Genome-wide mapping of human DNA-replication origins: levels of transcription at Orc1 sites regulate origin selection and replication timing
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ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE37583 | GEO | 2012/09/18
SECONDARY ACCESSION(S): PRJNA162295
REPOSITORIES: GEO
Similar Datasets
Project description:We report the genome-wide mapping of Orc1 binding-sites in mammals and their validation as active DNA-replication origins (ORIs). Orc1 sites are universally associated with transcription start sites (TSSs) of coding or non-coding RNAs. Transcription levels at the Orc1 sites directly correlate with replication timing, suggesting the existence of two classes of ORIs: those associated with moderate/high transcription levels (M-bM-^IM-%1 RNA copy/cell), replicating in early S and mapping to the TSSs of coding RNAs, and those associated with low transcription levels (<1 RNA copy/cell), replicating throughout the entire S and mapping to TSSs of non-coding RNAs. These findings are compatible with a scenario whereby TSS expression-levels influence the efficiency of Orc1 recruitment at G1 and the probability of firing during S. Identification of Orc1 binding sites in human cells
2012-09-18 | E-GEOD-37583 | biostudies-arrayexpress
Project description:Genomic mapping of DNA replication origins (ORIs) in mammals provides a powerful means for understanding the regulatory complexity of our genome. Here we combine a genome-wide approach to identify preferential sites of DNA replication initiation at 0.4% of the mouse genome with detailed molecular analysis at distinct classes of ORIs according to their location relative to the genes. Our study reveals that 85% of the replication initiation sites in mouse embryonic stem (ES) cells are associated with transcriptional units. Nearly half of the identified ORIs map at promoter regions and, interestingly, ORI density strongly correlates with promoter density, reflecting the coordinated organisation of replication and transcription in the mouse genome. Detailed analysis of ORI activity showed that CpG island promoter-ORIs are the most efficient ORIs in ES cells and both ORI specification and firing efficiency are maintained across cell types. Remarkably, the distribution of replication initiation sites at promoter-ORIs exactly parallels that of transcription start sites (TSS) suggesting a co-evolution of the regulatory regions driving replication and transcription. Moreover, we found that promoter-ORIs are significantly enriched in CAGE tags derived from early embryos relative to all promoters. This association implies that transcription initiation early in development sets the probability of ORI activation unveiling a new hallmark in ORI efficiency regulation in mammalian cells. Two biological replicates of lambda-exonuclease treated short nascent strands (100-600 or 300-800 nt in length) were co-hybridised with genomic DNA from the same cells to tiled genomic array covering 10.1 Mb of the mouse genome (Agilent Technologies)
2010-05-22 | E-GEOD-15082 | biostudies-arrayexpress
Project description:Genomic mapping of DNA replication origins (ORIs) in mammals provides a powerful means for understanding the regulatory complexity of our genome. Here we combine a genome-wide approach to identify preferential sites of DNA replication initiation at 0.4% of the mouse genome with detailed molecular analysis at distinct classes of ORIs according to their location relative to the genes. Our study reveals that 85% of the replication initiation sites in mouse embryonic stem (ES) cells are associated with transcriptional units. Nearly half of the identified ORIs map at promoter regions and, interestingly, ORI density strongly correlates with promoter density, reflecting the coordinated organisation of replication and transcription in the mouse genome. Detailed analysis of ORI activity showed that CpG island promoter-ORIs are the most efficient ORIs in ES cells and both ORI specification and firing efficiency are maintained across cell types. Remarkably, the distribution of replication initiation sites at promoter-ORIs exactly parallels that of transcription start sites (TSS) suggesting a co-evolution of the regulatory regions driving replication and transcription. Moreover, we found that promoter-ORIs are significantly enriched in CAGE tags derived from early embryos relative to all promoters. This association implies that transcription initiation early in development sets the probability of ORI activation unveiling a new hallmark in ORI efficiency regulation in mammalian cells.
2009-03-05 | GSE15082 | GEO
Project description:In metazoans, thousands of DNA replication origins (Oris) are activated to replicate DNA at each cell cycle. Although their timing of activation is better understood, their genomic organization and their genetic nature remain elusive. Here, we identified Oris by nascent strand (NS) purification and characterized their common features by performing a genome-wide analysis in both Drosophila and mouse cell lines. We show that in both species most CpG islands (CGI) contain Oris, although methylation is nearly absent in Drosophila, suggesting that this epigenetic mark is not crucial for defining the initiation event. Moreover, nascent strands at the borders of CGIs show a striking bimodal distribution, suggestive of a dual initiation event. We also found that Oris contain a unique nucleotide skew around NS peaks, characterized by G/T and C/A over-representation at 5’ and 3’ of the Ori sites, respectively. GC-rich elements are detected, which are good predictors of Oris, in both mouse and Drosophila, suggesting that common sequence features are part of metazoan Oris. In the heterochromatic chromosome 4 of Drosophila, Oris are strongly correlated with HP1 binding sites. At the chromosome level, we show that Oris are organized in Ori-rich and -poor regions that co-localize with early and late replicating domains, respectively. Finally, the genome-wide analysis was coupled with a DNA combing analysis of the in-vivo spacing of replication origins. The results suggest that Oris are in large excess, and organized in groups of site-specific but flexible origins that define replicons, where a single origin is used in each group. This organization provides both site specificity and Ori firing flexibility in each replicon, allowing possible adaptation of DNA replication to environmental cues and cell fates.
2011-07-28 | GSE29183 | GEO
Project description:In Schizosaccharomyces pombe, DNA replication origins (ORIs) and meiotic recombination hotspots lack consensus sequences and show a bias towards mapping at large intergenic regions (IGRs). To explore whether this preference depended on underlying chromatin features, we have generated genome-wide nucleosome profiles during mitosis and meiosis. We have found that meiotic double-strand break sites (DSB) colocalize strictly with nucleosome-depleted regions (NDRs) and that large IGRs include clusters of NDRs that overlap with almost half of all DSBs. By contrast, ORIs do not colocalize with NDRs and they are regulated independently of DSBs. Physical relocation of NDRs at ectopic loci or modification of their genomic distribution during meiosis was paralleled by the generation of new DSB sites. Over 80% of all meiotic DSBs colocalize with NDRs that are also present during mitosis, indicating that the recombination pattern is largely dependent on constitutive properties of the genome and, to a lesser extent, on the transcriptional profile during meiosis. The organization of ORIs and of DSBs regions in S. pombe reveals similarities and differences relative to Saccharomyces cerevisiae.
2011-12-31 | GSE28879 | GEO
Project description:Full genome replication in eukaryotes depends on the function of thousands of DNA replication origins (ORIs). The genome-wide identification of ORI location, achieved for animal and plant cells in culture, has been important to define their DNA and chromatin features. A major challenge in the field is to approach the biology of ORIs in whole organisms to understand their developmental plasticity. Here, we have determined the ORI location, activity and chromatin landscape in two developmental stages of Arabidopsis thaliana. We found that ORIs associate with multiple chromatin signatures including the most frequent at TSS but also at proximal and distal gene regulatory regions or repressed Polycomb domains. In constitutive heterochromatin, a high fraction of ORIs colocalize with GC-rich retrotransposons. Quantitative analysis of ORI activity led us to conclude that strong ORIs possess high scores of local GC content and clusters of GGN trinucleotides that may form G quadruplexes and other G-rich structures. We also found that development primarily influences ORI firing strength rather than the location of ORIs in different genomic loci. Moreover, ORIs that preferentially fire at early vegetative stages colocalize with GC-rich heterochromatin whereas those at later stages associate with transcribed genes. Our results provide the first identification of ORI features in a whole organism, opening new ways of studying DNA replication in different cell types in the context of development under normal and mutant conditions.
2018-04-15 | GSE109668 | GEO
Project description:In Trypanosoma brucei, genes are arranged in Polycistronic Transcription Units (PTUs), which are demarcated by transcription start and stop sites. Transcription start sites are also binding sites of Origin Recognition Complex 1 (ORC1). These suggest that transcription and replication in trypanosomes must occur in highly ordered and cooperative manners. Not coincidently, our previous genetic screen, a LOss of transcription Silencing (LOS) screen, identified a T. brucei MCM-BP, which forms a complex with subunits of the replicative helicase MCM. Here, I show that TbMCM-BP is required for DNA replication and transcription. TbMCM-BP depletion causes a significant reduction of replicating cells in S phase and genome-wide impairments of replication origin activation. Moreover, levels of sense and antisense transcripts increase at boundaries of PTUs in the absence of TbMCM-BP. TbMCM-BP is also important for transcriptional repression of the specialized subtelomeric PTUs, the Bloodstream-form Expression-Sites (BESs), which house the gene of antigenic importance, VSG. In the absence of TbMCM-BP, expression of silent VSGs is elevated, silent promoter regions are derepressed, and antisense transcription increases downstream of the silent promoters. This study reveals that TbMCM-BP, a replication initiation protein, guides transcription to properly start and stop, and also helps it move in the correct direction.
2018-10-19 | GSE118232 | GEO
Project description:Genomic integrity requires faithful chromosome duplication. Origins of replication are the genomic sites where DNA replication initiates in every cell cycle. There are multiple origins scattered throughout the eukaryotic genome whose genome-wide identification has been a hard challenge, especially in multicellular organisms. Thus, very little is known on the distinctive features of origins in terms of DNA sequence and chromatin context at a genomic scale. As part of a project for profiling replication origins in Arabidopsis thaliana, we have performed ChIP-chip analysis of the binding of ORC1 and CDC6, two proteins involved in initiation of DNA replication. Here, we provide the data of the ORC1-bound and CDC6-bound genomic sites using as control genomic DNA.
2011-02-06 | GSE21928 | GEO
Project description:DNA replication of eukaryotic chromosomes initiates at a number of discrete loci, called replication origins. Distribution and regulation of origins are important for complete duplication of the genome. Here, we determined locations of Orc1 and Mcm6, components of pre-replicative complex (pre-RC), on whole genome of Schizosaccharomyces pombe using a high-resolution tiling array. Pre-RC sites were identified in 460 intergenic regions, where Orc1 and Mcm6 colocalized. By mapping of 5-bromo-2â-deoxyuridine (BrdU)-incorporated DNA in the presence of hydroxyurea (HU), 307 pre-RC sites were identified as early-firing origins. In contrast, 153 pre-RC sites without BrdU incorporation were considered to be late and/or inefficient origins. Early and late origins tend to distribute separately in large chromosome regions. Inactivation of replication checkpoint by deletion of Cds1 resulted in BrdU incorporation with HU specifically at the late origins. An origin-exchange experiment showed that replication timing was not intrinsic to origin but dependent on its surrounding region. Interestingly, pericentromeric heterochromatin and the silent mating type locus replicated in the presence of HU, while the inner centromere or subtelomeric heterochromatin did not. Notably, MCM did not bind to inner centromeres where ORC was located. Thus, replication is differentially regulated in chromosome domains. Keywords: ChIP-chip analysis Experiment Design: ⢠The goal of the experiment â Genome-wide localization of ORC and MCM binding sites and identification of replication origins in Shizosaccaromyces pombe ⢠A brief description of the experiment (e.g., the abstract from the related publication) DNA replication of eukaryotic chromosomes initiates at a number of discrete loci, called replication origins. Distribution and regulation of origins are important for complete duplication of the genome. Here, we determined locations of Orc1 and Mcm6, components of pre-replicative complex (pre-RC), on whole genome of Schizosaccharomyces pombe using a high-resolution tiling array. Pre-RC sites were identified in 460 intergenic regions, where Orc1 and Mcm6 colocalized. By mapping of 5-bromo-2â-deoxyuridine (BrdU)-incorporated DNA in the presence of hydroxyurea (HU), 307 pre-RC sites were identified as early-firing origins. In contrast, 153 pre-RC sites without BrdU incorporation were considered to be late and/or inefficient origins. Early and late origins tend to distribute separately in large chromosome regions. Inactivation of replication checkpoint by deletion of Cds1 resulted in BrdU incorporation with HU specifically at the late origins. An origin-exchange experiment showed that replication timing was not intrinsic to origin but dependent on its surrounding region. Interestingly, pericentromeric heterochromatin and the silent mating type locus replicated in the presence of HU, while the inner centromere or subtelomeric heterochromatin did not. Notably, MCM did not bind to inner centromeres where ORC was located. Thus, replication is differentially regulated in chromosome domains. ⢠Keywords, for example, time course, cell type comparison, array CGH (the use of MGED ontology terms is recommended). Mitosis, Cell cycle, Schizosaccharomyces pombe, Whole-genome, Tiling array, Chromosome II, III array, Orc1, Orc4, Mcm6, BrdU-labeling, cds1Î. ⢠Experimental factors Distribution of the Orc1 and Mcm6 in WT in G1 phase (S. pombe). Distribution of the Orc4 in WT in asynchronous cells (S. pombe). Distribution of BrdU-incorporated DNA in WT and in cds1 deletion mutant in S phase in the presence of HU (S. pombe). ⢠Experimental design ChIP analysis: In all cases, hybridization data for ChIP fraction was compared with WCE (whole cell extract) fraction. Pombe whole-genome tiling array were used. BrdU analysis: Hybridization data for BrdU fraction (replicated DNA) was compared with Whole fraction (unreplicated DNA) or hybridization data for BrdU fraction of cds1Î cells was compared with that of WT cells. Pombe whole-genome tiling array were used. ⢠Quality control steps taken Different subunits of the same complex. Confirmation of several loci by q-PCR. Checking the BrdU-labeled DNA fraction in CsCl gradient by q-PCR or slot-blot analysis. ⢠Links to the publication, any supplemental websites or database accession numbers. GSE6523 Samples used, extract preparation and labelling: ⢠The origin of each biological sample ChIP analysis: Schizosaccharomyces pombe nda3-KM311 cdc10-129 strain harboring pREP81-cdc18 and pREP42-cdt1. BrdU analysis: Schizosaccharomyces pombe wild type (cdc25-22 nmt1-TK) and cds1Î strains. ⢠Manipulation of biological samples and protocols used ChIP analysis: Chromatin immunoprecipitation (ChIP) in G1 arrested cells or asynchronous cells were performed as previously described (Takahashi et al., 2003, EMBO). Hybridization to Affimetrix high-density oligonucleotide array of S. pombe chromosomes 2 and 3 and whole genome tiling array of S. pombe was performed essentially as previously described (Katou et al., 2003, nature) (Lengronne et al., 2004, nature). BrdU analysis: Growing cdc25-22 cells expressing Thymidine Kinase were arrested at G2/M boundary and released in the presence of BrdU and HU. BrdU was incorporated in nascent DNA in following S phase. The genomic DNA was digested by HaeIII and BrdU-labeled DNA was purified in CsCl density gradient centrifugation. Hybridization to Affimetrix high-density oligonucleotide array of S. pombe whole genome tiling array was performed essentially as previously described (Katou et al., 2003, nature) (Lengronne et al., 2004, nature).
2010-06-11 | E-GEOD-6523 | biostudies-arrayexpress
Project description:DNA replication of eukaryotic chromosomes initiates at a number of discrete loci, called replication origins. Distribution and regulation of origins are important for complete duplication of the genome. Here, we determined locations of Orc1 and Mcm6, components of pre-replicative complex (pre-RC), on whole genome of Schizosaccharomyces pombe using a high-resolution tiling array. Pre-RC sites were identified in 460 intergenic regions, where Orc1 and Mcm6 colocalized. By mapping of 5-bromo-2’-deoxyuridine (BrdU)-incorporated DNA in the presence of hydroxyurea (HU), 307 pre-RC sites were identified as early-firing origins. In contrast, 153 pre-RC sites without BrdU incorporation were considered to be late and/or inefficient origins. Early and late origins tend to distribute separately in large chromosome regions. Inactivation of replication checkpoint by deletion of Cds1 resulted in BrdU incorporation with HU specifically at the late origins. An origin-exchange experiment showed that replication timing was not intrinsic to origin but dependent on its surrounding region. Interestingly, pericentromeric heterochromatin and the silent mating type locus replicated in the presence of HU, while the inner centromere or subtelomeric heterochromatin did not. Notably, MCM did not bind to inner centromeres where ORC was located. Thus, replication is differentially regulated in chromosome domains. Keywords: ChIP-chip analysis
2007-03-05 | GSE6523 | GEO