Sdc2 regulates dendrite outgrowth through Sarm1. (A) Cultured hippocampal neurons were transfected with the indicated plasmids at 2 DIV and then fixed for immunostaining with GFP and Sdc2 antibodies at 5 DIV. pSuper and pGW1 are the vectors for RNAi knockdown and gene expression, respectively. Insets (enlarged from the boxed regions) show the filopodia induced by Sdc2. Bar, 30 µm. (B) Total dendrite lengths. (C) Number of primary dendrites. (D) Density of dendritic filopodia. Because the vector control and Sarm1i¹ alone did not obviously induce filopodia formation, only neurons transfected with Sdc2 alone or both Sdc2 and Sarm1i¹ were subjected to quantitative analysis of filopodia. Thirty transfected neurons were collected randomly from each group. The experiments were repeated three times; data represent mean values ± SEM (error bar). *, P < 0.05; ***, P < 0.0005.