Abstract
By binding to actin filaments, non-muscle myosin II (NMII) generates actomyosin networks that hold unique contractile properties. Their dynamic nature is essential for neuronal biology including the establishment of polarity, growth cone formation and motility, axon growth during development (and axon regeneration in the adult), radial and longitudinal axonal tension, and synapse formation and function. In this review, we discuss the current knowledge on the spatial distribution and function of the actomyosin cytoskeleton in different axonal compartments. We highlight some of the apparent contradictions and open questions in the field, including the role of NMII in the regulation of axon growth and regeneration, the possibility that NMII structural arrangement along the axon shaft may control both radial and longitudinal contractility, and the mechanism and functional purpose underlying NMII enrichment in the axon initial segment. With the advances in live cell imaging and super resolution microscopy, it is expected that in the near future the spatial distribution of NMII in the axon, and the mechanisms by which it participates in axonal biology will be further untangled.
Highlights
Myosins are one of the largest and most divergent protein families comprising over 35 classes
Our knowledge on Non-muscle myosin II (NMII) positioning along the axon will certainly evolve in a manner that will allow us to understand its participation in axonal radial contractility and longitudinal tension, and comprehend how NMII activity does not interfere with the length of the extended membrane periodic skeleton (MPS) spectrin tetramers
The NMII structure, regulation and function in diverse cell types have received intense attention, there are still several open questions related to the organization and role of actomyosin networks in neurons
Summary
Myosins are one of the largest and most divergent protein families comprising over 35 classes (reviewed in [1,2]). In reports from the early 1970s, in addition to striated and smooth muscle cells, myosins were shown to be present in several other cell types, including platelets, granulocytes, fibroblasts, and neurons (reviewed in [3]). These myosins were designated as vertebrate cytoplasmic myosins and nowadays are commonly referred to as non-muscle myosins (NM). We will explore the involvement of NMII in axonal biology, from neuronal polarization to growth cone motility and neurite outgrowth, to its spatial arrangement and function, both in the axon initial segment (AIS) and in the axon shaft
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