Iron depletion in the intestines ofMalvoliomutant flies does not occur in the absence of a multicopper oxidase

Abstract

SUMMARYMalvolio (Mvl) encodes the sole Drosophila melanogaster homologue of divalent metal transporter-1 (DMT1). The Drosophila transporter has been implicated in iron, manganese and copper cellular import. Indeed, the extent of metal specificity for this family of transporters is still under investigation in many eukaryotic species. Here, we revisit metal accumulation in Mvl mutants raised under normal and metal-supplemented diets. We found iron deficiency in Mvl mutant flies, whereas whole body copper and manganese concentrations remained unaltered. Iron supplementation restored total body iron concentrations in Mvl mutants, but without replenishing iron stores in the middle midgut, suggesting a role for Mvl in systemic iron trafficking, in addition to a role in intestinal iron absorption. Interestingly, dietary copper sulphate supplementation further exacerbated the iron deficiency. We investigated whether dietary copper affected iron storage through the function of an insect multicopper oxidase (MCO), because the mammalian MCO ceruloplasmin is known to regulate iron storage in the liver. We identified a Drosophila MCO mutant that suppressed aspects of the Mvl mutant phenotype and most notably Mvl, MCO3 double mutants showed normal intestinal iron storage. Therefore, MCO3 may encode an insect ferroxidase. Intriguingly, MCO3 mutants had a mild accumulation of copper, which was suppressed in Mvl mutants, revealing a reciprocal genetic interaction between the two genes. Supplementary material available online at

The Digestive Tract of Drosophila melanogaster

“…Copper export from the intestine to the hemolymph is mediated by the P-type ATPase dATP7, which is localized at the basal membrane (26). Iron uptake is, in part, mediated by the divalent transporter ion transporter 1 (DMT1) homolog Malvolio (11). In addition to their role in iron storage, ferritins also mediate iron export from the midgut to the hemolymph (107,181).…”

Multicopper oxidase-1 is a ferroxidase essential for iron homeostasis in Drosophila melanogaster

“…Divalent metal transporter 1 (DMT1) transports iron from the diet into midgut epithelial cells (8). Ferritin has two functions in insects: iron storage (comparable to the function of mammalian ferritin) and iron transport (9).…”

“…MCO2 orthologues are laccases that participate in pigmentation and sclerotization of newly synthesized cuticle (15). D. melanogaster MCO3, which has no known orthologues outside of Drosophilidae, is predicted to be a ferroxidase because it contains a putative iron-binding residue, and loss of function leads to an increase in iron accumulation in the midgut; however, evidence of ferroxidase activity and information about when and where DmMCO3 is expressed are not available (8). Because MCO2 orthologues are known to be laccases, and most other insect MCOs, including DmMCO3, are found in only a subset of insect species, we decided to focus on MCO1.…”

Conserved metallomics in two insect families evolving separately for a hundred million years

“…A similar result holds in the present study for 14 species of Tephritidae, suggesting a conservative selection mechanism has been in place in natural populations over a period of approximately 100 million years (Beverley and Wilson 1984; Wulbeck and Simpson 2000). An alternative explanation is that the fruit fly genomic mutations do not normally affect the metallome, however mutations affecting metal accumulation are known in laboratory strains of D. melanogaster (for example reducing iron, Bettedi et al 2011; reducing copper, Hua et al 2011; reducing zinc, Afshar et al 2013; reducing manganese, Freeman et al 2013), which in general are non-lethal and show little effect on fitness.…”

“…Mutations in the X-chromosome of D. melanogaster can cause dramatic changes in total body zinc accumulation (Afshar et al 2013) and mutations in an iron transporter (Bettedi et al 2011), or flies heterozygous for mutations in the iron storage protein ferritin (Gutierrez et al 2013), accumulate less iron in their bodies. Similarly, flies heterozygous for mutations in Syntaxin 5 accumulate less copper (Norgate et al 2010).…”