Analysis of switching mechanism between self-renewal and differentiation in ES cells

在本研究中，我们试图阐明小鼠胚胎干细胞中白血病抑制因子（leukemia inhibitory factor， LIF）调控的未分化胚胎干细胞向分化胚胎细胞转换的分子机制。首先，利用DNA微阵列技术，我们搜索了表达局限于自我更新的ES细胞或分化的ES细胞的分子，并发现了几个有趣的基因，如转录因子（Zfp 57和GABPα）， polycomb家族蛋白（Eed），癌蛋白（β-catenin）和一个新基因（stat3激活基因3，S3A3）。接下来，我们研究了这些分子在胚胎干细胞中的作用。Zfp57虽然是胚胎干细胞自我更新的良好标记，但在胚胎干细胞自我更新中却被证明是不可缺少的。ed是维持“完全”无差别状态所必需的。虽然S3A3对于ES细胞的自我更新是必不可少的，但敲除该基因可促进ES细胞向内胚层分化，提示S3A3是内胚层分化的负向调节因子。因此，我们将该基因重新命名为STAT3下游基因和分化调节因子（Sddr）。我们还发现GABPα通过抑制Oct-3/4抑制因子来控制Oct-3/4的表达，LIF刺激核β-catenin的稳定，而β-catenin又与Oct-3/4结合，诱导Nanog的表达。这些结果表明，LIF通过控制多种分子，包括Eed、Sddr、GABPα和β-catenin，调节从自我更新的ES细胞向分化的ES细胞的转换。

In this study, we tried to clarify the molecular mechanism of switching from undifferentiated ES cells to differentiated ES cells, which is regulated by leukemia inhibitory factor (LIF) in mouse ES cells.At first, using DNA microarray method, we searched for molecules whose expression is restricted to either self-renewing ES cells or differentiating ES cells, and found several interesting genes, such as transcription factors (Zfp 57 and GABPα), a polycomb family protein (Eed), an oncoprotein (β-catenin) and a novel gene (STAT3-activated gene 3, S3A3).We next examined the role of these molecules in ES cells. Zfp57, though it is a good marker for self-renewing ES cells, was turned out to be dispensable for ES cell self-renewal. Eed was required for the maintenance of the "complete" undifferentiated state. Although S3A3 is dispensable for ES cell self-renewal, knockout of this gene promoted differentiation of ES cells into endoderm, suggesting that S3A3 is a negative regulator of endoderm differentiation. We thus renamed this gene as STAT3 downstream gene and differentiation regulator (Sddr). We also found that GABPα controls Oct-3/4 expression through suppression of Oct-3/4 repressors, and that LIF stimulates the stabilization of nuclear β-catenin, which in turn binds with Oct-3/4 to induce the expression of Nanog. These results suggest that LIF regulates the switching from self-renewing ES cells to differentiated ES cells through control of a variety of molecules, including Eed, Sddr, GABPα and β-catenin.