Myelin Palingenesis

Myelin is a membrane with unique characteristics that set it apart from any other membrane. It has a very high lipid:protein ratio (approximately 75:25) not found in other multilamellar membranes; it has a high content of two glycolipids--galactocerebrosides and sulfatides--which account for 26.5% of its lipids. The physiological role of these glycolipids in myelin and/or oligodendrocytes is unknown, but evidence that Abs directed against them interfere with myelination has been presented. Moreover, one of the early events in the process of oligodendrocyte differentiation prior to myelination is the acquisition of galactocerebroside on their surface. In earlier work, we have demonstrated that adhesion of oligodendrocytes to a positively charged substratum signals the commencement of myelinogenesis. Among the events that take place following adhesion are the rapid synthesis of glycolipids. Since over time in culture, oligodendrocytes elaborate multilamellar membranes that contain all the myelin characteristic proteins, we undertook to investigate whether these structures also accumulate myelin characteristic glycolipids. We have used three monoclonal antibodies--two are directed against galactocerebroside, the third one is an antisulfatide--in conjunction with the immunogold method, at the electron microscopic level, to examine the distribution of these glycolipids in the multilammelar structures that accumulate in long-term oligodendrocyte cultures. Our data show that galactocerebrosides and sulfatides are present in the multilamellar structures. Staining is easily demonstrated on the outermost membrane. However, as was the situation with myelin proteins, detection of these glycolipids on the inner lamellae is only achieved at the expense of destroying the ultrastructure. This is so, independent of whether the structures are compact or not.(ABSTRACT TRUNCATED AT 250 WORDS)