Radial component of the central myelin in neurologic mutant mice

The radial component of central myelin, a series of radially oriented interlamellar tight junctions, was investigated in three neurologic mutant mice with myelin disorders--quaking, jimpy, and twitcher. In normal adult mice, the radial component of compacted myelin sheaths was usually localized deep in the myelin sheath lying under the cytoplasm of oligodendroglia, in particular between outer and inner tongues. In quaking mice, there were numerous rows of interlamellar tight junctions in the compacted myelin sheaths, and a single tight junction was frequently found between the opposing plasma membranes of oligodendroglia. The junctions were usually closely associated with cytoplasmic islands of oligodendroglia, but redundant myelin sheaths without associated axons or islands of oligodendroglia also occasionally revealed numerous radial components or rows of interlamellar tight junctions. In jimpy mice, the radial component was very poorly developed and could not be detected in the majority of myelin sheaths. Rare radial components were usually extended only partially across the myelin sheaths. In contrast to quaking and jimpy mice, the pattern and distribution of the radial component in twitcher mice were identical in the preclinical stage to that of the normal mouse. These observations further suggest that myelination is abnormal in quaking and jimpy mice but not in the twitcher mouse.