May function as a growth and differentiation factor involved in neuritogenesis. May induce ERBB3 activation. Binds TNR and probably TNC (By similarity). Interacts with ERBB3 and GOPC. Interacts with MDK; this interaction is independent of the presence of chondroitin sulfate chains and promotes elongation of oligodendroglial precursor-like cells (By similarity). Partially enriched in lipid rafts (By similarity). Also detected in the endoplasmic reticulum and the Golgi (PubMed:10617623). Expressed in olfactory bulb, hippocampus, brain stem, spinal cord, cerebrum and cerebellum. Expressed by Purkinje cells in the cerebellum (at protein level). Expressed in immature and mature cerebellum (isoform 1, isoform 2 and isoform 3). The proteoglycan form decreases from birth to adulthood in the cerebellum concomitant with non-proteoglycan form increase. In the cerebrum the maximum of expression of the proteoglycan is detected 15 days after birth and then decreases gradually to reach half-level at adulthood (at protein level). 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. In the cerebellum the 2 forms coexist while in the cerebrum the proteoglycan form is predominant. Phosphorylated; in intracellular and extracellular parts. Altered synaptic transmission at early developmental stages. Different forms of various molecular weight have been observed. Such forms are possibly due to different levels of glycosylation, phosphorylation and/or protein cleavage. Major isoform. Truncated N-terminus. Truncated N-terminus.