title: Distinct functions of two olfactory marker protein genes derived from teleost-specific whole genome duplication.
abstract: BACKGROUND
  Whole genome duplications (WGDs) have been proposed to have made a significant impact on vertebrate evolution. Two rounds of WGD (1R and 2R) occurred in the common ancestor of Gnathostomata and Cyclostomata, followed by the third-round WGD (3R) in a common ancestor of all modern teleosts. The 3R-derived paralogs are good models for understanding the evolution of genes after WGD, which have the potential to facilitate phenotypic diversification. However, the recent studies of 3R-derived paralogs tend to be based on in silico analyses. Here we analyzed the paralogs encoding teleost olfactory marker protein (OMP), which was shown to be specifically expressed in mature olfactory sensory neurons and is expected to be involved in olfactory transduction.
  
  
  RESULTS
  Our genome database search identified two OMPs (OMP1 and OMP2) in teleosts, whereas only one was present in other vertebrates. Phylogenetic and synteny analyses suggested that OMP1 and 2 were derived from 3R. Both OMPs showed distinct expression patterns in zebrafish; OMP1 was expressed in the deep layer of the olfactory epithelium (OE), which is consistent with previous studies of mice and zebrafish, whereas OMP2 was sporadically expressed in the superficial layer. Interestingly, OMP2 was expressed in a very restricted region of the retina as well as in the OE. In addition, the analysis of transcriptome data of spotted gar, a non-teleost fish, revealed that single OMP gene was expressed in the eyes.
  
  
  CONCLUSIONS
  We found distinct expression patterns of zebrafish OMP1 and 2 at the tissue and cellular level. These differences in expression patterns may be explained by subfunctionalization as the model of molecular evolution. Namely, single OMP gene was speculated to be originally expressed in the OE and the eyes in the common ancestor of all Osteichthyes (bony fish including tetrapods). Then, two OMP gene paralogs derived from 3R-WGD reduced and specialized the expression patterns. This study provides a good example for analyzing a functional subdivision of the teleost OE and eyes as revealed by 3R-derived paralogs of OMPs.
authors.affiliation: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, 226-8501, Japan. hisuzuki@bio.titech.ac.jp.
authors.forename: Hikoyu
authors.initials: H
authors.lastname: Suzuki
authors.affiliation: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, 226-8501, Japan. mnikaido@bio.titech.ac.jp.
authors.forename: Masato
authors.initials: M
authors.lastname: Nikaido
authors.affiliation: Department of Dementia and Higher Brain Function, Integrated Neuroscience Research Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, 156-8506, Japan. yamagishi-km@igakuken.or.jp.
authors.forename: Kimiko
authors.initials: K
authors.lastname: Hagino-Yamagishi
authors.affiliation: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, 226-8501, Japan. nokada@fais.or.jp.|Foundation for Advancement of International Science, Tsukuba, 305-0821, Japan. nokada@fais.or.jp.|Department of Life Sciences, National Cheng Kung University, Tainan, 701, Taiwan. nokada@fais.or.jp.
authors.forename: Norihiro
authors.initials: N
authors.lastname: Okada
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019143:Evolution, Molecular; D005399:Fishes / Q000145:classification / Q000235:genetics*; D020440:Gene Duplication; D016678:Genome; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D051842:Olfactory Marker Protein / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D012160:Retina / Q000378:metabolism; D016415:Sequence Alignment; D026801:Synteny; D059467:Transcriptome; D015027:Zebrafish / Q000235:genetics
chemical_list: D051842:Olfactory Marker Protein