Cited by 200Microtubule and mitosis dynamicsAlzheimer's disease research and treatmentsCellular Mechanics and Interactions

Tau co-organizes dynamic microtubule and actin networks

Open access
Elie, Auréliane, Prezel, Elea, Guérin, Christophe, Denarier, Eric, Ramirez-Rios, Sacnicte, Serre, Laurence, Andrieux, Annie, Fourest-Lieuvin, Anne +2 more·2015·Scientific Reports

Abstract

The crosstalk between microtubules and actin is essential for cellular functions. However, mechanisms underlying the microtubule-actin organization by cross-linkers remain largely unexplored. Here, we report that tau, a neuronal microtubule-associated protein, binds to microtubules and actin simultaneously, promoting in vitro co-organization and coupled growth of both networks. By developing an original assay to visualize concomitant microtubule and actin assembly, we show that tau can induce guided polymerization of actin filaments along microtubule tracks and growth of single microtubules along actin filament bundles. Importantly, tau mediates microtubule-actin co-alignment without changing polymer growth properties. Mutagenesis studies further reveal that at least two of the four tau repeated motifs, primarily identified as tubulin-binding sites, are required to connect microtubules and actin. Tau thus represents a molecular linker between microtubule and actin networks, enabling a coordination of the two cytoskeletons that might be essential in various neuronal contexts.

AI snapshot

Written from the paper’s full text.

TL;DR

Tau binds microtubules and F-actin simultaneously and acts as a molecular linker that co-organizes dynamic microtubule and actin networks in vitro. At least two of tau’s four repeat motifs are required for this cross-linking, while coupled growth does not alter the intrinsic elongation rates of either polymer.

Key findings

  • Recombinant 4R-tau bound F-actin with an apparent Kd of 241 ± 43 nM, close to its Kd for microtubules (280 ± 52 nM), and bundled F-actin without significantly changing actin assembly or elongation speed (1.78 ± 0.28 vs. 1.76 ± 0.41 μm/min for control vs. tau).
  • In a live TIRF co-assembly assay, tau induced guided polymerization of actin along microtubule tracks and growth of microtubules along actin bundles; up to 60% of the microtubule network co-aligned with F-actin, versus no more than 14% with fascin.
  • Co-alignment did not change growth rates: microtubules grew at 1.28 ± 0.17 μm/min alone (n = 52) and 1.31 ± 0.16 μm/min when co-aligned with actin (n = 41); F-actin along microtubules grew at 1.21 ± 0.16 μm/min (n = 80) versus 1.29 ± 0.29 μm/min for isolated actin (n = 35).
  • Tau mutants with 2, 3, or 4 repeats gave about 50% microtubule–actin co-alignment, whereas 1R- and 0R-tau almost abolished cross-linking, indicating that at least two repeat motifs are needed to bridge the polymers.

Methods

  • In vitro reconstituted cell-free assays using purified recombinant human tau isoforms and mutants, bovine brain tubulin, rabbit skeletal muscle actin, fascin, and profilin.
  • Binding and bundling were measured by co-sedimentation, light scattering, low-speed sedimentation, and fluorescence microscopy; dynamic co-organization was visualized by dual-color TIRF microscopy with simultaneous tubulin and actin polymerization.
  • Image analysis used ImageJ and custom macros/kymographs to quantify microtubule–actin overlap, elongation rates, and F-actin curvature; statistics were performed in Prism 6.

Limitations

  • The paper states that whether and how phosphorylation sites in or near tau’s repeats modulate F-actin affinity and microtubule/actin cross-linking “remain to be elucidated.”
  • The study is entirely in vitro using reconstituted cell-free systems; no cellular or in vivo validation of the proposed linker function is presented.
  • The text makes evident that tubulin and tau concentrations/ratios were adjusted for different tau constructs to synchronize polymerization and avoid excessive microtubule nucleation, so the reconstituted conditions may not reflect physiological concentrations.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1038/srep09964

Cites

49 of 49 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

3 of 13 cited sources checked · 2 supported · 0 flagged · accuracy not yet measured

  • Findingown data

    The percentage of the microtubule surface associated with actin filaments in the presence of 1R- and 0R-tau strongly decreased to values comparable to those obtained with fascin.

    “In these conditions, the percentage of the microtubule surface associated with actin filaments strongly decreased to values comparable to those obtained with fascin (Fig. 3b).”
    Quote in the paperSubstantial claim
  • Findingown data

    Tau promotes the appearance of bundled F-actin in a concentration-dependent manner.

    “tau influenced actin organization by promoting the apparition of bundled F-actin in a concentration dependent manner, as revealed by light scattering (Fig. 1d) and low-speed sedimentation assays (Fig. 1e, see also Supplementary Fig. S1f).”
    Quote in the paperSubstantial claim
  • Findingown data

    Tau mediates microtubule-actin co-alignment.

    “tau mediates microtubule-actin co-alignment without changing polymer growth properties”
    • Also stated in: § Tau coordinates dynamic microtubules and actin filaments · plain
      “tau promotes the co-alignment of microtubules and actin filaments”
    • Also stated in: § Tau simultaneously binds to microtubules and actin filaments · plain
      “hybrid bundles of co-aligned microtubules and actin filaments appeared in the presence of tau”
    Quote in the paperSubstantial claim
  • Findingown data

    ΔN-tau cross-links both polymers in growing conditions similarly to full-length tau.

    “and cross-links both polymers in growing conditions similarly to the full-length tau (Fig. 3b, Supplementary Movie S5).”
    Quote in the paperSubstantial claim
  • Findingown data

    Tau does not significantly affect actin assembly properties.

    “We found that tau did not significantly affect actin assembly properties by using pyrene-actin polymerization and F-actin sedimentation (Supplementary Fig. S1d and e).”
    Quote in the paperNot a substantial claim
  • Classified as probably not a substantial claim. 3
  • May combine two claims. 8
  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Several in vitro studies have reported the association with actin of full-length tau and tau sub-regions containing the microtubule-binding sites, although this direct interaction has been controverted.

    “Accordingly, several in vitro studies have reported the association with actin of the full-length tau1718 and tau sub-regions containing the microtubule-binding sites1920, although this direct interaction has been controverted21.”
    Quote in the paperNot a substantial claim1 of 3 sources checked
    • cites [1718]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [1920]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [21] Roger, B., Al-Bassam, J., Dehmelt, L., Milligan, R & Halpain, S. MAP2c, but not tau, binds and bundles F-actin via its microtubule binding domain. Curr. Biol. 14, 363–71 (2004). source
  • May combine two claims.

    Premisecitation

    In vivo, tau co-localizes with actin in differentiating PC12 cells and in the post-synaptic compartments of mature neurons.

    “In vivo, tau co-localizes with actin in differentiating PC12 cells22 and in the post-synaptic compartments of mature neurons23.”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites [22] Yu, J.-Z. & Rasenick, M. M. Tau associates with actin in differentiating PC12 cells. FASEB J. 20, 1452–61 (2006). source
    • cites [23] Frandemiche, M. L. et al. Activity-dependent tau protein translocation to excitatory synapse is disrupted by exposure to amyloid-beta oligomers. J. Neurosci. 34, 6084–97 (2014). source

      Citation 23 attaches to the postsynaptic-neuron part of the sentence, not the PC12-cell part. Figure 4 shows tau and F-actin colocalizing in dendritic spines of cultured cortical neurons after synaptic activation, while Figure 1 reports only limited colocalization under resting conditions. These cell-culture observations do not establish the claim's in vivo setting. (LLM, conf=0.86)

      Experimental — accuracy not yet measured
  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    The interaction of tau with microtubules in neurons is well documented and more recent studies have proposed that tau also binds to actin.

    “The interaction of tau with microtubules in neurons is well documented and more recent studies have proposed that tau also binds to actin34.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [34] Morris, M., Maeda, S., Vossel, K. & Mucke, L. The many faces of tau. Neuron 70, 410–26 (2011). source
  • May combine two claims.

    Findingown data

    Fascin induces cross-linking of actin filaments but neither affects microtubule organization nor promotes microtubule/actin interactions.

    “Addition of fascin, a specific actin-bundler29, induced cross-linking of actin filaments, but neither affected microtubule organization nor promoted microtubule/actin interactions (Fig. 2a, Supplementary Movie S2).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [29] Edwards, R. A. & Bryan, J. Fascins, a family of actin bundling proteins. Cell. Motil. Cytoskeleton 32, 1–9 (1995). source
  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    Tau is a neuronal microtubule-associated protein that promotes microtubule polymerization and bundling and is responsible for microtubule stabilization in axons.

    “Tau is a neuronal microtubule-associated protein that promotes microtubule polymerization and bundling7891011, and is responsible for microtubule stabilization in axons1213.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites 7891011

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [1213]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationown data

    Tau is a molecular linker between microtubule and actin networks, enabling in vitro co-organization and coupled growth of the two networks.

    “Tau thus represents a molecular linker between microtubule and actin networks, enabling a coordination of the two cytoskeletons that might be essential in various neuronal contexts.”
    • Also stated in: § Discussion · boosted
      “Our work demonstrates that tau acts as a molecular linker between microtubules and actin filaments, enabling the in vitro co-organization and coupled growth of the two networks (Fig. 4).”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Premiseown data

    Overall, these data support a role for tau as a regulator of microtubules and actin, and suggest that tau is a potential linker between the two cytoskeletons.

    “Overall, these data support a role for tau as a regulator of microtubules and actin, and suggest that tau is a potential linker between the two cytoskeletons as hypothesized some years ago1.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [1] Rodriguez, O. C. et al. Conserved microtubule – actin interactions in cell movement and morphogenesis. Nat. Cell. Biol. 5, 599–609 (2003). source
  • May combine two claims.

    Interpretationown data

    A minimum of two tau repeats are required to bridge polymers, with one repeat bound to microtubules and the other one to actin filaments.

    “Our results suggest a mechanism whereby a minimum of two tau repeats are required to bridge polymers, with one repeat bound to microtubules and the other one to actin filaments (Fig. 4).”
    Quote in the paperSubstantial claim
8 of 8

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Actin fluorophore differs between methods descriptions

    Minor

    The protein-purification section says actin was labelled with Alexa-568 or pyrene, but the actin-polymerization assay specifies Alexa-468-labelled actin. The described fluorophore is inconsistent.

1 of 1

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Authors
Elie, A., Prezel, E., Guérin, C., Denarier, E., Ramirez-Rios, S., Serre, L., Andrieux, A., Fourest-Lieuvin, A., Blanchoin, L., & Arnal, I.
Affiliations
  • Inserm (FR)
  • Centre National de la Recherche Scientifique (FR)
Corresponding author
Arnal, Isabelle
Venue
Scientific Reports
Published
2015-05-05
Volume
5
Issue
1
Pages
9964-9964
ISSN
2045-2322 (ISSN-L)
OpenAlex
W1803223003
Cited by
200
References
49
Citations by year
2026: 14 · 2025: 16 · 2024: 17 · 2023: 11 · 2022: 18 · 2021: 27 · 2020: 26 · 2019: 27 · 2018: 16 · 2017: 15 · 2016: 12
FWCI
7.62
Type
journal article
Language
en
Open access
Locations
  • Scientific Reports (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • HAL (submittedVersion, other-oa)
Funders
  • Agence Nationale de la Recherche (MALZ 2011)
  • Institut National de la Santé et de la Recherche Médicale
  • Fondation pour la Recherche Médicale
  • Ministère de l'Enseignement Supérieur et de la Recherche
  • Centre National de la Recherche Scientifique
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Microtubule and mitosis dynamics
  • Health Sciences › Medicine › Physiology › Alzheimer's disease research and treatments
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Cellular Mechanics and Interactions
Keywords
tau protein, tubulin binding site, neuronal cytoskeleton
MeSH terms
Actins, Binding Sites, Cross-Linking Reagents, Actin Cytoskeleton, Microtubules, Motion, Protein Binding, Protein Conformation, tau Proteins

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