与脊椎动物不同，文昌鱼的口形成于身体左侧，因此文昌鱼与脊椎动物的口是否为同源器官一直存在争议。仅靠组织学方法不能全面解释文昌鱼与脊椎动物口的同源关系问题，如能阐明口发育过程分子调控机制，将从发育机制角度回答上述问题。前期研究中我们发现敲除Hedgehog（Hh）基因导致文昌鱼口发育异常，说明Hh信号通路对文昌鱼口的发育是必须的。为深入研究Hh信号通路在文昌鱼口发育过程中的功能与机制，本项目将进一步构建Smo基因敲除突变体，利用组织切片、透射电镜等方法检测Smo敲除和Hh信号通路上调对文昌鱼口发育的影响，确定Hh信号通路在文昌鱼口发育过程中的功能。在此基础上分析口特异基因表达、基膜溶解以及Hh信号通路与Nodal信号通路作用关系，阐明Hh信号通路参与文昌鱼口发育调控的机制。项目成果将对全面理解文昌鱼口发育过程分子调控机制具有重要意义，同时也将为回答文昌鱼口与脊动物口是否同源提供理论依据。

Unlike vertebrates, amphioxus exhibits a unique pattern of mouth formation, in which the mouth initially opens on the left lateral side of body. Therefore, it has been debatable if the amphioxus mouth is homologous to its vertebrate counterpart. Histological examination can not fully explain that issue. If the regulatory mechanism of amphioxus mouth formation is elucidated, the molecular evidence will be provided to understand that issue. In our recent study, it has been found that the loss of Hedgehog(Hh) function results in the failure of mouth formation in amphioxus, indicating that the Hh signal plays a key role in amphioxus mouth development. To further probe the functions and regulatory mechanism of Hh signalling in amphioxus mouth formation, we will make comprehensive analysis of mouth development in Smo knockout and Hh signal upregulated amphioxus using the methods of in situ hybridization, histological sections and immunofluorescence. In addition, we will also examine the specific genes expression of mouth，the basement membrane dissolution and the regulatory relationship of Hh signal and Nodal signal in amphioxus mouth formation, the results will be significant for the full understanding of molecular regulation mechanism of amphioxus mouth development and providing molecular evidence to explain if the mouths of amphioxus and vertebrates are homologous organs.