The loss of Kif1bβ or Fignl1 similarly increases dynein-based Rab3 retrograde transport velocity. (A) Still images extracted from time-lapse recordings of Rab3-Dendra2 vesicles in SMN axons of 50-hpf Tg(mnGFF7) larvae injected with control MO (MO Ctl), MO Kif1bβ, or MO Fignl1 and a UAS:Rab3-Dendra2 plasmid. Scale bar, 10 µm. (B) Representative kymograms of Rab3-Dendra2 vesicle transport in control, Kif1bβ and Fignl1 morphant sMN axons. Vertical black lines represent static vesicles. Vertical scale bar, 2 min; horizontal scale bar, 10 µm. (C–J) Mean anterograde (C, E, G, and I) and retrograde (D, F, H, and J) velocities (C, D, G, and H) or run lengths (E, F, I, and J) of Rab3-vesicles measured in control (n = 20; C–J), Kif1bβ (n = 20; C–F), or Fignl1 morphant (n = 20; G–J) SMN axons. *, P ≤ 0.05, ***, P ≤ 0.001, ns, nonsignificant (P > 0.05); unpaired two-tailed t test with Welch’s correction and Mann–Whitney test for velocity and run length comparisons, respectively. Error bars are SEM. (K–L) Mean number of static vesicles related to a 100-µm axon portion. ns, nonsignificant (P > 0.05); Mann–Whitney test. Error bars are SEM.