Natural antisense transcripts regulate the neuronal stress response and excitability

Abstract

Neurons regulate ionic fluxes across their plasma membrane to maintain their excitable properties under varying environmental conditions. However, the mechanisms that regulate ion channels abundance remain poorly understood. Here we show that pickpocket 29 (ppk29), a gene that encodes a Drosophila degenerin/epithelial sodium channel (DEG/ENaC), regulates neuronal excitability via a protein-independent mechanism. We demonstrate that the mRNA 3′UTR of ppk29 affects neuronal firing rates and associated heat-induced seizures by acting as a natural antisense transcript (NAT) that regulates the neuronal mRNA levels of seizure (sei), the Drosophila homolog of the human Ether-à-go-go Related Gene (hERG) potassium channel. We find that the regulatory impact of ppk29 mRNA on sei is independent of the sodium channel it encodes. Thus, our studies reveal a novel mRNA dependent mechanism for the regulation of neuronal excitability that is independent of protein-coding capacity.DOI: http://dx.doi.org/10.7554/eLife.01849.001

TheDrosophilaERG channelseizureplays a role in the neuronal homeostatic stress response

“…However, we found no effect of the s ei mutation on larval locomotion at 13°C relative to wild type controls (Fig 2H). Thus, although the precise biophysical role of hERG-type voltage-gated potassium channels in regulating neuronal excitability remains elusive, the in vivo data presented here, as well as previously published in vitro studies [34, 35], indicate that hERG channels play a specific role in maintaining optimal neuronal activity by protecting neurons from environmentally-induced hyperexcitability but not hypoexcitability [25].…”

“…Mutations in the seizure (sei) gene were initially identified in a forward genetic screen for temperature-sensitive (ts) alleles of excitability-related genes in Drosophila [23, 24]. Because sei was assumed to be an essential component of general neuronal excitability, the two original EMS-induced sei mutant alleles were assumed to be structural ts alleles [18, 23-25]. However, because recent studies indicate that these sei alleles are more likely null or hypomorphic [25], we hypothesized that the action of the sei channel is specifically required for the ability of neurons to respond to acute heat stress.…”

“…Because sei was assumed to be an essential component of general neuronal excitability, the two original EMS-induced sei mutant alleles were assumed to be structural ts alleles [18, 23-25]. However, because recent studies indicate that these sei alleles are more likely null or hypomorphic [25], we hypothesized that the action of the sei channel is specifically required for the ability of neurons to respond to acute heat stress. Thus, we next used a null allele of sei [43, 44] to demonstrate that sei activity is specifically required for the ability of adult flies to resist the impact of acute heat stress (Fig 2A-B).…”

“…The sei gene is expressed in diverse neuronal and non-neuronal cell types, including cardiac and muscle cells [32, 51]. Previous studies by us and others have shown that mutations in sei increase the overall organismal sensitivity to acute heat stress [23-25]. Yet, whether this organismal phenotype is driven by the action of sei in all cell types that express it was unknown.…”

“…To test our hypothesis, we first employed a reverse genetic approach to identify candidate genes specifically involved in the neuronal homeostatic response to acute heat stress. By using a tissue-specific RNAi knockdown screen of voltage-gated potassium channels, we identified seizure (sei) , the fly ortholog of the mammalian hERG channel (KCNH2) [18, 21-25], as an essential element in the neuronal homeostatic response to acute heat stress. Previous studies have indicated that dominant hERG mutations, which are one of the primary genetic causes for the cardiac Long QT Syndrome (LQTS) in humans [26, 27], are also associated with a high prevalence of generalized seizures [28].…”