Characterization of free fatty acid receptor family in rainbow trout (Oncorhynchus mykiss): towards a better understanding of their involvement in fatty acid signalisation.

Since 20 years of research, free fatty acids receptors (FFARs) have received considerable attention in mammals. To date, four FFARs (FFAR1, FFAR2, FFAR3 and FFAR4) are especially studied owing to their physiological importance in various biological processes. This ubiquitist group of G protein-coupled receptors (GPCRs) are majors reports in the key physiological functions such as the regulation of energy balance, metabolism or fatty acid sensing. However, up till date, even some studies were interested in their potential involvement in fatty acid metabolism, no genome investigation of these FFARs have been carried out in teleost fish. Through genome mining and phylogenetic analysis, we identified and characterised 7 coding sequences for ffar2 in rainbow trout whereas no ffar3 nor ffar4 gene have been found. This larger repertoire of ffar2 genes in rainbow trout results from successive additional whole-genome duplications which occurred in early teleosts and salmonids, respectively. A syntenic analysis was used to assign a new nomenclature to the salmonid ffar2 and showed a clear conservation of genomic organisation, further supporting the identity of these genes as ffar2. RT-qPCR was then used to examine, firstly during ontogenesis and secondly on feeding response the expression pattern of ffar1 and ffar2 genes in proximal gut and brain of all trout ffar genes. Overall, this study presents a comprehensive overview of the ffar family in rainbow trout.