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Proc Natl Acad Sci U S A. 2019 Feb 26;116(9):3594-3603. doi: 10.1073/pnas.1821638116. Epub 2019 Feb 11.

Functional integrity of the contractile actin cortex is safeguarded by multiple Diaphanous-related formins.

Author information

1
Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany.
2
Institute of Complex Systems, ICS-7: Biomechanics, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany.
3
Division of Molecular Cell Biology, Zoological Institute, Technische Universität Braunschweig, 38106 Braunschweig, Germany.
4
Molecular Cell Biology Group, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany.
5
Ann Romney Center for Neurologic Diseases, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115.
6
Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom.
7
Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany; faix.Jan@mh-hannover.de.

Abstract

The contractile actin cortex is a thin layer of filamentous actin, myosin motors, and regulatory proteins beneath the plasma membrane crucial to cytokinesis, morphogenesis, and cell migration. However, the factors regulating actin assembly in this compartment are not well understood. Using the Dictyostelium model system, we show that the three Diaphanous-related formins (DRFs) ForA, ForE, and ForH are regulated by the RhoA-like GTPase RacE and synergize in the assembly of filaments in the actin cortex. Single or double formin-null mutants displayed only moderate defects in cortex function whereas the concurrent elimination of all three formins or of RacE caused massive defects in cortical rigidity and architecture as assessed by aspiration assays and electron microscopy. Consistently, the triple formin and RacE mutants encompassed large peripheral patches devoid of cortical F-actin and exhibited severe defects in cytokinesis and multicellular development. Unexpectedly, many forA - /E -/H - and racE - mutants protruded efficiently, formed multiple exaggerated fronts, and migrated with morphologies reminiscent of rapidly moving fish keratocytes. In 2D-confinement, however, these mutants failed to properly polarize and recruit myosin II to the cell rear essential for migration. Cells arrested in these conditions displayed dramatically amplified flow of cortical actin filaments, as revealed by total internal reflection fluorescence (TIRF) imaging and iterative particle image velocimetry (PIV). Consistently, individual and combined, CRISPR/Cas9-mediated disruption of genes encoding mDia1 and -3 formins in B16-F1 mouse melanoma cells revealed enhanced frequency of cells displaying multiple fronts, again accompanied by defects in cell polarization and migration. These results suggest evolutionarily conserved functions for formin-mediated actin assembly in actin cortex mechanics.

KEYWORDS:

RhoGTPase; actin cortex; cell migration; cytokinesis; formin

PMID:
30808751
PMCID:
PMC6397521
[Available on 2019-08-11]
DOI:
10.1073/pnas.1821638116
[Indexed for MEDLINE]

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