Functional Research Of FoxO Gene In Insect Molt In Helicoverpa Armigera

Background and SignificanceInsects are the largest group with a greatest population. So they have a huge impact on humans. Now we investigate insects not only for the pest control or insect utilization, but also to explore the mechanism. To accomplish life cycles, insects need to go through sevel molting. The insect cuticle was closely interrelated to survival in the evolutionary process. The tissue was covered by cuticle consist of chitin, protein and lipid. The cuticle protect insect from dehydration and predators, and made the motion possible. The old cuticle had to digest and absorb to form new cuticle without cuticular malleability. Few molting was necessary:the molting in larva, the molting to pupal and the molting to adult.The molting was a complicated physiological process, protease functioned great. Carboxypeptidase and aminopeptidase degraded pepitede from carbonyl end and amino-terminal respectively. The molting is regulated by20-hydroxyecdysone (20E) and juvenile hormone (JH).20E initiates molting and JH determines the nature of molt. Receptor EcR/USP is activated by20E to pass signals to downstream effctor genes. JH signal pathway was considered to function by antagoning with20E signal pathway.It was reported that insulin signal pathway coordinately regulate insect development with20E signal pathway. Insulin adjusted the growth rate,20E decided the duration time of growth. These two key factors determined the critical weight. In Drosophila melanogaster, mutant of insulin-like pipitede led to grow delay, it suggests the necessary of insulin (Broughton, Piper et al.2005). FoxO (Forkhead O) was an important target protein of insulin. Under rich nutrient or insulin growth factor, FoxO was phosphorylated to stay in cytoplasm, when in lack of insulin, FoxO was activated and translocated to nucleus, bind to response element and regulate gene transcription(Tower2011). Fed of20E could release the inhibiton of FoxO from insulin. FoxO could bind to at least700promoters, involved in a vatiety of physiological processe like growth, celular differentiation, cell cycle, tumor suppression, apoptosis and metabolism (Alic, Andrews et al.2011). FoxO regulated a series of gene expression to suppress cancer, degration of FoxO would result in the cancer cells proliferation and survival (Huang and Tindall2011). Over-expression of FoxO up-regulated dilp6(insulin-like peptide6) mRNA level in fat body, so to extend the life of D. melanogaster (Bai, Kang et al.2012). In innate imunity, FoxO could up-regulate dPrxV (PeroxiredoxinV) expression so to play against intestinal infection (Ahn, Lee et al.2012).Our experiments showed that FoxO was highly expressed in molt and metamorphosis stage.20E up regulated its expression level. Abnormal molt occurred after FoxO was knockdown. Further experiment showed that FoxO raised CPA expression, so as to old cuticle deration. Our findings enriched FoxO functional research, and perfect mystery of insect molt mechanism. For highly conservation of arthropod cutile, study in H.armigera could guide molting behavior of other species. Methods and Acquired ResultsBy using Laboratory established epidermal (HaEpi) cell line and in larvae experimental platform, in conjunction with technologies such as molecular biology and cell biology, we proved thar FoxO played an important role in insect molt.FoxO affected insect molt through activation of CPA expression. FoxO was highly expressed in molting stages.20E could upregulate the expression of FoxO, and FoxO translocated to nucleus at6h in HaEpi cell line. RNAi of FoxO led to abnormal molting (the rate of abnormity was62%), this indicated that FoxO was necessaty for insect molt. When FoxO was knockdown, Br-Z2and CPA was downregulated. These results suggest that FoxO affected insect molt through activation of CPA expression.