Twitcher 5 Jackson: a new remutation in the Galc gene.

Authors:Son Yong Karst, Patricia F. Ward-Bailey, Richard Samples, Kenneth R. Johnson, Leah Rae Donahue and Muriel T. Davisson

Source of Support:

The research was supported by NIH/NCRR grant RR01183 to the Mouse Mutant Resources (M.T.Davisson,PI) and Cancer Center Core Grant CA34196.

Mutation (allele) symbol: Galctwi-5J

Mutation (allele) name: twitcher 5 Jackson

Gene symbol: Galc

Strain of origin: BXD32/TyJ

Current strain name: BXD32/TyJ-Galctwi-5J/J

Stock #: 003613 (view JAX® Mice Data Sheet for additional information including Price and Supply Information)

Phenotype categories: neurological

Origin and Description

 

A new autosomal recessive remutation to Galctwi arose spontaneously and was discovered by Martha Buzzell and Ben Taylor in a production colony of BXD32/TyJ mice at the Jackson Laboratory.

Mice homozygous for the new Galctwi-5J remutation can be recognized at about 14-16 days of age by a moderate tremor and a smaller body size. Clinical weakness and wasting follows and death occurs usually about 21 days, but no more than 30 days.

The original twitcher (Galctwi ) phenotype was described on a mixed C57BL/6J and CE/J background. Clinical symptoms were first observed by day 30 and homozygous mice 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 strain (> 10 backcrosses) reduced the onset of symptoms.

The gene underlying the twi mutation encodes galactosylceramidase (GALC), which 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 myelination and myelin metabolism.

This strain is maintained by breeding hosts of homozygous ovarian transplanted mice to their sibling males and then intercrossing the heterozygous offspring.Heterozygous mice have normal life spans and are good breeders.

Genetic Analysis

This new remutation has recessive inheritance as shown by the results of mating hosts of homozygous ovarian transplanted mice to an unrelated male CAST/EiJ mouse. This mating produced only unaffected F1 progeny proving that the new mutation has recessive inheritance. These unaffected F1 hybrids were intercrossed and generated affected F2 animals for linkage analysis.

Using our standard mapping protocols this new mutation was mapped to Chromosome 12 where the original Galctwi mutation is located, between D12Mit6 (NCBI36 position 92.1Mb) and D12Mit262 (NCBI36 position 111.3Mb)

We also performed a direct test for allelism to confirm this new mutation to be a re-mutation of twitcher. A Galctwi heterozygous female was mated to a new mutant heterozygous male mouse, and this mating produced 15 offspring in 2 litters, of which 5 progeny were born with the Galctwi phenotype proving allelism.

Pathology

 

A routine pathological screen of 2 and 4 week old mutants showed that they had acutely necrotic neurons in ca3 of hippocampus and in deeper layers of cerebral cortex. These neurons have brightly eosinophilic cytoplasm and shrunken nuclei. Four week old mutants had peripheral nerves with deficient myelin and macrophages within vacuoles (digestion chambers). This suggested degeneration of peripheral nerves.

The eyes of two homozygous mice at 25 days of age were examined with an ophthalmoscope and found to be normal eyes.

Hearing as assessed by auditory brain stem response testing (ABR) of one homozygous mutant mouse at 25 days of age and one age-matched control showed both animals to have moderate hearing impairment. The hearing loss is likely due to the BxD32/TyJ strain background.

Acknowledgements

 

We thank Martha Buzzell and Ben Taylor for discovery of the mutant, Roderick Bronson and Coleen Kane for pathological screening, Kelly Kane for hearing assessment, Norm Hawes and Ron Hurd for eye examinations.