CHARACTERIZATION AND TRANSCRIPTIONAL PROFILES OF A DROSOPHILA GENE ENCODING AN INSECT DEFENSIN - A STUDY IN INSECT IMMUNITY

Insect defensins are a family of 4-kDa, cationic, inducible antibacter ial peptides which bear six cysteine residues engaged in three intramo lecular disulfide bridges. They owe their name to certain sequence sim ilarities with defensins from mammalian neutrophiles and macrophages. We report the characterization of a novel defensin isoform from Drosop hila and the cloning of the gene encoding a preprodefensin. The gene, which is intronless and present in a single copy/haploid genome, maps at position 46CD on the right arm of the second chromosome. The analys is of the upstream region of the gene reveals the presence of multiple putative cis-regulatory sequences similar to mammalian regulatory mot ifs of acute-phase-response genes. Transcriptional profiles indicate t hat the Drosophila defensin gene is induced by bacterial challenge wit h acute-phase kinetics. It is also expressed in the absence of immune challenge during metamorphosis. These and other data on the Drosophila defensin gene lead us to suggest that insect and mammalian defensins have evolved independently.