Potentially involved in docking of synaptic vesicles at presynaptic active zones. Apical receptor involved in membrane fusion of apical vesicles (By similarity). Essential for survival of retinal photoreceetors (PubMed:33974130). Interacts with REEP6 (PubMed:28369466). Isoform 3B interacts with PRPH2 in rod and cone photoreceptors (PubMed:26406599). Isoform 3B interacts with ROM1 (PubMed:26406599). Isoform 3B interacts with SNAP25 (PubMed:26406599). Isoform 3B interacts with VAMP2 (PubMed:26406599). Localized to the inner and outer plexiform layers, the cell body and the inner segments of photoreceptors. Colocalizes with SNAP25 and ROM1 in the inner segment and outer nuclear layer of the retina (at protein level) (PubMed:26406599). Partially colocalizes with PRPH2 in the inner segment of the retina (at protein level) (PubMed:26406599). Expressed in the retina (at protein level). Knockout animals show progressive photoreceptor degeneration. At 5 weeks of age, an approximately 60% decrease in thickness of the outer nuclear layer (ONL) and in the number of ONL neuronal somata is observed, indicating that a large number of photoreceptors have died. In some of the remaining rods, rhodopsin is appropriately localized to the outer segments, but a marked amount of rhodopsin mislocalized to the outer plexiform layer. At 8 and 12 weeks of age, increasing cell loss and further ectopic expression of rhodopsin are observed. Cone photoreceptor loss and ectopic expression of opsin in cones is also observed. Quantification of the progressive degenerative phenotype reveals a rapid loss in the number of neuronal somata in the ONL, indicative of photoreceptor death, whereas the number of cells in the inner nuclear layer, including horizontal, bipolar, and amacrine cells, is no different from that of controls. Belongs to the syntaxin family.