Required for depolarization-dependent survival of cultured cerebellar granule neurons. May mediate homophilic as well as heterophilic cell-cell interaction with AMIGO1 or AMIGO3. May contribute to signal transduction through its intracellular domain. Binds itself as well as AMIGO1 and AMIGO3. Associated with nucleus as well as plasma membrane. Restricted to somata of cerebellar as well as hippocampal neurons. Highest levels in the lung. High levels in cerebellar granule neurons and Purkinje cells. Also in pyramidal cells between CA1 and CA3 regions of the hippocampus and granule cells of the dentate gyrus. High level expression in cerebellum of newborn rats is down-regulated to 50% by postnatal day 14. Belongs to the immunoglobulin superfamily. AMIGO family.