Zinc accumulation in heterozygous mutants of fumble, the pantothenate kinase homologue of Drosophila

Aedes aegypti dyspepsia encodes a novel member of the SLC16 family of transporters and is critical for reproductive fitness

As a key vector for major arthropod-borne viruses (arboviruses) such as dengue, Zika and chikungunya, control of Aedes aegypti represents a major challenge in public health. Bloodmeal acquisition is necessary for the reproduction of vector mosquitoes and pathogen transmission. Blood contains potentially toxic amounts of iron while it provides nutrients for mosquito offspring; disruption of iron homeostasis in the mosquito may therefore lead to novel control strategies. We previously described a potential iron exporter in Ae. aegypti after a targeted functional screen of ZIP (zinc-regulated transporter/Iron-regulated transporter-like) and ZnT (zinc transporter) family genes. In this study, we performed an RNAseq-based screen in an Ae. aegypti cell line cultured under iron-deficient and iron-excess conditions. A subset of differentially expressed genes were analyzed via a cytosolic iron-sensitive dual-luciferase reporter assay with several gene candidates potentially involved in iron transport. In vivo gene silencing resulted in significant reduction of fecundity (egg number) and fertility (hatch rate) for one gene, termed dyspepsia. Silencing of dyspepsia reduced the induction of ferritin expression in the midgut and also resulted in delayed/impaired excretion and digestion. Further characterization of this gene, including a more direct confirmation of its substrate (iron or otherwise), could inform vector control strategies as well as to contribute to the field of metal biology.

Oxidative stress caused by lead (Pb) induces iron deficiency in Drosophila melanogaster

Toxic elements exposure disturbs the homeostasis of essential elements in organisms, but the mechanism remains elusive. In this study, we demonstrated that Drosophila melanogaster exposed to Lead (Pb, a pervasive environmental threat to human health) exhibited various health defects, including retarded development, decreased survival rate, impaired mobility and reduced egg production. These phenotypes could be significantly modulated by either intervention of dietary iron levels or altering expression of genes involved in iron metabolism. Further study revealed that Pb exposure leads to systemic iron deficiency. Strikingly, reactive oxygen species (ROS) clearance significantly increased iron uptake by restoring the expression of iron metabolism genes in the midgut and subsequently attenuated Pb toxicity. This study highlights the role of ROS in Pb induced iron dyshomeostasis and provides unique insights into understanding the mechanism of Pb toxicity and suggests ideal ways to attenuate Pb toxicity by iron supplementation therapy or ROS clearance.

Intestinal response to dietary manganese depletion inDrosophila

Metabolic adaptations to manganese deficiency.

Anatomy and Physiology of the Digestive Tract of Drosophila melanogaster

The gastrointestinal tract has recently come to the forefront of multiple research fields. It is now recognized as a major source of signals modulating food intake, insulin secretion and energy balance. It is also a key player in immunity and, through its interaction with microbiota, can shape our physiology and behavior in complex and sometimes unexpected ways. The insect intestine had remained, by comparison, relatively unexplored until the identification of adult somatic stem cells in the Drosophila intestine over a decade ago. Since then, a growing scientific community has exploited the genetic amenability of this insect organ in powerful and creative ways. By doing so, we have shed light on a broad range of biological questions revolving around stem cells and their niches, interorgan signaling and immunity. Despite their relatively recent discovery, some of the mechanisms active in the intestine of flies have already been shown to be more widely applicable to other gastrointestinal systems, and may therefore become relevant in the context of human pathologies such as gastrointestinal cancers, aging, or obesity. This review summarizes our current knowledge of both the formation and function of the Drosophila melanogaster digestive tract, with a major focus on its main digestive/absorptive portion: the strikingly adaptable adult midgut.

Biogenesis of zinc storage granules in Drosophila melanogaster

Membrane transporters and sequestration mechanisms concentrate metal ions differentially into discrete subcellular microenvironments for use in protein cofactors, signalling, storage or excretion. Here we identify zinc storage granules as the insect's major zinc reservoir in principal Malpighian tubule epithelial cells of Drosophila melanogaster The concerted action of Adaptor Protein-3, Rab32, HOPS and BLOC complexes as well as of the white-scarlet (ABCG2-like) and ZnT35C (ZnT2/ZnT3/ZnT8-like) transporters is required for zinc storage granule biogenesis. Due to lysosome-related organelle defects caused by mutations in the homologous human genes, patients with Hermansky-Pudlak syndrome may lack zinc granules in beta pancreatic cells, intestinal paneth cells and presynaptic vesicles of hippocampal mossy fibers.

Copper and Zinc Homeostasis: Lessons from Drosophila melanogaster

Maintenance of metal homeostasis is crucial for many different enzymatic activities and in turn for cell function and survival. In addition, cells display detoxification and protective mechanisms against toxic accumulation of metals. Perturbation of any of these processes normally leads to cellular dysfunction and finally to cell death. In the last years, loss of metal regulation has been described as a common pathological feature in many human neurodegenerative diseases. However, in most cases, it is still a matter of debate whether such dyshomeostasis is a primary or a secondary downstream defect. In this review, we will summarize and critically evaluate the contribution of Drosophila to model human diseases that involve altered metabolism of metals or in which metal dyshomeostasis influence their pathobiology. As a prerequisite to use Drosophila as a model, we will recapitulate and describe the main features of core genes involved in copper and zinc metabolism that are conserved between mammals and flies. Drosophila presents some unique strengths to be at the forefront of neurobiological studies. The number of genetic tools, the possibility to easily test genetic interactions in vivo and the feasibility to perform unbiased genetic and pharmacological screens are some of the most prominent advantages of the fruitfly. In this work, we will pay special attention to the most important results reported in fly models to unveil the role of copper and zinc in cellular degeneration and their influence in the development and progression of human neurodegenerative pathologies such as Parkinson's disease, Alzheimer's disease, Huntington's disease, Friedreich's Ataxia or Menkes, and Wilson's diseases. Finally, we show how these studies performed in the fly have allowed to give further insight into the influence of copper and zinc in the molecular and cellular causes and consequences underlying these diseases as well as the discovery of new therapeutic strategies, which had not yet been described in other model systems.

What can flies tell us about zinc homeostasis?

Zinc is an essential micronutrient for all organisms. For multicellular organisms, zinc uptake, storage, distribution and export are tightly regulated at both cellular and organismal levels, to cope with the multiple requirements versus the toxicity of the metal ion. During the past decade, the fruit fly Drosophila melanogaster has become an important model organism for the elucidation of metazoan zinc homeostasis. This review describes our current knowledge of various zinc transporters in Drosophila, with an emphasis on the process of dietary zinc uptake in the fly. We also discuss how Drosophila was used as a model to facilitate our understanding of the role of zinc in neurodegenerative diseases.

Ferritin Assembly in Enterocytes of Drosophila melanogaster

Ferritins are protein nanocages that accumulate inside their cavity thousands of oxidized iron atoms bound to oxygen and phosphates. Both characteristic types of eukaryotic ferritin subunits are present in secreted ferritins from insects, but here dimers between Ferritin 1 Heavy Chain Homolog (Fer1HCH) and Ferritin 2 Light Chain Homolog (Fer2LCH) are further stabilized by disulfide-bridge in the 24-subunit complex. We addressed ferritin assembly and iron loading in vivo using novel transgenic strains of Drosophila melanogaster. We concentrated on the intestine, where the ferritin induction process can be controlled experimentally by dietary iron manipulation. We showed that the expression pattern of Fer2LCH-Gal4 lines recapitulated iron-dependent endogenous expression of the ferritin subunits and used these lines to drive expression from UAS-mCherry-Fer2LCH transgenes. We found that the Gal4-mediated induction of mCherry-Fer2LCH subunits was too slow to effectively introduce them into newly formed ferritin complexes. Endogenous Fer2LCH and Fer1HCH assembled and stored excess dietary iron, instead. In contrast, when flies were genetically manipulated to co-express Fer2LCH and mCherry-Fer2LCH simultaneously, both subunits were incorporated with Fer1HCH in iron-loaded ferritin complexes. Our study provides fresh evidence that, in insects, ferritin assembly and iron loading in vivo are tightly regulated.

Ferritin Is Required in Multiple Tissues during Drosophila melanogaster Development

In Drosophila melanogaster, iron is stored in the cellular endomembrane system inside a protein cage formed by 24 ferritin subunits of two types (Fer1HCH and Fer2LCH) in a 1:1 stoichiometry. In larvae, ferritin accumulates in the midgut, hemolymph, garland, pericardial cells and in the nervous system. Here we present analyses of embryonic phenotypes for mutations in Fer1HCH, Fer2LCH and in both genes simultaneously. Mutations in either gene or deletion of both genes results in a similar set of cuticular embryonic phenotypes, ranging from non-deposition of cuticle to defects associated with germ band retraction, dorsal closure and head involution. A fraction of ferritin mutants have embryonic nervous systems with ventral nerve cord disruptions, misguided axonal projections and brain malformations. Ferritin mutants die with ectopic apoptotic events. Furthermore, we show that ferritin maternal contribution, which varies reflecting the mother's iron stores, is used in early development. We also evaluated phenotypes arising from the blockage of COPII transport from the endoplasmic reticulum to the Golgi apparatus, feeding the secretory pathway, plus analysis of ectopically expressed and fluorescently marked Fer1HCH and Fer2LCH. Overall, our results are consistent with insect ferritin combining three functions: iron storage, intercellular iron transport, and protection from iron-induced oxidative stress. These functions are required in multiple tissues during Drosophila embryonic development.

Elemental mapping of the entire intact Drosophila gastrointestinal tract

The main role of the animal gastrointestinal (GI) tract is the selective absorption of dietary nutrients from ingested food sources. One class of vital micronutrients are the essential biometals such as copper, zinc and iron, which participate in a plethora of biological process, acting as enzymatic or structural co-factors for numerous proteins and also as important cellular signalling molecules. To help elucidate the mechanisms by which biometals are absorbed from the diet, we mapped elemental distribution in entire, intact Drosophila larval GI tracts using synchrotron X-ray fluorescence microscopy. Our results revealed distinct regions of the GI tract enriched for specific metals. Copper was found to be concentrated in the copper cell region but also in the region directly anterior to the copper cells and unexpectedly, in the middle midgut/iron cell region as well. Iron was observed exclusively in the iron cell region, confirming previous work with iron-specific histological stains. Zinc was observed throughout the GI tract with an increased accumulation in the posterior midgut region, while manganese was seen to co-localize with calcium specifically in clusters in the distal Malpighian tubules. This work simultaneously reveals distribution of a number of biologically important elements in entire, intact GI tracts. These distributions revealed not only a previously undescribed Ca/Mn co-localization, but also the unexpected presence of additional Cu accumulations in the iron cell region.

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

Μetal cofactors are required for enzymatic catalysis and structural stability of many proteins. Physiological metal requirements underpin the evolution of cellular and systemic regulatory mechanisms for metal uptake, storage and excretion. Considering the role of metal biology in animal evolution, this paper asks whether metal content is conserved between different fruit flies. A similar metal homeostasis was previously observed in Drosophilidae flies cultivated on the same larval medium. Each species accumulated in the order of 200 µg iron and zinc and approximately ten-fold less manganese and copper per gram dry weight of the adult insect. In this paper, data on the metal content in fourteen species of Tephritidae, which are major agricultural pests worldwide, are presented. These fruit flies can be polyphagous (e.g., Ceratitis capitata) or strictly monophagous (e.g., Bactrocera oleae) or oligophagous (e.g., Anastrepha grandis) and were maintained in the laboratory on five distinct diets based on olive oil, carrot, wheat bran, zucchini and molasses, respectively. The data indicate that overall metal content and distribution between the Tephritidae and Drosophilidae species was similar. Reduced metal concentration was observed in B. oleae. Feeding the polyphagous C. capitata with the diet of B. oleae resulted in a significant quantitative reduction of all metals. Thus, dietary components affect metal content in some Tephritidae. Nevertheless, although the evidence suggests some fruit fly species evolved preferences in the use or storage of particular metals, no metal concentration varied in order of magnitude between these two families of Diptera that evolved independently for over 100 million years.

Involvement of superoxide dismutase in oxidative stress in the oriental fruit fly, Bactrocera dorsalis: molecular cloning and expression profiles

BACKGROUND

Bactrocera dorsalis, one of the most economically important fruit fly pests in East Asia, is well adapted to various environmental conditions. Pesticides, pathogens and other stresses can cause oxidative damage in most organisms. The superoxide dismutase (SOD) family contains some of the most important enzymes in the antioxidant protection system of the fruit fly and other organisms.

RESULTS

Four full-length cDNA sequences encoding one MnSOD (BdSOD2-1) and three Cu-ZnSODs (BdSOD1-1, BdSOD1-2 and BdSOD1-3) were cloned. The expression profiles of these four genes under different stresses showed them to be involved in response to detrimental conditions including heavy metals, pesticides, extreme temperatures and lipopolysaccharide (LPS) stresses. More specifically, the expression levels of these genes were found to be depressed in the presence of copper, zinc and manganese. The expression of all four SOD genes increased upon exposure to lead, cadmium, low temperature (0 °C) and LPS stresses. Only BdSOD1-3 transcription increased significantly at high temperature (40 °C) exposure. The expressions levels of BdSOD1-2 and BdSOD1-3 increased significantly in the presence of β-cypermethrin and malathion, but only the expression of BdSOD2-1 increased in the presence of avermectin treatment.

CONCLUSION

These different expression profiles suggest that the four BdSODs play different roles and respond to different oxidative stresses in B. dorsalis. Some BdSODs undergo specific reaction in the response to specific oxidative stresses.

Genome-wide association study identifies loci affecting blood copper, selenium and zinc

Genetic variation affecting absorption, distribution or excretion of essential trace elements may lead to health effects related to sub-clinical deficiency. We have tested for allelic effects of single-nucleotide polymorphisms (SNPs) on blood copper, selenium and zinc in a genome-wide association study using two adult cohorts from Australia and the UK. Participants were recruited in Australia from twins and their families and in the UK from pregnant women. We measured erythrocyte Cu, Se and Zn (Australian samples) or whole blood Se (UK samples) using inductively coupled plasma mass spectrometry. Genotyping was performed with Illumina chips and > 2.5 m SNPs were imputed from HapMap data. Genome-wide significant associations were found for each element. For Cu, there were two loci on chromosome 1 (most significant SNPs rs1175550, P = 5.03 × 10(-10), and rs2769264, P = 2.63 × 10(-20)); for Se, a locus on chromosome 5 was significant in both cohorts (combined P = 9.40 × 10(-28) at rs921943); and for Zn three loci on chromosomes 8, 15 and X showed significant results (rs1532423, P = 6.40 × 10(-12); rs2120019, P = 1.55 × 10(-18); and rs4826508, P = 1.40 × 10(-12), respectively). The Se locus covers three genes involved in metabolism of sulphur-containing amino acids and potentially of the analogous Se compounds; the chromosome 8 locus for Zn contains multiple genes for the Zn-containing enzyme carbonic anhydrase. Where potentially relevant genes were identified, they relate to metabolism of the element (Se) or to the presence at high concentration of a metal-containing protein (Cu).

A recessive X-linked mutation causes a threefold reduction of total body zinc accumulation in Drosophila melanogaster laboratory strains

A newly identified human locus on chromosome 15 was recently associated with zinc accumulation. Based on a prior report of a threefold difference in zinc accumulation between fumble¹ heterozygous mutants and control fly strains, it was suggested that phosphopantothenoylcysteine decarboxylase might affect zinc status through its effects on vitamin B5 (pantothenate) metabolism. We report here that outcrossed fumble¹ heterozygous mutant flies with low zinc content have been recovered, suggesting that pantothenate metabolism did not alter zinc homeostasis in fumble¹ heterozygous flies. We show instead that the Drosophila condition of low body zinc accumulation is an X-chromosome-linked recessive trait.

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Flies with a threefold reduction in zinc accumulation remain viable and fertile.

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There is no causal association between zinc accumulation and fly pantothenate kinase mutants.

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A widespread X-linked mutation causes a threefold reduction in zinc accumulation in Drosophila.

Iron absorption in Drosophila melanogaster

The way in which Drosophila melanogaster acquires iron from the diet remains poorly understood despite iron absorption being of vital significance for larval growth. To describe the process of organismal iron absorption, consideration needs to be given to cellular iron import, storage, export and how intestinal epithelial cells sense and respond to iron availability. Here we review studies on the Divalent Metal Transporter-1 homolog Malvolio (iron import), the recent discovery that Multicopper Oxidase-1 has ferroxidase activity (iron export) and the role of ferritin in the process of iron acquisition (iron storage). We also describe what is known about iron regulation in insect cells. We then draw upon knowledge from mammalian iron homeostasis to identify candidate genes in flies. Questions arise from the lack of conservation in Drosophila for key mammalian players, such as ferroportin, hepcidin and all the components of the hemochromatosis-related pathway. Drosophila and other insects also lack erythropoiesis. Thus, systemic iron regulation is likely to be conveyed by different signaling pathways and tissue requirements. The significance of regulating intestinal iron uptake is inferred from reports linking Drosophila developmental, immune, heat-shock and behavioral responses to iron sequestration.

Insertion mutants in Drosophila melanogaster Hsc20 halt larval growth and lead to reduced iron-sulfur cluster enzyme activities and impaired iron homeostasis

Despite the prominence of iron-sulfur cluster (ISC) proteins in bioenergetics, intermediary metabolism, and redox regulation of cellular, mitochondrial, and nuclear processes, these proteins have been given scarce attention in Drosophila. Moreover, biosynthesis and delivery of ISCs to target proteins requires a highly regulated molecular network that spans different cellular compartments. The only Drosophila ISC biosynthetic protein studied to date is frataxin, in attempts to model Friedreich's ataxia, a disease arising from reduced expression of the human frataxin homologue. One of several proteins involved in ISC biogenesis is heat shock protein cognate 20 (Hsc20). Here we characterize two piggyBac insertion mutants in Drosophila Hsc20 that display larval growth arrest and deficiencies in aconitase and succinate dehydrogenase activities, but not in isocitrate dehydrogenase activity; phenotypes also observed with ubiquitous frataxin RNA interference. Furthermore, a disruption of iron homeostasis in the mutant flies was evidenced by an apparent reduction in induction of intestinal ferritin with ferric iron accumulating in a subcellular pattern reminiscent of mitochondria. These phenotypes were specific to intestinal cell types that regulate ferritin expression, but were notably absent in the iron cells where ferritin is constitutively expressed and apparently translated independently of iron regulatory protein 1A. Hsc20 mutant flies represent an independent tool to disrupt ISC biogenesis in vivo without using the RNA interference machinery.

Genes for iron metabolism influence circadian rhythms in Drosophila melanogaster

Haem has been previously implicated in the function of the circadian clock, but whether iron homeostasis is integrated with circadian rhythms is unknown. Here we describe an RNA interference (RNAi) screen using clock neurons of Drosophila melanogaster. RNAi is targeted to iron metabolism genes, including those involved in haem biosynthesis and degradation. The results indicate that Ferritin 2 Light Chain Homologue (Fer2LCH) is required for the circadian activity of flies kept in constant darkness. Oscillations of the core components in the molecular clock, PER and TIM, were also disrupted following Fer2LCH silencing. Other genes with a putative function in circadian biology include Transferrin-3, CG1358 (which has homology to the FLVCR haem export protein) and five genes implicated in iron-sulfur cluster biosynthesis: the Drosophila homologues of IscS (CG12264), IscU (CG9836), IscA1 (CG8198), Iba57 (CG8043) and Nubp2 (CG4858). Therefore, Drosophila genes involved in iron metabolism are required for a functional biological clock.

Systematic functional characterization of putative zinc transport genes and identification of zinc toxicosis phenotypes in Drosophila melanogaster

The heavy metal zinc is an essential component of the human diet and is incorporated as a structural component in up to 10% of all mammalian proteins. The physiological importance of zinc homeostasis at the cellular level and the molecular mechanisms involved in this process have become topics of increasing interest in recent years. We have performed a systematic functional characterization of the majority of the predicted Drosophila Zip (Zinc/iron regulated transporter-related protein) and ZnT genes, using the Gal4-UAS system to carry out both ubiquitous and targeted over expression and suppression studies for thirteen of the seventeen putative zinc transport genes identified to date. We find that six of these thirteen genes may be essential for fly viability and that three of the remaining seven demonstrate over expression phenotypes. Our findings reaffirm the previously proposed function of dZnT63C (CG17723: FBgn005432) as an important zinc efflux protein and indicate that the fly homolog of hZip1, dZip42C.1 (CG9428: FBgn0033096), is a strong zinc importer in Drosophila. By combining over expression of dZip42C.1 with suppression of dZnT63C we were able to produce easily identifiable zinc toxicosis phenotypes which can be rescued or worsened by modifying dietary zinc content. Our findings show that a genetically based zinc toxicosis situation can be therapeutically treated or exacerbated by modifications to the diet, providing a sensitized background for future, more detailed studies of Zip / ZNT function.

Ferritin overexpression in Drosophila glia leads to iron deposition in the optic lobes and late-onset behavioral defects

Cellular and organismal iron storage depends on the function of the ferritin protein complex in insects and mammals alike. In the central nervous system of insects, the distribution and relevance of ferritin remain unclear, though ferritin has been implicated in Drosophila models of Alzheimers' and Parkinsons' disease and in Aluminum-induced neurodegeneration. Here we show that transgene-derived expression of ferritin subunits in glial cells of Drosophila melanogaster causes a late-onset behavioral decline, characterized by loss of circadian rhythms in constant darkness and impairment of elicited locomotor responses. Anatomical analysis of the affected brains revealed crystalline inclusions of iron-loaded ferritin in a subpopulation of glial cells but not significant neurodegeneration. Although transgene-induced glial ferritin expression was well tolerated throughout development and in young flies, it turned disadvantageous at older age. The flies we characterize in this report contribute to the study of ferritin in the Drosophila brain and can be used to assess the contribution of glial iron metabolism in neurodegenerative models of disease.

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

Malvolio (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.

Evidence for evolutionary constraints in Drosophila metal biology

Mutations in single Drosophila melanogaster genes can alter total body metal accumulation. We therefore asked whether evolutionary constraints maintain biologically abundant metal ions (iron, copper, manganese and zinc) to similar concentrations in different species of Drosophilidae, or whether metal homeostasis is a highly adaptable trait as shown previously for triglyceride and glycogen storage. To avoid dietary influences, only species able to grow and reproduce on a standard laboratory medium were selected for analysis. Flame atomic absorption spectrometry was used to determine metal content in 5-days-old adult flies. Overall, the data suggest that the metallome of the nine species tested is well conserved. Meaningful average values for the Drosophilidae family are presented. Few statistically significant differences were noted for copper, manganese and zinc between species. In contrast, Drosophila erecta and Drosophila virilis showed a 50% increase above average and a 30% decrease below average in iron concentrations, respectively. The changes in total body iron content correlated with altered iron storage in intestinal ferritin stores of these species. Hence, the variability in iron content could be accounted for by a corresponding adaptation in iron storage regulation. We suggest that the relative expression of the multitude of metalloenzymes and other metal-binding proteins remains overall similar between species and likely determines relative metal abundances in the organism. The availability of a complete and annotated genome sequence of different Drosophila species presents opportunities to study the evolution of metal homeostasis in closely related organisms that have evolved separately for millions or dozens of million years.