Figure 7.

FOXP2^R553H mutation impairs intracellular endosome transport and neurite outgrowth of striatal neurons, which is rescued by the knockdown of Dctn1. (A) The flow chart of the experiment in E–H. (B–E) Time-lapse video microscopy showing trafficking of TrkB-RFP endosomes in dendrites of cultured striatal neurons. The kymographs show trajectories of TrkB-RFP vesicles during a 3-min recording. Triangles with the same colours indicate the positions of the same vesicles in the dendrite. The distance and speed of TrkB-RFP vesicles were reduced in FOXP2^R553H-expressing neurons (D) compared with control FOXP2^WT-expressing neurons (B). The abnormalities of TrkB-RFP-labelled vesicle transport were rescued by knocking down Dctn1 in FOXP2^R553H-expressing neurons (E). (B′–E′) Kymographs generated from time-lapse video microscopy of trajectories of TrkB-mRFP vesicles for 180 s. (F and G) Quantitative analysis of TrkB-RFP endosome transport. Cultured cells in each group were prepared from at least four litters of P0 neonatal mice. (H) The flow chart of the experiment in I–N. (I–K) The dendritic complexity (J) and total lengths (K) were reduced in FOXP2^R553H-expressing striatal neurons (I′) compared with FOXP2^WT-expressing striatal neurons (I) in vivo. The heatmap of each neuron represents a 3D volumetric colour rendering of the image stack while each new path segment is traced. (L–N) The reductions in dendritic arborization (M) and total lengths (N) were rescued in shDctn1;FOXP2^R553H-expressing striatal neurons (L′) compared with control shLacZ;FOXP2^R553H-expressing striatal neurons (L) in vivo. *^,#P < 0.05, **^,##P < 0.01, ***^,###P < 0.001. One-way ANOVA with Tukey's HSD post hoc test was used in F–G. Two-way ANOVA with Tukey's HSD post hoc test was used in J and M. Significant differences between groups in J and M were quantified by the simple main effect of two-way ANOVA. Student's t-test was used in K and N. Data are mean ± SEM.