| The formation of tubes during embryogenesis is an important step in the formation of many organs. To better understand this process, I have focused on the formation of two tubular organs in Drosophila melanogaster : the salivary duct and the trachea. Both tissues are specified as epithelial sheets on the surface of the embryo, and invaginate into the embryo to form tubes. However, the duct becomes a simple, wishbone-shaped tube, while the trachea forms a highly branched tubular network. Despite the significant differences in their final structures, both structures require the transcription factor trachealess (trh) in order to form tubes. In trh mutant embryos, the cells of the salivary duct and trachea remain in a sheet on the surface of the embryo. The trh mutant phenotype could be due to a loss of cell fate or due to a defect in tube formation. To differentiate between these possibilities, I have investigated the role of trh in the development of the salivary duct and trachea. I found three genes that are expressed in the duct cells independently of trh, showing that trh does not regulate duct cell fate but instead regulates tube formation. To understand how trh directs tube formation, I have tested a collection of salivary duct and tracheal genes for regulation by trh. I have identified eight genes that are dependent on trh for their expression. I have also determined the minimal in vitro binding site for TRH with its partner Tango (TAN), in preparation of molecular analysis of these TRH regulated genes. My analysis of salivary duct genes also identified a role for the Notch ligand Serrate (Ser) in the specification of the salivary gland imaginal ring cells. |
