Oligodendroglial expression and deposition of four major myelin constituents in the myelin sheath during development. An in vivo study.

We have studied the sequence of expression in the oligodendrocyte of four myelin constituents: galactosylceramide (GalC), myelin basic protein (MBP), proteolipid protein (PLP) and Wolfgram protein (W1). These investigations were performed on freshly dissociated cell preparations from mouse olfactory bulb and cerebellum before and during early myelinogenesis. Our data showed that the first myelin antigen to be detected in the oligodendrocyte was GalC, followed 24 h later by W1 and after a 5-day time lag (relative to GalC) by MBP. Expression of PLP occurred shortly after that of MBP. This sequence of events was identical in the cerebellum and in the olfactory bulb, but it commenced earlier in the cerebellum (E18) than in the olfactory bulb (P2). Deposition of these components in the nascent myelin sheaths was studied on tissue sections. These histological preparations showed that the temporal order of deposition of the myelin constituents did not correlate with their order of expression in the oligodendrocyte. As judged both by the intensity of the labeling and the number of positive fibers, W1 and MBP were the first antigens to be deposited, followed by PLP and finally by GalC. Furthermore, this deposition process was initiated immediately after completion of expression of these antigens in the oligodendrocyte.