Assembly and Mechanics of the Mitotic Spindle

有丝分裂纺锤体是一种在细胞分裂前分离染色体的分子机器。传统的说法是，纺锤体的组装是微管(长动态聚合物)随机捕获染色体的结果。在此之后，纺锤体的长度由分子马达对连接纺锤体极和染色体的微管施加的向内张力和由其他马达对连接纺锤体极的重叠微管产生的向外压缩的平衡来维持。越来越多的证据表明，纺锤体的组装和维护依赖于由微管、分子马达、染色体和调控蛋白组成的更复杂的相互连接的网络，这一图景受到了挑战。从工程角度来看，这种分子机器的三个设计原则尤其重要：主轴组装迅速，组装准确，机械坚固，但延展性强。这种设计是如何通过随机相互作用和非永久性分子部分来实现的？主轴是如何自组装的？是什么决定了它的机械性能？数学和计算模型将被用来定量研究动态不稳定的微管捕获染色体的过程。组装的动力学与机械力相耦合，力、运动、染色体捕获和组装误差校正之间的相互作用将被研究。然后，建立了一个由短微管和分子马达组成的凝胶的粗粒流体动力学模型，以阐明减数分裂和体外纺锤体的自组织原理。通过将它们的预测与定量数据进行比较，对模型进行了检验和改进。该项目使用数学分析、计算机模拟和模型驱动实验的新组合来开发一种新的有丝分裂纺锤体-动态分子机器的定量模型，细胞在细胞分裂之前使用该模型来分离染色体。这个模型的预测有助于揭示细胞用来快速、准确和机械地分离染色体的机制。同时模拟了有丝分裂纺锤体的组装、纠错和机制，为实验产生了可检验的预测。这样的模型不仅对于理解基本细胞生物学的基本问题至关重要，而且对于微调源于非整倍体(即染色体数量异常)的多种疾病的药物设计策略也至关重要。

The mitotic spindle is a molecular machine that segregates chromosomes prior to cell division. The traditional picture is that the spindle assembles as a result of microtubules (long dynamic polymers) randomly capturing chromosomes. After this, the spindle length is maintained by a balance of inward tension exerted by molecular motors on the microtubules connecting spindle poles and chromosomes, and outward compression generated by other motors on the overlapping microtubules connecting the spindle poles. This picture is being challenged by mounting evidence indicating that spindle assembly and maintenance rely on much more complex interconnected networks of microtubules, molecular motors, chromosomes and regulatory proteins. From an engineering point of view, three design principles of this molecular machine are especially important: the spindle assembles rapidly, it assembles accurately, and it is mechanically robust, yet malleable. How is this design achieved with randomly interacting and impermanent molecular parts? How does the spindle self-assemble? What determines its mechanical properties? Mathematical and computational modeling will be used to examine quantitatively the process of the capture of chromosomes by dynamically unstable microtubules. Kinetics of the assembly are coupled with mechanical forces, and interplay between forces, movements, chromosome capture and assembly error correction will be investigated. Then a coarse grained hydrodynamic-like model of a gel of short microtubules and molecular motors is developed to elucidate the self-organization principles for meiotic and in vitro spindles. The models are tested and refined by comparison of their predictions with quantitative data. This project uses a novel combination of mathematical analysis, computer simulations and model-driven experiments to develop a novel quantitative model of the mitotic spindle-dynamic molecular machine that the cell uses to segregate chromosomes prior to cell division. Predictions of this model help reveal the mechanisms the cell uses to segregate the chromosomes fast, accurately and in a mechanically robust way. The assembly, error correction, and mechanics of the mitotic spindle are simulated simultaneously, generating testable predictions for the experiment. Such models are crucial for understanding not only the fundamental question of basic cell biology, but also to fine-tune drug design strategies for numerous diseases that stem from aneuploidy, i.e., an abnormal number of chromosomes.