Promotes growth and fasciculation of neurites from cultured hippocampal neurons. May be involved in fasciculation as well as myelination of developing neural axons. May have a role in regeneration as well as neural plasticity in the adult nervous system. May mediate homophilic as well as heterophilic cell-cell interaction and contribute to signal transduction through its intracellular domain (PubMed:12629050). Assembled with KCNB1 modulates the gating characteristics of the delayed rectifier voltage-dependent potassium channel KCNB1 (By similarity). Homodimer, and heterodimer with AMIGO2 and AMIGO3 (PubMed:12629050). Interacts with KCNB1 (By similarity). Associated with axons of neuronal cells (PubMed:12629050). Colocalizes with KCNB1 at high-density somatodendritic clusters on the surface of hippocampal and cortical neurons (By similarity). Expressed at moderate levels in the central nervous system of stage 13-14 embryos. Highest levels at this stage in fiber tracts from dorsal root ganglia and trigeminal ganglion to the spinal cord as well as in fibers on both sides of the Purkinje cell layer of the cerebellum. Expression is down-regulated during postnatal stages P6 to P10 followed by up-regulation at the onset of myelination. High level expression in most myelinated axon tracts of the adult including cerebellum, pons, medulla, and spinal cord as well as in nonmyelinated fiber tracts in the striatum lucidum CA3 region of the hippocampus. By HMGB1/amphoterin; in cultured hippocampal neurons. The LRR repeat region mediates homodimerization. Belongs to the immunoglobulin superfamily. AMIGO family.