REGULATED BREATHLESS RECEPTOR TYROSINE KINASE-ACTIVITY REQUIRED TO PATTERN CELL-MIGRATION AREA BRANCHING IN THE DROSOPHILA TRACHEAL SYSTEM

Receptor tyrosine kinases (RTKs) are members of a diverse class of sig naling molecules well known for their roles in cell fate specification , cell differentiation, and oncogenic transformation. Recently several RTKs have been implicated in cell and axon motility, and RTKs are kno wn to mediate chemotactic guidance of tissue culture cells. We have in vestigated whether the Drosophila FGF receptor homolog, Breathless (BT L), whose activity is necessary for each phase of branching morphogene sis in the embryonic tracheal system, might play a role in guiding the directed migration of tracheal cells. We found that expression of a c onstitutively active receptor during tracheal development interfered w ith directed tracheal cell migration and led to extra secondary and te rminal branch-forming cells. Reduction in endogenous BTL signaling enh anced the cell migration defects while suppressing the ectopic branchi ng defects. These results are consistent with a model for tracheal dev elopment in which spatially regulated BTL activity slides tracheal cel l migration and quantitatively regulated BTL activity determines the p atterns of secondary and terminal branching cell fates.