Synthesis of Myelin Membranes and Assembly of the Myelin Sheath

  The prevailing hypothesis of myelin sheath formation is that an OLG emits a process that upon reaching the axon surrounds it multiple times to generate the myelin sheath. The implication is that the myelin sheath is not more than a multilayer extension of a modified OLG plasma membrane (PM).

  However, several reports have established that OLG PM and the myelin sheath differ compositionally beyond the major myelin proteins and lipids/glycolipids. In this breakthrough publication ^[13], we have challenged this 50 year-old model by demonstrating that: i) myelin membranes (MyMs) – assembled as tubules – are synthesized as independent entities; ii) MyMs are packaged and matured in and transported by a novel organelle named “myelinophore organelle”(MFO); and iii) the myelin sheath is stochastically built by homotypic fusion of MyMs within the confines of an OLG process. The demonstration that the myelin sheath resides within the OLG process suggests that the axolemma and OLG PM face one another, thereby allowing for direct cross-talk between the two cell types.