12/23/2023 0 Comments Theine plateau wasp locationHowever, methods used for these studies prevented analysis of large numbers of sites, and suffered from possible loss of actin filaments during unroofing and extraction of the cells. On the other hand, studies on fixed mammalian cells raised the possibility that actin assembly may at least in some cases be initiated asymmetrically at clathrin coats 14, 15. In yeast cells, where turgor pressure is particularly high, super-resolution data suggest that actin assembles symmetrically around CME sites and indicate that actin regulators including Las17, which is yeast WASP, are present in a ring surrounding the base of the clathrin coat symmetrically 13. A detailed understanding of how actin forces are harnessed to aid vesicle formation and scission depends on understanding which CME sites assemble actin, where filament assembly occurs around the endocytic membrane, and when. Interestingly, actin does not assemble at all CME sites in mammalian cells, suggesting highly localized differences in requirement for actin assembly, the nature of which is obscure 6, 11, 12. Several studies have demonstrated that dependence of CME on actin assembly increases under elevated membrane tension 6, 7, 8, 9, 10. These forces are generated through the combined actions of proteins that directly bend the membrane and actin filament assembly 1, 2, 3, 4, 5 (Supplementary Fig. We propose that actin assembles preferentially at stalled CME sites where it pulls vesicles into the cell asymmetrically, much as a bottle opener pulls off a bottle cap.įormation of clathrin-coated vesicles requires forces to first bend the membrane into a sphere or tube, and to then break the thin neck that connects the vesicle to the plasma membrane. In addition, N-WASP and the Arp2/3 complex are recruited to one side of CME sites, where they are positioned to stimulate asymmetric actin assembly and force production. When endocytic dynamics of unperturbed CME sites are compared, sites with actin assembly show a distinct signature, a delay between completion of coat expansion and vesicle scission, indicating that actin assembly occurs preferentially at stalled CME sites. Here, branched actin network geometry at CME sites was analyzed using three different advanced imaging approaches. How actin networks are organized with respect to mammalian CME sites and how assembly forces are harnessed, are not fully understood. Interestingly, actin does not assemble at all CME sites in mammalian cells. Actin assembly facilitates vesicle formation in several trafficking pathways, including clathrin-mediated endocytosis (CME).
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