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Cell adhesion molecule involved in a diverse range of contact-mediated interactions among neurons, astrocytes, oligodendrocytes, and myotubes. It is widely but transiently expressed in many tissues early in embryogenesis. Four main isoforms exist, including CD56; (ANTIGENS, CD56); but there are many other variants resulting from alternative splicing and post-translational modifications. (From Pigott & Power, The Adhesion Molecule FactsBook, 1993, pp115-119)