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Genome Organization Drives Chromosome Fragility [nsRNA-seq]

ABSTRACT: In this study, we show that evolutionarily conserved chromosome loop anchors bound by CTCF and cohesin are vulnerable to DNA double strand breaks (DSBs) mediated by topoisomerase 2B (TOP2B). Polymorphisms in the genome that redistribute CTCF/cohesin occupancy concomitantly rewire DNA cleavage sites to novel contact domain boundaries. While transcription and replication coupled genomic rearrangements have been well documented, we demonstrate that DSBs at loop anchors are transcription-, replication-, and cell type- independent. DSBs are continuously formed throughout interphase, are enriched on both sides of strong topological domain borders, and frequently occur at breakpoint clusters commonly translocated in acute leukemias and prostate cancers. Thus, loop anchors serve as preferred and promiscuous fragile sites that generate DSBs and chromosomal rearrangements.

ORGANISM(S): Mus musculus

PROVIDER: GSE99196 | GEO | 2017/06/28

SECONDARY ACCESSION(S): PRJNA387543

REPOSITORIES: GEO

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Genome Organization Drives Chromosome Fragility [ChIP-seq]

Project description:In this study, we show that evolutionarily conserved chromosome loop anchors bound by CTCF and cohesin are vulnerable to DNA double strand breaks (DSBs) mediated by topoisomerase 2B (TOP2B). Polymorphisms in the genome that redistribute CTCF/cohesin occupancy concomitantly rewire DNA cleavage sites to novel contact domain boundaries. While transcription and replication coupled genomic rearrangements have been well documented, we demonstrate that DSBs at loop anchors are transcription-, replication-, and cell type- independent. DSBs are continuously formed throughout interphase, are enriched on both sides of strong topological domain borders, and frequently occur at breakpoint clusters commonly translocated in acute leukemias and prostate cancers. Thus, loop anchors serve as preferred and promiscuous fragile sites that generate DSBs and chromosomal rearrangements.

2017-06-28 | GSE99195 | GEO

Genome Organization Drives Chromosome Fragility [END-seq]

2017-06-28 | GSE99194 | GEO

Spatial chromosome folding and active transcription drive DNA fragility and formation of oncogenic MLL translocations [RNA-Seq]

Project description:How spatial chromosome organization influences genome integrity is still poorly understood. Here we show that DNA double-strand breaks (DSBs) mediated by topoisomerase 2 (TOP2) activities, are enriched at chromatin loop anchors with high transcriptional activity. Recurrent DSBs occur at CTCF/cohesin bound sites at the bases of chromatin loops and their frequency positively correlates with transcriptional output and directionality. The physiological relevance of this preferential positioning is indicated by the finding that genes recurrently translocating to drive leukemias, are highly transcribed and are enriched at loop anchors. These genes accumulate DSBs at recurrent hot spots that give rise to chromosomal fusions relying on the activity of both TOP2 isoforms and on transcriptional elongation. We propose that transcription and 3D chromosome folding jointly pose a threat to genomic stability, and are key contributors to the occurrence of genome rearrangements that drive cancer.

2019-06-12 | GSE121741 | GEO

Spatial chromosome folding and active transcription drive DNA fragility and formation of oncogenic MLL translocations [BLISS-Seq]

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Replication stress underlies genomic instability at CTCF/cohesin-binding sites in cancer

Project description:CCCTC-binding factor (CTCF) and cohesin play a significant role in the formation of chromatin loops and topologically associating domains (TADs), which influence gene expression and DNA replication. CTCF/cohesin-binding sites (CBSs) present at the loop anchors and TAD boundaries are frequently mutated in cancer; however, the molecular mechanisms underlying this remain unclear. Here, we investigate whether the binding of CTCF/cohesin on DNA imposes constraints on DNA replication, leading to replication stress and genomic instability. Our results reveal that CTCF and cohesin remain cobound to DNA during replication (S phase) in cancer cells (HeLa). Further, examination of replication stress through ChIP-seq of the DNA damage response/repair proteins (MRE11, STN1, FANCD2, γH2AX, RAD51 and ATM) showed high enrichment of these proteins at CBSs (as compared to their immediate flanking regions and control sites) and positively correlated with the binding strength of CTCF/cohesin at CBSs in the S phase. Moreover, analysis of somatic mutations from cancer genomes supports that the enrichment of mutations at CBSs is significantly higher in samples harbouring somatic copy number deletion in MRE11 and STN1 compared to wild-type samples. Together, these results demonstrate that the co-binding of CTCF/cohesin on the DNA during the S phase causes replication stress and DNA strand breaks, and this could lead to genome instability at CBSs observed in cancer.

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Universal dynamics of cohesin-mediated loop extrusion

Project description:Most animal genomes are partitioned into Topologically Associating Domains (TADs), created by cohesin-mediated loop extrusion and defined by convergently oriented CTCF sites. The dynamics of loop extrusion and its regulation remains poorly characterized in vivo. Here, we tracked TAD anchors in living human cells to visualize and quantify cohesin-dependent loop extrusion across multiple endogenous genomic regions. We show that TADs are dynamic structures whose anchors are brought in proximity about once per hour and for 6-19 min (~16% of the time). TADs are continuously subjected to extrusion by multiple cohesin complexes, extruding loops at ~0.1 kb/s. Remarkably, despite strong differences of Hi-C patterns between the chromatin regions, their dynamics is consistent with the same density, residence time and speed of cohesin. Our results suggest that TAD dynamics is governed primarily by CTCF site location and affinity, which allows genome-wide predictive models of cohesin-dependent interactions.

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A three-dimensional map of the human genome at kilobase resolution reveals prinicples of chromatin looping

Project description:We use in situ Hi-C to probe the three-dimensional architecture of genomes, constructing haploid and diploid maps of nine cell types. The densest, in human lymphoblastoid cells, contains 4.9 billion contacts, achieving 1-kilobase resolution. We find that genomes are partitioned into local domains, which are associated with distinct patterns of histone marks and segregate into six subcompartments. We identify ~10,000 loops. These loops frequently link promoters and enhancers, correlate with gene activation, and show conservation across cell types and species. Loop anchors typically occur at domain boundaries and bind CTCF. CTCF sites at loop anchors occur predominantly (>90%) in a convergent orientation, with the asymmetric motifs ‘facing’ one another. The inactive X-chromosome splits into two massive domains and contains large loops anchored at CTCF-binding repeats. in situ Hi-C and dilution Hi-C were used to probe the three-dimensional structure of the genome in eight diverse human cell types and one mouse cell type

2014-12-11 | E-GEOD-63525 | biostudies-arrayexpress

Sensitivity of cohesin-chromatin association to high salt treatment corroborates non-topological mode of loop extrusion

Project description:Cohesin is a key organizer of chromatin folding in eukaryotic cells. Two basic activities of this ring-shaped protein complex are maintenance of sister chromatid cohesion and establishment of long-range DNA-DNA interactions through the process of loop extrusion. Though basic principles of both cohesion and loop extrusion have been described we still do not understand several crucial mechanistic details. One of such unresolved issues is the question of whether a cohesin ring topologically embraces DNA string(s) during loop extrusion. Here we show that cohesin complexes residing on CTCF-occupied genomic sites in mammalian cells do not interact with DNA topologically. We assessed stability of cohesin-dependent loops and cohesin association with chromatin in high ionic strength conditions in G1-synchronised HeLa cells. We found that increased salt concentration completely displaces cohesin from those genomic regions which correspond to CTCF-defined loop anchors. Unsurprisingly, CTCF-anchored cohesin loops also dissipate in these conditions. As topologically-engaged cohesin is considered to be salt-resistant, our data corroborate a non-topological model of loop extrusion.

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Cohesin-mediated loop anchors confine the location of human replication origins

Project description:Cohesin-mediated loop anchors confine the location of human replication origins

| PRJNA785887 | ENA

ChIP-seq data in mESCs show ZFP661 suppresses cohesin binding at CTCF barriers

Project description:In this assay, we aimed to investigate the occupancy of ZFP661 in the mouse genome and its possible role in regulating the occupancies of CTCF and cohesin, which are two key factors in establishing 3D chromatin structures. To achieve this, we performed ChIP-seq in ZFP661-3HA endogenously tagged mESCs (for ZFP661), Zfp661 knockout (KO) mESCs (for CTCF and RAD21), and ZFP661-3HA overexpressing (OE) mESCs (for ZFP661, CTCF, RAD21, KAP1, and H3K9me3). Our results reveal that 1) ZFP661 binding peaks were co-occupied with those of CTCF; 2) ZFP661 binds exclusively inside the CTCF loop anchors; and 3) ZFP661 can suppress cohesin binding at CTCF barriers without altering CTCF binding.

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