Function of receptor mediated endocytosis in Hydra morphogenetic signaling

本研究的总体目的是了解膜运输在形态发生信号传导中的作用。对于形态原Notch的内吞作用是信号传递和Wnt信号传递所必需的，一些研究假设受体介导的内吞作用是信号转导所必需的。本研究将分析内吞作用在Wnt信号传导中的作用，并研究九头蛇典型和非典型Wnt配体内吞和胞吐作用的差异。水螅是一种古老的、非常简单的多细胞系统，然而，它拥有一套几乎完整的Wnt基因，否则只有脊椎动物才知道。尽管它们在胚胎发生、细胞分化和癌症中起着至关重要的作用，但迄今为止，人们对配体摄取和加工的机制知之甚少。基于九头蛇简单的身体结构和清晰的细胞分化模式，我们有望对形态因子相关膜运输的动力学和功能有更深入的了解。第一个目的是阐明Wnt配体和受体沿质膜分泌途径的分泌途径。本研究的第二个目的是分析这些蛋白的内吞途径：网格蛋白介导的内吞作用还是不依赖于网格蛋白的内吞作用？Wnt与其受体结合后的细胞和分子命运是本项目的主要课题。为了研究受体介导的Wnt内吞作用的机制，采用膜片钳电容测量离体水螅细胞。它们允许在活细胞的质膜上直接测量内吞和胞吐。这项工作不仅将增加我们对膜运输在Wnt信号传导中的作用的认识，而且还将提供有关受体介导的形态因子内吞作用的机制的信息。考虑到Wnt信号在发育、人类疾病和癌症中的重要性，对Wnt膜转运及其相互作用蛋白的新认识具有重要意义。

The overall aim of this study is to understand the role of membrane trafficking in morphogenetic signaling. For the morphogen Notch endocytosis is essential for signaling and also for Wnt signaling several studies let presume that receptor mediated endocytosis is necessary for signal transduction. The function of endocytosis in Wnt signaling will be analyzed in this study and differences in endo- and exocytosis of canonical and noncanonical Wnt ligands in Hydra will be examined. Hydra is an ancient and very simple multicellular system that posses, however, an almost complete set of Wnt genes, otherwise only known from vertebrates. Despite their crucial function in embryogenesis, cell differentiation and cancer, the mechanisms of ligand uptake and processing are only poorly understood so far. Based on Hydra’s simple body plan and its clear patterns of differentiated cells, major insights into the dynamics and function of morphogen-related membrane trafficking are expected. The first aim is to clarify the secretory route of Wnt ligands and receptors along the secretory pathway to the exocytosis at the plasma membrane. The second aim of this study is to analyze the endocytotic route these proteins take: clathrin mediated or clathrin independent endocytosis? The cellular and molecular fate after binding of Wnt to its receptor is a major topic of this project. To investigate the mechanism of receptor mediated endocytosis of Wnt, patch clamp capacitance measurements on isolated Hydra cells are used. They allow the direct measurement of endo- and exocytosis at the plasma membrane of living cells. This work will not only increase our knowledge of the role of membrane trafficking in Wnt signaling but also provide information about the mechanisms involved in receptor mediated endocytosis of morphogens in general. Considering the importance of Wnt signaling in development, human diseases, and cancer, new insights in membrane trafficking of Wnt and interacting proteins are of major significance.