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Mutations in the founder of the MIP gene family underlie cataract development in the mouse
1Department of Molecular Genetics, University College London, UK.
Abstract:
The major intrinsic protein (MIP) of the vertebrate eye lens is the first identified member of a sequence-related family of cell-membrane proteins that appears to have evolved by gene duplication. Several members of the MIP family transport water (aquaporins), glycerol and other small molecules in microbial, plant and animal cells. Mutations in two aquaporin homologues of MIP underlie an autosomal recessive form of nephrogenic diabetes insipidus and absence of the Colton blood group antigens in humans, whereas, mutation of a third MIP-like gene underlies 'big brain' development in Drosophila. Here we show that distinct mutations in the murine Mip gene underlie one form of autosomal dominant cataract in the mouse. The cataract Fraser mutation is a transposon-induced splicing error that substitutes a long terminal repeat sequence for the carboxy-terminus of MIP. The lens opacity mutation is an amino-acid substitution that inhibits targeting of MIP to the cell-membrane. These allelic cataract mutations provide the first direct evidence that MIP plays a crucial role in the development of a transparent eye lens.
Insights
Mutations in the major intrinsic protein (MIP) gene cause hereditary cataracts in mice. This research provides the first direct evidence linking MIP to eye lens transparency and cataract development.
Area of Science:
- Molecular Biology
- Genetics
- Ophthalmology
Background:
- The major intrinsic protein (MIP) is a cell-membrane protein family with members known as aquaporins that transport small molecules.
- MIP family gene mutations are linked to nephrogenic diabetes insipidus, Colton blood group absence in humans, and 'big brain' development in Drosophila.
Purpose of the Study:
- To investigate the role of the murine Mip gene in the development of hereditary cataracts.
- To identify the specific mutations in the Mip gene responsible for cataract formation in mice.
Main Methods:
- Genetic analysis of mouse models with hereditary cataracts.
- Characterization of mutations within the Mip gene, including splicing errors and amino acid substitutions.
Main Results:
- Distinct mutations in the Mip gene were identified as the cause of autosomal dominant cataract in mice.
- The 'Fraser' cataract mutation resulted from a transposon-induced splicing error affecting the MIP carboxy-terminus.
- Another mutation caused an amino acid substitution, inhibiting MIP's cell-membrane targeting.
Conclusions:
- These findings provide the first direct evidence that MIP is crucial for maintaining eye lens transparency.
- Understanding Mip gene mutations offers insights into the molecular mechanisms of hereditary cataracts.