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Rumpshaker behaves like juvenile-lethal Plp mutations when combined with shiverer in double mutant mice
S Billings-Gagliardi1, J J Nunnari, M K Wolf
1Department of Cell Biology, University of Massachusetts Medical School, Worcester, Mass. 01655, USA. Susan.Gagliardi@umassmed.edu
Abstract:
The phenotypes of double mutant mice whose genomes are homozygous for an Mbp (myelin basic protein) mutation and hemizygous for a juvenile-lethal Plp (proteolipid protein) mutation were compared in earlier studies. The results suggested that the shiverer Mpb mutation might have some unexplained ability to partially rescue oligodendrocytes (OLs) from the 'death sentence' that is imposed by the Plp mutations. Conversely, they also indicated that the juvenile-lethal Plp mutations may normalize shiverer OL morphology by reducing the numbers of microprocesses. The Plp mutation rumpshaker produces a mild hypomyelination without reduction in OL numbers and a normal lifespan. This report describes double mutant mice combining two Mbp mutations with rumpshaker, utilizing a common B6C3F1 hybrid-based genetic background. Initial studies on B6C3F1 rumpshaker optic nerve and spinal cord white matter showed unanticipated signs of OL death, with morphologic criteria suggestive of an apoptotic mechanism. In shiverer*rumpshaker double mutant mice, this small class of dying cells could not be identified. White matter morphology was similar to that of mice expressing only the shiverer mutation, except that OL microprocesses were far less abundant. This evidence suggests that, despite their distinctive phenotypic differences, rumpshaker may share more characteristics with the juvenile-lethal Plp mutations than has previously been recognized.
Insights
The myelin basic protein (MBP) mutation partially rescues oligodendrocytes (OLs) from proteolipid protein (PLP) mutation-induced death. Combining MBP and PLP mutations in mice reveals shared characteristics between PLP mutations and the rumpshaker mutation.
Area of Science:
- Neuroscience
- Genetics
- Cell Biology
Background:
- Previous studies compared double mutant mice with myelin basic protein (MBP) and juvenile-lethal proteolipid protein (PLP) mutations.
- These studies indicated potential rescue of oligodendrocytes (OLs) by the shiverer MBP mutation and normalization of OL morphology by PLP mutations.
- The PLP mutation rumpshaker causes mild hypomyelination without OL reduction and a normal lifespan.
Purpose of the Study:
- To investigate the phenotypes of double mutant mice combining two MBP mutations with the rumpshaker PLP mutation.
- To analyze the effects of these combined mutations on oligodendrocyte survival and white matter morphology.
- To compare the characteristics of the rumpshaker mutation with other juvenile-lethal PLP mutations.
Main Methods:
- Generation and analysis of double mutant mice (shiverer*rumpshaker) on a B6C3F1 hybrid background.
- Morphological examination of optic nerve and spinal cord white matter.
- Assessment of oligodendrocyte death and microprocess formation.
Main Results:
- Wild-type rumpshaker mice exhibited unexpected oligodendrocyte death with apoptotic features.
- In shiverer*rumpshaker double mutants, this class of dying cells was absent.
- White matter morphology in double mutants resembled shiverer mice, but with significantly fewer OL microprocesses.
Conclusions:
- The rumpshaker mutation may share more characteristics with juvenile-lethal PLP mutations than previously assumed.
- Despite distinct phenotypic differences, interactions between MBP and PLP mutations influence oligodendrocyte survival and morphology.
- Further research is warranted to elucidate the precise mechanisms underlying these interactions.
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