Cells expressing the NG2 antigen contact nodes of Ranvier in adult CNS white matter

The NG2 antibody, which recognises an integral membrane chondroitin sulphat e, labels a significant population of cells in adult CNS white matter tract s of the rat optic nerve and anterior medullary velum (AMV). Adult NG2+ cel ls are highly complex with multiple branching processes and we show by EM i mmunocytochemistry that they extend perinodal processes, which contact node s of Ranvier. NG2+ cells do not react to conventional immunohistochemical m arkers for adult glia and so we reservedly term them NG2P cells. In vitro, NG2 labels oligodendrocyte-type-2 astrocyte (O-2A) progenitors that can giv e rise to oligodendrocytes or type-2 astrocytes, depending on the culture m edium. Thus, it is possible that NG2P cells may be derived from the same st em cells as oligodendrocytes. Interestingly, NG2+ cells identified previous ly in adult CNS displayed phenotypic characteristics of O-2(adult) progenit ors and it is possible that, like them, NG2P cells might retain the capacit y of generating oligodendrocytes in the adult CNS. This may be an important role of NG2P cells in demyelinating diseases such as multiple sclerosis. I t is significant therefore that the perinodal processes of NG2P cells conta ct the only sites of exposed axolemma in myelinated axons, so that NG2P cel ls are ideally situated to detect and respond to changes in axonal function during demyelination. A further implication of our finding is that NG2P ce lls may perform functions at nodes of Ranvier previously attributed to peri nodal astrocytes, including the clustering and maintenance of sodium channe ls in the axon membrane at nodes, during development and following demyelin ation. GLIA 26:84-91, 1999. (C) 1999 Wiley-Liss, Inc.