Salt-inducible kinases regulate growth through the Hippo signalling pathway in Drosophila


The specification of tissue size during development involves the coordinated action of many signalling pathways responding to organ-intrinsic signals, such as morphogen gradients, and systemic cues, such as nutrient status. The conserved Hippo (Hpo) pathway, which promotes both cell-cycle exit and apoptosis, is a major determinant of size control. The pathway core is a kinase cassette, comprising the kinases Hpo and Warts (Wts) and the scaffold proteins Salvador (Sav) and Mats, which inactivates the pro-growth transcriptional co-activator Yorkie (Yki). We performed a split-TEV-based genome-wide RNAi screen for modulators of Hpo signalling. We characterize the Drosophila salt-inducible kinases (Sik2 and Sik3) as negative regulators of Hpo signalling. Activated Sik kinases increase Yki target expression and promote tissue overgrowth through phosphorylation of Sav at Ser 413. As Sik kinases have been implicated in nutrient sensing, this suggests a link between the Hpo pathway and systemic growth control.

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Figure 1: A split TEV screen for modulators of the Yki/14.3.3 interaction.
Figure 2: Salt-inducible kinases inhibit the Hpo pathway.
Figure 3: Sik2 promotes Yki target gene expression.
Figure 4: Activated Sik2 induces wing growth through the Hpo pathway.
Figure 5: Depletion of the Sik kinases reduces the level of wing growth.
Figure 6: Sik kinases bind to and phosphorylate the Hpo pathway core member Sav.
Figure 7: Sik kinases phosphorylate the Hpo pathway core member Sav.
Figure 8: Sik2 inhibits Hpo signalling by phosphorylating Sav.


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We thank A. Kerai for help with re-screening candidates; T. Gilbank, S. Maloney and F. Earl for maintaining flies; L. Muthusamy for sequencing and helping with plating RNAi libraries; the Vienna Drosophila RNAi Centre for fly stocks; and O. Shaham and B. Thompson for comments on the manuscript. We are very grateful to P. Gaspar for help with fly genetics; F. Josue and P. Langton for advice; and A. Teleman and A. Celik for sharing reagents and exchanging unpublished data before publication. We thank K-A. Nave (Göttingen) for ongoing support. M.C.W. and M.J.R. acknowledge the support by the Bundesministerium für Wirtschaft und Forschung (grants 03EFT6N1 and 16V0008). M.C.W. was supported by an EMBO Long-Term Fellowship. The Tapon laboratory is supported by Cancer Research UK.

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M.C.W. designed the study and experiments and performed most of the experiments. M.V.H. cloned and analysed the full-length Sik3 ORFs and performed the experiments in Figs 5f–i and 8g–j and Supplementary Figs S3k,l and S4f–l. I.G. performed the experiments in Fig. 5a–e and Supplementary Fig. S4a–e and contributed western blot data. T.M.M. contributed phosphatase-treated western blot data, and E.C. helped with cloning. R.E.S., M.J., R.I. and M.H. helped perform and analyse the screen. M.J.R. provided the split TEV technology and supported the study. N.T. conceived and supervised the study. M.C.W. and N.T. wrote the manuscript.

Correspondence to Nicolas Tapon.

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Wehr, M., Holder, M., Gailite, I. et al. Salt-inducible kinases regulate growth through the Hippo signalling pathway in Drosophila. Nat Cell Biol 15, 61–71 (2013).

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