Collaborative Cross mice reveal extreme epilepsy phenotypes and genetic loci for seizure susceptibility

Abstract

Objective: Animal studies remain essential for understanding mechanisms of epilepsy and identifying new therapeutic targets. However, existing animal models of epilepsy do not reflect the high level of genetic diversity found in the human population. The Collaborative Cross (CC) population is a genetically diverse recombinant inbred panel of mice. The CC offers large genotypic and phenotypic diversity, inbred strains with stable genomes that allow for repeated phenotypic measurements, and genomic tools including whole genome sequence to identify candidate genes and candidate variants. Methods: We evaluated multiple complex epileptic traits in a sampling of 35 CC inbred strains using the flurothyl-induced seizure and kindling paradigm. We created an F2 population of 297 mice with extreme seizure susceptibility and performed quantitative trait loci (QTL) mapping to identify genomic regions associated with seizure sensitivity. We used quantitative RNA sequencing from CC hippocampal tissue to identify candidate genes and whole genome sequence to identify genetic variants likely affecting gene expression. Results: We identified new mouse models with extreme seizure susceptibility, seizure propagation, epileptogenesis, and SUDEP (sudden unexpected death in epilepsy). We performed QTL mapping and identified one known and seven novel loci associated with seizure sensitivity. We combined whole genome sequencing and hippocampal gene expression to pinpoint biologically plausible candidate genes (eg, Gabra2) and variants associated with seizure sensitivity. Significance: New mouse models of epilepsy are needed to better understand the complex genetic architecture of seizures and to identify therapeutics. We performed a phenotypic screen utilizing a novel genetic reference population of CC mice. The data we provide enable the identification of protective/risk genes and novel molecular mechanisms linked to complex seizure traits that are currently challenging to study and treat. | GU et al. 2 | MATERIALS AND METHODS 2.1 | Mice All mice (Table S1) were raised on standard mouse chow and kept on a 12:12 light/dark cycle. All mouse work was

Gabra2 is a genetic modifier of Scn8a encephalopathy in the mouse*

“…The level of Gabra2 transcript is 4.5‐fold higher in strain SJL/J than in C57BL/6J (Figure 5B). This is consistent with other strains carrying the wild‐type allele 23,32 …”

“…Strain C57BL/6J carries a hypomorphic variant of Gabra2 that was first identified by its effect on exacerbation of seizures in Scn1a haploinsufficient mice 33 . The hypomorphic B6 allele was also found to confer sensitivity to flurothyl‐induced seizures in the Collaborative Cross 32 . Mulligan et al 23 identified a splice site mutation in strain C57BL/6J that is responsible for reducing expression of Gabra2 to 25% of wild‐type levels.…”

Paradoxical hyperexcitability from NaV1.2 sodium channel loss in neocortical pyramidal cells

“…It is well-established that common genetic variants play a major role in a range of neurodevelopmental disorders, including epilepsy (Leu et al, 2019; Speed et al, 2014) and autism spectrum disorder (Gaugler et al, 2014). Furthermore, genetic background is a well-defined determinant of seizure severity in several murine epilepsy (Gu et al, 2020; Kang et al, 2019), including Scn2a +/- mice in which aberrant EEG signals can be observed in Scn2a +/- mice on a pure C57Bl/6J background but not when Scn2a +/- C57Bl/6J mice are crossed to Black Swiss mice (Mishra et al, 2017). Based on this, one prediction would be that seizure frequency or severity should be higher in children with protein truncating variants than those that exhibit partial LoF missense variants that temper, rather than completely eliminate, channel function.…”

Content and Performance of the MiniMUGA Genotyping Array: A New Tool To Improve Rigor and Reproducibility in Mouse Research

“…We have also illustrated examples of how this array can be used for new genetic discovery, including sex chromosome abnormalities, genomic duplications and also in the expansion of genetic mapping approaches. This array and these associated data highlight the utility of genetic quality control for more robust and reproducible science in the mouse and is already being widely used by the research community (Smith et al 2019, Gu et al 2020, Yu et al 2020. Figure 1.…”