EM: Wnt/Wingless signaling in Drosophila

The Wingless (Wg) pathway represents one of the best-characterized intercellular signaling networks. Studies performed in Drosophila over the last 30 years have contributed to our understanding of the role of Wg signaling in the regulation of tissue growth, polarity, and patterning. These studies have revealed mechanisms conserved in the vertebrate Wnt path-ways and illustrate the elegance of using theDrosophilamodel to understand evolutionarily conservedmodes of gene regulation. In this article, we describe the function ofWg signaling in patterning the Drosophila embryonic epidermis and wing imaginal disc. As well, we present an overview of the establishment of the Wg morphogen gradient and discuss the differential modes of Wg-regulated gene expression. Evolutionarily conserved cell signaling path-ways regulate the development of metazoans through their reiterative implementation, both spatially and temporally. Wnt signaling repre-sents one such pathway that hasmultiple, essen-tial roles during both embryogenesis and adult homeostasis to regulate cell proliferation, cel