Regulatory proteins and the regulation of immune response in Drosophila melanogaster

Abstract: Insect antibacterial peptides are regulated at the transcriptional level. The otherwise silent antibacterial Cecropin genes are strongly induced upon bacterial challenge. We have demonstrated that an intact conserved upstream region, including an insect kB-motif, is necessary for tissue-specific expression of Cecropin in fat body and hemocytes of Drosophila melanogaster. Transfection studies in a hemocyte cell line indicate positively acting elements upstream of the conserved region. Our in vivo data suggest the activity of a negatively acting upstream element. We were able to quantify the expression of a reporter gene in transgenic animals.The conserved insect kB-motif is bound by Drosophila Rel-proteins. We have demonstrated that Dif is bound to Cactus, an inhibitory factor of the IkB-family, in a hemocyte line. Immune challenge results in nuclear translocation of a truncated form of Dif and of one form of Cactus. We have demonstrated the co-localization of Dif and Cactus in the CNS of Drosophila larvae. Dif and Cactus are expressed at high levels in the mushroom bodies and in small subsets of neurosecretory cells. The cytoplasmic localization of Dif and Cactus in the CNS was not affected by bacterial challenge. Cactus displayed changes in localization along the dark-light cycle.Our experiments demonstrated that immunocompetence has developed by stage 16 in Drosophila embryos. Upon bacterial challenge subgroups of cells the epidermis were induced to express Cecropin. In the larval stages abrasion induces epidermal expression while bacterial injection into the hemocoel results in expression in the fat body. A conserved upstream region is necessary for tissue-specific expression in first and second instar larvae and embryos.