Essential roll of SOX5 in the semicircular canal development of zebrafish
ゼブラフィッシュ三半規管形成に必須な SOX5 の機能

Syumpei Tanino1,3,Gembu Abe2, Koichi Kawakami2,Harukazu Nakamura1,3, JUN-ICHI Funahashi1,3

1)ep. Mol. Neurobiol., IDAC, Tohoku Univ., 2)Div. of Mol. and Dev. Biology, NIG 3)Dept. of Mol. Neurobiol., Graduate Sch. of Life Science, Tohoku Univ.

Semicircular canals of zebrafish is an intriguing model system to study the mechanism of morphogenesis. The formation of semicircular canals begins with the development of protrusions that extend inward from the wall of otic vesicle into the lumen. The protrusions from opposite walls meet and fuse with each other to form three pillars of tissue spanning the lumen. The toroidal space surrounding each pillar becomes a semicircular canal. All of these development can be observed in the live fish by compound microscope. To study semicircular canal morphogenesis with the resolution of cellular level, we have attempted to isolate the fish that specifically express GFP in the otic vesicle. By screening Tol2-Gal4 gene trap lines, we have identified the line that expresses GFP at the tip of the growing protrusions. The initiation of GFP expression in the otic vesicle coincides well with the beginning of the protrusions. Scanning genome sequence in the vicinity of trap-construct-inserted site revealed that it was in the Sox5 locus. In situ hybridization confirmed that the expression pattern of Sox5 and that of GFP driven by Gal4 is identical. We have attempted to interfere Sox5 translation with morpholino oligo-nucleotides. Knocking down Sox5 resulted in failure of development of the protrusions. This phenotype was rescued by co-injection of capped Sox5 mRNA. These results suggest that Sox5 plays a critical roll in semicircular canal morphogenesis.