Abstracts

Susceptibility to seizure-induced excitotoxic cell death varies among inbred mouse strains due to variation in genetic background. Our QTL mapping studies have shown that distal chromosome 18 ([italic]Sicd1[/italic])[italic] [/italic]contains a gene(s) conferring different susceptibility to seizure-induced excitotoxic cell death between C57BL/6J (B6) and FVB/NJ (FVB) inbred mouse strains. We have verified that the causal gene(s) reside in the [italic]Sicd1 [/italic]QTL utilizing congenic strains. We found the congenic strains having the [italic]Sicd1 [/italic]QTL-resistant locus from a cell-death resistant strain (B6) and the remainder of their genome from a cell-death susceptible strain (FVB) are less susceptible to seizure-induced excitotoxic cell death as compared to the cell-death susceptible strain (FVB). We hypothesized that a strain-specific variation in one or more genes is responsible for the [italic]Sicd1 [/italic]QTL effect., We have focused on two potential candidate genes, Galr1 and Mbp, based on their putative role in modulating seizure susceptibility and excitatory amino acid-induced cell death. To test this hypothesis we sought to identify sequence variants in the Galr1 and Mbp genes between B6 and FVB strains using DNA sequencing. As a complimentary method to identify the [italic]Sicd1 [/italic]QTL gene(s), we have examined changes in gene expression at the mRNA level of Galr1 and Mbp in hippocampal homogenates from both the parental inbred and the reciprocal congenic strains. Studies are underway to detect aberrant splicing based on cDNA sequencing and differential expression of Galr1 and Mbp at the protein level between our parental strains, B6 and FVB, as well as our reciprocal congenic strains., Based on preliminary results, no coding sequence variants have been detected in the Galr1 and Mbp genes. We have found genotype-dependent differences in Galr1 mRNA expression between B6 and FVB parental strains using qRT-PCR (P=0.023). Differential expression of hippocampal mRNA for Galr1 was also found by qRT-PCR between the FVB.B6-Chr18 congenic strain and the parental FVB strain. In contrast, no statistically significant differences in Mbp mRNA expression were observed either between the parental strains or recombinant congenic strains (P=0.816)., Based on the expression variation and its putative role in modulating seizure susceptibility and excitatory amino acid-induced cell death we consider Galr1 as a strong candidate gene responsible for the [italic]Sicd1 [/italic]QTL effect. Follow-up studies whether there is functional expression differences in Galr1 gene between B6 and FVB would support Galr1 as a [italic]Sicd1 [/italic]QTL gene. Results from the proposed studies will add to our understanding of the molecular determinants critical for the pathogenesis of seizure-induced excitotoxic cell death., (Supported by NS038696 to P.E.S.)