Program in Systems Biology, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA, USA.
Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, USA.
Nat Cell Biol. 2019 Nov;21(11):1393-1402. doi: 10.1038/s41556-019-0406-2. Epub 2019 Nov 4.
Chromosome folding is modulated as cells progress through the cell cycle. During mitosis, condensins fold chromosomes into helical loop arrays. In interphase, the cohesin complex generates loops and topologically associating domains (TADs), while a separate process of compartmentalization drives segregation of active and inactive chromatin. We used synchronized cell cultures to determine how the mitotic chromosome conformation transforms into the interphase state. Using high-throughput chromosome conformation capture (Hi-C) analysis, chromatin binding assays and immunofluorescence, we show that, by telophase, condensin-mediated loops are lost and a transient folding intermediate is formed that is devoid of most loops. By cytokinesis, cohesin-mediated CTCF-CTCF loops and the positions of TADs emerge. Compartment boundaries are also established early, but long-range compartmentalization is a slow process and proceeds for hours after cells enter G1. Our results reveal the kinetics and order of events by which the interphase chromosome state is formed and identify telophase as a critical transition between condensin- and cohesin-driven chromosome folding.
染色体折叠会随着细胞周期的进程而改变。在有丝分裂过程中，凝缩素将染色体折叠成螺旋环阵列。在间期，黏合蛋白复合物产生环和拓扑关联域（TAD），而一个单独的分隔过程则驱动活性和非活性染色质的分离。我们使用同步细胞培养来确定有丝分裂染色体构象如何转变为间期状态。通过使用高通量染色体构象捕获（Hi-C）分析、染色质结合测定和免疫荧光，我们表明，在末期，凝缩素介导的环消失，并形成一种缺乏大多数环的短暂折叠中间产物。在胞质分裂时，黏合蛋白介导的 CTCF-CTCF 环和 TAD 的位置出现。隔室边界也很早就建立起来，但长距离分隔是一个缓慢的过程，在细胞进入 G1 后数小时仍在进行。我们的结果揭示了形成间期染色体状态的动力学和事件顺序，并确定末期是由凝缩素和黏合蛋白驱动的染色体折叠之间的关键转变。
