Yoshida-Koide Urara, Matsuda Takahiko, Saikawa Kunikazu, Nakanuma Yasuni, Yokota Takashi, Asashima Makoto, Koide Hiroshi
Department of Stem Cell Biology, Graduate School of Medical Science, Kanazawa University, 13-1 Takara-machi, Kanazawa, Ishikawa 920-8640, Japan.
Biochem Biophys Res Commun. 2004 Jan 16;313(3):475-81. doi: 10.1016/j.bbrc.2003.11.138.
Embryonic stem (ES) cells, derived from the inner cell mass of blastocyst can differentiate into multiple cell lineages. In this study, we examined the possible involvement of Ras in ES cell differentiation. We found that Ras was activated upon formation of embryoid bodies (EBs), an initial step in ES cell differentiation. When expressed during EB differentiation, a dominant-negative mutant of Ras suppressed induction of marker genes for extraembryonic endoderm differentiation, including GATA-4, GATA-6, alpha-fetoprotein, and hepatocyte nuclear factor 3beta, while an activated mutant promoted their induction. Expression of a Ras mutant that selectively activates the Raf/MEK/Erk pathway also enhanced induction of extraembryonic endoderm markers, and treatment with a MEK inhibitor resulted in their decreased expression. In addition, Ras stimulated downregulation of Nanog, a suppressor of endoderm differentiation in ES cells. These data suggest that Ras activation during EB differentiation plays a crucial role in initiation of extraembryonic endoderm differentiation.
胚胎干细胞（ES细胞）来源于囊胚的内细胞团，能够分化为多种细胞谱系。在本研究中，我们检测了Ras在ES细胞分化过程中可能发挥的作用。我们发现，在胚状体（EB）形成时Ras被激活，而EB形成是ES细胞分化的起始步骤。当在EB分化过程中表达时，Ras的显性负性突变体抑制了包括GATA-4、GATA-6、甲胎蛋白和肝细胞核因子3β在内的胚外内胚层分化标志物基因的诱导，而激活突变体则促进了这些基因的诱导。选择性激活Raf/MEK/Erk通路的Ras突变体的表达也增强了胚外内胚层标志物的诱导，并且用MEK抑制剂处理导致它们的表达下降。此外，Ras刺激了Nanog的下调，Nanog是ES细胞中内胚层分化的抑制因子。这些数据表明，EB分化过程中的Ras激活在胚外内胚层分化起始中起关键作用。
