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Title: Does loop extrusion alone build and stiffen mitotic chromosomes?
Plain: Before division, each long chromosome is packed within minutes into a compact rod. Motors called condensins form loops around a helical axis, and whether loop formation alone explains the rod's shape, stiffness and the separation of the two copies is not settled.
Precise: Hi-C time courses support nested condensin II and condensin I loops arranged around a helical scaffold (Gibcus and co-workers, 2018). Determine whether a polymer model with measured condensin extrusion rates, densities and loop sizes, and no added crosslinks, reproduces mitotic Hi-C maps, the compaction ratio, the stretching elasticity of isolated chromatids, and sister-chromatid resolution together with topoisomerase II activity.
Settled by: Parameter-free polymer simulation compared with Hi-C, imaging and micromechanical measurements of mitotic chromosomes under condensin and topoisomerase II depletion.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: partially-resolved
Status note: The helical loop architecture was reported in 2018 (Science, doi 10.1126/science.aao6135); a quantitative account of chromosome mechanics from extrusion alone is not established, to this survey's knowledge.
Posed since: (empty)