Modeling Contractile Ring Constriction in Fission Yeast

描述(申请人提供)：细胞质分裂是结束细胞周期的过程，在这个过程中母细胞质分裂成两部分。作为细胞分裂的关键步骤，它对生命至关重要，在这个过程中的缺陷与癌症、神经疾病和出生缺陷有关。动物和真菌通过收缩肌球蛋白收缩环来完成胞质分裂，肌球蛋白收缩环由产生力量的肌球蛋白马达蛋白、肌动蛋白细丝和其他成分组成。虽然关于分子部分已经有了很大的了解，但这些部分如何协调以产生功能收缩机器仍然不太清楚。这一直是困难的，因为从实验上测量这些部分是如何在时空上组织的是具有挑战性的，并且需要数学模型来将假设的排列转化为关键的可观测参数，如环收缩速率。本研究项目是一个数学建模和计算模拟的程序，以裂解酵母为模型系统，建立细胞质分裂的原理，因为涉及的许多蛋白质在酵母和动物之间是保守的，所以可能是通用的。建模将作为与一位研究酵母胞质分裂的实验同事紧密的理论-实验合作的一部分进行。将采用增加复杂性的三阶段策略，从更简单的收缩系统开始，以酵母收缩的完全复杂性结束，酵母收缩伴随着分离而发生，即子细胞之间细胞壁物质的沉积。A阶段将包括对静止的哺乳动物细胞应激纤维、在伤口愈合和其他环境中重要的收缩肌球蛋白结构的研究。应力纤维的特性相对较好，其动力学已被直接测量。阶段B将涉及酵母原生质体，即没有细胞壁的细胞，其中可以发生环状收缩，而不会出现分离的并发症。在C相中，我们将研究野生型酵母的收缩-分离。长期目标是建立应力纤维和裂解酵母收缩环中的收缩力产生和动力学机制，并确定这些系统之间的共性。该模型的具体目的是：(I)测试肌动蛋白、肌球蛋白、肌动蛋白成核剂/解聚剂和其他关键成分的假设排列和周转规律。特别是为了确定环和应力纤维中的排列是肌节(周期性的，肌样的)还是非肌节的(随机的)。(Ii)检验肌动蛋白周转受内部压力调节的假说。(Iii)应用模型来预测激光消融实验和自发切断事件的结果，这些事件可以揭示肌动球蛋白结构的其他隐藏特征。激光烧蚀实验已经在应力纤维上进行。(4)验证环在野生型酵母收缩中调节隔膜生长的假说。这些目标将通过与实验的连续对话进行建模来实现，旨在揭示细胞动力收缩环的新的结构和动力学特征。 与公共卫生相关：细胞质分裂是在细胞周期结束时将一个细胞分裂成两个子细胞。它的功能障碍与癌症、神经疾病和出生缺陷有关。该项目旨在促进对酵母中胞质分裂和胞质分裂机制的了解，这将有助于开发与胞质分裂相关的病理疗法。

DESCRIPTION (provided by applicant): Cytokinesis is the process ending the cell cycle in which the mother cell cytoplasm divides into two. As a critical step in cell division it is fundamentally important to life and defects in the process are associated with cancer, neurological disease and birth defects. Animals and fungi accomplish cytokinesis by constriction of an actomyosin contractile ring built from force-producing myosin motor proteins, actin filaments and other com- ponents. While much is established about the molecular parts it remains much less clear how these parts coordinate to produce a functional contractile machine. This has been difficult because experimentally mea- suring how the parts are spatiotemporally organized is challenging and mathematical modeling is needed to translate hypothesized arrangements into key observables such as ring constriction rate. This research project is a program of mathematical modeling and computational simulation focusing on fission yeast as a model sys- tem to establish principles of cytokinesis which may be general since many proteins involved are conserved between yeast and animals. The modeling will proceed as part of a tight theory-experiment collaboration with an experimental colleague studying yeast cytokinesis. A 3-phase strategy of increasing complexity will be adopted, starting with a simpler contractile system and ending with the full complexity of yeast constriction which occurs concomitantly with septation, the deposition of cell wall material between daughter cells. Phase A will consist in a study of stationary mammalian cell stress fibers, contractile actomyosin structures important in wound healing and other contexts. Stress fibers are relatively well characterized and their kinetics have been directly measured. Phase B will address yeast protoplasts, cells lacking cell wall in which ring constric- tion can occur without the complication of septation. In phase C constriction-septation in wild type yeast will be studied. The long term goals are to establish mechanisms of contractile force generation and kinetics in stress fibers and the fission yeast contractile ring and to determine the commonality between these systems. The specific aims of the modeling are: (i) To test hypothetical arrangements and turnover rules of actin, myosin, actin nucleators/depolymerization agents and other key components. In particular, to determine whether ar- rangements are sarcomeric (periodic, muscle-like) or non-sarcomeric (random) in the ring and stress fibers. (ii) To test the hypothesis that actin turnover is regulated by internal stresses. (iii) To apply models to predict outcomes of laser ablation experiments and spontaneous severing events which can reveal otherwise hidden features of actomyosin structures. Laser ablation experiments have already been performed on stress fibers. (iv) To test the hypothesis that the ring regulates septum growth in wild type yeast constriction. These aims will be accomplished by modeling efforts in a continuous dialog with experiments aiming to reveal new structural and kinetic features of the cytokinetic contractile ring. PUBLIC HEALTH RELEVANCE: Cytokinesis is the partitioning of a cell into two daughter cells at the end of the cell cycle. Its malfunction is associated with cancer, neurological disease and birth defects. The project aims to advance understanding of cytokinesis in yeast and cytokinesis mechanisms in general which will aid development of therapies for cytokinesis-related pathologies.