Department of Physics, Lehigh University, Bethlehem, PA 18015, USA.
J Phys Condens Matter. 2011 Sep 21;23(37):374103. doi: 10.1088/0953-8984/23/37/374103. Epub 2011 Aug 23.
Actomyosin bundles frequently form through aggregation of membrane-bound myosin clusters. One such example is the formation of the contractile ring in fission yeast from a broad band of cortical nodes. Nodes are macromolecular complexes containing several dozens of myosin-II molecules and a few formin dimers. The condensation of a broad band of nodes into the contractile ring has been previously described by a search, capture, pull and release (SCPR) model. In SCPR, a random search process mediated by actin filaments nucleated by formins leads to transient actomyosin connections among nodes that pull one another into a ring. The SCPR model reproduces the transport of nodes over long distances and predicts observed clump-formation instabilities in mutants. However, the model does not generate transient linear elements and meshwork structures as observed in some wild-type and mutant cells during ring assembly. As a minimal model of node alignment, we added short-range aligning forces to the SCPR model representing currently unresolved mechanisms that may involve structural components, cross-linking and bundling proteins. We studied the effect of the local node alignment mechanism on ring formation numerically. We varied the new parameters and found viable rings for a realistic range of values. Morphologically, transient structures that form during ring assembly resemble those observed in experiments with wild-type and cdc25-22 cells. Our work supports a hierarchical process of ring self-organization involving components drawn together from distant parts of the cell followed by progressive stabilization.
肌球蛋白簇通过细胞膜结合的肌球蛋白簇聚集而经常形成肌动球蛋白束。一个这样的例子是裂殖酵母收缩环的形成，它来自于广泛的皮质节点带。节点是包含数十个肌球蛋白 II 分子和几个formin 二聚体的大分子复合物。广泛的节点带凝聚成收缩环以前曾被一个搜索、捕获、拉伸和释放（SCPR）模型描述过。在 SCPR 中，formin 引发的肌动蛋白丝介导的随机搜索过程导致节点之间的短暂肌动球蛋白连接，将彼此拉成一个环。SCPR 模型再现了节点的长距离运输，并预测了突变体中观察到的聚集体形成不稳定性。然而，该模型不能产生如在一些野生型和突变细胞中观察到的环组装过程中的瞬时线性元件和网格结构。作为节点对准的最小模型，我们向 SCPR 模型中添加了短程对准力，代表目前尚未解决的机制，这些机制可能涉及结构成分、交联和束集蛋白。我们从数值上研究了局部节点对准机制对环形成的影响。我们改变了新的参数，并发现了在现实范围内可行的环。形态上，在环组装过程中形成的瞬态结构类似于在野生型和 cdc25-22 细胞实验中观察到的结构。我们的工作支持了一个涉及从细胞的远距离部分聚集组件的环自组织的分层过程，随后是逐渐的稳定化。
