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

中枢神经系统(CNS)髓鞘的结构特征之一是存在放射状成分，它在动物的广泛系统发育中被描述为连接复合体，在髓鞘中呈放射状和之字形分布。然而，其生化成分仍不得而知。我们先前报道，髓鞘相关的少突胶质细胞碱性蛋白(MOBP)在mRNA水平上仅在少突胶质细胞中大量表达，仅次于髓鞘碱性蛋白(MBP)和蛋白脂蛋白(PLP)，并且与MBP有一些共同的特征。我们在这里发现MOBP也富含在放射状成分的髓鞘组分中，提示MOBP与放射状成分有关。在MOBP缺陷的小鼠中，形成了致密的髓鞘，但径向成分是直的，相邻的两个径向成分之间的间隙较窄。结合冰冻断口观察表明，径向成分的胞质成分MOBP在一定的时间间隔内与径向成分的胞外成分紧密结合，使径向成分由径向的直线方向变为排列整齐的斜字形方向。此外，暴露于六氯苯致髓鞘损伤的MOBP缺陷小鼠的髓鞘显示主要致密线变宽。我们的结论是，MOBP对于放射状成分的正常组织是必不可少的，并维持髓鞘的完整性。

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.