Abstracts

RATIONALE: Mice from various inbred strains are resistant to excitotoxin-induced cell death at different strain-specific levels. In particular, C57Bl/6 mice exhibit resistance to kainate-induced cell death, while mice from the FVB/N strain exhibit susceptibility. Breeding studies have demonstrated that the kainate-induced cell death resistance phenotype is a monogenic and highly penetrant autosomal dominant trait. We now report an investigation of the genetic basis for excitotoxic cell death susceptibility using F1 X FVB/N backcrosses (N2) to establish chromosomal locations of genes controlling susceptibility to kainate-induced cell death. At ths end of this activity, participants should be able to assess the importance of genetic diversity in seizure-induced damage.
METHODS: To confirm the mode of inheritance and determine the genetic loci that confer resistance to excitotoxic cell death, (C57BL/6 X FVB/N)F1 mice were backcrossed in both directions to susceptible FVB/N mice to determine phenotypic differences in susceptibility to kainate-induced cell death in 400 progeny. Microsatellite mapping techniques were then used to isolate the chromosomal segments containing resistance or susceptibility loci in the N2 population by performing an initial genome screen with 87 polymorphic microsatellite primer pairs. Quantitative trait loci (QTL) mapping methods were used to identify regions of the genome that contribute to variation in susceptibility to kainate-induced cell death.
RESULTS: As reported previously, N2 mice displayed two predominant phenotypes responding either like resistant (C57BL/6) or susceptible (FVB/N) mice. Logistic regression analysis revealed significant or suggestive evidence for QTLs that influence susceptibility to kainate-induced cell death on chromosomes 15 and 4. We detected the locus of greatest effect on proximal Chr 15 (LOD=2.2) between markers D15Mit174 and D15Mit156 (29 cM wide). We detected two other QTLs on Chr 4. Interestingly, the two QTLs on Chr 4 act in completely different ways, in that the locus on proximal Chr 4 is associated with C57BL/6-derived susceptibility while the locus on distal Chr 4 is associated with FVB/N-derived susceptibility. However, as expected for a monogenic trait, kainate-induced cell death susceptibility loci were primarily derived from [ssquote]susceptible[ssquote] strains (FVB/N).
CONCLUSIONS: This study represents the first analysis of differential inbred mouse strain susceptibility to kainate-induced cell death. While in the present experiment we found three QTLs that influence the severity of kainate-induced damage in C57BL/6 and FVB/N mice, future studies are aimed at confirming or eliminating candidate genes for kainate-induced cell death susceptibility using functional characterization and higher resolution mapping studies. We conclude that susceptibility to kainate-induced cell death is genetically controlled. Due to the high degree of similarity between the mouse and human genomes, identification of the location of specific genes modulating susceptibility to excitotoxin-induced cell death will provide important insights into the manner in which genetic predisposition affects the pathogenesis of human epilepsy.
[Supported by: The James D. and Delia B. Baxter Foundation and NIH grant NS38696-01]