Attenuation of decapentaplegic signaling via a localized chondroitin-sulfated signaling sink

Glycosaminoglycans (GAGs) are long linear polysaccharides made of disaccharide repeats. The GAGs heparan and chondroitin are found ubiquitously on cell surfaces in many organisms and are involved in regulating developmental signaling, immunity, and mediating many cell-cell interactions. In Drosophila melanogaster, GAGs are synthesized downstream of the gene mummy (mmy), which encodes the Drosophila UDP-N-acetylglucosamine pyrophosphorylase, the enzyme performing the final catalytic step in UDP-GlcNAc synthesis. mmy encodes an antagonist of Decapentaplegic (Dpp) signaling, and mmy mutant embryos have expanded ectopic Dpp activity in the dorsal epidermis. We confirmed through multiple tests that the mmy-mediated effects on Dpp signaling occur downstream of dpp transcription and that mmy activates a switch from short-range to long-range signaling in the epidermis. To identify downstream effectors of Dpp signal restriction, we screened 23 of the 25 Drosophila β-1,3-glycosyltransferases functioning downstream of Mmy. Embryos depleted of either wanderlust (wand), which encodes a putative chondroitin sulfate synthase, or super sex combs, which encodes an O-GlcNAc transferase, had Dpp activity expanded ectopically beyond the LE epidermis, identifying these transferases as a Dpp antagonists. We further characterized wand and determined that it is expressed in embryonic cardiac cells and that it antagonizes Dpp signaling in the mesoderm as well as the epidermis. Taken together, these data suggest that mmy, through wand, synthesizes a chondroitin-sulfated sink that alters the signaling range of Dpp. Future work will involve characterizing the role of other chondroitin sulfate-synthesizing genes in Drosophila signaling regulation, determining the nature of the Dpp-chondroitin interaction, exploring the role of chondroitin sulfate in imaginal disc and testes signaling, and identifying the specific GAGmodified targets that enact epidermal signal regulation. These data will provide new insights into regulation of Dpp signaling via glycosylation.