B6(AU)-Tub^tub/J

Stock number: 000562
Product name: tubby
Research areas: Diabetes and Obesity Research, Endocrine Deficiency Research, Internal/Organ Research, Neurobiology Research, Sensorineural Research

Description

These mice carry a spontaneous mutation at the Tub locus characterized by maturity-onset obesity.

Detailed description

Mice homozygous for the tubby spontaneous mutation experience maturity-onset obesity. Homozygous mutant mice are recognizable by increased body weight at 3 to 4 months in males and at 4 to 6 months in females. Both sexes are fertile. The increased weight is composed of excess adipose tissue. Blood glucose is normal, but plasma insulin is increased prior to obvious signs of obesity and may rise to 20 times normal by 6 months. Despite elevated plasma total cholesterol, triglycerides, and high-density lipoprotein cholesterol, homozygous mutant mice do not exhibit atherosclerotic fatty streak blood vessel lesions. Tubby mutant mice also exhibit retinal degeneration, initially believed due to the presence of another mutation which was called rd5, but since demonstrated to be a pleiotropic effect of the Tub^tub mutation (Ohlemiller et al., 1997); the retinal phenotype is moderated by a QTL on Chromosome 11 (Ikeda et al., 2002). Tubby homozygotes additionally exhibit progressive hearing loss. The hearing loss is due to apoptotic degeneration of the organ of Corti and loss of afferent neurons. Quantitative trait locus (QTL) analysis identified a region on Chromosome 2 (designated modifier of tubby hearing 1, moth1) whose wild-type allele protects tubby mice from hearing loss (Ikeda et al., 1999); the gene has been identified as Mtap1a, encoding a microtubule-associated protein (Ikeda et al., 2002). A locus suggestively associated with protection from retinal degeneration maps to the same region of Chromosome 2 (Ikeda et al., 2002). Mice homozygous for a targeted null mutation in the tubby gene (not currently available from The Jackson Laboratory) exhibit a phenotype identical to that conferred by the spontaneous tubby mutation (Stubdal, et al., 2000).

Development

The Tub^tub mutation arose spontaneously in 1977 in The Jackson Laboratory Animal Resources colony of C57BL/6J which was then at F125. After initial maintenance on the C57BL/6J background, a C57BL/6J-Tub^tub homozygous male was bred with a female congenic B6.AU-Hbb^p and the Hbb^p +/Hbb^s Tub^tub offspring were sibling mated. The colony was maintained by breeding siblings Hbb^p +/Hbb^s Tub^tub x Hbb^p +/Hbb^s Tub^tub or vice versa for many years and in 2002 reached F87. In 2004 isozyme testing for Hbb alleles was replace with PCR testing for the Tub^tub allele and the colony reached F90. (Coleman et al., 1978; Coleman and Eicher, 1990.)

Allele

Symbol: Tub^tub
Name: tubby
MGI accession ID: MGI:1861349
Generation method: Spontaneous
Marker symbol: Tub
Marker name: tubby bipartite transcription factor
Chromosome: 7
Strain of origin: C57BL/6J
Molecular note: A G-to-T mutation of the first nucleotide of intron 11 eliminates exon 11 splice donor site G-GT by changing it to G-TT, leading to mis-splicing in the form of retention of intron 11.
General note: The phenotype associated with retinal degeneration in the tubby stock was referred to as a separate locus, rd5. rd5 was identified in the tubby stock but absent from the parental C57BL/6J stock. Based on the tight linkage of the two phenotypes and the molecular defect underlying the tub mutation, it seemed likely that tub and rd5 were the same gene. This was further supported by a knockout of the tub gene that recapitulated the retinal degeneration phenotype.