The neuronal adhesion protein TAG-1 is expressed by Schwann cells and oligodendrocytes and is localized to the juxtaparanodal region of myelinated fibers

The neural cell adhesion molecule TAG-1, which is a glycosylphosphatidylinositol-linked member of the Ig superfamily, is expressed by various neuronal populations in the developing CNS and PNS. We demonstrate here that Schwann cells and oligodendrocytes also express TAG-1. In the PNS, TAG-1 is detected in ensheathing Schwann cells early postnatally and is maintained throughout adulthood. In mature myelinated fibers of the CNS and PNS, TAG-1 is localized to the juxtaparanodal region. The CNS of the UDP-galactose ceramide galactosyl transferase^-/- (CGT^-/-) mouse mutants, which do not synthesize the abundant galactolipids of myelin, display severely disrupted axoglial interactions at the paranodal region. In contrast, axoglial interactions in the PNS of these mutants are less affected. Interestingly, TAG-1 localization is completely undetected in myelinated fibers of the CNS. In the PNS of these mutants, TAG-1 abnormally localizes in the paranodal region. These data raise the intriguing possibility that TAG-1 localization in the juxtaparanodal area mediates, or at least requires, the axoglial contact normally displayed in this region. The abnormal localization of TAG-1 in the CGT mutants might contribute to the disrupted axoglial interactions observed in these animals.