{
  "id": 2256147,
  "title": "Loop statistics and fountain geometry reveal effective two-sided cohesin extrusion and crowding-induced arm desynchronization",
  "url": "https://urgent.news/2026/08/20/loop-statistics-and-fountain-geometry-reveal-effective-two-sided",
  "topic": "science",
  "section": "Science",
  "published": "2026-08-20T00:00:00.000Z",
  "source": {
    "name": "bioRxiv",
    "slug": "biorxiv",
    "url": "https://www.biorxiv.org/content/10.64898/2026.08.20.745948v1?rss=1"
  },
  "original_language": "en",
  "account": "The study delves into the intricate dynamics of cohesin-driven loop extrusion, which is pivotal in shaping chromosome organization. However, the factors governing loop lengths and coordination between the extruding arms in living cells remain elusive. The presence of broad extrusion fountains in Hi-C maps suggests that the asymmetry in arm extrusion might originate from the physical phenomenon of arm desynchronization. The researchers have now devised a kinetic theory to elucidate this process through transient chromatin roadblocks and neighboring cohesins. The abundance, lifetime, and partial permeability of these roadblocks, along with cohesin crowding, contribute to an effective obstacle density that renormalizes processivity, thereby determining the mean loop length. The full loop-length distributions reveal that asymmetric extrusion, while remaining exponential, can also produce a finite-length peak characteristic of effectively two-sided extrusion. ChIA-PET and MNase HiChIP data align with these predictions, casting doubt on the notion of purely one-sided extrusion. Furthermore, cohesin crowding exacerbates the desynchronization of the arms, preserving a residual correlation of approximately 1/4. This anisotropy, observed across three vertebrates, supports the hypothesis that local cohesin crowding could be the primary driver behind fountain formation. The analysis also uncovers cohesin-loading regions ranging from 30 to 100 kilobases, with Danio rerio exhibiting a loading width that is comparable to the enhancer enrichment extent. This finding supports a model where an enhancer-rich loading platform functions as a collective barrier, facilitating outward extrusion towards surrounding promoters. The study underscores how coordinated cohesin and roadblock kinetics collectively dictate loop statistics, sculpt chromosome-contact patterns, and potentially aid in the enhancer-promoter search mechanism.",
  "summary": "Cohesin-driven loop extrusion shapes chromosome organization, yet what determines loop lengths and coordination between the extruding arms in vivo remains unclear. Broad extrusion \"fountains\" in Hi-C maps point to arm desynchronization, whose physical origin is unknown. Here we develop a kinetic theory of extrusion through transient chromatin roadblocks and neighbouring cohesins. Roadblock…",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}