Joensuu Merja, Belevich Ilya, Rämö Olli, Nevzorov Ilya, Vihinen Helena, Puhka Maija, Witkos Tomasz M, Lowe Martin, Vartiainen Maria K, Jokitalo Eija
Cell and Molecular Biology Program, Institute of Biotechnology, 00014 University of Helsinki, Helsinki, Finland Electron Microscopy Unit, Institute of Biotechnology, 00014 University of Helsinki, Helsinki, Finland Faculty of Life Sciences, University of Manchester, Manchester M13 9PL, United Kingdom.
Mol Biol Cell. 2014 Apr;25(7):1111-26. doi: 10.1091/mbc.E13-12-0712. Epub 2014 Feb 12.
The endoplasmic reticulum (ER) comprises a dynamic three-dimensional (3D) network with diverse structural and functional domains. Proper ER operation requires an intricate balance within and between dynamics, morphology, and functions, but how these processes are coupled in cells has been unclear. Using live-cell imaging and 3D electron microscopy, we identify a specific subset of actin filaments localizing to polygons defined by ER sheets and tubules and describe a role for these actin arrays in ER sheet persistence and, thereby, in maintenance of the characteristic network architecture by showing that actin depolymerization leads to increased sheet fluctuation and transformations and results in small and less abundant sheet remnants and a defective ER network distribution. Furthermore, we identify myosin 1c localizing to the ER-associated actin filament arrays and reveal a novel role for myosin 1c in regulating these actin structures, as myosin 1c manipulations lead to loss of the actin filaments and to similar ER phenotype as observed after actin depolymerization. We propose that ER-associated actin filaments have a role in ER sheet persistence regulation and thus support the maintenance of sheets as a stationary subdomain of the dynamic ER network.
内质网（ER）由具有不同结构和功能域的动态三维（3D）网络组成。内质网的正常运作需要在动态、形态和功能内部以及它们之间保持复杂的平衡，但这些过程在细胞中是如何耦合的尚不清楚。通过活细胞成像和3D电子显微镜，我们确定了肌动蛋白丝的一个特定子集定位于由内质网片层和小管定义的多边形，并描述了这些肌动蛋白阵列在内质网片层持久性中的作用，从而通过表明肌动蛋白解聚导致片层波动和转变增加，并导致小且数量较少的片层残余物以及内质网网络分布缺陷，在维持特征性网络结构中发挥作用。此外，我们确定肌球蛋白1c定位于内质网相关的肌动蛋白丝阵列，并揭示了肌球蛋白1c在调节这些肌动蛋白结构中的新作用，因为肌球蛋白1c的操作导致肌动蛋白丝丢失，并导致与肌动蛋白解聚后观察到的类似内质网表型。我们提出，内质网相关的肌动蛋白丝在内质网片层持久性调节中起作用，从而支持将片层维持为动态内质网网络的一个固定子域。
