Physiological and pathological roles of myelin-associated oligodendrocytic basic protein (MOBP) in myeklin of central nervous system.

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One of the structural features that characterize the central nervous system (CNS) myelin is the existence of the radial component, which has been described as a junctional complex in a wide phylogenetic range of animals, and runs radially and zigzaging through the myelin sheath. The biochemical composition, however, remains unknown. We previously reported that myelin-associated oligodendrocytic basic protein (MOBP) was abundantly expressed specifically in oligodendrocytes at the mRNA level, only next to myelin basic protein (MBP) and proteolipid protein (PLP) in rat, and shared several characteristics with MBP.We show here that MOBP was also enriched in the radial component-enriched myelin fraction, suggesting that MOBP was associated with the radial component. In MOBP-deficient mice, the compact myelin was formed, but the radial component was straight with a narrower space between two adjacent radial components. These observations combined with the freeze-fracture examination suggested that MOBP,cytoplasmic constituent of the radial component, was anchored tightly to the extracellular constituent of the radial component at some interval, and changed the course of the radial component from straight radial direction to well-organized oblique zigzag one. Furthermore, the myelin from MOBP-deficient mice exposed to hexachlorophene, known as a dysmyelinating agent, showed widening of the major dense lines. We conclude that MOBP is essential for normal organization of the radial component, and maintains the integrity of the myelin sheath.