Novel microtubule-associated protein-2 isoform is expressed early in humanoligodendrocyte maturation

We have identified a developmentally regulated, oligodendrocyte-specific pr otein, designated microtubule-associated protein-2 expressing exon 13 (MAP- 2+13), in the human central nervous system (CNS). Monoclonal antibodies dir ected against MAP-2+13 labeled oligodendrocytes in the white matter of huma n fetal spinal cord. Double-label immunofluorescence and confocal microscop y, and immunoelectron microscopy localized MAP-2+13 to the soma and extendi ng processes of fetal oligodendrocytes, but not to the myelin sheath. The i mmunoreactivity was throughout the perikarya. Ultrastructural examination o f the fetal myelin sheaths showed them to be thin and not fully compacted, indicating that myelination was in progress. There was no overlap in staini ng of GFAP+ astrocytes and MAP-2+13+ oligodendrocytes. MAP-2+13 was also ex pressed in intermediate filament-negative "radial glia" extending from the central canal to the subpial surface. In the mature CNS, MAP-2+13 also mark ed cells of oligodendroglial morphology, but these cells were rare. These f inding demonstrate that in the human CNS, MAP-2+13 is a novel protein trans iently expressed in cells of oligodendroglial lineage. (C) 2000 Wiley-Liss, Inc.