Myelin Basic Protein Gene Expression, Oligodendrocyte Metabolism and Myelin Stability in the MLD Mutant Mouse
Myelin-deficient (mld) is an autosomal recessive mutation in mice exhibiting a severe deficit in the synthesis of myelin basic protein (MBP). In order to understand the mechanisms involved in the regulation of MBP synthesis in these mutants, the amounts of MBP and MBP mRNA were measured in control, heterozygous and homozygous mld brains. Using in vitro translation of poly(A+) RNA in a cell-free system, in situ hybridization, and filter hybridization with a radiolabelled probe pMBP-1, the levels of MBP and MBP-specific mRNA were found to be very low but detectable in mld homozygotes and intermediate in heterozygotes. MBP specific mRNA and its translation products were of normal size. These results indicate that the mld mutation is expressed co-dominantly in heterozygotes and affects a cis-acting regulatory element controlling the MBP gene.
In the presence of low amounts of MBP, the myelin lamellae were poorly compacted and unstable. This instability was demonstrated by increased levels of cholesterol esters, the presence of degraded myelin-associated glycoprotein (dMAG), and fast turnover rates of MAG and sulfatides. In mld, oligodendrocytes accumulated inclusion bodies, vacuoles and rough endoplasmic reticulum. This material was heavily immunostained for MAG. Simultaneously, MAG and Wolfgram protein, two proteins present in uncompacted myelin sheath and paranodal loops exhibited increased rates of synthesis. These results suggest that the regulation of the synthesis of myelin constituents cannot proceed when a major myelin protein is missing.
KeywordsCholesterol Sucrose Sedimentation Electrophoresis Polypeptide
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- 3.D. P Doolittle and K. M. Schweikart, Myelin deficient, a new neurological mutant in the mouse, J. Heredity 68: 331 (1977).Google Scholar
- 4.F. Lachapelle, C. de Baecque, C. Jacque, J.-M. Bourre, A. Delassalle, D. Doolittle, J. J. Hauw, and N. Baumann, Comparison of morphological and biochemical defects of two probably allelic mutations of the mouse, myelin deficient (mld) and shiverer (shi), in: “Neurological Mutations Affecting Myelination, INSERM Symposium No 14” N. Baumann, ed., Elsevier/North-Holland Biomédical Press, Amsterdam, 27–32 (1980).Google Scholar
- 5.J. M. Bourre, C. Jacque, A. Delassalle, J. Nguyen-Legros, O. Dumont, F. Lachapelle, M. Raoul, C. Alvarez, and N. Baumann, Density profile and basic protein measurements in the myelin range of particulate material from normal developing mouse brain and from neurological mutants (Jimpy; Quaking; Trembler; Shiverer; and its mld allele) obtained by zonal centrifugation, J. Neurochem., 35: 458 (1980).CrossRefGoogle Scholar
- 18.D. A. Kirschner, A. L. Ganser, and D. L. D. Caspar, Diffraction studies of molecular organization and membrane interactions in myelin, in: “Myelin”, P. Morell, ed., Plenum Press, New York, 51 (1984).Google Scholar
- 19.G. Almazan, H. Ginalski-Winkelmann, and J.-M. Matthieu, Myelin metabolism in a dysmyelinating mutant mouse (mld), Trans. Am. Soc. Neurochem. 14: 129 (Abstr.) (1983).Google Scholar
- 20.J.-M. Matthieu, Myelin basic protein and the stability of the multila-mellar myelin structure, Bull. Schwei. Akad. Med. Wiss. 101 (1982).Google Scholar
- 21.J.-M. Matthieu, H. Ginalski-Winkelmann, D. Johnson, P. Burgisser, R. H. Quarles, J. F. Poduslo, and R. Krstic, Composition and metabolism of CNS myelin from young mld mice, Trans. Am. Soc. Neurochem. 13: 215 (Abstr.) (1982).Google Scholar
- 22.F. X. Omlin and J.-M. Matthieu, Myelin-associated glycoprotein (MAG): Immunocytochemical localization in both oligodendrocytes and myelin loops of myelin deficient (mld) mutant mice, Soc. Neurosci. Abstr. 10: 949 (1984).Google Scholar
- 23.J.-M. Matthieu and F. X. Omlin, Myelin-associated glycoprotein in the CNS of myelin-deficient (mld) mutant mice. An immunochemical and immunocytochemical study, Trans. Am. Soc. Neurochem. 16: 139 (Abstr.) (1985).Google Scholar
- 24.M. Kimura, H. Inoko, M. Katsuki, A. Ando, T. Sato, T. Hirose, H. Takashima, S. Inayama, H. Okano, K. Takamatsu, K. Mikoshiba, Y. Tsukada, and I. Watanabe, Molecular genetic analysis of myelin-deficient mice: shiverer mutant mice show deletion in gene(s) coding for myelin basic protein, J. Neurochem. 44: 692 (1985).CrossRefGoogle Scholar
- 30.N. K. Zeller, T. N. Behar, M. E. Dubois-Dalcq, and R. A. Lazzarini, The timely expression of myelin basic protein gene in cultured rat brain oligodendrocytes is independent of continuous neuronal influences, J. Neurosci. 5: 2955 (1985).Google Scholar
- 36.D. E. Frail and P. E. Braun, Two developmentally regulated messenger RNAs differing in their coding region may exist for the myelin-associated glycoprotein, J. Biol. Chem. 259: 14857 (1984).Google Scholar
- 41.E. E. Golds and P. E. Braun, Organization of membrane proteins in the intact myelin sheath, J. Biol. Chem. 251: 4729 (1976).Google Scholar
- 42.J. F. Poduslo and P. E. Braun, Topographical arrangement of membrane proteins in the intact myelin sheath, J. Biol. Chem. 250: 1099 (1975).Google Scholar
- 43.A. Ganser and D. A. Kirschner, Myelin structure in the absence of basic protein in the shiverer mouse, in: “Neurological Mutation Affecting Myelination, INSERM Symposium No 14”, N. Baumann, ed., Elsevier/North Holland Biomedical Press, Amsterdam, 171 (1980).Google Scholar
- 53.M. V. Gardinier, P. L. Deininger, and W. B. Macklin, Myelin proteolipid mRNAs in normal and jimpy brain development, Trans. Am. Soc. Neurochem., 17: 109 (1986).Google Scholar
- 55.A. Akowitz, K. Scheid, E. Barbarese, and J. H. Carson, A partial duplication of the myelin basic protein gene in mld mice, Trans. Am. Soc. Neurochem., 17: 108 (1986).Google Scholar