Fig. 6. Cultured oligodendrocytes develop morphologically and biochemically distinct membrane domains. (A) Confocal analysis of co-stained primary oligodendrocytes demonstrates association of PLP (green), MAG (red, top images) and MOG (red, bottom images) with distinct membrane domains. Dashed circles delineate cell bodies and boxed areas are enlarged in a' and a''. Asterisks indicate membrane sheets. Arrows indicate the typical localization of MAG (a') and MOG (a''). Scale bars: 5 µm. (B) Subfractionation of myelin and oligodendroglial membranes by discontinuous density gradient centrifugation in heavy (H), medium (M) and light (L) membrane fractions, analyzed by western blotting (nonreducing conditions, thus the dimeric form of PLP is prominent). Myelin was isolated from postnatal day 10 (P10) mouse brain at a developmental stage analogous to that of the cells in culture. Note that the compact myelin domain (indicated by PLP in light fractions) is beginning to develop at this early state of myelination and is thus underrepresented in the light fraction. Claudin11/OSP, which delineates the non-compact domain, is used as an additional marker. Syntaxin 6 was used as a marker of Golgi and endosomal membranes.