title: Liquid behavior of cross-linked actin bundles.
abstract: The actin cytoskeleton is a critical regulator of cytoplasmic architecture and mechanics, essential in a myriad of physiological processes. Here we demonstrate a liquid phase of actin filaments in the presence of the physiological cross-linker, filamin. Filamin condenses short actin filaments into spindle-shaped droplets, or tactoids, with shape dynamics consistent with a continuum model of anisotropic liquids. We find that cross-linker density controls the droplet shape and deformation timescales, consistent with a variable interfacial tension and viscosity. Near the liquid-solid transition, cross-linked actin bundles show behaviors reminiscent of fluid threads, including capillary instabilities and contraction. These data reveal a liquid droplet phase of actin, demixed from the surrounding solution and dominated by interfacial tension. These results suggest a mechanism to control organization, morphology, and dynamics of the actin cytoskeleton.
authors.affiliation: James Franck Institute, University of Chicago, Chicago, IL 60637.
authors.forename: Kimberly L
authors.initials: KL
authors.lastname: Weirich
authors.affiliation: James Franck Institute, University of Chicago, Chicago, IL 60637.|Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom.|Institute for the Physics of Living Systems, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Shiladitya
authors.initials: S
authors.lastname: Banerjee
authors.affiliation: James Franck Institute, University of Chicago, Chicago, IL 60637.
authors.forename: Kinjal
authors.initials: K
authors.lastname: Dasbiswas
authors.affiliation: James Franck Institute, University of Chicago, Chicago, IL 60637.|Department of Physics, University of Chicago, Chicago, IL 60637.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Witten
authors.affiliation: James Franck Institute, University of Chicago, Chicago, IL 60637.|Department of Chemistry, University of Chicago, Chicago, IL 60637.
authors.forename: Suriyanarayanan
authors.initials: S
authors.lastname: Vaikuntanathan
authors.affiliation: James Franck Institute, University of Chicago, Chicago, IL 60637; gardel@uchicago.edu.|Department of Physics, University of Chicago, Chicago, IL 60637.|Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637.
authors.forename: Margaret L
authors.initials: ML
authors.lastname: Gardel
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000648:ultrastructure; D000199:Actins / Q000737:chemistry*; D003432:Cross-Linking Reagents / Q000737:chemistry*; D004548:Elasticity; D064448:Filamins / Q000737:chemistry*; D007700:Kinetics; D008954:Models, Biological; D012996:Solutions; D013816:Thermodynamics; D014783:Viscosity
chemical_list: D000199:Actins; D003432:Cross-Linking Reagents; D064448:Filamins; D012996:Solutions
keywords: actin; cytoskeleton; liquid crystal; phase separation