Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, 02454.
Department of Bioengineering, Faculty of Biology, Lomonosov Moscow State University, Moscow 119234, Russia.
Mol Biol Cell. 2020 Aug 15;31(18):1988-2001. doi: 10.1091/mbc.E19-12-0693. Epub 2020 Jun 24.
Cellular actin arrays are often highly organized, with characteristic patterns critical to their in vivo functions, yet the mechanisms for establishing these higher order geometries remain poorly understood. In formin-polymerized actin cables are spatially organized and aligned along the mother-bud axis to facilitate polarized vesicle traffic. Here, we show that the bud neck-associated F-BAR protein Hof1, independent of its functions in regulating the formin Bnr1, binds to actin filaments and organizes actin cables in vivo. Hof1 bundles actin filaments and links them to septins in vitro. F-actin binding is mediated by the "linker" domain of Hof1, and its deletion leads to cable organization defects in vivo. Using superresolution imaging, we show that Hof1 and septins are patterned at the bud neck into evenly spaced axial pillars (∼200 nm apart), from which actin cables emerge and grow into the mother cell. These results suggest that Hof1, while bound to septins at the bud neck, not only regulates Bnr1 activity, but also binds to actin cables and aligns them along the mother-bud axis. More broadly, these findings provide a strong example of how an actin regulatory protein can be spatially patterned at the cell cortex to govern actin network geometry.
细胞肌动蛋白阵列通常高度组织化，具有对其体内功能至关重要的特征模式，但建立这些更高阶几何形状的机制仍知之甚少。在丝状肌动蛋白聚合形成的肌动蛋白电缆中，空间上沿着母细胞-芽细胞的轴排列并对齐，以促进极化囊泡运输。在这里，我们表明，芽颈相关的 F-BAR 蛋白 Hof1 独立于其在调节形成蛋白 Bnr1 中的功能，与肌动蛋白丝结合并在体内组织肌动蛋白电缆。Hof1 束状肌动蛋白丝，并在体外将它们与 septin 连接。F-actin 的结合是由 Hof1 的“连接”结构域介导的，其缺失导致体内电缆组织缺陷。通过超分辨率成像，我们表明 Hof1 和 septin 在芽颈处形成均匀间隔的轴向柱（相隔约 200nm），肌动蛋白电缆从这些柱中出现并延伸到母细胞中。这些结果表明，Hof1 不仅在芽颈处与 septin 结合，调节 Bnr1 活性，还与肌动蛋白电缆结合并沿母细胞-芽细胞的轴排列它们。更广泛地说，这些发现为肌动蛋白调节蛋白如何在细胞皮层上进行空间模式化以控制肌动蛋白网络几何形状提供了一个强有力的例子。
