Slit-induced axon retraction requires regulation of filopodia dynamics. (A) DIC time-lapse images of littermate control and mve DRG axons 1 min before and 20 min after bath application of 3 nM Slit. The distal-most leading edge is marked by a white dashed line, and growth cone areas shaded either blue (control) or green (mve) in panel i are enlarged and aligned for easy comparison in ii. (B) Area measurements were generated by manually outlining growth cones just before ligand addition (Apre) and 20 min after stimulation with the indicated ligands (Apost). Fractional change in area is calculated as 1 − (Apre − Apost)/Apre. Negative values indicate a decrease in growth cone area. (C) Growth cone position tracked from time-lapse DIC images; traces normalized so that the origin corresponds to growth cone position at the time of Slit stimulation (colored line, mean; shaded area, 95% confidence interval). n ≥ 18 for each condition. (D) DRG neurons stimulated with 5 nM Slit and either 25 nM CD or DMSO (control). Slit-induced filopodium elongation is observed in controls (i, white arrows), but not in CD-treated growth cones. CD blocks Slit-induced axon retraction; compare positions of growth cone leading edge (dashed lines in i) and growth cone position (ii, tracked as in C). Bars, 10 µm. n = 18 for each condition.