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Canonical Nucleosome Organization at Promoters Forms During Genome Activation

ABSTRACT: The organization of nucleosomes influences transcriptional activity by controlling accessibility of DNA binding proteins to the genome. Genome-wide nucleosome binding profiles have identified a canonical nucleosome organization at gene promoters, where arrays of well-positioned nucleosomes emanate from nucleosome-depleted regions. The mechanisms of formation and the function of canonical promoter nucleosome organization remain unclear. Here we analyze the genome-wide location of nucleosomes during zebrafish embryogenesis and show that well-positioned nucleosome arrays appear on thousands of promoters during the activation of the zygotic genome. The formation of canonical promoter nucleosome organization is independent of DNA sequence preference, transcriptional elongation, and robust RNA polymerase II (Pol II) binding. Instead, canonical promoter nucleosome organization correlates with the presence of Histone H3 Lysine 4 trimethylation (H3K4me3) and affects future transcriptional activation. These findings reveal that genome activation is central to the organization of nucleosome arrays during early embryogenesis.

ORGANISM(S): Mus musculus

PROVIDER: GSE51766 | GEO | 2013/10/29

SECONDARY ACCESSION(S): PRJNA224977

REPOSITORIES: GEO

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Canonical Nucleosome Organization at Promoters Forms During Genome Activation

Project description:The organization of nucleosomes influences transcriptional activity by controlling accessibility of DNA binding proteins to the genome. Genome-wide nucleosome binding profiles have identified a canonical nucleosome organization at gene promoters, where arrays of well-positioned nucleosomes emanate from nucleosome-depleted regions. The mechanisms of formation and the function of canonical promoter nucleosome organization remain unclear. Here we analyze the genome-wide location of nucleosomes during zebrafish embryogenesis and show that well-positioned nucleosome arrays appear on thousands of promoters during the activation of the zygotic genome. The formation of canonical promoter nucleosome organization is independent of DNA sequence preference, transcriptional elongation, and robust RNA polymerase II (Pol II) binding. Instead, canonical promoter nucleosome organization correlates with the presence of Histone H3 Lysine 4 trimethylation (H3K4me3) and affects future transcriptional activation. These findings reveal that genome activation is central to the organization of nucleosome arrays during early embryogenesis.

2013-10-18 | GSE44269 | GEO

Canonical nucleosome organization at promoters forms during genome activation

Project description:The position of nucleosomes influences DNA accessibility to DNA-binding proteins. Genome-wide nucleosome profiles often report the observation of a canonical nucleosome organization at gene promoters where arrays of well-positioned nucleosomes emanate from nucleosome-depleted regions. It is unclear how this canonical promoter nucleosome organization forms and how it is related to transcription activation and the establishment of histone marks during development. Here we report the genome-wide organization of nucleosomes during zebrafish embryogenesis and show that well-positioned nucleosome arrays appear in thousands of promoters during the activation of the zygotic genome. The formation of canonical promoter nucleosome organization cannot be explained by DNA sequence preference, and is independent of transcription and the presence of RNA polymerase II, but strongly correlates with the presence of Histone H3 Lysine 4 trimethylation (H3K4me3). Our study further suggests that promoter nucleosome structure primes genes to future transcription activation. Together, this study reveals that genome activation but not transcription underlies the organization of nucleosome arrays during early embryogenesis. MNase-seq to generate nucleosome organization in two stages of zebrafish development; two biological replicates for each stage. 7 ChIP-seq experiments in three stages.

2013-10-18 | E-GEOD-44269 | biostudies-arrayexpress

Nucleosome organization in mouse embryonic stem cells

Project description:The position of nucleosomes influences DNA accessibility to DNA-binding proteins. Genome-wide nucleosome profiles often report the observation of a canonical nucleosome organization at gene promoters where arrays of well-positioned nucleosomes emanate from nucleosome-depleted regions. It is unclear how this canonical promoter nucleosome organization forms and how it is related to transcription activation and the establishment of histone marks during development. Here we report the genome-wide organization of nucleosomes during zebrafish embryogenesis and show that well-positioned nucleosome arrays appear in thousands of promoters during the activation of the zygotic genome. The formation of canonical promoter nucleosome organization cannot be explained by DNA sequence preference, and is independent of transcription and the presence of RNA polymerase II, but strongly correlates with the presence of Histone H3 Lysine 4 trimethylation (H3K4me3). Our study further suggests that promoter nucleosome structure primes genes to future transcription activation. To determine whether the occlusions are consistent in mammalian pluripotent cells, we performed the same analyses in mouse embryonic stem cells and found similar relationships. MNase-seq to generate nucleosome organization in mouse embryonic stem cell (J1)

2013-10-29 | E-GEOD-51766 | biostudies-arrayexpress

Stable nucleosome positions in HOX clusters; human K562 and HeLa cells

Project description:The distribution of nucleosomes along the genome is a significant aspect of chromatin structure and is thought to influence gene regulation through modulation of DNA accessibility. However, properties of nucleosome organization remain poorly understood, particularly in mammalian genomes where nucleosome positions have not been examined beyond isolated loci and promoter regions. Towards this goal we used tiled microarrays to identify stable nucleosome positions along the HOX gene clusters in human cell lines. We show that nucleosome positions exhibit sequence properties and long-range organization that are different from those characterized in other organisms. Despite overall variability of inter-nucleosome distances, specific loci contain regular nucleosomal arrays with 195bp periodicity. Moreover, such arrays tend to occur preferentially toward the 3’ ends of genes. Through comparison of different cell lines, we find that increased gene expression correlates with increased positioning of nucleosomes, suggesting an unexpected role for transcription in the establishment of well-positioned nucleosomes. Keywords: human chromatin nucleosome positions, nucleosomes, ChIP-chip

2008-02-20 | GSE10042 | GEO

Hrp3-TAP_Purification from Schizosaccharomyces pombe

Project description:Hrp3_Purification from Schizosaccharomyces pombe 972h- Eukaryotic genome is composed of repeating units of nucleosomes to form chromatin arrays. A canonical gene is marked by nucleosome free region (NFR) at its 5’ end followed by uniformly spaced arrays of nucleosomes. In fission yeast we show both biochemically and in vivo that both Hrp1 and Hrp3 are key determinants of uniform spacing of genic arrays.

2014-05-16 | PXD000041 | Pride

Stepwise reconstitution of genomic nucleosome organization with pure proteins

Project description:Nucleosome arrays begin at nucleosome-free promoter regions (NFRs) and regulate gene expression. Reconstituting such organization throughout a genome with purified proteins is a critical challenge in establishing biochemical mechanisms for chromosome assembly. Here we establish a four-step hierarchical building plan for yeast genomic nucleosome organization using only purified components: genomic DNA, histones, site-specific organizing factors Abf1 and Reb1, and the chromatin remodelers RSC, ISW2, INO80, and ISW1a. First, RSC makes NFRs by translating promoter poly(dA:dT) tracts into directional nucleosome removal. Second, +1 nucleosomes are positioned by INO80 at most genes potentially involving DNA shape, or by ISW2 using gene-specific Abf1 and Reb1. Third, INO80 or ISW2 create arrays with wide spacing. Fourth, ISW1a tightens the spacing and creates properly positioned arrays. We conclude that entire genomes use a simple set of rules and proteins, without transcription, to build a common chromatin architecture. In this study, nucleosomes were assembled using Salt Gradient Dialysis (SGD) on yeast genomic DNA library. Assembled nucleosomes were either left untreated (labelled as "SGD", control), treated with whole cell extract (WCE), mutant extracts (rsc3ts WCE, isw1 isw2 chd1 WCE), purified remodelers; singly or in combinations (RSC, ISW1a, ISW1b, ISW2, INO80, CHD1, SWI/SNF), combinations of mutant extracts and chromatin remodelers or combination of General Regulatory Factors (Abf1, Reb1) and chromatin remodelers. The resulting nucleosome positions were mapped genome-wide using MNase-(anti-H3-ChIP)-Seq.

2016-08-14 | E-GEOD-72106 | biostudies-arrayexpress

S. pombe genome-wide nucleosome mapping reveals positioning mechanisms distinct from S. cerevisiae

Project description:Positioned nucleosomes limit the access of proteins to DNA and implement regulatory features encoded in eukaryotic genomes. Here we generated the first genome-wide nucleosome positioning map for Schizosaccharomyces pombe and annotated transcription start and termination sites genome-wide. Using this resource we found surprising differences compared to the nucleosome organization in the distantly related yeast Saccharomyces cerevisiae [the cerevisiae data has been published by others (PMID: 17873876) and the raw data is deposited at ArrayExpress(E-MEXP-1172)]. DNA sequence guides nucleosome positioning differently, e.g., poly(dA:dT) elements are not enriched in S. pombe nucleosome-depleted regions (NDRs). Regular nucleosomal arrays emanate more asymmetrically, i.e., mainly co-directionally with transcription, from promoter NDRs, but promoters harbouring the histone variant H2A.Z show regular arrays also upstream. Regular nucleosome phasing in S. pombe has a very short repeat length of 154 base pairs, and requires a remodeler, Mit1, conserved in humans but not found in S. cerevisiae. Nucleosome positioning mechanisms are evidently not universal but evolutionarily plastic.

2010-02-01 | GSE16040 | GEO

Genome-wide nucleosome positioning is orchestrated by genomic regions associated with DNase I hypersensitivity in rice

Project description:Nucleosome positioning dictates the DNA accessibility for regulatory proteins, and thus is critical for gene expression and regulation. It has been well documented that only a subset of nucleosomes are reproducibly positioned (phased) in eukaryotic genomes. The most prominent example of phased nucleosomes is the context of genes, where phased nucleosomes flank the transcriptional starts sites (TSSs). It is unclear, however, what factors influence nucleosome phasing in regions that are not close to genes. We performed a combinational mapping of nucleosome positioning and DNase I hypersensitive sites (DHSs) across the rice genome. We discovered that DHSs located in a variety of contexts, both genic and intergenic, were flanked by strongly phased nucleosome arrays. Our results support the barrier model for nucleosome organization as a general feature of eukaryote genomes, including plant genomes, and not limited to TSSs. Specifically, regions bound with regulatory proteins, including intergenic regions, can serve as barriers that organize phased nucleosome arrays on both sides. Our results also suggest that rice DHSs often span a single, phased nucleosome, similar to the H2A.Z-containing nucleosomes observed in DHSs in the human genome. We propose that genome-wide nucleosome positioning in the eukaryotic genomes is orchestrated by genomic regions associated with regulatory proteins.

2014-05-01 | GSE53027 | GEO

Well-positioned nucleosomes punctuate polycistronic Pol II transcription units and flank silent VSG gene arrays in Trypanosoma brucei

Project description:Trypanosoma brucei, a member of the Excavates supergroup, falls in an evolutionarily ancient branch of eukaryotes. We have mapped nucleosome positions in T. brucei and identified a map that differs from that of other eukaryotes in several important ways. Unlike in other eukaryotes, the RNA polymerase II initiation regions in T. brucei do not exhibit pronounced nucleosome depletion, and show little evidence for defined -1 and +1 nucleosomes. In contrast, a well-positioned nucleosome is present directly on the splice acceptor sites within the polycistronic transcription units. The RNA polyadenylation sites were depleted of nucleosomes, with a single well-positioned nucleosome present immediately downstream of the predicted sites. The regions flanking the silent Variant Surface Glycoprotein (VSG) gene arrays showed extensive arrays of well-positioned nucleosomes, which may act to repress cryptic transcription initiation. The silent VSG genes themselves exhibited a less regular nucleosomal pattern in both bloodstream and procyclic form trypanosomes. The DNA replication origins, when present within arrays of silent VSG genes, displayed a defined nucleosomal organization compared with replication origins in other chromosomal core regions. Our results indicate that some organizational features of chromatin are evolutionarily ancient, and may already have been present in the last eukaryotic common ancestor.

2017-03-13 | GSE90593 | GEO

Gene expression at four stages of the developing zebrafish embryo

Project description:Nucleosome arrangement in promoter regions has been shown to play an important role in gene regulation. Genome wide studies in yeast, flies, worms, mammalian ES and transformed cell lines have found well positioned nucleosomes with an area of nucleosome depletion flanking transcription start sites. This Nucleosome arrangement has been shown to be dependent on sequence (cis-regulatory factors), DNA binding factors (trans-regulatory factors) and ATP-dependant chromatin modifiers. However, little is understood about how the nascent embryonic genome positions nucleosomes during development. This is particularly intriguing since the embryonic genome undergoes a whole scale rechromatinization event upon fusion of sperm and oocyte. Using four stages of early embryonic zebrafish development we map nucleosome positions at the promoter region of 34 zebrafish hox genes. We find that nucleosome arrangement at the hox promoters is a dynamic process which happens over several stages. We also find evidence that trans-regulatory factors play a greater role in nucleosome positioning over cis-regulatory elements. Finally we provide evidence that transcriptional activation is the driving force behind the arrangement of nucleosomes at the promoters of hox gene during early development. Four tissue types: 2, 4, 6, and 9 hours post fertilzation embryos. Two treatments: Untreated (WT), and Retinoic Acid treated embryos(RA).

2013-12-09 | E-GEOD-43756 | biostudies-arrayexpress

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