branchless encodes a Drosophila FGF homolog that controls tracheal cell migration and the pattern of branching

The role of the branchless (bnl) gene in regulating the development of the insect tracheal system was analyzed in Drosophila mutants with misexpressed bnl gene. The bnl mutants exhibited defective or aberrant tracheal branching with unbranched elongated tracheal metameres. The lethal mutations indicated the role of Drosophila bnl gene in regulating the development of the insect tracheal system by encoding fibroblast growth factors that promote tracheal cell migration.