受限细丝-马达混合物模型中的纺锤体与活性涡旋
Spindles and active vortices in a model of confined filament-motor mixtures
AI总结：
本文通过数值模拟受限离散细丝-马达蛋白模型，发现了纺锤体、星体和涡旋等结构的自发形成，揭示了压力、马达速度与密度对自组织状态的影响，并强调需进一步理解活性凝胶微观活动与宏观自组织间的联系。
摘要：
亚细胞结构的稳健自组织是支配细胞生命动力学与演化的关键原则。在正在进行分裂的裂殖酵母细胞中，有丝分裂纺锤体从微管、马达蛋白与受限细胞壁的相互作用中自发产生，并且在准二维微管-驱动蛋白实验中观察到星体和涡旋的自组装。目前尚无清晰的微观图像来说明驱动这种图案形成的活性马达的作用，且连续介质建模对细丝尺度结构的相关性仍不确定。在此，我们展示了对局限于加压圆柱形箱体中的离散细丝-马达蛋白模型进行数值模拟的结果。稳定的纺锤体、向列构型、星体和高密度半星体自发出现，后两者也曾在局限于乳液液滴内的细胞质中被观察到。我们给出了状态图，描绘了随着压力、马达速度和马达密度变化时每种稳态的边界。我们进一步强调了一个参数区间，在该区间内形成的涡旋表现出所有细丝的集体旋转，但在收缩为半星体之前具有有限的寿命。对寿命分布的量化表明这种收缩是一个泊松过程。具有固定体积的等效系统表现出持久的涡旋，并伴有旋转方向的随机切换，其切换时间服从与加压系统中收缩时间相似的统计规律。此外，我们表明，增加马达从细丝正端脱离的速率既可以破坏涡旋，也可以将一些星体转变为涡旋。基于我们的发现，我们主张需要更深入地理解支撑活性凝胶宏观自组织的微观活动，并敦促开展进一步的实验以帮助弥合这些长度尺度。
英文摘要：
Robust self-organization of subcellular structures is a key principle governing the dynamics and evolution of cellular life. In fission yeast cells undergoing division, the mitotic spindle spontaneously emerges from the interaction of microtubules, motor proteins and the confining cell walls, and asters and vortices have been observed to self-assemble in quasi-two dimensional microtubule-kinesin assays. Their is no clear microscopic picture of the role of the active motors driving this pattern formation, and the relevance of continuum modeling to filament-scale structures remains uncertain. Here we present results of numerical simulations of a discrete filament-motor protein model confined to a pressurised cylindrical box. Stable spindles, nematic configurations, asters and high-density semi-asters spontaneously emerge, the latter pair having also been observed in cytosol confined within emulsion droplets. State diagrams are presented delineating each stationary state as the pressure, motor speed and motor density are varied. We further highlight a parameter regime where vortices form exhibiting collective rotation of all filaments, but have a finite life-time before contracting to a semi-aster. Quantifying the distribution of life-times suggests this contraction is a Poisson process. Equivalent systems with fixed volume exhibit persistent vortices with stochastic switching in the direction of rotation, with switching times obeying similar statistics to contraction times in pressurised systems. Furthermore, we show that increasing the detachment rate of motors from filament plus-ends can both destroy vortices and turn some asters into vortices. Based on our findings we argue the need for a deeper understanding of the microscopic activities underpinning macroscopic self-organization in active gels and urge further experiments to help bridge these lengths.
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