Drosophila mitoferrin is essential for male fertility: evidence for a role of mitochondrial iron metabolism during spermatogenesis

Trace and essential elements as vital components to improve the performance of the male reproductive system: Implications in cell signaling pathways

Successful male fertilization requires the main processes such as normal spermatogenesis, sperm capacitation, hyperactivation, and acrosome reaction. The progress of these processes depends on some endogenous and exogenous factors. So, the optimal level of ions and essential and rare elements such as selenium, zinc, copper, iron, manganese, calcium, and so on in various types of cells of the reproductive system could affect conception and male fertility rates. The function of trace elements in the male reproductive system could be exerted through some cellular and molecular processes, such as the management of active oxygen species, involvement in the action of membrane channels, regulation of enzyme activity, regulation of gene expression and hormone levels, and modulation of signaling cascades. In this review, we aim to summarize the available evidence on the role of trace elements in improving male reproductive performance. Also, special attention is paid to the cellular aspects and the involved molecular signaling cascades.

Mitochondrial Differentiation during Spermatogenesis: Lessons from Drosophila melanogaster

Numerous diseases can arise as a consequence of mitochondrial malfunction. Hence, there is a significant focus on studying the role of mitochondria in cancer, ageing, neurodegenerative diseases, and the field of developmental biology. Mitochondria could exist as discrete organelles in the cell; however, they have the ability to fuse, resulting in the formation of interconnected reticular structures. The dynamic changes between these forms correlate with mitochondrial function and mitochondrial health, and consequently, there is a significant scientific interest in uncovering the specific molecular constituents that govern these transitions. Moreover, the specialized mitochondria display a wide array of variable morphologies in their cristae formations. These inner mitochondrial structures are closely associated with the specific functions performed by the mitochondria. In multiple cases, the presence of mitochondrial dysfunction has been linked to male sterility, as it has been observed to cause a range of abnormal spermatogenesis and sperm phenotypes in different species. This review aims to elucidate the dynamic alterations and functions of mitochondria in germ cell development during the spermatogenesis of Drosophila melanogaster.

Male vitellogenin regulates gametogenesis through a testis-enriched big protein in Chrysopa pallens

In insects, vitellogenin (Vg) is generally viewed as a female-specific protein. Its primary function is to supply nutrition to developing embryos. Here, we reported Vg from the male adults of a natural predator, Chrysopa pallens. The male Vg was depleted by RNAi. Mating with Vg-deficient male downregulated female Vg expression, suppressed ovarian development and decreased reproductive output. Whole-organism transcriptome analysis after male Vg knockdown showed no differential expression of the known spermatogenesis-related regulators and seminal fluid protein genes, but a sharp downregulation of an unknown gene, which encodes a testis-enriched big protein (Vcsoo). Separate knockdown of male Vg and Vcsoo disturbed the assembly of spermatid cytoplasmic organelles in males and suppressed the expansion of ovary germarium in mated females. These results demonstrated that C. pallens male Vg signals through the downstream Vcsoo and regulates male and female reproduction.

Emerging roles of ferroptosis in male reproductive diseases

Ferroptosis is a type of programmed cell death mediated by iron-dependent lipid peroxidation that leads to excessive lipid peroxidation in different cells. Ferroptosis is distinct from other forms of cell death and is associated with various diseases. Iron is essential for spermatogenesis and male reproductive function. Therefore, it is not surprising that new evidence supports the role of ferroptosis in testicular injury. Although the molecular mechanism by which ferroptosis induces disease is unknown, several genes and pathways associated with ferroptosis have been linked to testicular dysfunction. In this review, we discuss iron metabolism, ferroptosis, and related regulatory pathways. In addition, we analyze the endogenous and exogenous factors of ferroptosis in terms of iron metabolism and testicular dysfunction, as well as summarize the relationship between ferroptosis and male reproductive dysfunction. Finally, we discuss potential strategies to target ferroptosis for treating male reproductive diseases and provide new directions for preventing male reproductive diseases.

Membrane Transporters Involved in Iron Trafficking: Physiological and Pathological Aspects

Iron is an essential transition metal for its involvement in several crucial biological functions, the most notable being oxygen storage and transport. Due to its high reactivity and potential toxicity, intracellular and extracellular iron levels must be tightly regulated. This is achieved through transport systems that mediate cellular uptake and efflux both at the level of the plasma membrane and on the membranes of lysosomes, endosomes and mitochondria. Among these transport systems, the key players are ferroportin, the only known transporter mediating iron efflux from cells; DMT1, ZIP8 and ZIP14, which on the contrary, mediate iron influx into the cytoplasm, acting on the plasma membrane and on the membranes of lysosomes and endosomes; and mitoferrin, involved in iron transport into the mitochondria for heme synthesis and Fe-S cluster assembly. The focus of this review is to provide an updated view of the physiological role of these membrane proteins and of the pathologies that arise from defects of these transport systems.

RpS3 Is Required for Spermatogenesis of Drosophila melanogaster

Ribosomal proteins (RPs) constitute the ribosome, thus participating in the protein biosynthesis process. Emerging studies have suggested that many RPs exhibit different expression levels across various tissues and function in a context-dependent manner for animal development. Drosophila melanogaster RpS3 encodes the ribosomal protein S3, one component of the 40S subunit of ribosomes. We found that RpS3 is highly expressed in the reproductive organs of adult flies and its depletion in male germline cells led to severe defects in sperm production and male fertility. Immunofluorescence staining showed that RpS3 knockdown had little effect on early germ cell differentiation, but strongly disrupted the spermatid elongation and individualization processes. Furthermore, we observed abnormal morphology and activity of mitochondrial derivatives in the elongating spermatids of RpS3-knockdown testes, which could cause the failure of axoneme elongation. We also found that RpS3 RNAi inhibited the formation of the individualization complex that takes charge of disassociating the spermatid bundle. In addition, excessive apoptotic cells were detected in the RpS3-knockdown testes, possibly to clean the defective spermatids. Together, our data demonstrated that RpS3 plays an important role in regulating spermatid elongation and individualization processes and, therefore, is required for normal Drosophila spermatogenesis.

Mitoferrin-1 Promotes Proliferation and Abrogates Protein Oxidation via the Glutathione Pathway in Glioblastoma

Median overall survival is very low in patients with glioblastoma (GBM), largely because these tumors become resistant to therapy. Recently, we found that a decrease in the cytosolic labile iron pool underlies the acquisition of radioresistance. Both cytosolic and mitochondrial iron are important for regulating ROS production, which largely facilitates tumor progression and response to therapy. Here, we investigated the role of the mitochondrial iron transporters mitoferrin-1 (MFRN1) and mitoferrin-2 (MFRN2) in GBM progression. Analysis of The Cancer Genome Atlas database revealed upregulation of MFRN1 mRNA and downregulation of MFRN2 mRNA in GBM tumor tissue compared with non-GBM tissue, yet only the tumor expression level of MFRN1 mRNA negatively correlated with overall survival in patients. Overexpression of MFRN1 in glioma cells significantly increased the level of mitochondrial iron, enhanced the proliferation rate and anchorage-independent growth of these cells, and significantly decreased mouse survival in an orthotopic model of glioma. Finally, MFRN1 overexpression stimulated the upregulation of glutathione, which protected glioma cells from 4-hydroxynonenal-induced protein damage. Overall, these results demonstrate a mechanistic link between MFRN1-mediated mitochondrial iron metabolism and GBM progression. Manipulation of MFRN1 may provide a new therapeutic strategy for improving clinical outcomes in patients with GBM.

Cytochrome c1-like is required for mitochondrial morphogenesis and individualization during spermatogenesis in Drosophila melanogaster

The Drosophila testis is an excellent system for studying the process from germ stem cells to motile sperm, including the proliferation of male germ cells, meiosis of primary spermatocytes, mitochondrial morphogenesis, and spermatid individualization. We previously demonstrated that ocnus (ocn) plays an essential role in male germ cell development. Among those genes and proteins whose expression levels were changed as a result of ocn knockdown, cytochrome c1-like (cyt-c1L) was downregulated significantly. Here, we show that cyt-c1L is highly expressed in the testis of D. melanogaster. Knockdown or mutation of cyt-c1L in early germ cells of flies resulted in male sterility. Immunofluorescence staining showed that cyt-c1L knockdown testes had no defects in early spermatogenesis; however, in late stages, in contrast to many individualization complexes (ICs) composed of F-actin cones that appeared at different positions in control testes, no actin cones or ICs were observed in cyt-c1L knockdown testes. Furthermore, no mature sperm were found in the seminal vesicle of cyt-c1L knockdown testes whereas the control seminal vesicle was full of mature sperm with needle-like nuclei. cyt-c1L knockdown also caused abnormal mitochondrial morphogenesis during spermatid elongation. Excessive apoptotic signals accumulated in the base of cyt-c1L knockdown fly testes. These results suggest that cyt-c1L may play an important role in spermatogenesis by affecting the mitochondrial morphogenesis and individualization of sperm in D. melanogaster.

Ferroptosis: A Novel Type of Cell Death in Male Reproduction

Ferroptosis, an iron-dependent type of regulated cell death, is triggered by the accumulation of lethal lipid peroxides. Due to its potential in exploring disease progression and highly targeted therapies, it is still a widely discussed topic nowadays. In recent studies, it was found that ferroptosis was induced when testicular tissue was exposed to some high-risk factors, such as cadmium (Cd), busulfan, and smoking accompanied by a variety of reproductive damage characteristics, including changes in the specific morphology and ferroptosis-related features. In this literature-based review, we summarize the related mechanisms of ferroptosis and elaborate upon its relationship network in the male reproductive system in terms of three significant events: the abnormal iron metabolism, dysregulation of the Cyst(e)ine/GSH/GPX4 axis, and lipid peroxidation. It is meaningful to deeply explore the relationship between ferroptosis and the male reproductive system, which may provide suggestions regarding pristine therapeutic targets and novel drugs.

Are There Associations between Seminal Plasma Advanced Oxidation Protein Products and Selected Redox-Associated Biochemical Parameters in Infertile Male Patients? A Preliminary Report

Oxidative stress (OS) is one of the reasons for male infertility. Seminal plasma contains a multitude of enzymes and ions which influence OS and thus may affect male fertility. The aim of the study was to check for associations between seminal plasma advanced oxidation protein products (AOPP) concentrations and levels of selected biochemical parameters (total protein, iron, uric acid, magnesium, calcium) in infertile men, and establish whether they are associated with sperm disorders. Seminal plasma AOPP, as well as total protein, iron, uric acid, calcium, and magnesium concentrations, were determined for the following patient groups: normozoospermic (N; n = 33), teratozoospermic (T; n = 30), asthenoteratozoospermic (AT; n = 18), and oligoasthenoteratozoospermic (OAT; n = 28). AOPP concentrations were significantly higher in N and T groups in comparison to AT and OAT groups. Total protein concentrations were significantly lower in the T group in comparison to the AT and OAT groups, whereas iron concentrations significantly decreased in the OAT group in comparison to the T and N patients. AOPP differentiates AT patients from men with other sperm disorders. Our results suggest that asthenozoospermia may be connected with total protein levels. Insufficient iron levels may reflect a decrease in sperm count.

Mitoferrin, Cellular and Mitochondrial Iron Homeostasis

Iron is essential for many cellular processes, but cellular iron homeostasis must be maintained to ensure the balance of cellular signaling processes and prevent disease. Iron transport in and out of the cell and cellular organelles is crucial in this regard. The transport of iron into the mitochondria is particularly important, as heme and the majority of iron-sulfur clusters are synthesized in this organelle. Iron is also required for the production of mitochondrial complexes that contain these iron-sulfur clusters and heme. As the principal iron importers in the mitochondria of human cells, the mitoferrins have emerged as critical regulators of cytosolic and mitochondrial iron homeostasis. Here, we review the discovery and structure of the mitoferrins, as well as the significance of these proteins in maintaining cytosolic and mitochondrial iron homeostasis for the prevention of cancer and many other diseases.

Effects of Ferroptosis on Male Reproduction

Ferroptosis is a relatively novel form of regulated cell death that was discovered in 2012. With the increasing research related to the mechanisms of ferroptosis, previous studies have demonstrated that the inactive of the intracellular antioxidant system and iron overload can result in the accumulation of reactive oxygen species (ROS), which can ultimately cause lipid peroxidation in the various cell types of the body. ROS accumulation can cause sperm damage by attacking the plasma membrane and damaging DNA. Acute ferroptosis causes oxidative damage to sperm DNA and testicular oxidative stress, thereby causing male reproductive dysfunction. This review aims to discuss the metabolic network of ferroptosis, summarize and analyze the relationship between male reproductive diseases caused by iron overload as well as lipid peroxidation, and provide a novel direction for the research and prevention of various male reproductive diseases.

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 Effects of Essential and Non-Essential Metal Toxicity in the Drosophila melanogaster Insect Model: A Review

The biological effects of environmental metal contamination are important issues in an industrialized, resource-dependent world. Different metals have different roles in biology and can be classified as essential if they are required by a living organism (e.g., as cofactors), or as non-essential metals if they are not. While essential metal ions have been well studied in many eukaryotic species, less is known about the effects of non-essential metals, even though essential and non-essential metals are often chemically similar and can bind to the same biological ligands. Insects are often exposed to a variety of contaminated environments and associated essential and non-essential metal toxicity, but many questions regarding their response to toxicity remain unanswered. Drosophila melanogaster is an excellent insect model species in which to study the effects of toxic metal due to the extensive experimental and genetic resources available for this species. Here, we review the current understanding of the impact of a suite of essential and non-essential metals (Cu, Fe, Zn, Hg, Pb, Cd, and Ni) on the D. melanogaster metal response system, highlighting the knowledge gaps between essential and non-essential metals in D. melanogaster. This review emphasizes the need to use multiple metals, multiple genetic backgrounds, and both sexes in future studies to help guide future research towards better understanding the effects of metal contamination in general.

The association between metal exposure and semen quality in Chinese males: The mediating effect of androgens

As a crucial factor in male reproduction, androgens may represent an intermediate biological mechanism linking metal exposure with effects on semen quality. This study aimed to investigate the association between metal exposure and semen quality, and to assess the mediating role of seminal androgens between metal exposure and semen quality. We investigated the presence of 10 metals in semen and assessed their effect on semen quality in 1136 men recruited from a hospital in Shenzhen, China. Of these, 464 subjects were randomly selected for 4 androgens detection in semen. Cross-sectional associations between single/multiple metals, androgen levels and semen quality were explored by multivariable linear regressions. Mediation analysis was performed to detect the role of seminal androgens on the association between metal exposure and semen quality. Seminal selenium and iron were positively associated with both sperm concentration and total sperm count. Negative associations were observed between both manganese and zinc and sperm concentration, molybdenum and total sperm count, copper and sperm motility. Furthermore, we found significant dose-dependent relationships between both iron and selenium levels and dihydrotestosterone (DHT), arsenic levels and testosterone, as well as zinc and dehydroepiandrosterone. Mediation analysis indicated that higher seminal iron and selenium were associated with an increasing sperm concentration after controlling for DHT, with 10.32% and 12.89% of these associations were mediated by DHT, respectively. A similar mediation effect of DHT was observed in the associations between iron and selenium levels and total sperm count (13.39% and 21.57% mediation, respectively). Our findings suggested that the presence of selenium and iron in semen was beneficial to sperm concentration and total count. Seminal manganese, zinc, molybdenum and copper may be associated with reduced semen quality. The associations between seminal selenium and iron and sperm concentration and total count were partially explained by the concomitant variation of seminal DHT.

Drosophila melanogaster Mitochondrial Carriers: Similarities and Differences with the Human Carriers

Mitochondrial carriers are a family of structurally related proteins responsible for the exchange of metabolites, cofactors and nucleotides between the cytoplasm and mitochondrial matrix. The in silico analysis of the Drosophila melanogaster genome has highlighted the presence of 48 genes encoding putative mitochondrial carriers, but only 20 have been functionally characterized. Despite most Drosophila mitochondrial carrier genes having human homologs and sharing with them 50% or higher sequence identity, D. melanogaster genes display peculiar differences from their human counterparts: (1) in the fruit fly, many genes encode more transcript isoforms or are duplicated, resulting in the presence of numerous subfamilies in the genome; (2) the expression of the energy-producing genes in D. melanogaster is coordinated from a motif known as Nuclear Respiratory Gene (NRG), a palindromic 8-bp sequence; (3) fruit-fly duplicated genes encoding mitochondrial carriers show a testis-biased expression pattern, probably in order to keep a duplicate copy in the genome. Here, we review the main features, biological activities and role in the metabolism of the D. melanogaster mitochondrial carriers characterized to date, highlighting similarities and differences with their human counterparts. Such knowledge is very important for obtaining an integrated view of mitochondrial function in D. melanogaster metabolism.

Potential risk of organophosphate exposure in male reproductive system of a non-target insect model Drosophila melanogaster

Based on several adverse reports of pesticides on reproductive efficiency of various organisms, studies on "reproductive toxicity" have gained importance. Fecundity, reflecting reproductive success of any organism, is governed by several factors from female and male reproductive systems. This present study explored morphological and biochemical alterations in the male reproductive system of a non-target model organism, Drosophila melanogaster following chronic sub-lethal exposure (1^st instar larvae differentially exposed to 1-6 μg/mL until adulthood) to the organophosphate (OP) pesticide, acephate (chronic LC₅₀ 8.71 μg/mL). This study demonstrates altered testis structure, decreased germ cell viability and gross body weight, increased activities of oxidative stress marker lipid peroxidase (LPO), and the endogenous antioxidant enzyme catalase (CAT)in addition with altered expression of reproductive marker proteins like vitellogenin and mitoferrin in acephate-exposed flies when compared to control counterparts. Altered reproductive behavior, indicated by a significant decline in the number of mating pairs, validates the adverse effect of chronic acephate exposure on male reproduction in the non-target insect model D. melanogaster.

Maelstrom regulates spermatogenesis of the silkworm, Bombyx mori

The spermatogenesis of animal is essential for the reproduction and a very large number of genes participate in this procession. The Maelstrom (Mael) is identified essential for spermatogenesis in both Drosophila and mouse, though the mechanisms appear to differ. It was initially found that Mael gene is necessary for axis specification of oocytes in Drosophila, and recent studies suggested that Mael participates in the piRNA pathway. In this study, we obtained Bombyx mori Mael mutants by using a binary transgenic CRISPR/Cas9 system and analyzed the function of Mael in B. mori, a model lepidopteran insect. The results showed that BmMael is not necessary for piRNA pathway in the ovary of silkworm, whereas it might be essential for transposon elements (TEs) repression in testis. The BmMael mutation resulted in male sterility, and further analysis established that BmMael was essential for spermatogenesis. The spermatogenesis defects occurred in the elongation stage and resulted in nuclei concentration arrest. RNA-seq and qRT-PCR analyses demonstrated that spermatogenesis defects were associated with tight junctions and apoptosis. We also found that BmMael was not involved in the silkworm sex determination pathway. Our data provide insights into the biological function of BmMael in male spermatogenesis and might be useful for developing novel methods to control lepidopteron pests.

Microelements in seminal and serum plasma are associated with fresh semen quality in Yorkshire boars

This study aimed to explore associations between semen quality and trace element level in serum and seminal plasma in Yorkshire boars. Semen quality of 112 Yorkshire boars was assessed for 13 weeks to calculate semen utilization rate, which was then divided into three categories: low utilization rate group (LG, < 60% utilization rate), medium utilization rate group (MG, 60-80%), and high utilization rate group (HG, > 80%). After grouping, serum and seminal plasma samples of selected boars were collected to determine concentrations of 10 elements including Ca, Mg, Cu, Fe, Zn, Mn, Se, Cr, Pb and Cd using inductively coupled plasma mass spectrometry. Results showed the increase of semen utilization rate was accompanied by the increase of sperm motility and the decrease of abnormal sperm rate among three groups (P < 0.01). Serum Fe concentration in LG boars was lower than that in HG boars (P < 0.05). Regression analysis revealed serum Fe concentration was positively correlated with sperm motility (r = 0.251; P < 0.05), while negatively correlated with abnormal sperm rate (r = -0.207; P < 0.05). However, MG and HG boars had lower serum Se concentration than LG boars (P < 0.05), and serum Se concentration contribution to sperm motility varied in a quadratic manner (Sperm motility = -0.0004 Se_(serum)² +0.136 Se+74.06; r = 0.300; P < 0.01). Semen utilization rate tended to decrease with the increase of seminal plasma Pb concentration (P = 0.09). Regression analysis exhibited seminal plasma Pb negatively related to sperm motility (r = -0.237; P < 0.05), while positively correlated with abnormal sperm rate (r = 0.237; P < 0.05). Furthermore, seminal plasma Pb was the most influential factor among trace element in serum and seminal plasma on sperm motility basing on the generalized linear model analysis (P < 0.05). Sperm motility decreased by approximately 3.47% when seminal plasma Pb concentration increased from 0 μg/L to 11.16 μg/L. In conclusion, deficiency of serum Fe reduces semen utilization rate by impairing sperm motility and morphology, whereas excessive serum Se decreases sperm motility. More importantly, the mere existence of seminal plasma Pb has more impact on semen quality than other trace elements in serum and seminal plasma in Yorkshire boars.

Glycoprotein Hormone Receptor Knockdown Leads to Reduced Reproductive Success in Male Aedes aegypti

Glycoprotein hormone receptors mediate a diverse range of physiological functions in vertebrate and invertebrate organisms. The heterodimeric glycoprotein hormone GPA2/GPB5 and its receptor LGR1, constitute a recently discovered invertebrate neuroendocrine signaling system that remains to be functionally characterized. We previously reported that LGR1 is expressed in the testes of adult Aedes aegypti mosquitoes, where its immunoreactivity is particularly regionalized. Here, we show that LGR1 immunoreactivity is associated with the centriole adjunct of spermatids and is observed transiently during spermatogenesis in mosquitoes, where it may act to mediate the regulation of flagellar development. RNA interference to downregulate LGR1 expression was accomplished by feeding mosquito larvae with bacteria that produced LGR1-specific dsRNA, which led to defects in spermatozoa, characterized with shortened flagella. LGR1 knockdown mosquitoes also retained ∼60% less spermatozoa in reproductive organs and demonstrated reduced fertility compared to controls. To date, the endocrine regulation of spermatogenesis in mosquitoes remains an understudied research area. The distribution of LGR1 and detrimental effects of its knockdown on spermatogenesis in A. aegypti indicates that this heterodimeric glycoprotein hormone signaling system contributes significantly to the regulation of male reproductive biology in this important disease-vector.

Prolonged Bat Call Exposure Induces a Broad Transcriptional Response in the Male Fall Armyworm (Spodoptera frugiperda; Lepidoptera: Noctuidae) Brain

Predation risk induces broad behavioral and physiological responses that have traditionally been considered acute and transitory. However, prolonged or frequent exposure to predators and the sensory cues of their presence they broadcast to the environment impact long-term prey physiology and demographics. Though several studies have assessed acute and chronic stress responses in varied taxa, these attempts have often involved a priori expectations of the molecular pathways involved in physiological responses, such as glucocorticoid pathways and neurohormone production in vertebrates. While relatively little is known about physiological and molecular predator-induced stress in insects, many dramatic insect defensive behaviors have evolved to combat selection by predators. For instance, several moth families, such as Noctuidae, include members equipped with tympanic organs that allow the perception of ultrasonic bat calls and facilitate predation avoidance by eliciting evasive aerial flight maneuvers. In this study, we exposed adult male fall armyworm (Spodoptera frugiperda) moths to recorded ultrasonic bat foraging and attack calls for a prolonged period and constructed a de novo transcriptome based on brain tissue from predator cue-exposed relative to control moths kept in silence. Differential expression analysis revealed that 290 transcripts were highly up- or down-regulated among treatment tissues, with many annotating to noteworthy proteins, including a heat shock protein and an antioxidant enzyme involved in cellular stress. Though nearly 50% of differentially expressed transcripts were unannotated, those that were are implied in a broad range of cellular functions within the insect brain, including neurotransmitter metabolism, ionotropic receptor expression, mitochondrial metabolism, heat shock protein activity, antioxidant enzyme activity, actin cytoskeleton dynamics, chromatin binding, methylation, axonal guidance, cilia development, and several signaling pathways. The five most significantly overrepresented Gene Ontology terms included chromatin binding, macromolecular complex binding, glutamate synthase activity, glutamate metabolic process, and glutamate biosynthetic process. As a first assessment of transcriptional responses to ecologically relevant auditory predator cues in the brain of moth prey, this study lays the foundation for examining the influence of these differentially expressed transcripts on insect behavior, physiology, and life history within the framework of predation risk, as observed in ultrasound-sensitive Lepidoptera and other 'eared' insects.

Metal tolerance protein MTP6 affects mitochondrial iron and manganese homeostasis in cucumber

Members of the cation diffusion facilitator (CDF) family have been identified in all kingdoms of life. They have been divided into three subgroups, namely Zn-CDF, Fe/Zn-CDF, and Mn-CDF, based on their putative specificity to transported metal ions. The plant metal tolerance protein 6 (MTP6) proteins fall into the Fe/Zn-CDF subgroup; however, their function in iron/zinc transport has not yet been confirmed. Here, we characterized the MTP6 protein from cucumber, Cucumis sativus. When expressed in yeast and in protoplasts isolated from Arabidopsis cells, CsMTP6 localized in mitochondria and contributed to the efflux of Fe and Mn from these organelles. Immunolocalization of CsMTP6 in cucumber membranes confirmed this association with mitochondria. Root expression and protein levels of CsMTP6 were significantly up-regulated in conditions of Fe deficiency and excess, but were not affected by Mn availability. These results indicate that MTP6 proteins contribute to the distribution of Fe and Mn between the cytosol and mitochondria of plant cells, and are regulated by Fe to maintain mitochondrial and cytosolic iron homeostasis under varying conditions of Fe availability.

FAM210B is an erythropoietin target and regulates erythroid heme synthesis by controlling mitochondrial iron import and ferrochelatase activity

Erythropoietin (EPO) signaling is critical to many processes essential to terminal erythropoiesis. Despite the centrality of iron metabolism to erythropoiesis, the mechanisms by which EPO regulates iron status are not well-understood. To this end, here we profiled gene expression in EPO-treated 32D pro-B cells and developing fetal liver erythroid cells to identify additional iron regulatory genes. We determined that FAM210B, a mitochondrial inner-membrane protein, is essential for hemoglobinization, proliferation, and enucleation during terminal erythroid maturation. Fam210b deficiency led to defects in mitochondrial iron uptake, heme synthesis, and iron-sulfur cluster formation. These defects were corrected with a lipid-soluble, small-molecule iron transporter, hinokitiol, in Fam210b-deficient murine erythroid cells and zebrafish morphants. Genetic complementation experiments revealed that FAM210B is not a mitochondrial iron transporter but is required for adequate mitochondrial iron import to sustain heme synthesis and iron-sulfur cluster formation during erythroid differentiation. FAM210B was also required for maximal ferrochelatase activity in differentiating erythroid cells. We propose that FAM210B functions as an adaptor protein that facilitates the formation of an oligomeric mitochondrial iron transport complex, required for the increase in iron acquisition for heme synthesis during terminal erythropoiesis. Collectively, our results reveal a critical mechanism by which EPO signaling regulates terminal erythropoiesis and iron metabolism.

Cucumber metal tolerance protein 7 (CsMTP7) is involved in the accumulation of Fe in mitochondria under Fe excess

The plant metal tolerance protein family (MTP) includes 12 members that have been classified into three phylogenetically different subgroups - Zn-cation diffusion facilitator (CDF), Fe/Zn-CDF and Mn-CDF - based on their putative metal specificity. To date, only members belonging to the Zn-CDF or Mn-CDF group have been characterized functionally. The plant Fe/Zn-CDF subgroup includes two proteins, MTP6 and MTP7, but their function and metal specificity have not been confirmed. In this study we showed that cucumber CsMTP7 is a highly specific mitochondrial Fe importer that is able to confer yeast tolerance to Fe excess through increased accumulation of Fe in the mitochondria. We also demonstrated that CsMTP7 contributes to the increased accumulation of Fe in the mitochondria of Arabidopsis thaliana protoplasts. The transcripts and mitochondrial levels of CsMTP7 and ferritin - the iron-storing protein - are significantly increased in cucumber roots in response to Fe excess. This finding suggests that CsMTP7 and ferritin work in concert to accumulate Fe in plant mitochondria. As genes that encode orthologous proteins have been identified in phylogenetically distant organisms, including Archaea, cyanobacteria, humans and plants, but not in yeast, we concluded that the MTP7-mediated mitochondrial Fe accumulation may be conserved in the species, and express mitochondrial ferritin for mitochondrial Fe storage.

Iron and a Man's Reproductive Health: the Good, the Bad, and the Ugly

PURPOSE OF REVIEW

To discuss the physiologic and pathologic effects of iron on men's reproductive health.

RECENT FINDINGS

Iron overload diseases are associated with hypogonadotropic hypogonadism, infertility, and sexual dysfunction in men. Recent findings have elucidated the roles by which iron may affect the male reproductive axis. Iron is requisite for life. Iron can also catalyze the production of reactive oxygen species. To maintain balance, the human body tightly regulates dietary iron absorption. Severe iron overload disorders-e.g., hereditary hemochromatosis and β-thalassemia-occur when these regulatory mechanisms are deficient. While iron is necessary, the male reproductive system is particularly sensitive to iron overload. Hypogonadotropic hypogonadism, infertility, and sexual dysfunction commonly occur if excess iron from iron overload disorders is not removed. The average male in the USA consumes significantly more iron than needed to replace daily losses. How this degree of iron loading may affect one's reproductive health remains less clear, but there is evidence it may have adverse effects.

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.

67Ga as a biosensor of iron needs in different organs: Study performed on male and female rats subjected to iron deficiency and exercise

The aim of the present study was to determine the iron needs in different organs and tissues using ⁶⁷Ga as a biosensor in males and females rats subjected to iron deficiency (ID) and voluntary exercise (EX). ⁶⁷Ga citrate was injected i.p. to female and male Wistar rats (n=5/sex/group). Groups: Control (sedentary conditions), Control+EX, ID and ID+EX. To determine the ⁶⁷Ga uptake, samples from the following regions of interest (ROIs) were extracted 12h post-injection: blood, liver, gonads, bone marrow, heart, adrenal glands, skeletal muscle, stomach, kidney, eyeball, sciatic nerve, small intestine and peritoneum. The total ⁶⁷Ga uptake was 412% higher in ID subjects than in control subjects, being 1011% higher in ID-males than ID-females. In ID-females, the ROIs with the greater ⁶⁷Ga uptake were blood, kidney and bone marrow, while in ID-males they were sciatic nerve, eyeball and adrenals, which demonstrates that the biodistribution differed between sexes in sedentary conditions but when subjected to EX, the biodistribution was similar in each sex group although females had a greater ⁶⁷Ga uptake. In ID+EX subjects, the ROIs that showed the highest uptake were sciatic nerve, eyeball and adrenal glands. Using ⁶⁷Ga as a biosensor, it is possible to identify the needs of iron that each organ requires to perform their functions in normal physiological conditions. In addition, a higher or lower ⁶⁷Ga uptake in a specific organ may indicate its malfunction or show damage.

Pathological changes in Sertoli cells and dysregulation of divalent metal transporter 1 with iron responsive element in the testes of idiopathic azoospermia patients

Iron is essential for rapidly dividing spermatocytes during normal mammalian spermatogenesis. Decreased transferrin and transferrin receptor levels were observed in seminal plasma from idiopathic azoospermia (IA) patients, suggesting disturbed iron metabolism in IA testes. However, how Sertoli cells (SCs) contribute to the iron homoeostasis in IA is still unclear. In this study, we analysed 30 IA and 30 age-matched obstructive azoospermia (OA) patients undergoing testicular sperm aspiration (TESA). SCs hyperplasia was indicated by higher SC density and Ki-67 labelling index in the IA TESA specimens. The attenuated expression of superoxide dismutase (SOD) suggested an impaired antioxidative capacity in IA testes. We further detected increased levels of iron importer divalent metal transporter 1 with iron responsive element (DMT1 + IRE) in IA testes, whereas the increasing trend of iron exporter ferroportin 1 (FPN1) was not statistically significant. Next, we demonstrated that iron regulatory protein 1 (IRP1) and hypoxia-inducible factor-1α (HIF-1α), which can potentially bind to the IRE and hypoxia-responsive element in the DMT1 + IRE mRNA, were both up-regulated in IA testes. Unexpectedly, HIF-2α was down-regulated in IA testes. These results indicate that there is a dysregulation of DMT1 + IRE in IA testes, which might due to the up-regulation of IRP1 and HIF-1α.

Mitochondrial ferritin deficiency reduces male fertility in mice

Mitochondrial ferritin (FtMt) is a functional ferritin targeted to mitochondria that is highly expressed in the testis. To investigate the role of FtMt in the testis we set up a series of controlled matings between FtMt gene-deletion mice (FtMt–/–) with FtMt+/+ mice. We found that the number of newborns per litter and the fertility rate were strongly reduced for the FtMt–/– males, but not for the females, indicating that FtMt has an important role for male fertility. The morphology of the testis and of the spermatozoa of FtMt–/– mice was normal and we did not detect alterations in sperm parameters or in oxidative stress indices. In contrast, we observed that the cauda epididymides of FtMt–/– mice were significantly lighter and contained a lower number of spermatozoa compared with the controls. Also, the ATP content of FtMt–/– spermatozoa was found to be lower than that of FtMt+/+ spermatozoa. These data show that FtMt contributes to sperm epididymis maturation and to male fertility.

Identification of SLC25A37 as a major depressive disorder risk gene

Major depressive disorder (MDD) is one of the most prevalent and disabling mental disorders, but the genetic etiology remains largely unknown. We performed a meta-analysis (14,543 MDD cases and 14,856 controls) through combining the GWAS data from the Major Depressive Disorder Working Group of the Psychiatric GWAS Consortium and the CONVERGE consortium and identified seven SNPs (four of them located in the downstream of SCL25A37) that showed suggestive associations (P < 5.0 × 10^-7) with MDD. Systematic integration (Sherlock integrative analysis) of brain eQTL and GWAS meta-analysis identified SCL25A37 as a novel MDD risk gene (P = 2.22 × 10^-6). A cis SNP (rs6983724, ∼28 kb downstream of SCL25A37) showed significant association with SCL25A37 expression (P = 1.19 × 10^-9) and suggestive association with MDD (P = 1.65 × 10^-7). We validated the significant association between rs6983724 and SCL25A37 expression in independent expression datasets. Finally, we found that SCL25A37 is significantly down-regulated in hippocampus and blood of MDD patients (P = 3.49 × 10^-3 and P = 2.66 × 10^-13, respectively). Our findings implicate that the SCL25A37 is a MDD susceptibility gene whose expression may influence MDD risk. The consistent down-regulation of SCL25A37 in MDD patients in three independent samples suggest that SCL25A37 may be used as a potential biomarker for MDD diagnosis. Further functional characterization of SCL25A37 may provide a potential target for future therapeutics and diagnostics.

Green tea polyphenols require the mitochondrial iron transporter, mitoferrin, for lifespan extension in Drosophila melanogaster

Green tea has been found to increase the lifespan of various experimental animal models including the fruit fly, Drosophila melanogaster. High in polyphenolic content, green tea has been shown to reduce oxidative stress in part by its ability to bind free iron, a micronutrient that is both essential for and toxic to all living organisms. Due to green tea's iron-binding properties, we questioned whether green tea acts to increase the lifespan of the fruit fly by modulating iron regulators, specifically, mitoferrin, a mitochondrial iron transporter, and transferrin, found in the hemolymph of flies. Publicly available hypomorph mutants for these iron regulators were utilized to investigate the effect of green tea on lifespan and fertility. We identified that green tea could not increase the lifespan of mitoferrin mutants but did rescue the reduced male fertility phenotype. The effect of green tea on transferrin mutant lifespan and fertility were comparable to w¹¹¹⁸ flies, as observed in our previous studies, in which green tea increased male fly lifespan and reduced male fertility. Expression levels in both w¹¹¹⁸ flies and mutant flies, supplemented with green tea, showed an upregulation of mitoferrin but not transferrin. Total body and mitochondrial iron levels were significantly reduced by green tea supplementation in w¹¹¹⁸ and mitoferrin mutants but not transferrin mutant flies. Our results demonstrate that green tea may act to increase the lifespan of Drosophila in part by the regulation of mitoferrin and reduction of mitochondrial iron.

Testis-Specific Bb8 Is Essential in the Development of Spermatid Mitochondria

Mitochondria are essential organelles of developing spermatids in Drosophila, which undergo dramatic changes in size and shape after meiotic division, where mitochondria localized in the cytoplasm, migrate near the nucleus, aggregate, fuse and create the Nebenkern. During spermatid elongation the two similar mitochondrial derivatives of the Nebenkern start to elongate parallel to the axoneme. One of the elongated mitochondrial derivatives starts to lose volume and becomes the minor mitochondrial derivative, while the other one accumulates paracrystalline and becomes the major mitochondrial derivative. Proteins and intracellular environment that are responsible for cyst elongation and paracrystalline formation in the major mitochondrial derivative need to be identified. In this work we investigate the function of the testis specific big bubble 8 (bb8) gene during spermatogenesis. We show that a Minos element insertion in bb8 gene, a predicted glutamate dehydrogenase, causes recessive male sterility. We demonstrate bb8 mRNA enrichment in spermatids and the mitochondrial localisation of Bb8 protein during spermatogenesis. We report that megamitochondria develop in the homozygous mutant testes, in elongating spermatids. Ultrastructural analysis of the cross section of elongated spermatids shows enlarged mitochondria and the production of paracrystalline in both major and minor mitochondrial derivatives. Our results suggest that the Bb8 protein and presumably glutamate metabolism has a crucial role in the normal development and establishment of the identity of the mitochondrial derivatives during spermatid elongation.

The Structure of the Complex between Yeast Frataxin and Ferrochelatase: CHARACTERIZATION AND PRE-STEADY STATE REACTION OF FERROUS IRON DELIVERY AND HEME SYNTHESIS

Frataxin is a mitochondrial iron-binding protein involved in iron storage, detoxification, and delivery for iron sulfur-cluster assembly and heme biosynthesis. The ability of frataxin from different organisms to populate multiple oligomeric states in the presence of metal ions, e.g. Fe(2+) and Co(2+), led to the suggestion that different oligomers contribute to the functions of frataxin. Here we report on the complex between yeast frataxin and ferrochelatase, the terminal enzyme of heme biosynthesis. Protein-protein docking and cross-linking in combination with mass spectroscopic analysis and single-particle reconstruction from negatively stained electron microscopic images were used to verify the Yfh1-ferrochelatase interactions. The model of the complex indicates that at the 2:1 Fe(2+)-to-protein ratio, when Yfh1 populates a trimeric state, there are two interaction interfaces between frataxin and the ferrochelatase dimer. Each interaction site involves one ferrochelatase monomer and one frataxin trimer, with conserved polar and charged amino acids of the two proteins positioned at hydrogen-bonding distances from each other. One of the subunits of the Yfh1 trimer interacts extensively with one subunit of the ferrochelatase dimer, contributing to the stability of the complex, whereas another trimer subunit is positioned for Fe(2+) delivery. Single-turnover stopped-flow kinetics experiments demonstrate that increased rates of heme production result from monomers, dimers, and trimers, indicating that these forms are most efficient in delivering Fe(2+) to ferrochelatase and sustaining porphyrin metalation. Furthermore, they support the proposal that frataxin-mediated delivery of this potentially toxic substrate overcomes formation of reactive oxygen species.

miR-8-3p regulates mitoferrin in the testes of Bactrocera dorsalis to ensure normal spermatogenesis

Genetics-enhanced sterile insect techniques (SIT) are promising novel approaches to control Bactrocera dorsalis, the most destructive horticultural pest in East Asia and the Pacific region. To identify novel genetic agents to alter male fertility of B. dorsalis, previous studies investigated miRNA expression in testes of B. dorsalis. One miRNA, miR-8-3p was predicted to bind the 3'UTR of putative B. dorsalis mitoferrin (bmfrn). The ortholog of bmfrn in D. melanogaster is essential for male fertility. Here we show that bmfrn has all conserved amino acid residues of known mitoferrins and is most abundantly expressed in B. dorsalis testes, making miR-8-3p and mitoferrin candidates for genetics-enhanced SIT. Furthermore, using a dual-luciferase reporter system, we show in HeLa cells that miR-8-3p interacts with the 3'UTR of bmfrn. Dietary treatments of adult male flies with miR-8-3p mimic, antagomiR, or bmfrn dsRNA, altered mitoferrin expression in the testes and resulted in reduced male reproductive capacity due to reduced numbers and viability of spermatozoa. We show for the first time that a mitoferrin is regulated by a miRNA and we demonstrate miR-8-3p as well as bmfrn dsRNA to be promising novel agents that could be used for genetics-enhanced SIT.

A Trypanosomatid Iron Transporter that Regulates Mitochondrial Function Is Required for Leishmania amazonensis Virulence

Iron, an essential co-factor of respiratory chain proteins, is critical for mitochondrial function and maintenance of its redox balance. We previously reported a role for iron uptake in differentiation of Leishmania amazonensis into virulent amastigotes, by a mechanism that involves reactive oxygen species (ROS) production and is independent of the classical pH and temperature cues. Iron import into mitochondria was proposed to be essential for this process, but evidence supporting this hypothesis was lacking because the Leishmania mitochondrial iron transporter was unknown. Here we describe MIT1, a homolog of the mitochondrial iron importer genes mrs3 (yeast) and mitoferrin-1 (human) that is highly conserved among trypanosomatids. MIT1 expression was essential for the survival of Trypanosoma brucei procyclic but not bloodstream forms, which lack functional respiratory complexes. L. amazonensis LMIT1 null mutants could not be generated, suggesting that this mitochondrial iron importer is essential for promastigote viability. Promastigotes lacking one LMIT1 allele (LMIT1/Δlmit1) showed growth defects and were more susceptible to ROS toxicity, consistent with the role of iron as the essential co-factor of trypanosomatid mitochondrial superoxide dismutases. LMIT1/Δlmit1 metacyclic promastigotes were unable to replicate as intracellular amastigotes after infecting macrophages or cause cutaneous lesions in mice. When induced to differentiate axenically into amastigotes, LMIT1/Δlmit1 showed strong defects in iron content and function of mitochondria, were unable to upregulate the ROS-regulatory enzyme FeSOD, and showed mitochondrial changes suggestive of redox imbalance. Our results demonstrate the importance of mitochondrial iron uptake in trypanosomatid parasites, and highlight the role of LMIT1 in the iron-regulated process that orchestrates differentiation of L. amazonensis into infective amastigotes.

Leishmaniasis is a serious parasitic disease that affects 12 million people worldwide, with clinical manifestations ranging from self-healing cutaneous lesions to deadly visceralizing disease. A vaccine is not available, and new and less toxic drugs against this protozoan parasite are urgently needed. Following introduction into vertebrate hosts during a sand fly blood meal, Leishmania parasites undergo extensive changes in morphology and metabolism that are critical for adaptation to life inside host macrophages and replication as amastigotes. Earlier studies identified major events that occur during amastigote differentiation, but the signaling mechanism initiating this process remained poorly understood. Previously we demonstrated a novel role for the reactive oxygen species (ROS) H₂O₂ in initiating amastigote differentiation, a process proposed to be dependent on iron availability inside the parasite’s mitochondria. In this study we identify LMIT1, a Leishmania transmembrane protein that functions as a mitochondrial iron transporter and is conserved in other trypanosomatid protozoan parasites. Reduced LMIT1 expression impairs mitochondrial function in the infective amastigote stage, abolishing parasite virulence. Our findings identify LMIT1 as a promising new drug target, and support the conclusion that iron-dependent ROS signals generated in the mitochondria regulate differentiation of virulent Leishmania amastigotes.

Mitochondrial iron supply is required for the developmental pulse of ecdysone biosynthesis that initiates metamorphosis in Drosophila melanogaster

Synthesis of ecdysone, the key hormone that signals the termination of larval growth and the initiation of metamorphosis in insects, is carried out in the prothoracic gland by an array of iron-containing cytochrome P450s, encoded by the halloween genes. Interference, either with iron-sulfur cluster biogenesis in the prothoracic gland or with the ferredoxins that supply electrons for steroidogenesis, causes a block in ecdysone synthesis and developmental arrest in the third instar larval stage. Here we show that mutants in Drosophila mitoferrin (dmfrn), the gene encoding a mitochondrial carrier protein implicated in mitochondrial iron import, fail to grow and initiate metamorphosis under dietary iron depletion or when ferritin function is partially compromised. In mutant dmfrn larvae reared under iron replete conditions, the expression of halloween genes is increased and 20-hydroxyecdysone (20E), the active form of ecdysone, is synthesized. In contrast, addition of an iron chelator to the diet of mutant dmfrn larvae disrupts 20E synthesis. Dietary addition of 20E has little effect on the growth defects, but enables approximately one-third of the iron-deprived dmfrn larvae to successfully turn into pupae and, in a smaller percentage, into adults. This partial rescue is not observed with dietary supply of ecdysone's precursor 7-dehydrocholesterol, a precursor in the ecdysone biosynthetic pathway. The findings reported here support the notion that a physiological supply of mitochondrial iron for the synthesis of iron-sulfur clusters and heme is required in the prothoracic glands of insect larvae for steroidogenesis. Furthermore, mitochondrial iron is also essential for normal larval growth.

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.

Green tea polyphenols extend the lifespan of male drosophila melanogaster while impairing reproductive fitness

Green tea is a popular beverage believed to have many health benefits, including a reduction in the risks of heart disease and cancer. Rich in polyphenolic compounds known as catechins, green tea and its components have been shown to increase the lifespan of various animal models, including Drosophila melanogaster. Here, we investigated the gender-specific effects of green tea on the lifespan of fruit flies and observed that green tea extended the lifespan of male flies only. This effect was found to be independent of typical aging interventions, such as dietary restriction, modulation of oxidative energy metabolism, and improved tolerance to environmental stresses. The one exception was that green tea did protect male flies against iron toxicity. Since there is an inverse correlation between lifespan and reproduction, the impact of green tea on male reproductive fitness was also investigated. We found that green tea negatively impacted male fertility as shown by a reduced number of offspring produced and increased mating latency. We further identified that the lifespan extension properties of green tea was only observed in the presence of females which alludes to a reproductive (or mating) dependent mechanism. Our findings suggest that green tea extends the lifespan of male flies by inhibiting reproductive potential, possibly by limiting iron uptake. To our knowledge, our study is the first to report the negative impact of green tea on Drosophila male reproduction. Our results also support previous studies that suggest that green tea might have a negative effect on reproductive fitness in humans.

Transcriptome profiling of the testis reveals genes involved in spermatogenesis and marker discovery in the oriental fruit fly, Bactrocera dorsalis

The testis is a highly specialized tissue that plays a vital role in ensuring fertility by producing spermatozoa, which are transferred to the female during mating. Spermatogenesis is a complex process, resulting in the production of mature sperm, and involves significant structural and biochemical changes in the seminiferous epithelium of the adult testis. The identification of genes involved in spermatogenesis of Bactrocera dorsalis (Hendel) is critical for a better understanding of its reproductive development. In this study, we constructed a cDNA library of testes from male B. dorsalis adults at different ages, and performed de novo transcriptome sequencing to produce a comprehensive transcript data set, using Illumina sequencing technology. The analysis yielded 52 016 732 clean reads, including a total of 4.65 Gb of nucleotides. These reads were assembled into 47 677 contigs (average 443 bp) and then clustered into 30 516 unigenes (average 756 bp). Based on BLAST hits with known proteins in different databases, 20 921 unigenes were annotated with a cut-off E-value of 10(-5). The transcriptome sequences were further annotated using the Clusters of Orthologous Groups, Gene Orthology and the Kyoto Encyclopedia of Genes and Genomes databases. Functional genes involved in spermatogenesis were analysed, including cell cycle proteins, metalloproteins, actin, and ubiquitin and antihyperthermia proteins. Several testis-specific genes were also identified. The transcripts database will help us to understand the molecular mechanisms underlying spermatogenesis in B. dorsalis. Furthermore, 2913 simple sequence repeats and 151 431 single nucleotide polymorphisms were identified, which will be useful for investigating the genetic diversity of B. dorsalis in the future.

Iron and copper in male reproduction: a double-edged sword

Iron and copper are essential trace nutrients playing important roles in general health and fertility. However, both elements are highly toxic when accumulating in large quantities. Their direct or indirect impact on the structure and function of male gonads and gametes is not completely understood yet. Excess or deficiency of either element may lead to defective spermatogenesis, reduced libido, and oxidative damage to the testicular tissue and spermatozoa, ultimately leading to fertility impairment. This review will detail the complex information currently available on the dual roles iron and copper play in male reproduction.

Ferritin protect shrimp Litopenaeus vannamei from WSSV infection by inhibiting virus replication

Iron is considered as an essential element for all living organisms. Therefore, limiting iron availability may be key part of the host's innate immune response to various pathogens. Ferritin is a major iron storage protein in living cells and plays an important role in iron homeostasis. One way the host can transiently reduce iron bioavailability is by ferritin over expression. In invertebrates, ferritin was found to be up-regulated after pathogens challenge and is considered to be an important element in the innate immune system. This study was designed to investigate the involvement of ferritin in shrimp Litopenaeus vannamei defense against WSSV. We discovered that the viral load of shrimp injected with recombinant ferritin protein was lower than that of control group. The suppression of ferritin by dsRNA increased susceptibility to WSSV with 3-fold high viral copies. The present study documented that ferritin protected shrimp L. vannamei from WSSV by inhibiting virus replication. We presume that ferritin reduce iron availability, leading to inhibit the activity of ribonucleotide reductase and delay the replication of virus genome. This study provided new insights into the understanding of molecular responses and defense mechanisms in shrimp against WSSV.

Three conserved histidine residues contribute to mitochondrial iron transport through mitoferrins

Iron is an essential element for almost all organisms. In eukaryotes, it is mainly used in mitochondria for the biosynthesis of iron-sulfur clusters and haem group maturation. Iron is delivered into the mitochondrion by mitoferrins, members of the MCF (mitochondrial carrier family), through an unknown mechanism. In the present study, the yeast homologues of these proteins, Mrs3p (mitochondrial RNA splicing 3) and Mrs4p, were studied by inserting them into liposomes. In this context, they could transport Fe2+ across the proteoliposome membrane, as shown using the iron chelator bathophenanthroline. A series of amino acid-modifying reagents were screened for their effects on Mrs3p-mediated iron transport. The results of the present study suggest that carboxy and imidazole groups are essential for iron transport. This was confirmed by in vivo complementation assays, which demonstrated that three highly conserved histidine residues are important for Mrs3p function. These histidine residues are not conserved in other MCF members and thus they are likely to play a specific role in iron transport. A model describing how these residues help iron to transit smoothly across the carrier cavity is proposed and compared with the structural and biochemical data available for other carriers in this family.

Expression of the yeast cation diffusion facilitators Mmt1 and Mmt2 affects mitochondrial and cellular iron homeostasis: evidence for mitochondrial iron export

Mmt1 and Mmt2 are highly homologous yeast members of the cation diffusion facilitator transporter family localized to mitochondria. Overexpression of MMT1/2 led to changes in cellular metal homeostasis (increased iron sensitivity, decreased cobalt sensitivity, increased sensitivity to copper), oxidant generation, and increased sensitivity to H2O2. The phenotypes due to overexpression of MMT1&2 were similar to that seen in cells with deletions in MRS3 and MRS4, genes that encode the mitochondrial iron importers. Overexpression of MMT1&2 resulted in induction of the low iron transcriptional response, similar to that seen in Δmrs3Δmr4 cells. This low iron transcriptional response was suppressed by deletion of CCC1, the gene that encodes the vacuolar iron importer. Measurement of the activity of the iron-dependent gentisate 1,2-dioxygenase from Pseudaminobacter salicylatoxidans expressed in yeast cytosol, showed that changes in Mmt1/2 levels affected cytosol iron concentration even in the absence of Ccc1. Overexpression of MMT1 resulted in increased cytosolic iron whereas deletion of MMT1/MMT2 led to decreased cytosolic iron. These results support the hypothesis that Mmt1/2 function as mitochondrial iron exporters.

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.

Iron levels change in larval Heliothis virescens tissues following baculovirus infection

Inductively coupled plasma mass spectrometry and (59)Fe radiotracers were used to investigate changes in levels of Fe in the tissues of 4th instar Heliothis virescens larvae following infection with Helicoverpa zea single nucleopolyhedrovirus (HzSNPV) or with Autographa californica multiple nucleopolyhedrovirus. Baculovirus infection led to significant changes in hemolymph Fe levels late in infection. (24)Na radiotracer ingested by 4th instar larvae was rapidly cleared to nearly undetectable levels 6 h post-ingestion. In contrast, (59)Fe radiotracer fed to 4th instar larvae declined within the first few hours of ingestion and then remained constant at approximately 60% of the initial tracer activity. While Fe radiotracer levels among larval tissues changed, whole insect tracer levels did not decline from 6 to 60 h post-ingestion. Tissues from HzSNPV larvae had higher radiotracer levels in the hemolymph and midgut 36 and 60 h post-infection. The protein-bound/free ratio of (59)Fe was significantly higher in baculovirus infected hemolymph than in uninfected hemolymph at 60 h post-infection, indicating that Fe released from damaged cells is protein-bound. In both studies, hemolymph Fe levels were higher in HzSNPV infected larvae. This first study of tissue Fe levels during viral infection of an insect clearly demonstrates that Fe homeostasis is substantially disrupted.

Drosophila spermiogenesis: Big things come from little packages

Drosophila melanogaster spermatids undergo dramatic morphological changes as they differentiate from small round cells approximately 12 μm in diameter into highly polarized, 1.8 mm long, motile sperm capable of participating in fertilization. During spermiogenesis, syncytial cysts of 64 haploid spermatids undergo synchronous differentiation. Numerous changes occur at a subcellular level, including remodeling of existing organelles (mitochondria, nuclei), formation of new organelles (flagellar axonemes, acrosomes), polarization of elongating cysts and plasma membrane addition. At the end of spermatid morphogenesis, organelles, mitochondrial DNA and cytoplasmic components not needed in mature sperm are stripped away in a caspase-dependent process called individualization that results in formation of individual sperm. Here, we review the stages of Drosophila spermiogenesis and examine our current understanding of the cellular and molecular mechanisms involved in shaping male germ cell-specific organelles and forming mature, fertile sperm.