From the Department of Medical Genetics and Division of Morbid Genomics, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu 610041, China.
From the Department of Medical Genetics and Division of Morbid Genomics, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu 610041, China.
J Biol Chem. 2010 Feb 5;285(6):4243-4250. doi: 10.1074/jbc.M109.079533. Epub 2009 Dec 9.
Piwi proteins are required for germ cell proliferation, differentiation, and germ line stem cell maintenance. In normal tissues, human and mouse Piwil2 are primarily expressed in testis but widely expressed in tumors. However, the underlying mechanism remains largely unknown. In vertebrates, transforming growth factor (TGF)-beta signaling plays an important role in patterning embryo and control of cell growth and differentiation. A previous study has shown a role for Zili, a Piwil2 gene in zebrafish, in germ cells in zebrafish. Here we report that zili functions in patterning the early embryo and inhibits TGF-beta signaling. Whole mount expression analysis shows that zili expresses not only in PGCs but also in axis. Ectopic expression of zili causes fusion of the eyes and reduction of mesodermal marker genes expression, suggesting that zili functions to inhibit Nodal signaling and mesoderm formation. Genetic interaction shows that zili inhibits Nodal and bone morphogenetic protein signaling. The results of protein interaction assays identify that Zili binds to Smad4 via its N-terminal domain and prevents the formation of Smad2/3/4 and Smad1/5/9/4 complexes to antagonize TGF-beta signaling. This work shows that zili plays a role in early embryogenesis beyond germ line as a novel negative regulator of TGF-beta signaling, extending the function of Piwi proteins in vertebrates.
Piwi 蛋白对于生殖细胞的增殖、分化和生殖干细胞的维持是必需的。在正常组织中，人和小鼠的 Piwil2 主要在睾丸中表达，但在肿瘤中广泛表达。然而，其潜在的机制在很大程度上仍是未知的。在脊椎动物中，转化生长因子 (TGF)-β信号在胚胎模式形成和细胞生长及分化的控制中起着重要作用。先前的研究表明，Piwil2 基因在斑马鱼中的 Zili 基因在生殖细胞中起作用。在这里，我们报告了 zili 在早期胚胎模式形成中起作用，并抑制 TGF-β信号。整体表达分析表明，zili 不仅在 PGCs 中表达，而且在轴中也表达。zili 的异位表达导致眼睛融合和中胚层标记基因表达减少，表明 zili 抑制 Nodal 信号和中胚层形成。遗传相互作用表明，zili 抑制 Nodal 和骨形态发生蛋白信号。蛋白质相互作用分析的结果表明，Zili 通过其 N 端结构域与 Smad4 结合，并阻止 Smad2/3/4 和 Smad1/5/9/4 复合物的形成，从而拮抗 TGF-β信号。这项工作表明，zili 在生殖系之外的早期胚胎发生中发挥作用，作为 TGF-β信号的一种新型负调节剂，扩展了 Piwi 蛋白在脊椎动物中的功能。
