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Hypersensitive Nucleosomes in Chromatin Are Intrinsic to the Structure of Active, Tissue-Specific Enhancers [MNase-Seq]

ABSTRACT: In higher eukaryotes, enhancers and promoters share many properties, including binding of transcription factors, existing in open chromatin, and bidirectional transcription. Yet the structural features that distinguish enhancers and promoters are unclear. Genome-wide micrococcal nuclease (MNase) studies previously interpreted MNase hypersensitivity to indicate that active enhancers and promoters are nucleosome-free, yet other studies found histone variants and post-translational modifications at active enhancers. We find that prior MNase genomic studies have an overdigestion bias and that low-level MNase digestion, coupled with mapping core histones, reveals two classes of MNase-hypersensitive sites: at active promoters, which are nucleosome depleted, and at tissue-specific enhancers, which retain core histones and co-bound transcription factors substantially more than promoters. Hypersensitivity of active enhancer nucleosomes may reflect their preferential exposure in chromatin and can be maintained by pioneer transcription factors such as FoxA. These findings unveil fundamental differences in the chromatin structure of active enhancers and promoters.

ORGANISM(S): Mus musculus

PROVIDER: GSE57558 | GEO | 2016/04/08

SECONDARY ACCESSION(S): PRJNA246703

REPOSITORIES: GEO

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Hypersensitive Nucleosomes in Chromatin Are Intrinsic to the Structure of Active, Tissue-Specific Enhancers [ChIP-Seq]

Project description:In higher eukaryotes, enhancers and promoters share many properties, including binding of transcription factors, existing in open chromatin, and bidirectional transcription. Yet the structural features that distinguish enhancers and promoters are unclear. Genome-wide micrococcal nuclease (MNase) studies previously interpreted MNase hypersensitivity to indicate that active enhancers and promoters are nucleosome-free, yet other studies found histone variants and post-translational modifications at active enhancers. We find that prior MNase genomic studies have an overdigestion bias and that low-level MNase digestion, coupled with mapping core histones, reveals two classes of MNase-hypersensitive sites: at active promoters, which are nucleosome depleted, and at tissue-specific enhancers, which retain core histones and co-bound transcription factors substantially more than promoters. Hypersensitivity of active enhancer nucleosomes may reflect their preferential exposure in chromatin and can be maintained by pioneer transcription factors such as FoxA. These findings unveil fundamental differences in the chromatin structure of active enhancers and promoters.

2016-04-08 | GSE57557 | GEO

Hypersensitive Nucleosomes in Chromatin Are Intrinsic to the Structure of Active, Tissue-Specific Enhancers [ChIP-exo]

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Effects of MBD3 depletion on nucleosome occupancy in MCF-7 cells

Project description:We and others have identified that MBD3/NuRD localizes at active promoters and enhancers, suggesting an active role of NuRD at open chromatin region. Because NuRD includes nucleosome remodelers, CHD3 and CHD4, we hypothesized that NuRD regulates nucleosome organization at open chromatin region. To test this idea, we performed micrococcal nuclease digestion followed by massively parallel sequencing (MNase-seq) in MBD3 knockdowned MCF-7 cells. We observed the decrease of nucleosome occupancy at promoters and enhancers in MBD3 knockdowned cells. Our results suggest a regulatory role of MBD3/NuRD at open chromatin region. Mapped nucleosome positioning in control (shLuc) and MBD3 knockdowned MCF-7 cells, in duplicate.

2013-10-31 | E-GEOD-51097 | biostudies-arrayexpress

Effects of MBD3 depletion on nucleosome occupancy in MCF-7 cells

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Pioneer transcription factor FoxA maintains an open nucleosome configuration for tissue-specific gene activation [MNase-Seq]

Project description:Nuclear DNA is wrapped around core histones to form nucleosomes, which constrains how transcription factors bind to gene regulatory sequences. Pioneer transcription factors have the special ability to bind target DNA on nucleosomes and initiate gene regulatory events, often leading to a local opening of chromatin. Yet the nucleosomal status of such open chromatin, e.g., at active enhancers, is not clear. Here we develop a combination of low and high levels of MNase digestion along with core histone ChIP-seq to assess the presence of nucleosomes at enhancers and promoters in mouse liver. We find that liver-specific enhancers retain preferentially MNase-accessible nucleosomes, with factors bound, substantially more than ubiquitous enhancers. Furthermore, the pioneer factor FoxA2 is required to keep enhancer nucleosomes accessible in chromatin at active liver genes. Thus, nucleosomes are not exclusively repressive to gene regulation when they are retained with, and exposed by, pioneer factors.

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Project description:Open chromatin provides access to a wide spectrum of DNA binding proteins for DNA metabolism processes such as transcription, repair, recombination, and replication. In this regard, open chromatin profiling has been widely used to identify the location of regulatory regions, including promoters, enhancers, insulators, silencers, replication origins, and recombination hotspots. Regulatory DNA elements are made accessible by nucleosome-depeleted states. Thus, nucleosome remodelling and modification should be intimately coupled with open chromatin formation and regulation. However, our knowledge of nucleosome regulation is largely limited to promoter regions, which comprise only a subset of all regulatory loci in the genome. In order to examine nucleosome patterns in open chromatin regions, we performed micrococcal nuclease (MNase) sequencing for a laboratory strain of yeast. Nucleosome occupancy profiled by Micrococcal nuclease (MNase) digestion

2013-01-06 | E-GEOD-34923 | biostudies-arrayexpress

Chromatin landscape of Leishmania major

Project description:We sought to identify nuclease-hypersensitive sites and to quantify nucleosome positions in an effort to identify cis-regulatory elements in the protozoan parasite Leishmania major. Using micrococcal nuclease digestion of chromatin (MNAse-seq), we report that few nuclease hypersensitive sites are present within the presumed regions of RNA polymerase II-mediated transcription initiation, and that similar numbers of nuclease hypersensitive sites were found in control datasets. However, utilizing an independent approach (FAIRE), we observe that a heterogeneous population of nuclease hypersensitive sites are present in and around these regions, and that nucleosomes within these regions are susceptible to MNAse overdigestion.

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Project description:We employed an MNase-Transcription Start Site Sequence Capture method to map and determine the accessibility of all nucleosomes, including those that contain H2A.Z, at high coverage for all human Pol II promoters. We uncovered unexpected features of nucleosomal organization in epithelial cells and following transition to a mesenchymal and malignant state. In contrast to the prevailing model, we observe many different types of active and inactive promoter structures that differ in their nucleosome organization and sensitivity to MNase digestion. Further, we found that H2A.Z has an important role in the assembly of repressed promoters into an inaccessible state. Finally, we uncovered a new promoter type in which a stable H2A.Z nucleosome occupies the TSS of an active promoter.

2020-06-01 | GSE134298 | GEO

Multiple roles of H2A.Z in regulating promoter chromatin architecture in human cells (Mnase-seq & ChIP-seq)

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Two Distinct Promoter Nucleosome Architectures at Protein-Coding Genes in Yeast

Project description:Previous studies indicate that eukaryotic promoters display a stereotypical chromatin landscape characterized by a well-positioned +1 nucleosome near the transcription start site and an upstream -1 nucleosome that together demarcate a nucleosome-free (or depleted) region. Here we present evidence that there are two distinct types of promoters distinguished by the resistance of the -1 nucleosome to micrococcal nuclease digestion. These different architectures are characterized by two sequence motifs that are broadly deployed at one set of promoters where a nuclease-sensitive ("fragile") nucleosome forms, but concentrated in a more narrow, nucleosome-free region at all other promoters. The RSC nucleosome remodeler acts through the motifs to establish stable +1 and -1 nucleosome positions, while binding of a small set of general regulatory (pioneer) factors at fragile nucleosome promoters plays a key role in their destabilization. We propose that the fragile nucleosome promoter architecture is adapted for regulation of highly expressed, growth-related genes. MNase-seq profiles obtained with various MNase concentrations from wild-type cells and cells depleted of different factors. ChIP-seq using anti-RNA polymerase II antibody, anti-histone H2A antibody, and anti-histone H3 antibody.

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