Pereira Laura, Yi Fei, Merrill Bradley J
Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 900 S. Ashland Ave., Molecular Biology Research Building, Room 1268, Mail Code 669, Chicago, IL 60607, USA.
Mol Cell Biol. 2006 Oct;26(20):7479-91. doi: 10.1128/MCB.00368-06. Epub 2006 Aug 7.
The dual function of stem cells requires them not only to form new stem cells through self-renewal but also to form lineage-committed cells through differentiation. Embryonic stem cells (ESC), which are derived from the blastocyst inner cell mass, retain properties of self-renewal and the potential for lineage commitment. To balance self-renewal and differentiation, ESC must carefully control the levels of several transcription factors, including Nanog, Sox2, and Oct4. While molecular mechanisms promoting transcription of these genes have been described, mechanisms preventing excessive levels in self-renewing ESC remain unknown. By examining the function of the TCF family of transcription factors in ESC, we have found that Tcf3 is necessary to limit the steady-state levels of Nanog mRNA, protein, and promoter activity in self-renewing ESC. Chromatin immunoprecipitation and promoter reporter assays showed that Tcf3 bound to a promoter regulatory region of the Nanog gene and repressed its transcriptional activity in ESC through a Groucho interaction domain-dependent process. The absence of Tcf3 caused delayed differentiation of ESC in vitro as elevated Nanog levels persisted through 5 days of embryoid body formation. These new data support a model wherein Tcf3-mediated control of Nanog levels allows stem cells to balance the creation of lineage-committed and undifferentiated cells.
干细胞的双重功能要求它们不仅通过自我更新形成新的干细胞，还通过分化形成定向分化的细胞。胚胎干细胞（ESC）来源于囊胚的内细胞团，具有自我更新特性和定向分化潜能。为了平衡自我更新和分化，ESC必须精确调控包括Nanog、Sox2和Oct4在内的多种转录因子的水平。虽然促进这些基因转录的分子机制已被阐明，但在自我更新的ESC中防止这些因子水平过高的机制仍不清楚。通过研究转录因子TCF家族在ESC中的功能，我们发现Tcf3对于限制自我更新的ESC中Nanog mRNA、蛋白质的稳态水平以及启动子活性是必需的。染色质免疫沉淀和启动子报告基因分析表明，Tcf3结合到Nanog基因的启动子调控区域，并通过依赖于Groucho相互作用结构域的过程在ESC中抑制其转录活性。缺乏Tcf3会导致ESC在体外分化延迟，因为在胚胎体形成的5天中，Nanog水平持续升高。这些新数据支持了一个模型，即Tcf3介导的对Nanog水平的调控使干细胞能够平衡定向分化细胞和未分化细胞的产生。
