Isolation and characterisation of main olfactory and vomeronasal receptor gene families from the Atlantic salmon ( Salmo salar)

Abstract

The Atlantic salmon ( Salmo salar) has been widely used as a model species in studies of olfactory signal transduction and processing. Here we report the isolation and characterisation of salmon olfactory receptor ( SOR) and salmon vomeronasal receptor ( SVR) partial sequences from Atlantic salmon. Six groups of SOR sequences ( SORA–F) and three groups of SVR sequences ( SVRA–C) were identified. All SORB, SORF, SVRB and SVRC sequences contained uninterrupted open reading frames. However, all SORA sequences and members of the SVRA sequence family contained multiple stop codons while SORC and SORE sequences were truncated in the 3′ region of the sequence. Full length SORF and almost complete SORB sequences displayed amino acid residues and motifs conserved in fish olfactory receptor genes. In sequence phylogenies, SOR sequences fell into the main olfactory receptor ( MOR) type I clade and were most closely related to either δ or ζ reference sequences, while all SVR sequences grouped within a clade of fish type 2 vomeronasal receptor ( V2R) sequences. A family of sequences ( Sasa CaSR1–6), isolated using the same degenerate primers that amplified SVR sequences, clustered within a group of calcium sensing receptor ( CaSR) sequences. Analysis of tissue expression patterns of sequences by reverse transcriptase polymerase chain reaction showed that they were transcribed in olfactory epithelium ( SORB, SORF, all SVR and Sasa CaSR sequences), testis ( SORB, SORD and Sasa CaSR) and/or anterior kidney ( SORB and Sasa CaSR). Similar analysis of expression supported the identification of SORA sequences as non-transcribed pseudogene(s). Although the level of occurrence of OR pseudogenes is within the range found for other, well-characterised vertebrate OR genomes, it does not seem to reflect the importance of olfaction in the biology of the Atlantic salmon.