Insulin-like Growth Factor Promoted Cell Proliferation Of Imaginal Tissues In Helicoverpa Armigera

Research background and existing scientific questions:Insulin-like growth factors（IGFs）,members of insulin-like peptides（ILPs）superfamily,can promote tissue growth.There were many related studies in mammals,but few in insects,only in Drosophila melanogaster（D.melanogaster）and Bombyx mori（B.mori）.Tissue remodeling occurs in the development of holometamorphosis insects,which is that larval tissues are under degradation and imaginal tissues are under proliferation.The molecular mechanism behind these events has been the focus of entomologists.Studies had shown that IGFs were highly expressed in the fat bodies of B.mori and D.melanogaster during metamorphosis,but the function of IGFs in imaginal tissue formation is still unclear.Helicoverpa armigera（H.armigera）is a major agricultural pest,and its metamorphosis development is closely related to the population size and threat of its disaster damage.According to the aforementioned scientific questions,taking H.armigera as the experimental material,experiments were carried out to determine the function of IGFs in metamorphosis development.Research results:1.An IGF was identified in H.armigera by the bioinformatics method.By aligning with human IGF-I and IGF-II,it was named Insulin-like growth factor-2-like（IGF-2like）.The Igf-2-like was highly expressed in the fat body during metamorphosis.2.The expression of Igf-2-like was up-regulated by 20-hydroxyecdysone（20E）in vivo.3.The rabbit polyclonal antibody against IGF-2-like was obtained and the expression levels of IGF-2-like in the epidermis,midgut,fat body,brain and hemolymph of H.armigera were detected by Western blotting.It was found that IGF-2-like was highly expressed in the midgut and fat body during molting metamorphosis,and also expressed in the brain and epidermis,the expression was low in hemolymph without blood cells.4.Tissue immunofluorescence showed the localization of IGF-2-like in the midgut and fat body.It was found that IGF-2-like was localized in the midgut cells of imago at sixth instar 96 h（6th-96 h）and fat body cells of imago at sixth instar 120 h（6th-120 h）.5.Using feeding interference and dsRNA injection interference to knock down Igf-2like in larvae,it was found that both methods caused delayed pupation.6.Knockdown of Igf-2-like inhibited the expression of c-Myc,thereby inhibiting the growth of imaginal midgut and fat body,resulting in smaller body size and longer life span of adults.Conclusion and significanceThis study identified the IGF,IGF-2-like,of H.armigera,and proved that 20E upregulated the expression of Igf-2-like,making it highly expressed during molting metamorphosis;IGF-2-like was located in the imaginal midgut and fat body during molting metamorphosis;Downregulation of IGF-2-like expression will lead to the down-regulation of c-Myc expression,knocking down the expression of Igf-2-like would reduce the expression of c-Myc,delay the time of larval pupation,inhibit the growth of imaginal midgut and fat body proliferation,and make adults smaller in size and longer in life.This study provided theoretical knowledge for 20E to promote the development of imaginal tissues and organs,enriched the research on IGFs signaling pathway,and provided target genes for pest control.