Adhesion molecule that promotes lamina-specific synaptic connections in the retina and is specifically required for the formation of neuronal circuits that detect motion (PubMed:26287463). Acts by promoting formation of synapses between two specific retinal cell types: the retinal ganglion cells W3B-RGCs and the excitatory amacrine cells VG3-ACs. Formation of synapses between these two cells plays a key role in detection of motion (PubMed:26287463). Promotes synaptic connectivity via homophilic interactions (PubMed:26287463). Homodimer; mediates homophilic interactions to promote cell adhesion (PubMed:15703275, PubMed:26287463). Interacts (via PDZ-binding motif) with MAGI1, MAGI2, DLG2, DLG3 and DLG4 (PubMed:20219992). Expressed in retinal ganglion cells (RGCs) that form synapses in distinct inner plexiform layer (IPL) sublaminae. Specifically expressed in specific subsets of retinal ganglion cells (RGCs), named W3B-RGCs, that specifically respond when the timing of the movement of a small object differs from that of the background, but not when they coincide (at protein level). Also present in excitatory amacrine cell type called VG3-ACs, that provide strong and selective input W3B-RGCs (at protein level) (PubMed:26287463). Expressed at low levels in the glomeruli (PubMed:15213259). Highly expressed in many fetal tissues, inlcuding kidney but shows markedly lower expression in adult organs. Expression in kidney is high throughout development with maximal expression occurring near birth. the PDZ-binding motif mediates interaction with PDZ domain-containing proteins MAGI1, MAGI2, DLG2, DLG3 and DLG4 and is required for is required for synaptic localization in photoreceptors. Mice are viable and fertile but show decreased synaptic connectivity between the retinal ganglion cells W3B-RGCs and the excitatory amacrine cells VG3-ACs. Due to intron retention. Belongs to the sidekick family. Discerning change - Issue 176 of February 2016