Conservation of members of the free fatty acid receptor gene family in common carp.

Accumulating evidence supports the crucial role intestinal microbiota and their metabolites play in the homeostasis of organisms. An important class of metabolites that have been shown to affect the immune system are short chain fatty acids (SCFAs). These SCFAs can affect the host cells via passive diffusion or via ligation to receptors, among others G-protein coupled receptor (GPR) 41 and 43. GPR41 and GPR43 are both part of a family of GPR40-related receptors. Mammalian studies have shown an important role for GPR41 and GPR43 in the modulation of immune responses by SCFAs. However, up till date, no validated coding sequences for orthologues of these SCFA receptors have been published for teleost fish. We used genomic resources and cDNA cloning, to identify and validate ten coding sequences for gpr40L genes in common carp. Phylogenetic analysis showed a division into three subclasses, putatively named class a, b and c, and showed the common carp genes had a closer phylogenetic relationship to mammalian GPR43 than to mammalian GPR41. Synteny analysis revealed a clear conservation of syntenic relationships between gpr40L in the genomes of spotted gar and common carp with the relevant region in the human genome. This conservation of synteny validates the genes identified, as gpr40L. Finally, presence of gpr40L genes was investigated in silico for genomes of 25 different, mostly teleost, fish species largely confirming the observations for gpr40L of common carp with regards to both, subdivision in three subclasses a-c and conservation of synteny. Our data provide an important first step towards an understanding of the role and function of receptors for SCFAs and immunomodulation in fish.