Confocal Imaging: Mitotic chromosomes are self-entangled and disentangle through a Topoisomerase II-dependent two stage exit from mitosis

The topological state of chromosomes determines their mechanical properties, dynamics, and function. Recent work indicated that interphase chromosomes are largely free of entanglements. Here, we use Hi-C, polymer simulations and multi-contact 3C, and propose that, in contrast, mitotic chromosomes are self-entangled. We explore how a mitotic self-entangled state is converted into an unentangled interphase state during mitotic exit. Most mitotic entanglements are removed during anaphase/telophase, with remaining ones removed during early G1, in a Topoisomerase II-dependent process. Polymer models suggest a two-stage disentanglement pathway: first, decondensation of mitotic chromosomes with remaining condensin loops produces entropic forces that bias Topoisomerase II activity towards decatenation. At the second stage, the loops are released, and formation of new entanglements is prevented by lower Topoisomerase II activity, allowing the establishment of unentangled and territorial G1 chromosomes. When mitotic entanglements are not removed, in experiment and models, a normal interphase state cannot be acquired. Original microscopy images supporting this dataset are included in this repository.染色体的拓扑状态决定了其力学特性、动态特性与生物学功能。近期研究表明，间期（interphase）染色体整体上几乎无缠结。本研究采用Hi-C技术、聚合物模拟（polymer simulations）与多接触3C（multi-contact 3C）实验手段，提出相悖的结论：有丝分裂（mitotic）染色体处于自缠结状态。我们探究了在有丝分裂退出（mitotic exit）过程中，有丝分裂自缠结状态如何转变为无缠结的间期状态。绝大多数有丝分裂缠结在后期（anaphase）/末期（telophase）被清除，剩余缠结则在早G1期（early G1）通过依赖于拓扑异构酶II（Topoisomerase II）的生物学过程完成清除。聚合物模拟模型揭示了两阶段解缠结通路：首先，保留凝缩蛋白（condensin）环的有丝分裂染色体发生去凝缩，由此产生的熵力（entropic forces）会使拓扑异构酶II的活性偏向解连环（decatenation）过程；在第二阶段，凝缩蛋白环被释放，同时较低的拓扑异构酶II活性可阻止新缠结的形成，最终得以建立无缠结且具有区域化特征的G1期染色体。若有丝分裂缠结未被清除，无论在实验体系还是模型体系中，均无法形成正常的间期状态。 支撑该数据集的原始显微图像已收录于本存储库中。