSION(S): PRJNA141861

REPOSITORIES: GEO

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LATE-REPLICATING HETEROCHROMATIN IS CHARACTERISED BY DECREASED CYTOSINE METHYLATION IN THE HUMAN GENOME (expression)

Project description:Heterochromatin is believed to be associated with increased levels of cytosine methylation. With the recent availability of genome-wide, high-resolution molecular data reflecting cytosine methylation or heterochromatic organization, such relationships can be explored systematically. As a well-defined surrogate for heterochromatin, we tested the relationship between DNA replication timing and cytosine methylation in two human cell types, unexpectedly finding that the later-replicating, more heterochromatic regions to be less methylated than early-replicating regions. When we integrated gene expression data into the study, we found that regions of increased gene expression were earlier replicating, as previously identified, and that transcription-targeted cytosine methylation (TTCM) in gene bodies accounts for the positive correlation with early replication. A Self-Organising Map (SOM) approach was able to identify genomic regions with early replication and increased methylation but lacking annotated transcripts, which would have been missed in simple two variable analyses and may encode unrecognized intergenic transcripts. We conclude that the relationship of cytosine methylation with heterochromatin is not simple, and depends on whether the genomic context is tandemly-repetitive sequences often found near centromeres, which are known to be heterochromatic and methylated, or the remaining majority of the genome, where cytosine methylation is targeted preferentially to the transcriptionally-active, euchromatic compartment of the genome. comparison of human fibroblast and GM06690

2011-08-05 | E-GEOD-27518 | biostudies-arrayexpress

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LATE-REPLICATING HETEROCHROMATIN IS CHARACTERISED BY DECREASED CYTOSINE METHYLATION IN THE HUMAN GENOME

Project description:This SuperSeries is composed of the following subset Series: GSE27518: LATE-REPLICATING HETEROCHROMATIN IS CHARACTERISED BY DECREASED CYTOSINE METHYLATION IN THE HUMAN GENOME (expression) GSE27537: LATE-REPLICATING HETEROCHROMATIN IS CHARACTERISED BY DECREASED CYTOSINE METHYLATION IN THE HUMAN GENOME (HELP assay) Refer to individual Series

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Relics of repeat-induced point mutation direct heterochromatin formation in Neurospora crassa

Project description:Both RNAi-dependent and -independent mechanisms have been implicated in the establishment of heterochromatin domains, which may be stabilized by feedback loops involving chromatin proteins and modifications of histones and DNA. Neurospora crassa sports features of heterochromatin found in higher eukaryotes, namely cytosine methylation (5mC), methylation of histone H3 lysine9 (H3K9me) and HETEROCHROMATIN PROTEIN-1 (HP1), and provides a model to investigate heterochromatin establishment and maintenance. We mapped the distribution of HP1, 5mC, H3K9me3 and H3K4me2 at 100bp-resolution and explored their interplay. HP1, H3K9me3 and DNA methylation were extensively colocalized and defined 44 heterochromatic domains on linkage group VII, all relics of repeat-induced point mutation (RIP). Interestingly, the centromere was found in a striking ~350kb heterochromatic domain with no detectable H3K4me2. 5mC was not found in genes, in contrast to the situation in plants and animals. H3K9me3 is required for HP1 localization and DNA methylation. Here, we show that localization of H3K9me3 is independent of 5mC or HP1 at virtually all heterochromatin regions. In addition, we observed complete restoration of DNA methylation patterns after depletion and reintroduction of the H3K9 methylation machinery, indicating that the signals for de novo heterochromatin formation lie upstream of H3K9 methylation. These data show that A:T rich RIPâd DNA efficently directs methylation of H3K9, which in turn, directs methylation of associated cytosines. Immunoprecipitation experiments using antibodies to 5mC, H3K9me3, epitope-tagged HP1, and H3K4me2 were performed. The immunoprecipitate fraction was labeled with Cy5 and the total input was labeled with Cy3. Samples were hybridized to a N. crassa LGVII tiling path microarray.

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