| Budget Amount *help |
¥16,940,000 (Direct Cost: ¥15,500,000、Indirect Cost: ¥1,440,000)
Fiscal Year 2007: ¥6,240,000 (Direct Cost: ¥4,800,000、Indirect Cost: ¥1,440,000)
Fiscal Year 2006: ¥10,700,000 (Direct Cost: ¥10,700,000)
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| Research Abstract |
The complex signaling pathways that vertebrate embryo uses to convey left-right information have been beginning to be unveiled for the last decade, using forward-and reverse-genetic approaches in both mouse and zebrafish, or via experimental embryology in frog and chick. In this projected we have examined the mechanisms of LR specification using medaka fish, an emerging model organism, through approaches of genetics and experimental embryology.
1. Among the five medaka mutants isolated for LR defects, we have isolated the responsible genes for three mutants, ktu, abc and aA90. The first two encodes novel genes and the rest encodes cytoplasmic dynein heavy chain2 (dhc2). In this project, we focused on the ktu gene because this is higly conserved from a unicellular organism to human with motile cilia/flagella. The medaka ktu mutant is a typical randomized mutant, and positional cloning has identified Ktu as a novel cytoplasmic protein. In the absence of Ktu, most outer and inner dynein arms are missing in the axoneme, leading to a loss of motility. Biochemical data demonstrate that Ktu is one of the long-sought proteins involved in pre-assembly of dynein arm complexes in the cytoplasm before IFT loads them for the ciliary compartment(paper submitted).
2. During the course of the study, we isolated the earliest asymmetric gene in teleost Kupffer's vesicle(KV, an equivalent organ to the mouse node). This gene is called charon, encoding a member of the Cerberus/DAN family proteins. The medaka charon displays asymmetric expression with more intense expression on the right side and found to be directly regulated by liquid flow generated by motile cilia on the KV epithelium. This gene could be a reliable gene marker for LR asymmetry in fish and thus will be useful for the analysis of the early steps downstream of fluid flow.
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