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The differentiation of synthesis from incorporation of basic protein in Quaking mutant mouse myelin
Abstract:
The incorporation of radioactive label into the myelin basic protein isolated from whole brain and from purified myelin of Quaking mice and normal littermates was compared. four Quaking mice (32 days) and 4 littermate controls were injected intracranially with 150 muCi [2-3H]glycine and 25 muCi of [2-14C]glycine, respectively. One hour later, the 8 mice were sacrificed and their brains combined for common homogenization. The 3H/14C ratios of the small and large basic protiens in whole brain were 3.44 and 2.48 respectively, while the 3H/14C ratios for these proteins in myelin were 0.79 and 1.00, respectively. In the same experiment, the microsomal fraction had a 3H/14C ratio of 2.98 which is the expected ratio for normal incorporation. The results indicate that the synthesis of basic protein in whole brain of Quaking mouse proceeds at a normal rate, but specifically, the incorporation of basic protein into myelin is depressed suggesting a defect at the step of assembly of myelin components into a final membrane product.
Insights
The Quaking mouse model shows normal synthesis of myelin basic protein in the whole brain. However, its incorporation into the myelin sheath is significantly reduced, indicating a defect in myelin assembly.
Area of Science:
- Neuroscience
- Biochemistry
- Genetics
Background:
- The Quaking mouse is a model organism for studying myelin disorders.
- Myelin basic protein (MBP) is a critical component of the myelin sheath.
Purpose of the Study:
- To investigate the synthesis and incorporation of myelin basic protein (MBP) in Quaking mice.
- To determine if the Quaking mutation affects MBP synthesis or its assembly into myelin.
Main Methods:
- Quaking mice and littermate controls were injected with radioactive glycine isotopes ([2-3H]glycine and [2-14C]glycine).
- Brains were analyzed for the incorporation ratios of radioactive labels into MBP in whole brain and purified myelin fractions.
- Microsomal fractions were analyzed as a control for normal incorporation.
Main Results:
- The synthesis rate of MBP in the whole brain of Quaking mice was comparable to controls.
- The incorporation of MBP into purified myelin was significantly lower in Quaking mice compared to controls.
- The 3H/14C ratios indicated normal incorporation in the microsomal fraction, but depressed incorporation into myelin.
Conclusions:
- The Quaking mutation does not impair the synthesis of myelin basic protein.
- A defect in the assembly of myelin components into the final membrane structure is suggested in Quaking mice.
- This points to a specific issue in myelin formation rather than protein synthesis.
