The functional architecture of axonal actin


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Abstract

The cytoskeleton builds and supports the complex architecture of neurons. It orchestrates the specification, growth, and compartmentation of the axon: axon initial segment, axonal shaft, presynapses. The cytoskeleton must then maintain this intricate architecture for the whole life of its host, but also drive its adaptation to new network demands and changing physiological conditions. Microtubules are readily visible inside axon shafts by electron microscopy, whereas axonal actin study has long been focused on dynamic structures of the axon such as growth cones. Super-resolution microscopy and live-cell imaging have recently revealed new actin-based structures in mature axons: rings, hotspots and trails. This has caused renewed interest for axonal actin, with efforts underway to understand the precise organization and cellular functions of these assemblies. Actin is also present in presynapses, where its arrangement is still poorly defined, and its functions vigorously debated. Here we review the organization of axonal actin, focusing on recent advances and current questions in this rejuvenated field.HighlightsThe cytoskeleton supports axonal growth, maintenance and adaptation.Actin has classically been studied in dynamic parts of the developing axon.New axonal actin structures: rings, hotspots, trails… have recently been discovered.The role of actin in the shaft of mature axon is now reevaluated in the light of these discoveries.Actin organization within the presynapse is still poorly known, and its functions debated.

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