Assembly and Mechanics of the Mitotic Spindle

有丝分裂纺锤体是在细胞分裂之前分离染色体的分子机器。 传统的观点认为，纺锤体的组装是微管（长的动态聚合物）随机捕获染色体的结果。 在此之后，纺锤体长度通过分子马达施加在连接纺锤体极和染色体的微管上的向内张力和由其他马达在连接纺锤体极的重叠微管上产生的向外压缩的平衡来维持。 越来越多的证据表明，纺锤体的组装和维持依赖于微管、分子马达、染色体和调节蛋白的更复杂的互连网络，这一观点受到了挑战。 从工程的角度来看，这种分子机器的三个设计原则特别重要：主轴组装迅速，组装准确，机械坚固，但具有延展性。 这种设计是如何通过随机相互作用和非永久性分子部分实现的？ 主轴如何自组装？ 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结合，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，一个粗粒度的流体动力学模型的凝胶短微管和分子马达的发展，阐明减数分裂和体外纺锤体的自组织原则。 模型进行了测试，并通过与定量数据的预测比较，完善。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，细胞用于在细胞分裂前分离染色体。 该模型的预测有助于揭示细胞用于快速，准确和机械稳健地分离染色体的机制。 同时模拟有丝分裂纺锤体的组装、误差校正和力学，为实验产生可检验的预测。 这些模型不仅对于理解基础细胞生物学的基本问题至关重要，而且对于微调用于许多源于非整倍性的疾病的药物设计策略也至关重要，染色体数目异常。

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.