A Kinome RNAi Screen in Drosophila Identifies Novel Genes Interacting with Lgl, aPKC and Crb Cell Polarity Genes in Epithelial Tissues

In both Drosophila melanogaster and mammalian systems, epithelial structure and underlying cell polarity are essential for proper tissue morphogenesis and organ growth. Cell polarity interfaces with multiple cellular processes that are regulated by the phosphorylation status of large protein networks. To gain insight into the molecular mechanisms that coordinate cell polarity with tissue growth, we screened a boutique collection of RNAi stocks targeting the kinome for their capacity to modify Drosophila 'cell polarity' eye and wing phenotypes. Initially we identified kinase or phosphatase genes whose depletion modified adult eye phenotypes associated with the manipulation of cell polarity complexes (via overexpression of Crb or aPKC). We next conducted a secondary screen to test whether these cell polarity modifiers altered tissue overgrowth associated with depletion of Lgl in the wing. These screens identified Hippo, JNK, and Notch signalling pathways, previously linked to cell polarity regulation of tissue growth. Furthermore, novel pathways, not previously connected to cell polarity regulation of tissue growth were identified, including Wingless (Wg/Wnt), Ras and lipid/Phospho-inositol-3-kinase (PI3K) signalling pathways. Additionally, we demonstrated that the 'nutrient sensing' kinases, Salt Inducible Kinase 2 and 3 (SIK2 and 3) are potent modifiers of cell polarity phenotypes and regulators of tissue growth. Overall, our screen has revealed novel cell-polarity interacting kinases and phosphatases that affect tissue growth, providing a platform for investigating molecular mechanisms coordinating cell polarity and tissue growth during development.

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