Elsevier

Neuroscience

Volume 102, Issue 2, 15 January 2001, Pages 307-317
Neuroscience

A gain-of-function mutation in the sodium channel gene Scn2a results in seizures and behavioral abnormalities

https://doi.org/10.1016/S0306-4522(00)00479-6Get rights and content

Abstract

The GAL879-881QQQ mutation in the cytoplasmic S4–S5 linker of domain 2 of the rat brain IIA sodium channel (Nav1.2) results in slowed inactivation and increased persistent current when expressed in Xenopus oocytes. The neuron-specific enolase promoter was used to direct in vivo expression of the mutated channel in transgenic mice. Three transgenic lines exhibited seizures, and line Q54 was characterized in detail. The seizures in these mice began at two months of age and were accompanied by behavioral arrest and stereotyped repetitive behaviors. Continuous electroencephalogram monitoring detected focal seizure activity in the hippocampus, which in some instances generalized to involve the cortex. Hippocampal CA1 neurons isolated from presymptomatic Q54 mice exhibited increased persistent sodium current which may underlie hyperexcitability in the hippocampus. During the progression of the disorder there was extensive cell loss and gliosis within the hippocampus in areas CA1, CA2, CA3 and the hilus. The lifespan of Q54 mice was shortened and only 25% of the mice survived beyond six months of age. Four independent transgenic lines expressing the wild-type sodium channel were examined and did not exhibit any abnormalities.

The transgenic Q54 mice provide a genetic model that will be useful for testing the effect of pharmacological intervention on progression of seizures caused by sodium channel dysfunction. The human ortholog, SCN2A, is a candidate gene for seizure disorders mapped to chromosome 2q22-24.

Section snippets

Transgene constructs

Plasmid pNSE-Ex4 containing the 4 kb promoter fragment from the rat NSE gene that includes 2.8 kb of flanking sequence, exon 1, intron 1 and 6 bp of exon 215 was provided by J. G. Sutcliffe (Scripps Institute, La Jolla, CA). Plasmid pBS-polyA, containing a 196 bp BamHI fragment from pCMVβ with a SV40 polyadenylation cassette, was provided by J. S. Chamberlain (University of Michigan). The 6.5 kb rat Scn2a cDNA constructs contain the FLAG epitope (DYKDDDDK) immediately downstream of the

Characterization of the GAL879-881QQQ channel in Xenopus oocytes

The mutant channel was characterized in Xenopus oocytes using a cut-open oocyte voltage clamp. The mutant channel inactivated more slowly than the WT channel (Fig. 1A). However, the slower inactivation did not result from a change in the magnitude of the time constants for either the fast or slow component of inactivation, which were similar for the mutant and WT channels during depolarizations ranging from −20 mV to +50 mV. The slower inactivation resulted from a significant decrease in the

Discussion

Sodium currents generated by expression of the GAL879-881QQQ mutant channel in Xenopus oocytes exhibited a slower rate of inactivation than the WT channel, increased percentage of current that inactivated with a slow time constant, and increased persistent current. Very similar sodium currents were detected in hippocampal neurons from Q54 transgenic mice expressing the mutant channel. The increase in persistent current was statistically significant in the neuronal context, in the presence of

Acknowledgements

We thank Julie Jones and Laurie Weiss for advice and assistance, Leslie Sprunger for helpful discussions, and Sally Camper and Roger Albin for review of the manuscript. Supported by NIH grants NS34509 (MHM) and NS26729 (ALG), the Organogenesis Postdoctoral Training Program T32 HD07505 and National Research Service Award NS10692 (JAK), NINDS awards KO8 NS01748 and KO2 NS02081 (JK), and National Multiple Sclerosis Grant RG1912 and grants from the Medical Research Service and Rehabilitation

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