Mutation of the Glc-2 Gene May Confer Dominant Ivermectin Resistance

Abstract

Background: Ivermectin is a widely used anti-parasitic drug that binds to and activates glutamate-gated chloride channels (GluCls), giving it its nematocidal (nematode-killing) properties. Due to excessive use of ivermectin, frequent cases of resistance to this nematicide are being reported, suggesting that ivermectin is beginning to lose its efficacy. This project seeks to study whether a mutation of the glc-2 gene, which encodes for a β subunit of the GluCl channel, confers ivermectin resistance. We hypothesize that a glc-2 mutation achieves nematicide resistance by creating a defective GluCl channel that cannot bind to ivermectin. Methods: We used classical genetics to obtain the desired mutants from stock worms. We then tested the worms for resistance profile using ivermectin sensitivity assays. Finally, we examined in vivo interactions by expressing relevant RNA in a heterologous system and performed electrophysiological recordings. Results: We were able to demonstrate that presence of the defective glc-2 leads to increased resistance profiles when given the chance to associate with select GluClα subunits (e.g. AVR-15). We also demonstrated that co-injection of glc-2 and glc-3 compromises GluCl response to L-glutamate, a critical indicator of channel functionality. Conclusion: Our results lend strong support to our hypothesis that glc-2 is able to interact with certain α subunits of GluCl to confer ivermectin resistance. This finding provides a framework for future dominant ivermectin resistance studies.