Srivastava Vasudha, Robinson Douglas N
Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.
Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.
Curr Biol. 2015 Mar 2;25(5):663-70. doi: 10.1016/j.cub.2015.01.025. Epub 2015 Feb 19.
Cell-shape changes associated with processes like cytokinesis and motility proceed on several-second timescales but are derived from molecular events, including protein-protein interactions, filament assembly, and force generation by molecular motors, all of which occur much faster [1-4]. Therefore, defining the dynamics of such molecular machinery is critical for understanding cell-shape regulation. In addition to signaling pathways, mechanical stresses also direct cytoskeletal protein accumulation [5-7]. A myosin-II-based mechanosensory system controls cellular contractility and shape during cytokinesis and under applied stress [6, 8]. In Dictyostelium, this system tunes myosin II accumulation by feedback through the actin network, particularly through the crosslinker cortexillin I. Cortexillin-binding IQGAPs are major regulators of this system. Here, we defined the short timescale dynamics of key cytoskeletal proteins during cytokinesis and under mechanical stress, using fluorescence recovery after photobleaching and fluorescence correlation spectroscopy, to examine the dynamic interplay between these proteins. Equatorially enriched proteins including cortexillin I, IQGAP2, and myosin II recovered much more slowly than actin and polar crosslinkers. The mobility of equatorial proteins was greatly reduced at the furrow compared to the interphase cortex, suggesting their stabilization during cytokinesis. This mobility shift did not arise from a single biochemical event, but rather from a global inhibition of protein dynamics by mechanical-stress-associated changes in the cytoskeletal structure. Mechanical tuning of contractile protein dynamics provides robustness to the cytoskeletal framework responsible for regulating cell shape and contributes to cytokinesis fidelity.
与胞质分裂和细胞运动等过程相关的细胞形状变化发生在几秒的时间尺度上，但它们源自分子事件，包括蛋白质-蛋白质相互作用、细丝组装以及分子马达产生的力，所有这些都发生得快得多[1-4]。因此，定义这种分子机制的动力学对于理解细胞形状调控至关重要。除了信号通路外，机械应力也指导细胞骨架蛋白的积累[5-7]。基于肌球蛋白II的机械传感系统在胞质分裂期间和施加应力时控制细胞收缩性和形状[6, 8]。在盘基网柄菌中，该系统通过肌动蛋白网络的反馈，特别是通过交联蛋白皮层肌动蛋白I来调节肌球蛋白II的积累。与皮层肌动蛋白结合的IQGAP是该系统的主要调节因子。在这里，我们利用光漂白后的荧光恢复和荧光相关光谱技术，定义了胞质分裂期间和机械应力下关键细胞骨架蛋白的短时间尺度动力学，以研究这些蛋白之间的动态相互作用。包括皮层肌动蛋白I、IQGAP2和肌球蛋白II在内的赤道富集蛋白的恢复速度比肌动蛋白和极性交联蛋白慢得多。与间期皮层相比，赤道蛋白在沟处的流动性大大降低，这表明它们在胞质分裂期间被稳定下来。这种流动性变化并非源于单一的生化事件，而是源于细胞骨架结构中与机械应力相关的变化对蛋白质动力学的整体抑制。收缩蛋白动力学的机械调节为负责调节细胞形状的细胞骨架框架提供了稳健性，并有助于胞质分裂的保真度。
