MOLECULAR REGULATION OF EARLY XENOPUS DEVELOPMENT

Wnt途径已经成为脊椎动物早期轴规范的关键调节因子。该建议旨在确定Wnt途径如何在早期胚胎中被激活，以及这如何导致Spemann组织者的诱导。在非洲爪哇，Wnt通路是由精子诱导的胚胎皮质旋转激活的。这种激活不需要Wnt配体，因此可以在细胞内调节。继早期发现Wnt信号转导中的一个关键事件是抑制激酶GSK-3之后，该实验室最近发现了一种新的抑制性GSK-3结合蛋白GBP，并证明了它是背轴诱导所必需的。这项提议的一个主要目的是准确地确定GBP如何抑制GSK-3的活性，GSK-3是多蛋白质复合体的一部分。由于GBP可能是局部的或局部激活的，对皮质旋转的反应，调查将确定GBP在胚胎中的位置，它是否被区域修饰，以及它是否与非洲爪哇早期胚胎中的其他蛋白质结合。其他研究将询问GBP对Wnt信号的调节是否在整个发育过程中都被使用，或者GBP是否仅仅是Wnt通路的一个专门的母体调节因子，仅用于背轴规范。第二个主要领域将具体调查Spemann组织者的激活是如何受到监管的。由于组织者是对Wnt途径介导的转录抑制作出反应而形成的，因此将对这种抑制的分子基础进行研究。此外，由于皮质旋转的主要作用是确保Wnt途径在赤道被激活，因此将研究限制组织者形成到胚胎赤道的因素。由于Wnt通路与正常脊椎动物的发育和肿瘤发生有关，这些研究将对理解出生缺陷和癌症的分子基础具有重要意义。

The Wnt pathway has emerged as a critical regulator of early axis specification in vertebrates. This proposal aims to determine how the Wnt pathway becomes activated in the early embryo, and how this leads to the induction of the Spemann organizer. In Xenopus, the Wnt pathway is activated by a sperm-induced rotation of the embryonic cortex. This activation does not require Wnt ligands, and may therefore be regulated intracellularly. Following the earlier discovery that a key event in Wnt- signalling is inhibition of the kinase GSK-3, this laboratory has recently identified a novel, inhibitory GSK-3 binding protein, GBP, and demonstrated that it is required for dorsal axis induction. A major aim of this proposal is to determine precisely how GBP inhibits the activity of GSK-3, which functions as part of a multi-protein complex. Since GBP may be localized or activated locally in response to cortical rotation, investigations will determine where GBP is found in the embryo, whether it is regionally modified, and whether it binds other proteins in the early Xenopus embryo. Additional studies will ask whether the regulation of Wnt signalling by GBP is used throughout development, or whether GBP is solely a specialized maternal regulator of the Wnt pathway used only for dorsal axis specification. A second major area will investigate specifically how the activation of the Spemann organizer is regulated. Since the organizer forms in response to a Wnt pathway-mediated transcriptional depression, the molecular basis of this depression will be investigated. Furthermore, the factors that restrict the formation of the organizer to the equator of the embryo will be investigated since the principle role of the cortical rotation is to ensure that the Wnt pathway is activated at the equator. Since the Wnt pathway is implicated in normal vertebrate development and oncogenesis, these studies will be important in understanding the molecular basis of birth defects and cancer.