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The effect of the shiverer mutation on myelin basic protein expression in homozygous and heterozygous mouse brain
Abstract:
We report (a) that the shiverer mutation has pleiotropic phenotypic effects on myelin basic protein expression in the CNS of homozygous (shi/shi) mice and (b) that each of the effects of the shiverer allele is expressed co-dominantly with the wild-type allele in heterozygous (+/shi) animals. First, the total amount of myelin basic protein, as determined by radioimmunoassay, that accumulates in the CNS is approximately 0.1% of the wild-type amount in shi/shi animals and approximately 50% in +/shi animals. Second, the four major forms of myelin basic protein, with molecular weights of 21,500, 18,500, 17,000, and 14,000, that are present in wild-type mouse CNS are undetectable in either whole brain or purified myelin of shi/shi animals, and each of the four proteins is reduced commensurately in brain and myelin of +/shi animals. Third, the small amount of myelin basic protein-related material that does accumulate in the shi/shi brain consists of several polypeptides, with molecular weights ranging from 25,000 to 100,000, the pattern of which is different from that found in wild-type brain. The pattern of myelin basic protein-related polypeptides in +/shi brain is a composite of the wild type and the shiverer mutant. Fourth, messenger RNA from shi/shi brain, when translated in vitro, encodes a set of myelin basic protein-related polypeptides qualitatively similar to that encoded by wild-type messenger RNA, except that the 18,500 and 14,000 translation products are greatly reduced, while other myelin basic protein-related translation products are spared. The pattern of myelin basic protein-related translation products for +/shi messenger RNA is intermediate between the patterns for +/+ and shi/shi messenger RNAs. The results suggest that the genetic lesion in the shiverer mutation impinges on the structural gene (or genes) encoding myelin basic protein or on a cis-acting regulatory element controlling that gene (or genes).
Insights
The shiverer mutation in mice significantly impacts myelin basic protein (MBP) expression in the central nervous system (CNS). This mutation affects MBP levels, forms, and related mRNA, with effects being co-dominant in heterozygous animals.
Area of Science:
- Neuroscience
- Genetics
- Molecular Biology
Background:
- Myelin basic protein (MBP) is crucial for central nervous system (CNS) myelin formation.
- The shiverer mutation in mice provides a model to study MBP gene regulation and function.
- Understanding MBP expression is key to deciphering myelin disorders.
Purpose of the Study:
- To investigate the pleiotropic phenotypic effects of the shiverer mutation on MBP expression in mouse CNS.
- To determine the co-dominant nature of the shiverer allele with the wild-type allele in heterozygous mice.
- To elucidate the molecular basis of MBP alterations caused by the shiverer mutation.
Main Methods:
- Radioimmunoassay to quantify MBP levels in homozygous (shi/shi) and heterozygous (+/shi) mice.
- Analysis of MBP forms and related polypeptides in brain and purified myelin.
- In vitro translation of messenger RNA (mRNA) from shi/shi and +/shi mouse brains to assess MBP-related products.
Main Results:
- Homozygous shi/shi mice showed approximately 0.1% of wild-type MBP levels, while heterozygous +/shi mice had approximately 50%.
- All four major MBP forms were undetectable in shi/shi mice and reduced in +/shi mice.
- Shiverer mutation affected MBP-related polypeptides and mRNA translation products, with intermediate patterns in heterozygotes.
Conclusions:
- The shiverer mutation has significant, co-dominant effects on MBP expression in the CNS.
- The genetic lesion likely affects the structural gene for MBP or a cis-acting regulatory element.
- These findings provide insights into MBP gene regulation and the molecular pathology of myelin defects.