How dynein and microtubules rotate the nucleus

Abstract

In living cells, a fluctuating torque is exerted on the nuclear surface but the origin of the torque is unclear. In this study, we found that the nuclear rotation angle is directionally persistent on a time scale of tens of minutes, but rotationally diffusive on longer time scales. Rotation required the activity of the microtubule motor dynein. We formulated a model based on microtubules undergoing dynamic instability, with tensional forces between a stationary centrosome and the nuclear surface mediated by dynein. Model simulations suggest that the persistence in rotation angle is due to the transient asymmetric configuration of microtubules exerting a net torque in one direction until the configuration is again randomized by dynamic instability. The model predicts that the rotational magnitude must depend on the distance between the nucleus and the centrosome. To test this prediction, rotation was quantified in patterned cells in which the cell's centrosome was close to the projected nuclear centroid. Consistent with the prediction, the angular displacement was found to decrease in these cells relative to unpatterned cells. This work provides the first mechanistic explanation for how nuclear dynein interactions with discrete microtubules emanating from a stationary centrosome cause rotational torque on the nucleus.

Moving Cell Boundaries Drive Nuclear Shaping during Cell Spreading

“…There is mounting evidence that the cytoskeleton exerts forces on the nucleus to position it (20,(46)(47)(48). In this study, however, we show that as long as the cell was able to spread, inhibiting actomyosin forces, microtubulebased forces and intermediate filaments, as well as the LINC complex, did not prevent nuclear flattening.…”

“…Such forces likely originate in the cytoskeleton, which is known to link to the nuclear surface through the LINC (linker of nucleoskeleton to cytoskeleton) complex (17)(18)(19). Candidates for shaping the nucleus include microtubule motors that can shear the nuclear surface (20,21) and intermediate filaments that can passively resist nuclear shape changes by packing around the nuclear envelope or transmitting forces from actomyosin contraction to the nuclear surface (22,23). The actomyosin cytoskeleton that can push (24), pull (25,26), or shear and drag the nuclear surface (27,28) is also assumed to be a significant component of the nuclear shaping machinery in the cell.…”

The nucleus is an intracellular propagator of tensile forces in NIH 3T3 fibroblasts

“…Microtubule motors -like dynein and kinesin -generate shear forces on the nuclear surface that result in nuclear rotations in fibroblasts (Levy and Holzbaur, 2008;Wu et al, 2011), can cause nuclear translocations in epithelial cells (Wilson and Holzbaur, 2012) and are required for nuclear migration in Caenorhabditis elegans embryos Meyerzon et al, 2009). Actomyosin forces have been hypothesized to pull on the nucleus (Chancellor et al, 2010;Friedl et al, 2011;Sims et al, 1992;Wang et al, 2009;Wu et al, 2014), push on it (Friedl et al, 2011;Roth et al, 1995;Zhang et al, 2007) and shear it (Folker et al, 2011;Kim et al, 2014;Luxton et al, 2010).…”

Chemical Engineering Principles in the Field of Cell Mechanics

“…Using similar approaches, we have also shown that dynein-microtubule interactions can bend growing microtubules and cause the nucleus to rotate. 23,24 This work shows the power of combined engineering modeling/analysis, state-ofthe art tools of molecular cell biology, and sophisticated biophysical measurements.…”