Localized Myosin II Activity Regulates Assembly and Plasticity of the Axon Initial Segment

Berger, Stephen; Leo‐Macias, Alejandra; Yuen, Stephanie K.; Khatri, Latika; Pfennig, Sylvia; Zhang, Yanqing; Agullo‐Pascual, Esperanza; Caillol, Ghislaine; Zhu, Min–Sheng; Rothenberg, Eli; Melendez‐Vasquez, Carmen V.; Delmar, Mario; Leterrier, Christophe; Salzer, James L.

doi:10.1016/j.neuron.2017.12.039

Cited by 84 publications

(134 citation statements)

References 81 publications

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“…pMLC was found to have a punctate distribution along the length of the axons ( Figure S10). A recent study had also reported pMLC distribution along the entire length of 3 DIV rat hippocampal axons (38). The latter study and our results also indicate that pMLC is not commonly colocalised with the F-actin patches.…”

Section: Discussionsupporting

confidence: 81%

Cytoskeletal mechanisms of axonal contractility

Mutalik¹,

Joseph²,

Pullarkat³

et al. 2017

Preprint

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Mechanotransduction is likely to be an important mechanism of signalling in thin, elongated cells like neurons. Maintenance of pre-stress or rest tension may facilitate mechanotransduction in these cells. In recent years, functional roles for mechanical tension in neuronal development and physiology are beginning to emerge but the cellular mechanisms regulating neurite tension remain poorly understood. Active contraction of neurites is a potential mechanism of tension regulation. In this study, we have explored cytoskeletal mechanisms mediating active contractility of neuronal axons. We have developed a simple assay where we evaluate contraction of curved axons upon trypsin-mediated detachment. We show that curved axons undergo contraction and straighten upon de-adhesion. Axonal straightening was found to be actively driven by actomyosin contractility, while microtubules may subserve a secondary role. We find that while axons show a monotonous decrease in length upon contraction, subcellularly, the cytoskeleton shows a heterogeneous contractile response. Further, using an assay for spontaneous development of tension without trypsin-induced de-adhesion, we show that axons are intrinsically contractile. These experiments, using novel experimental approaches, implicate the axonal cytoskeleton in tension homeostasis. Our data suggest that while globally the axon behaves as a mechanical continuum, locally the cytoskeleton is remodelled heterogeneously.

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Section: Discussionsupporting

confidence: 81%

Cytoskeletal mechanisms of axonal contractility

Mutalik¹,

Joseph²,

Pullarkat³

et al. 2017

Preprint

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“…We next took advantage of PREM of unroofed neurons to determine the ultrastructural localization of MPS components known to specifically localize along the AIS (Leterrier, 2018). The phosphorylated myosin light-chain (pMLC), an activator of myosin II, was recently reported to associate with the MPS along the initial segment (Berger et al, 2018), together with its partner tropomyosin (Abouelezz et al, 2019b). We found concentrated pMLC at the AIS, with areas showing a ~200 nm periodic pattern on SMLM images ( Fig.…”

Section: Ultrastructural Organization Of Proximal Mps Componentsmentioning

confidence: 95%

“…Rabbit polyclonal anti 480-kDa ankG (residues 2735-2935 of rat 480-kDa ankG, 1:300 for IF, 1:100 for IG) was a gift from Vann Bennett (Duke University, Durham, NC) (Jenkins et al, 2015). Rabbit anti phospho-Myosin Light Chain 2 Thr18/Ser19 (pMLC) was from Cell Signaling Technologies (#3674, 1:50 for IF, 1:20 for IG) (Berger et al, 2018).…”

Section: Antibodies and Reagentsmentioning

confidence: 99%

Ultrastructure of the axonal periodic scaffold reveals a braid-like organization of actin rings

Vassilopoulos

Gibaud

Jimenez

et al. 2019

Preprint

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Recent super-resolution microscopy studies have unveiled a periodic scaffold of actin rings regularly spaced by spectrins under the plasma membrane of axons. However, ultrastructural details are unknown, limiting a molecular and mechanistic understanding of these enigmatic structures. Here, we combine platinum-replica electron and optical super-resolution microscopy to investigate the cortical cytoskeleton of axons at the ultrastructural level. Immunogold labeling and correlative super-resolution/ electron microscopy allow us to unambiguously resolve actin rings as braids made of two long, intertwined actin filaments connected by a dense mesh of aligned spectrins. This molecular arrangement contrasts with the currently assumed model of actin rings made of short, capped actin filaments. Along the proximal axon, we resolved the presence of phospho-myosin light chain and the scaffold connection with microtubules via ankyrin G. We propose that braided rings explain the observed stability of the actin-spectrin scaffold and ultimately participate in preserving the axon integrity.

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“…Tpm3.1 recruits and activates myosin IIB (Bryce et al, 2003;Gateva et al, 2017), and recent work has revealed an important role for myosin II in AIS structure (Berger et al, 2018;Evans et al, 2017;Wang et al, 2018).…”

Section: Tpm31 Inhibition Leads To the Gradual Collapse Of The Ais Amentioning

confidence: 99%

“…While actin patches are not exclusive to the AIS, AIS actin patches are more stable than patches along the distal axon; the washing away of diffuse molecules by cell permeabilization led to the loss of actin patches in the distal axon, but not in the AIS (Watanabe et al, 2012). In addition, recent work showed that the actin-based non-muscle myosin II is involved in AIS structure and plasticity (Berger et al, 2018;Evans et al, 2017) and associates with axonal F-actin (Wang et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Tropomyosin Tpm3.1 is required to maintain the structure and function of the axon initial segment

Abouelezz

Stefen

Segerstråle

et al. 2019

Preprint

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ABSTRACTThe axon initial segment (AIS) is the site of action potential initiation and serves as a vesicular filter and diffusion barrier that help maintain neuronal polarity. Recent studies have revealed details about a specialized structural complex in the AIS. While an intact actin cytoskeleton is required for AIS formation, pharmacological disruption of actin polymerization compromises the AIS vesicle filter but does not affect overall AIS structure. In this study, we found that the tropomyosin isoform Tpm3.1 decorates a population of relatively stable actin filaments in the AIS. Inhibiting Tpm3.1 in cultured hippocampal neurons led to the loss of AIS structure, the AIS vesicle filter, the clustering of sodium ion channels, and reduced firing frequency. We propose that Tpm3.1-decorated actin filaments form a stable actin filament network under the AIS membrane which provides a scaffold for membrane organization and AIS proteins.

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Localized Myosin II Activity Regulates Assembly and Plasticity of the Axon Initial Segment

Cited by 84 publications

References 81 publications

Cytoskeletal mechanisms of axonal contractility

Cytoskeletal mechanisms of axonal contractility

Ultrastructure of the axonal periodic scaffold reveals a braid-like organization of actin rings

Tropomyosin Tpm3.1 is required to maintain the structure and function of the axon initial segment

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