Tubulogenesis in Drosophila: a requirement for the trachealess gene product

The trachealess (trh) gene of Drosophila is required for embryonic tube formation. In trh mutants, tube-forming cells of the salivary gland, trachea, and filzkörper fail to invaginate to form tubes and remain on the embryo surface. We identified a P-element insertion that disrupts trh function and used the insert to clone and characterize trh. trh is expressed in the salivary duct, trachea, and filzköper primordia, and expression persists in these cells throughout embryogenesis. trh expression in the salivary duct is controlled by the homeotic gene, Sex combs reduced (Scr), and by another salivary gland gene, fork head (fkh). trh is homologous to two transcription factors: the human hypoxia-inducible factor-1 alpha and the Drosophila Single-minded protein.