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Molecular genetic analysis of the mldr mouse: a spontaneous revertant at the mld locus containing a recombinant
K Ainger1, E Barbarese, L Berman
1Department of Biochemistry, University of Connecticut Health Center, Farmington 06032.
Abstract:
The mld mutation is a complex genetic lesion affecting the myelin basic protein (MBP) locus in the mouse. The mutation consists of a variety of DNA rearrangements including: tandem duplication of the MBP structural gene, partial inversion of the 3' end of the upstream gene copy, duplication of a region flanking the rearrangement junction in the upstream copy and insertion between the two gene copies of a segment of extraneous DNA not associated with the wild-type MBP locus. The net result of the mutation is a dysfunctional MBP locus. Homozygous mld/mld mice produce very little MBP and consequently very little myelin. They exhibit a clinical phenotype characteristic of hypomyelination (shaking, convulsions). We have discovered a revertant mld mouse which does not exhibit clinical symptoms of hypomyelination. Genetic analysis indicates that the reversion is allelic to mld. We have designated the revertant locus mldr. Restriction analysis of mldr genomic DNA indicates that there is a single intact MBP gene. Analysis of various junction regions using the polymerase chain reaction indicates that the single MBP gene in mldr is derived by recombination from the 5' end of the upstream gene and the 3' end of the downstream gene. Studies on MBP expression in mldr mice indicate that the developmental regulation, level of expression and pattern of post-transcriptional processing of MBP gene products in mldr are similar to wild type. These results indicate that the recombinant MBP gene in mldr is fully functional. From this we infer that the MBP-deficient phenotype of the original mld mutant is attributable to the complex rearrangements in the upstream gene copy which render the locus dysfunctional.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
The mld mutation in mice causes hypomyelination due to complex DNA rearrangements affecting the myelin basic protein (MBP) gene. A revertant mldr mouse with a functional MBP gene demonstrates that these rearrangements, not the gene itself, cause the disease.
Area of Science:
- Neuroscience
- Genetics
- Molecular Biology
Background:
- The myelin basic protein (MBP) gene locus in mice is affected by the mld mutation, a complex genetic lesion.
- Homozygous mld/mld mice exhibit hypomyelination, producing minimal MBP and myelin, leading to clinical symptoms like shaking and convulsions.
Purpose of the Study:
- To investigate the genetic basis of the mld mutation and identify the cause of hypomyelination.
- To characterize a newly discovered revertant mld mouse (mldr) and its functional MBP gene.
Main Methods:
- Restriction analysis of mldr genomic DNA.
- Polymerase chain reaction (PCR) analysis of junction regions.
- Analysis of MBP expression in mldr mice.
Main Results:
- The mld mutation involves tandem duplication, partial inversion, and insertion of extraneous DNA within the MBP locus.
- A revertant mldr mouse possesses a single, intact MBP gene formed by recombination between the upstream and downstream gene copies.
- MBP expression in mldr mice is similar to wild-type, indicating a fully functional recombinant MBP gene.
Conclusions:
- The dysfunctional MBP locus in mld mice is caused by complex DNA rearrangements, not an intrinsic defect in the MBP gene itself.
- The recombinant MBP gene in mldr mice is functional, restoring normal myelin production and eliminating hypomyelination symptoms.