PTPδ is required for increments of dendritic protrusions and Shank2 puncta by IL1RAPL1. A, FLAG-IL1RAPL1 expressed in cortical neurons failed to increase dendritic protrusions and Shank2 puncta in coculture with cortical neurons from Ptprd−/− mice. B, C, Numbers of dendritic protrusions (B) and Shank2 puncta (C) of EGFP-transfected and EGFP- and FLAG-IL1RAPL1-transfected cortical neurons surrounded by cortical neurons from Ptprd+/+ or Ptprd−/− mice (n = 25–29 neurons). All values represent mean ± SEM. **p < 0.01, Tukey's test. Scale bar, 10 μm.