Characterization of a gene-trap knockout mouse model ofScn2aencoding voltage-gated sodium channel Nav1.2

Abstract

Recent large-scale genomic studies have revealed SCN2A as one of the most frequently mutated gene in patients with neurodevelopmental disorders including autism spectrum disorder and intellectual disability. SCN2A encodes for voltage-gated sodium channel isoform 1.2 (Nav1.2), which is mainly expressed in the central nervous system and responsible for the propagation of neuronal action potentials. Homozygous knockout (null) of Scn2a is perinatal lethal, whereas heterozygous knockout of Scn2a results in mild behavior abnormalities. To achieve a more substantial, but not complete, reduction of Scn2a expression, we characterized a Scn2a deficient mouse model using a targeted gene trap knockout (gtKO) strategy to recapitulate loss-of-function SCN2A disorders. This model produces viable homozygous mice (Scn2a gtKO/gtKO ) that can survive to adulthood, with markedly low but detectable Nav1.2 expression. Although Scn2a gtKO/gtKO adult mice possess normal olfactory, taste, hearing, and mechanical sensitivity, they have decreased thermal and cold tolerance. Innate behaviors are profoundly impaired including impaired nesting, marble burying, and mating. These mice also have increased food and water intake with subsequent increases in fecal excretion of more but smaller fecal boli. This novel Scn2a gene trap knockout mouse thus provides a unique model to study pathophysiology associated with Scn2a deficiency.

Severe deficiency of voltage-gated sodium channel NaV1.2 elevates neuronal excitability in adult mice

“…We found that the heterozygous (HET) Scn2a WT/gtKO mice have ~60% of WT NaV1.2 protein level in the CPu tissues, whereas the homozygous (HOM) Scn2a gtKO/gtKO mice have a much lower level at 34% ( Figure S1C ). This result is largely consistent with our initial characterization of this mouse model using whole-brain samples ( 22 ). To understand how a severe deficiency of NaV1.2 affects neuronal excitability, we performed ex vivo patch-clamp recordings in brain slices from adult Scn2a gtKO/gtKO mice.…”

“…To understand how a severe NaV1.2 deficiency affects the function of neurons, we utilized a gene-trap knockout mouse model of Scn2a . Homozygous Scn2a gtKO/gtKO mice (referred to as HOM herein) can survive to adulthood, and have a substantial reduction of NaV1.2 expression (~25% of the WT level) ( 22 ). Because the gene-trap cassette contains a LacZ element, which is driven by the native NaV1.2 promoter ( Figure S1A ) ( 23, 24 ), we used LacZ -staining as a surrogate to determine the expression and distribution of NaV1.2 in the brain.…”

“…C57BL/6N- Scn2a1 tm1aNarl /Narl (referred to as Scn2a WT/gtKO ) mice were generated from the National Laboratory Animal Center Rodent Model Resource Center based on a modified gene-trap design ( 23, 24 ). The generation and basic characterization of this mouse model are available in our recent article ( 22 ). The targeting construct (tm1a trapping cassette) was electroporated into C57BL/6N embryonic stem cells, and founders in a pure C57BL/BN background were obtained to produce mice for experiments.…”

“…A more substantial reduction of gene expression could be essential to produce robust phenotypes in the mouse model of NaV1.2 deficiency. Because Scn2a null (100% knockout) is lethal, we thus generated a novel NaV1.2-deficient mouse model via a gene-trap knockout (gtKO) strategy ( 22 ). These mice display many behavioral abnormalities, modeling aspects of phenotypes in humans with SCN2A deficiency ( 22 ).…”

“…Because Scn2a null (100% knockout) is lethal, we thus generated a novel NaV1.2-deficient mouse model via a gene-trap knockout (gtKO) strategy ( 22 ). These mice display many behavioral abnormalities, modeling aspects of phenotypes in humans with SCN2A deficiency ( 22 ). Using this unique mouse model, we investigated how severe NaV1.2 deficiency affects neuronal excitabilities of principal neurons in the cortico-striatal circuit.…”