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Expression of muscle-related genes and two MyoD genes during amphioxus notochord development

Authors

  • Aki Urano,

    1. Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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    • 1The first two authors contributed equally to this work.

  • Miho M. Suzuki,

    1. Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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    • 1The first two authors contributed equally to this work.

    • 2Present address: Wellcome Trust Centre for Cell Biology, Institute of Cell and Molecular Biology, University of Edinburgh, Edinburgh EH9 3JR, UK.

  • Peijun Zhang,

    1. Institute of Oceanology, the Chinese Academy of Sciences, Qingdao, Shandong, P.R. China
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  • Nori Satoh,

    Corresponding author
    1. Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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  • Gouki Satoh

    1. Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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    • 3Present address: Seto Marine Biological Laboratory, Kyoto University, 459 Shirahama, Nishimuro-gun, Wakayama 649-2211, Japan.


*Author for correspondence (e-mail: satoh@ascidian.zool.kyoto-u.ac.jp)

Abstract

Summary The notochord is one of the diagnostic features of the phylum Chordata. Despite the similarities in the early morphogenetic patterns of the notochords of various chordates, they are strikingly distinct from one another at the histological level. The amphioxus notochord is one example of an evolutionary novelty because it is made up of muscle cells. Our previous expressed sequence tag analysis, targeting messenger RNAs expressed in the adult amphioxus notochord, demonstrated that many muscle-related genes are expressed there. To characterize amphioxus notochord cells and to gain insights into the myogenic program in the notochord, we determined the spatial and temporal expre-ssion patterns of these muscle-related genes during amphioxus development. We found that BbNA1 (notochord actin), Amphi-Trop I (troponin I), Amphi-TPmyosin (tropo-myosin), Amphi-MHC2 (myosin heavy chain), Amphi-nMRLC (notochord-specific myosin regulatory light chain), Amphi-nTitin/MLCK (notochord-specific titin/myosin light chain kinase), Amphi-MLP/CRP3 (muscle LIM protein), and Amphi-nCalponin (notochord-specific calponin) are expres-sed with characteristic patterns in notochord cells, including the central cells, dorsally located cells, and ventrally located cells, suggesting that each notochord cell has a unique molecular architecture that may reflect its function. In addition, we characterized two MyoD genes (Amphi-MyoD1 and Amphi-MyoD2) to gain insight into the genetic circuitry governing the formation of the notochord muscle. One of the MyoD genes (Amphi-MyoD2) is expressed in the central notochord cells, and the coexistence of Amphi-MyoD2 transcripts along with the Amphi-MLP/CRP3 transcripts implies the participation of Amphi-MyoD2 in the myogenic program in the notochord muscle.

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