The NALCN regulator UNC-80 functions in a subset of interneurons to affect C. elegans avoidance response to the plant hormone methyl salicylate.

Abstract

NALCN (Na+ leak channel, non-selective), UNC80 and UNC79 form a non-selective, voltage-independent cation channel complex that affects a broad array of neuronal activities. The molecular and neuronal mechanisms underlying the functions of the NALCN complex remain unclear. In a screen for Caenorhabditis elegans mutants with defective avoidance response to the plant hormone methyl salicylate (MeSa), we isolated novel loss-of-function (lf) mutations in unc-80 and unc-79. unc-80 and unc-79 lf mutants exhibited defective MeSa avoidance but wild type-like responses to other odorants. Lf mutants of C. elegans nca/NALCN exhibited similar MeSa-specific avoidance defect, while lf mutants of the NALCN regulatory gene nlf-1 avoided MeSa like wild type. Using fluorescent transgenic animals, we identified a subset of unc-80-expressing neurons. Neuron-specific transgene rescue and knockdown experiments suggest that a subset of interneurons, primarily including AVA, AVE and AVG, might play a necessary and sufficient role in mediating unc-80 regulation of the MeSa avoidance. We found that unc-79 was expressed in neurons largely overlapping those expressing unc-80, which is supported by the rescue of unc-80(lf) defects using an unc-80 transgene driven by an unc-79 promoter. We also suggest that C. elegans locomotion responds more sensitively to the changes of expression levels of NALCN-related genes than the MeSa avoidance does. Together, our results identified NALCN-related genes as key regulators of the MeSa avoidance behavior and provided novel genetic and neuronal insights into the function of the NALCN channel complex.\n\nAuthor summaryNALCN (Na+ leak channel, non-selective) is a non-selective, voltage-independent cation channel that affects multiple neuronal activities and behaviors. Mutations in NALCN and its regulator UNC80 can cause serious neurological diseases. The regulation and function of the NALCN channel complex remain to be understood. From a genetic screen, we surprisingly found that the nematode Caenorhabditis elegans requires NALCN and its two regulators UNC-80 and UNC-79 to escape from the plant stress hormone methyl salicylate (MeSa). Using methods including transgenic neuronal labeling, rescues and knockdowns, we found that unc-80-expression in a subset of head interneurons, including AVA, AVE and AVG, might be necessary and sufficient to elicit the MeSa avoidance response. We also found that unc-79 functions in overlapping neurons as unc-80 to regulate C. elegans behaviors. Our findings provide novel molecular and neuronal mechanisms for understanding the regulation and function of the NALCN channel complex.