Myelin galactolipids: Mediators of axon-glial interactions?

The precise alignment of myelin segments along the length of the axon is es sential for the saltatory propagation of an electrical impulse. Furthermore , node of Ranvier formation and function are dependent on the proper intera ctions between myelinating glial cells and the axon. Nevertheless, the mole cules that regulate the placement and association of myelinating cells with axons remain largely unidentified. Recently, however, the analysis of muta nt mice incapable of synthesizing the galactolipids of myelin has revealed defects in these processes. The galactolipid-deficient mice display alterat ions in the spacing of internodal segments along the axon: large unmyelinat ed gaps are common and overlapping myelin segments are observed. Moreover, the normal tight association between the lateral loops of the myelinating c ell and the axonal membrane at the paranode region is also disrupted in the se animals. Strikingly, there is a complete absence of transverse bands at the axon-glial junction, with the lateral loops frequently turning away fro m the axon. These data indicate that the galactolipids play an essential ro le in axon-glial interactions and node of Ranvier formation. GLIA 29:149-15 3, 2000. (C) 2000 Wiley-Liss, Inc.