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The piconewton forces generated by molecular motors carrying cargo along microtubules, or by microtubules polymerizing against the cell cortex or artificial boundaries, are sufficient to deform long microtubules. When microtubules are sparse in the cytoplasm, their deformations are disordered, characterized by high-frequency buckling and inducing only localized cytoplasmic flows. When the microtubules are instead arranged in a dense forest, the nature of the microtubule deformations and induced cytoplasmic flows can change dramatically, giving rise to long-range order and coherent flows. Using a combination of experiments, large-scale simulations of microtubules interacting hydrodynamically through a viscous fluid, and a coarse-grained theory for dense beds of filaments, we elucidate the mechanisms that underlie the self-organization of microtubule ensembles and their subsequent generation of cell-spanning rotation in two examples: cytoplasmic streaming in the Drosophila melanogaster oocyte, and spontaneous rotation of artificially confined asters in Xenopus laevis extract.

Also available on Zoom: https://ucdavis.zoom.us/j/98969645841