Résumé
The forces generated by microtubules (MTs) and their associated motors orchestrate essential cellular processes ranging from vesicular trafficking to centrosome positioning [1, 2]. To date, most studies have focused on MT force exertion by motors anchored to a static surface, such as the cell cortex in vivo or glass surfaces in vitro [2–4]. However, motors also transport large cargos and endomembrane networks, whose hydrodynamic interactions with the viscous cytoplasm should generate sizable forces in bulk. Such forces may contribute to MT aster centration, organization, and orientation [5–14] but have yet to be evidenced and studied in a minimal reconstituted system. By developing a bulk motility assay, based on stabilized MTs and dynein-coated beads freely floating in a viscous medium away from any surface, we demonstrate that the motion of a cargo exerts a pulling force on the MT and propels it in opposite direction. Quantification of resulting MT movements for different motors, motor velocities, over a range of cargo sizes and medium viscosities shows that the efficiency of this mechanism is primarily determined by cargo size and MT length. Forces exerted by cargos are additive, allowing us to recapitulate tug-of-war situations or bi-dimensional motions of minimal asters. These data also reveal unappreciated effects of the nature of viscous crowders and hydrodynamic interactions between cargos and MTs, likely relevant to understand this mode of force exertion in living cells. This study reinforces the notion that endomembrane transport can exert significant forces on MTs.
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•A bulk motility assay reconstitutes dynein pulling microtubules in the cytoplasm•A single motile cargo in a viscous solution generates near pN forces on a microtubule•Forces are additive, recapitulating a length-dependent model•Tug-of-war situations yield centration of minimal asters in bulk
By developing a bulk motility assay, Palenzuela et al. demonstrate that the sole motion of dynein-driven cargos in a viscous solution can generate pulling forces that move microtubules in the direction opposite to the cargo’s. These data provide key support for dynein pulling in bulk cytoplasm as an important mode of cytoskeleton force exertion.