Involved in both the retinal photoreceptor ribbon synapse formation and physiological functions of visual perception. Necessary for proper bipolar dendritic tip apposition to the photoreceptor ribbon synapse. Promotes matrix assembly and cell adhesiveness. Interacts with DAG1 alpha-dystroglycan. Detected in the synaptic cleft of the ribbon synapse around the postsynaptic terminals of bipolar cells (PubMed:18641643). Colocalizes with BSN, CTBP2 and DAG1 in photoreceptor synaptic terminals (PubMed:18641643). Expressed in the outer plexiform layer (first synaptic region) but not in the inner plexiform layer (second synaptic region) of the retina (at protein level). Strongly expressed in the photoreceptor layer of the retina. Moderately expressed in pineal gland and brain. Weakly expressed in lung and ovary. Expressed in the apical side of the neuroblastic layer (NBL) of the retina at 14.5 dpc and 17.5 dpc. At 16.5 dpc, present in rib cartilage and hair follicle (at protein level). O-glycosylated; contains chondroitin sulfate and heparan sulfate. No morphological abnormalities. Knockout mice are viable and fertile. However, the terminal of bipolar cells do not appose to the synapse terminals in the rod photoreceptor ribbon synapses. The signal transmission from the rod photoreceptor to the rod bipolar cells is less sensitive and is delayed compared to the wild type mouse. The signal transmission from cone photoreceptors to the cone bipolar cells is also impaired. These mice show reduced visual function.