Control of Cell Number in Developing Retina

描述（申请人提供）：我的长期科学目标是了解指定视网膜细胞数量的分子机制。使用果蝇的复眼作为实验模型，我的实验室发现河马通路是这一过程的核心机制。Hippo通路的核心包括一个激酶级联，其中Ste20激酶Hippo （Hpo）磷酸化并激活NDR家族激酶疣（Wts）。反过来，Wts通过将癌蛋白Yorkie （Yki）从细胞核中排除，使其磷酸化并失活，而Yki通常在细胞核中作为dna结合转录因子扇贝（Sd）的辅助激活因子。我们的研究进一步确立了河马的关键作用

DESCRIPTION (provided by applicant): 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.