Nr-CAM: a cell adhesion molecule with ligand and receptor functions.

Nr-CAM Ng-CAM-related cell adhesion molecule) is expressed only in the nervous system on a subset of neurons and non-neuronal cells, including floor-plate cells in the spinal cord and Schwann cells. It is a member of the immunoglobulin (Ig) superfamily and can bind by a homophilic mechanism but its heterophilic interactions may be of greater biological significance. Nr-CAM functions as a neuronal receptor for neurite-growth-promoting stimuli provided by contactin/F11, neurofascin, and RPTPbeta. In addition, by binding to neuronal receptors such as axonin-1, it can modulate axonal guidance. Nr-CAM can also interact laterally with contactin/F11 within the plasma membrane in the form of a complex that may transmit signals to regulate axonal growth. This review summarizes the structure and expression of Nr-CAM and discusses its potential functions as a ligand and as a receptor during neural development.