May function as a growth and differentiation factor involved in neuritogenesis. May induce ERBB3 activation. Interacts with ERBB3 and GOPC. Binds TNR and probably TNC (By similarity). Interacts with MDK; this interaction is independent of the presence of chondroitin sulfate chains and promotes elongation of oligodendroglial precursor-like cells (PubMed:16901907). In neurons, localizes to synaptic junctions. Also detected in the endoplasmic reticulum and the Golgi (By similarity). Partially enriched in lipid rafts (PubMed:11929867). Expressed in cerebral cortex and cerebellum. Expressed in retina (at protein level). Expression starts at E16 in the cerebral cortex and increases to reach a maximum 20 days after birth. Then it decreases till adulthood to be expressed half of the peak level. In the retina, expression reaches a maximum at postnatal day 14 (P14). It starts weakly at E16 in the retinal pigment epithelium (RPE). At P0 it is detected in nerve fiber layer (NFL), ganglion cell layer (GCL), inner plexiform layer (IPL) and RPE. At P7, it becomes intense in the NFL and IPL. At P14, expression becomes intense in the area of outer segments (OS) of the photoreceptor cells as well as in RPE, whereas in the inner layers it becomes gradually fainter. From P21 to P42, it decreases in inner retinal layers. OS and RPE still express, whereas expression in the NFL and IPL decreases (at protein level). Up-regulated in nucleus accumbens shell by cocaine administration. N-glycosylated. O-glycosylated; contains chondroitin sulfate glycans. Part-time proteoglycan, expressed in part as a proteoglycan exhibiting chondroitin sulfate glycans and in part as a non-proteoglycan form. The relative amount of both forms depends on tissues and tissues maturation (By similarity). Phosphorylated; in intracellular and extracellular parts. Different forms of various molecular weight have been observed. Such forms are possibly due to different levels of glycosylation, phosphorylation and/or protein cleavage (By similarity).