Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD, USA.
Laboratory of Cell Structure and Dynamics, National Institute on Deafness and other Communication Disorders, NIH, Bethesda, MD, USA.
Nat Cell Biol. 2019 Aug;21(8):933-939. doi: 10.1038/s41556-019-0365-7. Epub 2019 Jul 29.
Actomyosin networks, the cell's major force production machineries, remodel cellular membranes during myriad dynamic processes by assembling into various architectures with distinct force generation properties. While linear and branched actomyosin architectures are well characterized in cell-culture and cell-free systems, it is not known how actin and myosin networks form and function to remodel membranes in complex three-dimensional mammalian tissues. Here, we use four-dimensional spinning-disc confocal microscopy with image deconvolution to acquire macromolecular-scale detail of dynamic actomyosin networks in exocrine glands of live mice. We address how actin and myosin organize around large membrane-bound secretory vesicles and generate the forces required to complete exocytosis. We find that actin and non-muscle myosin II (NMII) assemble into previously undescribed polyhedral-like lattices around the vesicle membrane. The NMII lattice comprises bipolar minifilaments as well as non-canonical three-legged configurations. Using photobleaching and pharmacological perturbations in vivo, we show that actomyosin contractility and actin polymerization together push on the underlying vesicle membrane to overcome the energy barrier and complete exocytosis. Our imaging approach thus unveils a force-generating actomyosin lattice that regulates secretion in the exocrine organs of live animals.
肌动球蛋白网络是细胞的主要力量产生机制，通过组装成具有不同产生力特性的各种结构，在无数动态过程中重塑细胞膜。虽然在线粒体和无细胞系统中已经很好地描述了线性和分支的肌动球蛋白结构，但尚不清楚肌动球蛋白网络如何形成和发挥作用，以重塑复杂的三维哺乳动物组织中的膜。在这里，我们使用带有图像反卷积的四维度旋转盘共聚焦显微镜，在活鼠的外分泌腺中获取动态肌动球蛋白网络的宏观尺度细节。我们研究了肌动球蛋白如何围绕大型膜结合的分泌泡进行组织，并产生完成胞吐作用所需的力。我们发现肌动蛋白和非肌肉肌球蛋白 II（NMII）在囊泡膜周围组装成以前未描述的多面体形晶格。NMII 晶格包括双极微丝以及非典型的三脚结构。通过体内光漂白和药理学扰动，我们表明肌动球蛋白收缩性和肌动蛋白聚合共同推动下的囊泡膜克服能量障碍并完成胞吐作用。因此，我们的成像方法揭示了一种产生力的肌动球蛋白晶格，它调节活体动物外分泌器官中的分泌。
