Cell-cell communication in Xenopus development

描述(申请人提供)：非洲爪蛙的早期胚胎为发现控制细胞信号和分化的分子机制提供了一个有利的系统。当胚胎被切成两半时，它可以自我调节，形成一个比例良好的有机体。最近的实验表明，自我调节是由一种新的细胞外生化途径介导的。BMP生长因子家族的信号被一种名为Chordin的背部蛋白拮抗。Chordin被Tolloid家族腹侧表达的锌金属蛋白酶降解。反过来，这种蛋白酶被腹壁分泌的FrizzledRelated Protein(SFRP)抑制。在这里，我们建议通过探索三个广泛的问题来研究细胞-细胞信号：1)胚胎背极和腹极的细胞如何远距离相互通信？我们的假设是，类似生化活性的分泌分子在胚胎的相反两极表达，但在相反的转录控制下，为理解分化细胞的发育领域如何自我调节提供了关键。2)其他sFRPs是否为锌金属蛋白酶的抑制剂？需要检验的假设是，存在于许多胞外蛋白质中的Frizzled域可能提供了一个模块，调节胞外分子的蛋白质分解，可能是在Wnt生长因子的控制下。3)多种生长因子信号输入是如何在细胞内整合的？我们将测试BMP、Wnt和受体酪氨酸激酶信号通路是否会聚在转录因子Smad1的磷酸化状态，调节其活性。研究这三个特定目标将有助于对细胞如何相互交流提供一个综合的观点，不仅在胚胎中，而且在成人组织和人类胚胎干细胞中也是如此。待研究的信号通路中的基因涉及许多与医学相关的过程，如中枢神经系统诱导、细胞和组织分化、同卵和连体双胞胎的形成、神经诱导、纤维和结缔组织疾病以及癌症。

Description (provided by applicant): The early embryo of the frog Xenopus provides a favorable system for discovering the molecular mechanisms that control cell signaling and differentiation. When an embryo is cut in half, it can self-regulate to form a well-proportioned organism. Recent experiments have elucidated that self-regulation is mediated by a novel extracellular biochemical pathway. Signaling by the BMP family of growth factors is antagonized by a dorsal protein called Chordin. Chordin is degraded by a ventrally-expressed zinc metalloproteinase of the Tolloid family. In turn, this protease is inhibited by a ventrally secreted Frizzled-Related Protein (sFRP). Here we propose to investigate cell-cell signaling by exploring three broad questions: 1) How do cells in the dorsal and ventral poles of the embryo communicate with each other across long distances? Our hypothesis is that secreted molecules of similar biochemical activity expressed at opposite poles of the embryo, but under opposite transcriptional control, provide the key to understanding how developmental fields of differentiating cells self-regulate. 2) Are other sFRPs inhibitors of zinc metalloproteinases? The hypothesis to be tested is that Frizzled domains, which are present in many extracellular proteins, might provide a module that regulates the proteolysis of extracellular molecules, perhaps under the control of Wnt growth factors. 3) How are multiple growth factor signaling inputs integrated intracellularly? We will test whether the BMP, Wnt, and Receptor Tyrosine Kinase signaling pathways converge on the phosphorylation state of the transcription factor Smadl, regulating its activity. Investigating these three specific aims will help provide an integrated view of how cells communicate with each other, not only in embryos but also in adult tissues and in human embryonic stem cells. Genes in the signaling pathways to be studied are involved in many processes of medical relevance, such as central nervous system induction, cell and tissue differentiation, the formation of identical and conjoined twins, neural induction, fibrotic and connective tissue disease, and cancer.