BREATHLESS, A DROSOPHILA FGF RECEPTOR HOMOLOG, IS REQUIRED FOR THE ONSET OF TRACHEAL CELL-MIGRATION AND TRACHEOLE FORMATION

Breathless, a Drosophila FGF receptor homolog (DFGF-R1), was shown to be essential for the migration of the tracheal cells and the posterior midline glia cells. The temporal requirement for the activity of this receptor was dissected by a dominant-negative construct lacking a fun ctional cytoplasmic tyrosine-kinase domain. Induction of the construct prior to the onset of tracheal or glial cell migration produced pheno types that were similar to those observed in the corresponding tissues of breathless null mutant embryos. However, this effect is not detect ed if the dominant-negative receptor is induced after the initiation o f tracheal cell migration, indicating that Breathless is required prim arily at the onset of the migration process. Induction of the construc t after the tracheal branches are completed, blocked the formation of tracheoles, i.e. extension of cellular processes by the terminal trach eal cells, demonstrating that Breathless plays an essential role in th is process as well. The requirement for Breathless at the onset of mig ration and the diversity of processes in which it participates, sugges t that the receptor is involved in triggering transcription factors, w hich may be distinct for each context.