Hpo Signaling Research Articles

The TEAD/TEF Family Protein Scalloped Mediates Transcriptional Output of the Hippo Growth-Regulatory Pathway

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 demonstrate that sd is required for yki-induced tissue overgrowth and target gene expression, and that sd activity is conserved in its mammalian 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.

Mob as tumor suppressor is activated by Hippo kinase for growth inhibition in Drosophila

Tissue growth and organ size are determined by coordinated cell proliferation and apoptosis in development. Recent studies have demonstrated that Hippo (Hpo) signaling plays a crucial role in coordinating these processes by restricting cell proliferation and promoting apoptosis. Here we provide evidence that the Mob as tumor suppressor protein, Mats, functions as a key component of the Hpo signaling pathway. We found that Mats associates with Hpo in a protein complex and is a target of the Hpo serine/threonine protein kinase. Mats phosphorylation by Hpo increases its affinity with Warts (Wts)/large tumor suppressor (Lats) serine/threonine protein kinase and ability to upregulate Wts catalytic activity to target downstream molecules such as Yorkie (Yki). Consistently, our epistatic analysis suggests that mats acts downstream of hpo. Coexpression analysis indicated that Mats can indeed potentiate Hpo-mediated growth inhibition in vivo. Our results support a model in which Mats is activated by Hpo through phosphorylation for growth inhibition, and this regulatory mechanism is conserved from flies to mammals.

The tumour suppressor Hippo acts with the NDR kinases in dendritic tiling and maintenance

Precise patterning of dendritic fields is essential for neuronal circuit formation and function, but how neurons establish and maintain their dendritic fields during development is poorly understood. In Drosophila class IV dendritic arborization neurons, dendritic tiling, which allows for the complete but non-overlapping coverage of the dendritic fields, is established through a 'like-repels-like' behaviour of dendrites mediated by Tricornered (Trc), one of two NDR (nuclear Dbf2-related) family kinases in Drosophila. Here we report that the other NDR family kinase, the tumour suppressor Warts/Lats (Wts), regulates the maintenance of dendrites; in wts mutants, dendrites initially tile the body wall normally, but progressively lose branches at later larval stages, whereas the axon shows no obvious defects. We further provide biochemical and genetic evidence for the tumour suppressor kinase Hippo (Hpo) as an upstream regulator of Wts and Trc for dendrite maintenance and tiling, respectively, thereby revealing important functions of tumour suppressor genes of the Hpo signalling pathway in dendrite morphogenesis.