| Loss-of-function of the Drosophila sprouty ( spry) gene leads to the presence of extra secondary branches in the embryonic tracheal system. This work describes a new function of spry in larval terminal cells of the Drosophila tracheal system. We find that spry functions cell autonomously in these cells to modulate terminal branching of the larval tracheal system. Specifically, we find larval dorsal branch terminal cells (DBTCs) overexpressing spry form fewer terminal branches than wild-type controls, whereas DBTCs in spry− animals form more terminal branches. Furthermore, individual homozygous spry − DBTCs in an otherwise heterozygous tracheal system form more terminal branches than spry+ cells. These data indicate that spry functions cell autonomously to control terminal branch extension.; The mechanism of action of the Drosophila Spry protein, a receptor tyrosine kinase (RTK) inhibitor, is not well understood. We identified a processed form of Spry that lacks the N-terminus, and we characterized the subcellular localization and membrane topology of both forms of Spry in cells. We show that Sprys are tightly associated with cellular membranes, and although both forms are primarily intracellular, ∼5% is detected extracellularly in cell surface antibody accessibility and biotinylation experiments. 40% of Spry associated with membrane vesicles is fully protected from proteases; this protected population appears to be lumenal in membrane vesicles, and may correspond to intracellular trafficking forms of cell-surface Spry. The identification of extracellular Spry supports the possibility that Spry has functions outside its role as an intracellular inhibitor of RTK pathways.; The protein tyrosine phosphatase Corkscrew (Csw), and its mammalian homolog SHP-2, are positive effectors of RTK signaling. The substrates that Csw/SHP-2 dephosphorylate to transduce the RTK signal are largely unknown. Recently, phosphorylation of a conserved tyrosine residue was found to be essential for vertebrate Sprouty activity. Here we provide evidence that Csw/SHP-2 and Sprouty regulate some of the same developmental processes and pathways in vivo. We go on to show that Csw/SHP-2 can bind Sprouty and dephosphorylate a critical tyrosine residue both in vivo and in vitro . Thus, Sprouty is one of the long-sought targets of Csw/SHP-2, which stimulates signaling by inactivating a pathway inhibitor. |
