title: Structural organization of the actin cytoskeleton at sites of clathrin-mediated endocytosis.
abstract: BACKGROUND
  The dynamic actin cytoskeleton plays an important role in clathrin-mediated endocytosis (CME). However, its exact functions remain uncertain as a result of a lack of high-resolution structural information regarding actin architecture at endocytic sites.
  
  
  RESULTS
  Using platinum replica electron microscopy in combination with electron tomography, we found that actin patches associated with clathrin-coated structures (CCSs) in cultured mouse cells consist of a densely branched actin network, in which actin filament barbed ends are oriented toward the CCS. The shape of the actin network varied from a small lateral patch at the periphery of shallow CCSs, to a collar-like arrangement around partly invaginated CCSs with actin filament barbed ends abutting the CCS neck, to a polarized comet tail in association with highly constricted or fully endocytosed CCSs.
  
  
  CONCLUSIONS
  Our data suggest that the primary role of the actin cytoskeleton in CME is to constrict and elongate the bud neck and drive the endocytosed vesicles from the plasma membrane. Moreover, in these processes, barbed ends directly push onto the load, as in a conventional propulsion mechanism. Based on our findings, we propose a model for initiation, evolution, and function of the dendritic actin network at CCSs.
authors: Department of Biology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors: Agnieszka
authors: A
authors: Collins
authors: Anthony
authors: A
authors: Warrington
authors: Kenneth A
authors: KA
authors: Taylor
authors: Tatyana
authors: T
authors: Svitkina
mesh_terms: D000199:Actins / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D002478:Cells, Cultured; D002966:Clathrin / Q000378:metabolism* / Q000648:ultrastructure; D022163:Clathrin-Coated Vesicles / Q000378:metabolism* / Q000648:ultrastructure; D003599:Cytoskeleton / Q000378:metabolism* / Q000648:ultrastructure; D004705:Endocytosis; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D014057:Tomography, X-Ray Computed; D000097573:Red Fluorescent Protein
chemical_list: D000199:Actins; D002966:Clathrin; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D000097573:Red Fluorescent Protein