WINGLESS SIGNALING GENERATES PATTERN THROUGH 2 DISTINCT MECHANISMS

wingless (wg) and its vertebrate homologues, the Wnt genes, play criti cal roles in the generation of embryonic pattern, In the developing Dr osophila epidermis, wg is expressed in a single row of cells in each s egment, but it influences cell identities in all rows of epidermal cel ls in the 10- to 12-cell-wide segment, Wg signaling promotes specifica tion of two distinct aspects of the wild-type intrasegmental pattern: the diversity of denticle types present in the anterior denticle belt and the smooth or naked cuticle constituting the posterior surface of the segment, We have manipulated the expression of wild-type and mutan t wg transgenes to explore the mechanism by which a single secreted si gnaling molecule can promote these distinctly different cell fates, We present evidence consistent with the idea that naked cuticle cell fat e is specified by a cellular pathway distinct from the denticle divers ity-generating pathway. Since these pathways are differentially activa ted by mutant Wg ligands, we propose that at least two discrete classe s of receptor for Wg may exist, each transducing a different cellular response, We also find that broad Wg protein distribution across many cell diameters is required for the generation of denticle diversity, s uggesting that intercellular transport of the Wg protein is an essenti al feature of pattern formation within the epidermal epithelium. Final ly, we demonstrate that an 85 amino acid region not conserved in verte brate Wnts is dispensable for Wg function and we discuss structural fe atures of the Wingless protein required for its distinct biological ac tivities.