Seizure Suppression bytop1Mutations inDrosophila

Abstract

DNA topoisomerase I is an essential nuclear enzyme involved in resolving the torsional stress associated with DNA replication, transcription, and chromatin condensation. Here we report the discovery of a seizure-suppressor mutant, top1 JS , which suppresses seizures in a Drosophila model of human epilepsy. A P-element mutagenesis screen using easily shocked seizure-sensitive mutant as a genetic background identified top1 JS , which plays a novel role in regulating nervous system excitability. Plasmid rescue, excision, complementation, and sequencing analyses verified that top1JS results from a P-element insertion in the 5Ј untranslated region. Quantitative reverse transcription analysis on wild-type and mutant fly heads showed that the top1 JS mutation causes reduced transcription level in the CNS, suggesting a partial loss-of-function mutation. Electrophysiological experiments revealed normal seizure thresholds in top1 JS mutants, which are different from other seizure suppressors identified previously, suggesting a novel mechanism underlying seizure suppression by top1 JS . The pharmacological camptothecin feeding experiment and cell death analysis suggested that the seizure suppression by top1 JS may occur via increased neuronal apoptosis. Furthermore, overexpression of the DIAP1 (Drosophila inhibitor of apoptosis 1) gene rescues top1 JS suppression, providing additional support for a neural apoptosis suppression mechanism. The top1 JS mutation is the first viable partial loss-of-function mutation identified in higher eukaryotes, and the results presented here point to a novel function for topo I in construction and/or maintenance of circuits required for seizure propagation in vivo.

Disruption of Endocytosis with the Dynamin Mutantshibirets1Suppresses Seizures inDrosophila

“…However, a minor decrease in bang sensitivity was seen in the shi ts ; sda double mutant ( Figure 1B). Bang sensitivity in sda has been described previously as easier to suppress than eas or para bss1 (Zhang et al 2002;Song et al 2007). Because SCN1A sodium channel mutations in human patients are heterozygous, we also tested heterozygous para bss1 /+ flies, which show semidominant bang sensitivity.…”

Seizure suppression through manipulating splicing of a voltage-gated sodium channel

“…For example, topoisomerase 1 ( top1 JS ) and gilgamesh mutant flies, as well as the topoisomerase 1 inhibitor, camptothecin, reduce the severity of bss 1 seizure behaviour (Song et al , 2007; Howlett et al , 2013). In this study, the candidates of our screen are seizure suppressor genes which regulate a common downstream gene transcript, DmNa v .…”

Topoisomerase 1 inhibition reversibly impairs synaptic function

“…TOP1 deletion is lethal in flies and mice (46,47). However, a mutation that reduced TOP1 expression in the fly brain was not lethal and suppressed seizure-like behavior (47).…”

“…TOP1 deletion is lethal in flies and mice (46,47). However, a mutation that reduced TOP1 expression in the fly brain was not lethal and suppressed seizure-like behavior (47). Feeding flies TOP1 inhibitors, including camptothecin (a derivative of topotecan) and apigenin (a flavone found in fruits and vegetables) also suppressed seizures (48).…”