《生命科学》 2017, 29(10): 1007-1015

Nodal/Smad2靶基因的系统鉴定及其在早期胚胎发育中的功能机制

宁国柱1，孟安明2，王　强1*

(1 中国科学院动物研究所膜生物学国家重点实验室，北京 100101；2 清华大学生命科学学院
    膜生物学国家重点实验室/清华大学-北京大学生命科学联合中心，北京 100084)

摘　要：摘　要：Nodal/Smad2 信号通路在脊椎动物胚胎中内胚层诱导及其背腹分化中发挥着主导作用，但是在胚胎早期发育中，Nodal/Smad2 信号调控哪些靶基因表达，这些靶基因如何在Nodal/Smad2 信号下游发挥作用，人们仍然所知甚少。以国家自然科学基金委员会“细胞编程与重编程的表观遗传机制”重大研究计划为依托，王强实验室在全基因组水平上对斑马鱼胚胎原肠早期Nodal/Smad2 信号通路的靶基因进行了系统鉴定，并通过分析Smad2 结合区域的其他转录因子保守的结合序列的出现频率，鉴定了一批潜在的Smad2 的协同转录因子。研究发现，Nodal/Smad2 的靶基因主要由转录因子、发育相关基因及重要信号通路的调控因子组成，其中F-actin 捆绑蛋白Fascin1a 和鸟核苷酸交换因子Net1 分别通过调控受体内吞与Smad2 转录活性反馈调控Nodal 信号转导和中内胚层形成，而BPTF 做为Smad2 协同转录因子，通过调节核小体滑动来调控wnt8a 表达，在中枢神经系统后部化过程中发挥重要作用。相关研究工作构建了Nodal/Smad2 信号在斑马鱼中内胚层诱导及体轴建立中的分子网络，为理解脊椎动物早期胚胎发育过程中的基因表达调控机制提供了有意义的线索。

Global identification of Nodal/Smad2 target genes and their regulatory functions in early embryogenesis

NING Guo-Zhu1， MENG An-Ming2， WANG Qiang1*

(1 State Key Laboratory of Membrane Biology， CAS Center for Excellence in Molecular Cell Science， Institute of Zoology， Chinese Academy of Sciences， Beijing 100101， China; 2 State Key Laboratory of Membrane Biology， Tsinghua-Peking Center for Life Sciences， School of Life Sciences， Tsinghua University， Beijing 100084， China)

Abstract: Abstract: Nodal/Smad2 signaling pathway plays pivotal roles in mesendoderm induction and axis determination during late blastulation and early gastrulation in vertebrate embryos. However， Nodal/Smad2 direct target genes and their regulatory functions during those critical developmental stages have not been systematically identified.Supported by grants from the major research project of “Epigenetic Mechanisms of Cell Programming and Reprogramming” of National Natural Science Foundation of China， our lab systemically uncovers a large number of Nodal/Smad2 targets in early gastrulas and suggests cooperative roles of Smad2 and other transcription factors in controlling target gene transcription. We find that Nodal/Smad2 target genes are mainly composed of transcription factors， signaling molecules， and developmental regulators. Among these identified Nodal/Smad2 target genes， the actin-bundling protein Fascin1a is found to promote the trafficking of internalized receptors from clathrin-coated vesicles to early endosomes， and the guanine nucleotide exchange factor Net1 associates with Smad2 in the nucleus to increase Smad2 transcriptional activity. These positive feedback loops are required for Nodal/Smad2 signal transduction and mesendoderm formation. In addition， bromodomain and PHD finger-containing transcription factor BPTF， the largest subunit of the nucleosome remodeling factor complex， physically interacts with Smad2 to mediate nucleosome remodeling and hence wnt8a expression and neural posteriorization. These findings will be valuable for studying the regulatory cascades during germ layer formation and patterning of vertebrate embryos.