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

本研究试图阐明白血病抑制因子（leukemia inhibitory factor，LIF）调控小鼠ES细胞由未分化向分化转换的分子机制，首先利用DNA微阵列技术，寻找在自我更新和分化的ES细胞中表达受限的分子，发现了几个感兴趣的基因，如转录因子（Zfp 57和GABPα）、多梳家族蛋白（Eed）、癌蛋白（β-catenin）和新基因（STAT 3-activated gene 3，S3 A3）。Zfp 57是ES细胞自我更新的良好标记，但在ES细胞自我更新中却被证明是一个缺陷。Eed是维持“完全”未分化状态所必需的。虽然S3 A3是ES细胞自我更新的抑制因子，但该基因的敲除促进ES细胞向内胚层分化，表明S3 A3是内胚层分化的负调节因子。因此，我们将该基因重新命名为STAT 3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阻遏物来控制Oct-3/4的表达，并且LIF刺激核β-catenin的稳定化，其进而与Oct-3/4结合以诱导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，调节自我更新ES细胞向分化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.