A Genetic Screen Identifies That Adck1 Is Involved In The Regulation Of Drosophila Innate Immunity

Background:Drosophila innate immunity is the most important defense system against invading microorganisms,which consists of humoral and cellular immune defenses.Humoral immune defense relies on fat body to synthesise and secrete antimicrobial peptides into the hemolymph to kill foreign pathogens,while cellular immune defense depends on phagocytosis and/or melanization to clear pathogens.Protein kinases are a family of enzymes which can phosphorylate proteins.Phosphorylation is an important post-translational modification mechanism,which is essential for many biological processes including cell differentiation,apotosis,cell renewal,immune responses.Aim:To identify new kinases that may regulate immune responses in Drosophila,we carried out a small-scale genetic screen.Method:The screen employs the Gal4/Gal80^ts/UAS system to knockdown 56 protein kinase-coding genes in adult stage,followed by infecting the flies with Gram-positive and Gram-negetive bacteria respectively,then examine the survial rate.Result:Based on the results of the primary and secondary screens,three candidate genes（Adck1,Doa,Pitslre）were found to be likely involved in Drosophila innate immune responses,among which Adck1 was chosen for further analyses in this thesis.Adck1 knockdown led to a decreased survival rate and a higher bacterial load as compared to the control flies after infection,indicating that Adck1 knockdown flies are more sensitive to bacteria infection,and the overgrown bacteria killed the host flies.Three mechanisms（phagocytosis,melanization and production of AMPs）have been reported to antagonize bacterial infections in Drosophila.Our results show that knockdown of Adck1had no effect on antimicrobial peptides production or phagocytosis,but led to the cleavage of PPO1,suggesting that Adck1 may be involved in the process of melanization.Conclusion:In summary,we performed an RNAi screen of 56 protein kinase-coding genes,and identified that Adck1 regulates Drosophila immunity by modulating the process of melanization.However,how Adck1 regulates melanization at the molecular level needs to be further studied.