Drosophila Eye as a Model to Study Regulation of Growth Control: The Discovery of Size Control Pathways

Regulation of growth control is essential for normal development and for maintaining homeostasis in all organisms. Growth regulation involves control of cell proliferation and coordinate regulation of processes required for normal developmental patterning, e.g., regulation of cell growth, signaling from morphogens, other patterning genes, and regulation of programmed cell death. The common fruit fly Drosophila melanogaster is particularly well-suited for studying genetic regulation of growth control given the large variety of genetic tools available, and the ability to study tissue- and cell-specific defects in flies. The eye imaginal disc is a favored model for studying growth regulation because the genetic hierarchy of eye development and the regulation of cell cycles are well-understood. The eye imaginal disc is a very versatile model system particularly for genetic screens, as the phenotypes are relatively easy to score, and lethal mutants can be recovered. In this chapter, we focus on the regulation of growth control through the Hippo and insulin-receptor/tuberous sclerosis complex (TSC)-Target of Rapamycin (TOR) pathways—beginning with the genetic screens through which the initial pathway mutants were identified, the components of these complex signaling networks, and the regulatory relationships that are currently known amongst and between pathway components.