| Homothorax (Hth) and Teashirt (Tsh) are two transcription factors expressed in the progenitor cells of the developing Drosophila eye imaginal disc. In coordination with the Dpp/TGFbeta morphogen signal, Hth and Tsh function together to repress retinal differentiation genes in progenitor cells. Using genetic approach, I found that Hth and Tsh also promote progenitor cell proliferation and survival. Thus, the Hth+Tsh combinatorial code coordinates cell growth, survival and differentiation during Drosophila eye development.;To further investigate the mechanism of cell growth and survival controls by Hth and Tsh, I tested genetic interactions with four signal transduction pathways known to be involved in tissue growth regulation. Hippo tumor suppressor pathway genetically interacts with Hth and Tsh, which serve as DNA-binding partners for co-activator Yorkie (Yki) to turn on target gene microRNA bantam; bantam has pleotropic effects on cell proliferation and survival. Thus, Hth and Tsh provides the spatial cue for Yki activation and bantam expression specifically in the progenitor cells of the developing eye disc.;Genetic interaction tests among Hth, Tsh, and three other signaling pathways, Wingless, Notch and Jak-Stat, suggested that Hth and Tsh do not function with these pathways to control growth and survival in the developing eye disc.;Loss-of-function genetic evidences are essential for necessity arguments, but so far, mosaic mutant analysis on Tsh has been hindered by a technical difficulty due to tsh gene location. I devised a new method to make mosaic animal containing tsh null mutant clones. This new method will help address if Tsh is necessary in the growth and survival control or if it functions redundantly with other factors during development. |
