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Deletion of a non-canonical regulatory sequence causes loss of Scn1a expression and epileptic phenotypes in mice

ABSTRACT: Background: Genes with multiple co-active promoters appear common in brain, yet little is known about functional requirements for these potentially redundant genomic regulatory elements. SCN1A, which encodes the NaV1.1 sodium channel alpha subunit, is one such gene with two co-active promoters. Mutations in SCN1A are associated with epilepsy, including Dravet Syndrome (DS). The majority of DS patients harbor coding mutations causing SCN1A haploinsufficiency, however putative causal non-coding promoter mutations have been identified. Methods: To determine the functional role of one of these potentially redundant Scn1a promoters, we focused on the non-coding Scn1a 1b regulatory region, previously described as a non-canonical alternative transcriptional start site. We bred a transgenic mouse line with deletion of the extended evolutionarily-conserved 1b non-coding interval and characterized changes in gene and protein expression, and assessed seizure activity and alteration in behavior. Results: Mice harboring a deletion of the 1b non-coding interval exhibited surprisingly severe reductions of Scn1a and NaV1.1 expression throughout the brain. This was accompanied by electroencephalographic and thermal-evoked seizures, and some behavioral deficits. Conclusions: This work contributes to functional dissection of the regulatory wiring of a major epilepsy risk gene, SCN1A. We identified the 1b region as a critical disease-relevant regulatory element and provide evidence

ORGANISM(S): Mus musculus

PROVIDER: GSE169481 | GEO | 2021/03/26

REPOSITORIES: GEO

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Project description:Dravet syndrome is a developmental and epileptic encephalopathy characterized by seizures, behavioral abnormalities, developmental deficits, and elevated risk of sudden unexpected death in epilepsy (SUDEP). Most patient cases are caused by de novo loss-of-function mutations in the gene SCN1A, causing a haploinsufficiency of the alpha subunit of the voltage-gated sodium channel NaV1.1. Within the brain, NaV1.1 is primarily localized to the axons of inhibitory neurons, and decreased NaV1.1 function is hypothesized to reduce GABAergic inhibitory neurotransmission within the brain, driving neuronal network hyperexcitability and subsequent pathology. We have developed a human in vitro model of Dravet syndrome using differentiated neurons derived from patient iPSC and enriched for GABA expressing neurons. Neurons were plated on high definition multielectrode arrays (HD-MEAs), permitting recordings from the same cultures over the 7-weeks duration of study at the network, single cell, and subcellular resolution. Using this capability, we characterized the features of axonal morphology and physiology. Neurons developed increased spiking activity and synchronous network bursting. Recordings were processed through a spike sorting pipeline for curation of single unit activity and to assess the effects of pharmacological treatments. At 7-weeks, the application of the GABAAR receptor agonist muscimol eliminated network bursting, indicating the presence of GABAergic neurotransmission. To identify the role of NaV1.1 on neuronal and network activity, cultures were treated with a dose-response of the NaV1.1 potentiator δ-theraphotoxin-Hm1a. This resulted in a strong increase in firing rates of putative GABAergic neurons, an increase in the intraburst firing rate, and eliminated network bursting. These results validate that potentiation of NaV1.1 in Dravet patient iPSC-derived neurons results in decreased firing synchrony in neuronal networks through increased GABAergic neuron activity and support the use of human neurons and HD-MEAs as viable high-throughput electrophysiological platform to enable therapeutic discovery.

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Deletion of a non-canonical regulatory sequence causes loss of Scn1a expression and epileptic phenotypes in mice

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