MOLECULAR REGULATION OF EARLY XENOPUS DEVELOPMENT

Wnt通路已经成为脊椎动物早期轴特化的关键调节因子。 该提案旨在确定Wnt通路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。 在非洲爪蟾中，Wnt通路被精子诱导的胚胎皮质旋转激活。 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信号传导中的关键事件是激酶GSK-3的抑制之后，该实验室最近鉴定了一种新的抑制性GSK-3结合蛋白GBP，并证明其是背轴诱导所需的。 该提案的主要目的是精确确定GBP如何抑制GSK-3的活性，GSK-3作为多蛋白复合物的一部分发挥作用。 由于GBP可能是本地化或激活本地响应皮质旋转，调查将确定GBP被发现在胚胎中，它是否是区域修改，以及它是否结合其他蛋白质在早期非洲爪蟾胚胎。 进一步的研究将询问GBP对Wnt信号传导的调节是否在整个发育过程中使用，或者GBP是否仅仅是Wnt通路的一种专门的母体调节剂，仅用于背轴特化。第二个主要领域将专门研究如何激活Spemann组织者的监管。 由于组织者的形式响应Wnt通路介导的转录抑制，这种抑郁症的分子基础将进行调查。 此外，将研究将组织者形成限制在胚胎赤道的因素，因为皮质旋转的主要作用是确保Wnt通路在赤道被激活。 由于Wnt通路与正常脊椎动物的发育和肿瘤发生有关，这些研究对于理解出生缺陷和癌症的分子基础将是重要的。

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.