The highly stereotyped tissue patterns that emerge during metazoan embryogenesis require precise spatial and temporal feedback regulation of key signal transduction pathways. Secreted Wnt proteins initiate intercellular signal transduction cascades that regulate cell morphology, execute cell fate decisions, and maintain stem cells. Altered Wnt signal transduction causes a growing list of diseases, including osteoporosis and dozens of types of cancer, and may contribute to the pathogenesis of several other diseases. The long-term goal of this proposal is to understand the mechanisms by which the effects of Wnt signals are spatially regulated during development. In the fruit fly Drosophila, the naked cuticle (nkd) gene is the only zygotic gene that spatially limits the effects of the Wnt signal Wingless (Wg) during early embryonic development. Nkd targets the Wnt signaling component Dishevelled (Dsh). Although the biochemical mechanisms of Dsh function are unknown, Dsh transmits signals from Frizzled (Fz) receptors to a large protein complex that triggers degradation of the Wnt effector and oncogene beta-catenin. Preliminary data indicate that Nkd may regulate Dsh phosphorylation, localization, and accumulation, each of which is important for Dsh function. The proposed experiments are designed to elucidate the molecular mechanism(s) by which Nkd limits Wnt signaling through Dsh in well-characterized tissues in a model genetic organism. The specific aims are: 1) to determine the subcellular locus (loci) of Nkd action and its regulation during Wnt signaling in vivo; 2) to investigate the regulation and consequences of the biochemical interaction between Nkd, Dsh, and key Dsh-associated proteins; and 3) to discover additional regulator(s) of Nkd activity and begin to investigate their mechanism(s) of action. Because nkd is conserved in vertebrates, the proposed experiments will help create a new paradigm highly relevant to mammalian biology and disease. The potential health relevance of this project to developmental biology, stem cell biology, and disease-related research is substantial considering the wide employment of Wnt signaling throughout metazoan biology. [unreadable] [unreadable]