MICROTUBULE-ASSOCIATED PROTEINS IN DEVELOPING OLIGODENDROCYTES - TRANSIENT EXPRESSION OF A MAP2C ISOFORM IN OLIGODENDROCYTE PRECURSORS

The morphological differentiation of oligodendrocytes is characterized by the formation of multiple, microtubule-rich processes which endow these cells with the ability to myelinate many axons simultaneously. S ince microtubule-associated proteins (MAPs) strongly influence the str ucture and function of microtubules, we have investigated their expres sion in cultured differentiating oligodendrocytes in order to gain ins ights into MAP function during process formation and stabilization. MA P1B has been compared with two other structural MAPs: MAP4, which is a n ubiquitously expressed protein, and MAP2, which hitherto was thought to be confined to neurons and reactive astrocytes, Immunofluorescence microscopy showed that the colocalization of MAP4 with microtubules i n oligodendrocyte processes is not as extensive as found previously fo r MAP1B (Vouyiouklis and Brophy: J Neurosci Res 35:257-267, 1993). Nev ertheless, like MAP1B, the expression of MAP4 increases during oligode ndrocyte differentiation. In contrast, the expression of MAP2 is trans iently elevated in preoligodendrocytes but declines precipitously at t he onset of terminal differentiation. Cells of the oligodendrocyte lin eage exclusively express a novel isoform of MAP2c which is primarily l ocalized in the cell bodies of preoligodendrocytes. This suggests that MAP2c assists in the initiation of process extension rather than in t he stabilization of microtubules in the cytoplasm-filled membranous ex tensions of mature cells. MAP-tau was not expressed at any development al stage by oligodendrocytes. The distinct subcellular localizations a nd patterns of developmental expression of MAP1B, MAP4, and MAP2c sugg est that these MAPs have different roles in the regulation of the micr otubule network during the differentiation of myelin-forming oligodend rocytes. (C) 1995 Wiley-Liss, Inc.