Compromised mRNA processing and epilepsy in Brunol4 mutant mice. W. Frankel, Y. Yang, C. Mahaffey, T. Maddatu, G. Cox, J. Graber. The Jackson Laboratory, Bar Harbor, ME.
   Idiopathic epilepsy is a common disorder with a strong genetic component, usually exhibiting complex inheritance. While both complex and monogenic seizure-prone animals have been reported, multigenic models with well-defined genetic lesions have yet to be developed. Here we describe frequent-flyer mice, in which a transgene insertion disrupts expression of the Bruno-like 4 gene. Brunol4 haploinsufficiency results in dominant, recurrent limbic and tonic-clonic seizures in older, relatively healthy mice. Null homozygous mutants, which are small and do not thrive as well as littermates, have a more severe phenotype including both convulsions and absence seizures with frequent spike-wave discharges. Both genotypes show low seizure threshold before overt seizure onset. All mutant phenotypes are affected by strain background. Brunol4 encodes a brain-specific RNA binding protein. Its expression is concentrated in neurons of brain regions controlling synchronization and oscillation (e.g. cerebral cortex, hippocampus, thalamus), suggesting it is involved in the maintenance of normal neuronal rhythmic activities. Using microarrays we identified multiple transcripts with altered expression in mutant brain, some of which were implicated in epilepsy by prior studies and others which are novel. At least four molecules critical to neuronal excitation (HTR2C, SYN2, SNCA and NSF) are selectively reduced at transcript and protein level. Analysis of the 3 UTR of these genes identified a highly conserved U/G rich motif. RNA-protein immunoprecipitation in neurons suggests direct interaction between BRUNOL4 and this sequence, the consequences of which on the target RNA are being investigated in primary culture using reporter and mRNA decay studies. We suggest that BRUNOL4 modulates neuronal excitability at the RNA level through fine-tuning the stability of transcripts encoding proteins critical to neuronal excitation. Brunol4 mutant mice represent the first animal model where compromised mRNA processing leads to epilepsy. They also demonstrate how a single gene disruption can lead to multiple, more incremental molecular disturbances, mimicking a genetically complex disorder.