Characterization and transcriptional profiles of a Drosophila gene encoding an insect defensin

Abstract

Insect defensins are a family of 4‐kDa, cationic, inducible antibacterial peptides which bear six cysteine residues engaged in three intramolecular disulfide bridges. They owe their name to certain sequence similarities with defensins from mammalian neutrophiles and macrophages. We report the characterization of a novel defensin isoform from Drosophila 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 analysis of the upstream region of the gene reveals the presence of multiple putative cis‐regulatory sequences similar to mammalian regulatory motifs of acute‐phase‐response genes. Transcriptional profiles indicate that the Drosophila defensin gene is induced by bacterial challenge with 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.

Genomic organization of the KTX2 gene, encoding a ‘short’ scorpion toxin active on K+ channels

“…The upstream sequences of the KTX 2 gene were compared to those of the Drosophila defensin gene: the upstream sequences of the Drosophila defensin gene have no CAAT box, and possess sequence motifs homologous to response elements for transcription factors of the promoters of genes encoding acute-phase proteins in mammals [15]. They both exhibit an Oct-1 site.…”

“…from top to bottom, the a-toxin AaH I' from the Tunisian Androctonus australis [19]; the ß-toxin y from the Brazilian scorpion Tityus serrulatus [20]; cDNA of toxins active on the voltage-dependent K + channel, i.e. KTX2 [4]; gene of the defensin from the fly Drosophila megalogaster [15]. high A+T content Comparison of sequenced scorpion toxin genes: genes of toxins active on voltage-dependent Na + channels, i.e.…”

Two distinct pathways can control expression of the gene encoding the Drosophila antimicrobial peptide metchnikowin

“…between positions À40 and À200 (Charlet et al, 1996;Dimarcq et al, 1994;Engstrom et al, 1993). Our analysis also revealed other consensus nucleotide sequence motifs in the metchnikowin promoter, corresponding to mammalian NF-IL6 response elements (Hocke et al, 1992), GATA sites (Orkin, 1992), and interferon consensus response elements (Figure 4(c)).…”

“…Recent studies indicate that in Drosophila at least seven distinct peptides, and their isoforms, participate in the humoral immune response. Five of these peptides, cecropins , diptericin (Wicker et al, 1990), drosocin , attacin (Asling et al, 1995) and insect defensin (Dimarcq et al, 1994), are selectively active against bacteria, whereas drosomycin, is solely active against fungi (Fehlbaum et al, 1994). The seventh and most recently discovered molecule, metchnikowin, is unique among the antimicrobial peptides of Drosophila in that it is active against both bacteria and fungi (Levashina et al, 1995).…”

Structure and Expression Analysis of theCecropin-EGene from the Silkworm,Bombyx mori

“…Cecropins are induced rapidly after infection with gram-negative and gram-positive bacteria and fungi. 12,13) The expression pattern of the Cecropin genes in silkworm is not identical across different types of microbial infection, 9,10) suggesting that different signaling pathways regulate immune gene expression in a distinct manner. Identification and analysis of additional silkworm Cecropins that are differentially expressed after immune challenge should help us to understand the regulatory mechanisms of insect immune responses.…”