斑马鱼的胚盾(shield organizer)是原肠期胚胎发育的组织中心，对体轴的建立和中内胚层的形成有着至关重要的作用。斑马鱼胚盾的形成与Nodal/Smad2信号的激活密切相关。然而在胚盾形成过程中对于这些信号通路的调控仍所知甚少。鸟苷酸交换因子net1是我们鉴定的一个Nodal/Smad2的靶基因，在原肠早期特异高表达于胚盾。我们的初步的研究结果表明net1可能通过调控Nodal/Smad2信号通路，在胚盾形成和中内胚层诱导中发挥重要的作用。本项目将深入探讨net1在胚盾形成和中内胚层诱导中的功能，Nodal信号调控net1表达的分子机制和net1对Nodal信号通路的调控机理，构建Nodal信号通过调控其靶基因net1表达，net1又对Nodal信号反馈调控所形成的基因调控网络。本项目还将在小鼠胚胎干细胞向中内胚层前体细胞定向分化过程中，研究net1的功能在进化中的保守性。

Zebrafish embryonic shield organizer, which resides on the dorsal side of the vertebrate gastrula, plays an essential role in patterning the body axis and specifying the mesendodermal layers. The organizer is itself induced by earlier signals. Nodal/Smad2 singnal has essential functions in organizer development and also in the formation of mesoderm and endoderm, but the intrinsic regulation mechanism of Nodal/Smad2 signal during shield organizer formation and mesendoderm induction is unclear. The guanine nucleotide exchange factor net1 is one of the Nodal/Smad2 direct targets as we identified during early gastrula stages. We found that net1 was specifically expressed in the shield organizer, and net1 morphants showed severe defects in organizer formation and mesendoderm induction. In the present study, we will further explore the function of net1 during organizer formation and mesendoderm induction. How the expression of net1 is regulated by Nodal/Smad2 signal pathway and how Nodal/Smad2 signal is controlled by net1 will also be investigated to reconstruct the gene regulatory networks underlying embryonic development. Furthermore, the conserved function of net1 in mesendoderm induction will be studied in mouse embryo stem cell differentiation system.