Authors

P McVeigh¹; D Wells¹; E McCammick¹; P McCusker¹; J E Hodgkinson²; S Paterson²; A Mousley¹; N J Marks¹; A G Maule¹;  ¹ Queen's University Belfast, UK;  ² University of Liverpool, UK

Discussion

GPCRs are established drug targets in human medicine.  Despite their considerable appeal as anthelmintic targets, poor understanding of GPCR diversity and function in parasitic helminths has thwarted progress towards GPCR-targeted anti-parasite drugs.  To facilitate GPCR research in the liver fluke, Fasciola hepatica, we have generated the first profile of GPCRs from the F. hepatica genome.  Our dataset describes 147 high confidence GPCRs, representing the largest cohort of GPCRs, and the largest set of in silico ligand-receptor predictions, yet reported in any parasitic helminth.  All GPCRs fall within the established GRAFS nomenclature, comprising three glutamate, 135 rhodopsin, two adhesion, five frizzled, one smoothened, and one secretin GPCR.  Amongst rhodopsins were 18 highly diverged receptors that maintained core rhodopsin signatures, but lacked significant similarity with non-flatworm sequences, providing a new sub-group of potential flukicide targets.  Seventy-six orthologous sequences in other flatworm genomes identified these as new members of existing groups (PROF1/Srfb, Rho-L, Rho-R, Srfa, Srfc) of flatworm-specific rhodopsins.  These receptors imply flatworm specific GPCR functions, and/or co-evolution with unique flatworm ligands, and could facilitate the development of selective anthelmintics.  Liver fluke homologues of deorphanised rhodopsins displayed sequence conservation of ligand binding domains.  These data enabled high confidence ligand-receptor matching of 17 receptors activated by acetylcholine, neuropeptide F/Y, octopamine or serotonin.  RNA-Seq analyses showed expression of 101 GPCRs across various developmental stages, with the majority expressed most highly in the pathogenic, intra-mammalian, juvenile parasites.  These data identify a broad complement of GPCRs in F. hepatica, including rhodopsins likely to have key functions in neuromuscular control and sensory perception, as well as frizzled and adhesion/secretin families implicated, in other species, in growth, development and reproduction.  This catalogue of liver fluke GPCRs provides new opportunities to study flatworm biology and to advance anthelmintic discovery.  Ongoing work aims to localise sites of GPCR gene expression through in situ hybridisation and investigate GPCR functions through RNA interference (RNAi).