Developmental profile and differential localization of mRNAs of myelin proteins (MBP and PLP) in oligodendrocytes in the brain and in culture.

We applied the in situ hybridization technique to localize the mRNAs for two myelin proteins: proteolipid protein (PLP) and myelin basic protein (MBP). In the oligodendrocyte in primary culture, PLP mRNA was located exclusively in the cell body throughout development. However, MBP mRNA was first located in the cell body and was rapidly distributed to the processes but not to the membranous sheets formed from the tips and lengths of the processes. Expression of PLP and MBP genes progressed in the caudo-cranial direction in the brain as far as we examined it in the tissue sections up to the 30th postnatal day: mRNAs of both genes were first detected in the pons and the medulla oblongata on the 3rd postnatal day and then in the cerebellum and the anterior part of the brain. PLP mRNA was located exclusively in the cell body throughout development. The number of PLP mRNA-positive cells reached a plateau in the posterior part of the brain on the 18th postnatal day, whereas it continued to increase in the anterior part of the brain by the 30th day. MBP mRNA was first expressed in the cell body, but later, it was found along the myelin sheath.