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Myelin basic protein is affected by reduced synthesis of myelin proteolipid protein in the jimpy mouse
1Research Institute, Hospital for Sick Children, Toronto, Ont., Canada.
Abstract:
Myelin basic proteins (MBPs) from 6-day-old, 10-day-old, 20-day-old and adult normal mouse brain were compared with those from 20-day-old jimpy (dysmyelinating mutant) mouse brain to determine the effect of reduced levels of proteolipid protein (PLP) on MBPs. Alkaline-urea-gel electrophoresis showed that 6-day-old and 10-day-old normal and jimpy MBPs lacked charge microheterogeneity, since C8 (the least cationic of the components; not be confused with complement component C8) was the only charge isomer present. In contrast, MBPs from 20-day-old and adult normal mouse brain displayed extensive charge microheterogeneity, having at least eight components. A 32 kDa MBP was the major isoform observed on immunoblots of acid-soluble protein from 6-day-old and 10-day-old normal and 20-day-old jimpy mouse brain. There were eight bands present in 20-day-old and adult normal mouse brain. Purified human MBP charge heteromers C1, C2, C3 and C4 reacted strongly with rat 14 kDa MBP antiserum, whereas the reaction with human C8 was weak. This suggested that MBPs from early-myelinating and jimpy mice did not react to MBP antisera because C8 was the major charge isomer in these animals. Purification of MBPs from normal and jimpy brain by alkaline-gel electrophoresis showed that both normal and jimpy MBPs have size heterogeneity when subjected to SDS/PAGE. However, the size isoforms in normal mouse brain (32, 21, 18.5, 17 and 14 kDa) differed from those in jimpy brain (32, 21, 20, 17, 15 and 14 kDa) in both size and relative amounts. Amino acid analyses of MBPs from jimpy brain showed an increase in glutamic acid, alanine and ornithine, and a decrease in histidine, arginine and proline. The changes in glutamic acid, ornithine and arginine are characteristic of the differences observed in human C8 when compared with C1.
Insights
Myelin basic proteins (MBPs) in jimpy mice, a dysmyelinating mutant, show altered charge and size heterogeneity compared to normal mice. These changes in MBP composition may explain their reduced reactivity with MBP antisera.
Area of Science:
- Neuroscience
- Biochemistry
- Genetics
Background:
- Myelin basic proteins (MBPs) are crucial for myelin sheath formation and maintenance in the central nervous system.
- The jimpy mouse is a model for dysmyelination, characterized by reduced levels of proteolipid protein (PLP).
Purpose of the Study:
- To investigate the impact of reduced proteolipid protein (PLP) levels on the composition of myelin basic proteins (MBPs) in jimpy mice.
- To compare MBP charge and size heterogeneity between normal and jimpy mouse brains at different developmental stages.
Main Methods:
- Alkaline-urea-gel electrophoresis was used to analyze MBP charge microheterogeneity.
- Immunoblots and SDS/PAGE were employed to examine MBP isoforms and size heterogeneity.
- Amino acid analysis was performed on MBPs from jimpy and normal mouse brains.
Main Results:
- MBPs from early-myelinating (6-10 day old) normal and jimpy mice lacked charge microheterogeneity, with only the C8 isomer present.
- MBPs from adult normal mice exhibited extensive charge microheterogeneity (at least eight components).
- Jimpy mouse MBPs displayed different size isoforms and relative amounts compared to normal mouse MBPs, with altered amino acid composition.
Conclusions:
- The C8 MBP isomer is predominant in early development and in jimpy mice, potentially explaining their weak reaction with MBP antisera.
- Differences in MBP size heterogeneity and amino acid composition in jimpy mice suggest a link between PLP levels and MBP processing.
- These findings contribute to understanding the molecular basis of dysmyelination and MBP heterogeneity.