Role of the DSC1 Channel in Regulating Neuronal Excitability in Drosophila melanogaster: Extending Nervous System Stability under Stress

摘要

Voltage-gated ion channels are essential for electrical signaling in neurons and other excitable cells. Among them, voltage-gated sodium and calcium channels are four-domain proteins, and ion selectivity is strongly influenced by a ring of amino acids in the pore regions of these channels. Sodium channels contain a DEKA motif (i.e., amino acids D, E, K, and A at the pore positions of domains I, II, III, and IV, respectively), whereas voltage-gated calcium channels contain an EEEE motif (i.e., acidic residues, E, at all four positions). Recently, a novel family of ion channel proteins that contain an intermediate DEEA motif has been found in a variety of invertebrate species. However, the physiological role of this new family of ion channels in animal biology remains elusive. DSC1 in Drosophila melanogaster is a prototype of this new family of ion channels. In this study, we generated two DSC1 knockout lines using ends-out gene targeting via homologous recombination. DSC1 mutant flies exhibited impaired olfaction and a distinct jumpy phenotype that is intensified by heat shock and starvation. Electrophysiological analysis of the giant fiber system (GFS), a well-defined central neural circuit, revealed that DSC1 mutants are altered in the activities of the GFS, including the ability of the GFS to follow repetitive stimulation (i.e., following ability) and response to heat shock, starvation, and pyrethroid insecticides. These results reveal an important role of the DSC1 channel in modulating the stability of neural circuits, particularly under environmental stresses, likely by maintaining the sustainability of synaptic transmission. Author Summary Voltage-gated sodium and calcium channels are four-domain proteins that are essential for electrical signaling in neurons and other excitable cells. Recent genomic and functional analyses reveal a novel family of four-domain, Ca~(2+)-selective cation channels in a variety of invertebrates, from sea anemones to insects. The amino acid sequences and gating properties of these channels appear to be intermediate between sodium and calcium channels; as such, these channels could potentially be an important evolutionary link between sodium and calcium channels. Despite the intriguing nature of this family of cation channels, their role in animal physiology remains mysterious. In this study, taking advantage of the genetic tractability of the fruit fly, Drosophila melanogaster , we examined the physiological role of such a channel, called DSC1, in this model insect. We generated two DSC1 knockout lines and conducted behavioral and electrophysiological analyses. Our results show that the DSC1 channel contributes to neuronal excitability regulation and plays a unique role in retaining stability of the nervous system function in response to environmental stresses, including heat shock and starvation. Interestingly, the DSC1 knockout flies were also more susceptible to pyrethroid insecticides, which are used globally as a major weapon against the malaria-carrying mosquitoes.