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Competition for actin between two distinct F-actin networks defines a bistable switch for cell polarization

Nature Cell Biology volume 17, pages 14351445 (2015) | Download Citation


Symmetry-breaking polarization enables functional plasticity of cells and tissues and is yet not well understood. Here we show that epithelial cells, hard-wired to maintain a static morphology and to preserve tissue organization, can spontaneously switch to a migratory polarized phenotype after relaxation of the actomyosin cytoskeleton. We find that myosin II engages actin in the formation of cortical actomyosin bundles and thus makes it unavailable for deployment in the process of dendritic growth normally driving cell motility. Under low-contractility regimes, epithelial cells polarize in a front–back manner owing to the emergence of actin retrograde flows powered by dendritic polymerization of actin. Coupled to cell movement, the flows transport myosin II from the front to the back of the cell, where the motor locally ‘locks’ actin in contractile bundles. This polarization mechanism could be employed by embryonic and cancer epithelial cells in microenvironments where high-contractility-driven cell motion is inefficient.

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The authors wish to acknowledge E. Bonder (Rutgers University, Newark, New Jersey, USA), T. Omelchenko (Sloan-Kettering Institute, New York, New York, USA) and J. Vasiliev (National Cancer Research Center, Moscow, Russia) for providing epithelial cell lines. We are grateful to I. Ethell (University of California Riverside, California, USA), S. Narumiya (Kyoto University, Japan), K. Kaibuchi (Nagoya University, Japan) and R. Horwitz (University of Virginia, Charlottesville, Virginia, USA) for sharing genetic constructs. We also thank M. Piel (Institut Curie, Paris, France) and D. Bonazzi (Institut Pasteur, Paris, France) for comments on the manuscript. This research was supported by a postdoctoral fellowship from the Leukemia & Lymphoma Society (grant no. 5388-13) to A.J.L., and the National Institutes of Health grants R01 GM071868 to G.D. and GM068952 to A.M. All light microscopy experiments described in the present work were performed at the Nikon Imaging Center of Harvard Medical School, Boston, Massachusetts.

Author information

Author notes

    • Alexis J. Lomakin
    •  & Kun-Chun Lee

    These authors contributed equally to this work.

    • Alexis J. Lomakin
    • , Kun-Chun Lee
    • , Sangyoon J. Han
    • , Alex Mogilner
    •  & Gaudenz Danuser

    Present addresses: Institut Curie, CNRS UMR 144, 26 rue d’Ulm, 75005 Paris, France (A.J.L.); Lyda Hill Department of Bioinformatics, UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9039, USA (S.J.H. and G.D.); Courant Institute and Department of Biology, New York University, 251 Mercer Street, New York City, New York 10012, USA (K.-C.L. and A.M.).


  1. Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue Boston, Massachusetts 02115, USA

    • Alexis J. Lomakin
    • , Sangyoon J. Han
    • , Duyen A. Bui
    •  & Gaudenz Danuser
  2. Department of Microbiology & Immunobiology, Harvard Medical School, 77 Avenue Louis Pasteur Boston, Massachusetts 02115, USA

    • Alexis J. Lomakin
  3. Department of Neurobiology, Physiology and Behavior, University of California, Davis, 1 Shields Avenue Davis, California 95616, USA

    • Kun-Chun Lee
    •  & Alex Mogilner
  4. Department of Mathematics, University of California, Davis, 1 Shields Avenue Davis, California 95616, USA

    • Kun-Chun Lee
    •  & Alex Mogilner
  5. National High Magnetic Field Laboratory and Department of Biological Science, Florida State University, 1800 E. Paul Dirac Drive Tallahassee, Florida 32310, USA

    • Michael Davidson


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A.J.L., K.-C.L., A.M. and G.D. designed the project. A.J.L. and K.-C.L. performed all key experiments and analysed the data. D.A.B. performed 3D experiments. S.J.H. developed the software for membrane protrusivity and myosin flow analyses. M.D. generated fluorescence reporters for live-cell imaging experiments. A.J.L., A.M. and G.D. wrote the manuscript. All authors discussed the results and implications, and commented on the manuscript at all stages.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Alex Mogilner or Gaudenz Danuser.

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  1. 1.

    A single IAR-2 epithelial cell 24 h after plating on a glass surface.

    Differential interference contrast (DIC) videomicroscopy. Time, hours:minutes. Scale bar, 10 μm.

  2. 2.

    Spontaneous symmetry breaking upon acute inhibition of myosin-II.

    DIC movie is shown on the left; tracking of the cell boundary based on the time sequence of DIC images is shown on the right. IAR-2 cells were pretreated with 25 μM blebbistatin for 5 min and subsequently imaged in blebbistatin-containing medium. Time, hours:minutes. Scale bar, 10 μm.

  3. 3.

    A myosin-II-inhibited epithelial cell IAR-2 3 h after addition of the myosin-II drug blebbistatin.

    DIC videomicroscopy. Time, hours:minutes. Scale bar, 10 μm.

  4. 4.

    The recoil response of a marginal actin bundle upon localized cortical laser ablation (COLA).

    A peripheral region of an IAR-2 cell expressing mEmerald-LifeAct and filmed by spinning disk confocal microscopy. The site of ablation is marked by a square; white arrows show the free ends of the ring upon ablation. Time, minutes:seconds. Scale bar, 3 μm.

  5. 5.

    Mass-balance between branched and bundled actin in cell shape and polarity determination (1).

    At myosin strengths lower than in control situations, the bundled actomyosin and branched actin networks spatially segregate around the cell boundary while the cell polarizes, and stable cell motility ensues. The dynamic cell boundary is shown in the coordinate system moving with the geometric center of the cell; hence, the cell appears stationary, while in fact it is moving steadily to the right, which is shown below and also by the grid moving with the lab frame. Color scale, red—protrusion; blue—retraction.

  6. 6.

    Mass-balance between branched and bundled actin in cell shape and polarity determination (2).

    In a control situation, the bundled actomyosin network effectively inhibits the branched actin networks all around the cell periphery. The cell remains symmetric and non-motile. Initial perturbations relax and do not destabilize the symmetric cell state. An intense perturbation is introduced closer to the end of the movie that wipes out part of the actomyosin bundle. The cell becomes motile temporarily and quickly reverts into the stationary symmetric circular state. Color scale, red—protrusion; blue—retraction.

  7. 7.

    Mass-balance between branched and bundled actin in cell shape and polarity determination (3).

    At very low myosin strength, the branched actin network effectively inhibits the bundled actomyosin all around the periphery causing incoherent symmetry breaking of the cell but not coherent motility. Color scale, red—protrusion; blue—retraction.

  8. 8.

    Acute inhibition of myosin-II in stationary epithelial cells stimulates retrograde flow of myosin-II concomitant with the depletion of cortical myosin-II from the cell edge.

    IAR-2 cells expressing mCherry-MRLC were pretreated with 25 μM blebbistatin for 5 min and subsequently imaged by spinning disk confocal microscopy in blebbistatin-containing medium. Time, minutes:seconds. Scale bar, 1 μm.

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