DNA accessibility is not the primary determinant of chromatin-mediated gene regulation (yeast III)
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ABSTRACT:
ORGANISM(S): Saccharomyces cerevisiae
PROVIDER: GSE120956 | GEO | 2019/08/27
REPOSITORIES: GEO
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Project description:DNA accessibility is thought to be of major importance in regulating gene expression. We test this hypothesis using a restriction enzyme as a probe of chromatin structure and as a proxy for transcription factors. We measured the digestion rate and the fraction of accessible DNA at all genomic AluI sites in budding yeast and mouse liver nuclei. Hepatocyte DNA is more accessible than yeast DNA, consistent with longer linkers between nucleosomes, and indicating that DNA accessibility is primarily determined by nucleosome spacing. Remarkably, AluI sites in inactive mouse promoters are accessible in some cells. Furthermore, euchromatin and heterochromatin have very similar accessibilities. Cell-to-cell heterogeneity in DNA accessibility has implications for chromatin models of gene regulation: a transcription factor binding site is blocked in some cells, but not in all cells, guaranteeing neither activation nor repression.
2019-08-27 | GSE120955 | GEO
Project description:DNA accessibility is thought to be of major importance in regulating gene expression. We test this hypothesis using a restriction enzyme as a probe of chromatin structure and as a proxy for transcription factors. We measured the digestion rate and the fraction of accessible DNA at all genomic AluI sites in budding yeast and mouse liver nuclei. Hepatocyte DNA is more accessible than yeast DNA, consistent with longer linkers between nucleosomes, and indicating that DNA accessibility is primarily determined by nucleosome spacing. Remarkably, AluI sites in inactive mouse promoters are accessible in some cells. Furthermore, euchromatin and heterochromatin have very similar accessibilities. Cell-to-cell heterogeneity in DNA accessibility has implications for chromatin models of gene regulation: a transcription factor binding site is blocked in some cells, but not in all cells, guaranteeing neither activation nor repression.
2019-08-27 | GSE115691 | GEO
Project description:DNA accessibility is thought to be of major importance in regulating gene expression. Here we test this hypothesis, using a restriction enzyme as a probe of chromatin structure and as a proxy for transcription factors. We measured the digestion rate and the fraction of accessible DNA at all genomic AluI sites in budding yeast and mouse liver nuclei. Hepatocyte DNA is more accessible than yeast DNA, consistent with longer linkers between nucleosomes. Remarkably, AluI sites in inactive mouse promoters are accessible in some cells. Furthermore, heterochromatin and euchromatin have very similar accessibilities. Cell-to-cell heterogeneity in DNA accessibility has implications for chromatin models of gene regulation: a transcription factor binding site is blocked in some cells, but not in all cells, guaranteeing neither activation nor repression.
2019-08-27 | GSE115692 | GEO
Project description:In eukaryotes, DNA is packaged into chromatin. It has become evident that the degree of packaging is not uniform along the genome. More compact chromatin greatly hinder access of transcription factors or other DNA-binding or modifying proteins, and DNA accessibility is an important yet poorly studied layer of regulation. The aim of the study was to map DNA accessibility in chromatin of Arabidopsis leaf nuclei using DNaseI sensitivity as a proxy for accessibility. Chromatin was digested with DnaseI and genomic fragments of >17kb were hybridized to AGRONOMICS1 tiling arrays.
2013-05-01 | E-TABM-1219 | biostudies-arrayexpress
Project description:Eukaryotic genomes are packaged into chromatin, which is composed of condensed filaments of regularly spaced nucleosomes, resembling beads on a string. The nucleosome contains ~147 bp of DNA wrapped almost twice around a central core histone octamer. The packaging of DNA into chromatin represents a challenge to transcription factors and other proteins requiring access to their binding sites. Consequently, control of DNA accessibility is thought to play a key role in gene regulation. Here, we measure DNA accessibility genome-wide in living budding yeast cells by inducible expression of DNA methyltransferases. We find that the yeast genome is globally accessible to the methylase in living cells, unlike in nuclei, where DNA accessibility is severely limited. Gene bodies are methylated at only slightly slower rates than promoters, indicating that yeast chromatin is highly dynamic in vivo. In contrast, centromeres are strongly protected in vivo. Global shifts in nucleosome positions occur in cells as they are depleted of RSC, or ISW1 and CHD1, indicating that global nucleosome dynamics are at least partly attributable to ATP-dependent chromatin remodelers. We propose that virtually all yeast chromatin is in a state of continuous flux in living cells, but static in nuclei, suggesting that chromatin packaging is not generally repressive.
2024-03-22 | GSE230306 | GEO
Project description:Eukaryotic genomes are packaged into chromatin, which is composed of condensed filaments of regularly spaced nucleosomes, resembling beads on a string. The nucleosome contains ~147 bp of DNA wrapped almost twice around a central core histone octamer. The packaging of DNA into chromatin represents a challenge to transcription factors and other proteins requiring access to their binding sites. Consequently, control of DNA accessibility is thought to play a key role in gene regulation. Here, we measure DNA accessibility genome-wide in living budding yeast cells by inducible expression of DNA methyltransferases. We find that the yeast genome is globally accessible to the methylase in living cells, unlike in nuclei, where DNA accessibility is severely limited. Gene bodies are methylated at only slightly slower rates than promoters, indicating that yeast chromatin is highly dynamic in vivo. In contrast, centromeres are strongly protected in vivo. Global shifts in nucleosome positions occur in cells as they are depleted of RSC, or ISW1 and CHD1, indicating that global nucleosome dynamics are at least partly attributable to ATP-dependent chromatin remodelers. We propose that virtually all yeast chromatin is in a state of continuous flux in living cells, but static in nuclei, suggesting that chromatin packaging is not generally repressive.
2024-03-22 | GSE229797 | GEO
Project description:Cell-to-cell variation is a universal feature of life that impacts a wide range of biological phenomena, from developmental plasticity to tumor heterogeneity. While recent advances have improved our ability to document cellular phenotypic variation the fundamental mechanisms that generate variability from identical DNA sequences remain elusive. Here we reveal the landscape and principles of cellular DNA regulatory variation by developing a robust method for mapping the accessible genome of individual cells via assay of transposase accessible chromatin sequencing (ATAC-seq). Single-cell ATAC-seq (scATAC-seq) maps from hundreds of single-cells in aggregate closely resemble accessibility profiles from tens of millions of cells and provides insights into cell-to-cell variation. Accessibility variance is systematically associated with specific trans-factors and cis-elements, and we discover combinations of trans-factors associated with either induction or suppression of cell-to-cell variability. We further identify sets of trans-factors associated with cell-type specific accessibility variance across 6 cell types. Targeted perturbations of cell cycle or transcription factor signaling evoke stimulus-specific changes in this observed variability. The pattern of accessibility variation in cis across the genome recapitulates chromosome topological domains de novo, linking single-cell accessibility variation to three-dimensional genome organization. All together, single-cell analysis of DNA accessibility provides new insight into cellular variation of the “regulome.” Profiles of single cell epigenomes, assayed using scATAC-seq, across 8 cell types and 4 targeted cell manipulations. The complete data set contains a total of 1,632 assayed wells.
2015-06-17 | E-GEOD-65360 | biostudies-arrayexpress
Project description:Most yeast genes have a nucleosome-depleted region (NDR) at the promoter and an array of regularly spaced nucleosomes phased relative to the transcription start site. We have examined the interplay between RSC (a conserved essential SWI/SNF-type complex that determines NDR size) and the ISW1, CHD1 and ISW2 nucleosome spacing enzymes in chromatin organization and transcription, using isogenic strains lacking all combinations of these enzymes. The contributions of these remodelers to chromatin organization are largely combinatorial, distinct and non-redundant, supporting a model in which the +1 nucleosome is positioned by RSC and then used as a reference nucleosome by the spacing enzymes. Defective chromatin organization correlates with altered RNA polymerase II (Pol II) distribution. RSC-depleted cells exhibit low levels of elongating Pol II and high levels of terminating Pol II, consistent with defects in both termination and initiation, suggesting that RSC facilitates both. Cells lacking both ISW1 and CHD1 show the opposite Pol II distribution, suggesting elongation and termination defects. These cells have extremely disrupted chromatin, with high levels of close-packed di-nucleosomes near the 5’-ends of genes. We propose that ISW1 and CHD1 facilitate Pol II elongation by separating close-packed nucleosomes and by eliminating long linkers to prevent cryptic initiation.
2019-01-16 | GSE117514 | GEO
Project description:The basic unit of genome packaging is the nucleosome, and nucleosomes have long been proposed to restrict DNA accessibility both to damage and to transcription. However, nucleosome number in cells was considered fixed, and no condition was described where nucleosome number was reduced. We show here that mammalian cells lacking High Mobility Group Box 1 protein (HMGB1) contain a reduced amount of core, linker and variant histones, and a correspondingly reduced number of nucleosomes. Yeast nhp6 mutants lacking NHP6A and –B proteins, which are related to HMGB1, also have a reduced amount of histones and fewer nucleosomes. Nucleosome limitation in both mammalian and yeast cells increases the sensitivity of DNA to damage, increases transcription globally, and the relative expression of about 10% of genes. In yeast nhp6 cells the loss of more than one nucleosome in four does not affect the location of nucleosomes and their spacing, but nucleosomal occupancy. The decrease in nucleosomal occupancy is non-uniform, and our results can be modelled assuming that different nucleosomal sites compete for the available histones: sites with high affinity are almost always packaged into nucleosomes both in wt and nucleosome-depleted cells, whereas sites with low affinity are less frequently packaged in nucleosome-depleted cells. We suggest that by modulating the occupancy of nucleosomes histone availability may constitute a novel layer of epigenetic regulation. This microarray experiment forms part of a larger study of the effects of nucleosome depletion on transcription Using the Affymetrix Yeast Genome 2.0 Array, yeast nhp6 mutants (lacking NHP6A and NHP6B proteins) were compared to wildtype yeast cells (3 biological replicates per condition)
2011-05-19 | E-GEOD-23711 | biostudies-arrayexpress
Project description:Hematopoietic stem cells (HSCs) exhibit considerable cell-intrinsic changes with age. Epigenetic alterations are one of the hallmarks of HSC aging, and profiling of DNA methylation and histone modifications has provided potential mechanisms that contribute to HSC aging. Chromatin accessibility reflects a comprehensive transcriptional network operating in cells; however, it has not yet been investigated in HSC aging. Here we performed an integrated analysis of aged HSCs on transcriptome, chromatin accessibilities, and histone modifications. Alterations in chromatin accessibility preferentially took place in HSCs with aging, the cells at the top of hematopoietic hierarchy, suggesting that the age-associated alterations in chromatin accessibility are memorized in HSCs and are inherited to downstream progenitor cells. However, most genes with differentially accessible regions (DARs) were not actively transcribed and kept poised for activation in aged HSCs. Motifs of ATF/CREB, STAT, and CNC family transcription factors were significantly enriched at DARs in aged HSCs. These transcription factors are activated in response to external stresses such as cytokine and inflammation signals and oxidative stresses, suggesting that the long-term exposure to such stress signals have changed chromatin accessibility in HSCs to augment responses by such trained HSCs to subsequent stimuli. In contrast, aged HSC-specific gene expression occurred mainly at gene loci with poised accessible regions but not DARs without accompanying drastic chromatin reorganization, suggesting that altered cell-extrinsic stimuli or signals from aged niche largely account for this process. Our findings provide key epigenetic molecular insights into HSC aging and serve as a reference for future analysis.
2020-12-05 | GSE162659 | GEO