Gene Expression Divergence and Evolutionary Analysis of the Drosomycin Gene Family inDrosophila melanogaster
Drosomycin(Drs) encoding an inducible 44-residue antifungal peptide is clustered with six additional genes,Dro1, Dro2, Dro3, Dro4, Dro5,andDro6, forming a multigene family on the 3L chromosome arm inDrosophila melanogaster. To get further insight into the regulation of each member of the drosomycin gene family, here we investigated gene expression patterns of this family by either microbe-free injury or microbial challenges using real time RT-PCR. The results indicated that among the sevendrosomycingenes,Drs, Dro2, Dro3, Dro4,andDro5showed constitutive expressions. Three out of five,Dro2, Dro3,andDro5, were able to be upregulated by simple injury. Interestingly,Drsis an only gene strongly upregulated whenDrosophilawas infected with microbes. In contrast to these five genes,Dro1andDro6were not transcribed at all in either noninfected or infected flies. Furthermore, by5′rapid amplification of cDNA ends, two transcription start sites were identified inDrsandDro2, and one inDro3, Dro4,andDro5. In addition, NF-κB binding sites were found in promoter regions ofDrs, Dro2, Dro3,andDro5, indicating the importance of NF-κB binding sites for the inducibility ofdrosomycingenes. Based on the analyses of flanking sequences of each gene inD. melanogasterand phylogenetic relationship ofdrosomycinsinD. melanogasterspecies-group, we concluded that gene duplications were involved in the formation of the drosomycin gene family. The possible evolutionary fates ofdrosomycingenes were discussed according to the combining analysis of gene expression pattern, gene structure, and functional divergence of these genes.