Study On New Mechanisms Of Wnt/β-Catenin And Hippo Signalings For Regulating Organ Development In Drosophila

Drosophila melenogaster is widely used as an in vivo model to screen for new functional genes due to its abundant tools for genetic manipulation and short life cycle. In this study, by gain of function screening approach, we discovered Nek2 and licorne from the UAS-ORF library of 655 growth-regulating genes in Drosophila, they are involved in the regulation of the Wnt/β-Catenin pathway and the Hippo pathway respectively, which regulates cell growth and organ development.The evolutionarily conserved Wnt/β-Catenin pathway plays pivotal roles in embryonic development, energy homeostasis and stem cell maintenance. Here we found that Nek2 regulates Wnt signal transduction via phosphorylating Dsh, a key component of the Wnt/β-Catenin pathway. Interestingly, the phosphorylations of Dsh by Nek2 have dual-functions. While the phosphorylation on the N-terminus of Dsh acelerated the activation Wnt/β-Catenin signaling and promoted the signal transduction, the phosphorylation on the C-terminus of Dsh mediated its degradation and prevented excessive activation when Wnt/β-Catenin signaling reached a certain threshold. The dual-regulation mechanism can accelerate the signal transduction when the pathway is turned on, and avoid inappropriately sustained activation of the pathway. This complicated strategy ensures a precise regulation of downstream target gene expression. In addition, we found Dρo (CKIε homolog) had redundant functions with Nek2. Expression of Wnt target genes and Drosophila organ development were severely obstructed when both Nek2 and dco were knocked-down.The Hippo signaling pathway is crucial in regulating cell proliferation and tissue growth. And its dysregulation contributes to tumorgensis. Core components of the Hippo pathway include Hippo, Salvador, Warts and Mats. Transcriptional co-activator, Yorkie is phosphorylated by Warts and retained in the cytoplasm by interaction with 14-3-3 protein. Here we identified that the Hippo pathway integrates with p38 MAPK signaling. Overexpression of licorne or its upstream regulator, Mekkl, promoted Hippo signaling target gene transcription in wing discs and triggered tissue overgrowth. Similarly to yorkie mutant, loss of licorne in ovary follicle cell negatively regulates expanded and cut expression, and positively regulated FasⅢ expression. By genetic epistasis analysis, we demonstrated that licorne acted upstream of wts, yki, and p38b mediated the effects of licorne and Mekkl on Hippo signaling. We further elucidated that activated p38 signaling promoted F-actin accumulation, which subsequently suppressed the Hippo pathway. In addition, MKK3 (Licorne homolog) promoted YAP translocation to nuclear and activated transcription of its target genes, CTGF and Cyr61 in mammalian cells. Which indicated that regulation of the Hippo signaling pathway by Licorne is conserved in evolution.