动物左右轴建立是胚胎发育中的重要事件，其形成机制一直是发育生物学和动物形态学研究热点。Shh信号对鸡胚左右轴建立至关重要，但在其它动物类群中是否也参与左右不对称形成尚存争议。文昌鱼进化地位特殊，其基因构成、器官结构及胚胎发生均与脊椎动物相似但又十分简洁，是研究Shh信号功能的良好模型。为此我们建立了文昌鱼Shh基因缺失突变体，发现Shh突变导致Cer表达消失，Nodal、Lefty和Pitx表达由单一左侧变为左右对称，并且器官左右分布紊乱。为阐明Shh信号在文昌鱼左右轴建立中的功能以及Shh信号对Cer基因的调控机制，我们将采用基因敲除、过表达、转基因、原位杂交、石蜡切片、光镜电镜等方法，系统分析该信号通路成员Shh、Ptch和Gli在文昌鱼左右轴建立中的功能。此外我们还将考查Shh信号在文昌鱼不对称器官口形成中的作用，从发育机制的角度探讨文昌鱼口与脊椎动物口是否同源的问题。

Left-right axis formation is essential for animal development, and clarifying the mechanism underling this process has been always a hot issue in the fields of both developmental and morphological biology. Shh signaling is obligatory for the left-right axis development in chick, but whether it is required in other animals is unclear. Amphioxus occupies a key position in the phylogeny of chordates, and has a relatively simple and evolutionarily conserved genome structure, morphology and embryogenesis, making it an ideal model for studying developmental roles of Shh signaling. To the end, we recently generated an amphioxus mutant of Shh gene. Our preliminary analysis shows that Shh loss of function abolishes the expression of Cer gene essential for left-right axis formation, and disturbs positioning of organs along the left-right axis. To clarify the function of Shh signaling in the development of amphioxus asymmetry and the regulatory mechanism of Shh signaling on Cer expression, in this proposal we will make comprehensive analysis on the roles of three Shh signaling components (Shh, Ptch and Gli) in the establishment of amphioxus laterality. In addition, we will also examine the role of Shh signaling in the formation of amphioxus mouth and try to find molecular evidence to evaluate whether mouths of amphioxus and vertebrates are homologous organs.