Dataset Information

Julius seizure, a Drosophila Mutant, Defines a Neuronal Population Underlying Epileptogenesis.

ABSTRACT: Epilepsy is a neural disorder characterized by recurrent seizures. Bang-sensitive Drosophila represent an important model for studying epilepsy and neuronal excitability. Previous work identified the bang-sensitive gene slamdance (sda) as an allele of the aminopeptidase N gene. Here we show through extensive genetic analysis, including recombination frequency, deficiency mapping, transposon insertion complementation testing, RNA interference (RNAi), and genetic rescue that the gene responsible for the seizure sensitivity is julius seizure (jus), formerly CG14509, which encodes a novel transmembrane domain protein. We also describe more severe genetic alleles of jus RNAi-mediated knockdown of jus revealed that it is required only in neurons and not glia, and that partial bang-sensitivity is caused by knockdown in GABAergic or cholinergic but not glutamatergic neurons. RNAi knockdown of jus at the early pupal stages leads to strong seizures in adult animals, implicating that stage as critical for epileptogenesis. A C-terminal-tagged version of Jus was generated from a fosmid genomic clone. This fosmid fusion rescued the bang-sensitive phenotype and was expressed in the optic lobes and the subesophageal and thoracic abdominal ganglia. The protein was primarily localized in axons, especially in the neck connectives, extending into the thoracic abdominal ganglion.

SUBMITTER: Horne M

PROVIDER: S-EPMC5340337 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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julius seizure, a Drosophila Mutant, Defines a Neuronal Population Underlying Epileptogenesis.

Horne Meghan M Krebushevski Kaitlyn K Wells Amelia A Tunio Nahel N Jarvis Casey C Francisco Glen G Geiss Jane J Recknagel Andrew A Deitcher David L DL

Genetics 20170111 3

Epilepsy is a neural disorder characterized by recurrent seizures. Bang-sensitive Drosophila represent an important model for studying epilepsy and neuronal excitability. Previous work identified the bang-sensitive gene slamdance (sda) as an allele of the aminopeptidase N gene. Here we show through extensive genetic analysis, including recombination frequency, deficiency mapping, transposon insertion complementation testing, RNA interference (RNAi), and genetic rescue ...[more]

PMID: 28082408

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Project description:ObjectivesThe M-current is a low-threshold voltage-gated potassium current generated by Kv7 subunits that regulates neural excitation. It is important to note that M-current suppression, induced by activation of Gq-coupled neurotransmitter receptors, can dynamically regulate the threshold of action-potential firing and firing frequency. Here we sought to directly examine whether M-current suppression is involved in seizures and epileptogenesis.MethodsKv7.2 knock-in mice lacking the key protein kinase C (PKC) phosphorylation acceptor site for M-current suppression were generated by introducing an alanine substitution at serine residue 559 of mouse Kv7.2, mKv7.2(S559A). Basic electrophysiologic properties of the M-current between wild-type and Kv7.2(S559A) knock-in mice were analyzed in primary cultured neurons. Homozygous Kv7.2(S559A) knock-in mice were used to evaluate the protective effect of mutant Kv7.2 channel against chemoconvulsant-induced seizures. In addition, pilocarpine-induced neuronal damage and spontaneously recurrent seizures were evaluated after equivalent chemoconvulsant-induced status epilepticus was achieved by coadministration of the M-current-specific channel inhibitor, XE991.ResultNeurons from Kv7.2(S559A) knock-in mice showed normal basal M-currents. Knock-in mice displayed reduced M-current suppression when challenged by a muscarinic agonist, oxotremorine-M. Kv7.2(S559A) mice were resistant to chemoconvulsant-induced seizures with no mortality. Administration of XE991 transiently exacerbated seizures in knock-in mice equivalent to those of wild-type mice. Valproate, which disrupts neurotransmitter-induced M-current suppression, showed no additional anticonvulsant effect in Kv7.2(S559A) mice. After experiencing status epilepticus, Kv7.2(S559A) knock-in mice did not show seizure-induced cell death or spontaneous recurring seizures.SignificanceThis study provides evidence that neurotransmitter-induced suppression of M-current generated by Kv7.2-containing channels exacerbates behavioral seizures. In addition, prompt recovery of M-current after status epilepticus prevents subsequent neuronal death and the development of spontaneously recurrent seizures. Therefore, prompt restoration of M-current activity may have a therapeutic benefit for epilepsy.

Project description:There is clinical need to extend the understanding of epilepsy and to find novel approaches to treat this condition. Bang-sensitive (bs) Drosophila mutants, which exhibit reduced thresholds for seizure, offer an attractive possibility to combine tractable genetics, electrophysiology, and high-throughput screening. However, despite these advantages, the precise electrophysiological aberrations that contribute to seizure have not been identified in any bs mutant. Because of this, the applicability of Drosophila as a preclinical model has not yet been established. In this study, we show that electroshock of bs slamdance (sda) larvae was sufficient to induce extended seizure-like episodes. Whole cell voltage-clamp recordings from identified motoneurons (termed aCC and RP2) showed synaptic currents that were greatly increased in both amplitude and duration. Current-clamp recordings indicated that these inputs produced longer-lived plateau depolarizations and increased action potential firing in these cells. An analysis of voltage-gated currents in these motoneurons, in both first and third instar larvae, revealed a consistently increased persistent Na(+) current (I(Nap)) and a reduced Ca(2+) current in first instar larvae, which appeared normal in older third instar larvae. That increased I(Nap) may contribute to seizure-like activity is indicated by the observation that feeding sda larvae the antiepileptic drug phenytoin, which was sufficient to reduce I(Nap), rescued both seizure-like episode duration and synaptic excitation of motoneurons. In contrast, feeding of either anemone toxin, a drug that preferentially increases I(Nap), or phenytoin to wild-type larvae was sufficient to induce a bs behavioral phenotype. Finally, we show that feeding of phenytoin to gravid sda females was sufficient to both reduce I(Nap) and synaptic currents and rescue the bs phenotype in their larval progeny, indicating that a heightened predisposition to seizure may arise as a consequence of abnormal embryonic neural development.

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Dataset Information

Julius seizure, a Drosophila Mutant, Defines a Neuronal Population Underlying Epileptogenesis.

Publications

<i>julius seizure</i>, a <i>Drosophila</i> Mutant, Defines a Neuronal Population Underlying Epileptogenesis.

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