Organization of oligodendroglial membrane sheets. I: Association of myelin basic protein and 2′,3′‐cyclic nucleotide 3′‐phosphohydrolase with cytoskeleton

Abstract

Membrane sheets elaborated by cultured murine oligodendroglia provide a unique system for examining associations between myelin proteins and cytoskeletal elements. Interactions can be observed and manipulated more readily than in the multilamellar myelin membrane in vivo. Immunocytochemical staining of 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) shows that it is distributed diffusely in some regions of membrane sheets, but colocalized with tubulin in lacy networks and major veins in other regions. Staining with phalloidin also reveals two distributions of F-actin: 1) small aggregates within the diffuse CNPase regions and 2) filaments colocalized with tubulin and CNPase in the lacy networks and veins. Application of colchicine at 10 micrograms/ml for 4 hr disrupts microtubular structures in the lacy network, while those in major veins remain intact. This suggests that microtubules in the lacy network are treadmilling more rapidly than those in the major veins. The distribution of CNPase and F-actin is not altered under these conditions. In contrast, cytochalasin B disrupts F-actin, microtubules, and CNPase in the lacy networks, indicating that cross-linking between these three proteins is disrupted. Both colchicine and cytochalasin B cause fusion of myelin basic protein (MBP) domains in membrane sheets. This appears to be a consequence of disruption of microtubules in the lacy networks, which normally outline the MBP domains. In summary, these results provide evidence for 1) direct association of CNPase with F-actin and tubulin in cytoskeletal structures and 2) organization of MBP into domains via association with microtubules in the lacy networks.

Juxtanodin: An oligodendroglial protein that promotes cellular arborization and 2′,3′-cyclic nucleotide-3′-phosphodiesterase trafficking

“…Tubulin, actin, and associated proteins have been well documented in oligodendrocytes, but the molecular mechanisms underlying the motility of the oligodendroglia͞myelin sheath remain poorly understood (16). The following evidence supports a role of JN in binding͞ regulating oligodendroglial cytoskeleton: (i) JN showed substantial colocalization in the myelin sheath with CNPase, a known cytoskeleton-related oligodendroglial protein (17)(18)(19). ( The physiological functions of CNPase have been attributed to its roles in regulating tubulin polymerization͞distribution (17) and in myelin-axon interaction.…”

“…( The physiological functions of CNPase have been attributed to its roles in regulating tubulin polymerization͞distribution (17) and in myelin-axon interaction. CNPase also cross-links with actin (18,19). Like JN, CNPase is found mainly in the cytoplasmcontaining noncompact regions of the myelin sheath (20,21).…”

Classic 18.5- and 21.5-kDa Myelin Basic Protein Isoforms Associate with Cytoskeletal and SH3-Domain Proteins in the Immortalized N19-Oligodendroglial Cell Line Stimulated by Phorbol Ester and IGF-1

“…Associated microtubule-associated proteins (MAPs) such as tau link them [31-33, 66, 67]. Oligodendrocytes in culture produce membrane sheets containing major veins and a lacy network of cytoskeletal proteins, where actin filaments and microtubules are co-localized [68]. MBP is co-localized with these cytoskeletal veins of actin filaments and microtubules, and also with cortical actin filaments in cultured OLGs.…”

Microtubule Organization and Stability in the Oligodendrocyte

“…Mature oligodendrocytes do not contain intermediate filaments, although oligodendrocyte progenitors have been shown to contain vimentin (Raff et al, 1984). A number of authors have noted a relationship between cytoskeletal elements and myelin constituents (Dyer and Benjamins, 1989;Gillespie et al, 1989;Wilson and Brophy, 1989), and microtubules also seem to play a role in the spatial segregation of myelin protein mRNAs in the oligodendrocyte (Colman et al, 1982;Trapp et al, 1987;Amur-Umarjee et al, 1990).…”