Expression of PSD-93 and related MAGUKs in cerebellum of PSD-93 knock-out mice. Immunohistochemical staining of cerebellum from wild-type (WT) and PSD-93 knock-out (KO) mice using a pan-antibody that cross-reacts with all four neuronal MAGUKs. In wild-type mouse, strong staining of Purkinje neurons represents PSD-93 (Brenman et al., 1996b; Kim et al., 1996). Staining of the granule cell layer reflects expression of SAP-102 and SAP-97 (Muller et al., 1995, 1996), and labeling of small cone-shaped structures (or pinceaux) beneath the Purkinje cells (arrowheads) represents PSD-95 (Kistner et al., 1993). In the PSD-93 knock-outs, staining is selectively lost from the Purkinje cells. A pan-antibody was used for this Figure to show that no other MAGUK proteins are expressed at detectable levels in Purkinje neurons of the PSD-93 knock-outs. Magnification, 60×.