O'Farrell 9724706 To produce a body having coherent shape and structure, development must control the size of each body part. Detailed knowledge of development and cell cycle control in Drosophila provides unique advantages for an exploration of the mechanisms that coordinate development, cell proliferation and size. Dr. O'Farrell will examine this coordination in imaginal discs, the larval precursors to the adult cuticular structures. Imaginal cells grow exponentially during larval life but arrest when this disc reaches a mature size. Wingless (Wg) and Decapentaplegic (Dpp) are pattern regulators that are also synergistic activators of growth and proliferation in discs. Nitric oxide synthase (NOS) inhibits proliferation and its activity rises at about the time proliferation arrests in discs. He will explore the hierarchy of the inputs controlling proliferation by examining the effect of a perturbation (e.g. induction of Wg and Dpp) on the other processes (e.g., activation of NOS), and the ability of other treatments (e.g., induction of various cell cycle regulators) to override the perturbation. These epistasis like experiments should begin to outline the pathway of regulation used in size control and give us entries to begin a more detailed dissection of the controls. To provide probes for this pathway dissection Dr. O'Farrell will define the basis of cell cycle arrest upon termination of growth. Measurement of the levels of various cell cycle regulators and analysis of the ability of ectopic expression to bypass the arrest will define the limiting cell cycle regulators. Because control of growth (increase in mass regulates cell cycle, he will develop probes for growth. The rate of protein synthesis governs when cell achieve the size threshold required for division, and the translational initiation factor eIF4E has important inputs into cell cycle regulation. Using transgenes and a drug (rapamycin) that impairs eIF4E activity, he will explore its involvement in growth an d cell cycle quiescence. He will use similar techniques to alter cyclin D levels and activity, because it is implicated in the coupling of translation and cell cycle. As a measure of growth quiescence, he will use a newly developed in situ procedure to assess the level of nascent rRNA transcripts. Together these experiments should provide the ground work for detailed dissection of the controls of tissue and organ size.
