Cooperation of N-cadherin and neuroligin-1 is mediated by the scaffolding protein S-SCAM in cultured cortical neurons. (A and B) Inhibition of S-SCAM function by expression of truncated S-SCAM proteins blocks the induction of presynaptic vesicle clusters by neuroligin-1-EGFP (transfected at 4–5 DIV, analyzed at 6–7 DIV). (A) DsRed2-VAMP2 was coexpressed with either EGFP or neuroligin-1-EGFP (Nlg-GFP) and either full-length S-SCAM (S-SCAM full) or S-SCAM with PDZ5 deleted (S-SCAM-PDZ5 del) or S-SCAM with WW and PDZ1 deleted (S-SCAM-PDZ1 del). (Left) EGFP-labeled dendrites. (Center) Thresholded DsRed2-VAMP2 puncta. (Right) Overlay of EGFP fluorescence (green) and DsRed2-VAMP2 puncta (red) to visualize vesicle clusters on dendrites. (Scale bars: 2 μm.) (B) Changes in vesicle cluster density upon neuroligin-1-EGFP expression. Type of coexpressed S-SCAM is indicated below bars. S-SCAM-full, n = 16; S-SCAM-PDZ5del, n = 20; S-SCAM-PDZ1del, n = 17. (C–E) Clustering of neuroligin-1-EGFP and colocalization with vesicle clusters depends on S-SCAM function. (C) Overlay images of thresholded neuroligin-1-EGFP puncta (green) and DsRed2-VAMP2 puncta (red) to visualize colocalization. Type of coexpressed S-SCAM is indicated. (Scale bar, 2 μm.) Density of neuroligin-1-EGFP puncta on dendrites (D), and colocalization of neuroligin-1-EGFP puncta with DsRed2-VAMP2 puncta (E). No S-SCAM, n = 27; S-SCAM full, n = 16; S-SCAM PDZ5del, n = 20; S-SCAM PDZ1del, n = 17. (F) Colocalization of immunoctochemically stained endogeneous N-cadherin puncta with endogeneous neuroligin puncta depends on S-SCAM function. No S-SCAM, n = 13; S-SCAM full, n = 11; S-SCAM PDZ5del, n = 12; S-SCAM PDZ1del, n = 13. (G and H) RNAi-mediated S-SCAM knockdown in low-density cultures of cortical neurons (transfected at 2 DIV, analyzed at 8 DIV). Quantification of immunocytochemically stained neuroligin puncta (G) and VAMP2 puncta (H) at 8 DIV. Control, no transfection; Mismatch, mismatch control; KD, knockdown. Mean ± SEM; *P < 0.05; **P < 0.01; ***P < 0.001, one-way ANOVA; unpaired t test in G and H.