The Hippo (Hpo) kinase cascade restricts tissue growth by inactivating the transcriptional coactivator Yorkie (Yki), which regulates the expression of target genes such as the cell death inhibitor diap1 by unknown mechanisms. Here we identify the TEAD/TEF family protein Scalloped (Sd) as a DNA-binding transcription factor that partners with Yki to mediate the transcriptional output of the Hpo growth-regulatory pathway. The diap1 (th) locus harbors a minimal Sd-binding Hpo Responsive Element (HRE) that mediates transcriptional regulation by the Hpo pathway. Sd binds directly to Yki, and a Yki missense mutation that abrogates Sd-Yki binding also inactivates Yki function in vivo. We further emonstrate that sd is required for yki-induced tissue overgrowth and target gene expression, and that sd activity is conserved in itsmammalian homolog. Our results uncover a heretofore missing link in the Hpo signaling pathway and provide a glimpse of the molecular events on a Hpo-responsive enhancer element.

Coordination of cell proliferation and cell death is essential to attain proper organ size during development and for maintaining tissue homeostasis throughout postnatal life. In Drosophila, these two processes are orchestrated by the Hippo kinase cascade, a growth-suppressive pathway that ultimately antagonizes the transcriptional coactivator Yorkie (Yki). Here we demonstrate that a single phosphorylation site in Yki mediates the growthsuppressive output of the Hippo pathway.Hippo-mediated phosphorylation inactivates Yki by excluding it from the nucleus, whereas loss of Hippo signaling leads to nuclear accumulation and therefore increased Yki activity.We further delineate a mammalian Hippo signaling pathway that culminates in the phosphorylation of YAP, the mammalian homolog of Yki. Using a conditional YAP transgenic mouse model, we demonstrate that the mammalian Hippo pathway is a potent regulator of organ size, and that its dysregulation leads to tumorigenesis. These results uncover a universal size-control mechanism in metazoan.

Coordination between cell proliferation and cell death is essential to maintain homeostasis in multicellular organisms. In Drosophila, these two processes are resultregulated by a pathway involving the Ste20-like ki-nase Hippo (Hpo) and the NDR family kinase Warts (Wts; also called Lats). Hpo phosphorylates and acti-supvates Wts, which in turn, through unknown mecha-nisms, negatively regulates the transcription of cell-cycle and cell-death regulators such as cycE and reguladiap1.Here we identify Yorkie (Yki), the Drosophila ortholog of the mammalian transcriptional coactiva-Hartor yes-associated protein (YAP), as a missing link between Wts and transcriptional regulation. Yki is re-quired for normal tissue growth and diap1 transcrip-tion and is phosphorylated and inactivated by Wts. Overexpression of yki phenocopies loss-of-function mutations of hpo or wts, including elevated transcrip-tion of cycE and diap1, increased proliferation, de-fective apoptosis, and tissue overgrowth. Thus, Yki is coora critical target of the Wts/Lats protein kinase and a potential oncogene.

The coordination between cell proliferation and cell death is essential to maintain homeostasis within multicellular organisms. The mechanisms underlying this regulation are yet to be completely understood.Here, we report the identification of hippo (hpo) as a gene that regulates both cell proliferation and cell death in Drosophila. hpo encodes a Ste-20 family protein kinase that binds to and phosphorylates the tumor uppressor protein Salvador (Sav), which is known to interact with the Warts (Wts) protein kinase. Loss of behpo results in elevated ranscription of the cell cycle elimiregulator cyclin E and the cell-death inhibitor diap1,leading to increased proliferation and reduced apopto-studsis.Further, we show that hpo, sav, and wts define a pathway that regulates diap1 at the transcriptional level. A human homolog of hpo completely rescues the overgrowth phenotype of Drosophila hpomutants, suggesting that hpo might play a conserved role for growth control in mammals.