A Twist-like bHLH gene is a downstream factor of an endogenous FGF and determines mesenchymal fate in the ascidian embryos

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  • Kaoru S. Imai
    Department of Zoology, Graduate School of Science, Kyoto University,Sakyo-ku, Kyoto 606-8502, Japan
  • Nori Satoh
    Department of Zoology, Graduate School of Science, Kyoto University,Sakyo-ku, Kyoto 606-8502, Japan
  • Yutaka Satou
    Department of Zoology, Graduate School of Science, Kyoto University,Sakyo-ku, Kyoto 606-8502, Japan

抄録

<jats:p>Ascidian larvae develop mesenchyme cells in their trunk. A fibroblast growth factor (FGF9/16/20) is essential and sufficient for induction of the mesenchyme in Ciona savignyi. We have identified two basic helix-loop-helix (bHLH) genes named Twist-like1 and Twist-like2 as downstream factors of this FGF. These two genes are phylogenetically closely related to each other, and were expressed specifically in the mesenchymal cells after the 110-cell stage. Gene-knockdown experiments using a specific morpholino oligonucleotide demonstrated that Twist-like1 plays an essential role in determination of the mesenchyme and that Twist-like2 is a downstream factor of Twist-like1. In addition, both overexpression and misexpression of Twist-like1 converts non-mesenchymal cells to mesenchymal cells.</jats:p><jats:p>We also demonstrate that the upstream regulatory mechanisms of Twist-like1 are different between B-line mesenchymal cells and the A-line mesenchymal cells called `trunk lateral cells'. FGF9/16/20 is required for the expression of Twist-like1 in B-line mesenchymal precursor cells, whereas FGF, FoxD and another novel bHLH factor called NoTrlc are required for Twist-like1 to be expressed in the A-line mesenchymal precursor cells. Therefore, two different but partially overlapping mechanisms are required for the expression of Twist-like1 in the mesenchymal precursors, which triggers the differentiation of the mesenchyme in Ciona embryos.</jats:p>

収録刊行物

  • Development

    Development 130 (18), 4461-4472, 2003-09-15

    The Company of Biologists

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