title: Evolution of dimorphisms of the proteasome subunit beta type 8 gene (PSMB8) in basal ray-finned fish.
abstract: The proteasome subunit beta type 8 (PSMB8) gene encodes a catalytic subunit of immunoproteasome that plays a central role in the processing of antigenic peptides presented by major histocompatibility complex class I molecules. The A- and F-type alleles defined by the 31st amino acid residue determining cleaving specificity have been identified from ray-finned fish, amphibia, and reptiles. These two types show extremely long-term trans-species polymorphism in Polypteriformes, Cypriniformes, and Salmoniformes, suggesting the presence of very ancient lineages termed A and F. To elucidate the evolution of the PSMB8 dimorphism in basal ray-finned fish, we analyzed Pantodon buchholzi (Osteoglossiformes), seven species of Anguilliformes, and Hypomesus nipponensis (Osmeriformes). Both A and F lineage sequences were identified from P. buchholzi and H. nipponensis, confirming that these two lineages have been conserved by basal ray-finned fish. However, both the A- and F-type alleles found in Anguilliformes species belonged to the F lineage irrespective of their types. This apparently suggests that the A lineage was lost in the common ancestor of Anguilliformes, and recovery of the A type within the F lineage occurred in Anguilliformes. The apparent loss of the F lineage and recovery of the F type within the A lineage have already been reported from tetrapods and higher teleosts. However, this is the first report on the reverse situation and reveals the dynamic evolution of the PSMB8 dimorphism.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
authors.forename: Megumi
authors.initials: M
authors.lastname: Noro
authors.forename: Masaru
authors.initials: M
authors.lastname: Nonaka
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D005091:Exons; D005399:Fishes / Q000145:classification / Q000235:genetics*; D014644:Genetic Variation; D008969:Molecular Sequence Data; D009024:Morphogenesis / Q000235:genetics*; D010802:Phylogeny; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry / Q000235:genetics*; D016415:Sequence Alignment
chemical_list: C077436:LMP7 protein; D046988:Proteasome Endopeptidase Complex