Phase separation of Ki-67 during mitotic exit

将细胞划分为功能单元是细胞生命的一个关键原则。除了膜结合细胞器，真核细胞还利用无膜生物分子凝聚物来局部浓缩蛋白质和核酸。虽然我们开始了解无膜凝析油组装和分解的原理，但我们对这种凝析油表面发生的生物过程知之甚少。最大的无膜细胞组件，有丝分裂染色体的表面，被内在无序的蛋白Ki-67所覆盖。我们先前的研究表明Ki-67具有双重功能。在早期有丝分裂中，Ki-67起表面活性物质的作用，防止染色体塌陷成单一染色质团块，而在退出有丝分裂时，Ki-67则积极促进染色体聚集。Ki-67是如何在这两种相反的活动--染色体分散和染色体聚集--之间切换的，目前还不清楚。在这里，我概述了一个跨学科的研究计划，该计划将细胞生物学和蛋白质组学方法与新的体外重建系统相结合，以深入了解Ki-67从染色体排斥物转变为染色体吸引物的物理化学性质。该项目的结果不仅有可能揭示有丝分裂染色体的生物物理性质，而且有可能揭示发生在无膜组装表面的细胞组织的新的一般原理。

Compartmentalization into functional units is a key principle of cellular life. In addition to membrane-bound organelles, eukaryotic cells utilize membrane-less biomolecular condensates to locally concentrate proteins and nucleic acids. While we are beginning to understand the principles that underlie membrane-less condensate assembly and disassembly, we know very little about the biological processes that take place at the surface of such condensates. The surface of the largest membrane-less cellular assembly, the mitotic chromosome, is covered by the intrinsically disordered protein Ki-67. Our previous studies have revealed that Ki-67 has dual functionality. In early mitosis, Ki-67 functions as a surfactant to prevent chromosomes from collapsing into a single chromatin mass, whereas it actively promotes chromosome clustering during exit from mitosis. How Ki-67 switches between these two opposing activities – chromosome dispersal and chromosome clustering – has remained unknown. Here, I outline an interdisciplinary research program that combines cell biological and proteomics approaches with novel in-vitro reconstitution systems to gain insight into the physicochemical properties that underlie the switch of Ki-67 from chromosome repellent to chromosome attractant. The results from this project have the potential to not only reveal new insights into the biophysical nature of mitotic chromosomes but have the potential to reveal new general principles of cellular organization that occur on the surface of membrane-less assemblies.