Characterization of mouse myelin basic protein messenger RNAs with a myelin basic protein cDNA clone.

Abstract

Using a family of synthetic tetradecamer oligonucleotides as a primer for cDNA synthesis and a second family of tetradecamers as a hybridization probe, we have prepared and isolated a cDNA clone of mouse myelin basic protein (MBP). The clone, pNZ111, corresponds to the region of the mRNA that codes for an amino acid sequence present in all four major forms of MBP (2)(3)(4)(5). Large amounts of the membrane are produced relative to the size of the myelin-forming cell. The process involves the synthesis of myelin-specific proteins followed by their integration into the growing membrane. During early myelinogenesis, membranes are formed that are loosely whorled around the axon. As myelin maturation proceeds, compaction of these membranes occurs to form the tight multilamellar structure characteristic of myelin.The myelin basic protein (MBP) constitutes about 33% of the protein of the myelin sheath in the central nervous system and 1-10% in the peripheral (6, 7). In most species, the predominant form of the MBP has a molecular mass of 18.5 kilodaltons (kDa), and the primary sequence of this protein is well conserved in animals as distantly related as the chicken, human, and rat (8-10). Two major forms of MBP predominate in rats and mice: one of these corresponds to the single major protein found in other species (18.5 kDa) and the other has a molecular mass of 14 kDa. In rats, the 14-kDa MBP is identical in sequence to the 18.5-kDa MBP, except for an internal deletion of residues 118-158 [numbered according to Martenson (11)] near the carboxyl terminus of the protein (10, 12). Two quantitatively minor forms of MBP have been found in rats and mice-a 21.5-kDa protein that is presumably identical to the 18.5-kDa MBP, except for the inclusion of a 25-30 amino acid sequence in the NH2-terminal half of the molecule and a 17-kDa MBP that bears the same relationship to the 14-kDa MBP (13).Myelination occurs postnatally in mouse brain beginning 8-10 days postpartum and continuing actively for 7-10 wk, with the maximal rate of myelin deposition occurring at about 18 days (4). Maximal synthesis of the 18.5-kDa and 14-kDa MBPs occurs at 18 days in vivo and coincides closely with the peak of myelin synthesis (14). During myelin maturation in the mouse, the proportions of the four MBPs in the membrane change (15-17) and this may be due to alterations in the relative rates of synthesis of the four proteins with age. With maturation, the proportion of the two minor MBPs (i.e., the 21.5 kDa and 17 kDa in myelin falls relative to the 18.5-kDa proteins and the 14-kDa/18.5-kDa MBP ratio increases dramatically. This latter change has been correlated with the relative rate of synthesis of these two proteins in vivo (14). Recently, Carson et al. (18) have identified trace amounts of larger forms of MBP that appear during the early stages of myelination. Identification of these larger forms has depended on immunoreagents and the relationships of the amino acid sequences to the major MBPs have, as yet, not been determined.We have r...

Central Nervous System Inflammation and Neurological Disease in Transgenic Mice Expressing the CC Chemokine CCL21 in Oligodendrocytes

“…1C) showed transgene expression in their brain tissues. Consistent with previous reports (12,43), transgene expression driven by the 2-kb murine MBP promoter was developmentally regulated, peaking at 2-3 wk postnatally (data not shown). Expression of CCL19 or CCL21 protein in the CNS of the transgenic mice was analyzed by immunohistochemical staining.…”

Oligodendrocyte precursor hypercellularity and abnormal retina development in mice overexpressing PDGF‐B in myelinating tracts

“…Myelination takes place during the first weeks of postnatal life in the mouse (Zeller et al, 1984). That the 3.2 kb MBP promoter fragment used in this study gives the expression pattern of the endogenous MBP gene was demonstrated in a previous study (Foran and Peterson, 1992).…”

“…In the mouse, myelination and the initiation of MBP synthesis commences near birth. The MBP promoter is most active during the period of myelin acquisition peaking at 2-3 weeks after birth and decreasing thereafter to reach a relatively stable level at approximately one-fourth of the peak value (Zeller et al, 1984). In a previous transgenic investigation of MBP regulation, 3.2 kb of MBP 5Ј flanking sequences was shown to be capable of driving oligodendrocyte-specific expression of LacZ (Foran and Peterson, 1992).…”

Study of the expression of myelin proteolipid protein (lipophilin) using a cloned complementary DNA

“…To understand the basic defect in these diseases and the regulation of MBP and PLP expression, studies have been initiated to examine these proteins at the gene level. Recently the isolation of cDNA clones for MBP have been reported (10)(11)(12). We here describe the molecular cloning of a complementary DNA (cDNA) for PLP and provide preliminary evidence that the two proteins are coordinately regulated at the mRNA level during development.…”