title: Evolution of the RH gene family in vertebrates revealed by brown hagfish (Eptatretus atami) genome sequences.
abstract: In vertebrates, there are four major genes in the RH (Rhesus) gene family, RH, RHAG, RHBG, and RHCG. These genes are thought to have been formed by the two rounds of whole-genome duplication (2R-WGD) in the common ancestor of all vertebrates. In our previous work, where we analyzed details of the gene duplications process of this gene family, three nucleotide sequences belonging to this family were identified in Far Eastern brook lamprey (Lethenteron reissneri), and the phylogenetic positions of the genes were determined. Lampreys, along with hagfishes, are cyclostomata (jawless fishes), which is a sister group of gnathostomata (jawed vertebrates). Although those results suggested that one gene was orthologous to the gnathostome RHCG genes, we did not identify clear orthologues for other genes. In this study, therefore, we identified three novel cDNA sequences that belong to the RH gene family using de novo transcriptome analysis of another cyclostome: the brown hagfish (Eptatretus atami). We also determined the nucleotide sequences for the RHBG and RHCG genes in a red stingray (Dasyatis akajei), which belongs to the cartilaginous fishes. The phylogenetic tree showed that two brown hagfish genes, which were probably duplicated in the cyclostome lineage, formed a cluster with the gnathostome RHAG genes, whereas another brown hagfish gene formed a cluster with the gnathostome RHCG genes. We estimated that the RH genes had a higher evolutionary rate than the RHAG, RHBG, and RHCG genes. Interestingly, in the RHBG genes, only the bird lineage showed a higher rate of nonsynonymous substitutions. It is likely that this higher rate was caused by a state of relaxed functional constraints rather than positive selection nor by pseudogenization.
authors.affiliation: Department of Biomolecular Functional Engineering, College of Engineering, Ibaraki University, 4-12-1 Nakanarusawa-cho, Hitachi 316-8511, Japan.
authors.forename: Akinori
authors.initials: A
authors.lastname: Suzuki
authors.affiliation: Department of Biomolecular Functional Engineering, College of Engineering, Ibaraki University, 4-12-1 Nakanarusawa-cho, Hitachi 316-8511, Japan.
authors.forename: Hidero
authors.initials: H
authors.lastname: Komata
authors.affiliation: Department of Biomolecular Functional Engineering, College of Engineering, Ibaraki University, 4-12-1 Nakanarusawa-cho, Hitachi 316-8511, Japan.
authors.forename: Shogo
authors.initials: S
authors.lastname: Iwashita
authors.affiliation: Department of Biomolecular Functional Engineering, College of Engineering, Ibaraki University, 4-12-1 Nakanarusawa-cho, Hitachi 316-8511, Japan.
authors.forename: Shotaro
authors.initials: S
authors.lastname: Seto
authors.affiliation: Department of Biomolecular Functional Engineering, College of Engineering, Ibaraki University, 4-12-1 Nakanarusawa-cho, Hitachi 316-8511, Japan.
authors.forename: Hironobu
authors.initials: H
authors.lastname: Ikeya
authors.affiliation: Department of Biomolecular Functional Engineering, College of Engineering, Ibaraki University, 4-12-1 Nakanarusawa-cho, Hitachi 316-8511, Japan.
authors.forename: Mitsutoshi
authors.initials: M
authors.lastname: Tabata
authors.affiliation: Department of Biomolecular Functional Engineering, College of Engineering, Ibaraki University, 4-12-1 Nakanarusawa-cho, Hitachi 316-8511, Japan. Electronic address: takashi.kitano.evolution@vc.ibaraki.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kitano
mesh_terms: D000818:Animals; D004272:DNA, Mitochondrial / Q000737:chemistry / Q000145:classification / Q000378:metabolism; D019143:Evolution, Molecular; D020869:Gene Expression Profiling; D016678:Genome; D006196:Hagfishes / Q000145:classification / Q000235:genetics*; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000145:classification / Q000235:genetics; D012204:Rh-Hr Blood-Group System / Q000145:classification / Q000235:genetics*; D017422:Sequence Analysis, DNA
chemical_list: D004272:DNA, Mitochondrial; D012336:RNA, Ribosomal, 16S; D012204:Rh-Hr Blood-Group System
keywords: Duplication; Evolutionary rate; Gene family; Hagfish; RH blood group