Plays a role in tight junction biogenesis and in the establishment of cell polarity in epithelial cells (By similarity). Also involved in adherens junction biogenesis (By similarity). Functions in cellular patterning of the retina (PubMed:11992120). Localizes to the apical region of the cell membrane, in the vicinity of junctional complexes in the neuroepithelium and the photoreceptor layer. Enriched in the areas immediately apical to the adherens junctions-associated actin bundles. Expressed in the retina and in the neural tube. Expressed early in development. The PDZ domain is required for apical location. Belongs to the MAGUK family.