Research On Insect Metamorphosis From The Points Of Proteome And O-GlcNAcylation

Insects are a dominant terrestrial group on the Earth with wide distribution and tremendous amount,which originated from Ordovices of 480 million years ago.For the holometabolous insects,metamorphosis produce distinct morphology between larva and adult,which enhance their adaptability to environment,and attribute to the evolutionary success.The lives of holometabolous insects are segmented into characteristic number of instars by molts.Previous molts progress the larval from one instar to the next,while final molts switch the molting direction to metamorphosis.How insects initiate their metamorphosis is one of the most frequently stated problems in research about insect's physiology and development.Existing researches show that the metamorphosis of insects are coordinated by various hormones.20E(20-hydroxyecdysone)combines with EcR(Ecdysone Receptor)and USP(Ultraspiracle protein)to form a transcriptional complex and then induce the downstream gene transcription to initiate the molting process.JH(Juvenile hormone)determines the nature of molting.In the presence of JH,20E directs larval molting,while when larva acquires enough nutrients to survive metamorphosis and reach a "critical weight",circulating JH is removed.Then Br(Broad)come up at the time of pupal commitment in response to 20E and initiate metamorphosis through induce the transcription factors needed for pupal differentiation.These studies elaborate the basic framework of hormones regulating insect molting metamorphosis,but the details of the mechanism of action are not fully understood.What other molecules involve in the process of molting and metamorphosis still needs further identification.In addition,O-GlcNAcylation(O-linked N-acetylglucosamine)is a nutrient responsive post-translational modification.N-acetylglucosamine moieties are obtained from Hexosamine biosynthesis pathway.The dynamic cycling of this modification is controlled by a pair of enzymes,OGT(O-GlcNAc transferase)and OGA(O-GlcNAcase).O-GlcNAcylation participates in various physiological processes by modifying transcription factors,kinases,etc.More life processes in which O-GlcNAcylation was involved and the mechanisms underlying the temporal control of O-GlcNAc signaling need to be further explored.The nutrient state between feeding stage and metamorphosis of holometabolous insect are very different,which provide ideal model to make research on O-GlcNAcylation.In this study,we use Helicoverpa armigera,a holometabolous crop pest that belongs to Lepidoptera,the species with the greatest impacts on agriculture,as a model to identify more proteins involve in metamorphosis,and explore the mechanism of metamorphosis at the point of view of O-GlcNAcylation.The proteome of fifth and sixth instar larvae at feeding and molting stages are identified by liquid chromatography-mass spectrometry separately.Bioinformatics analysis was used to compare the DE(differentially expressed)proteins which involve in larval molting and metamorphic molting.The results show that the up-regulated proteins enrich in the amino sugar metabolism pathway both in larval molting and metamorphic molting.This may relate to the metabolism of chitin involve in the replacement of integument,and the HBP metabolism which provide GlcNAc group O-GlcNAcylation.In addition,the up-regulated proteins in the larval molting are also enrich in the lipid transport process,while the up-regulated proteins in the metamorphic molting stage mainly relate to protein catabolism and odorant binding.These DE proteins may be related to the determination of molting properties.In summary,this study further identifies DE proteins involved in molting and metamorphosis,and state that O-GlcNAc modification can inhibit the early occurrence of insect metamorphosis by inhibiting the 20E signaling pathway,which provides new insights into the molecular mechanism of insect metamorphosis and biological control of pests.