Stargazer: A Simple Genetic Model for Epilepsy

Jackson Laboratory, Bar Harbor ME

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Abstract

DESCRIPTION (provided by applicant): Epilepsy is characterized by recurrent brain seizures with variable age of onset and degree of severity of disease. This disorder is also very prevalent - ranking as the most common neurological affliction in the human population. This proposal is focused on absence epilepsy, characterized by brief losses of consciousness and distinctive EEGs showing repetitive spike-wave discharges (SWDs). Several mouse models with this form of spontaneous generalized epilepsy have been characterized and the mutated genes have been identified. Significantly, mutations in the voltage-dependent calcium channel (VDCC) subunits represent four of these six models. The stargazer mouse has the longest and most frequently recurring SWDs of all the mouse models. We have previously identified the stargazer mutation in Cacng2, which encodes the gamma2 subunit of the VDCC. We now have three alleles of stargazer with heterogeneous phenotypes, and have further generated a targeted mutation in the closely-related family member, Cacng4. This mutant has no detectable phenotypic abnormality on its own, but when coupled with Cacng2 mutations, displays increased absence seizure activity. The relationship between these Cacng products to the calcium channel subunits, beta4 and alpha1A, will be examined by utilizing the lethargic2J and tottering4J mutant mice. We will construct targeted mutations in the two related genes, Cacng3 and Cacng8. In addition to characterizing these single gene mutants for in vitro calcium channel activity, individual calcium subunit expression and absence seizures, we will construct novel double mutants to determine more subtle seizure associations and VDCC subunit interactions. Absence seizures are most prevalent in children indicating that there is an important developmental aspect to this disorder in humans. To study this in mice, we will construct a conditional mutation in the stargazer gene, Cacng2, and correlate the loss of Cacng2 expression at specific embryonic and postnatal time periods with absence seizure activity. All of these studies will contribute to our long-term goal of understanding the neurophysiology of the VDCC gamma subunits and their role in epilepsy.