Identification And Analysis Of BHLH Transcription Factor Family Members In Monarch Butterfly,Danaus Plexippus

Basic helix-loop-helix(bHLH)transcription factors are widely distributed in animals,plants and fungi,which form a large transcription factor superfamily.The bHLH transcription factors play important roles in regulating the growth and development of organisms.Animal bHLH transcription factors can be divided into 45 families according to their functional features.Meanwhile,these 45 families are divided into six high-order groups,i.e.groups A,B,C,D,E and F,according to their target DNA elements to bind and their own structural characters.Group A-F has 22,12,7,1,2,and 1 families,respectively.Monarch butterfly(Danaus plexippus)is a model species of Papilio genus in Lepidoptera,which is the only migratory butterfly on the earth.Therefore,it is of great significance and value to study monarch butterfly's gene expression patterns.Analysis and identification of bHLH family members in monarch butterfly are beneficial for further studying their migratory behaviors,circadian rhythm responses and other biological processes.In this paper,a series of bioinformatics methods were employed to identify and classify the bHLH transcription factors of monarch butterfly,including Blast searches,multi-sequence alignment and phylogenetic analysis.Moreover,these bHLH members were compared and analyzed with those of other insects.The obtained results are as follows:1.A total of 55 bHLH family members were found in monarch butterfly genome,which can be classified into 40 bHLH families and 6 high-order groups.Group A-F has 22,12,7,1,2,and 1 members,respectively.By analyzing the special domains of monarch butterfly bHLH proteins,it was found that they own the common animal bHLH protein domains in each group.2.Among these identified 55 bHLH family members,49 members have corresponding protein sequences in Gen Bank protein database.Among them,annotations of 24 proteins are consistent with our classifications,those of 8 proteins are inconsistent with our classifications,and the rest 17 are hypothetical proteins.Therefore,our study provided useful information for revising 25 annotations and adding 6 new bHLH proteins for monarch butterfly.3.Monarch butterfly has 2 members in E12/E47,MyoD,Twist and Hand families,respectively,while other insects generally have only one member.Monarch butterfly has 3 members in AHR family,while other insects generally have 2 members.The above five bHLH family members are involved in regulating development of muscle,heart and trachea,which means monarch butterfly may have evolved special developmental regulation mechanisms so as to adapt to long-distance migration.4.We also investigated intron distributions in coding regions of b HLH motifs in 14 insect species.The general features of intron distributions in coding regions of insect bHLH motifs were found as follows: Group B shares certain intron structures with groups A,C,E and F,indicating that group A,C,E and F bHLH motifs have inherited the intron structure of group B at various degrees;Only group A bHLH motifs have introns in helix 1 region that are most possibly inserted by insects for creating new bHLH genes.The above results not only provide a good basis for further studies on the regulation mechanisms of bHLH transcription factors in monarch butterfly's growth and development,but also accumulate useful information for comparing insect bHLH gene structures and functions,and for studying the evolution mechanism of insect bHLH genes.