Ng-CAM, A Neuron-Glia and Neuron-Neuron Cell Adhesion Molecule

The neuron-glia cell adhesion molecule(Ng-CAM) mediates both neuron-glia and neuron-neuron adhesion. It is synthesized in neurons from a 6kb mRNA as 200kDa forms which are cleaved to yield two components of 135 kDa and 80 kDa. Amino acid sequence analysis indicates that it contains six immunoglobulin domains and five fibronectin type IIV repeals, a transmembrane domain and a cytoplasmic region. Ng-CAM mediates neuron-neuron adhesion by a homophilic mechanism and neuron-astrocyte adhesion by a heterophilic mechanism. The protein is expressed on neurons and Schwann cells but not on astrocytes. It is most prevalent during development on cell bodies of migrating neurons and on axons during formation of nerves; Ng-CAM expression is greatly increased following nerve injury. Anti-Ng-CAM antibodies inhibited migration of granule cells along Bergmann glia in the cerebellar explants and fasciculation of neurites in outgrowths from explants of dorsal root ganglia. In summary, Ng-CAM on neurons can bind to Ng-CAM on adjacent neurons and to as yet unidentified ligands on astrocytes.