The Low Content Of 20-hydroxyecdysone In Wing Disk Determines Differential Gene Expression And Wing Development In Helicoverpa Armigera

Research background and scientific questionsInsects are the most numerous and diverse metazoan group in nature and are closely related to human life.Therefore,the study of insect growth and development can provide knowledge for human to use beneficial insects and control pests.Insect wings act a pivotal part in insect migration,feeding and reproduction.The development of insect wings involves cell proliferation and hormone regulation.Therefore,it is of great theoretical and practical significance to study the development of insect wings.The development of the insects are mainly regulated by three kinds of hormones,including insulin and insulin-like peptide(ILPs),juvenile hormone(JH)and 20-hydroxyecdysone(20E).ILPs plays an important role in promoting the growth of tissue cells and the metabolism of nutrients.Human insulin-like peptide relaxin takes an active part in angiogenesis,anti-apoptosis and anti-inflammation.JH maintains the larval state.20E promotes the apoptosis of larval tissues and the formation of adult tissues,which plays a major role in insect metamorphosis and development.The wings of adult are rapidly proliferated and grown from the wing disk of the larval in the metamorphosis stage.It has been reported that 20E promotes the proliferation of the wing disk,and ILPs plays a role in the development of the wing.However,at the same time the midgut of the larvae is undergoing apoptosis.The molecular mechanism of the two tissues undergoing the opposite cellular process in hemolymph with the same 20E titer is unknown.Research resultsTaking H.armigera as the experimental subject and using the laboratory research platform of cell and insect body,this paper explored the reason why the developmental fate of wing disk is different from that of midgut in the metamorphosis period by using the methods of biochemistry and molecular biology.This research studied the regulation mechanism of 20E on wing disk growth,the function of a relaxin-like insulin-like peptide Ilp6 in H.armigera,whose kinship is close to the relaxin of Homo sapiens,in the wing disk development and obtained the following results:apoptosis related genes were highly expressed in the midgut and poorly expressed in the wing disk,on the contrary,the cell proliferation related genes were highly expressed in the wing disk,but they were poorly expressed in the midgut,maybe it is the reason why the fates of the two tissues in the metamorphosis were different;Insulin receptor and 20E nuclear receptor were not significantly differentially expressed in the midgut and the wing disk,but the 20E cell membrane receptor GPCR was highly expressed in the midgut and poorly expressed in the wing disk,indicating that the membrane signaling pathway of 20E played an important role in the different fates of the two tissues.Injection of human recombinant insulin had no promoting effect on the growth of the wing disk,while injection of 20E had a significant promoting effect on the growth of the wing disk,indicating that 20E is a hormone promoting the growth of the wing disk.However,the promoting effect of 20E on the growth of wing disk depends on a certain concentration.There was an upper limit of the amount of 20E from hemolymph into the midgut and the wing disk,but the content of 20E in the wing disk was lower than that in the midgut,which may be the reason for the genes differential expressions in the two tissues that were regulated by 20E.Ilp6 was highly expressed in the fat body and the wing disk and the lockdown of Ilp6 through RNA interference caused abnormal wing development and delayed pupation,indicating that Ilp6 took an active part in the development process.Conclusion,innovative points and significances1.The expression of apoptotic and proliferation related genes makes the development fate of the wing disk is different from the midgut during metamorphosis.2.The intake of 20E in the wing disk was significantly lower than that in the midgut,and the low content of 20E in the wing disk promoted the growth of the wing disk.3.Ilp6 is highly expressed in the fat body and wing disk and is involved in the wing growth and metamorphosis.This paper explained the mechanism of the different developmental fates of the midgut and the wing disk under the regulation of 20E during metamorphosis,provided a reference for understanding the development of wing disk.