Organization and functional roles of the cytoskeleton in oligodendrocytes

Mature oligodendrocytes are characterized by their numerous cytoplasmic ext ensions and flat membranous sheets. These sheets contain an extensive cytos keletal network of microtubules (MTs) that maintain the cellular morphology , are specifically important for cellular sorting, and provide the rails fo r organelle trafficking. Mitochondria are localized in the primary and seco ndary processes and follow the tracks of the MTs in the cytoplasmic extensi ons. Oligodendrocytes express microtubule associated proteins (MAPs), speci fically MAP2 and tau, which might be involved in the regulation and stabili zation of the dynamic MT network in the myelin-containing cellular processe s. Tau and MAP2 heterogeneity increases during oligodendroglia maturation, and in mature oligodendrocytes tau mRNA with four MT binding domains are mo re prominent than in progenitor cells. Filamentous cell inclusions are a un ifying mechanism underlying a variety of late-onset neurodegenerative disor ders and have mainly been viewed as neuron-specific. Recent evidence indica ted that glial changes occur in CNS degenerative diseases and seem to be a more common feature than previously thought. Glial fibrillary tangles (GFTs ) in oligodendrocytes were observed in familial multiple system tauopathy, and glial cytoplasmic inclusions (GCIs) and oligodendroglia degeneration ar e the histological hallmark of multiple system atrophy (MSA). GCIs are asso ciated with MTs and contain stress proteins and MAPs. Thus, neurons and gli al cells share common cytoskeletal pathologies. During health and disease, MAPs might be important regulators of the structural stability and plastici ty of the oligodendroglia cytoskeleton. (C) 2001 Wiley-Liss, Inc.