title: Networks of polarized actin filaments in the axon initial segment provide a mechanism for sorting axonal and dendritic proteins.
abstract: Trafficking of proteins specifically to the axonal or somatodendritic membrane allows neurons to establish and maintain polarized compartments with distinct morphology and function. Diverse evidence suggests that an actin-dependent vesicle filter within the axon initial segment (AIS) plays a critical role in polarized trafficking; however, no distinctive actin-based structures capable of comprising such a filter have been found within the AIS. Here, using correlative light and scanning electron microscopy, we visualized networks of actin filaments several microns wide within the AIS of cortical neurons in culture. Individual filaments within these patches are predominantly oriented with their plus ends facing toward the cell body, consistent with models of filter selectivity. Vesicles carrying dendritic proteins are much more likely to stop in regions occupied by the actin patches than in other regions, indicating that the patches likely prevent movement of dendritic proteins to the axon and thereby act as a vesicle filter.
authors.affiliation: Department of Biology, Program in Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Kaori
authors.initials: K
authors.lastname: Watanabe
authors.forename: Sarmad
authors.initials: S
authors.lastname: Al-Bassam
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Miyazaki
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Wandless
authors.forename: Paul
authors.initials: P
authors.lastname: Webster
authors.forename: Don B
authors.initials: DB
authors.lastname: Arnold
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism* / Q000648:ultrastructure; D000199:Actins / Q000378:metabolism*; D000818:Animals; D001369:Axons / Q000378:metabolism* / Q000648:ultrastructure; D002478:Cells, Cultured; D003712:Dendrites / Q000378:metabolism* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D051381:Rats
chemical_list: D000199:Actins; D009419:Nerve Tissue Proteins