MCM complexes are barriers that restrict loops and TADs
Ontology highlight
ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE155971 | GEO | 2022/03/07
REPOSITORIES: GEO
Similar Datasets
Project description:Eukaryotic genomes are compacted into loops and topologically associating domains (TADs), which contribute to transcription, recombination and genomic stability. Cohesin extrudes DNA into loops that are thought to lengthen until CTCF boundaries are encountered. Little is known about whether loop extrusion is impeded by DNA-bound macromolecular machines. We demonstrate that the replicative helicase MCM is a barrier that restricts loop extrusion in G1 phase. Single-nucleus Hi-C of one-cell embryos revealed that MCM loading reduces CTCF-anchored loops and decreases TAD boundary insulation, suggesting loop extrusion is impeded before reaching CTCF. Single-molecule imaging shows that MCMs are physical barriers that constrain cohesin translocation in vitro. Simulations are consistent with MCMs as abundant, random barriers. We conclude that distinct loop extrusion barriers contribute to shaping 3D genomes.
2022-03-08 | GSE196300 | GEO
Project description:Eukaryotic genomes are compacted into loops and topologically associating domains (TADs), which contribute to transcription, recombination and genomic stability. Cohesin extrudes DNA into loops that are thought to lengthen until CTCF boundaries are encountered. Little is known about whether loop extrusion is impeded by DNA-bound machines. Here we show that the minichromosome maintenance (MCM) complex is a barrier that restricts loop extrusion in G1 phase. Single-nucleus Hi-C of mouse zygotes revealed that MCM loading reduces CTCF-anchored loops and decreases TAD boundary insulation, suggesting loop extrusion is impeded before reaching CTCF. This effect extends to HCT116 cells, where MCMs affect the number of CTCF-anchored loops and gene expression. Simulations suggest that MCMs are abundant, randomly positioned, partially permeable barriers. Single-molecule imaging shows that MCMs are physical barriers that frequently constrain cohesin translocation in vitro. Remarkably, chimaeric yeast MCMs harbouring a cohesin-interaction motif from human MCM3 induce cohesin pausing, suggesting that MCMs are “active” barriers with binding sites. These findings raise the possibility that cohesin can arrive by loop extrusion at MCMs, which determine the genomic sites at which sister chromatid cohesion is established. Based on in vivo, in silico and in vitro data, we conclude that distinct loop extrusion barriers shape the 3D genome.
2022-03-08 | GSE196496 | GEO
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.
2024-07-28 | GSE273257 | GEO
Project description:Mammalian genomes are organized into compartments, topologically-associating domains (TADs) and loops to facilitate gene regulation and other chromosomal functions. Compartments are formed by nucleosomal interactions, but how TADs and loops are generated is unknown. It has been proposed that cohesin forms these structures by extruding loops until it encounters CTCF, but direct evidence for this hypothesis is missing. Here we show that cohesin suppresses compartments but is essential for TADs and loops, that CTCF defines their boundaries, and that WAPL and its PDS5 binding partners control the length of chromatin loops. In the absence of WAPL and PDS5 proteins, cohesin passes CTCF sites with increased frequency, forms extended chromatin loops, accumulates in axial chromosomal positions (vermicelli) and condenses chromosomes to an extent normally only seen in mitosis. These results show that cohesin has an essential genome-wide function in mediating long-range chromatin interactions and support the hypothesis that cohesin creates these by loop extrusion, until it is delayed by CTCF in a manner dependent on PDS5 proteins, or until it is released from DNA by WAPL.
2017-12-07 | GSE102884 | GEO
Project description:Complex genomes show intricate organization in three-dimensional (3D) nuclear space. Current models posit that cohesin extrudes loops to form self-interacting domains delimited by the DNA binding protein CTCF. Here, we describe and quantitatively characterize cohesin-propelled, jet-like chromatin contacts as landmarks of loop extrusion in quiescent mammalian lymphocytes. Experimental observations and polymer simulations indicate that narrow origins of loop extrusion favor jet formation. Unless constrained by CTCF, jets propagate symmetrically for 1-2 Mb, providing an estimate for the range of in vivo loop extrusion. Asymmetric CTCF binding deflects the angle of jet propagation as experimental evidence that cohesin-mediated loop extrusion can switch from bi- to unidirectional and is controlled independently in both directions. These data offer new insights into the physiological behavior of in vivo cohesin-mediated loop extrusion and further our understanding of the principles that underlie genome organization.
2022-08-15 | GSE199059 | GEO
Project description:Cohesin organizes mammalian interphase chromosomes by reeling chromatin fibers into dynamic loops. "Loop extrusion" is obstructed when cohesin encounters a properly oriented CTCF protein. It has been proposed that transcription relocalizes or interferes with cohesin, and that active transcription start sites function as cohesin loading sites, but how these effects, and transcription in general, shape chromatin is unknown. To determine whether transcription can modulate loop extrusion, we studied cells in which the primary extrusion barriers could be removed by CTCF depletion and cohesin’s residence time and abundance on chromatin could be increased by Wapl knockout. We found evidence that transcription directly interacts with loop extrusion through a novel "moving barrier" mechanism, but not by loading cohesin at active promoters. Hi-C experiments showed intricate, cohesin-dependent genomic contact patterns near actively transcribed genes, and in CTCF-Wapl double knockout (DKO) cells, genomic contacts were enriched between sites of transcription-driven cohesin localization ("cohesin islands"). Similar patterns also emerged in polymer simulations in which transcribing RNA polymerases (RNAPs) acted as "moving barriers" by impeding, slowing, or pushing loop-extruding cohesins. The model predicts that cohesin does not load preferentially at promoters and instead accumulates at TSSs due to the barrier function of RNAPs. We tested this prediction by new ChIP-seq experiments, which revealed that the "cohesin loader" Nipbl co-localizes with cohesin, but, unlike in previous reports, Nipbl did not accumulate at active promoters. We propose that RNAP acts as a new type of barrier to loop extrusion that, unlike CTCF, is not stationary in its precise genomic position, but is itself dynamically translocating and relocalizes cohesin along DNA. In this way, loop extrusion could enable translocating RNAPs to maintain contacts with distal regulatory elements, allowing transcriptional activity to shape genomic functional organization.
2023-03-13 | GSE196621 | GEO
Project description:MCM complexes are barriers that restrict cohesin-mediated loop extrusion
| PRJNA805206 | ENA
Project description:Mammalian chromosomes are partitioned into topologically associating domains (TADs) by the loop-extrusion activity of cohesin that is blocked at specific DNA sites bound by CTCF. Chromosome structure inside TADs is highly variable in single cells, yet little is known about its temporal dynamics, how it influences the rates and durations of chromosomal contacts, and how it depends on CTCF and cohesin. To address these questions we combine two quantitative live-cell imaging strategies that minimize locus-specific confounding effects. We show that loop extrusion by cohesin globally reduces the mobility of the chromatin fiber in living cells, while also increasing the rates of formation and durations of contacts between sequences inside the same TAD. Quantitative analysis of high-resolution microscopy data reveals that contacts assemble and disassemble frequently in the course of the cell cycle, and become substantially more frequent and longer in the presence of convergent CTCF sites. Comparison with polymer modeling additionally reveals that cohesin-mediated CTCF loops last around 10 minutes on average. Our data support the notion that chromosome structure within TADs is highly dynamic and provide a quantitative framework for understanding the principles that link chromosome structure to biological function.
2022-02-27 | GSE197237 | GEO
Project description:Mammalian chromosomes are partitioned into topologically associating domains (TADs) by the loop-extrusion activity of cohesin that is blocked at specific DNA sites bound by CTCF. Chromosome structure inside TADs is highly variable in single cells, yet little is known about its temporal dynamics, how it influences the rates and durations of chromosomal contacts, and how it depends on CTCF and cohesin. To address these questions we combine two quantitative live-cell imaging strategies that minimize locus-specific confounding effects. We show that loop extrusion by cohesin globally reduces the mobility of the chromatin fiber in living cells, while also increasing the rates of formation and durations of contacts between sequences inside the same TAD. Quantitative analysis of high-resolution microscopy data reveals that contacts assemble and disassemble frequently in the course of the cell cycle, and become substantially more frequent and longer in the presence of convergent CTCF sites. Comparison with polymer modeling additionally reveals that cohesin-mediated CTCF loops last around 10 minutes on average. Our data support the notion that chromosome structure within TADs is highly dynamic and provide a quantitative framework for understanding the principles that link chromosome structure to biological function.
2022-02-27 | GSE197234 | GEO
Project description:Mammalian chromosomes are partitioned into topologically associating domains (TADs) by the loop-extrusion activity of cohesin that is blocked at specific DNA sites bound by CTCF. Chromosome structure inside TADs is highly variable in single cells, yet little is known about its temporal dynamics, how it influences the rates and durations of chromosomal contacts, and how it depends on CTCF and cohesin. To address these questions we combine two quantitative live-cell imaging strategies that minimize locus-specific confounding effects. We show that loop extrusion by cohesin globally reduces the mobility of the chromatin fiber in living cells, while also increasing the rates of formation and durations of contacts between sequences inside the same TAD. Quantitative analysis of high-resolution microscopy data reveals that contacts assemble and disassemble frequently in the course of the cell cycle, and become substantially more frequent and longer in the presence of convergent CTCF sites. Comparison with polymer modeling additionally reveals that cohesin-mediated CTCF loops last around 10 minutes on average. Our data support the notion that chromosome structure within TADs is highly dynamic and provide a quantitative framework for understanding the principles that link chromosome structure to biological function.
2022-02-27 | GSE197231 | GEO