Figure 7: Two endocytic pathways cooperatively promote dendrite pruning.

(a) Representative images of C4da neurons taken at 14 h a.p.f.. Dendrites are visualized with mCD8-GFP. Scale bar, 100 μm. (b) Quantification of the pruning phenotype in control and ca-beta mutant neurons overexpressing Nrg. Box plots indicate the median (white line), 25th/75th percentiles (box), the data range except for outliers (whiskers), and outliers (circles). **P<0.001, Steel–Dwass test. (c) Quantification of the pruning phenotype in neurons expressing either Kir2.1 or Vps32 shRNA, or both. *P=0.007, **P<0.001, Steel–Dwass test. (d) The local endocytosis in the proximal dendrite induces deformation of plasma membrane (varicosity formation and dendrite thinning), which is likely to contribute to compartmentalization of VGCCs-mediated Ca²⁺ transients. In parallel, the global endocytosis occurs early in metamorphosis to degrade the cell surface molecule Nrg in a Vps4/Vps32-dependent manner. These two endocytic mechanisms likely promote dendrite pruning in a cooperative manner (see Discussion for details). Since dendritic Ca²⁺ transients were detected precociously in nrg mutant neurons³⁶, global endocytosis might possibly have some minor influence on the initiation of Ca²⁺ transients (dashed arrow).