Biomedical subjects

Wayne N Frankel

Publications and source records attributed to Wayne N Frankel.

25 records · Page 2Linked to original sources

PubMed2004

Mice carrying the szt1 mutation exhibit increased seizure susceptibility and altered sensitivity to compounds acting at the m-channel.

PURPOSE: Mutations in the genes that encode subunits of the M-type K+ channel (KCNQ2/KCNQ3) and nicotinic acetylcholine receptor (CHRNA4) cause epilepsy in humans. The purpose of this study was to examine the effects of the Szt1 mutation, which not only deletes most of the C-terminus of mouse Kcnq2, but also renders the Chnra4 and Arfgap-1 genes hemizygous, on seizure susceptibility and sensitivity to drugs that target the M-type K+ channel. METHODS: The proconvulsant effects of the M-channel blocker linopirdine (LPD) and anticonvulsant effects of the M-channel enhancer retigabine (RGB) were assessed by electroconvulsive threshold (ECT) testing in C57BL/6J-Szt1/+ (Szt1) and littermate control C57BL/6J+/+ (B6) mice. The effects of the Szt1 mutation on minimal clonic, minimal tonic hindlimb extension, and partial psychomotor seizures were evaluated by varying stimulation intensity and frequency. RESULTS: Szt1 mouse seizure thresholds were significantly reduced relative to B6 littermates in the minimal clonic, minimal tonic hindlimb extension, and partial psychomotor seizure models. Mice were injected with LPD and RGB and subjected to ECT testing. In the minimal clonic seizure model, Szt1 mice were significantly more sensitive to LPD than were B6 mice [median effective dose (ED50) = 3.4 +/- 1.1 mg/kg and 7.6 +/- 1.0 mg/kg, respectively]; in the partial psychomotor seizure model, Szt1 mice were significantly less sensitive to RGB than were B6 mice (ED50 = 11.6 +/- 1.4 mg/kg and 3.4 +/- 1.3 mg/kg, respectively). CONCLUSIONS: These results suggest that the Szt1 mutation alters baseline seizure susceptibility and pharmacosensitivity in a naturally occurring mouse model.

Animals↗

PubMed2004

Mutation rate and predicted phenotypic target sizes in ethylnitrosourea-treated mice.

Chemical mutagenesis of the mouse is ongoing in several centers around the world, with varying estimates of mutation rate and number of sites mutable to phenotype. To address these questions, we sequenced approximately 9.6 Mb of DNA from G1 progeny of ethylnitrosourea-treated mice in a large, broad-spectrum screen. We identified 10 mutations at eight unique sites, including six nonsynonymous coding substitutions. This calibrates the nucleotide mutation rate for two mutagenesis centers, implies significance criteria for positional cloning efforts, and provides working estimates of effective genetic target sizes for selected phenotypes.

Alkylating Agents↗

PubMed2003

Spontaneous deletion of epilepsy gene orthologs in a mutant mouse with a low electroconvulsive threshold.

The electroconvulsive threshold (ECT) test has been used extensively to determine the protection conferred by antiepileptic drug candidates against induced seizures in rodents. Despite its clinical relevance, the potential of ECT to identify mouse epilepsy models in genetic studies has not been thoroughly assessed. We adopted the ECT test to screen the progeny of ethylnitrosourea treated male C57BL/6J mice. In a small-scale screen, several mutant lines conferring a low threshold to ECT minimal clonic seizures were mapped to the telomeric region of mouse chromosome 2 in independent founder families. This high incidence was suggestive of a single spontaneous event that pre-existed in the founders of mutagenized stock. Genetic and physical mapping led to the discovery that several lines shared a single mutation, Szt1 (seizure threshold-1), consisting of a 300 kb deletion of genomic DNA involving three known genes. Two of these genes, Kcnq2 and Chrna4, are known to be mutated in human epilepsy families. Szt1 homozygotes and heterozygotes display similar phenotypes to those found in the respective Kcnq2 knockout mutant mice, suggesting that Kcnq2 haploinsufficiency is at the root of the Szt1 seizure sensitivity. Our results provide a novel genetic model for epilepsy research and demonstrate that the approach of using ECT to study seizures in mice has the potential to lead to the identification of human epilepsy susceptibility genes.

Animals↗

PubMed2003

Phenotypic heterogeneity in the stargazin allelic series.

The stargazer mutant mouse is characterized by its ataxic gait, head tossing, and absence seizures. The mutation was identified in the gamma 2 subunit gene of the high voltage-dependent calcium channel, Cacng2. Subsequently, two allelic variants of stargazer have arisen, waggler and stargazer 3J. In this study, we have compared these new alleles to the original stargazer allele. All three mutations affect the Cacng2 mRNA levels as they all arise from disruptions within the introns of this gene. Our results show that the mutations cause reduced Cacng2 mRNA and protein levels. Stargazer and waggler mice have the least amount of mRNA and undetectable protein, whereas stargazer 3J appears to be the mildest allele, both in terms of the phenotype and protein expression. Electroencephalographic (EEG) analysis confirmed that stargazer has frequent spike-wave discharges (SWDs); the average duration of each discharge burst is 5 seconds and recurs every minute. The waggler allele causes a greater variation in SWD activity depending on the individual mouse, and the stargazer 3J mouse has no SWDs. The preliminary characterization of this heterogeneous allelic series provides a basis to explore more biochemical and physiological parameters relating to the role of the Cacng2 product in calcium channel activity, AMPA receptor localization, and cerebellar disturbances.

Action Potentials↗

PubMed2002

Initial sequencing and comparative analysis of the mouse genome.

The sequence of the mouse genome is a key informational tool for understanding the contents of the human genome and a key experimental tool for biomedical research. Here, we report the results of an international collaboration to produce a high-quality draft sequence of the mouse genome. We also present an initial comparative analysis of the mouse and human genomes, describing some of the insights that can be gleaned from the two sequences. We discuss topics including the analysis of the evolutionary forces shaping the size, structure and sequence of the genomes; the conservation of large-scale synteny across most of the genomes; the much lower extent of sequence orthology covering less than half of the genomes; the proportions of the genomes under selection; the number of protein-coding genes; the expansion of gene families related to reproduction and immunity; the evolution of proteins; and the identification of intraspecies polymorphism.

Animals↗

PubMed2002

The harlequin mouse mutation downregulates apoptosis-inducing factor.

Harlequin (Hq) mutant mice have progressive degeneration of terminally differentiated cerebellar and retinal neurons. We have identified the Hq mutation as a proviral insertion in the apoptosis-inducing factor (Aif) gene, causing about an 80% reduction in AIF expression. Mutant cerebellar granule cells are susceptible to exogenous and endogenous peroxide-mediated apoptosis, but can be rescued by AIF expression. Overexpression of AIF in wild-type granule cells further decreases peroxide-mediated cell death, suggesting that AIF serves as a free radical scavenger. In agreement, dying neurons in aged Hq mutant mice show oxidative stress. In addition, neurons damaged by oxidative stress in both the cerebellum and retina of Hq mutant mice re-enter the cell cycle before undergoing apoptosis. Our results provide a genetic model of oxidative stress-mediated neurodegeneration and demonstrate a direct connection between cell cycle re-entry and oxidative stress in the ageing central nervous system.

Aging↗

PubMed2002

The muscular dystrophy with myositis (mdm) mouse mutation disrupts a skeletal muscle-specific domain of titin.

Muscular dystrophy with myositis (mdm) is a recessive mouse mutation that causes severe and progressive muscular degeneration. Here we report the identification of the mdm mutation as a complex rearrangement that includes a deletion and a LINE insertion in the titin (Ttn) gene. Mutant allele-specific splicing results in the deletion of 83 amino acids from the N2A region of TTN, a domain thought to bind calpain-3 (CAPN3) the product of the human limb-girdle muscular dystrophy type 2A (LGMD2A) gene. The Ttn(mdm) mutant mouse may serve as a model for human tibial muscular dystrophy, which maps to the TTN locus at 2q31 and shows a secondary reduction of CAPN3 similar to that observed in mdm skeletal muscle. This is the first demonstration that a mutation in Ttn is associated with muscular dystrophy and provides a novel animal model to test for functional interactions between TTN and CAPN3.

Animals↗