Figure 3.

(a) A sequence of images showing axonal retraction in response to treatment with F-actin-disrupting drug Latrunculin-A (Lat-A) at 1 μM. The retraction front characterized by a sharp change in radius propagates toward the soma, leaving a thin tube behind. Note that frames two to five have the same time gap. The relative movement of the front and the extraneous particle indicate a flow profile with decreasing velocity away from the front (also see Video S6). (b) Plots show the retracted length (thinned segment) measured from the growth cone end and normalized with total axon length for control axons, those pretreated with the myosin-II inhibitor blebbistatin (blebbi), and those pretreated with the microtubule stabilizer Taxol. The length of the axonal segment over which beading can be seen after treatment with noco, also measured from the growth cone, is shown for comparison. Each curve is an average taken over n > 20 axons, and the error bars are standard errors of the mean. The nonnormalized and nonaveraged data for Lat-A and noco are shown in Fig. S4. (c and d) Phase-contrast (grayscale) and corresponding fluorescence images show F-actin (red) and microtubule (green) on the left side and F-actin (red) and neurofilament (blue) on the right side.