種別 ワークショップ 提案者 西田 睦（東大海洋研） 趣旨 脊椎動物は，よく発達した骨格系，筋肉系，神経系，循環系などに特徴づけられる非常に組織化された体制をもっており，著しく高い活動性を有する生き物である。脊椎動物の主要な系統はいずれも"魚型"の動物であるが，そのひとつがわれわれヒトを含む四肢動物となっている。この高度に組織化された活動的な動物の進化を明らかにするには，基礎にある魚型の動物の多様性をしっかりとおさえ，その土台の上に，鍵となる遺伝的変化がどのようなものであったのかを解明することが必要である。21世紀に入り，フグ，メダカ，ゼブラフィッシュという３種の魚類のゲノムシーケンシングが急速に進みつつあり，比較ゲノム学的な側面からこの課題にアプローチする条件が現実のものとなりつつある。一方，魚類のミトコンドリアゲノムの全塩基対解読も急速に進展しており，400種を超える解析から魚型動物の主要な系統間の関係に新たな光が当てられ，比較研究のために不可欠な信頼に足る系統枠が構築されつつある。さらに，脊椎動物とともに脊索動物門を構成する尾索動物（ホヤ類）や頭索動物(ナメクジウオ類）についての研究も，ゲノム解析を含めて大きく展開しており，これらとの比較はさらに立体的な脊椎動物進化の理解をもたらすこと間違いない。本ワークショップでは，これらの新しい研究がどこまで進展しているかを何人かの研究者に提示していただき，より総合的・本格的な比較研究の展望について議論する。 予定講演者の氏名、所属、タイトル
- 「ミトコンドリア全ゲノム解析に基づく魚類の新しい系統像構築」
○宮 正樹（千葉中央博）
・Major patterns of the ray-finned fish phylogenies: A new perspective based on >200 complete mitochondrial DNA sequences
○Masaki Miya (Nat. Hist. Mus. & Inst.,)Actinopterygii, the ray-finned fish, is the most diversified group of all vertebrates, currently comprising over 25,000 species placed in 42 orders, 431 families, and 4075 genera. Because of the enormous species diversity involved, ancient origin that goes back some 400 million years ago, and the wide ranging variations not only in morphology but also in behavior, ecology, and physiology, there remains much controversy over the higher-level relationships of actinopterygians. Our research group has determined complete mitochondrial DNA sequences from unprecedentedly large number of species (ca. 500) that covers a whole spectrum of actinopterygian diversity. We will present results from phylogenetic analyses of this large data set which is divided into the following three hierarchical levels: 1) basal actinopterygians; 2) higher actinopterygians; and 3) percomorphs. We have discovered many examples of previously-unrecognized, major comprehensive groups of actinopterygians with high statistical support through preliminary phylogenetic analysis.- 「硬骨魚類 Hox クラスターの進化」
○堀 寛、黒沢仁、高橋昌義、高松尚文、佐中笑、住友万里子、猪熊亮一、堤真紀子、＊浅川修一、＊清水信義、＃新井理、＃小原雄治（名古屋大学大学院生命理学、＊慶應義塾大学医学部、＃国立遺伝学研究所生物遺伝資源情報総合センター）
・Evolution of Hox cluster organization in fish
○Hori H, Kurosawa G, Takahashi M, Takamatsu N, Sanaka E, Sumitomo M, Inokuma R, Tsutsumi M, *Asakawa S, *Shimizu N, #Shin-i T, #Kohara Y (Dept. Biol., Nagoya Univ., *Dept. Mol. Biol., Keio Univ., #Cent. Genet. Res. Info., NIG, Japan)Hox genes play a key role in determination of axial and appendicular skeletal morphology and may be a key component of the evolution of diverse metazoan body forms. It has been widely assumed that differences in their organization and deployment are thought to play a important role in producing variant body patterns in all vertebrate evolution. While mammals have four clusters composed of 39 Hox genes, the number of Hox genes and clusters is diversified in among teleost fish. To test the possibility that Hox organization may have varied since the origin of jawed vertebrates, we have studied the Hox gene clusters in medaka fish. We isolated BAC clones that cover the entire Hox gene loci, and characterized them by shot-gun sequencing. Although it has not been completed, at least 46 Hox genes are encoded in seven clusters in medaka. Our data show that gene organization of the medaka clusters is quite similar to that of Fugu clusters, but there is a little difference from zebrafish clusters, and an unprecedented degree of variation when compared with the present mammalian clusters.- Fugu genome: a compact reference vertebrate genome
○B.Venkatesh (Institute of Molecular and Cell Biology, Singapore)The Japanese pufferfish, Fugu rubripes, is a specialized teleost belonging to the order Tetraodontiformes and family Tetraodontidae. It is unique among vertebrates in that it has the smallest vertebrate genome yet characterized. Its haploid genome size is only 365 Mb, about one-eighth the size of the human genome and one-quarter the size of the zebrafish genome. Thus, it constitutes an interesting model for understanding the evolution and divergence of vertebrates. A 'draft' sequence of the Fugu genome was determined by the 'whole-genome shotgun' sequencing strategy and annotated using automated annotation pipeline. About 30,000 genes have been predicted in the Fugu genome, similar to that in the human genome. As previously predicted, Fugu genome contains less than 15% repetitive sequences, which largely accounts for the compact genome size. Comparisons of the Fugu and the human genome sequences have identified several novel genes in the human genome, a set of about 8000 genes in the human genome that are either quite divergent or absent in Fugu (and presumably in other fishes), conserved syntenic regions and duplicated genes. Since the conserved syntenic regions share a common evolutionary history, they should be useful for understanding the evolutionary changes in the fish and mammalian lineages.- 「メダカ遺伝子地図にみられる魚類ゲノム倍加の痕跡」
The ancient teleost specific genome duplication hypothesis-A view from Medaka EST map
三谷啓志（東大院新領域先端生命）、 成瀬清（東大院理学系生物科学）、 田中実（北大院理学系生物科学）、 三田和英（農業生物資源研究所）、 嶋昭紘（東大院新領域先端生命）
Hiroshi Mitani (Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo), Kiyoshi Naruse (Department of Biological Sciences, Graduate School of Science, University of Tokyo), Minoru Tanaka (Division of Biological Sciences, Graduate School of Science, Hokkaido University), Kazuei Mita (Department of Genome Research, Laboratory of Insect Genome, National Institute of Agrobiological Sciences), Akihiro Shima (Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo)Medaka (Oryzias latipes) is emerging as an important model fish that is phylogenically distant from zebrafish but closer to pufferfish. With the recent additions of the genetic toolkits such as BAC recourses and WGS sequences, the highly dense genome markers based on polymorphic inbred strains, which is essential for genome assembly with high quality also come to be available. About 1600 markers including 1000 randomly selected EST markers were mapped, and all of them are successfully grouped into 24 linkage groups that correspond to medaka chromosome number. This genomic map is a powerful tool for positional cloning of mutated genes in medaka, and the syntenies of medaka, pufferfish and zebrafish genes to human genome provide evidence of the whole genome duplication occurred after divergence of fish and tetrapods and before divergence of medaka and zebrafish. For a gene regulation study, polyploidy in model fish species might be advantageous, since regulatory elements and functional domains in each of the fish duplicates may have unique roles in their function. And medaka and zebrafish may have considerably different sets of genes with subfunctional or neofunction because this degeneration process would have affected different genes in the two fish lineage.