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Elucidating Combinatorial Chromatin States at Single-Nucleosome Resolution

ABSTRACT: Chromatin Immunoprecipitation followed by sequencing (ChIP-seq) has been instrumental to our current view of chromatin structure and function. It allows genome-wide mapping of histone marks, which demarcate biologically relevant domains. However, ChIP-seq is an ensemble measurement reporting the average occupancy of individual marks in a cell population. Consequently, our understanding of the combinatorial nature of chromatin states relies almost exclusively on correlation between the genomic distributions of individual marks. Here, we report the development of Combinatorial-iChIP to determine the genome-wide co-occurrence of histone marks at single nucleosome resolution. By comparing to null model, we show that certain combinations of overlapping marks (H3K36me3 and H3K79me3) co-occur more frequently than expected by chance, while others (H3K4me3 and H3K36me3) do not, reflecting differences in the underlying chromatin pathways. We further use combinatorial-iChIP to illuminate aspects of the Set2-RPD3S pathway. This approach promises to improve our understanding of the combinatorial complexity of chromatin. Combinatorial iChIP in yeast.

ORGANISM(S): Saccharomyces cerevisiae

SUBMITTER: Nir Friedman

PROVIDER: E-GEOD-84240 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Elucidating Combinatorial Chromatin States at Single-Nucleosome Resolution

Project description:Chromatin Immunoprecipitation followed by sequencing (ChIP-seq) has been instrumental to our current view of chromatin structure and function. It allows genome-wide mapping of histone marks, which demarcate biologically relevant domains. However, ChIP-seq is an ensemble measurement reporting the average occupancy of individual marks in a cell population. Consequently, our understanding of the combinatorial nature of chromatin states relies almost exclusively on correlation between the genomic distributions of individual marks. Here, we report the development of Combinatorial-iChIP to determine the genome-wide co-occurrence of histone marks at single nucleosome resolution. By comparing to null model, we show that certain combinations of overlapping marks (H3K36me3 and H3K79me3) co-occur more frequently than expected by chance, while others (H3K4me3 and H3K36me3) do not, reflecting differences in the underlying chromatin pathways. We further use combinatorial-iChIP to illuminate aspects of the Set2-RPD3S pathway. This approach promises to improve our understanding of the combinatorial complexity of chromatin.

2016-08-02 | GSE84240 | GEO

The ATP-dependent chromatin remodeling enzyme Fun30 represses transcription by sliding promoter proximal nucleosomes [seq]

Project description:The evolutionarily conserved ATP-dependent chromatin remodeling enzyme Fun30 has recently been shown to play important roles in heterochromatin silencing and DNA repair. However, how Fun30 remodels nucleosomes is not clear. Here we report a nucleosome sliding activity of Fun30 and its role in transcriptional repression. We observed that Fun30 repressed the expression of genes involved in amino acid and carbohydrate metabolism, the stress response, and meiosis. In addition, Fun30 was localized at the 5M-bM-^@M-2 and 3M-bM-^@M-2 ends of genes and within the open reading frames of its targets. Consistent with its role in gene repression, we observed that Fun30-target genes lacked histone modifications often associated with gene activation and showed an increased level of ubiquitinated histone H2B. Furthermore, genome-wide nucleosome mapping analysis revealed that the length of the nucleosome-free region at the 5M-bM-^@M-2 end of a subset of genes was changed in Fun30-depleted cells. In addition, the positions of the -1, +2 and +3 nucleosomes at the 5M-bM-^@M-2 end of target genes were significantly shifted, while position of the +1 nucleosome remained largely unchanged in the fun30M-NM-^T mutant. Finally, we demonstrated that affinity purified single-component Fun30 exhibited nucleosome sliding activity in an ATP-dependent manner. These results define a role for Fun30 in regulation of transcription and indicate that Fun30 remodels chromatin at the 5M-bM-^@M-2 end of genes by sliding promoter proximal nucleosomes. Micrococcal nuclease digested mononucleosome DNA from wild type and fun30D cells were sequenced by illumina Genome Analyzer. Genome-wide nucleosome positioning and occupancy were analyzed.

2013-07-08 | E-GEOD-48562 | biostudies-arrayexpress

Effects of Histone H3 depletion on nucleosome occupancy and positioning through the S. cerevisiae genome [single-end MNase-seq]

Project description:Experiments performed over the past three decades have shown that nucleosomes are transcriptional repressors. In Saccharomyces cerevisiae, depletion of histone H4 results in the genome-wide transcriptional de-repression of hundreds genes. The mechanism of de-repression is hypothesized to be rooted directly in chromatin changes. To test this, we reproduced classical H4 depletion experiments by conditional repression of all histone H3 transcription, which depletes the supply of nucleosomes in vivo. RNA-seq results were consistent with the earlier studies, but much more sensitive, revealing nearly 2500 de-repressed genes. Changes in chromatin organization were determined by MNase-seq. Nucleosomes that were preferentially retained occurred in regions of high DNA-encoded nucleosome affinity, and were marked with H3K36me2, which is linked to transcription elongation. Nucleosomes harboring acetyl marks or that contained the variant histone H2A.z were preferentially lost. Genes that were de-repressed lost or rearranged nucleosomes at their promoter, but not in the gene body. Therefore, a combination of DNA-encoded nucleosome stability and nucleosome composition dictates which nucleosomes will be lost under conditions of limiting histone protein. This, in turn, governs which genes will experience a loss of regulatory fidelity. MNase-seq experiments consist of three wildtype (1 single-end and 2 paired-end) and four mutant (DCB200.1/H3 shutoff; 2 single-end, 2 paired-end) replicates. Each replicate contains two timepoints reflecting chromatin immediately after ("O hours") and 3 hours after transition to media containing dextrose. RNA-seq data includes three replicates from wildtype or H3 depleted cells after 3 hours in media containing dextrose.

2012-09-26 | E-GEOD-29291 | biostudies-arrayexpress

Genome-wide nucleosome positioning during embryonic stem cell development [MNase-Seq]

Project description:We determined genome-wide nucleosome occupancy in mouse embryonic stem cells and their neural progenitor and embryonic fibroblast counterparts to assess features associated with nucleosome positioning during lineage commitment. Cell type and protein specific binding preferences of transcription factors to sites with either low (e.g. Myc, Klf4, Zfx) or high (e.g. Nanog, Oct4 and Sox2) nucleosome occupancy as well as complex patterns for CTCF were identified. Nucleosome depleted regions around transcription start and termination sites were broad and more pronounced for active genes, with distinct patterns for promoters classified according to their CpG-content or histone methylation marks. Throughout the genome nucleosome occupancy was dependent on the presence of certain histone methylation or acetylation modifications. In addition, the average nucleosome-repeat length increased during differentiation by 5-7 base pairs, with local variations for specific genomic regions. Our results reveal regulatory mechanisms of cell differentiation acting through nucleosome repositioning. We have determined genome-wide nucleosome position maps in mouse embryonic stem cells (ESCs), neural progenitor cells (NPCs) derived from these ESCs by retinoic acid induced differentiation as well as mouse embryonic fibroblasts (MEFs) from the corresponding mouse strain

2012-10-21 | E-GEOD-40910 | biostudies-arrayexpress

Nucleosome occupancy profiles in young and old mouse liver [MNase-Seq]

Project description:Aging is accompanied by physiological impairments, which, in insulin-responsive tissues, including the liver, predispose individuals to metabolic disease. However, the molecular mechanisms underlying these changes remain largely unknown. Here, we analyze genome-wide profiles of RNA and chromatin organization in the liver of young (3 months) and old (21 months) mice. Transcriptional changes suggest that de-repression of the nuclear receptors PPARM-NM-1, PPARM-NM-3, and LXRM-NM-1 in aged mouse liver leads to activation of targets regulating lipid synthesis and storage, whereas age-dependent changes in nucleosome occupancy are associated with binding sites for both known regulators (forkhead factors and nuclear receptors) and for novel candidates associated with nuclear lamina (Hdac3 and Srf) implicated to govern metabolic function of aging liver. Winged-helix factor Foxa2 and nuclear receptor co-repressor Hdac3 exhibit reciprocal binding pattern at PPARM-NM-1 targets contributing to gene expression changes that lead to steatosis in aged liver. Genome-wide nucleosome profiles (MNase-Seq) from young (3 months) and old (21 months) mouse livers

2014-10-23 | E-GEOD-58005 | biostudies-arrayexpress

Histone chromatin modifications in control and Med12-deficient mouse HSPCs

Project description:Using iChIP, we map H3K27Ac, H3K4me3 and H3K4me1 in small populations (HSPCs) in the presence or absence of Med12 and identify affected super-enhancers. iChIP was performed using previously published protocols (Lara-Astiaso et al, 2014 Immunogenetics. Chromatin state dynamics during blood formation - Science, 345, 6199) Examination of histone modification in mouse HSPCs with and without Med12

2016-08-25 | E-GEOD-76052 | biostudies-arrayexpress

Chromatin state dynamics during blood formation (ChIP-Seq)

Project description:We develop a new ChIpseq method (iChIP) to profile chromatin states of low cell number samples. We use IChIP to profile the chromatin dynamics during hematopoiesis across 16 different cell types which include the principal hematopoietic progenitors

2014-08-08 | GSE59636 | GEO

Chromatin state dynamics during blood formation (ATAC-seq)

2014-08-08 | GSE59992 | GEO

Chromatin state dynamics during blood formation (RNA-Seq)

2014-08-08 | GSE60101 | GEO

Frequent and Transient Acquisition of Pluripotency During Somatic Cell Trans-Differentiation with iPSCs Reprogramming Factors (ATAC-Seq)

Project description:Recent reports have proposed a new paradigm for obtaining mature somatic cell types from fibroblasts without going through a pluripotent state, by briefly expressing canonical iPSC reprogramming factors Oct4, Sox2, Klf4 and c-Myc (abbreviated as OSKM), in cells expanded in lineage differentiation promoting conditions. Here we apply genetic lineage tracing for endogenous Nanog, Oct4 and X chromosome reactivation during OSKM induced trans-differentiation, as these molecular events mark final stages for acquisition of induced pluripotency. Remarkably, the vast majority of reprogrammed cardiomyocytes or neural stem cells derived from mouse fibroblasts via OSKM mediated trans-differentiation were attained after transient acquisition of pluripotency, and followed by rapid differentiation. Our findings underscore a molecular and functional coupling between inducing pluripotency and obtaining “trans-differentiated” somatic cells via OSKM induction, and have implications on defining molecular trajectories assumed during different cell reprogramming methods. poly RNA-Seq and Chromatin accesibility (ATAC-seq) were measured during conversion of mouse embryonic fibroblasts to neural stem cells using OSKM trans-differentiation method, as well as in mouse emrbyonic fibroblasts, iPSCs and mouse ESCs.

2015-04-30 | E-GEOD-67298 | biostudies-arrayexpress

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