Required, with CNTNAP2, for radial and longitudinal organization of myelinated axons. Plays a role in the formation of functional distinct domains critical for saltatory conduction of nerve impulses in myelinated nerve fibers. Demarcates the paranodal region of the axo-glial junction. In association with contactin involved in the signaling between axons and myelinating glial cells. Interacts with CNTN1/contactin in cis form. Predominantly expressed in brain. In myelinated nerve fibers of the CNS predominantly found in paranodal axoglial junctions. In unmyelinated nerve fibers of the CNS diffusely distributed along the entire surface. Weak expression is detected in ovary, pancreas, colon, lung, heart, intestine and testis. Detected on postnatal day 7 in cerebellum. Follows a caudorostral progression according to the myelination process. Appears to redistribute from the internode to the paranodal region during myelin compaction and maturation (PubMed:9396755). Expression reaches maximal levels between days 14 and 18 and remains at the same levels until adulthood. Belongs to the neurexin family.