Opposing actions of CSW and RasGAP modulate the strength of torso RTK signaling in the Drosophila terminal pathway

In Drosophila, specification of embryonic terminal cells is controlled by T orso receptor tyrosine kinase. here, we analyze the molecular basis of posi tive (Y630) and negative (Y918) phosphotyrosine (pY) signaling sites on Tor so. We find that the Drosophila homolog of RasGAP associates with pY918 and is a negative effector of Torso signaling. Further, we show that the tyros ine phosphatase Corkscrew (CSW), which associates with pY630 Torso signalin g site, thus identifying Torso to be a substrate of CSW in the terminal pat hway. CSW also serves as an adaptor protein for DRK binding, physically lin king Torso to Ras activation. The opposing actions of CSW and RasGAP modula te the strength of the Torso signal, contributing to the establishment of p recise boundaries for terminal structure development.