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.

Extendingjulius seizure, a bang-sensitive gene, as a model for studying epileptogenesis: Cold shock, and a new insertional mutation

“…RNAijus expression with elav-, VGAT-, VGlut, and ChAT-GAL4 drivers all provided significant cold-sensitivity relative to flies carrying only the GAL4 or RNAi construct. Of the neurotransmitter-specific GAL4s, ChAT-GAL4 was the most effective RNAi-jus driver for causing cold-sensitive paralysis, just as it was for inducing bang-sensitivity [12]. In the previous study we had not observed bang-sensitivity when the RNAi-jus contruct was expressed with a glutamatergic driver (V-glut-GAL4), but did more recently when we raised flies at 29 C to increase GAL4 function (data not shown).…”

“…caused by jus GFSTF and the differing subcellular localization of the MiMiC tag from the C-terminally tagged genomic fosmid construct previously reported [12] suggests that mislocalization may be partially responsible for the mutant phenotype caused by the MiMiC insertion. This mislocalization may stem from the failure of Jus GFSTF to bind to axonal-targeting proteins such as X11L [14].…”

“…While the MiMiC tagged protein likely does not represent the endogenous localization of Jus, its tendency to localize to cell bodies can be used more easily in colocalization studies than one that localizes to axons. We previously showed that a GAL4 line driven by genomic DNA from the jus locus (w; P{y[+t7.7] w [+mC] = GMR55G02-GAL4}attP2) was able to rescue the bang-sensitive phenotype of jus sda iso7.8 [12]. To explore the neuronal overlap between the GAL4 expression and jus GFSTF , we generated a line with a nuclear localized UAS-nls-mCherry reporter and jus GFSTF and crossed it to the GAL4 above.…”

“…Our recent work identified sda iso7.8 (now jus sda iso7.8 ) as an allele of julius seizure, the previously uncharacterized CG14509 gene. jus is expressed in a limited number of neurons during development, selective RNAi knockdown of jus results in BS adults, and a developmentally defined stage is important for the severity of the jus BS phenotype [12]. Thus, julius seizure has many of the features with which to study the process of epileptogenesis.…”

Shortened Lifespan and Other Age-Related Defects in Bang Sensitive Mutants ofDrosophila melanogaster

“…Other bs mutant do not appear to affect mitochondrial function directly. The bs mutant paralyzed bss ( abbreviated as bss for the remainder of this paper ) is an allele of the Na channel gene, while the cellular role of julius seizure remains unclear (Parker et al 2011; Horne et al 2017 ) . However, all of these strains of bs mutants show very similar, if not identical, neurological phenotypes.…”