Figure 3.

Effects of actin depletion on microtubule transport in the axon. A, Time-lapse images reveal a microtubule moving in the anterograde direction through the photobleached region. Brightness and contrast were adjusted to best reveal the moving microtubule. Red arrows mark the leading and trailing ends of the microtubule. B, Analysis of microtubule transport events demonstrated that the frequency (events per minute) of anterograde transport was significantly reduced in actin-depleted axons (^*p < 0.001;χ² test), whereas the frequency of retrograde transport was not significantly affected. C, Histogram of microtubule lengths displays no significant difference between control and latrunculin-treated neurons. D, Histogram depicting the mean velocity distributions of both anterograde and retrograde microtubule transport in control and latrunculin-treated neurons. A significant increase in mean velocity was detected in both anterograde and retrograde microtubule movements (p < 0.005 and p < 0.001, respectively; two-tailed t test). E, Histogram showing the distributions of the instantaneous velocities of microtubules chosen randomly from the total observed microtubule population shown in D. No significant difference was detected between the instantaneous velocities of moving microtubules between control and actin-depleted axons. F, The combined data from D and E depicting microtubule velocity change as a function of transport directionality shows a significant increase in the mean microtubule transport velocities that is bidirectional (^*p < 0.01; two-tailed t test). A small but insignificant increase is seen in comparing control and latrunculin-treated instantaneous velocities. Scale bar, 5 μm.