Targeted Deletion of the tub Mouse Obesity Gene Reveals that tubby Is a Loss-of-Function Mutation
| Autor: | Rosana Kapeller, Olga Charlat, Troy Chickering, Judy H. Dunmore, Dennis Huszar, James Deeds, Catherine A. Lynch, Qing Fang, Patrick W. Kleyn, Victoria Fairchild-Huntress, Hilde Stubdal, Ann Moriarty |
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| Rok vydání: | 2000 |
| Předmět: |
Male
Retinal degeneration Aging Positional cloning RNA Splicing Restriction Mapping Biology Tubby protein Weight Gain Retina Mice Exon Mutant protein Retinitis pigmentosa Mammalian Genetic Models with Minimal or Complex Phenotypes otorhinolaryngologic diseases medicine Animals Missense mutation Obesity Molecular Biology Adaptor Proteins Signal Transducing Sequence Deletion Mice Knockout Genetics Sex Characteristics Homozygote Retinal Degeneration Proteins Exons Cell Biology medicine.disease Phenotype Cochlea Mice Inbred C57BL Female |
| Zdroj: | Molecular and Cellular Biology. 20:878-882 |
| ISSN: | 1098-5549 |
| DOI: | 10.1128/mcb.20.3.878-882.2000 |
| Popis: | The mouse tubby phenotype is characterized by maturity-onset obesity accompanied by retinal and cochlear degeneration. A positional cloning effort to find the gene responsible for this phenotype led to the identification of tub, a member of a novel gene family of unknown function. A splice defect mutation in the 3* end of the tub gene, predicted to disrupt the C terminus of the Tub protein, has been implicated in the genesis of the tubby phenotype. It is not clear, however, whether the Tub mutant protein retains any biological activity, or perhaps has some dominant function, nor is it established that the tubby mutation is itself responsible for all of the observed tubby phenotypes. To address these questions, we generated tub-deficient mice and compared their phenotype to that of tubby mice. Our results demonstrate that tubby is a loss-of-function mutation of the tub gene and that loss of the tub gene is sufficient to give rise to the full spectrum of tubby phenotypes. We also demonstrate that loss of photoreceptors in the retina of tubby and tub-deficient mice occurs by apoptosis. In addition, we show that Tub protein expression is not significantly altered in the ob, db, or melanocortin 4 receptor-deficient mouse model of obesity. The tubby strain of obese mice arose spontaneously in a mouse colony at the Jackson Laboratory (5). The tubby phenotype is inherited in an autosomal recessive manner and is characterized by late-onset weight gain accompanied by progressive retinal and cochlear degeneration (16, 17). The combination of these phenotypes resembles human syndromes, such as Usher’s (retinal and cochlear degeneration), BardetBiedl, and Alstrom’s (obesity and sensory deficits). The obesity of tubby mice is relatively mild and late in onset, resembling the weight gain in human populations more closely than that observed in other murine models of obesity, such as obese (ob) and diabetes (db) (4). Weight gain in tubby mice occurs relatively slowly, and the mice reach about twice the weight of their unaffected siblings. Tubby mice are not sterile, but they become infertile after significant obesity develops. The retinal and cochlear degeneration has been proposed to be due to apoptosis of retinal and cochlear neurosensory cells. The identity of the tub gene was determined by positional cloning (11, 14). The expression pattern of tub mRNA appears to be specific for the nervous system (10). tub is a member of a novel gene family of unknown function (7). Tub family proteins are quite hydrophilic but otherwise lack any distinguishing features that might provide insight into their function. There are no recognizable structural motifs or obvious homology to any known proteins. The tubby mutation is a G-to-T transversion that abolishes the donor splice site in the penultimate exon (exon 11), resulting in an aberrant transcript (11). Translation of intron sequence results in the substitution of the Tub C-terminal 44 amino acids with 24 different amino acids encoded by the intron. The aberrant transcript is expressed at elevated levels in tubby mice (5), but Tub expression at the protein level has not been investigated. The C terminus is highly conserved among Tub family members (15), suggesting that the tubby mutation may have disrupted a domain important for the biological function of tub. Strikingly, mutation of the tub family member TULP1 ,a t a position exactly corresponding to that mutated in the murine tub allele, was recently found to be the cause of a form of retinitis pigmentosa (RP 14) in humans (1, 7). Three other pathogenic missense mutations of TULP1 have been characterized (7), and they all fall within the highly conserved carboxy-terminal 250 amino acids of Tub. Despite elucidation of the molecular basis of the tubby mutation, it remains unclear whether the tubby phenotype represents a complete or partial loss of function or possibly even a gain of function. Furthermore, it has not been established whether the suite of tubby phenotypes (obesity, insulin resistance, and retinal and cochlear degeneration) are necessarily all attributable to mutation of the tub gene. It has not been ruled out that some features of the phenotype may be caused by a tightly linked, as yet unidentified gene. |
| Databáze: | OpenAIRE |
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