Neuroendocrine regulation of Drosophila development

All holometabolous insects undergo metamorphosis to become sexually mature adults. Metamorphosis is initiated by brain-derived prothoracicotropic hormone (PTTH) which stimulates production of the molting hormone ecdysone via an incompletely identified signaling pathway. In this talk we will present data demonstrating that Torso, a receptor tyrosine kinase that regulates embryonic terminal cell fate in Drosophila, is the PTTH receptor. Trunk, the embryonic Torso ligand, is related to PTTH and ectopic expression of PTTH in the embryo partially rescues trunk mutants. In larvae, torso is expressed specifically in the prothoracic gland (PG), and its loss phenocopies removal of PTTH. Activation of Torso by PTTH stimulates Erk phosphorylation, and loss of Erk in the PG phenocopies loss of PTTH/Torso. We conclude that PTTH initiates metamorphosis by activation of the Torso/Erk pathway.