Hedgehog (Hh) signalling in tracheal cell migration : The main chemoattractant involved in tracheal cell migration is fibroblast growth factor (FGF) homologue branchless (Bnl). Bnl activates the FGF receptor (FGFR) breathless (Btl) on the tracheal tip-cells leading to the migration of tracheal cells. Hedegehog (Hh) can regulate tracheal cell migration in two ways, the direct effect and the indirect effect. In the direct effect, Hh expression results in the extension of the termianl cells of the dorsal branch. The indirect effect of Hh in tracheal cell migration is through the positive regulation of bnl expression. The bnl expression is regulated by Hh signalling via a transcription factor known as stripe. Solution Hedgehog (Hh) signalling in tracheal cell migration : The main chemoattractant involved in tracheal cell migration is fibroblast growth factor (FGF) homologue branchless (Bnl). Bnl activates the FGF receptor (FGFR) breathless (Btl) on the tracheal tip-cells leading to the migration of tracheal cells. Hedegehog (Hh) can regulate tracheal cell migration in two ways, the direct effect and the indirect effect. In the direct effect, Hh expression results in the extension of the termianl cells of the dorsal branch. The indirect effect of Hh in tracheal cell migration is through the positive regulation of bnl expression. The bnl expression is regulated by Hh signalling via a transcription factor known as stripe..