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 (By similarity). 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 (By similarity). Highest level in cerebellum, retina, liver, and lung. Lower levels in cerebrum, kidney, small intestine, spleen and testis. Belongs to the immunoglobulin superfamily. AMIGO family.