Tam Wai-Leong, Lim Chin Yan, Han Jianyong, Zhang Jinqiu, Ang Yen-Sin, Ng Huck-Hui, Yang Henry, Lim Bing
Stem Cell and Developmental Biology, Genome Institute of Singapore, #02-01, Genome, Singapore.
Stem Cells. 2008 Aug;26(8):2019-31. doi: 10.1634/stemcells.2007-1115. Epub 2008 May 8.
The Wnt signaling pathway is necessary both for maintaining undifferentiated stem cells and for directing their differentiation. In mouse embryonic stem cells (ESCs), Wnt signaling preferentially maintains "stemness" under certain permissive conditions. T-cell factor 3 (Tcf3) is a component of the Wnt signaling and a dominant downstream effector in ESCs. Despite the wealth of knowledge regarding the importance of Wnt signaling underlying stem cells functions, the precise mechanistic explanation by which the effects are mediated is unknown. In this study, we identified new regulatory targets of Tcf3 using a whole-genome approach and found that Tcf3 transcriptionally represses many genes important for maintaining pluripotency and self-renewal, as well as those involved in lineage commitment and stem cell differentiation. This effect is in part mediated by the corepressors transducin-like enhancer of split 2 and C-terminal Binding Protein (CtBP). Notably, Tcf3 binds to and represses the Oct4 promoter, and this repressive effect requires both the Groucho and CtBP interacting domains of Tcf3. Interestingly, we find that in mouse preimplantation development embryos, Tcf3 expression is coregulated with Oct4 and Nanog and becomes localized to the inner cell mass of the blastocyst. These data demonstrate an important role for Tcf3 in modulating the appropriate level of gene transcription in ESCs and during embryonic development. Disclosure of potential conflicts of interest is found at the end of this article.
Wnt信号通路对于维持未分化的干细胞及其分化导向都是必需的。在小鼠胚胎干细胞（ESC）中，Wnt信号在某些允许条件下优先维持“干性”。T细胞因子3（Tcf3）是Wnt信号的一个组成部分，也是ESC中的主要下游效应因子。尽管关于Wnt信号在干细胞功能中的重要性已有丰富的知识，但介导这些效应的精确机制尚不清楚。在本研究中，我们使用全基因组方法鉴定了Tcf3的新调控靶点，发现Tcf3转录抑制许多对维持多能性和自我更新很重要的基因，以及那些参与谱系定向和干细胞分化的基因。这种效应部分由共抑制因子分裂样增强子2（transducin-like enhancer of split 2）和C末端结合蛋白（CtBP）介导。值得注意的是，Tcf3结合并抑制Oct4启动子，这种抑制作用需要Tcf3的Groucho和CtBP相互作用结构域。有趣的是，我们发现在小鼠植入前发育胚胎中，Tcf3的表达与Oct4和Nanog共同调控，并定位于囊胚的内细胞团。这些数据证明了Tcf3在调节ESC和胚胎发育过程中适当水平的基因转录方面的重要作用。潜在利益冲突的披露见本文末尾。
