Essential multidomain scaffolding protein required for normal development. Recruits channels, receptors and signaling molecules to discrete plasma membrane domains in polarized cells. May play a role in adherens junction assembly, signal transduction and cell proliferation (By similarity). May play a role in synapse assembly and function. A number of isoforms are produced. At 4 days-post-fertilization (dpf), expressed in the inner and outer plexiform layers and the ganglion cell layer of the retina, the marginal zone of the tegmentum, and in the developing craniofacial cartilage. Belongs to the MAGUK family.