The uptake of avermectins in Caenorhabditis elegans is dependent on Intra-Flagellar Transport and other protein trafficking pathways

Parasitic nematodes are globally important and place a heavy disease burden on infected humans, crops and livestock, while commonly administered anthelmintics used for treatment are being rendered ineffective by increasing levels of resistance. Although the modes of action and resistance mechanisms caused by detoxification and target site insensitivity for these compounds is well documented, the mechanisms for uptake, which can also cause resistance, are still poorly defined. It has recently been shown in the model nematode Caenorhabditis elegans that the avermectins or macrocyclic lactones such as ivermectin and moxidectin gain entry though the sensory cilia of the amphid neurons. This study interrogated the molecular mechanisms involved in the uptake of avermectins using a combination of forward genetics and targeted resistance screening approaches along with visualising a BODIPY labelled ivermectin analog and confirmed the importance of intraflagellar transport in this process. This approach also identified the protein trafficking pathways used by the downstream effectors and the components of the ciliary basal body that are required for effector entry into these non-motile structures. Mutations in many of the genes under investigation also resulted in resistance to the unrelated anthelmintic drugs albendazole and levamisole, giving insights into the potential mechanisms of multidrug resistance observed in field isolates of the parasitic nematodes that are a scourge of ruminant livestock. In total 50 novel C. elegans anthelmintic survival associated genes were identified in this study, three of which (daf-6, rab-35 and inx-19) are associated with broad spectrum cross resistance. When combined with previously known resistance genes, there are now 53 resistance associated genes which are directly involved in amphid, cilia and IFT function.