Self-straining of actively crosslinked microtubule networks

• Published in: Nature physics 2019-12, Vol.15 (12), p.1295-1300
• Main Authors: Fürthauer, Sebastian, Lemma, Bezia, Foster, Peter J., Ems-McClung, Stephanie C., Yu, Che-Hang, Walczak, Claire E., Dogic, Zvonimir, Needleman, Daniel J., Shelley, Michael J.
• Format: Article
• Language: English
• Subjects: 639/301/1034; 639/301/1034/1036; 639/301/923; 639/766/747; Atomic; Behavior; Biology; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Coupling (molecular); Crosslinking; Experiments; Gels; Granulation; Mathematical and Computational Physics; Microscopy; Molecular; Molecular motors; Networks; Optical and Plasma Physics; Photobleaching; Physics; Physics and Astronomy; Polarity; Spindles; Strain rate; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-019-0642-1

Cytoskeletal networks are foundational examples of active matter and central to self-organized structures in the cell. In vivo, these networks are active and densely crosslinked. Relating their large-scale dynamics to the properties of their constituents remains an unsolved problem. Here, we study an in vitro active gel made from aligned microtubules and XCTK2 kinesin motors. Using photobleaching, we demonstrate that the gel’s aligned microtubules, driven by motors, continually slide past each other at a speed independent of the local microtubule polarity and motor concentration. This phenomenon is also observed, and remains unexplained, in spindles. We derive a general framework for coarse graining microtubule gels crosslinked by molecular motors from microscopic considerations. Using microtubule–microtubule coupling through a force–velocity relationship for kinesin, this theory naturally explains the experimental results: motors generate an active strain rate in regions of changing polarity, which allows microtubules of opposite polarities to slide past each other without stressing the material. In a model system crosslinked by motors, cytoskeletal polymers slide past each other at speeds independent of their polarity. This behaviour is best described within an active-gel framework that deviates from the dilute limit set by existing theory.