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

Differential gene expression of Asian citrus psyllids infected with 'Ca. Liberibacter asiaticus' reveals hyper-susceptibility to invasion by instar fourth-fifth and teneral adult stages

The bacterial pathogen Candidatus Liberibacter asiaticus (CLas) is the causal agent of citrus greening disease. This unusual plant pathogenic bacterium also infects its psyllid host, the Asian citrus psyllid (ACP). To investigate gene expression profiles with a focus on genes involved in infection and circulation within the psyllid host of CLas, RNA-seq libraries were constructed from CLas-infected and CLas-free ACP representing the five different developmental stages, namely, nymphal instars 1-2, 3, and 4-5, and teneral and mature adults. The Gbp paired-end reads (296) representing the transcriptional landscape of ACP across all life stages and the official gene set (OGSv3) were annotated based on the chromosomal-length v3 reference genome and used for de novo transcript discovery resulting in 25,410 genes with 124,177 isoforms. Differential expression analysis across all ACP developmental stages revealed instar-specific responses to CLas infection, with greater overall responses by nymphal instars, compared to mature adults. More genes were over-or under-expressed in the 4-5th nymphal instars and young (teneral) adults than in instars 1-3, or mature adults, indicating that late immature instars and young maturing adults were highly responsive to CLas infection. Genes identified with potential for direct or indirect involvement in the ACP-CLas circulative, propagative transmission pathway were predominantly responsive during early invasion and infection processes and included canonical cytoskeletal remodeling and endo-exocytosis pathway genes. Genes with predicted functions in defense, development, and immunity exhibited the greatest responsiveness to CLas infection. These results shed new light on ACP-CLas interactions essential for pathogenesis of the psyllid host, some that share striking similarities with effector protein-animal host mechanisms reported for other culturable and/or fastidious bacterial- or viral- host pathosystems.

Clinical and Molecular Aspects of Iron Metabolism in Failing Myocytes

Heart failure (HF) is a common disease that causes significant limitations on the organism's capacity and, in extreme cases, leads to death. Clinically, iron deficiency (ID) plays an essential role in heart failure by deteriorating the patient's condition and is a prognostic marker indicating poor clinical outcomes. Therefore, in HF patients, supplementation of iron is recommended. However, iron treatment may cause adverse effects by increasing iron-related apoptosis and the production of oxygen radicals, which may cause additional heart damage. Furthermore, many knowledge gaps exist regarding the complex interplay between iron deficiency and heart failure. Here, we describe the current, comprehensive knowledge about the role of the proteins involved in iron metabolism. We will focus on the molecular and clinical aspects of iron deficiency in HF. We believe that summarizing the new advances in the translational and clinical research regarding iron deficiency in heart failure should broaden clinicians' awareness of this comorbidity.

Molecular physiology of iron trafficking in Drosophila melanogaster

Iron homeostasis in insects is less-well understood comparatively to mammals. The classic model organism Drosophila melanogaster has been recently employed to explore how iron is trafficked between and within cells. An outline for iron absorption, systemic delivery, and efflux is thus beginning to emerge. The proteins Malvolio, ZIP13, mitoferrin, ferritin, transferrin, and IRP-1A are key players in these processes. While many features are shared with those in mammals, some physiological differences may also exist. Notable remaining questions include the existence and identification of functional transferrin and ferritin receptors, and of an iron exporter like ferroportin, how systemic iron homeostasis is controlled, and the roles of different tissues in regulating iron physiology. By focusing on aspects of iron trafficking, this review updates on presently known complexities of iron homeostasis in Drosophila.

The roles of metals in insect-microbe interactions and immunity

Metal ions play essential roles in diverse physiological processes in insects, including immunity and interactions with microbes. Some, like iron, are essential nutrients and therefore are the subject of a tug-of-war between insects and microbes. Recent findings showed that the hypoferremic response mediated by Transferrin 1 is an essential defense mechanism against pathogens in insects. Transferrin 1 and the overall iron metabolism were also implicated in mediating interactions between insects and beneficial microbes. Other metals, like copper and zinc, can interfere with insect immune effectors, and either enhance (antimicrobial peptides) or reduce (reactive oxygen species) their activity. By covering recent advances in the field, this review emphasizes the importance of metals as essential mediators of insect-microbe interactions.

Plasmalogens improve swimming performance by modulating the expression of genes involved in amino acid and lipid metabolism, oxidative stress, and ferroptosis in an Alzheimer's disease zebrafish model

Plasmalogens (PLs) are critical to human health. Studies have reported a link between the downregulation of PLs levels and cognitive impairments in patients with Alzheimer's disease (AD). However, the underlying mechanisms remain to be clarified. In the present study, an AlCl₃-induced AD zebrafish model was established, and the model was used to elucidate the neuroprotective effects of PLs on AD by analysing the transcriptional profiles of zebrafish in the control, AD model, AD_PL, and PL groups. Chronic AlCl₃ exposure caused swimming performance impairments in the zebrafish, yet PLs supplementation could improve the dyskinesia recovery rate in the AD zebrafish model. Through transcriptional profiling, a total of 5413 statistically significant differentially expressed genes (DEGs) were identified among the groups. In addition to the DEGs involved in amino acid metabolism, we found that the genes related to iron homeostasis, lipid peroxidation, and oxidative stress, all of which contribute to ferroptosis, were dramatically altered among different groups. These results suggest that seafood-derived PLs, in addition to their role in eliminating oxidative stress, can improve the swimming performance in AlCl₃-exposed zebrafish partly by suppressing neuronal ferroptosis and accelerating synaptic transmission at the transcriptional level. This study provides evidence for PLs to be developed as a functional food supplement to relieve AD symptoms.

Transcriptomic analysis reveals the inhibition of reproduction in rice brown planthopper, Nilaparvata lugens, after silencing the gene of MagR (IscA1)

MagR (IscA1) is a member of the iron-sulphur cluster assembly proteins, which plays vital roles in many physiological processes, such as energy metabolism, electron transfer, iron homeostasis, heme biosynthesis and physiologically magnetic response. Its deletion leads to the loss of mitochondrial DNA, inactivation of iron-sulphur proteins and abnormal embryonic development in organisms. However, the physiological roles of MagR in insects are unclear. This study characterized the effects and molecular regulatory mechanism of MagR gene silencing on the reproduction of brachypterous female adults of Nilaparvata lugens. After silencing the MagR gene using RNAi approach, the duration of reproductive period was shortened and the fecundity and hatchability reduced significantly. A total of 479 differentially expressed genes (DEGs) were identified for female adults after 2 days of dsRNA injection through RNA-sequencing technology, including 352 significantly upregulated DEGs and 127 significantly downregulated DEGs, among which 44 DEGs were considered the key genes involved in the effects of NlMagR silencing on the reproduction, revealing the regulatory mechanism of MagR at RNA transcription level and providing a new strategy for the control of N. lugens.

The Magnetic Receptor of Monascus ruber M7: Gene Clone and Its Heterologous Expression in Escherichia coli

It is well known that many organisms can perceive the magnetic field (MF), including the geomagnetic field, but how to feel MF is unclear. Recently, a study has claimed that a biological compass, namely a complex of the magnetic receptor (MagR) and blue light (BL) receptor (cryptochrome), has been found in Homo sapiens, Drosophila melanogaster, and Danaus plexippus, which may bring some new ideas to explore the mechanism of biomagnetism. Monascus spp. are edible filamentous fungi that can produce abundant beneficial secondary metabolites and have been used to produce food colorants for nearly 2000 years in the world, especially in China, Japan, and Korea. In this work, we firstly treated M. ruber M7 by BL (500 lux,465–467 nm), MF (5, 10, 30 mT), and the combination of MF and BL (MF-BL), respectively. The results revealed that, compared with the control (CK, neither BL nor MF), the MF alone had no effect on the growth and morphological characteristics of M7, but BL made the colonial diameters only 66.7% of CK’s and inhibited the formation of cleistothecia. Under MF-BL, the colony diameters were still 66.7% of CK’s, but the colonial growth and cleistothecia production inhibited by BL were partially restored. Then, we have found that the magR gene widely exists in the genomes of animals, plants, and microorganisms, and we have also discovered a magR gene in the M7 genome, hereinafter referred to mr-magR. Finally, the full-length cDNA of mr-magR was successfully cloned and expressed in Escherichia coli BL21 (DE3), and the Mr-MagR protein was purified by a Ni⁺-NTA column and identified by Western blot. These results have laid a foundation for further investigation on the relationship between Mr-MagR and BL receptor(s) that might exist in M7. According to a literature search, it is the first time to report magR in filamentous fungi.

Cellular iron sensing and regulation: Nuclear IRP1 extends a classic paradigm

The classic view is that iron regulatory proteins operate at the post-transcriptional level. Iron Regulatory Protein 1 (IRP1) shifts between an apo-form that binds mRNAs and a holo-form that harbors a [4Fe4S] cluster. The latter form is not considered relevant to iron regulation, but rather thought to act as a non-essential cytosolic aconitase. Recent work in Drosophila, however, shows that holo-IRP1 can also translocate to the nucleus, where it appears to downregulate iron metabolism genes, preparing the cell for a decline in iron uptake. The shifting of IRP1 between states requires a functional mitoNEET pathway that includes a glycogen branching enzyme for the repair or disassembly of IRP1's oxidatively damaged [3Fe4S] cluster. The new findings add to the notion that glucose metabolism is modulated by iron metabolism. Furthermore, we propose that ferritin ferroxidase activity participates in the repair of the IRP1 [3Fe4S] cluster leading to the hypothesis that cytosolic ferritin directly contributes to cellular iron sensing.

Conserved Tao Kinase Activity Regulates Dendritic Arborization, Cytoskeletal Dynamics, and Sensory Function in Drosophila

Dendritic arborization is highly regulated and requires tight control of dendritic growth, branching, cytoskeletal dynamics, and ion channel expression to ensure proper function. Abnormal dendritic development can result in altered network connectivity, which has been linked to neurodevelopmental disorders, including autism spectrum disorders (ASDs). How neuronal growth control programs tune dendritic arborization to ensure function is still not fully understood. Using Drosophila dendritic arborization (da) neurons as a model, we identified the conserved Ste20-like kinase Tao as a negative regulator of dendritic arborization. We show that Tao kinase activity regulates cytoskeletal dynamics and sensory channel localization required for proper sensory function in both male and female flies. We further provide evidence for functional conservation of Tao kinase, showing that its ASD-linked human ortholog, Tao kinase 2 (Taok2), could replace Drosophila Tao and rescue dendritic branching, dynamic microtubule alterations, and behavioral defects. However, several ASD-linked Taok2 variants displayed impaired rescue activity, suggesting that Tao/Taok2 mutations can disrupt sensory neuron development and function. Consistently, we show that Tao kinase activity is required in developing and as well as adult stages for maintaining normal dendritic arborization and sensory function to regulate escape and social behavior. Our data suggest an important role for Tao kinase signaling in cytoskeletal organization to maintain proper dendritic arborization and sensory function, providing a strong link between developmental sensory aberrations and behavioral abnormalities relevant for Taok2-dependent ASDs.SIGNIFICANCE STATEMENT Autism spectrum disorders (ASDs) are linked to abnormal dendritic arbors. However, the mechanisms of how dendritic arbors develop to promote functional and proper behavior are unclear. We identified Drosophila Tao kinase, the ortholog of the ASD risk gene Taok2, as a regulator of dendritic arborization in sensory neurons. We show that Tao kinase regulates cytoskeletal dynamics, controls sensory ion channel localization, and is required to maintain somatosensory function in vivo Interestingly, ASD-linked human Taok2 mutations rendered it nonfunctional, whereas its WT form could restore neuronal morphology and function in Drosophila lacking endogenous Tao. Our findings provide evidence for a conserved role of Tao kinase in dendritic development and function of sensory neurons, suggesting that aberrant sensory function might be a common feature of ASDs.

Impact of Autophagy and Aging on Iron Load and Ferritin in Drosophila Brain

Biometals such as iron, copper, potassium, and zinc are essential regulatory elements of several biological processes. The homeostasis of biometals is often affected in age-related pathologies. Notably, impaired iron metabolism has been linked to several neurodegenerative disorders. Autophagy, an intracellular degradative process dependent on the lysosomes, is involved in the regulation of ferritin and iron levels. Impaired autophagy has been associated with normal pathological aging, and neurodegeneration. Non-mammalian model organisms such as Drosophila have proven to be appropriate for the investigation of age-related pathologies. Here, we show that ferritin is expressed in adult Drosophila brain and that iron and holoferritin accumulate with aging. At whole-brain level we found no direct relationship between the accumulation of holoferritin and a deficit in autophagy in aged Drosophila brain. However, synchrotron X-ray spectromicroscopy revealed an additional spectral feature in the iron-richest region of autophagy-deficient fly brains, consistent with iron-sulfur. This potentially arises from iron-sulfur clusters associated with altered mitochondrial iron homeostasis.

An assessment of the translational relevance of Drosophila in drug discovery

INTRODUCTION

Drosophila melanogaster offers a powerful expedient and economical system with facile genetics. Because of the high sequence and functional conservation with human disease-associated genes, it has been cardinal in deciphering disease mechanisms at the genetic and molecular level. Drosophila are amenable to and respond well to pharmaceutical treatment which coupled to their genetic tractability has led to discovery, repositioning, and validation of a number of compounds. Areas covered: This review summarizes the generation of fly models of human diseases, their advantages and use in elucidation of human disease mechanisms. Representative studies provide examples of the utility of this system in modeling diseases and the discovery, repositioning and testing on pharmaceuticals to ameliorate them. Expert opinion: Drosophila offers a facile and economical whole animal system with many homologous organs to humans, high functional conservation and established methods of generating and validating human disease models. Nevertheless, it remains relatively underused as a drug discovery tool probably because its relevance to mammalian systems remains under question. However, recent exciting success stories using Drosophila disease models for drug screening, repositioning and validation strongly suggest that fly models should figure prominently in the drug discovery pipeline from bench to bedside.

The Tiny Drosophila Melanogaster for the Biggest Answers in Huntington's Disease

The average life expectancy for humans has increased over the last years. However, the quality of the later stages of life is low and is considered a public health issue of global importance. Late adulthood and the transition into the later stage of life occasionally leads to neurodegenerative diseases that selectively affect different types of neurons and brain regions, producing motor dysfunctions, cognitive impairment, and psychiatric disorders that are progressive, irreversible, without remission periods, and incurable. Huntington's disease (HD) is a common neurodegenerative disorder. In the 25 years since the mutation of the huntingtin (HTT) gene was identified as the molecule responsible for this neural disorder, a variety of animal models, including the fruit fly, have been used to study the disease. Here, we review recent research that used Drosophila as an experimental tool for improving knowledge about the molecular and cellular mechanisms underpinning HD.

Iron Sulfur and Molybdenum Cofactor Enzymes Regulate the Drosophila Life Cycle by Controlling Cell Metabolism

Iron sulfur (Fe-S) clusters and the molybdenum cofactor (Moco) are present at enzyme sites, where the active metal facilitates electron transfer. Such enzyme systems are soluble in the mitochondrial matrix, cytosol and nucleus, or embedded in the inner mitochondrial membrane, but virtually absent from the cell secretory pathway. They are of ancient evolutionary origin supporting respiration, DNA replication, transcription, translation, the biosynthesis of steroids, heme, catabolism of purines, hydroxylation of xenobiotics, and cellular sulfur metabolism. Here, Fe-S cluster and Moco biosynthesis in Drosophila melanogaster is reviewed and the multiple biochemical and physiological functions of known Fe-S and Moco enzymes are described. We show that RNA interference of Mocs3 disrupts Moco biosynthesis and the circadian clock. Fe-S-dependent mitochondrial respiration is discussed in the context of germ line and somatic development, stem cell differentiation and aging. The subcellular compartmentalization of the Fe-S and Moco assembly machinery components and their connections to iron sensing mechanisms and intermediary metabolism are emphasized. A biochemically active Fe-S core complex of heterologously expressed fly Nfs1, Isd11, IscU, and human frataxin is presented. Based on the recent demonstration that copper displaces the Fe-S cluster of yeast and human ferredoxin, an explanation for why high dietary copper leads to cytoplasmic iron deficiency in flies is proposed. Another proposal that exosomes contribute to the transport of xanthine dehydrogenase from peripheral tissues to the eye pigment cells is put forward, where the Vps16a subunit of the HOPS complex may have a specialized role in concentrating this enzyme within pigment granules. Finally, we formulate a hypothesis that (i) mitochondrial superoxide mobilizes iron from the Fe-S clusters in aconitase and succinate dehydrogenase; (ii) increased iron transiently displaces manganese on superoxide dismutase, which may function as a mitochondrial iron sensor since it is inactivated by iron; (iii) with the Krebs cycle thus disrupted, citrate is exported to the cytosol for fatty acid synthesis, while succinyl-CoA and the iron are used for heme biosynthesis; (iv) as iron is used for heme biosynthesis its concentration in the matrix drops allowing for manganese to reactivate superoxide dismutase and Fe-S cluster biosynthesis to reestablish the Krebs cycle.

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.

Mitoferrin modulates iron toxicity in a Drosophila model of Friedreich's ataxia

Friedreich's ataxia is the most important recessive ataxia in the Caucasian population. Loss of frataxin expression affects the production of iron-sulfur clusters and, therefore, mitochondrial energy production. One of the pathological consequences is an increase of iron transport into the mitochondrial compartment leading to a toxic accumulation of reactive iron. However, the mechanism underlying this inappropriate mitochondrial iron accumulation is still unknown. Control and frataxin-deficient flies were fed with an iron diet in order to mimic an iron overload and used to assess various cellular as well as mitochondrial functions. We showed that frataxin-deficient flies were hypersensitive toward dietary iron and developed an iron-dependent decay of mitochondrial functions. In the fly model exhibiting only partial frataxin loss, we demonstrated that the inability to activate ferritin translation and the enhancement of mitochondrial iron uptake via mitoferrin upregulation were likely the key molecular events behind the iron-induced phenotype. Both defects were observed during the normal process of aging, confirming their importance in the progression of the pathology. In an effort to further assess the importance of these mechanisms, we carried out genetic interaction studies. We showed that mitoferrin downregulation improved many of the frataxin-deficient conditions, including nervous system degeneration, whereas mitoferrin overexpression exacerbated most of them. Taken together, this study demonstrates the crucial role of mitoferrin dysfunction in the etiology of Friedreich's ataxia and provides evidence that impairment of mitochondrial iron transport could be an effective treatment of the disease.

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.

Glia in Drosophila behavior

Glial cells constitute about 10 % of the Drosophila nervous system. The development of genetic and molecular tools has helped greatly in defining different types of glia. Furthermore, considerable progress has been made in unraveling the mechanisms that control the development and differentiation of Drosophila glia. By contrast, the role of glia in adult Drosophila behavior is not well understood. We here summarize recent work describing the role of glia in normal behavior and in Drosophila models for neurological and behavioral disorders.

Behavioral decline and premature lethality upon pan-neuronal ferritin overexpression in Drosophila infected with a virulent form of Wolbachia

Iron is required for organismal growth. Therefore, limiting iron availability may be a key part of the host’s innate immune response to various pathogens, for example, in Drosophila infected with Zygomycetes. One way the host can transiently reduce iron bioavailability is by ferritin overexpression. To study the effects of neuronal-specific ferritin overexpression on survival and neurodegeneration we generated flies simultaneously over-expressing transgenes for both ferritin subunits in all neurons. We used two independent recombinant chromosomes bearing UAS-Fer1HCH, UAS-Fer2LCH transgenes and obtained qualitatively different levels of late-onset behavioral and lifespan declines. We subsequently discovered that one parental strain had been infected with a virulent form of the bacterial endosymbiont Wolbachia, causing widespread neuronal apoptosis and premature death. This phenotype was exacerbated by ferritin overexpression and was curable by antibiotic treatment. Neuronal ferritin overexpression in uninfected flies did not cause evident neurodegeneration but resulted in a late-onset behavioral decline, as previously reported for ferritin overexpression in glia. The results suggest that ferritin overexpression in the central nervous system of flies is tolerated well in young individuals with adverse manifestations appearing only late in life or under unrelated pathophysiological conditions.

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.

An emerging role for Cullin-3 mediated ubiquitination in sleep and circadian rhythm: insights from Drosophila

Although the neurophysiological correlates of sleep have been thoroughly described, genetic mechanisms that control sleep architecture, long surmised from ethological studies, family histories and clinical observations, have only been investigated during the past decade. Key contributions to the molecular understanding of sleep have come from studies in Drosophila, benefitting from a strong history of circadian rhythm research. For instance, a number of recent papers have highlighted the role of the E3 ubiquitin ligase Cullin-3 in the regulation of circadian rhythm and sleep. We propose that different Cullin-3 substrate adaptors may affect specific molecular pathways and diverse aspects of circadian rhythm and sleep. We have previously shown that mutations in BTBD9, a risk factor for Restless Legs Syndrome (RLS) encoding a Cullin-3 substrate adaptor, lead to reduced dopamine, increased locomotion and sleep fragmentation. Here, we propose that Cullin-3 acts together with BTBD9 to limit the accumulation of iron regulatory proteins in conditions of iron deficiency. Our model is consistent with clinical observations implicating iron homeostasis in the pathophysiology of RLS and predicts that lack of BTBD9 leads to misregulation of cellular iron storage, inactivating the critical biosynthetic enzyme Tyrosine Hydroxylase in dopaminergic neurons, with consequent phenotypic effects on sleep.

Gene duplication, tissue-specific gene expression and sexual conflict in stalk-eyed flies (Diopsidae)

Gene duplication provides an essential source of novel genetic material to facilitate rapid morphological evolution. Traits involved in reproduction and sexual dimorphism represent some of the fastest evolving traits in nature, and gene duplication is intricately involved in the origin and evolution of these traits. Here, we review genomic research on stalk-eyed flies (Diopsidae) that has been used to examine the extent of gene duplication and its role in the genetic architecture of sexual dimorphism. Stalk-eyed flies are remarkable because of the elongation of the head into long stalks, with the eyes and antenna laterally displaced at the ends of these stalks. Many species are strongly sexually dimorphic for eyespan, and these flies have become a model system for studying sexual selection. Using both expressed sequence tag and next-generation sequencing, we have established an extensive database of gene expression in the developing eye-antennal imaginal disc, the adult head and testes. Duplicated genes exhibit narrower expression patterns than non-duplicated genes, and the testes, in particular, provide an abundant source of gene duplication. Within somatic tissue, duplicated genes are more likely to be differentially expressed between the sexes, suggesting gene duplication may provide a mechanism for resolving sexual conflict.