Y1087C mutant affects comigration between KIF1Bβ and IGF1R. (A) Kif1b^−/− hippocampal neurons (DIV8) coexpressing KIF1Bβ-EGFP (WT or Y1087C) and SP-IGF1Rβ-RFP. The boxed regions were analyzed. (B) Sequential records of representative IGF1Rβ comigration with KIF1Bβ (arrows) and representative movement of KIF1Bβ-1087C alone (arrowheads). (C) The individual kymograph patterns of KIF1Bβ (WT or Y1087C), SP-IGF1Rβ, and their merged image. Arrows indicate representative comigration. Arrowheads indicate the movement of KIF1Bβ-Y1087C alone. (D) Quantification of anterograde transport of IGF1R in Kif1b^−/− neurons transfected with KIF1Bβ WT (n = 10), KIF1Bβ Y1087C (n = 15), and null (n = 12). Plots and mean ± SD. Two-sided one-way ANOVA post hoc Tukey’s test was used. The P values are indicated in the graph. (E) Ratio of anterograde/retrograde transport of SP-IGF1Rβ-RFP. Plots and mean ± SD. n = 11–15. *, P > 0.05; ns, P > 0.05, one-sided Welch’s t test. (F) Velocity of four types of KIF1Bβ movements in anterograde, KIF1Bβ WT, or Y1087C with or without IGF1R. CoM, comigration. Plots and mean ± SD. Two-way ANOVA post hoc Tukey’s test was used. (G) Ratio of comigration to total KIF1Bβ moving in anterograde. Plots and mean ± SD. One-sided Welch’s t test was used. n = 11–15. The P values are indicated in the graph. Bars: 20 µm (A); 10 µm (B and l in C); 100 s (t in C).