Kinesin-5 depletion results in fewer bouts of retraction of axons and axonal branches. Time-lapse images of cultured rat primary sympathetic neurons treated with either control siRNA (left) or kinesin-5 siRNA (right) show the enhanced rates of axon and branch elongation in the kinesin-5-depleted neuron. Comparison of these neurons reveals that axonal elongation involves interspersed bouts of growth and retraction, with kinesin-5-depleted axons displaying substantially more bouts of growth and fewer bouts of retraction. These differences are also observed during branch initiation. Branches that arise from the control axon do not persist and retract back to the primary axon, whereas in the kinesin-5-depleted neuron multiple branches form and elongate, giving rise to secondary and tertiary branches that display a reduced frequency of stepwise retraction. Image frames were acquired at 3-min intervals for a duration of 5 h, and are presented for viewing with a display rate of one image per second. For data analysis and discussion related to Video 1, see Fig. 6. Bars, 20 µm.
