Depletion of Myo1b affects the length and lifespan of filopodia. (A–E) Cortical neurons transfected with plasmid encoding mGFP-F-tractin-P and control siRNA (A) or Myo1b-siRNA (B) were analyzed at DIV1 during 3 min (one frame/s) using spinning confocal microscopy. Images of the first frames of Video 7 (a and b) and the kymographs of 22 frames for the region marked by a purple lane are shown. Note that the two filopodia in a Myo1b-depleted cell collapse within 22 s, whereas those in the control cell remain stable. The ratio of filopodia per growth cone observed within 3 min (n = 18 or 15; C), the length of the filopodia (n = 199 or 153; D), and the ratio of filopodia per growth cone collapsing within 3 min (n = 18 or 15; E) have been quantified and represented as box plots for three independent experiments. T, time. (F–K) Cortical neurons expressing mGFP-F-tractin-P and control mCherry-shRNA (F) or Myo1b-mCherry-shRNA (G) were analyzed at DIV1 for 3 min (one frame/s) using spinning confocal microscopy. Merged images of the first frames of Video 8 (a and b) showing F-actin (gray) and mCherry (red) in the growth cone are shown. The magenta lanes mark the regions for which kymographs of the dynamics of filopodia for 22 s are shown. Bars, 13 µm. The ratio of filopodia per growth cone observed within 3 min (n = 10 or 12; H), the length of the filopodia (n = 58 or 91; I), the ratio of filopodia per growth cone collapsing within 3 min (n = 10 or 15; J), and the velocity of the elongation (n = 21 or 29; K) have been quantified and represented as box plots in three independent experiments. Data distribution was assumed to be normal. Unpaired t test. **, P < 0.01; ***, P < 0.001.