Farp1 increases excitatory synapse number. (A and B) Dendrites expressing GFP-Farp1 carry more excitatory presynaptic terminals than controls expressing myristoylated GFP (GFP^myr). (A) Confocal images of hippocampal neurons at 14 div coexpressing soluble Cherry (red) and GFP^myr (green; left column) or GFP-Farp1 (green; right). Cultures were immunostained for the excitatory presynaptic markers VGlut1/2 (blue). Boxed areas are enlarged below. Bars: (overview) 5 µm; (enlarged insets) 2 µm. (B) Quantification of images as in A. Farp1 increased VGlut puncta number (top) but size was unaffected (bottom). (438 and 456 puncta, respectively; three independent experiments.) (C–E) Lower spine density in SynCAM 1 KO neurons is rescued by Farp1. (C) Confocal images of WT and SynCAM 1 KO neurons at 21 div. Neurons expressed Cherry (red) as volume marker with or without GFP-Farp1 (green). Bars, 3 µm. (D) Quantification of mushroom spine density imaged as in C. Neurons were prepared from littermates. (WT, 430 spines; KO, 470; WT + GFP-Farp1, 422; KO + GFP-Farp1, 720; three independent experiments.) (E) Mushroom spine length imaged as in C (WT, 223 spines; KO, 98; WT + GFP-Farp1, 224; KO + GFP-Farp1, 305; three independent experiments). Error bars indicate mean ± SEM; *, P < 0.05; **, P < 0.01; ***, P < 0.001. n.s., not significant.