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Inefficient transcription of the myelin basic protein gene possibly causes hypomyelination in myelin-deficient mutant
Abstract:
A hereditary dysmyelination mutation, named myelin deficient (mld), is considered to be allelic to shiverer, a deletion mutation of the myelin basic protein (MBP) gene. The present study showed that MBP expression is greatly reduced in mld, but that it is still detectable. Northern blot analysis revealed that the pronounced decrease in the MBP level in mld resulted from a reduced mRNA level and was not caused by deletion of a large portion of the MBP gene as in shiverer. Southern blot studies with BamHI-digested chromosomal DNA suggested some part of the MBP gene, at least the 5'-portion, was duplicated in mld. These results indicated that the mld and shiverer mutations were different from each other, even though genetic allelism between the two was reconfirmed. We also examined the developmental pattern of the gene expression of MBP and that of another protein, myelin proteolipid protein (PLP), specifically expressed in the oligodendrocyte, in mld by RNA dot blot study. The mRNA level of MBP in mld was greatly reduced during the active myelination stages, gradually increasing and remaining constant in the later stages. The PLP-mRNA content in mld was almost normal (60-80% that of control) at any stage of development. All these findings imply that the primary defect in mld is due to reduced transcriptional activity of the MBP gene.
Insights
The myelin deficient (mld) mutation reduces myelin basic protein (MBP) gene expression due to decreased mRNA levels, not gene deletion. This hereditary dysmyelination defect stems from reduced MBP gene transcriptional activity.
Area of Science:
- Neuroscience
- Genetics
- Molecular Biology
Background:
- Hereditary dysmyelination mutations, like myelin deficient (mld) and shiverer, affect myelin basic protein (MBP) gene.
- The mld mutation was previously considered allelic to the shiverer mutation, a deletion in the MBP gene.
Purpose of the Study:
- To investigate the molecular basis of the myelin deficient (mld) mutation.
- To differentiate the mld mutation from the shiverer mutation at the genetic and molecular level.
- To analyze the expression patterns of myelin basic protein (MBP) and myelin proteolipid protein (PLP) in mld.
Main Methods:
- Northern blot analysis to assess MBP mRNA levels.
- Southern blot analysis with BamHI-digested chromosomal DNA to study MBP gene structure.
- RNA dot blot analysis to examine developmental gene expression of MBP and PLP.
Main Results:
- MBP expression was significantly reduced but detectable in mld, resulting from decreased mRNA levels.
- Unlike shiverer, mld did not involve a large deletion of the MBP gene; Southern blots suggested a duplication of the 5'-portion.
- MBP mRNA levels were reduced during active myelination in mld, while myelin proteolipid protein (PLP) mRNA levels remained near normal.
Conclusions:
- The mld and shiverer mutations are distinct, despite genetic allelism.
- The primary defect in the mld mutation is likely reduced transcriptional activity of the MBP gene.
- Dysmyelination in mld is specifically linked to impaired MBP gene expression.