Mechanistic insights into actin force generation during vesicle formation from cryo-electron tomography

• Published in: Developmental cell Vol. 57; no. 9; pp. 1132 - 1145.e5
• Main Authors: Serwas, Daniel, Akamatsu, Matthew, Moayed, Amir, Vegesna, Karthik, Vasan, Ritvik, Hill, Jennifer M., Schöneberg, Johannes, Davies, Karen M., Rangamani, Padmini, Drubin, David G.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 09-05-2022
• Subjects: actin; Actin Cytoskeleton - metabolism; Actins - metabolism; Clathrin - metabolism; clathrin-mediated endocytosis; cryo-electron tomography; cytoskeleton; Cytoskeleton - metabolism; Electron Microscope Tomography; Endocytosis; Humans; lipids; mathematical modeling; theory; trafficking; actin; lipids; cytoskeleton; mathematical modeling; cryo-electron tomography; trafficking; theory; clathrin-mediated endocytosis
• ISSN: 1534-5807; 1878-1551; 1878-1551
• DOI: 10.1016/j.devcel.2022.04.012

Actin assembly provides force for a multitude of cellular processes. Compared to actin-assembly-based force production during cell migration, relatively little is understood about how actin assembly generates pulling forces for vesicle formation. Here, cryo-electron tomography identified actin filament number, organization, and orientation during clathrin-mediated endocytosis in human SK-MEL-2 cells, showing that force generation is robust despite variance in network organization. Actin dynamics simulations incorporating a measured branch angle indicate that sufficient force to drive membrane internalization is generated through polymerization and that assembly is triggered from ∼4 founding “mother” filaments, consistent with tomography data. Hip1R actin filament anchoring points are present along the entire endocytic invagination, where simulations show that it is key to pulling force generation, and along the neck, where it targets filament growth and makes internalization more robust. Actin organization described here allowed direct translation of structure to mechanism with broad implications for other actin-driven processes.
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•Native-state description of force-producing actin networks during endocytosis•Branched actin filament assembly is triggered from multiple mother filaments•Actin force production is robust despite considerable network variability•Filament anchorage points are key to pulling force generation and efficiency
Actin filament polymerization generates forces essential for numerous cellular processes including vesicle formation, cell motility, and cytokinesis. Serwas et al. combined cryo-electron tomography of intact mammalian cells with mathematical modeling to gain mechanistic insights into how actin assembly forces pull on the plasma membrane to support endocytic vesicle formation.