Liu Yu, Asakura Masanori, Inoue Hironori, Nakamura Teruya, Sano Motoaki, Niu Zhiyv, Chen Michelle, Schwartz Robert J, Schneider Michael D
Center for Cardiovascular Development, Baylor College of Medicine, Houston, TX 77030, USA.
Proc Natl Acad Sci U S A. 2007 Mar 6;104(10):3859-64. doi: 10.1073/pnas.0609100104. Epub 2007 Feb 28.
Early steps for cardiac specification are problematic for the study of mammalian embryos, which has favored using pluripotent cells that recapitulate cardiac myogenesis. Furthermore, circuits governing cardiac specification have relevance to the application of ES cells and other cells for heart repair. In mouse teratocarcinoma cells, canonical Wnts that inhibit heart formation in avian or amphibian embryos and explants activate cardiogenesis, paradoxically. Here, we show that the Wnt/beta-catenin pathway also is essential for cardiac myogenesis to occur in ES cells, acting at a gastrulation-like stage, mediating mesoderm formation and patterning (two prerequisites for cardiac myogenesis itself). Among genes associated temporally with this step was Sox17, encoding an endodermal HMG-box transcription factor. Using lentiviral vectors for RNA interference in differentiating ES cells, an essential role for Sox17 was proven in cardiac muscle cell formation. Sox17 short-hairpin RNA suppresses cardiac myogenesis selectively, acting subsequent to mesoderm formation yet before induction of Mesp1 and Mesp2, a pair of related basic helix-loop-helix transcription factors that together are indispensable for creating heart mesoderm. Sox17 short-hairpin RNA blocks cardiac myogenesis non-cell autonomously and impairs the induction of Hex, a homeodomain transcription factor that is known to be required for the production of endoderm-derived heart-inducing factors.
心脏特化的早期步骤对于哺乳动物胚胎的研究来说存在问题，这使得人们倾向于使用能够重现心肌生成的多能细胞。此外，调控心脏特化的信号通路与胚胎干细胞及其他细胞在心脏修复中的应用相关。在小鼠畸胎瘤细胞中，在鸟类或两栖类胚胎及外植体中抑制心脏形成的经典Wnt信号反而激活了心脏发生。在此，我们表明Wnt/β-连环蛋白信号通路对于胚胎干细胞中心肌生成的发生也是必不可少的，它在类似原肠胚形成的阶段发挥作用，介导中胚层的形成和模式化（这是心肌生成本身的两个先决条件）。在与这一步骤时间上相关的基因中，有编码一种内胚层HMG盒转录因子的Sox17。利用慢病毒载体在分化的胚胎干细胞中进行RNA干扰，证实了Sox17在心肌细胞形成中具有重要作用。Sox17短发夹RNA选择性地抑制心肌生成，在中胚层形成之后但在诱导Mesp1和Mesp2之前发挥作用，Mesp1和Mesp2是一对相关的碱性螺旋-环-螺旋转录因子，共同对于形成心脏中胚层是不可或缺的。Sox17短发夹RNA非细胞自主性地阻断心肌生成，并损害Hex的诱导，Hex是一种同源结构域转录因子，已知其对于内胚层衍生的心脏诱导因子的产生是必需的。
