Axoglial junctions in the mouse mutant shiverer

Analysis of Shiverer central nervous tissue by the freeze-fracture method shows that axoglial junctions of the type found normally in the paranodal region occur commonly despite the gross reduction in myelin. On a substructural level these junctions appear identical to those that form between paranodal oligodendroglial processes and the axolemma. On a grosser level, however, they are bizarre in shape, arrangement and distribution. Isolated glial processes, or small sheaves of them, course among axons and form such junctions in an irregular patchy manner, usually without apparent relationship to paranodal regions. These aberrant junctions may be oriented transversely, obliquely or longitudinally with respect to the axonal axis. Axolemmal E face particle accumulations, which characterize normal nodes of Ranvier, are usually not found in the membrane adjacent to the aberrant junctional patches. Thus, axoglial junctional specializations of the paranodal type can form in this mutant in the absence of the myelin proteins that are deficient in Shiverer, and such junctions may appear in areas not related to other paranodal or nodal structures. The relevance of these findings to differentiation of the axolemma and to the neurological defects in this mutation is discussed.