Fig. 2. Tracking retrograde flow using GFP–myosin-IIA fluorescent spots. (A) A KO growth cone from a SCG neuron expressing GFP–myosin-IIA (the barely visible neurite is on the left side of the field). The spots of fluorescence sometimes align presumably along actin bundles. (B) A high magnification sequence from the KO cone showing the displacement of spots (the pair indicated by the arrowhead) over time. The lines through the images are for position reference and allow one to see the retrograde displacement (from top to bottom of image). Because many of the spots changed intensity, appeared and disappeared at different times, only a subset of spots could be identified with certainty in multiple frames. The elapsed time between images is 13 seconds. (C) Comparison of the average rate (±s.e.m.) of GFP–myosin-IIA spot displacement from wt and KO growth cones. The spots in the KO growth cones (n=11) move more than twice the speed of those in the wt (n=15). The individual rates were calculated from the total distance that spots moved over a minimum of three frames divided by the elapsed time (13 second intervals). A, bar, 12 µm; b, bar, 2 µm.