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MNase digestion-sensitive nucleosomes in Saccharomyces cerevisiae

ABSTRACT: The structural complexity of nucleosomes underlies their functional versatility. Here we report a new type of complexity – nucleosome fragility, manifested as high sensitivity to micrococcal nuclease, in contrast to the common presumption that nucleosomes are similar in resistance to MNase digestion. Using differential MNase digestion of chromatin and high-throughput sequencing, we have identified a special group of nucleosomes termed fragile nucleosomes throughout the yeast genome, nearly one thousand of which are at previously determined “nucleosome free” loci. Nucleosome fragility is broadly implicated in multiple chromatin processes, including transcription, translocation and replication, in correspondence to specific physiological states of cells. In the environmental-stress-response genes, the presence of fragile nucleosomes prior to the occurrence of environmental changes suggests that nucleosome fragility poises genes for swift up-regulation in response to the environmental changes. We propose that nucleosome fragility underscores distinct functional statuses of the chromatin and provides a new dimension for portraying the landscape of genome organization.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE26412 | GEO | 2011/01/24

SECONDARY ACCESSION(S): PRJNA136875

REPOSITORIES: GEO

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MNase digestion-sensitive nucleosomes in Saccharomyces cerevisiae

Project description:The structural complexity of nucleosomes underlies their functional versatility. Here we report a new type of complexity – nucleosome fragility, manifested as high sensitivity to micrococcal nuclease, in contrast to the common presumption that nucleosomes are similar in resistance to MNase digestion. Using differential MNase digestion of chromatin and high-throughput sequencing, we have identified a special group of nucleosomes termed fragile nucleosomes throughout the yeast genome, nearly one thousand of which are at previously determined “nucleosome free” loci. Nucleosome fragility is broadly implicated in multiple chromatin processes, including transcription, translocation and replication, in correspondence to specific physiological states of cells. In the environmental-stress-response genes, the presence of fragile nucleosomes prior to the occurrence of environmental changes suggests that nucleosome fragility poises genes for swift up-regulation in response to the environmental changes. We propose that nucleosome fragility underscores distinct functional statuses of the chromatin and provides a new dimension for portraying the landscape of genome organization. Comparing nucleosome occupancy under different MNase digestion levels and growth conditions.

2011-01-24 | E-GEOD-26412 | biostudies-arrayexpress

Nucleosome fragility is associated with future transcriptional response to developmental cues and stress in C. elegans

Project description:Nucleosomes have structural and regulatory functions in all eukaryotic DNA-templated processes. The position of nucleosomes on DNA and the stability of the underlying histone-DNA interactions affect the access of regulatory proteins to DNA. Both stability and position are regulated through DNA sequence, histone post-translational modifications, histone variants, chromatin remodelers, and transcription factors. Here, we explored the functional implications of nucleosome properties on gene expression and development in C. elegans embryos. We performed a time-course of micrococcal nuclease (MNase) digestion, and measured the relative sensitivity or resistance of nucleosomes throughout the genome. Fragile nucleosomes were defined by nucleosomal DNA fragments that were recovered preferentially in early MNase-digestion time points. Nucleosome fragility was strongly and positively correlated with the AT content of the underlying DNA sequence. There was no correlation between promoter nucleosome fragility and the levels of histone modifications or histone variants. Genes with fragile nucleosomes in their promoters tended to be lowly expressed and expressed in a context-specific way, operating in neuronal response, the immune system, and stress response. In addition to DNA-encoded nucleosome fragility, we also found fragile nucleosomes at locations where we expected to find destabilized nucleosomes, for example at transcription factor binding sites where nucleosomes compete with DNA-binding factors. Our data suggest that in C. elegans promoters, nucleosome fragility is in large part DNA-encoded, and that it poises genes for future context-specific activation in response to environmental stress and developmental cues.

2016-10-18 | GSE79567 | GEO

The esBAF and ISWI nucleosome remodeling complexes influence occupancy of overlapping dinucleosomes and fragile nucleosomes in murine embryonic stem cells

Project description:Nucleosome remodeling factors regulate the occupancy and positioning of nucleosomes genome-wide through ATP-driven DNA translocation. While many nucleosomes are well- and consistently positioned, some nucleosomes and nucleosome-like structures are more sensitive to nuclease digestion or transitory in nature. To better understand the role of nucleosome remodeling factors in generating and clearing these alternative nucleosome structures, we depleted murine embryonic stem cells of the remodeler ATPases BRG1 and SNF2H then performed MNase-seq in murine embryonic stem cells. We performed MNase-seq under high- and low-MNase conditions to assess the effects of nucleosome remodeling factors on nuclease-sensitive or “fragile” nucleosome occupancy. In parallel, we gel-extracted MNase-digested fragments to enrich for another alternative nucleosome structure, the overlapping dinucleosome. Overlapping dinucleosomes are composed of two canonical nucleosomes, asymmetrically lacking one H2A:H2B dimer and wrapped by ~250 bp of DNA. In vitro studies of nucleosome remodeling have suggested that the collision of adjacent nucleosomes by nucleosome sliding can stimulate formation of overlapping dinucleosomes. Using these methods, we were able to identify fragile nucleosomes and overlapping dinucleosomes near transcription start sites and gene-distal DNaseI hypersensitive sites in mouse embryonic stem cells, among other loci. We find that BRG1 consistently stimulates occupancy of fragile nucleosomes but represses occupancy of overlapping dinucleosomes through its nucleosome remodeling function, while SNF2H expression slightly increases fragile nucleosome occupancy.

2023-03-14 | GSE216057 | GEO

MNase-sensitive complexes in yeast: nucleosomes and non-histone barriers

Project description:Micrococcal nuclease (MNase) is commonly used to map nucleosomes genome-wide, but nucleosome maps are affected by the degree of digestion. It has been proposed that many yeast promoters are not nucleosome-free but occupied by easily digested, unstable, “fragile” nucleosomes. We analyzed the histone content of all MNase-sensitive complexes by MNase-ChIP-seq and Sonication-ChIP-seq. We find that yeast promoters are predominantly bound by non-histone protein complexes, with little evidence for fragile nucleosomes. We do detect MNase-sensitive nucleosomes elsewhere in the genome, including transcription termination sites. However, they have high A/T-content, suggesting that MNase sensitivity does not indicate instability, but the preference of MNase for A/T-rich DNA, such that A/T-rich nucleosomes are digested faster than G/C-rich nucleosomes. We confirm our observations by analyzing ChIP-exo, chemical mapping and ATAC-seq data from other laboratories. Thus, histone ChIP-seq experiments are essential to distinguish nucleosomes from other DNA-binding proteins that protect against MNase.

2016-12-15 | GSE83123 | GEO

MNase-seq analysis in human breast cancer cells

Project description:Nucleosomes are the most basic units of chromatin and are regulators of genome integrity and gene expression. The fundamental mechanism how nucleosomes are dynamically regulated is one of the main questions in chromatin organization; most of the study has, however, focused on its positioning. Here we performed HiLo-MNase-seq, which involves limit and partial digestion of chromatin by micrococcal nuclease (MNase) to identify the positioning of nucleosome array along with the kinetics of MNase digestion. We identified a subset of unique nucleosomes with fast digestion kinetics at the transcription factor binding sites that have been characterized as nucleosome depleted regions (NDRs). By inhibiting RNA polymerase II, we also showed that those nucleosomes changed its sensitivity to MNase in a context-dependent manner. These findings implicated a self-reinforcing regulatory network involving nucleosomes, Pol II, and transcription factors for fine-tuning of gene expression.

2020-02-01 | GSE77526 | GEO

MNase titration reveals differences between nucleosome occupancy and chromatin accessibility

Project description:Chromatin accessibility plays a fundamental role in gene regulation. One mechanism to regulate accessibility is nucleosome placement, which is often measured by quantifying protection of DNA from enzymatic digestion. We introduce a metric that uses micrococcal nuclease (MNase) digestion in a novel manner to measure chromatin accessibility by combining information from several digests of increasing depths. This metric, MACC, quantifies the inherent heterogeneity of nucleosome accessibility in which some nucleosomes are seen preferentially at high MNase and some at low MNase. MACC interrogates each genomic locus, measuring both location of nucleosomes and accessibility to MNase in the same assay. MACC can be performed either with or without a histone immunoprecipitation step, and thereby compares behavior of nucleosomes to that of non-histone proteins. We find that enhancers, promoters and other regulatory regions have changes in accessibility that do not correlate with changes in nucleosome occupancy. Moreover, we show that high nucleosome occupancy does not necessarily preclude high accessibility, revealing novel principles of chromatin regulation.

2016-04-18 | GSE78984 | GEO

Novel nucleosomal particles containing core histones and linker DNA but no histone H1

Project description:The nucleosome plays a central role in genome regulation. Traditional methods for mapping nucleosomes depend on the resistance of the nucleosome core to micrococcal nuclease (MNase). However, the lengths of the protected DNA fragments are heterogeneous, limiting the accuracy of nucleosome position information. To resolve this problem, we removed residual linker DNA by simultaneous digestion of yeast chromatin with MNase and exonuclease III (ExoIII). Paired-end sequencing of mono-nucleosomes revealed not only core particles (145-147 bp), but also intermediate particles in which ~8 bp project from one side (154 bp) or both sides (161 bp) of the nucleosome core. We term these particles "pseudo-chromatosomes" because they are present in yeast lacking linker histone. They are also observed after MNase-ExoIII digestion of chromatin reconstituted using recombinant core histones. We propose that the pseudo-chromatosome provides a DNA framework to facilitate H1 binding. Comparison of budding yeast nucleosome sequences obtained using micrococcal nuclease (MNase-seq) and MNase + exonuclease III (ExoIII) (MNase-ExoIII-seq): wild type cells and hho1-null cells. Nucleosome sequences from native chromatin and H1-depleted chromatin from mouse liver. Nucleosome sequences from a plasmid reconstituted into nucleosomes using recombinant yeast histones or native chicken erythrocyte histones.

2015-09-23 | E-GEOD-65889 | biostudies-arrayexpress

Quantitative MNase-seq accurately maps nucleosome occupancy levels

Project description:Chromatin mapping using micrococcal nuclease (MNase) has been the standard tool for mapping nucleosomes for >40 years. When coupled with DNA sequencing, MNase-seq can provide base-pair-resolution nucleosome maps. However, determining nucleosome occupancy using MNase-seq has been hampered by its aggressive endo-/exo-nuclease activities, whereby cleavages within linker regions produce oligo- and mono-nucleosomes whereas cleavages within nucleosomes destroy them. Here we introduce a theoretical framework for predicting nucleosome occupancies and an experimental protocol with appropriate spike-in normalization that confirms our theory and provides accurate occupancy levels over an MNase digestion time-course. As expected, DNaseI hypersensitive sites and transcription units are digested by MNase at elevated rates, and the apparent deficiency of nucleosomes at 3’ ends of Drosophila genes is an artifact of MNase preference for AT-rich DNA. Surprisingly, we observed no overall differences between Drosophila euchromatin and heterochromatin, which implies that heterochromatin compaction does not render nucleosomal DNA less accessible than euchromatin.

2019-08-27 | GSE128689 | GEO

Genome-wide profiling of nucleosome sensitivity and chromatin accessibility to MNase in D. melanogaster [RNA-seq]

Project description:Nucleosome structure and positioning play pivotal roles in gene regulation, DNA repair and other essential processes in eukaryotic cells. Nucleosomal DNA is thought to be uniformly inaccessible to DNA binding and processing factors, such as MNase. Here, we show, however, that nucleosome accessibility and sensitivity to MNase varies. Digestion of Drosophila chromatin with two distinct concentrations of MNase revealed two types of nucleosomes: sensitive and resistant. MNase-resistant nucleosome arrays are less accessible to low concentrations of MNase, whereas MNase-sensitive arrays are degraded by high concentrations. MNase-resistant nucleosomes assemble on sequences depleted of A/T and enriched in G/C containing dinucleotides. In contrast, MNase-sensitive nucleosomes form on A/T rich sequences represented by transcription start and termination sites, enhancers and DNase hypersensitive sites. Lowering of cell growth temperature to ~10°C stabilizes MNase-sensitive nucleosomes suggesting that variations in sensitivity to MNase are related to either thermal fluctuations in chromatin fiber or the activity of enzymatic machinery. In the vicinity of active genes and DNase hypersensitive sites nucleosomes are organized into synchronous, periodic arrays. These patterns are likely to be caused by “phasing” nucleosomes off a potential barrier formed by DNA-bound factors and we provide an extensive biophysical framework to explain this effect. RNA-seq S2 cells Drosophila melanogaster

2015-09-17 | E-GEOD-69335 | biostudies-arrayexpress

Genome-wide profiling of nucleosome sensitivity and chromatin accessibility to MNase in D. melanogaster [RNA-seq]

2015-09-17 | GSE69335 | GEO

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