A protein involved in central nervous system myelination: localization in the extracellular matrix and induction in...

G21.3, a monoclonal antibody previously shown to block central nervous system (CNS) myelination, is now demonstrated to recognize an extracellular matrix (ECM) component. The antigen is present on the surface of neurons but not oligodendrocytes and is highly abundant in the white matter of the adult rat brain; however, it is not found in isolated myelin. Double immunostaining studies indicate a neuronal and ependymal cell source of the G21.3 antigen and a developmental expression pattern distinct from known markers of CNS myelination. The antigen is found at low levels in non-neuronal tissue and is mainly localized to basement membranes. G21.3 immunoreactive proteins are upregulated by retinoic acid-induced differentiation of SK-N-SHF neuroblastoma cells. These results suggest that the G21.3 antigen is an axolemma-associated ECM component with roles in postnatal CNS development and cell-matrix interactions during morphological differentiation of neuroblastoma cells.