Differential modulation of C. elegans motor behavior by NALCN and two-pore domain potassium channels

Author summaryTwo-pore domain potassium channels (K2P) allow outward "leak" of potassium ions. The NALCN channel complex allows inward flow of sodium and other cations. K2Ps and NALCN are implicated in severe human diseases. Using the nematode Caenorhabditis elegans as a model to study the behavioral effects of K2P TWK-40 and NALCN, we found opposite effects of TWK-40 and NALCN on the body curvature. We identified five other K2P genes, including twk-2, twk-17, twk-30, twk-48 and unc-58, as potential modulators of the motor behavior and confirmed the behavioral effect of the previously studied twk-7. These twk genes interacted genetically with twk-40 in a variable manner, and twk-2 exhibited an interdependent relationship with twk-40. In addition, twk-2 and unc-58 appeared to affect the body curvature in opposition to NALCN, and twk-7 appeared to affect the locomotion in opposition to NALCN. Finally, we found that the chemical property of TWK-40 amino acid 159 can affect the channel activity. Together, we suggest that TWK-40 is a novel regulator of C. elegans motor behavior, five other K2Ps can potentially modulate the behavior, and some K2Ps and NALCN may oppositely affect the behavior. Two-pore domain potassium channels (K2P) are a large family of "background" channels that allow outward "leak" of potassium ions. The NALCN/UNC80/UNC79 complex is a non-selective channel that allows inward flow of sodium and other cations. It is unclear how K2Ps and NALCN differentially modulate animal behavior. Here, we found that loss of function (lf) in the K2P gene twk-40 suppressed the reduced body curvatures of C. elegans NALCN(lf) mutants. twk-40(lf) caused a deep body curvature and extended backward locomotion, and these phenotypes appeared to be associated with neuron-specific expression of twk-40 and distinct twk-40 transcript isoforms. To survey the functions of other less studied K2P channels, we examined loss-of-function mutants of 13 additional twk genes expressed in the motor circuit and detected defective body curvature and/or locomotion in mutants of twk-2, twk-17, twk-30, twk-48, unc-58, and the previously reported twk-7. We generated presumptive gain-of-function (gf) mutations in twk-40, twk-2, twk-7, and unc-58 and found that they caused paralysis. Further analyses detected variable genetic interactions between twk-40 and other twk genes, an interdependence between twk-40 and twk-2, and opposite behavioral effects between NALCN and twk-2, twk-7, or unc-58. Finally, we found that the hydrophobicity/hydrophilicity property of TWK-40 residue 159 could affect the channel activity. Together, our study identified twk-40 as a novel modulator of the motor behavior, uncovered potential behavioral effects of five other K2P genes and suggests that NALCN and some K2Ps can oppositely affect C. elegans behavior.