Identification And Functional Analysis Of The SUV39 Subfamily Of Histone Methyltransferases And Translation Initiation Factor EIF2? In The Red Larvae

Histone H3 lysine 9 methylation(H3K9me)is an important epigenetic modification that plays an important role in regulating heterochromatin formation and euchromatin gene silencing.Members of the SUV39 family as histone lysine methyltransferases that catalyze H3K9 methylation and are widely present in all insects.Currently,studies on the SUV39 subfamily mainly focus on Drosophila melanogaster,but there are few reports on the function of SUV39 in other insects.As an important model organism,Tribolium castaneum is an important representative of Coleoptera,and also a world grain storage pest,which is widely used in insect research.Because of its high RNAi efficiency,so it is a good material for studying gene function.In this study,the members of the SUV39 family were identified,the catalytic activity of H3K9 methylation of the SUV39 family was analyzed,and the important functions of this subfamily members in the growth and development of Tribolium castaneum were explored.First of all,according to the homologous comparison,we identified SUV39 subfamily of T.castaneum contains four members,in addition to the consistent with other species of three conservative members of the Su(var)3-9,G9 a and Egg,also found a new member of the Set-23.Phylogenetic analysis showed that four members of the SUV39 subfamily had existed before the differentiation of vertebrates and invertebrates.There were two copies of Tc Su(var)3-9,Tc G9 a and TcEgg in vertebrates,but only one copy in insects,which may be to adapt to the complex gene expression regulation in vertebrates.Catalytic analysis of H3K9 methylation activity of SUV39 family gene of T.castaneum showed that Tc Su(var)3-9 was responsible for H3K9mono-,di-and tri-methylation.Tc G9 a is responsible for mono-and di-methylation;TcEgg is responsible for di-and tri-methylation.However,Tc Set-23 lost the catalytic activity of H3K9 methylation.Then,we explored the biological functions of the four members mentioned above in T.castaneum.Interestingly,in the functional analysis of Su(var)3-9,we found that Su(var)3-9 and translation initiation factor e IF2? fused into a dicistronic transcription.Phylogenetic analysis of this element showed that Su(var)3-9/e IF2?gene fusion occurred in the common ancestor of winged insects and silverfish,and the dicistronic element is found only in insects.Further functional studies showed that Tc Su(var)3-9 and Tce IF2? had different functions,respectively.Tc Su(var)3-9 plays an important role in the regulation of the embryos development of T.castaneum,and the development of RNAi embryos stagnated and died in the anaphase of appendage formation.However,after Tce IF2? RNAi,the ecdysis and eclosion of the T.castaneum could not be achieved,and all died.Further mechanism analysis showed that Tce IF2?played an important role in the metamorphosis process of T.castaneum by regulating the synthesis of ecdysis hormone.Finally,functional analysis of TcEgg showed that the female was unable to lay eggs normally after TcEgg RNAi.The results of genital anatomy showed that the knockdown of this gene resulted in defects in the oogenesis process of the female.Further mechanism analysis revealed that TcEgg affected the maintenance and differentiation of Germ stem cells by regulating apoptosis related genes and BMP signaling pathways and is involved in the oogenesis of T.castaneum.Functional analysis of Tc G9 a showed that the development of RNAi embryos stagnated and died in the anaphase of appendage formation,suggesting that Tc G9 a played an important regulatory role in the embryo development of T.castaneum.After Tc Set-23 RNAi,there was no significant effect on the growth and development of T.castaneum.In this study,we explored the important role of SUV39 subfamily in the growth and development of T.castaneum,and provided a new basis for the research on the function of SUV39 subfamily in invertebrates.The regulatory functions of histone methylation in insects and the functions of dicistronic transcription Su(var)3-9/e IF2?were further revealed,it providing a new perspective on the relationship between ecdysis hormone synthesis and translation in insects.