Genomic organization and evolution of the vomeronasal type 2 receptor-like (OlfC) gene clusters in Atlantic salmon, Salmo salar

• Published in: Molecular Biology and Evolution
• Main Authors: Johnstone, Kimberley A., Ciborowski, Kate L., Lubieniecki, Krzysztof P., Chow, William, Phillips, Ruth B., Koop, Ben F., Jordan, William C., Davidson, William S.
• Format: Text
• Language: English
• Published: Oxford University Press 2009
• Subjects: Research Article; Atlantic salmon; Salmo salar
• Online Access: http://mbe.oxfordjournals.org/cgi/content/short/msp027v1; https://doi.org/10.1093/molbev/msp027

There are three major multigene superfamilies of olfactory receptors (OR, V1R and V2R) in mammals. The ORs are expressed in the main olfactory organ whereas the V1Rs and V2Rs are located in the vomeronasal organ. Fish only possess one olfactory organ in each nasal cavity, the olfactory rosette; therefore, it has been proposed that their V2R-like genes be classified as olfactory C family GPCRs ( OlfC ). There are large variations in the sizes of olfactory receptor gene repertoires. Previous studies have shown that fish have between 12 and 46 functional V2R-like genes whereas humans have lost all functional V2Rs and frog sp. have more than 240. Pseudogenization of V2R genes is a prevalent event across species. In the mouse and frog genomes there are approximately double the number of pseudogenes compared to functional genes. An oligonucleotide probe was designed from a conserved sequence from two Atlantic salmon OlfC genes and used to screen the Atlantic salmon BAC library. Hybridization positive BACs were matched to fingerprint contigs and representative BACs were shotgun cloned and sequenced. We identified 55 OlfC genes. Twenty-nine of the OlfC genes are classified as putatively functional genes and 26 as pseudogenes. The OlfC genes are found in two genomic clusters on chromosomes 9 and 20. Phylogenetic analysis revealed that the OlfC genes could be divided into ten subfamilies, with nine of these subfamilies corresponding to subfamilies found in other teleosts and one being salmon-specific. There is also a large expansion in the number of OlfC genes in one subfamily in Atlantic salmon. Subfamily gene expansions have been identified in other teleosts and these differences in gene number reflect species-specific evolutionary requirements for olfaction. Total RNA was isolated from the olfactory epithelium and other tissues from a pre-smolt to examine the expression of the odorant genes. Several of the putative OlfC genes that we identified are expressed only in the olfactory epithelium, consistent with these genes ...