Wingless and its signalling pathway have common and separable functions during tracheal development

The Drosophila tracheal tree consists of a tubular network of epithelial br anches that constitutes the respiratory system. Groups of tracheal cells mi grate towards stereotyped directions while they acquire specific tracheal f ates. This work shows that the wingless/WNT signalling pathway is needed wi thin the tracheal cells for the formation of the dorsal trunk and for fusio n of the branches, These functions are achieved through the regulation of t arget genes, such as spalt in the dorsal trunk and escargot in the fusion c ells. The pathway also aids tracheal imagination and helps guide the gangli onic branch. Moreover the wingless/WNT pathway displays antagonistic intera ctions with the DBP (decapentaplegic) pathway, which regulates branching al ong the dorsoventral axis. Remarkably, the wingless gene itself, acting thr ough its canonical pathway, seems not to be absolutely required for all the se tracheal functions. However, the artificial overexpression of wingless i n tracheal cells mimics the overexpression of a constitutively activated ar madillo protein. The results suggest that another gene product, possibly a WNT, could help to trigger the wingless cascade in the developing tracheae.