Figure 7.

Frictional asymmetry can give rise to directional motion of non-motor MAPs in dynamic microtubule arrays. (A) Schematic of the optical trapping assay. (B) Time course of microtubule relative motion. The microtubules are oscillated for 2 seconds, followed by a 2 second pause for imaging. (C) Images of the bead and microtubules, and intensity linescans before and after perturbations are shown for a parallel microtubule ‘sandwich.’ (D) Time course of GFP fluorescence images taken after each microtubule oscillation event. (E) Linescans of GFP intensity from images shown in (D). (F) ‘Center-of-mass’ positions of fluorescence signals taken for 3 parallel microtubule pairs. (G) Images of the bead and microtubules, and intensity linescans before and after perturbations are shown for an antiparallel microtubule ‘sandwich.’ (H) Time course of GFP fluorescence images taken after each microtubule oscillation event. (I) Linescans of GFP intensity from images shown in (H). (J) ‘Center-of-mass’ positions of fluorescence signals taken for 3 antiparallel microtubule pairs. Scale bars = 2 μm. (K–M) Microtubule image, GFP images before and after perturbations, and linescans of GFP intensities for (K) parallel microtubules crosslinked by NuMA-bonsai-tail II-GFP, (L) antiparallel microtubules crosslinked by NuMA-bonsai-tail II-GFP, and (M) antiparallel microtubules crosslinked by PRC1. Scale bars = 2 μm. (N) Change in position of the center of mass of GFP fluorescence after 20 seconds of perturbations at 10 Hz (NuMA, Parallel: N=10; NuMA, Antiparallel: N=9; PRC1, Antiparallel: N=10). (O) MAPs with asymmetric friction would cluster towards microtubule minus-ends in asters. A schematic of the energy landscape under force shows how rates of MAP motion differ with respect to filament polarity. (P) MAPs with asymmetric friction would remain evenly distributed in antiparallel microtubule bundles. A schematic of the energy landscape under force shows how rates of MAP motion remain the same with respect to filament polarity.