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The ChAHP complex counteracts chromatin looping at Ctcf sites that have emerged from recent SINE expansions

ABSTRACT: Ctcf and cohesin are key players in the three dimensional organization of chromatin. Whereas genome-wide Ctcf binding has diverged substantially between species due to transposon-mediated motif expansions, demarcation of topologically associating domains (TADs) by Ctcf is remarkably well conserved. Yet, the Ctcf consensus motif poorly predicts TADs and the majority of Ctcf sites are not at TAD boundaries. Here we demonstrate that the ChAHP complex (Chd4, Adnp, HP1) competes with Ctcf for a common set of genomic binding sites. In absence of ChAHP, novel insulated regions are formed at ChAHP bound sites, whereas proximal canonical boundaries are weakened. These data reveal that Ctcf-mediated loop formation is modulated by a distinct zinc-finger protein complex. Strikingly, ChAHP bound loci are mainly situated within evolutionary young SINE B2 transposable elements. This further implicates ChAHP in maintenance of evolutionary conserved spatial chromatin organization by buffering novel Ctcf binding sites that emerged through SINE expansions.

ORGANISM(S): Mus musculus

PROVIDER: GSE125129 | GEO | 2019/09/05

REPOSITORIES: GEO

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The ChAHP complex counteracts chromatin looping at Ctcf sites that have emerged from recent SINE expansions

Project description:The ChAHP complex counteracts chromatin looping at Ctcf sites that have emerged from recent SINE expansions

| PRJNA515300 | ENA

Molecular basis of CTCF binding polarity in genome folding

Project description:Current models propose that boundaries of mammalian topologically associating domains (TADs) arise from the ability of the CTCF protein to stop extrusion of chromatin loops by cohesin. While the orientation of CTCF motifs determines which pairs of CTCF sites preferentially stabilize loops, the molecular basis of this polarity remains mysterious. Here we report that CTCF positions cohesin but does not control its overall binding dynamics on chromatin by single molecule live imaging. Using an inducible complementation system, we found that CTCF mutants lacking the N-terminus cannot insulate TADs properly. Cohesin remained at CTCF sites in this mutant, albeit with reduced enrichment. Given that the orientation of the CTCF motif presents the CTCF N-terminus towards cohesin as it translocates from the interior of TADs, these observations explain how the orientation of CTCF binding sites determines the genomic distribution of chromatin loops.

2020-08-30 | GSE156868 | GEO

Epigenetic maintenance of topological domains in the rearranged gibbon genome [WBGS]

Project description:The relationship between evolutionary genome remodeling and the three-dimensional structure of the genome remain largely unexplored. Here we use the heavily rearranged gibbon genome to examine how evolutionary chromosomal rearrangements impact genome-wide chromatin interactions, topologically associating domains (TADs), and their epigenetic landscape. We use high-resolution maps of gibbon-human breaks of synteny (BOS), apply Hi-C in gibbon, measure an array of epigenetic features, and perform cross-species comparisons. We find that gibbon rearrangements occur at TAD boundaries, independent of the parameters used to identify TADs. This overlap is supported by a remarkable genetic and epigenetic similarity between BOS and TAD boundaries, namely presence of CpG islands and SINE elements, and enrichment in CTCF and H3K4me3 binding. Cross-species comparisons reveal that regions orthologous to BOS also correspond with boundaries of large (400-600kb) TADs in human and other mammalian species. The co-localization of rearrangement breakpoints and TAD boundaries may be due to higher chromatin fragility at these locations and/or increased selective pressure against rearrangements that disrupt TAD integrity. We also examine the small portion of BOS that did not overlap with TAD boundaries and gave rise to novel TADs in the gibbon genome. We postulate that these new TADs generally lack deleterious consequences. Lastly, we show that limited epigenetic homogenization occurs across breakpoints, irrespective of their time of occurrence in the gibbon lineage. Overall, our findings demonstrate remarkable conservation of chromatin interactions and epigenetic landscape in gibbons, in spite of extensive genomic shuffling.

2018-05-30 | GSE115063 | GEO

Epigenetic maintenance of topological domains in the rearranged gibbon genome [Hi-C]

2018-05-30 | GSE115062 | GEO

Epigenetic maintenance of topological domains in the rearranged gibbon genome [ChIP-seq]

2018-05-30 | GSE115064 | GEO

Evolutionary comparison reveals that diverging CCCTC-binding factor (CTCF) sites are signatures of ancestral topological associating domains borders

Project description:Comparison of conserved TAD boundaries reveals that diverging CTCF sites is an evolutionary conserved signature associated with TAD borders

2015-05-18 | GSE66900 | GEO

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

Project description:DNA replication occurs through an intricately regulated series of molecular events and is fundamental for genome stability. It is currently unknown how the location of replication origins is determined in the human genome. Here, we dissect the role for topologically associating domains (TADs), subTADs, and loops in the positioning of replication initiation zones (IZs). We stratify TADs/subTADs by the presence of corner-dots indicative of loops and the orientation of CTCF motifs. We find that high-efficiency, early replicating IZs localize to boundaries between adjacent corner-dot TADs anchored by high-density arrays of divergently and convergently-oriented CTCF motifs. By contrast, low-efficiency IZs localize to weak boundaries devoid of CTCF and corner-dots. Upon ablation of cohesin-mediated loop extrusion in G1, high-efficiency IZs become diffuse and de-localized specifically at boundaries with complex CTCF motif orientation. Moreover, G1 knock-down of the cohesin unloading factor WAPL results in gained long-range loops and narrowed localization of IZs at the same boundaries. Finally, targeted deletion or insertion of specific boundaries causes local replication timing shifts consistent with loss and gain of IZs, respectively. Our data support a model in which cohesin-mediated loop extrusion and stalling at a subset of genetically-encoded TAD/subTAD boundaries is an essential determinant of the precise location of replication initiation in human S phase.

2021-12-05 | GSE190117 | GEO

Modeling of DNA methylation in cis reveals principles of chromatin folding in vivo in the absence of crosslinking and ligation

Project description:Mammalian chromosomes are folded into intricate hierarchies of interaction domains, within which topologically associating domains (TADs) and CTCF-associated loops partition the physical interactions between regulatory sequences. Current understanding of chromosome folding largely relies on chromosome conformation capture (3C)-based experiments, where chromosomal interactions are detected as ligation products after crosslinking of chromatin. To measure chromosome structure in vivo, quantitatively and without relying on crosslinking and ligation, we have implemented a modified version of damID named damC. DamC combines DNA-methylation based detection of chromosomal interactions with next-generation sequencing and a biophysical model of methylation kinetics. DamC performed in mouse embryonic stem cells provides the first in vivo validation of the existence of TADs and CTCF loops and confirms 3C-based measurements of the scaling of contact probabilities. Combining damC with transposon-mediated genomic engineering shows that new loops can be formed between ectopically introduced and endogenous CTCF sites, which alters the partitioning of physical interactions within TADs. This orthogonal approach to 3C provides the first crosslinking- and ligation-free validation of the existence of key structural features of mammalian chromosomes and provides novel insights into how chromosome structure within TADs can be manipulated.

2019-06-03 | PXD013507 | Pride

Evolutionary comparison reveals that diverging CCCTC-binding factor (CTCF) sites are signatures of ancestral topological associating domains borders

Project description:Comparison of conserved TAD boundaries reveals that diverging CTCF sites is an evolutionary conserved signature associated with TAD borders 4C-seq samples for six gene family promoters in different samples: E9.5 and E14.5 mouse embryos ; 24hpf, 48hpf, 80%epiboly and Dome zebrafish embryos ; 48hpf S.purpuratus embryos

2015-05-18 | E-GEOD-66900 | biostudies-arrayexpress

Functional dissection of regulatory landscapes reveals non-essential and instructive roles of TADs in regulating gene expression [ChIP-Seq]

Project description:The genome is organized in megabasesized three-dimensional units, called Topologically Associated Domains (TADs), that are separated by boundaries. TADs bring distant cis-regulatory elements into proximity, facilitated by the cooperative action of cohesin and the DNA binding factor CTCF. However, how TADs and their boundaries impinge on enhancer function remains an open question. Here, we investigate TAD function in vivo in mice at the Sox9/Kcnj locus. We find that TADs are formed by a redundant system of CTCF sites requiring the removal of all major sites within the TAD and at the boundary for two neighboring TADs to fuse. TAD fusion resulted in a low degree of regulatory spread from the Sox9 to the Kcnj TAD, but no major changes in gene expression, indicating that TAD structures provide robustness and precision, but are not essential for developmental gene regulation. Gene misexpression and consecutive disease phenotypes, however, were attained by re-directing regulatory activity through inversions and/or the re-positioning of boundaries. Thus, efficient re-wiring of enhancer promoter interaction and aberrant disease causing gene activation is not induced by a mere loss of insulation but requires the re-direction of contacts.

2019-06-01 | GSE125293 | GEO

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