Analysis of turnover dynamics of the submembranous actin cortex |
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Authors: | Marco Fritzsche Alexandre Lewalle Tom Duke Karsten Kruse Guillaume Charras |
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Institution: | University of California, Davis;aLondon Centre for Nanotechnology, University College London, WC1H 0AH London, United Kingdom;bDepartment of Physics and Astronomy, University College London, WC1H 0AH London, United Kingdom;dDepartment of Cell and Developmental Biology, University College London, WC1H 0AH London, United Kingdom;cTheoretical Physics, Saarland University, 66123 Saarbrücken, Germany |
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Abstract: | The cell cortex is a thin network of actin, myosin motors, and associated proteins that underlies the plasma membrane in most eukaryotic cells. It enables cells to resist extracellular stresses, perform mechanical work, and change shape. Cortical structural and mechanical properties depend strongly on the relative turnover rates of its constituents, but quantitative data on these rates remain elusive. Using photobleaching experiments, we analyzed the dynamics of three classes of proteins within the cortex of living cells: a scaffold protein (actin), a cross-linker (α-actinin), and a motor (myosin). We found that two filament subpopulations with very different turnover rates composed the actin cortex: one with fast turnover dynamics and polymerization resulting from addition of monomers to free barbed ends, and one with slow turnover dynamics with polymerization resulting from formin-mediated filament growth. Our data suggest that filaments in the second subpopulation are on average longer than those in the first and that cofilin-mediated severing of formin-capped filaments contributes to replenishing the filament subpopulation with free barbed ends. Furthermore, α-actinin and myosin minifilaments turned over significantly faster than F-actin. Surprisingly, only one-fourth of α-actinin dimers were bound to two actin filaments. Taken together, our results provide a quantitative characterization of essential mechanisms underlying actin cortex homeostasis. |
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