1,2H. Noguchi, 2Y. Kuroki, 2A. Toyoda, 3H.S. Park, 3S.H. Choi, 3Y.S. Lee, 3D.S. Kim, 3D.W. Kim, 2,4M. Hattori, 2Y. Sakaki, 1T. Takagi, 2,5A. Fujiyama
1Dept. Comp. Sci., University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Japan., 2Genomic Sciences Center, RIKEN, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Japan., 3Genome Reseach Center, KRIBB, Korea, 4Informatics Res. Div., NII, Japan, 5Schl. Sci., Kitasato University, Japan
Cetaceans (whales, dolphins, and porpoises) are one of the most distinctive mammals. They descended from artiodactyls, such as hippopotamus, cattle, and pig, and still have some features of land mammals. However, cetaceans spend their whole lives in the water, and are fully adapted to an aquatic environment as typified by the whale-fish convergence in the form and evolution of echolocation system. Surprisingly, such remarkable transitions from land mammal to ancestral marine whale took less than 8 million years. Genomic sequences from such a distinctive species are very informative and useful for comparative study of mammals. Hence, we have constructed the genome BAC library (QGB1) of the false killer whale (Pseudorca crassidens) and performed comparative genome analysis. We have sequenced 150,000 BAC-ends (75,000 clones) and mapped them onto the human, dog, and cow genomes to construct a comparative map. All positions were converted to those of the human genome using synteny information of the land mammals. As a result, about 60% of the human genome (and genes) are covered by the mapped clones (paired-ends). Many end-sequences are remaining as singletons (mapped but unpaired), suggesting that genomic structures of these species are largely different. Candidate regions of deletions in the false killer whale (or insertions in the human) were estimated by singletons, and located human genes were examined. Significant numbers of olfactory receptors (ORs), keratin filaments, and other intermediate filaments are located in the regions. We mainly focus on olfactory nerve-related genes because cetaceans have lost the large part of olfactory nerve. Hence, we have completely sequenced some BAC clones containing OR clusters which are conserved between the land mammals, and we confirmed the regions are lacked in the false killer whale.
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