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J Cell Biol. 2015 Aug 3;210(3):401-17. doi: 10.1083/jcb.201506110. Epub 2015 Jul 27.

A dynamic formin-dependent deep F-actin network in axons.

Author information

1
Department of Pathology, University of California, San Diego, La Jolla, CA 92093.
2
Department of Pathology, University of California, San Diego, La Jolla, CA 92093 Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093.
3
Aix Marseille Université, Centre National de la Recherche Scientifique, Centre de Recherche en Neurobiologie et Neurophysiologie de Marseille (CRN2M) UMR7286, 13344 Marseille, France.
4
Department of Pathology, University of California, San Diego, La Jolla, CA 92093 Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093 s1roy@ucsd.edu.

Abstract

Although actin at neuronal growth cones is well-studied, much less is known about actin organization and dynamics along axon shafts and presynaptic boutons. Using probes that selectively label filamentous-actin (F-actin), we found focal "actin hotspots" along axons-spaced ∼3-4 µm apart-where actin undergoes continuous assembly/disassembly. These foci are a nidus for vigorous actin polymerization, generating long filaments spurting bidirectionally along axons-a phenomenon we call "actin trails." Super-resolution microscopy reveals intra-axonal deep actin filaments in addition to the subplasmalemmal "actin rings" described recently. F-actin hotspots colocalize with stationary axonal endosomes, and blocking vesicle transport diminishes the actin trails, suggesting mechanistic links between vesicles and F-actin kinetics. Actin trails are formin-but not Arp2/3-dependent and help enrich actin at presynaptic boutons. Finally, formin inhibition dramatically disrupts synaptic recycling. Collectively, available data suggest a two-tier F-actin organization in axons, with stable "actin rings" providing mechanical support to the plasma membrane and dynamic "actin trails" generating a flexible cytoskeletal network with putative physiological roles.

PMID:
26216902
PMCID:
PMC4523607
DOI:
10.1083/jcb.201506110
[Indexed for MEDLINE]
Free PMC Article

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