Cellular Mechanisms of Wingless/Wnt Signaling Activity

Wnt基因家族编码分泌的生长因子样分子，通过细胞间通讯调节细胞行为。成年雌性小鼠乳腺中wnt - 1的不适当表达可导致乳腺肿瘤或乳腺癌。发育中的小鼠胚胎中Wnt-1的正常表达调节细胞增殖并指定细胞身份。本研究以果蝇（Drosophila melanogaster）为模型系统，研究Wnt基因作用的细胞机制。果蝇无翼基因（wg）与小鼠Wnt-1基因高度同源，并在发育过程中发挥类似的影响细胞行为的信号功能。果蝇强大的遗传系统揭示了在发育的不同时期，基因指定了胚胎模式的不同方面。这些在时间上不同的信号活动在Wg蛋白内是单独可变的，这表明信号蛋白的结构特征影响细胞反应。此外，细胞内和细胞间Wg蛋白的分泌和转运似乎对Wg功能至关重要。通过在活胚胎中直接表达突变基因，研究不同的Wg信号活动的性质和细胞间转运的作用。在热休克启动子的控制下，具有正常Wg信号活动的特定亚群的突变Wg分子将无处不在地表达，或者使用GAL4-UAS二元表达系统在特定区域中表达。将评估胚胎模式和wg信号活动分子标记的表型后果，以确定观察到的不同wg信号活动的细胞基础。此外，在信号和运输过程中与Wg蛋白相互作用的分子将通过表征调节Wg信号功能的突变来确定。已经分离出一小部分改变wg突变表型的突变，其中一些突变显示出强烈提示直接参与wg信号通路的特征。这些修饰突变将被描述为遗传和分子特征，以确定它们与Wg相互作用的性质。这两种方法，在遗传易处理的果蝇系统中，将提供对细胞机制的洞察，通过Wg/Wnt分子指定细胞命运和控制细胞增殖。

9600539 Bejsovec The Wnt gene family encode secreted growth factor-like molecules that regulate cell behavior through cell-cell communication. Inappropriate expression of Wnt-l in the mammary glands of adult female mice results in mammary tumors, or breast cancer. Normal expression of Wnt-1 in developing mouse embryos regulates cell proliferation and specifies cellular identities. This proposal exploits the fruitfly, Drosophila melanogaster, as a model system to study the cellular mechanisms of Wnt gene action. The Drosophila wingless (wg) gene is highly homologous to the mouse Wnt-1 gene and performs similar signaling functions that influence cell behavior during development. The powerful genetic system of Drosophila has revealed that wg specifies different aspects of embryonic pattern at different times during development. These temporally distinct signaling activities are separately mutable within the Wg protein, suggesting that structural features of the signaling protein influence the cellular response. Furthermore, secretion and transport of Wg protein within and between cells appears to be essential to Wg function. The nature of the distinct Wg signaling activities and the role of intercellular Wg transport will be examined through the directed expression of mutant transgenes in living embryos. Mutant Wg molecules that possess defined subsets of the normal Wg signaling activities will be expressed either ubiquitously, under the control of the heat shock promoter, or in defined domains, using the GAL4-UAS binary expression system. The phenotypic consequences on embryonic pattern and on molecular markers of wg signaling activity will be assessed to determine the cellular basis for the distinct Wg signaling activities observed. In addition, molecules that interact with Wg protein during signaling and transport will be identified by characterizing mutations that modulate wg signaling function. A small collection of mutations that modify the wg mutant phenotype have been isolated and several mutations show features that strongly suggest a direct involvement in the wg signaling pathway. These modifier mutations will be characterized genetically and molecularly to determine the nature of their interaction with Wg. These two approaches, in the genetically tractable Drosophila system, will provide insight into the cellular machinery through which Wg/Wnt molecules specify cell fate and control cell proliferation.