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.
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C.E.W. acknowledges support by NIH R35GM122482. D.J.N. acknowledges the Kavli Institute for Bionano Science and Technology at Harvard University and National Science Foundation grants PHY-1305254, PHY-0847188, DMR-0820484 and DBI-0959721. P.J.F. acknowledges support from the Gordon and Betty Moore Foundation for support as a Physics of Living Systems Fellow through grant no. GBMF4513. M.J.S. acknowledges support from National Science Foundation grants DMR-0820341 (NYU MRSEC), DMS-1463962 and DMS-1620331. Z.D. acknowledges support from NSF MRSEC DMR-1420382.
The authors declare no competing interests.
Peer review information: Nature Physics thanks Karin John, Gijsje Koenderink and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Fürthauer, S., Lemma, B., Foster, P.J. et al. Self-straining of actively crosslinked microtubule networks. Nat. Phys. 15, 1295–1300 (2019). https://doi.org/10.1038/s41567-019-0642-1
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