Abstracts

Genetic Absence Epilepsy Rats from Strasbourg (GAERS) are an inbred strain of Wistar rats that spontaneously display absence-like seizures and are widely utilized in epilepsy research. In a recent GAERS genome-wide scan, voltage gated calcium channel [gamma]2-subunit ([italic]CACNG2[/italic]) was identified as a possible candidate gene. This gene also underlies the defect in stargazer mouse model of ataxia and absence epilepsy. This study compares the genetic sequence and mRNA expression of [italic]CACNG2[/italic] in GAERS vs. non-epileptic control (NEC) rats. Brains were extracted from NEC and GAERS rats after their phenotype was confirmed via EEG recording. RNA was extracted from the thalamus and cortex. DNA was extracted from liver tissue. Both cDNA and genomic DNA were used to sequence [italic]CACNG2[/italic]. Northern Blot analysis was performed on mRNA isolated from each subregion, and probed for [italic]CACNG2[/italic] and [beta]-actin PCR products We found no differences in the coding sequence of [italic]CACNG2[/italic] between NEC, GAERS and [italic]Rattus norvegicus[/italic] genome database. Northern blot analysis for [italic]CACNG2[/italic] revealed a 5.5 kilobase transcript in all animals with lower expression in the thalamus than in the cortex. No splice variants were detected between GAERS and NEC and messenger RNA expression levels were similar between the two strains. Results indicate that [italic]CACNG2[/italic] gene structure and its expression are not altered in GAERS. Absence epilepsy phenotype in GAERS is thought to be polygenic. By comparing [italic]CACNG2[/italic] between GAERS and their non-epileptic counterparts, this study eliminates this gene as a contributor to the epileptic phenotype in GAERS. (Supported by The Walter and Eliza Hall Institute of Medical Research and The University of Melbourne.)