Impaired signaling endosome motility reduces BDNF endocytosis. (A) Schematic model of two possible effects of Hook1 KD on distal axons. (B) Representative images of distal tips of axons with BDNF-Qdots. Arrows indicate BDNF-Qdots, and the dashed line is the cell outline. (C) Area of Qdots in the distal axons normalized by area of axon quantified. Scatter plot shows mean ± SEM; Kruskal–Wallis one-way ANOVA (ns, P > 0.082). Mock: n = 58 neurons; Hk1 KD: n = 46 neurons; Ciliobrevin D [CilioD]: n = 3–6 neurons. (D) Surface TrkB staining with anti-TrkB in distal axon of fixed neurons. Bottom panel (anti-Rabbit594) shows the secondary antibody only (as a control). (B and D) Bars, 5 µm. (E) Area of surface TrkB per micrometer axonal length. The anti-Rabbit 594 condition is a control for the secondary antibody. Scatter plot shows mean ± SEM; one-way ANOVA (***, P = 0.0004; **, P = 0.0055; ns, P = 0.9741). Mock: n = 40 neurons; Hk1 KD: n = 32 neurons; anti-Rabbit594: n = 10 neurons.