Yorkie controls tube length and apical barrier integrity in the developingDrosophilaairways

Epithelial organ size and shape depend on cell shape changes, cell-matrix communication and apical membrane growth. The Drosophila embryonic tracheal network is an excellent model to study these processes. Here, we show that the transcriptional co-activator of the Hippo pathway, Yorkie (YAP in vertebrates), plays distinct roles in the developing Drosophila airways. Yorkie exerts a cytoplasmic function by binding Drosophila Twinstar, the orthologue of the vertebrate actin-severing protein Cofilin, to regulate F-actin levels and apical cell membrane size, which are required for proper tracheal tube elongation. Second, Yorkie controls water-tightness of tracheal tubes by transcriptional regulation of the enzyme δ-aminolevulinate synthase ( Alas ). We conclude that Yorkie has a dual role in tracheal development to ensure proper tracheal growth and functionality. Short Summary This work identified an alternative role of the transcriptional co-activator Yorkie (Yki) in controlling water impermeability and tube size of the developing Drosophila airways. Tracheal impermeability is triggered by Yki-mediated transcriptional regulation of δ-aminolevulinate synthase , Alas , whereas tube elongation is controlled by binding of Yki to the actin severing factor Twinstar.