Dynein Forces and Centrosome Centering

Shape changes of individual microtubules following laser severing have been measured in Tanmay Lele's lab. Surprisingly, regions near newly created minus ends increased in curvature following severing, while regions near new microtubule plus ends depolymerized without any observable change in shape. With dynein inhibited, regions near severed minus ends straightened rapidly following severing. These observations suggest that dynein exerts a pulling force on the microtubule which buckles the newly created minus end. Moreover, the lack of any observable straightening suggests that dynein prevents lateral motion of microtubules. To explain these results, we developed a model for intracellular microtubule mechanics which predicts the enhanced buckling at the minus end of a severed microtubule. Our results show that microtubule shapes reflect a dynamic force balance, in which dynein motor and friction forces dominate elastic forces arising from bending moments. A centrosomal array of microtubules subjected to dynein pulling forces and resisted by dynein friction is predicted to center on the experimentally observed timescale, with or without the pushing forces derived from microtubule buckling at the cell periphery.

Dynein forces are sufficient to center the centrosome. (A) Representative images showing the centrosome in EGFP-α-tubulin expressing square endothelial cells; control cell (left) and dynein-inhibited cell transfected with DsRed-CC1 (right). Scale bar is 5μm. (B) Mean centrosome position in 42 control cells and 22 dynein inhibited cells; the statistical significance p < 0.01. The centrosome is consistently observed to be at or close to the center of the square in control cells, while it is substantially off-center in dynein-inhibited cells. Simulations of centrosome centering in square cells with (C) and without (D) dynein motor activity. The motor-driven microtubules (C) show considerable buckling near the cell periphery (clearly visible at t = 1 min) whereas without motor activity (D) the buckling is of Euler type. Only the motor-driven microtubules are observed to center an initially off-center centrosome. Movies illustrating the dynamics of an ensemble of microtubules with and without motor forces can be download by clicking on the links below.

Dynamics of an ensemble of microtubules without motor forces. Click here to download.

Dynamics of an ensemble of microtubules with motor forces. Click here to download.

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Last updated September 2017