INTERACTIONS BETWEEN THE EGF RECEPTOR AND DPP PATHWAYS ESTABLISH DISTINCT CELL FATES IN THE TRACHEAL PLACODES

The formation of the tracheal network in Drosophila is driven by stere otyped migration of cells from the tracheal pits. No cell divisions ta ke place during tracheal migration and the number of cells in each bra nch is fixed. This work examines the basis for the determination of tr acheal branch fates, prior to the onset of migration, We show that the EGF receptor pathway is activated by localized processing of the liga nd SPITZ in the tracheal placodes and is responsible for the capacity to form the dorsal trunk and visceral branch. The DPP pathway, on the contrary, is induced in the tracheal pit by local presentation of DPP from the adjacent dorsal and ventral ectodermal cells. This pathway pa tterns the dorsal and lateral branches, Elimination of both pathways b locks migration of all tracheal branches, Antagonistic interactions be tween the two pathways are demonstrated. The opposing activities of tw o pathways may refine the final determination of tracheal branch fates .