What can flies tell us about copper homeostasis?

Arthropods in landfills and their accumulation potential for toxic elements: A review

Landfills, as a source of potentially toxic elements (PTEs), pose a threat to the environment and human health. A literature review was conducted to explore the diversity of arthropods inhabiting solid waste landfills, as well as on the bioaccumulation of PTEs by arthropods. This review presents scientific papers over the last 20 years. Their importance in landfill ecosystems has been the subject of research; however, the issue of the accumulation of compounds such as toxic elements is emphasized only in a few studies. The bioaccumulation of PTEs was studied for 10 arthropod species that founded in landfills: Orthomorpha coarctata and Trigoniulus corallinus (class Diplopoda), Armadillidium vulgare and Trachelipus rathkii (class Malacostraca), the 6 species of the class Insecta - Zonocerus variegatus, Anacanthotermes ochraceus, Macrotermes bellicosus, Austroaeschna inermis, Calathus fuscipes and Harpalus rubripes.

Biological effects of a copper-based fungicide on the fruit fly, Drosophila melanogaster

The increased consumption of pesticides can have a negative environmental impact by increasing the essential metals to toxic levels. Bordasul® is a commonly used fungicide in Brazil and it is composed of 20% Cu, 10% sulfur, and 3.0% calcium. The study of fungicides in vivo in non-target model organisms can predict their environmental impact more broadly. The Drosophila melanogaster is a unique model due to its ease of handling and maintenance. Here, the potential toxicity of Bordasul® was investigated by assessing the development, survival, and behavior of exposed flies. Exposure to Bordasul® impaired the development (p < 0.01) and caused a significant reduction in memory retention (p < 0.05) and locomotor ability (p < 0.001). Fungicides are needed to assure the world's food demand; however, Bordasul® was highly toxic to D. melanogaster. Therefore, Bordasul® may be potentially toxic to non-target invertebrates and new environmentally-safe biofertilizers have to be developed to preserve the biota.

The relationship between heavy metals and metabolic syndrome using machine learning

Background

Exposure to high levels of heavy metals has been widely recognized as an important risk factor for metabolic syndrome (MetS). The main purpose of this study is to assess the associations between the level of heavy metal exposure and Mets using machine learning (ML) method.

Methods

The data used in this study are from the national health and nutrition examination survey 2003-2018. According to the demographic information and heavy metal exposure level of participants, a total of 22 variables were included. Lasso was used to screen out the key variables, and 9 commonly used ML models were selected to establish the associations with the 5-fold cross validation method. Finally, we choose the SHapley Additive exPlanations (SHAP) method to explain the prediction results of Adaboost model.

Results

11,667 eligible individuals were randomly divided into two groups to train and verify the prediction model. Through lasso, characteristic variables were selected from 24 variables as predictors. The AUC (area under curve) of the models selected in this study were all greater than 0.7, and AdaBoost was the best model. The AUC value of AdaBoost was 0.807, the accuracy was 0.720, and the sensitivity was 0.792. It is noteworthy that higher levels of cadmium, body mass index, cesium, being female, and increasing age were associated with an increased probability of MetS. Conversely, lower levels of cobalt and molybdenum were linked to a decrease in the estimated probability of MetS.

Conclusion

Our study highlights the AdaBoost model proved to be highly effective, precise, and resilient in detecting a correlation between exposure to heavy metals and MetS. Through the use of interpretable methods, we identified cadmium, molybdenum, cobalt, cesium, uranium, and barium as prominent contributors within the predictive model.

Biological effects of the frequent application of a copper-containing fungicide on the fruit fly Drosophila melanogaster

The increased consumption of pesticides has an environmental impact due to the dispersion of minerals. Bordasul® is a commonly used fungicide composed of 20% Cu, 10% sulfur, and 3.0% calcium to correct its deficiency in plants. The evaluation of fungicide effects in vivo models is designed to assess their impact on the environment more broadly. Drosophila melanogaster offers a unique model due to its ease of handling and maintenance. Here, the effects of Bordasul® were investigated, addressing the development, survival, and behavior of flies. Our findings showed that exposure to Bordasul® prevented the development of flies (p < 0.01). In addition to causing a significant reduction in memory retention (p < 0.05) and locomotion capacity (p < 0.001). Although fungicides are necessary to satisfy the world's food demand, we conclude that Bordasul® is highly toxic, and that safer media, such as biofertilizers, must be developed as effective alternatives.

Development of an interpretable machine learning model associated with heavy metals' exposure to identify coronary heart disease among US adults via SHAP: Findings of the US NHANES from 2003 to 2018

Limited information is available on the links between heavy metals' exposure and coronary heart disease (CHD). We aim to establish an efficient and explainable machine learning (ML) model that associates heavy metals' exposure with CHD identification. Our datasets for investigating the associations between heavy metals and CHD were sourced from the US National Health and Nutrition Examination Survey (US NHANES, 2003-2018). Five ML models were established to identify CHD by heavy metals' exposure. Further, 11 discrimination characteristics were used to test the strength of the models. The optimally performing model was selected for identification. Finally, the SHapley Additive exPlanations (SHAP) tool was used for interpreting the features to visualize the selected model's decision-making capacity. In total, 12,554 participants were eligible for this study. The best performing random forest classifier (RF) based on 13 heavy metals to identify CHD was chosen (AUC: 0.827; 95%CI: 0.777-0.877; accuracy: 95.9%). SHAP values indicated that cesium (1.62), thallium (1.17), antimony (1.63), dimethylarsonic acid (0.91), barium (0.76), arsenous acid (0.79), total arsenic (0.01) in urine, and lead (3.58) and cadmium (4.66) in blood positively contributed to the model, while cobalt (-0.15), cadmium (-2.93), and uranium (-0.13) in urine negatively contributed to the model. The RF model was efficient, accurate, and robust in identifying an association between heavy metals' exposure and CHD among US NHANES 2003-2018 participants. Cesium, thallium, antimony, dimethylarsonic acid, barium, arsenous acid, and total arsenic in urine, and lead and cadmium in blood show positive relationships with CHD, while cobalt, cadmium, and uranium in urine show negative relationships with CHD.

The gut microbiome analysis of Anastrepha obliqua reveals inter-kingdom diversity: bacteria, fungi, and archaea

The fruit fly Anastrepha obliqua is an economically important pest. The sterile insect technique to control it involves mass production and release of sterile flies to reduce the reproduction of the wild population. As noted in different Tephritidae, the performance of sterile males may be affected by the assimilation of nutrients under mass-rearing conditions. In the wild, the fly's life cycle suggests the acquisition of different organisms that could modulate its fitness and physiology. For A. obliqua, there is no information regarding microorganisms other than bacteria. This study analyzed bacteria, fungal, and archaea communities in the A. obliqua gut through denaturing gradient gel electrophoresis (DGGE) profiles of 16S (using a different set of primers for bacteria and archaea) and 18S ribosomal DNA markers. We found that wild flies presented higher microbial diversity related to fructose assimilation than laboratory species, suggesting that microorganisms have led to a specialized metabolism to process nutrients associated with an artificial diet. We identified species that have not been previously described in this fruit fly, especially actinobacteria and archaea, by employing different primer sets aimed at the same molecular marker but targeting diverse hypervariable regions of 16S rDNA. The possibility that Archaea affect fly fitness should not be ignored. This report on the intestinal microbial (bacteria, archaea, and fungi) composition of A. obliqua contributes to our understanding of the role of microorganisms in the development and physiology of the flies.

Regulation and biological function of metal ions in Drosophila

A conceptual framework is offered for critically approaching the formidable ability of insects to segregate metal ions to their multiple destinations in proteins and subcellular compartments. New research in Drosophila melanogaster suggests that nuclear iron regulatory proteins and oxidative stress transcription factors mediate metal-responsive gene expression. Identification of a zinc-regulated chaperone in the endoplasmic reticulum potentially explains membrane protein trafficking defects observed in zinc transporter mutants. Compartmentalized zinc is utilized in fertilization, embryogenesis and for the activation of zinc-finger transcription factors - the latter function demonstrated during muscle development, while dietary zinc is sensed through gating of a chloride channel. Another emerging theme in cellular metal homeostasis is that transporters and related proteins meet at endoplasmic reticulum-mitochondria associated membranes with physiologically relevant consequences during aging.

Metabolic aspects of phenolic compounds from Triplaris gardneriana seeds in the management of oxidative stress

Objective: Considering the limited number of studies that analyze the behavior of plant preparations in human body, this study aimed to characterize the phenolic compounds from Triplaris gardneriana extract (EETg) in terms of antioxidant and metabolic aspects, integrating in vitro, in silico and in vivo strategies.Methods: EETg was analyzed in relation to polyphenols release from the plant matrix under in vitro digestion, as well as the pharmacokinetic prediction of their major compounds by in silico simulation and understanding of its in vivo antioxidant effect in an alternative animal model.Results: About 35.22% of polyphenols from EETg proved to be accessible after enzymatic hydrolysis. A kinetics study showed that 40% of the total content of these phytochemicals was released from the extract accompanied by increased antioxidant capacity after 180 min of gastrointestinal simulation. A computational approach revealed that 7 out of 9 major phenolic compounds of EETg showed good pharmacokinetic parameters such as intestinal absorption and bioavailability score. In addition, the extract showed a protective effect on copper-induced oxidative stress in Drosophila melanogaster, evidenced by the restoration of basal levels of thiol and malondialdehyde contents. These biochemical observations were supported by the examination of histological features of D. melanogaster brain.Conclusion: It was demonstrated that the oral administration of EETg would provide phenolic compounds partially absorbable by the human gut and capable of providing health benefits associated with the inhibition of oxidative stress. Additionally, the results highlight the need to implement new approaches for the rational development of plant-based medicines.

Subcellular Localization of Copper-Cellular Bioimaging with Focus on Neurological Disorders

As an essential trace element, copper plays a pivotal role in physiological body functions. In fact, dysregulated copper homeostasis has been clearly linked to neurological disorders including Wilson and Alzheimer’s disease. Such neurodegenerative diseases are associated with progressive loss of neurons and thus impaired brain functions. However, the underlying mechanisms are not fully understood. Characterization of the element species and their subcellular localization is of great importance to uncover cellular mechanisms. Recent research activities focus on the question of how copper contributes to the pathological findings. Cellular bioimaging of copper is an essential key to accomplish this objective. Besides information on the spatial distribution and chemical properties of copper, other essential trace elements can be localized in parallel. Highly sensitive and high spatial resolution techniques such as LA-ICP-MS, TEM-EDS, S-XRF and NanoSIMS are required for elemental mapping on subcellular level. This review summarizes state-of-the-art techniques in the field of bioimaging. Their strengths and limitations will be discussed with particular focus on potential applications for the elucidation of copper-related diseases. Based on such investigations, further information on cellular processes and mechanisms can be derived under physiological and pathological conditions. Bioimaging studies might enable the clarification of the role of copper in the context of neurodegenerative diseases and provide an important basis to develop therapeutic strategies for reduction or even prevention of copper-related disorders and their pathological consequences.

Copper decreases associative learning and memory in Drosophila melanogaster

Copper is an essential element to all living organisms. Repeated use of metal-enriched chemicals, fertilizers, and organic substances may cause contamination at a large scale. Altered levels of Cu²⁺ may result in harmful effects and can be associated with memory and cognitive dysfunction. Studying simple, genetically tractable organisms such as Drosophila melanogaster, can reveal important data on the neural basis of conditioning. D. melanogaster is an important alternative experimental model to assess the toxic response to metals. In the present study, the effects of copper on flies' development and in learning and memory retention in male and female adult flies were investigated. We paired an odorant to pain perception and observed the aversion behavior over time. Exposure of D. melanogaster eggs to Cu²⁺ increased mortality of larvae, pupae, and adults and decreased memory retention in adults. Moreover, male flies demonstrated to be more susceptible to Cu²⁺ toxicity than females. The results therefore, reinforce the importance of controlling the anthropogenic heavy-metals soil contamination given their hazardous effects to living organisms.

Curcumin attenuates copper-induced oxidative stress and neurotoxicity in Drosophila melanogaster

Curcumin is a hydrophobic polyphenol derived from the rhizome of the Herb Curcuma longa belonging to the family Zingiberaceae. Curcumin possesses antioxidative, anti-inflammatory and anti-depressant-like properties. In this study, we evaluated the rescue role of Curcumin in Copper²⁺-induced toxicity in D. melanogaster. Adult, wild type flies were exposed to Cu²⁺ (1 mM) and/or Curcumin (0.2 and 0.5 mg/kg diet) in the diet for 7 days. The results indicated that Cu²⁺- fed flies had reduced survival compared to the control group. Copper toxicity was also associated with a marked decrease in total thiol (T-SH), as well as catalase and glutathione S-transferase activities, contemporaneous with increased acetylcholinesterase (AChE) activity, nitric oxide (nitrate and nitrite) and dopamine levels. Co-exposure of flies to Cu²⁺ and Curcumin prevented mortality, inhibited AChE activity and restored dopamine to normal levels (p < 0.05). Moreover, Curcumin restored eclosion rates, and the cellular antioxidant status, as well as alleviated the accumulation of nitric oxide level in the flies. Curcumin ameliorated oxidative damage in the flies as evidenced by the survival rates, longevity assay as well as the restoration of antioxidant status. Our findings thus suggest that Curcumin ameliorated Cu²⁺-induced neurotoxicity in D. melanogaster and as such could be considered an effective therapeutic agent in the prevention and treatment of disorders, where oxidative stress is implicated.

Intestinal response to dietary manganese depletion inDrosophila

Metabolic adaptations to manganese deficiency.

Targeting of copper-trafficking chaperones causes gene-specific systemic pathology in Drosophila melanogaster: prospective expansion of mutational landscapes that regulate tumor resistance to cisplatin

Copper, a transition metal, is an essential component for normal growth and development. It acts as a critical co-factor of many enzymes that play key roles in diverse cellular processes. The present study attempts to investigate the regulatory functions decisively controlling copper trafficking during development and aging of the Drosophila model system. Hence, through engagement of the GAL4/UAS genetic platform and RNAi technology, we herein examined the in vivo significance of Atox1 and CCS genes, products of which pivotally govern cellular copper trafficking in fly tissue pathophysiology. Specifically, we analyzed the systemic effects of their targeted downregulation on the eye, wing, neuronal cell populations and whole-body tissues of the fly. Our results reveal that, in contrast to the eye, suppression of their expression in the wing leads to a notable increase in the percentage of malformed organs observed. Furthermore, we show that Atox1 or CCS gene silencing in either neuronal or whole-body tissues can critically affect the viability and climbing capacity of transgenic flies, while their double-genetic targeting suggests a rather synergistic mode of action of the cognate protein products. Interestingly, pharmacological intervention with the anti-cancer drug cisplatin indicates the major contribution of CCS copper chaperone to cisplatin's cellular trafficking, and presumably to tumor resistance often acquired during chemotherapy. Altogether, it seems that Atox1 and CCS proteins serve as tissue/organ-specific principal regulators of physiological Drosophila development and aging, while their tissue-dependent downregulation can provide important insights for Atox1 and CCS potential exploitation as predictive gene biomarkers of cancer-cell chemotherapy responses.

Summary: We demonstrate the essential roles of Atox1 and CCS copper-trafficking chaperones in Drosophila development and aging. We also provide insights for their therapeutic exploitation as cisplatin regulators during cancer chemotherapy.

Biochemical CuSO4 Toxicity in Drosophila melanogaster Depends on Sex and Developmental Stage of Exposure

Copper is a transition metal that exists in different chemical forms (e.g., Cu²⁺,Cu⁺, and Cu⁰) and at high concentrations it is toxic. Here, we investigated the Cu²⁺-induced toxicity in Drosophila melanogaster, evaluating the survival, locomotion, and the activity of acetylcholinesterase (AChE) and glutathione S-transferase (GST) enzymes. Flies were exposed to Cu²⁺(0.1-1 mmol CuSO₄/kg of diet or approximately 0.1-1 mM Cu²⁺) and allowed to mate during 24 h. GST and AChE enzymes were evaluated in the larvae and in the head and the body (thorax + abdomen) of the adult male and females flies. The total number of adult females (0.4-1 mM) and males (0.75 and 1 mM) was decreased by CuSO₄. The climbing ability was hampered in flies exposed to 1 mM Cu²⁺. In larvae, Cu²⁺(0.4-1 mM) increased AChE activity (P < 0.002). In males' heads, 0.4 mM Cu²⁺ increased the AChE activity (P < 0.01). In adults' bodies, Cu²⁺inhibited the activity in both sexes, but with greater effectiveness in males (0.1 to 1 mM) than in females (1 mM). Regarding GST activity, 0.1 mM Cu²⁺increased, but 1 mM decrease GST in larvae. In the head of flies, Cu²⁺decreased the GST activity at intermediate (0.4 mM) and increased GST at the highest concentration (1 mM) in males. In the bodies, the effect of Cu²⁺was similar. In conclusion, Cu²⁺exposure in D. melanogaster disrupted locomotion and enzymatic parameters that can be related to changes in AChE and in the detoxifying GST enzyme.

Drosophila melanogaster as a Versatile Model Organism in Food and Nutrition Research

Drosophila melanogaster has been widely used in the biological sciences as a model organism. Drosophila has a relatively short life span of 60-80 days, which makes it attractive for life span studies. Moreover, approximately 60% of the fruit fly genes are orthologs to mammals. Thus, metabolic and signal transduction pathways are highly conserved. Maintenance and reproduction of Drosophila do not require sophisticated equipment and are rather cheap. Furthermore, there are fewer ethical issues involved in experimental Drosophila research compared with studies in laboratory rodents, such as rats and mice. Drosophila is increasingly recognized as a model organism in food and nutrition research. Drosophila is often fed complex solid diets based on yeast, corn, and agar. There are also so-called holidic diets available that are defined in terms of their amino acid, fatty acid, carbohydrate, vitamin, mineral, and trace element compositions. Feed intake, body composition, locomotor activity, intestinal barrier function, microbiota, cognition, fertility, aging, and life span can be systematically determined in Drosophila in response to dietary factors. Furthermore, diet-induced pathophysiological mechanisms including inflammation and stress responses may be evaluated in the fly under defined experimental conditions. Here, we critically evaluate Drosophila melanogaster as a versatile model organism in experimental food and nutrition research, review the corresponding data in the literature, and make suggestions for future directions of research.

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.

In vivo toxic effects of 4-methoxy-5-hydroxy-canthin-6-one in zebrafish embryos via copper dyshomeostasis and oxidative stress

Dysfunction of copper homeostasis can lead to a host of disorders, which might be toxic sometimes. 4-Methoxy-5-hydroxy-canthin-6-one (CAN) is one of the major constituents from Picrasma quassioides and responsible for its therapeutic effects. In this work, we evaluated the toxic effect of CAN (7.5μM) on zebrafish embryos. CAN treatment decreased survival, delayed hatching time and induced malformations (loss of pigmentation, pericardial edema, as well as hematologic and neurologic abnormalities). Besides, exogenous copper supplementation rescued the pigmentation and cardiovascular defects in CAN-treated embryos. Further spectroscopic studies revealed a copper-chelating activity of CAN. Then its regulation on the expressions of copper homeostasis related genes also be analyzed. In addition, CAN lowered the total activity of SOD, elevated the ROS production and altered the oxidative related genes transcriptions, which led to oxidative stress. In conclusion, we demonstrated that CAN (7.5μM) might exert its toxic effects in zebrafish embryos by causing copper dyshomeostasis and oxidative stress. It will give insight into the risk assessment and prevention of CAN-mediated toxicity.

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.

Genetic Diversity in Insect Metal Tolerance

Insects encounter a variety of metals in their environment, many of which are required at some concentration for normal organismal homeostasis, but essentially all of which are toxic at higher concentrations. Insects have evolved a variety of genetic, and likely epigenetic, mechanisms to deal with metal stress. A recurring theme in all these systems is complexity and diversity; even simple, single gene, cases are complex. Of the known gene families, the metallothioneins are perhaps the best understood and provide good examples of how diverse metal response is. Interestingly, there is considerable diversity across taxa in these metal-responsive systems, including duplications to form small gene families and complex expression of single loci. Strikingly, different species have evolved different mechanisms to cope with the same, or similar, stress suggesting both independent derivation of, and plasticity in, the pathways involved. It is likely that some metal-response systems evolved early in evolutionary time and have been conserved, while others have diverged, and still others evolved more recently and convergently. In addition to conventional genetics, insects likely respond to environmental metal through a variety of epigenetic systems, but direct tests are lacking. Ultimately, it is likely that classical genetic and epigenetic factors interact in regulating insect metal responses. In light of this diversity across species, future studies including a broad-based examination of gene expression in non-model species in complex environments will likely uncover additional genes and genetic and epigenetic mechanisms.

Drosophila melanogaster Models of Metal-Related Human Diseases and Metal Toxicity

Iron, copper and zinc are transition metals essential for life because they are required in a multitude of biological processes. Organisms have evolved to acquire metals from nutrition and to maintain adequate levels of each metal to avoid damaging effects associated with its deficiency, excess or misplacement. Interestingly, the main components of metal homeostatic pathways are conserved, with many orthologues of the human metal-related genes having been identified and characterized in Drosophila melanogaster. Drosophila has gained appreciation as a useful model for studying human diseases, including those caused by mutations in pathways controlling cellular metal homeostasis. Flies have many advantages in the laboratory, such as a short life cycle, easy handling and inexpensive maintenance. Furthermore, they can be raised in a large number. In addition, flies are greatly appreciated because they offer a considerable number of genetic tools to address some of the unresolved questions concerning disease pathology, which in turn could contribute to our understanding of the metal metabolism and homeostasis. This review recapitulates the metabolism of the principal transition metals, namely iron, zinc and copper, in Drosophila and the utility of this organism as an experimental model to explore the role of metal dyshomeostasis in different human diseases. Finally, a summary of the contribution of Drosophila as a model for testing metal toxicity is provided.

Functional studies of Drosophila zinc transporters reveal the mechanism for zinc excretion in Malpighian tubules

Background

Zinc is an essential metal involved in many physiological processes. Previous work has identified a set of zinc transporters involved in Drosophila dietary zinc absorption. However, zinc excretion and reabsorption, the other two important processes to maintain zinc homeostasis, are not as well understood. In this work, we screened all the potential zinc transporter Zip (SLC39) and ZnT (SLC30) members for their likely roles in zinc excretion in Malpighian tubules, an insect organ functionally analogous to mammalian kidneys.

Results

Zip71B (CG10006, most homologous to hZIP5), in addition to the previously characterized ZnT35C (CG3994), was identified as being critical in zinc excretion. Tubule-specific knockdown of Zip71B/dZip5 reduces zinc accumulation in the tubules, but increases zinc levels in the body, resulting in survival defect under zinc excess conditions. Zip71B/dZip5 is localized to the plasma membrane at the basolateral side of the tubules, and is functionally epistatic to the apically localized ZnT35C in regulating the tubule zinc homeostasis. Our results indicate that Zip71B/dZip5 is involved in zinc import into the tubular cells from the circulation, and ZnT35C in turn effluxes the tubular zinc out. Notably, mammalian ZIP5, which is expressed in the kidney, functions analogously to Zip71B/dZip5 in the fly while hZIP4 cannot complement the loss of Zip71B/dZip5 function. Furthermore, Zip71B/dZip5 expression is regulated by zinc so that, in response to toxic levels of zinc, the tubules can increase zinc efflux capability. We also characterized the role of dZnT1 (CG17723) in zinc reabsorption in Malpighian tubules. Finally, using a tubule calcification model, we were able to show that knockdown of Zip71B/dZip5 or ZnT35C was able to mitigate stone formation, consistent with their roles in tubular zinc homeostasis.

Conclusions

Our results start to sketch out a relatively complete picture of the zinc excretion process in Drosophila Malpighian tubules, and may provide a reference for relevant mammalian studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-017-0355-9) contains supplementary material, which is available to authorized users.

Copper comes of age in Melbourne

When we were asked to produce articles for this volume, it seemed appropriate to us to co-author an article on the history and impact of copper research in Melbourne. It is appropriate because over many years, decades in fact, we worked closely together and with Professor David Danks to identify the molecular defect in Menkes disease. This work was always carried out with the intention of understanding the nature of the copper homeostatic mechanisms and a "copper pathway" in the cell, that David had the prescience to predict must exist despite scepticism from granting agencies! He indeed inspired us to pursue research careers in this field. This article outlines some of this history.

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.

A novel Drosophila mitochondrial carrier protein acts as a Mg(2+) exporter in fine-tuning mitochondrial Mg(2+) homeostasis

The homeostasis of magnesium (Mg(2+)), an abundant divalent cation indispensable for many biological processes including mitochondrial functions, is underexplored. In yeast, the mitochondrial Mg(2+) homeostasis is accurately controlled through the combined effects of importers, Mrs2 and Lpe10, and an exporter, Mme1. However, little is known about this Mg(2+) homeostatic process in multicellular organisms. Here, we identified the first mitochondrial Mg(2+) transporter in Drosophila, the orthologue of yeast Mme1, dMme1, by homologous comparison and functional complementation. dMme1 can mediate the exportation of mitochondrial Mg(2+) when heterologously expressed in yeast. Altering the expression of dMme1, although only resulting in about a 10% change in mitochondrial Mg(2+) levels in either direction, led to a significant survival reduction in Drosophila. Furthermore, the reduced survival resulting from dMme1 expression changes could be completely rescued by feeding the dMME1-RNAi flies Mg(2+)-restricted food or the dMME1-over-expressing flies the Mg(2+)-supplemented diet. Our studies therefore identified the first Drosophila mitochondrial Mg(2+) exporter, which is involved in the precise control of mitochondrial Mg(2+) homeostasis to ensure an optimal state for survival.

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.

Decreased accumulation of cadmium in Drosophila selected for resistance suggests a mechanism independent of metallothionein

Heavy metals, including cadmium, are common contaminants in environments subject to human activity. Responses to exposure in the fruit fly, Drosophila melanogaster, are dosage-dependent and resistance is selectable. While metallothionein-mediated sequestration has been extensively studied as a mechanism of cadmium resistance, a link between selection for resistance and an increased accumulation of cadmium has yet to be demonstrated. To address this need, we have selected wild-type flies for cadmium resistance for 20 generations and tested metal content using mass spectrometry. Resistant flies were observed to contain lower levels of cadmium, arguing for a mechanism of cadmium resistance that is not mediated by increased sequestration. This, coupled with genetic evidence suggesting the involvement of factors located on the X chromosome, suggests a gene other than metallothionein may be involved in resistance in this line.

The effects of silver ions on copper metabolism in rats

The influence of short and prolonged diet containing silver ions (Ag-diet) on copper metabolism was studied. Two groups of animals were used: one group of adult rats received a Ag-diet for one month (Ag-A1) and another group received a Ag-diet for 6 months from birth (Ag-N6). In Ag-A1 rats, the Ag-diet caused a dramatic decrease of copper status indexes that was manifested as ceruloplasmin-associated copper deficiency. In Ag-N6 rats, copper status indexes decreased only 2-fold as compared to control rats. In rats of both groups, silver entered the bloodstream and accumulated in the liver. Silver was incorporated into ceruloplasmin (Cp), but not SOD1. In the liver, a prolonged Ag-diet caused a decrease of the expression level of genes, associated with copper metabolism. Comparative spectrophotometric analysis of partially purified Cp fractions has shown that Cp from Ag-N6 rats was closer to holo-Cp by specific enzymatic activities and tertiary structure than Cp from Ag-A1 rats. However, Cp of Ag-N6 differs from control holo-Cp and Cp of Ag-A1 in its affinity to DEAE-Sepharose and in its binding properties to lectins. In the bloodstream of Ag-N6, two Cp forms are present as shown in pulse-experiments on rats with the liver isolated from circulation. One of the Cp isoforms is of hepatic origin, and the other is of extrahepatic origin; the latter is characterized by a faster rate of secretion than hepatic Cp. These data allowed us to suggest that the disturbance of holo-Cp formation in the liver was compensated by induction of extrahepatic Cp synthesis. The possible biological importance of these effects is discussed.