An in vivo RNAi screen for novel regulators of the Hippo pathway in organ size control. Carole Poon^1,2, Xiaomeng Zhang^1,2,3, Jane Lin^1,2, Samuel Manning^1,2,3, Kieran Harvey^1,2,3. 1) Cell Growth and Proliferation Laboratory, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia; 2) Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria, Australia; 3) Department of Pathology, University of Melbourne, Parkville, Victoria, Australia.

   The Salvador-Warts-Hippo (SWH) pathway is an evolutionarily conserved regulator of tissue growth that is deregulated in human cancer. Upstream SWH pathway components convey signals via a core kinase cassette to the transcription coactivator Yorkie (Yki), which controls tissue growth by modulating genes that control cell proliferation and apoptosis. Large-scale phospho-proteome studies in vivo and in vitro indicate previously uncharacterised phosphorylation sites on SWH pathway proteins, suggesting that additional kinases may influence SWH signalling. To uncover such kinases, we performed a genetic RNA interference modifier screen against the Drosophila melanogaster kinome. From this screen, we identified kinases that are known to be associated with SWH signalling, such as members of the JNK cascade. Furthermore, we have discovered two new SWH kinases which control tissue growth and organ size during development in the fly: Tao-1 promotes Hippo activation to restrict tissue growth, and Hipk promotes tissue growth in a Yki-dependent manner. Importantly, we have shown that the ability of Tao-1 and Hipk to regulate SWH signalling is conserved in mammalian cells. Using both fly and mammalian systems, we will continue to investigate the role of other positive screen candidates in tissue growth regulation, and determine their relationship to the SWH pathway in organ size control.