Ligand receptor interactions in the Wnt signaling pathway in Drosophila.
Secreted Wnt proteins have numerous signaling functions during development, mediated by Frizzled molecules that act as Wnt receptors on the cell surface. In the genome of Drosophila, seven Wnt genes (including wingless; wg), and five frizzled genes have been identified. Relatively little is known about signaling and binding specificities of different Wnt and Frizzled proteins. We have developed an assay to determine the strength of binding between membrane-tethered Wnts and ligand binding domains of the Frizzled receptors. We found a wide spectrum of binding affinities, reflecting known genetic interactions. Most Wnt proteins can bind to multiple Frizzleds and vice versa, suggesting redundancy in vivo. In an extension of these experiments, we tested whether two different subdomains of the Wg protein would by themselves bind to Frizzled and generate a biological response. Whereas these two separate domains are secreted from cells, suggesting that they form independently folded parts of the protein, they were only able to evoke a response when co-transfected, indicating that both are required for function. In addition to the Frizzleds, members of the LRP family (represented by the arrow gene in Drosophila) are also necessary for Wnt signal transduction and have been postulated to act as co-receptors. We have therefore examined whether a soluble form of the Arrow molecule can bind to Wingless and Frizzled, but no interactions were detected.
Wu
Chi-hwa
CH
Howard Hughes Medical Institute, Department of Developmental Biology, Stanford University Medical School, California 94305-5323, USA.
Nusse
Roel
R
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D004330:Drosophila; D029721:Drosophila Proteins / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000378:metabolism; D026502:LDL-Receptor Related Proteins; D060850:LIM-Homeodomain Proteins; D008024:Ligands; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D008562:Membrane Glycoproteins / Q000096:biosynthesis; D008969:Molecular Sequence Data; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D011973:Receptors, LDL / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors / Q000378:metabolism; D051153:Wnt Proteins; D029961:Zebrafish Proteins
C108601:Awh protein, Drosophila; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D026502:LDL-Receptor Related Proteins; D060850:LIM-Homeodomain Proteins; D008024:Ligands; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D008562:Membrane Glycoproteins; C066176:Nrt protein, Drosophila; D011518:Proto-Oncogene Proteins; D011973:Receptors, LDL; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D051153:Wnt Proteins; D029961:Zebrafish Proteins