Universal dynamics of cohesin-mediated loop extrusion
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ABSTRACT:
PROVIDER: PRJNA1140881 | ENA |
REPOSITORIES: ENA
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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:Fertilization triggers assembly of higher-order chromatin structure from a nucleosomal state to generate a totipotent embryo. Chromatin loops and domains are detected in mouse zygotes by single-nucleus Hi-C (snHi-C) but not bulk Hi-C; both are absent in Drosophila embryos. We investigated whether zygotic chromatin structures are generated by cohesin-dependent loop extrusion. Using snHi-C of mouse knockout embryos, we demonstrate the zygotic genome folds into loops and domains that critically depend on Scc1-cohesin and are regulated in size by Wapl. Remarkably, we discovered distinct effects on maternal and paternal chromatin loop sizes, likely reflecting loop extrusion dynamics and reprogramming states. Polymer simulations based on snHi-C are consistent with a model where cohesin locally compacts chromatin and restricts inter-chromosomal interactions by active loop extrusion, whose processivity is controlled by Wapl. Our simulations and experimental data provide evidence that cohesin-dependent loop extrusion organizes mammalian genomes over multiple scales from the one-cell embryo onwards.
2017-08-25 | GSE100569 | 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:Genome function depends on regulated chromosome folding, and loop extrusion by the protein complex cohesin is essential for this multilayered organization. The chromosomal positioning of cohesin is controlled by transcription, and the complex also localizes to stalled replication forks. However, the role of transcription and replication in chromosome looping remains unclear. Here, we show that reduction of chromosome-bound RNA polymerase weakens normal cohesin loop extrusion boundaries, allowing cohesin to form new long-range chromosome cis interactions. Stress response genes activated by transcription inhibition are also shown to act as new loop extrusion boundaries. Furthermore, cohesin loop extrusion during early S-phase is jointly controlled by transcription and replication units. Together, the results reveal that replication and transcription machineries are chromosome folding regulators that block the progression of loop-extruding cohesin, opening for new perspectives on cohesin’s roles in genome function and stability.
2022-06-15 | GSE191207 | GEO
Project description:Genome function depends on regulated chromosome folding, and loop extrusion by the protein complex cohesin is essential for this multilayered organization. The chromosomal positioning of cohesin is controlled by transcription, and the complex also localizes to stalled replication forks. However, the role of transcription and replication in chromosome looping remains unclear. Here, we show that reduction of chromosome-bound RNA polymerase weakens normal cohesin loop extrusion boundaries, allowing cohesin to form new long-range chromosome cis interactions. Stress response genes activated by transcription inhibition are also shown to act as new loop extrusion boundaries. Furthermore, cohesin loop extrusion during early S-phase is jointly controlled by transcription and replication units. Together, the results reveal that replication and transcription machineries are chromosome folding regulators that block the progression of loop-extruding cohesin, opening for new perspectives on cohesin’s roles in genome function and stability.
2022-06-15 | GSE162193 | GEO
Project description:Genome function depends on regulated chromosome folding, and loop extrusion by the protein complex cohesin is essential for this multilayered organization. The chromosomal positioning of cohesin is controlled by transcription, and the complex also localizes to stalled replication forks. However, the role of transcription and replication in chromosome looping remains unclear. Here, we show that reduction of chromosome-bound RNA polymerase weakens normal cohesin loop extrusion boundaries, allowing cohesin to form new long-range chromosome cis interactions. Stress response genes activated by transcription inhibition are also shown to act as new loop extrusion boundaries. Furthermore, cohesin loop extrusion during early S-phase is jointly controlled by transcription and replication units. Together, the results reveal that replication and transcription machineries are chromosome folding regulators that block the progression of loop-extruding cohesin, opening for new perspectives on cohesin’s roles in genome function and stability.
2022-06-15 | GSE161522 | 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: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: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.
2021-07-20 | GSE166387 | GEO
Project description:The organization of the genome in three-dimensional space is highly dynamic, yet how these dynamics are regulated and the role they play in genome function is poorly understood. Here, we utilized acute depletion of NIPBL to characterize the role of cohesin-mediated loop extrusion in vivo. Using this approach, we find that many chromatin loops are rapidly diminished upon loss of NIBPL, consistent with recent single locus imaging studies showing that chromatin loops are transient. However, we also identified a subset of cohesin-dependent chromatin loops that are anchored in repressive chromatin and may be “long-lived”, given that they require NIPBL for their establishment upon mitotic exit, but are persistent when NIPBL is depleted from interphase cells. In addition to the reformation of 3D genome structures, mitotic exit coincides with widespread transcriptional activation. We found that NIPBL is essential for establishing the expression of lineage-defining genes during the M-G1 transition but has diminished impact in the steady-state maintenance of their expression. At genes sensitive to its depletion, NIPBL supports a unique local genome organization defined by greater spatial proximity to nearby enhancers and weaker transcription start site insulation of genomic contacts. Overall, we show that NIPBL-mediated loop extrusion is critical to genome organization and transcriptional regulation in vivo.
2024-10-07 | GSE277720 | GEO