Cortactin interacts with F-actin retrograde flow. (A) Fluorescent images of an axonal growth cone labeled with anti-cortactin antibody (green) and phalloidin for F-actin (red). Enlarged views of the filopodium in the white rectangle are shown to the right. Arrowheads indicate cortactin accumulation in a filopodium. (B) A fluorescent feature image of EGFP-cortactin in an axonal growth cone (left) and a time series of the boxed area at 5-s intervals (right). See Video 1. Yellow arrowheads denote a fluorescent feature of EGFP-cortactin moving retrogradely. (C) A fluorescent feature image of mCherry–β-actin (red) and EGFP-cortactin (green) coexpressed in an XTC fibroblast (left). The kymographs (right) of the peripheral region indicated by the rectangle in the left image show that the fluorescent features of EGFP-cortactin and those of actin moved at similar speeds (white lines). See Video 2. (D) Time-lapse fluorescent feature images of EGFP-cortactin in an axonal growth cone treated at 0 min with 1 µM cytochalasin D. See Video 4. Dotted lines indicate the leading edge of the growth cone and boundary of fluorescent features. Bars: (A, B, and D) 10 µm; (C) 5 µm.