CecC, a cecropin gene expressed during metamorphosis in Drosophila pupae

Abstract

Cecropins are antibacterial peptides, induced in insects in response to bacterial infections. In Drosophila, three cecropin genes have previously been characterized, CecA1, CecA2, and CecB, in a dense cluster at 99E on the third chromosome. From the same locus, we now describe a fourth member of the cecropin gene family, CecC, which is mainly expressed at the early pupal stage. In situ hybridization to immunized pupae show that CecC is induced in the anterior end of the larval hindgut and in other larval tissues that are undergoing histolysis. Within these other tissues it is often expressed in distinct foci that may correspond to hemocytes. A similar pattern of expression in the metamorphosing pupa is also observed for the CecA and CecB genes. Comparing the DNA sequences of the cecropin genes, a conserved region is observed about 30 bp upstream of the TATA box. It consists of three shorter motifs, two of which are reminiscent of a putative promoter element in immune protein genes from the cecropia moth.

The humoral antibacterial response of Drosophila

“…Studies performed on the expression profiles of the genes encoding cecropins [19,20,23], diptericin [21], defensin [25] and drosocin [24] in bacteria-challenged Drosophila yielded results similar to those obtained in other species of the recent insect orders (namely in Hvalophora cecropia (reviewed in [15]), Munduca sexta [26], Sarcophuga peregrina [ 11,27-291, Phormia terranovae [30]). The genes are rapidly transcribed following challenge (1 to 2 h), the transcription rate increases over a period varying between 6 and 24 h, depending on the gene, and thereafter either stops or levels off.…”

“…Not all the genes are transcribed with the same intensity during the response; the induction of the drosocin gene for instance is considerably stronger than that of defensin in larvae and adults of Drosophila [24,25]. Some of the genes are preferentially transcribed in challenged pupae: this is the case for the cecropin B and C genes, for instance, whose induced transcriptional rate is negligible in larvae and adults when compared to that of the cecropin A, and A, genes [23]. Interestingly, the expression of some of these genes can occur in the absence of an apparent immune challenge: the defensin gene for instance is expressed in normal early pupae [25] (cf.…”

“…In association with Hultmark's group, we isolated in 1990 [19,20,23] and diptericin [21] were deduced from DNA cloning studies; cecropin A was directly isolated from immune adults of Drosophila in our laboratory and the deduced sequence [19] was confirmed by Edman degradation and molecular mass determination (m/z = 4155.2). Bold residues differ among the three expressed cecropins [19,20,23]. We suspect diptericin to be post translationally modified by 0-glycosylation, as demonstrated in the case of diptericin from the fleshfly Phormia terranovae (unpublished).…”

“…We used an oligonucleotide probe corresponding to the peptide sequence of the newly-isolated diptericin from the fleshfly Phormia terranovae [22]. A fourth cecropin gene (C), encoding a peptide which differs from cecropin A by three conservative amino-acid replacements, was later described [23]. In essence, these studies established that Drosophila expresses, in response to bacterial challenge, genes encoding antibacterial peptides which are homologous to cecropins and diptericins, previously isolated from other insect species (Fig.…”

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

“…Interestingly, the most proximal of the regulatory region was shown to contain two motifs overlapping with the Rel sites, and similar in sequence to NF-IL6 response elements and a core motif recognized by interferon regulatory factor 1 (IRF-1). The cecropin A1 gene promoter, which has also been studied in detail, similarly contains conserved sequence motifs adjacent to the Rel site (Engstrom et al, 1993;Tryselius et al, 1992). Gel shift experiments and analysis of mutations in transient transfection assays have recently shown that one of these motifs, AGATAA, is functionally important; this motif is identical to the consensus sequence WGATAR, recognized in mammalian promoters by transcriptional activators of the GATA family (Kadalayil et al, 1997).…”