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

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: GSE27518 | GEO | 2011/08/06

SECONDARY ACCESSION(S): PRJNA141863

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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Replication timing and epigenome remodelling are associated with the nature of chromosomal rearrangements in cancer [Bisulfite-Seq]

Project description:DNA replication timing is known to facilitate the establishment of the epigenome, however, the intimate connection between replication timing and changes to the genome and epigenome in cancer remain largely uncharacterised. Here, we perform Repli-Seq and integrated epigenome analyses and demonstrate that genomic regions that undergo long-range epigenetic deregulation in prostate cancer also show concordant differences in replication timing. A subset of altered replication timing domains are conserved across cancers from different tissue origins. Notably, late-replicating regions in cancer cells display a loss of DNA methylation, and a switch in heterochromatin features from H3K9me3-marked constitutive to H3K27me3-marked facultative heterochromatin. Finally, analysis of 214 prostate and 35 breast cancer genomes reveal that late-replicating regions are prone to cis and early-replication to trans chromosomal rearrangements. Together, our data suggests that the nature of chromosomal rearrangement in cancer is related to the spatial and temporal positioning and altered epigenetic states of early-replicating compared to late-replicating loci.

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Bisulfite-seq from Neurospora crassa a wild type (WT) strain grown in minimum medium, a dim-3 strain grown in minimum medium, and a dim-3 strain grown with supplemented histidine

Project description:We report the placement of cytosine methylation from the filamentous fungus Neurospora crassa in wild type and dim-3 strains by bisulfite-sequencing. Compared to a wild type strain, the dim-3 strain has a global reduction in cytosine methylation, and this reduction in cytosine methylation is exacerbated by the supplementation of histidine to the growth medium. This global reduction in cytosine methylation results from a causative mutation in importin alpha (NUP-6), a component of the nuclear transport machinery, which severely reduces the level of the heterochromatic mark H3K9me3. NUP-6(dim-3) compromises the heterochromatic localization of several components of the DCDC, a histone H3K9 methyltransferase complex, which in turn reduces the level of Heterochromatin Protein-1 (HP1) found at heterochromatin and compromises the direct interaction between HP1 and the DNA methyltransferase dim-2. To determine whether the reduced level of cytosine methylation, as assayed by Southern blotting heterochromatic regions following digestion of genomic DNA with methylation-sensitive restriction endonucleases, is globally reduced at the A:T rich, repetitive DNA comprising heterochromatin, we performed Bisulfite-seq on a dim-3 strain (grown either in minimal medium or medium supplemented with histidine) and compared that to a wild type strain (grown in minimum medium; histidine does not reduce the levels of cytosine methylation in a wild type strain, as assayed by Southern blotting).

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Histone deacetylation and cytosine methylation are required for the normal compartmentalization of heterochromatin in the genome organization of Neurospora crassa [Hi-C]

Project description:Chromosomes must correctly fold in eukaryotic nuclei for proper genome function. Eukaryotic organisms hierarchically organize their genomes: in the fungus Neurospora crassa, chromatin fiber loops compact into Topologically Associated Domain (TAD)-like structures that are anchored by heterochromatic region aggregates. However, insufficient information exists on how histone post-translational modifications, including acetylation, impact genome organization. In Neurospora, the HCHC (HDA-1, CDP-2, HP1, CHAP) complex deacetylates heterochromatic regions including centromeres: loss of individual HCHC members increases centromeric acetylation and cytosine methylation. Here, we evaluate the role of the HCHC complex on genome organization using chromosome conformation capture with high-throughput sequencing (Hi-C) in Δcdp-2 or Δchap deletion strains. CDP-2 loss increases interactions between intra- and inter-chromosomal heterochromatic regions, while removal of CHAP decreases heterochromatic region compaction. Individual HCHC mutants exhibit different histone PTM patterns genome-wide: in Dcdp-2, heterochromatic H4K16 acetylation is increased, yet some heterochromatic regions lose H3K9 trimethylation, which locally increases inter-heterochromatin contacts; CHAP loss produces minimal acetylation changes but increases H3K9me3 enrichment in heterochromatin. Furthermore, deletion of the DIM-2 DNA methyltransferase in a Δcdp-2 background causes extensive genome disorder, as heterochromatic-euchromatic contacts increase despite additional H3K9me3 enrichment. Our results highlight how enhanced cytosine methylation ensures heterochromatic compartmentalization when silenced regions are acetylated.

2023-07-03 | GSE232934 | GEO

Histone deacetylation and cytosine methylation are required for the normal compartmentalization of heterochromatin in the genome organization of Neurospora crassa [ChIP-Seq]

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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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