A 76-bp Deletion in the Mip Gene Causes Autosomal Dominant Cataract in Hfi Mice

Hfi is a dominant cataract mutation where heterozygotes show hydropic lens fibers and homozygotes show total lens opacity. The Hfi locus was mapped to the distal part of mouse chromosome 10 close to the major intrinsic protein (Mip), which is expressed only in cell membranes of lens fibers. Molecular analysis of Mip revealed a 76-bp deletion that resulted in exon 2 skipping in Mip mRNA. In Hfi/Hfi this deletion resulted in a complete absence of the wildtype Mip. In contrast, Hfi/+ animals had the same amount of wildtype Mip as +/+. Results from pulse–chase expression studies excluded hetero-oligomerization of wildtype and mutant Mip as a possible mechanism for cataract formation in the Hfi/+. We propose that the cataract phenotype in the Hfi heterozygote mutant is due to a detrimental gain of function by the mutant Mip resulting in either cytotoxicity or disruption in processing of other proteins important for the lens. Cataract formation in the Hfi/Hfi mouse is probably a combined result of both the complete loss of wildtype Mip and a gain of function of the mutant Mip.     

Type IV procollagen missense mutations associated with defects of the eye, vascular stability, the brain, kidney function and embryonic or postnatal viability in the mouse, Mus musculus: an extension of the Col4a1 allelic series and the identification of the first two Col4a2 mutant alleles

The basement membrane is important for proper tissue development, stability, and physiology. Major components of the basement membrane include laminins and type IV collagens. The type IV procollagens Col4a1 and Col4a2 form the heterotrimer [alpha1(IV)]2[alpha2(IV)], which is ubiquitously expressed in basement membranes during early developmental stages. We present the genetic, molecular, and phenotypic characterization of nine Col4a1 and three Col4a2 missense mutations recovered in random mutagenesis experiments in the mouse. Heterozygous carriers express defects in the eye, the brain, kidney function, vascular stability, and viability. Homozygotes do not survive beyond the second trimester. Ten mutations result in amino acid substitutions at nine conserved Gly sites within the collagenous domain, one mutation is in the carboxy-terminal noncollagenous domain, and one mutation is in the signal peptide sequence and is predicted to disrupt the signal peptide cleavage site. Patients with COL4A2 mutations have still not been identified. We suggest that the spontaneous intraorbital hemorrhages observed in the mouse are a clinically relevant phenotype with a relatively high predictive value to identify carriers of COL4A1 or COL4A2 mutations.     

Enzyme-activity mutants in Mus musculus. I. Phenotypic description and genetic characterization of ethylnitrosourea-induced mutations

The specific activity of erythrocyte enzymes was measured to detect gene mutations in F(1)-offspring of male mice treatment with different doses (80, 160, or 250 mg/kg body weight) of ethylnitrosourea (ENU). Altogether 13,230 offspring were screened for 10 enzyme activities. Mutants with reduced activity as well as mutants with enhanced activity were found. Of the 36 independently observed mutations, 20 were homozygous lethal. Genetic and biochemical characterizations were routinely performed. These mutants provide insight into the mechanism of ENU mutagenesis and can serve as models for structure-function studies of the corresponding enzymes.     

Redox imbalance and mutagenesis in spleens of mice harboring a hypomorphic allele of Gpdx(a) encoding glucose 6-phosphate dehydrogenase

Mice harboring the activity-attenuated Gpdx(a-m2Neu) allele and also harboring a chromosomally integrated lacZ reporter gene to study mutagenesis (pUR288) were used to demonstrate that moderate glucose 6-phosphate dehydrogenase (G6PD) deficiency causes elevated mutagenesis and endogenous oxidative stress in the spleen. G6PD-deficient spleens with a residual enzyme activity of 22% exhibited a dramatic shift in the mutational pattern of lacZ (4.6-fold increase in the prevalence of recombination mutations of lacZ) together with a 1.8-fold increase in mutant frequencies in lacZ. A concomitant 3-fold reduction in catalase activity (dependent upon NADPH) indicated that the in vivo supply of G6PD-generated NADPH was insufficient. An additional 3-fold increase in oxidized glutathione suggested that redox control was disturbed in G6PD-deficient spleens. These findings indicate that G6PD is required for limiting oxidative mutagenesis in the mouse spleen. Gpdx(a-m2Neu) is the first hypomorphic allele of a mouse housekeeping gene associated with elevated somatic mutagenesis in vivo.     

Doublecortin and IGF-1R protein levels are reduced in spite of unchanged DNA methylation in the hippocampus of aged rats

Amino Acids - The aim of the current study was to investigate whether doublecortin (DCX), insulin-like growth factor receptor 1 (IGF-1R) and metabotropic glutamate receptor 5 (mGluR5) levels are...     

A 76-bp deletion in the Mip gene causes autosomal dominant cataract in Hfi mice.

Hfi is a dominant cataract mutation where heterozygotes show hydropic lens fibers and homozygotes show total lens opacity. The Hfi locus was mapped to the distal part of mouse chromosome 10 close to the major intrinsic protein (Mip), which is expressed only in cell membranes of lens fibers. Molecular analysis of Mip revealed a 76-bp deletion that resulted in exon 2 skipping in Mip mRNA. In Hfi/Hfi this deletion resulted in a complete absence of the wildtype Mip. In contrast, Hfi/+ animals had the same amount of wildtype Mip as +/+. Results from pulse-chase expression studies excluded hetero-oligomerization of wildtype and mutant Mip as a possible mechanism for cataract formation in the Hfi/+. We propose that the cataract phenotype in the Hfi heterozygote mutant is due to a detrimental gain of function by the mutant Mip resulting in either cytotoxicity or disruption in processing of other proteins important for the lens. Cataract formation in the Hfi/Hfi mouse is probably a combined result of both the complete loss of wildtype Mip and a gain of function of the mutant Mip.     

Enzyme-activity mutations detected in mice after paternal fractionated irradiation

(101/E1 × C3H/E1)F₁-hybrid male mice were exposed in a 24-h fractionation interval to either 3.0 + 3.0-Gy or 5.1 + 5.1-Gy X-irradiation, and mated to untreated Test-stock females. The offspring were examined for mutations at 7 recessive specific loci and for activity alterations of erythrocyte enzymes controlled presumably by 12 loci. No enzyme-activity mutant was found in 3610 F₁-offspring of the control group. In the experimental groups, no mutant was detected in 533 (3.0 + 3.0 Gy) and 173 (5.1 + 5.1 Gy) offspring from postspermatogonial germ cells treated. After treatment of spermatogonia, 1 mutant in 3388 F₁-offspring of the 3.0 + 3.0-Gy group, and 5 mutants in 3187 F₁ offspring of the 5.1 + 5.1-Gy group were found. The mutants were all genetically confirmed. The frequency (expressed as mutants/locus/gamete) of enzyme-activity mutations is 2 (5.1 + 5.1-Gy group) to 10 (3.0 + 3.0-Gy group) times lower than the frequency of recessive specific-locus mutations.     

Towards an understanding of the nature and fitness of induced mutations in germ cells of mice: homozygous viability and heterozygous fitness effects of induced specific-locus, dominant cataract and enzyme-activity mutations

A total of 219 specific-locus, 35 dominant cataract and 44 enzyme-activity mutations induced in spermatogonia of mice by radiation or ethylnitrosourea (ENU) treatment were characterized for homozygous viability as well as fitness effects on heterozygous carriers. For all 3 genetic endpoints, the frequency of homozygous lethal mutations was higher in the group of radiation-induced mutations than in the ENU-treatment group. These observations are consistent with the hypothesis that radiation-induced mutations recovered in the mouse are mainly due to small deletions while ENU induces mainly intragenic mutations. The overall fitness of mutant heterozygotes was reduced for the group of radiation-induced specific-locus, dominant cataract and enzyme-activity mutations while the ENU-induced mutations exhibited no reduction in fitness. The fitness reduction of heterozygous carriers for a newly occurring mutation in a population is important in determining the persistence of the mutation in a population, and thus the total number of individuals affected before a mutation is eventually eliminated from the population. For the present results a maximal persistence of 12 generations and a minimal persistence of 3 generations is estimated. These results are consistent with the 6-7-generation persistence time assumed by UNSCEAR (1982) in an estimate of the overall effects of radiation-induced mutations in man.     

Genetic,biochemical, and molecular characterization of nine glyceraldehyde-3-phosphate dehydrogenase mutants with reduced enzyme activity in <Emphasis Type="Italic">Mus musculus</Emphasis>

The first mutations causing hereditary glyceraldehyde-3-phosphate dehydrogenase (GAPDH) deficiency in the mouse are described. In the course of various mutagenicity experiments with chemical mutagens and irradiation, nine independent mutations causing approximately 50–55% residual activity in blood compared to wild type were identified at the Gapdh structural locus on chromosome 6. Breeding experiments displayed an autosomal semidominant mode of inheritance for all mutants. Two mutations are homozygous viable producing a GAPDH residual activity of less than 10%. Mortality of the remaining seven homozygous lethal lines occurs at an early postimplantation stage of development. The physiologic and hematologic analyses provided no indication for further altered traits in heterozygotes or homozygotes. The molecular characterization showed base substitutions resulting in amino acid exchanges in seven mutations, in one mutation a transversion creating a stop codon caused a truncated protein of 89 amino acids and two deletions generating truncated proteins of 73 and 9 amino acids, respectively.