My long-term scientific goal is to understand the molecular mechanisms that specify retina cell number. Using the compound eye of Drosophila as an experimental model, my laboratory has discovered the Hippo pathway as a central mechanism underlying this process. The core of the Hippo pathway comprises a kinase cascade in which the Ste20 kinase Hippo (Hpo) phosphorylates and activates the NDR family kinase Warts (Wts). Wts, in turn, phosphorylates and inactivates the oncoprotein Yorkie (Yki) by excluding it from the nucleus, where it normally functions as a coactivator for the DNA-binding transcription factor Scalloped (Sd). Our research further established a critical role for the Hippo pathway in controlling organ size in mammals, underscoring the importance of Drosophila as a powerful model to discover universal developmental mechanisms. Much of our recent efforts have focused on discovering the missing components of the Hippo pathway, with the ultimate goal of defining a complete Hippo signaling network that relays information from the extracellular milieu to nuclear gene transcription. We have made significant progress in the last grant period, including 1) the discovery of Crumbs as an apically localized transmembrane protein that regulates Hippo signaling by directly binding and localizing the tumor suppressor Expanded to apical membranes;2) discovery of a functionally conserved Hippo pathway in organisms representing unicellular relatives of Metazoa;3) discovery of verteporfin as the first small molecule inhibitor for Yki and its mammalian homologue YAP;4) discovery of default repression as a fundamental mechanism underlying Hippo-mediated growth regulation by demonstrating that Sd functions by default as a transcriptional repressor;5) elucidating the molecular mechanism by which Merlin regulates Hippo signaling by demonstrating a requirement for Merlin in direct binding and recruitment of the effector kinase Wts to the plasma membrane. In the coming project period, we will further elucidate the composition and regulation of the Hippo pathway through the following aims. First, we have identified, through biochemical screens, another protein kinase that can phosphorylate and activate Wts in a similar manner as Hpo. Our goal in this aim is to characterize the role of this Hpo-like kinase in growth control and Hippo signaling in vivo. Second, we have identified, through phenotype-based screens, a novel tumor suppressor that regulates Hippo signaling in a non-cell autonomous manner as well as a tumor suppressor complex that regulates Hippo signaling in a cell-autonomous manner. Our goal in this aim is to understand the molecular mechanisms by which these novel tumor suppressors regulate the Hippo pathway. Lastly, we have designed a sensitized genetic screen to identify additional components of the Hippo pathway. Our goal in this aim is to complete the genetic screen and to molecularly characterize candidate genes identified from the screen. Besides revealing fundamental mechanisms of eye development, the proposed studies will have general implications for the development of other tissues.

Public Health Relevance

The proposed studies will not only elucidate the fundamental mechanisms that regulate retina cell number, but also provide general insights into how cell number is determined in other organs during animal development and how aberrant regulation of this process could lead to tissue atrophy or hyperplasia. Such insights may facilitate the therapeutic interventions of relevant human diseases, including diseases of the retina.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Greenwell, Thomas
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Johns Hopkins University
Schools of Medicine
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Yu, Jianzhong; Pan, Duojia (2018) Validating upstream regulators of Yorkie activity in Hippo signaling through scalloped-based genetic epistasis. Development 145:
Zheng, Yonggang; Liu, Bo; Wang, Li et al. (2017) Homeostatic Control of Hpo/MST Kinase Activity through Autophosphorylation-Dependent Recruitment of the STRIPAK PP2A Phosphatase Complex. Cell Rep 21:3612-3623
Das, Arupratan; Fischer, Robert S; Pan, Duojia et al. (2016) YAP Nuclear Localization in the Absence of Cell-Cell Contact Is Mediated by a Filamentous Actin-dependent, Myosin II- and Phospho-YAP-independent Pathway during Extracellular Matrix Mechanosensing. J Biol Chem 291:6096-110
Liu, Bo; Zheng, Yonggang; Yin, Feng et al. (2016) Toll Receptor-Mediated Hippo Signaling Controls Innate Immunity in Drosophila. Cell 164:406-19
Chan, PuiYee; Han, Xiao; Zheng, Baohui et al. (2016) Autopalmitoylation of TEAD proteins regulates transcriptional output of the Hippo pathway. Nat Chem Biol 12:282-9
Deng, Hua; Wang, Wei; Yu, Jianzhong et al. (2015) Spectrin regulates Hippo signaling by modulating cortical actomyosin activity. Elife 4:e06567
Zheng, Yonggang; Wang, Wei; Liu, Bo et al. (2015) Identification of Happyhour/MAP4K as Alternative Hpo/Mst-like Kinases in the Hippo Kinase Cascade. Dev Cell 34:642-55
Pan, Duojia (2015) YAPing Hippo Forecasts a New Target for Lung Cancer Prevention and Treatment. J Clin Oncol 33:2311-3
Ni, Lisheng; Zheng, Yonggang; Hara, Mayuko et al. (2015) Structural basis for Mob1-dependent activation of the core Mst-Lats kinase cascade in Hippo signaling. Genes Dev 29:1416-31
Chen, Qian; Zhang, Nailing; Xie, Rui et al. (2015) Homeostatic control of Hippo signaling activity revealed by an endogenous activating mutation in YAP. Genes Dev 29:1285-97

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