Function Analysis Of Autophagy Related Protein Atg4B In Helicoverpa Armigera Development

Background and SignificanceInsect are found in almost every corner of the world and thus constitutes the largest number of animals in the world. Insect development including molting and metamorphosis and regulated by molting hormone (20-Hydroxyecdysone,20E) and juvenile hormone (JH). In the growth period, insect larvae maintain the low level of autophagy to adapt hungry. In insect metamorphosis period from larva to pupa, due to the rise of molting hormone, genetic regulation of programmed cell death (PCD) started, the low level of autophagy changed into a high level of autophagy and apoptosis, cause the larva tissue such as silkgland, midgut and fat body happened irreversible degradation. At present, reports of the relationship between autophagy and apoptosis are paradoxical, and some reports contradict each other, so we need to conduct the research. Insect midgut can be used as a good material research on relationship between autophagy and apoptosis because during metamorphosis period of the insect larvae to pupae, old larvae midgut tissue degradation dominated by autophagy and apoptosis. Autophagy related protein 4B (Atg4B) is one of autophagy core protein, known as a kind of cysteine protease, it can processeing pro-Atg8 to expose its C-terminal glycine for phosphatidyl ethanolamine (PE) lipidation on phagophore membranes. This thesis mainly studies on what kind of cell death happen in bollworm midgut degradation during metamorphosis. In theory, it can further reveal the molecular mechanism of autophagy in insect molting and metamorphosis, further on the application, it can provide target genes for pest control.Results and conclusionsBy using in vivo experiments on larvae of Helicoverpa armigera and in vitro experiments on H. armigera epidermal cell line (HaEpi), in conjunction with gene overexpression and gene knock down techniques, we have investigated Atg4B was highly expressed during molting and metamorphosis induced by 20E. RNA interference (RNAi) to knock down Atg4B expression delay the insect metamorphosis and the pupation time. Atg4B knockdown larvae will keep the larval structure during metamorphosis and no imaginal midgut was formed. HaEpi cells transfected with dsAtg4B loss the function of cleavage of Atg8-RFP at C-terminalfusion and the conversion of pro-Atg8 into Atg8-PE, block the formation of autophagosomes. This evidence suggests that Atg4B is critical to 20E promoted metamorphosis metamorphosis through larval midgut PCD.