A, D1 interaction with PSD-95 in HEK293T cells. Cells were transfected with cDNA constructs encoding HA-D1 or PSD-95-GFP or both. Immunoprecipitation (IP) was performed by incubation of cell lysates with the indicated antibodies followed by immunoblotting (IB). IgG was used as a control in all immunoprecipitation experiments. B, D1 association with PSD-95 in the brain of WT but not PSD-95 KO mice. DOC-extracted mouse forebrain tissues were immunoprecipitated with an anti-D1 antibody or an anti-PSD-95 antibody, and the blots were revealed by PSD-95 and D1 antibodies, respectively. C, subcellular distribution of D1. Subcellular fractionation was performed on mouse forebrain structures. 40 μg of fractionations were loaded to each lane for Western blot analysis. D1 was particularly enriched in the PSD (one Triton) fraction compared with total homogenates (H), nuclear fraction (P1), the crude synaptosome (P2), and synaptosome (SSM). D, D1 association with PSD-95 in the PSD. Solubilized PSD was immunoprecipitated with an anti-D1 antibody, and the blot was revealed by an antibody against PSD-95. E, D1 co-localized with PSD-95 clusters in processes of cultured striatal neurons.