title: Lineage-specific expansion of vomeronasal type 2 receptor-like (OlfC) genes in cichlids may contribute to diversification of amino acid detection systems.
abstract: Fish use olfaction to sense a variety of nonvolatile chemical signals in water. However, the evolutionary importance of olfaction in species-rich cichlids is controversial. Here, we determined an almost complete sequence of the vomeronasal type 2 receptor-like (OlfC: putative amino acids receptor in teleosts) gene cluster using the bacterial artificial chromosome library of the Lake Victoria cichlid, Haplochromis chilotes. In the cluster region, we found 61 intact OlfC genes, which is the largest number of OlfC genes identified among the seven teleost fish investigated to date. Data mining of the Oreochromis niloticus (Nile tilapia) draft genome sequence, and genomic Southern hybridization analysis revealed that the ancestor of all modern cichlids had already developed almost the same OlfC gene repertoire, which was accomplished by lineage-specific gene expansions. Furthermore, comparison of receptor sequences showed that recently duplicated paralogs are more variable than orthologs of different species at particular sites that were predicted to be involved in amino acid selectivity. Thus, the increase of paralogs through gene expansion may lead to functional diversification in detection of amino acids. This study implies that cichlids have developed a potent capacity to detect a variety of amino acids (and their derivatives) through OlfCs, which may have contributed to the extraordinary diversity of their feeding habitats.
authors.affiliation: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Nikaido
authors.forename: Hikoyu
authors.initials: H
authors.lastname: Suzuki
authors.forename: Atsushi
authors.initials: A
authors.lastname: Toyoda
authors.forename: Asao
authors.initials: A
authors.lastname: Fujiyama
authors.forename: Kimiko
authors.initials: K
authors.lastname: Hagino-Yamagishi
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Kocher
authors.forename: Karen
authors.initials: K
authors.lastname: Carleton
authors.forename: Norihiro
authors.initials: N
authors.lastname: Okada
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D023681:Cichlids / Q000145:classification* / Q000235:genetics*; D019143:Evolution, Molecular; D029941:Fish Proteins / Q000235:genetics*; D005784:Gene Amplification; D018628:Gene Dosage; D054834:Lipocalins / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D029941:Fish Proteins; D054834:Lipocalins