| To survive, develop, and reproduce in fluctuating environmental conditions, living organisms must tightly couple cell growth and metabolism to nutrient availability, cellular energy status, and growth factor signaling. The regulatory kinase Target of Rapamycin (TOR) has emerged as a convergence point for the transduction of multiple environmental and cellular signals into appropriate changes in growth and development.; The following study was designed to further our understanding of nutrient-mediated growth regulation through analysis of TOR misexpression phenotypes and identification of novel interactors in the TOR signaling pathway. Utilizing the genetic tools of the model organism Drosophila melanogaster, we performed targeted overexpression analysis both to elucidate the downstream effects of TOR signaling, as well as to provide a sensitized genetic background in which to screen for novel TOR interactors.; I describe the effects of wild-type and kinase-inactive TOR overexpression on cell and organ size, cell cycle progression, apoptosis, and autophagy induction. The complex and progressive nature of TOR misexpression phenotypes, as well as the similarities between wild-type and kinase-inactive TOR overexpression, indicates the importance of regulated binding interactions in TOR signaling. The utility of tissue-specific TOR misexpression phenotypes as genetic backgrounds for dominant-modifier deficiency, insertional, and EMS mutagenesis screens is explored.; I describe the identification and analysis of two novel TOR interactors identified as dominant enhancers of eyeless-driven TOR overexpression phenotypes. The recovery of five alleles of Drosophila Tra1/TRRAP, a direct activator-binding subunit of histone acetlytransferase (HAT) complexes has revealed a novel role for Tral in growth regulation. Analysis of two alleles of Drosophila Hsc70-4 (clathrin-uncoating ATPase) has revealed that TOR acts to mediate nutrient import, in part, by coordinately regulating bulk endocytic uptake and the targeted endocytic turnover of nutrient transporters such as Slimfast. We find that disruption of endocytosis affects cell size, cell cycle phasing, P13kinase signaling, autophagy induction, as well as tsc1 and TOR mutant phenotypes, indicating a critical role for cellular endocytosis in mediating proper growth regulation. These studies have broadened our understanding of the mechanisms through which eukaryotic organisms achieve a directed growth response appropriate to available nutrients, energy, and growth factor signaling. |
