What loop extrusion proposes
Loop extrusion describes a protein complex enlarging a DNA loop by bringing additional DNA into it. Fudenberg and colleagues tested this idea with simulated chromatin polymers and boundary sites. Their model reproduced domain-shaped features in published chromosome contact maps. A successful simulation shows that a mechanism can explain selected observations; it does not establish that it is the only mechanism in cells. [1]
What removing cohesin tests
Rao and colleagues engineered human HCT-116 cancer cells so that auxin treatment degraded RAD21, a cohesin subunit. Hi-C maps lost the loop domains detected before treatment, while compartment organization persisted. This separates two forms of genome organization in that experimental system; it does not mean that all chromosome folding disappears. [2]
Hi-C records how frequently pairs of DNA regions are captured together in a cell population. Such a map is a contact-frequency measurement, not a trajectory of one loop through time. The study supports a requirement for cohesin in its measured loop domains, but its depletion experiment alone does not directly film extrusion. [2]
What direct imaging adds
Davidson and colleagues imaged DNA loops in a purified-protein system containing human cohesin, its NIPBL–MAU2 partner and ATP. CTCF could impede loop growth, with stronger blocking from one orientation and at greater DNA tension. Some encounters passed the barrier. Thus CTCF is a conditional regulator in this assay, rather than an invariably closed gate. [3]
How to read the evidence
The simulation tests explanatory sufficiency, depletion tests necessity in one cell model, and reconstitution tests biochemical capability. None supplies a universal speed or loop lifetime for every living tissue. Extending these results to a particular cell type requires measurements in that context. [1] [2] [3]
Extending the live-cell evidence — 12 October 2026
Sabaté and colleagues tracked anchors of three endogenous TADs in HCT116 cells and compared live distances with Capture Micro-C and cohesin perturbation. Their model-based interpretation supports ongoing extrusion by multiple cohesin complexes with transient boundary proximity. The sampled human loci extend earlier mouse single-locus evidence, while the fluorescent-anchor readout still differs from directly watching cohesin move on DNA. Sabaté et al. (2025).
This addition uses primary studies. Access depth and claim limits are recorded with each added reference; it is a dated literature appraisal, not independent experimental replication.
Primary studies behind this guide
- Fudenberg et al. (2016), Cell Reports 15:2038–2049. Formation of Chromosomal Domains by Loop Extrusion. DOI: 10.1016/j.celrep.2016.04.085. Primary research.
- Rao et al. (2017), Cell 171:305–320.e24. Cohesin Loss Eliminates All Loop Domains. DOI: 10.1016/j.cell.2017.09.026. Primary research.
- Davidson et al. (2023), Nature 616:822–827. CTCF is a DNA-tension-dependent barrier to cohesin-mediated loop extrusion. DOI: 10.1038/s41586-023-05961-5. Primary research.
- Sabaté T, Lelandais B, Robert MC, et al. (2025). Uniform dynamics of cohesin-mediated loop extrusion in living human cells. Nature Genetics 57:3152–3164. DOI: 10.1038/s41588-025-02406-9. Primary research.
Independent update access: Consensus fetched primary abstract and Scite selected main-text passages, including study design and initial Results; not every supplementary analysis inspected. Primary source.
Scientific text and the identity and fit of the cited studies were checked on 3 October 2026. This guide covers the experiments described here; it is not an exhaustive literature review. See the audit record for access limits and remaining work.