Control of Body Size by TGF- Signaling. Lindsay Moss-Taylor, Michael O'Connor. University of Minnesota, Minneapolis, MN.

   Body size is tightly regulated during development to maximize adult fitness. In Drosophila, final body size is mainly determined by growth rate and duration of growth during juvenile stages; once maturation occurs, body size is set. The rate of growth is determined by insulin-like peptide (dilp) signaling, while the duration of growth is regulated by the neuropeptide prothoraciotropic hormone (PTTH). Manipulation of these pathways alters final body size by either accelerating or delaying ecdysone production and the onset of metamorphosis. Under normal growth conditions, termination of Drosophila juvenile development is triggered when third instar larvae achieve critical weight, a size after which starvation no longer delays the time to metamorphosis. How larvae sense critical weight and the relationship of critical weight to dilp and PTTH signaling remains largely unknown. We are investigating the newly identified role that TGF- ligand Activin plays in regulating Drosophila body size and timing of metamorphosis. We have found that mutations in dActivin (dAct) cause accelerated larval development and smaller final body size. Our preliminary results show that dAct is expressed in the Insulin Producing Cells (IPCs) in the central brain. Since increased insulin signaling in the IPCs advances metamorphosis, we will test the hypothesis that this TGF- ligand is affecting body size and developmental timing by regulating insulin production and/or release.