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Twitcher (Galctwi) mice carry a recessive spontaneous mutation in the Galc (galactosylceramidase) gene. Homozygotes are characterized by a neurological leukodystrophy, and die by about 40 days of age.Read More +
The twitcher mouse is a neurological leukodystrophy mutant line first observed in 1976 at The Jackson Laboratory. The Galctwi mutation involves a G to A transition
at codon 355 of the Galc (galactosylceramidase) gene, changing it from tryptophan to a stop codon (p.W355*). Northern analysis of homozygotes shows an absence of the most abundant mRNA (Sakai, 1996).
Initially characterized on a mixed C57BL/6J and CE/J background, a neurological phenotype was first observed by day 30 and homozygotes did not survive beyond three months of age. (Duchen LW, et. al., 1980) Subsequent backcrosses to C57BL/6J and the generation of a full congenic (> 10 backcrosses) shortened the time to onset to approximately 21 days with death by 40 days. Head tremors and decreased body weight are initial clinical indicators and mice are generally less active than unaffected littermates. Muscle weakness in the hindlimbs is a promiment feature with the health of the mutants progressively declining until death. There is a significant lack of myelin in the twitcher CNS, along with astrocytic gliosis. The nerves in the PNS are also demyelinated. The mutant CNS and PNS contain multinucleated, periodic acid-Schiff-positive globoid cells. Electron microscopic analysis shows these cells contain paracrystalline inclusions and twisted tubules.
Galactosylceramidase (GALC) is the enzyme responsible for the initial step of galactosylceramide (or galactocerebroside) degradation. Galactocerebroside is one of the most abundant and unique lipid constituents of the myelin sheath and the twitcher mouse is a useful mutant in which to study myelina tion and myelin metabolism. This substrate of the enzyme GALC, however, does not accumulate in tissues of affected mice (or humans). The pathologies are believed to result from the abnormal accumulation of the cytotoxic metabolite galactosylsphingosine (psychosine), another substrate of GALC that inhibits protein kinase C, that causes myelin-forming cells of the CNS and PNS to dysfunction and undergo apoptosis. Levels of myelin protein mRNAs are normal through postnatal day 20 but decline after day 25, corresponding to the observed pathological demyelinating changes. The data indicate that specific gene expression during myelination appears normal initially. Astrogliosis in the CNS is initiated prior to the appearance of myelin pathologies (as early as postnatal day 15) and GFAP mRNA is highly upregulated after day 20, presumably as a response to demyelination. Cytokines are believed to play a major role in the inflammatory responses associated with the disease course. TNF-alpha and IL-6 in the CNS appear to be induced by the pathological condition; reactive astrocytes and microglia contribute to the pathogenic course in the CNS of these mutants.(Taniike et al., 1998; Kobayashi et al., 1980; Suzuki and Suzuki, 1995; LeVine and Brown, 1997; Matsushima et al., 1994).
The twitcher mutation (Galctwi) arose spontaneously at The Jackson Laboratory in 1976 in the CE/J strain when that inbred was at generation F69. Subsequent studies (Sakai, 1996) demonstrated that the mutation involves a G to A transition at codon 355 of the Galc (galactosylceramidase) gene, changing it from tryptophan to a stop codon (p.W355*). The mutant subline was sibling bred for 2 generations and then the mutation was moved onto the C57BL/6J background by means of ovarian transplantation cross-intercross breeding. The female host carrying the homozygous mutation was crossed to a C57BL/6J male and the obligate heterozygote offspring were intercrossed to produce more homozygous females for ovarian transplantation. In 1983 C57BL/6J females were bred with heterozygous males at generation +F2N8F1 to generate embryos for cryopreservation.
Frozen stocks have subsequently been replenished several more times, with recoveries producing both wildtype and heterozygous pups. Currently, live maintenance of this line involves crosses of heterozygotes (male or female) with wildtype or C57BL/6J (Stock # 000664) inbred mice. A PCR genotyping assay has taken the place of test crosses.
In 2021, a 48 SNP (single nucleotide polymorphism) panel analysis, with 43 markers covering all 19 chromosomes and the X chromosome, as well as 5 markers that distinguish between the C57BL/6J and C57BL/6N substrains, was performed on the fist generation rederived mice at The Jackson Laboratory. This showed some mice with all 43 markers throughout the genome suggesting a C57BL/6 genetic background, and all 5 markers that determine C57BL/6J from C57BL/6N were found to be C57BL/6J. The other mice had the same results with the exception of one heterozygous marker - the C57BL/6 substrain marker on chromosome 19 [~50 Mbp]. Because this marker is the same for C57BL/6N and CE/J, these data suggest the mice are predominantly C57BL/6J, with some CE/J genomic contribution on chromosome 19.
|Allele Type||Spontaneous (Null/Knockout)|
|Allele Synonym(s)||galc-; twi|
|Gene Symbol and Name||Galc, galactosylceramidase|
|Strain of Origin||CE/J|
|Molecular Note||Sequence analysis comparisons of cDNA from livers of mice homozygous for this allele and +/+ mice showed a G to A transition at codon 355, changing it from tryptophan to a stop codon (p.W355*). Northern analysis showed absence of the most abundant mRNA of mouse galactocerebrosidase in mice homozygous for this allele.|
Mice heterozygous for the recessive twitcher allele (Galctwi) are viable and fertile. Homozygotes die by about 40 days of age. Heterozygote (female or male) x wildtype crosses are recommended to maintain a live colony. Heterozygote x heterozygote crosses will produce homozygous progeny for experimentation.
When using the twitcher mouse strain in a publication, please cite the originating article(s) and include JAX stock #000845 in your Materials and Methods section.