Drosophila melanogaster transferrin

Abstract

Drosophila melanogaster transferrin cDNA was cloned from an ovarian cDNA library by using a PCR fragment amplified by two primers designed from other dipteran transferrin sequences. The clone (2035 bp) encodes a protein of 641 amino acids containing a signal peptide of 29 amino acids. Like other insect transferrins, Drosophila transferrin appears to have a functional iron-binding site only in the N-terminal lobe. The C-terminal lobe lacks ironbinding residues found in other transferrins, and has large deletions which make it much smaller than functional C-terminal lobes in other transferrins. In-situ hybridization using a digoxigenin labeled transferrin cDNA probe revealed that the gene is located at position 17B1-2 on the X chromosome. Northern blot analysis showed that transferrin mRNA was present in the larval, pupal and adult stages, but was not detectable in the embryo. Iron supplementation of the diet resulted in lower levels of transferrin mRNA. When adult flies were inoculated with bacteria (Escherichia coli), transferrin mRNA synthesis was markedly increased relative to controls.Keywords: transferrin; Drosophila melanogaster; sequence; chromosome; expression; up-regulation; immunity.Iron is an essential nutrient required for nearly all living organisms. Ionic iron is also toxic by virtue of its ability to catalyze the formation of membrane-destroying free radicals. Ionic iron forms oxides that are insoluble at physiological pH. Thus, in order to absorb and transport iron, most organisms have acquired special cofactors and proteins that are capable of maintaining iron in a water soluble state.Iron metabolism has been studied extensively in vertebrates. In vertebrate serum, ferric ion is transported by transferrin, a single chain polypeptide (<80 kDa) consisting of two lobes with similar amino acid sequence, and each with a single ironbinding site [1,2]. Diferric transferrin is taken into cells by receptor-mediated endocytosis, iron is dissociated from transferrin in an acidic endosome, and is transferred to the cytoplasm. In cells, iron is incorporated into metalloproteins or stored in cytoplasm chelated with small molecules or within an iron storage protein, ferritin [3].As in vertebrates, both transferrin and ferritin are found in insects and the cDNAs for each from several insect species have been cloned. Insect transferrins have been reported from four insect species [4±7]. Whereas cockroach (Blaberus discoidalis) transferrin has two iron-binding sites and strongly resembles vertebrate serum transferrins [8], other insect transferrins from a moth (Manduca sexta), flesh fly (Sarcophaga peregrina) and mosquito (Aedes aegypti) have one iron-binding site only in the N-terminal lobe but not in the C-terminal lobe [4,6,7]. The properties of insect transferrins suggest that they may have different, possibly unique, functions in insects. Recently, we found that transferrin is up-regulated when mosquito cells in culture were challenged with heat-killed bacteria. This suggests a possible important role(s) of i...

Developmental and Organ-Specific Expression of Transferrin inDrosophila Melanogaster

“…Either it supplies iron necessary for ovogenesis and embryogenesis or it prevents the developing embryo from bacterial infection. The second hypothesis is consistent with the observed up-regulation of the transferrin messages following bacterial challenge (3). Furthermore, the transferrin gene of D. melanogaster (12) contains promotor region sequences known to bind nuclear-kappa B-like transcription factors involved in the insect immune response.…”

A proteomic approach for the analysis of instantly released wound and immune proteins in Drosophila melanogaster hemolymph

“…The presence of putative NF-Blike binding sites (37) is in agreement with our results and indicates that insect ferritins, like vertebrate serum ferritin, play a role in the immune response. So far, only the induction of transferrin genes had been demonstrated after infection (9,38).…”

The Genome Sequence of Drosophila melanogaster

“…Subunits of the www.sciencemag.org SCIENCE VOL 287 24 MARCH 2000 predominant secreted ferritins in insects are encoded by two highly expressed autosomal genes (62). Second, the dipteran transferrins studied so far appear to play antibiotic rather than iron-transport roles; one such transferrin was previously characterized in Drosophila (63). We have now identified two additional transferrins.…”