(A) Efficacy of Yap1 shRNA in neurons, analyzed by western blot. (B) Rat hippocampal neurons were transfected on DIV7 with the indicated constructs. An empty pLKO plasmid was used as the control. (C, D) Quantification of TDL (C) and Sholl analysis (D) of hippocampal neurons that were transfected with plasmids as in B or cotransfected with Yap1 shRNA and human Yap1-cDNA with a deleted TEAD-binding domain (Yap1 shRNA + Yap1 del60-89). Control: *n* = 40; Yap1 shRNA: *n* = 60; Yap1 shRNA + Yap1: *n* = 47; Yap1 shRNA + Yap1 del60-89: *n* = 51. To control; *p* < 0.0001; to Yap1 shRNA; *p* = 0.0011, *p* = 0.0264; to Yap1 shRNA + Yap1; *p* = 0.7244. (E) Reduction of dendritic tree complexity in hippocampal neurons from *Yap1 fl/fl* mice that were transfected with a Cre-expressing plasmid. (F) Cre expression in *Yap1 fl/fl* hippocampal neurons led to the down-regulation of Yap1 expression, analyzed by western blot. (G, H) Quantification of TDL (G) and Sholl analysis (H) of dendritic trees of hippocampal *Yap1 fl/fl* neurons that were transfected with either a control vector (*n* = 53) or a Cre-expressing plasmid (*n* = 53). *p* < 0.0001. Images were obtained from at least from three independent cultures. Statistical significance was analyzed using two-tailed unpaired *t* test (G), one-way analysis of variance followed by Tukey’s post hoc test (C), and two-way analysis of variance followed by Bonferroni’s post hoc test (D, H). Numerical values that underlie the graphs are shown in S1 Data. See S1 Table for detailed statistics for D and H. **p* < 0.05, ***p* < 0.01, *****p* < 0.0001. Bars represent the mean ± SEM. Scale bar = 50 μm. DIV, day in vitro; ns, not significant; SEM, standard error of the mean; shRNA, short-hairpin RNA; TDL, total dendrite length; TEAD, TEA domain; Yap1, Yes-associated protein 1.