Aedes aegypti ferritin

An 11-point time course midgut transcriptome across 72 h after bloodfeeding provides detailed temporal resolution of transcript expression in the arbovirus vector, Aedes aegypti

As the major vector for dengue, Zika, yellow fever, and chikungunya viruses, the mosquito Aedes aegypti is one of the most important insects in public health. These viruses are transmitted by bloodfeeding, which is also necessary for the reproduction of the mosquito. Thus, the midgut plays an essential role in mosquito physiology as the center for bloodmeal digestion and as an organ that serves as the first line of defense against viruses. Despite its importance, transcriptomic dynamics with fine temporal resolution across the entire digestion cycle have not yet been reported. To fill this gap, we conducted a transcriptomic analysis of A. aegypti female midguts across a 72-h bloodmeal digestion cycle for 11 time points, with a particular focus on the first 24 h. PCA analysis confirmed that 72 h is indeed a complete digestion cycle. Cluster and GO enrichment analysis showed the orchestrated modulation of thousands of genes to accomplish the midgut's role as the center for digestion, as well as nutrient transport with a clear progression with sequential emphasis on transcription, translation, energy production, nutrient metabolism, transport, and finally, autophagy by 24-36 h. We further determined that many serine proteases are robustly expressed as if to prepare for unexpected physiological challenges. This study provides a powerful resource for the analysis of genomic features that coordinate the rapid and complex transcriptional program induced by mosquito bloodfeeding.

MicroRNA Expression Prior to Biting in a Vector Mosquito Anticipates Physiological Processes Related to Energy Utilization, Reproduction and Immunity

Understanding the molecular and physiological processes underlying biting behavior in vector mosquitoes has important implications for developing novel strategies to suppress disease transmission. Here, we conduct small-RNA sequencing and qRT-PCR to identify differentially expressed microRNAs (miRNAs) in the head tissues of two subspecies of Culex pipiens that differ in biting behavior and the ability to produce eggs without blood feeding. We identified eight differentially expressed miRNAs between biting C. pipiens pipiens (Pipiens) and non-biting C. pipiens molestus (Molestus); six of these miRNAs have validated functions or predicted targets related to energy utilization (miR8-5-p, miR-283, miR-2952-3p, miR-1891), reproduction (miR-1891), and immunity (miR-2934-3p, miR-92a, miR8-5-p). Although miRNAs regulating physiological processes associated with blood feeding have previously been shown to be differentially expressed in response to a blood meal, our results are the first to demonstrate differential miRNA expression in anticipation of a blood meal before blood is actually imbibed. We compare our current miRNA results to three previous studies of differential messenger RNA expression in the head tissues of mosquitoes. Taken together, the combined results consistently show that biting mosquitoes commit to specific physiological processes in anticipation of a blood meal, while non-biting mosquitoes mitigate these anticipatory costs.

The evolution of sanguivory in vampire bats: origins and convergences

Blood-feeding (sanguivory) has evolved more than two dozen times among birds, fishes, insects, arachnids, molluscs, crustaceans, and annelids; however, among mammals, it is restricted to the vampire bats. Here, the authors revisit the question of how it evolved in that group. Evidence to date suggests that the ancestors of phyllostomids were insectivorous, and that carnivory, omnivory, and nectarivory evolved among phyllostomids after vampire bats diverged. Frugivory likely also evolved after vampire bats diverged, but the phylogeny is ambiguous on that point. However, vampire bats lack any genetic evidence of a frugivorous past, and the behavioural progression from frugivory to sanguivory is difficult to envision. Thus, the most parsimonious scenario is that sanguivory evolved in an insectivorous ancestor to vampire bats via ectoparasite-eating, wound-feeding, or some combination of the two—all feeding habits found among blood-feeding birds today. Comparing vampire bats with other sanguivores, the authors find several remarkable examples of convergence. Further, it was found that blood-feeding has been ca. 50 times more likely to evolve in a vertebrate lineage than in an invertebrate one. The authors hypothesize that this difference exists because vertebrates are more likely than invertebrates to have the biochemical necessities required to assimilate the components of vertebrate blood.

Differential Gene Expression Pattern of Importin β3 and NS5 in C6/36 Cells Acutely and Persistently Infected with Dengue Virus 2

The establishment of persistent dengue virus infection within the cells of the mosquito vector is an essential requirement for viral transmission to a new human host. The mechanisms involved in the establishment and maintenance of persistent infection are not well understood, but it has been suggested that both viral and cellular factors might play an important role. In the present work, we evaluated differential gene expression in Aedes albopictus cells acutely (C6/36-HT) and persistently infected (C6-L) with Dengue virus 2 by cDNA-AFLP. We observed that importin β3 was upregulated in noninfected cells compared with C6-L cells. Using RT-qPCR and plaque assays, we observed that Dengue virus levels in C6-L cells essentially do not vary over time, and peak viral titers in acutely infected cells are observed at 72 and 120 h postinfection. The expression level of importin β3 was higher in acutely infected cells than in persistently infected cells; this correlates with higher levels of NS5 in the nucleus of the cell. The differential pattern of importin β3 expression between acute and persistent infection with Dengue virus 2 could be a mechanism to maintain viral infection over time, reducing the antiviral response of the cell and the viral replicative rate.

Cloning, expression, and function of ferritins in the tick Haemaphysalis flava

The full-length cDNA of two ferritins of Haemaphysalis flava were cloned after which recombinant Hf-FER1 and Hf-FER2 were expressed and their function was analyzed. In addition, RNA interference (RNAi) based on the injection of Hf-fer1 or Hf-fer2 dsRNA into fully engorged female ticks was performed. The cDNA encoding Hf-FER1 is 834 bp in length. It contains an iron-responsive element in the 5' untranslated region and encodes 174 amino acid residues. The full-length cDNA of Hf-FER2 contains 696 bp and encodes 199 amino acids, including a putative signal peptide sequence. Hf-FER1 and Hf-FER2 both have the ferroxidase iron center and the ferrihydrite nucleation center. The evolutionary relationship of Hf-FER1 and Hf-FER2 was established, and the predicted quaternary structures were assembled as typical spherical shells composed of 24 subunits which was demonstrated by nature PAGE. Real-time PCR showed that Hf-fer1 and Hf-fer2 were expressed in all developmental stages, with the highest expression in fully engorged females. The expression of Hf-fer1 and Hf-fer2 were relatively high in unfed larvae. Hf-fer1 was expressed in all tissues and was especially abundant in the salivary glands of fully engorged females. In contrast, the highest levels of Hf-fer2 were found in the midgut of fully engorged females, and no expression was found in the salivary glands of this life stage. Both recombinant Hf-FER1 and Hf-FER2 had iron-binding capabilities. Silencing of both Hf-fer1 and Hf-fer2 affected fecundity. Compared to the control, the percentage of ticks that laid eggs in the Hf-fer1 and Hf-fer2 RNAi groups was 73.3% and 66.7%, respectively. The silenced ticks that laid eggs had lower egg weight to body weight ratios, and the eggs had abnormal morphologies. The hatchability of eggs with normal morphology in the Hf-fer1 and Hf-fer2 silenced groups was 47.8% and 22.8%, respectively, which was significantly different from the control group (P < 0.005). These findings indicate that Hf-FER1 and Hf-FER2 play important roles in the iron storage of H. flava.

The genomics of phenotypically differentiated Asellus aquaticus cave, surface stream and lake ecotypes

Organisms well suited for the study of ecotype formation have wide distribution ranges, where they adapt to multiple drastically different habitats repeatedly over space and time. Here we study such ecotypes in a Crustacean model, Asellus aquaticus, a commonly occurring isopod found in freshwater habitats as diverse as streams, caves and lakes. Previous studies focusing on cave vs. surface ecotypes have attributed depigmentation, eye loss and prolonged antennae to several south European cave systems. Likewise, surveys across multiple Swedish lakes have identified the presence of dark-pigmented "reed" and light-pigmented "stonewort" ecotypes, which can be found within the same lake. In this study, we sequenced the first draft genome of A. aquaticus, and subsequently use this to map reads and call variants in surface stream, cave and two lake ecotypes. In addition, the draft genome was combined with a RADseq approach to perform a quantitative trait locus (QTL) mapping study using a laboratory bred F₂ and F₄ cave × surface intercross. We identified genomic regions associated with body pigmentation, antennae length and body size. Furthermore, we compared genome-wide differentiation between natural populations and found several genes potentially associated with these habitats. The assessment of the cave QTL regions in the light-dark comparison of lake populations suggests that the regions associated with cave adaptation are also involved with genomic differentiation in the lake ecotypes. These demonstrate how troglomorphic adaptations can be used as a model for related ecotype formation.

SMRT sequencing of the full-length transcriptome of Odontotermes formosanus (Shiraki) under Serratia marcescens treatment

Odontotermes formosanus (Shiraki) is an important pest in the world. Serratia marcescens have a high lethal effect on O. formosanus, but the specific insecticidal mechanisms of S. marcescens on O. formosanus are unclear, and the immune responses of O. formosanus to S. marcescens have not been clarified. At present, genetic database resources of O. formosanus are extremely scarce. Therefore, using O. formosanus workers infected by S. marcescens and the control as experimental materials, a full-length transcriptome was sequenced using the PacBio Sequel sequencing platform. A total of 10,364 isoforms were obtained as the final transcriptome. The unigenes were further annotated with the Nr, Swiss-Prot, EuKaryotic Orthologous Groups (KOG), Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) Ortholog public databases. In a comparison between the control group and a Serratia marcescens-infected group, a total of 259 differentially expressed genes (DEGs) were identified, including 132 upregulated and 127 downregulated genes. Pathway enrichment analysis indicated that the expression of the mitogen-activated protein kinase (MAPK) pathway, oxidative stress genes and the AMP-activated protein kinase (AMPK) pathway in O. formosanus may be associated with S. marcescens treatment. This research intensively studied O. formosanus at the high-throughput full-length transcriptome level, laying a foundation for further development of molecular markers and mining of target genes in this species and thereby promoting the biological control of O. formosanus. Furthermore, these results will be helpful to clarify the action mechanisms of S. marcescens on O. formosanus, and also explore the relationship between O. formosanus and S. marcescens. In addition, this study will identify the immune response of O. formosanus to S. marcescens, which will provide a theoretical foundation for the development of new immunosuppressants for O. formosanus.

Iron and Ferritin Deposition in the Ovarian Tissues of the Yellow Fever Mosquito (Diptera: Culicidae)

Dengue, yellow fever, and Zika are viruses transmitted by yellow fever mosquito, Aedes aegypti [Linnaeus (Diptera: Culicidae)], to thousands of people each year. Mosquitoes transmit these viruses while consuming a blood meal that is required for oogenesis. Iron, an essential nutrient from the blood meal, is required for egg development. Mosquitoes receive a high iron load in the meal; although iron can be toxic, these animals have developed mechanisms for dealing with this load. Our previous research has shown iron from the blood meal is absorbed in the gut and transported by ferritin, the main iron transport and storage protein, to the ovaries. We now report the distribution of iron and ferritin in ovarian tissues before blood feeding and 24 and 72 h post-blood meal. Ovarian iron is observed in specific locations. Timing post-blood feeding influences the location and distribution of the ferritin heavy-chain homolog, light-chain homolog 1, and light-chain homolog 2 in ovaries. Understanding iron deposition in ovarian tissues is important to the potential use of interference in iron metabolism as a vector control strategy for reducing mosquito fecundity, decreasing mosquito populations, and thereby reducing transmission rates of vector-borne diseases.

The differential expression of Chironomus spp genes as useful tools in the search for pollution biomarkers in freshwater ecosystems

Insects of the Chironomidae family are characterized by a wide ecological diversity in freshwater ecosystems. The larvae have the physiological potential to tolerate environmental stress even when there is a low concentration of oxygen, the presence of toxic substances or when there are changes in temperature and salinity. On the other hand, it is important to consider that at a cellular level, when individual insects are exposed to environmental changes, it induces responses of groups of genes that govern the molecular mechanisms related to such tolerance. In this review, using fourth instar larvae of Chironomus spp. in natural conditions and of Chironomus columbiensis under controlled conditions, we will discuss the genetic expression of a group of genes that respond to detoxification and also the biological functions involved and impacted on by mining stressors. The study of macroinvertebrate bioindicator species and their gene expression as a result of mining activity opens a window on the search for genetic biomarkers that could be used in environmental pollution assessments in freshwater ecosystems.

Ironing out the Details: Exploring the Role of Iron and Heme in Blood-Sucking Arthropods

Heme and iron are essential molecules for many physiological processes and yet have the ability to cause oxidative damage such as lipid peroxidation, protein degradation, and ultimately cell death if not controlled. Blood-sucking arthropods have evolved diverse methods to protect themselves against iron/heme-related damage, as the act of bloodfeeding itself is high risk, high reward process. Protective mechanisms in medically important arthropods include the midgut peritrophic matrix in mosquitoes, heme aggregation into the crystalline structure hemozoin in kissing bugs and hemosomes in ticks. Once heme and iron pass these protective mechanisms they are presumed to enter the midgut epithelial cells via membrane-bound transporters, though relatively few iron or heme transporters have been identified in bloodsucking arthropods. Upon iron entry into midgut epithelial cells, ferritin serves as the universal storage protein and transport for dietary iron in many organisms including arthropods. In addition to its role as a nutrient, heme is also an important signaling molecule in the midgut epithelial cells for many physiological processes including vitellogenesis. This review article will summarize recent advancements in heme/iron uptake, detoxification and exportation in bloodfeeding arthropods. While initial strides have been made at ironing out the role of dietary iron and heme in arthropods, much still remains to be discovered as these molecules may serve as novel targets for the control of many arthropod pests.

Evolutionary transition from blood feeding to obligate nonbiting in a mosquito

The evolutionary transformation from a blood-feeding to an obligate nonbiting lifestyle is occurring uniquely within the genetic background of a single species of mosquito, Wyeomyia smithii, as a product of selection in nature. Associated genetic changes in metabolic pathways indicate a high anticipatory metabolic investment prior to consuming blood, presumably balanced by the reproductive benefits from an imminent blood meal. This evolutionary transformation provides a starting point for determining pivotal upstream genetic changes between biters and nonbiters and for identifying universal nonbiting genes or pathways in mosquitoes. If there is no bite, there is no transmission of pathogens; hence W. smithii offers a different approach to investigate control of blood-feeding vectors of human diseases.

The spread of blood-borne pathogens by mosquitoes relies on their taking a blood meal; if there is no bite, there is no disease transmission. Although many species of mosquitoes never take a blood meal, identifying genes that distinguish blood feeding from obligate nonbiting is hampered by the fact that these different lifestyles occur in separate, genetically incompatible species. There is, however, one unique extant species with populations that share a common genetic background but blood feed in one region and are obligate nonbiters in the rest of their range: Wyeomyia smithii. Contemporary blood-feeding and obligate nonbiting populations represent end points of divergence between fully interfertile southern and northern populations. This divergence has undoubtedly resulted in genetic changes that are unrelated to blood feeding, and the challenge is to winnow out the unrelated genetic factors to identify those related specifically to the evolutionary transition from blood feeding to obligate nonbiting. Herein, we determine differential gene expression resulting from directional selection on blood feeding within a polymorphic population to isolate genetic differences between blood feeding and obligate nonbiting. We show that the evolution of nonbiting has resulted in a greatly reduced metabolic investment compared with biting populations, a greater reliance on opportunistic metabolic pathways, and greater reliance on visual rather than olfactory sensory input. W. smithii provides a unique starting point to determine if there are universal nonbiting genes in mosquitoes that could be manipulated as a means to control vector-borne disease.

Exploring the Caste-Specific Multi-Layer Defense Mechanism of Formosan Subterranean Termites, Coptotermes formosanus Shiraki

The survival and foraging of Coptotermesformosanus Shiraki in a microbe-rich environment reflect the adaptation of an extraordinary, sophisticated defense mechanism by the nest-mates. We aimed to explore the host pathogen interaction by studying caste-specific volatile chemistry and genes encoding the antioxidant defense of winged imagoes, nymphs, soldiers and workers of Formosan subterranean termites. Qualitative analyses of C.formosanus Shiraki performed by HS-SPME/GC-MS showed considerable variations in the chemical composition of volatile organic compounds (VOCs) and their proportions among all the castes. Winged imagoes produced the most important compounds such as naphthalene and n-hexanoic acid. The antifungal activity of these compounds along with nonanal, n-pentadecane, n-tetradecane, n-heptadecane and methyl octanoate against the conidial suspensions of Metarhiziumanisopliae and Beauveriabassiana isolates enable us to suggest that the failure of natural fungal infection in the nest is due to the antiseptic environment of the nest, which is mainly controlled by the VOCs of nest-mates. In addition, conidial germination of M.anisopliae and B.bassiana isolates evaluated on the cuticle of each caste showed significant variations among isolates and different castes. Our results showed that the conidia of M.anisopliae 02049 exhibited the highest germination on the cuticle of all the inoculated castes. Moreover, we recorded the lowest germination of the conidia of B.bassiana 200436. Caste-specific germination variations enabled us to report for the first time that the cuticle of winged imagoes was found to be the most resistant cuticle. The analysis of the transcriptome of C.formosanus Shiraki revealed the identification of 17 genes directly involved in antioxidant defense. Expression patterns of the identified antioxidant genes by quantitative real-time PCR (qPCR) revealed the significantly highest upregulation of CAT, GST, PRXSL, Cu/Zn-SOD2, TXN1, TXN2, TXNL1, TXNL2, TXNL4A and TPx genes among winged imagoes upon infection with the most virulent isolate, M.anisopliae 02049. Furthermore, soldiers showed the least expression of genes encoding antioxidant defense. Our findings indicated that the volatile chemistry of nest-mates and genes encoding antioxidant defense greatly contribute to the survival and foraging of Formosan subterranean termites in a microbe-rich habitat.

Iron availability affects West Nile virus infection in its mosquito vector

Background

Mosquitoes are responsible for transmission of viruses, including dengue, West Nile and chikungunya viruses. Female mosquitoes are infected when they blood-feed on vertebrates, a required step for oogenesis. During this process, mosquitoes encounter high iron loads. Since iron is an essential nutrient for most organisms, including pathogens, one of the defense mechanisms for the host includes sequestration of iron away from the invading pathogen. Here, we determine whether iron availability affects viral replication in mosquitoes.

Methods

To elucidate effect of iron availability on mosquito cells during infection, Culex cells were treated with either ferric ammonium citrate (FAC) or the iron chelator, deferoxamine (DFX). Real time RT-PCR was performed using ferritin (heavy chain) and NRAMP as a measure of iron homeostasis in cells. To determine iron requirement for viral replication, Culex cells were knocked down for NRAMP using dsRNA. Finally, the results were validated in Culex mosquito-infection model, by treating infected mosquitoes with DFX to reduce iron levels.

Results

Our results show that infection of Culex cells led to induction in levels of ferritin (heavy chain) and NRAMP mRNAs in time-dependent manner. Results also showed that treatment of cells with FAC, reduced expression of NRAMP (iron transporter) and increase levels of ferritin (heavy chain). Interestingly, increasing iron levels increased viral titers; while reducing intracellular iron levels, either by NRAMP knock-down or using DFX, reduced viral titers. The results from Culex mosquito infection showed that mosquitoes treated with DFX had reduced viral titers compared with untreated controls in midgut as well as carcass 8 days pi. Saliva from mosquitoes treated with DFX also showed reduced viral titers compared with untreated controls, indicating low viral transmission capacity.

Conclusions

Our results indicate that iron is required for viral replication in mosquito cells. Mosquitoes respond to viral infection, by inducing expression of heavy chain ferritin, which sequesters available iron, reducing its availability to virus infected cells. The data indicates that heavy chain ferritin may be part of an immune mechanism of mosquitoes in response to viral infections.

The impact of metagenomic interplay on the mosquito redox homeostasis

Mosquitoes are exposed to oxidative challenges throughout their life cycle. The primary challenge comes from a blood meal. The blood digestion turns the midgut into an oxidative environment, which imposes pressure not only on mosquito fecundity and other physiological traits but also on the microbiota in the midgut. During evolution, mosquitoes have developed numerous oxidative defense mechanisms to maintain redox homeostasis in the midgut. In addition to antioxidants, SOD, catalase, and glutathione system, sufficient supply of the reducing agent, NADPH, is vital for a successful defense against oxidative stress. Increasing evidence indicates that in response to oxidative stress, cells reconfigure metabolic pathways to increase the generation of NADPH through NADP-reducing networks including the pentose phosphate pathway and others. The microbial homeostasis is critical for the functional contributions to various host phenotypes. The symbiotic microbiota is regulated largely by the Duox-ROS pathway in Drosophila. In mosquitoes, Duox-ROS pathway, heme-mediated signaling, antimicrobial peptide production and C-type lectins work in concert to maintain the dynamic microbial community in the midgut. Microbial mechanisms against oxidative stress in this context are not well understood. Emerging evidence that microbial metabolites trigger host oxidative response warrants further study on the metagenomic interplay in an oxidative environment like mosquito gut ecosystem. Besides the classical Drosophila model, hematophagous insects like mosquitoes provide an alternative model system to study redox homeostasis in a symbiotic metagenomic context.

Iron metabolism in hard ticks (Acari: Ixodidae): the antidote to their toxic diet

Ticks are notorious parasitic arthropods, known for their completely host-blood-dependent lifestyle. Hard ticks (Acari: Ixodidae) feed on their hosts for several days and can ingest blood more than a hundred times their unfed weight. Their blood-feeding habit facilitates the transmission of various pathogens. It is remarkable how hard ticks cope with the toxic nature of their blood meal, which contains several molecules that can promote oxidative stress including iron. While it is required in several physiological processes, high amounts of iron can be dangerous because iron can also participate in the formation of free radicals that may cause cellular damage and death. Here we review the current knowledge on heme and inorganic iron metabolism in hard ticks and compare it with that in vertebrates and other arthropods. We briefly discuss the studies on heme transport, storage and detoxification, and the transport and storage of inorganic iron, with emphasis on the functions of tick ferritins. This review points out other aspects of tick iron metabolism that warrant further investigation, as compared to mammals and other arthropods. Further understanding of this physiological process may help in formulating new control strategies for tick infestation and the spread of tick-borne diseases.

Alternative splicing contributes to the coordinated regulation of ferritin subunit levels in Bactrocera dorsalis (Hendel)

A constant ratio of ferritin heavy chain homolog (HCH) and light chain homolog (LCH) subunits seems to be required to compose the ferritin heteropolymer protein in insects. However, the mechanism by which insect LCH genes regulate protein levels remains unclear. We report that alternative promoters and alternative splicing contribute to maintaining a constant ratio of the two subunits, BdFer1HCH and BdFer2LCH (ferritin 1 HCH and ferritin 2 LCH), in Bactrocera dorsalis, a notorious quarantine pest. The genes BdFer1HCH and BdFer2LCH were identified with a series of potential transcription factor binding sites and were shown to be clustered within the genome in a "head to head" fashion. Thus, we unearthed a potential post-transcriptional mechanism to regulate the levels of LCH subunits, and confirmed that the expressions of BdFer1HCH and BdFer2LCH were induced by 20-hydroecdysone, iron overload, and immune challenge.

Characterization and recombinant protein expression of ferritin light chain homologue in the silkworm, Bombyx mori

The silkworm genome encodes three iron storage proteins or ferritins, Fer1HCH, Fer2LCH, and Fer3HCH. Probing our EST library constructed from 1-day-old silkworm eggs revealed only Fer2LCH mRNA, which encoded for a protein with a predicted putative N-glycosylation site. Developmental and tissue expression analyses during embryogenesis revealed that Fer2LCH mRNA was abundant from 6 h to 6 days after oviposition. Transcriptional expression of Fer2LCH during the postembryonic stage is also high in the larval fat body and mid-gut, and then is upregulated in all pupal tissues tested. We found that Fer2LCH mRNA contains an iron-responsive element, suggesting this ferritin subunit is subject to translational control. Although ferritin expression has been shown to increase following immune challenge in other insects, the levels of Fer2LCH mRNA were not significantly induced following viral or bacterial infection of Bombyx mori. Using a baculovirus expression system we expressed recombinant BmFer2LCH protein, which was detectable in the cytoplasmic fraction, likely in a compartment of the secretory pathway, and was shown to undergo posttranslational modifications including N-glycosylation. In particular, rBmFer2LCH carbohydrate chains were composed of mannose and GlcNAc. We suggest that Fer2LCH is important for iron homeostasis and maintaining normal organ function in silkworms.

The effect of bacterial challenge on ferritin regulation in the yellow fever mosquito, Aedes aegypti

Secreted ferritin is the major iron storage and transport protein in insects. Here, we characterize the message and protein expression profiles of yellow fever mosquito (Aedes aegypti) ferritin heavy chain homologue (HCH) and light chain homologue (LCH) subunits in response to iron and bacterial challenge. In vivo experiments demonstrated tissue-specific regulation of HCH and LCH expression over time post-blood meal (PBM). Transcriptional regulation of HCH and LCH was treatment specific, with differences in regulation for naïve versus mosquitoes challenged with heat-killed bacteria (HKB). Translational regulation by iron regulatory protein (IRP) binding activity for the iron-responsive element (IRE) was tissue-specific and time-dependent PBM. However, mosquitoes challenged with HKB showed little change in IRP/IRE binding activity compared to naïve animals. The changes in ferritin regulation and expression in vivo were confirmed with in vitro studies. We challenged mosquitoes with HKB followed by a blood meal to determine the effects on ferritin expression, and demonstrate a synergistic, time-dependent regulation of expression for HCH and LCH.

Multiple ferritins are vital to successful blood feeding and reproduction of the hard tick Haemaphysalis longicornis

Ticks are obligate hematophagous parasites and important vectors of diseases. The large amount of blood they consume contains great quantities of iron, an essential but also toxic element. The function of ferritin, an iron storage protein, and iron metabolism in ticks need to be further elucidated. Here, we investigated the function a newly identified secreted ferritin from the hard tick Haemaphysalis longicornis (HlFER2), together with the previously identified intracellular ferritin (HlFER1). Recombinant ferritins, expressed in Escherichia coli, were used for anti-serum preparation and were also assayed for iron-binding activity. RT-PCR and western blot analyses of different organs and developmental stages of the tick during blood feeding were performed. The localization of ferritins in different organs was demonstrated through an indirect immunofluorescent antibody test. RNA interference (RNAi) was performed to evaluate the importance of ferritin in blood feeding and reproduction of ticks. The midgut was also examined after RNAi using light and transmission electron microscopy. RT-PCR showed differences in gene expression in some organs and developmental stages. Interestingly, only HlFER2 was detected in the ovary during oviposition and in the egg despite the low mRNA transcript. RNAi induced a reduction in post-blood meal body weight, high mortality and decreased fecundity. The expression of vitellogenin genes was affected by silencing of ferritin. Abnormalities in digestive cells, including disrupted microvilli, and alteration of digestive activity were also observed. Taken altogether, our results show that the iron storage and protective functions of ferritin are crucial to successful blood feeding and reproduction of H. longicornis.

Reactive oxygen species production and Brugia pahangi survivorship in Aedes polynesiensis with artificial Wolbachia infection types

Heterologous transinfection with the endosymbiotic bacterium Wolbachia has been shown previously to induce pathogen interference phenotypes in mosquito hosts. Here we examine an artificially infected strain of Aedes polynesiensis, the primary vector of Wuchereria bancrofti, which is the causative agent of Lymphatic filariasis (LF) throughout much of the South Pacific. Embryonic microinjection was used to transfer the wAlbB infection from Aedes albopictus into an aposymbiotic strain of Ae. polynesiensis. The resulting strain (designated "MTB") experiences a stable artificial infection with high maternal inheritance. Reciprocal crosses of MTB with naturally infected wild-type Ae. polynesiensis demonstrate strong bidirectional incompatibility. Levels of reactive oxygen species (ROS) in the MTB strain differ significantly relative to that of the wild-type, indicating an impaired ability to regulate oxidative stress. Following a challenge with Brugia pahangi, the number of filarial worms achieving the infective stage is significantly reduced in MTB as compared to the naturally infected and aposymbiotic strains. Survivorship of MTB differed significantly from that of the wild-type, with an interactive effect between survivorship and blood feeding. The results demonstrate a direct correlation between decreased ROS levels and decreased survival of adult female Aedes polynesiensis. The results are discussed in relation to the interaction of Wolbachia with ROS production and antioxidant expression, iron homeostasis and the insect immune system. We discuss the potential applied use of the MTB strain for impacting Ae. polynesiensis populations and strategies for reducing LF incidence in the South Pacific.

Biological and molecular responses of Chironomus riparius (Diptera, Chironomidae) to herbicide 2,4-D (2,4-dichlorophenoxyacetic acid)

2,4-Dichlorophenoxyacetic acid (2,4-D) is an agricultural contaminant found in rural ground water. It remains to be determined whether neither 2,4-D poses environmental risks, nor is the mechanism of toxicity known at the molecular level. To evaluate the potential ecological risk of 2,4-D, we assessed the biological parameters including the survival rate, adult sex ratio of emerged adults, and mouthpart deformities in Chironomus riparius after long-term exposure to 2,4-D. The larvae were treated with 0.1, 1 or, 10microgL(-1) of 2,4-D for short- and long-term exposure periods. The sex ratio was changed in C. riparius exposed to only 10microgL(-1) of 2,4-D, whereas mouthpart deformities were observed as significantly higher in C. riparius exposed to 0.1microgL(-1) of 2,4-D. Survival rates were not significantly affected by 2,4-D. Furthermore, we evaluated the molecular and biochemical responses of biomarker genes such as gene expression of heat shock proteins (HSPs), ferritins and glutathione S-transferases (GSTs) in C. riparius exposed to 2,4-D for 24h. The expressions of HSP70, HSP40, HSP90 and GST levels in C. riparius were significantly increased after exposure to a 10microgL(-1) concentration of 2,4-D, whereas ferritin heavy and light chain gene expressions were significantly increased at all concentrations of 2,4-D exposure. Finally, these results may provide an important contribution to our understanding of the toxicology of 2,4-D herbicide in C. riparius. Moreover, the 2,4-D-mediated gene expressions may be generated by 2,4-D is the causative effects on most probable cause of the observed alterations. These biological, molecular and morphological parameters and the measured parameters can be used to monitor 2,4-D toxicity in an aquatic environment.

Insect ferritins: Typical or atypical?

Insects transmit millions of cases of disease each year, and cost millions of dollars in agricultural losses. The control of insect-borne diseases is vital for numerous developing countries, and the management of agricultural insect pests is a very serious business for developed countries. Control methods should target insect-specific traits in order to avoid non-target effects, especially in mammals. Since insect cells have had a billion years of evolutionary divergence from those of vertebrates, they differ in many ways that might be promising for the insect control field-especially, in iron metabolism because current studies have indicated that significant differences exist between insect and mammalian systems. Insect iron metabolism differs from that of vertebrates in the following respects. Insect ferritins have a heavier mass than mammalian ferritins. Unlike their mammalian counterparts, the insect ferritin subunits are often glycosylated and are synthesized with a signal peptide. The crystal structure of insect ferritin also shows a tetrahedral symmetry consisting of 12 heavy chain and 12 light chain subunits in contrast to that of mammalian ferritin that exhibits an octahedral symmetry made of 24 heavy chain and 24 light chain subunits. Insect ferritins associate primarily with the vacuolar system and serve as iron transporters-quite the opposite of the mammalian ferritins, which are mainly cytoplasmic and serve as iron storage proteins. This review will discuss these differences.

Wolbachia interferes with ferritin expression and iron metabolism in insects

Wolbachia is an intracellular bacterium generally described as being a facultative reproductive parasite. However, Wolbachia is necessary for oogenesis completion in the wasp Asobara tabida. This dependence has evolved recently as a result of interference with apoptosis during oogenesis. Through comparative transcriptomics between symbiotic and aposymbiotic individuals, we observed a differential expression of ferritin, which forms a complex involved in iron storage. Iron is an essential element that is in limited supply in the cell. However, it is also a highly toxic precursor of Reactive Oxygen Species (ROS). Ferritin has also been shown to play a key role in host-pathogen interactions. Measuring ferritin by quantitative RT-PCR, we confirmed that ferritin was upregulated in aposymbiotic compared to symbiotic individuals. Manipulating the iron content in the diet, we showed that iron overload markedly affected wasp development and induced apoptotic processes during oogenesis in A. tabida, suggesting that the regulation of iron homeostasis may also be related to the obligate dependence of the wasp. Finally, we demonstrated that iron metabolism is influenced by the presence of Wolbachia not only in the obligate mutualism with A. tabida, but also in facultative parasitism involving Drosophila simulans and in Aedes aegypti cells. In these latter cases, the expression of Wolbachia bacterioferritin was also increased in the presence of iron, showing that Wolbachia responds to the concentration of iron. Our results indicate that Wolbachia may generally interfere with iron metabolism. The high affinity of Wolbachia for iron might be due to physiological requirement of the bacterium, but it could also be what allows the symbiont to persist in the organism by reducing the labile iron concentration, thus protecting the cell from oxidative stress and apoptosis. These findings also reinforce the idea that pathogenic, parasitic and mutualistic intracellular bacteria all use the same molecular mechanisms to survive and replicate within host cells. By impacting the general physiology of the host, the presence of a symbiont may select for host compensatory mechanisms, which extends the possible consequences of persistent endosymbiont on the evolution of their hosts.

Iron loaded ferritin secretion and inhibition by CI-976 in Aedes aegypti larval cells

Ferritin is a multimer of 24 subunits of heavy and light chains. In mammals, iron taken into cells is stored in ferritin or incorporated into iron-containing proteins. Very little ferritin is found circulating in mammalian serum; most is retained in the cytoplasm. Female mosquitoes, such as Aedes aegypti (yellow fever mosquito, Diptera), require a blood meal for oogenesis. Mosquitoes receive a potentially toxic level of iron in the blood meal which must be processed and stored. We demonstrate by (59)Fe pulse-chase experiments that cultured A. aegypti larval CCL-125 cells take up iron from culture media and store it in ferritin found mainly in the membrane fraction and secrete iron-loaded ferritin. We observe that in these larval cells ferritin co-localizes with ceramide-containing membranes in the absence of iron. With iron treatment, ferritin is found associated with ceramide-containing membranes as well as in cytoplasmic non-ceramide vesicles. Treatment of CCL-125 cells with iron and CI-976, an inhibitor of lysophospholipid acyl transferases, disrupts ferritin secretion with a concomitant decrease in cell viability. Interfering with ferritin secretion may limit the ability of mosquitoes to adjust to the high iron load of the blood meal and decrease iron delivery to the ovaries reducing egg numbers.

Fate of blood meal iron in mosquitoes

Iron is an essential element of living cells and organisms as a component of numerous metabolic pathways. Hemoglobin and ferric-transferrin in vertebrate host blood are the two major iron sources for female mosquitoes. We used inductively coupled plasma mass spectrometry (ICP-MS) and radioisotope labeling to quantify the fate of iron supplied from hemoglobin or as transferrin in Aedes aegypti. At the end of the first gonotrophic cycle, approximately 87% of the ingested total meal heme iron was excreted, while 7% was distributed into the eggs and 6% was stored in different tissues. In contrast, approximately 8% of the iron provided as transferrin was excreted and of that absorbed, 77% was allocated to the eggs and 15% distributed in the tissues. Further analyses indicate that of the iron supplied in a blood meal, approximately 7% appears in the eggs and of this iron 98% is from hemoglobin and 2% from ferric-transferrin. Whereas, of iron from a blood meal retained in body of the female, approximately 97% is from heme and <1% is from transferrin. Evaluation of iron-binding proteins in hemolymph and egg following intake of (59)Fe-transferrin revealed that ferritin is iron loaded in these animals, and indicate that this protein plays a critical role in meal iron transport and iron storage in eggs in A. aegypti.

Exploring the midgut transcriptome of Phlebotomus papatasi: comparative analysis of expression profiles of sugar-fed, blood-fed and Leishmania-major-infected sandflies

Background

In sandflies, the blood meal is responsible for the induction of several physiologic processes that culminate in egg development and maturation. During blood feeding, infected sandflies are also able to transmit the parasite Leishmania to a suitable host. Many blood-induced molecules play significant roles during Leishmania development in the sandfly midgut, including parasite killing within the endoperitrophic space. In this work, we randomly sequenced transcripts from three distinct high quality full-length female Phlebotomus papatasi midgut-specific cDNA libraries from sugar-fed, blood-fed and Leishmania major-infected sandflies. Furthermore, we compared the transcript expression profiles from the three different cDNA libraries by customized bioinformatics analysis and validated these findings by semi-quantitative PCR and real-time PCR.

Results

Transcriptome analysis of 4010 cDNA clones resulted in the identification of the most abundant P. papatasi midgut-specific transcripts. The identified molecules included those with putative roles in digestion and peritrophic matrix formation, among others. Moreover, we identified sandfly midgut transcripts that are expressed only after a blood meal, such as microvilli associated-like protein (PpMVP1, PpMVP2 and PpMVP3), a peritrophin (PpPer1), trypsin 4 (PpTryp4), chymotrypsin PpChym2, and two unknown proteins. Of interest, many of these overabundant transcripts such as PpChym2, PpMVP1, PpMVP2, PpPer1 and PpPer2 were of lower abundance when the sandfly was given a blood meal in the presence of L. major.

Conclusion

This tissue-specific transcriptome analysis provides a comprehensive look at the repertoire of transcripts present in the midgut of the sandfly P. papatasi. Furthermore, the customized bioinformatic analysis allowed us to compare and identify the overall transcript abundance from sugar-fed, blood-fed and Leishmania-infected sandflies. The suggested upregulation of specific transcripts in a blood-fed cDNA library were validated by real-time PCR, suggesting that this customized bioinformatic analysis is a powerful and accurate tool useful in analysing expression profiles from different cDNA libraries. Additionally, the findings presented in this work suggest that the Leishmania parasite is modulating key enzymes or proteins in the gut of the sandfly that may be beneficial for its establishment and survival.

Biglutaminyl-biliverdin IX alpha as a heme degradation product in the dengue fever insect-vector Aedes aegypti

Hemoglobin digestion in the midgut of hematophagous animals results in the release of its prosthetic group, heme, which is a pro-oxidant molecule. Heme enzymatic degradation is a protective mechanism that has been described in several organisms, including plants, bacteria, and mammals. This reaction is catalyzed by heme oxygenase and results in formation of carbon monoxide, ferrous ion, and biliverdin IXalpha. During digestion, a large amount of a green pigment is produced and secreted into the intestinal lumen of Aedes aegypti adult females. In the case of another blood-sucking insect, the kissing-bug Rhodnius prolixus, we have recently shown that heme degradation involves a complex pathway that generates dicysteinyl-biliverdin IX gamma. The light absorption spectrum of the Aedes purified pigment was similar to that of biliverdin, but its mobility on a reverse-phase chromatography column suggested a compound less hydrophobic than biliverdin IXalpha. Structural characterization by ESI-MS revealed that the mosquito pigment is the alpha isomer of biliverdin bound to two glutamine residues by an amide bond. This biglutaminyl-biliverdin is formed by oxidative cleavage of the heme porphyrin ring followed by two subsequent additions of glutamine residues to the biliverdin IXalpha. The role of this pathway in the adaptation of this insect vector to a blood-feeding habit is discussed.

Molecular characterization of iron binding proteins from Glossina morsitans morsitans (Diptera: Glossinidae)

The regulation of iron is critical for maintaining homeostasis in the tsetse fly (Diptera: Glossinidae), in which both adult sexes are strict blood feeders. We have characterized the cDNAs for two putative iron-binding proteins (IBPs) involved in transport and storage; transferrin (GmmTsf1) and ferritin from Glossina morsitans morsitans. GmmTsf1 transcripts are detected in the female fat body and in adult reproductive tissues, and only in the adult developmental stage in a bloodmeal independent manner. In contrast, the ferritin heavy chain (GmmFer1HCH) and light chain (GmmFer2LCH) transcripts are expressed ubiquitously, suggesting a more general role for these proteins in iron transport and storage. Protein domain predictions for each IBP suggest both the conservation and loss of several motifs present in their vertebrate homologues. In concert with many other described insect transferrins (Tfs), putative secreted GmmTsf1 maintains 3 of the 5 residues necessary for iron-binding in the N-terminal lobe, but exhibits a loss of this iron-binding ability in the C-terminal lobe as well as a loss of large sequence blocks. Both putative GmmFer1HCH and GmmFer2LCH proteins have signal peptides, similar to other insect ferritins. GmmFer2LCH has lost the 5'UTR iron-responsive element (IRE) and, thus, translation is no longer regulated by cellular iron levels. On the other hand, GmmFer1HCH maintains both the conserved ferroxidase center and the 5'UTR IRE; however, transcript variants suggest a more extensive regulatory mechanism for this subunit.

Genes of the antioxidant system of the honey bee: annotation and phylogeny

Antioxidant enzymes perform a variety of vital functions including the reduction of life-shortening oxidative damage. We used the honey bee genome sequence to identify the major components of the honey bee antioxidant system. A comparative analysis of honey bee with Drosophila melanogaster and Anopheles gambiae shows that although the basic components of the antioxidant system are conserved, there are important species differences in the number of paralogs. These include the duplication of thioredoxin reductase and the expansion of the thioredoxin family in fly; lack of expansion of the Theta, Delta and Omega GST classes in bee and no expansion of the Sigma class in dipteran species. The differential expansion of antioxidant gene families among honey bees and dipteran species might reflect the marked differences in life history and ecological niches between social and solitary species.

The haemoxisome: a haem-iron containing structure in the Rhodnius prolixus midgut cells

Rhodnius prolixus midgut was analysed using transmission electron microscopy and electron spectroscopic imaging in order to localize the cellular structures involved in haem metabolism. In the posterior midgut, special cellular electron-dense structures were observed. These structures are here designated haemoxisomes. Haemoxisomes are present in the epithelial cells at various time points after a blood meal. Several days after the blood meal, some of them become less electron-dense. By electron spectroscopic imaging, large amounts of iron and oxygen were detected in these cellular structures. The iron is probably bound to the porphyrin ring as an iron-protoporphyrin IX complex, as detected using the diaminobenzidine technique. An interesting observation was the presence of endoplasmic reticulum surrounding the haemoxisomes during some special periods. Iron content was monitored in the posterior midgut epithelium and was found to be constant at the initial days after a blood meal, but slightly higher at the end of the digestive process (from 13th up to 20th day). These results are in agreement with the observation that the appearance of the haemoxisomes changes at the end of the digestive process. The ability to degrade haem seems to depend on the presence of endoplasmic reticulum as observed using a haem degradation assay in the presence of an endoplasmic reticulum-enriched fraction. Taken together these results suggest that haemoxisomes may play a role in intracellular haem detoxification.

Molecular mechanism of distorted iron regulation in the blood-CSF barrier and regional blood-brain barrier following in vivo subchronic manganese exposure

Previous studies in this laboratory indicated that manganese (Mn) exposure in vitro increases the expression of transferrin receptor (TfR) by enhancing the binding of iron regulatory proteins (IRPs) to iron responsive element-containing RNA. The current study further tested the hypothesis that in vivo exposure to Mn increased TfR expression at both blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier (BCB), which contributes to altered iron (Fe) homeostasis in the CSF. Groups of rats (10-11 each) received oral gavages at doses of 5 mg Mn/kg or 15 mg Mn/kg as MnCl(2) once daily for 30 days. Blood, CSF, and choroid plexus were collected and brain capillary fractions were separated from the regional parenchyma. Metal analyses showed that oral Mn exposure decreased concentrations of Fe in serum (-66%) but increased Fe in the CSF (+167%). Gel shift assay showed that Mn caused a dose-dependent increase of binding of IRP1 to iron responsive element-containing RNA in BCB in the choroid plexus (+70%), in regional BBB of capillaries of striatum (+39%), hippocampus (+56%), frontal cortex (+49%), and in brain parenchyma of striatum (+67%), hippocampus (+39%) and cerebellum (+28%). Real-time RT-PCR demonstrated that Mn exposure significantly increased the expression of TfR mRNA in choroid plexus and striatum with concomitant reduction in the expression of ferritin (Ft) mRNA. Collectively, these data indicate that in vivo Mn exposure results in Fe redistribution in body fluids through regulating the expression of TfR and ferritin at BCB and selected regional BBB. The disrupted Fe transport by brain barriers may underlie the distorted Fe homeostasis in the CSF.

Secreted ferritin: mosquito defense against iron overload?

The yellow fever mosquito, Aedes aegypti, must blood feed in order to complete her life cycle. The blood meal provides a high level of iron that is required for egg development. We are interested in developing control strategies that interfere with this process. We show that A. aegypti larval cells synthesize and secrete ferritin in response to iron exposure. Cytoplasmic ferritin is maximal at low levels of iron, consists of both the light chain (LCH) and heavy chain (HCH) subunits and reflects cytoplasmic iron levels. Secreted ferritin increases in direct linear relationship to iron dose and consists primarily of HCH subunits. Although the messages for both subunits increase with iron treatment, our data indicate that mosquito HCH synthesis could be partially controlled at the translational level as well. Importantly, we show that exposure of mosquito cells to iron at low concentrations increases cytoplasmic iron, while higher iron levels results in a decline in cytoplasmic iron levels indicating that excess iron is removed from mosquito cells. Our work indicates that HCH synthesis and ferritin secretion are key factors in the response of mosquito cells to iron exposure and could be the primary mechanisms that allow these insects to defend against an intracellular iron overload.

Genome-wide analysis of gene expression in adult Anopheles gambiae

With their genome sequenced, Anopheles gambiae mosquitoes now serve as a powerful tool for basic research in comparative, evolutionary and developmental biology. The knowledge generated by these studies is expected to reveal molecular targets for novel vector control and pathogen transmission blocking strategies. Comparisons of gene-expression profiles between adult male and nonblood-fed female Anopheles gambiae mosquitoes revealed that roughly 22% of the genes showed sex-dependent regulation. Blood-fed females switch the majority of their metabolism to blood digestion and egg formation within 3 h after the meal is ingested, in detriment to other activities such as flight and response to environment stimuli. Changes in gene expression are most evident during the first, second and third days after a blood meal, when as many as 50% of all genes showed significant variation in transcript accumulation. After laying the first cluster of eggs (between 72 and 96 h after the blood meal), mosquitoes return to a nongonotrophic stage, similar but not identical to that of 3-day-old nonblood-fed females. Ageing and/or the nutritional state of mosquitoes at 15 days after a blood meal is reflected by the down-regulation of approximately 5% of all genes. A full description of the large number of genes regulated at each analysed time point and each biochemical pathway or biological processes in which they are involved is not possible within the scope of this contribution. Therefore, we present descriptions of groups of genes displaying major differences in transcript accumulation during the adult mosquito life. However, a publicly available searchable database (http://www.angagepuci.bio.uci.edu/) has been made available so that detailed analyses of specific groups of genes based on their descriptions, functions or levels of gene expression variation can be performed by interested investigators according to their needs.

The hemolymph proteome of Anopheles gambiae

We used two-dimensional SDS-PAGE and microsequencing or peptide mass fingerprinting to identify major proteins in the hemolymph of Anopheles gambiae. We found approximately 280 protein spots in hemolymph and identified 28 spots, representing 26 individual proteins. Most of these proteins have known or predicted functions in immunity, iron transport, or lipid biology. Many of the proteins have been found in hemolymph in other insects but one protein is novel: a new member of the ML family (involved in lipid recognition). Three of the identified proteins increased in spot intensity or appeared de novo following bacterial injection: a phenoloxidase, and two chitinase-like proteins. A subset of proteins decreased following bacterial injections: these included the light and heavy chains of ferritin. Several proteins appeared in hemolymph following any wound or injection. Most of these are metabolic enzymes lacking signal peptides that are likely to be released as a result of damage to muscles and other tissues by injury. The map will provide a useful tool for examining changes in hemolymph proteins following blood feeding and infection by parasites.

Microarray analysis of genes showing variable expression following a blood meal in Anopheles gambiae

A microarray analysis of 14 900 genes of the malaria vector mosquito, Anopheles gambiae, shows that as many as 33% (4924) of their corresponding transcription products vary in abundance within 24 h after a blood meal. Approximately half (2388) of these products increase in their accumulation and the remainder (2536) decrease. Expression dynamics of 80% of the genes analysed by expressed sequence tag (EST) projects reported previously are consistent with the observations from this microarray analysis. Furthermore, the microarray analysis is more sensitive in detecting variation in abundance of gene products expressed at low levels and is more sensitive overall in that a greater number of regulated genes are detected. Major changes in transcript abundance were seen in genes encoding proteins involved in digestion, oogenesis and locomotion. The microarray data and an electronic hyperlinked version of all tables are available to the research community at http://www.angagepuci.bio.uci.edu/1/.

Alteration at translational but not transcriptional level of transferrin receptor expression following manganese exposure at the blood-CSF barrier in vitro

Manganese exposure alters iron homeostasis in blood and cerebrospinal fluid (CSF), possibly by acting on iron transport mechanisms localized at the blood-brain barrier and/or blood-CSF barrier. This study was designed to test the hypothesis that manganese exposure may change the binding affinity of iron regulatory proteins (IRPs) to mRNAs encoding transferrin receptor (TfR), thereby influencing iron transport at the blood-CSF barrier. A primary culture of choroidal epithelial cells was adapted to grow on a permeable membrane sandwiched between two culture chambers to mimic blood-CSF barrier. Trace (59)Fe was used to determine the transepithelial transport of iron. Following manganese treatment (100 microM for 24 h), the initial flux rate constant (K(i)) of iron was increased by 34%, whereas the storage of iron in cells was reduced by 58%, as compared to controls. A gel shift assay demonstrated that manganese exposure increased the binding of IRP1 and IRP2 to the stem loop-containing mRNAs. Consequently, the cellular concentrations of TfR proteins were increased by 84% in comparison to controls. Assays utilizing RT-PCR, quantitative real-time reverse transcriptase-PCR, and nuclear run off techniques showed that manganese treatment did not affect the level of heterogeneous nuclear RNA (hnRNA) encoding TfR, nor did it affect the level of nascent TfR mRNA. However, manganese exposure resulted in a significantly increased level of TfR mRNA and reduced levels of ferritin mRNA. Taken together, these results suggest that manganese exposure increases iron transport at the blood-CSF barrier; the effect is likely due to manganese action on translational events relevant to the production of TfR, but not due to its action on transcriptional, gene expression of TfR. The disrupted protein-TfR mRNA interaction in the choroidal epithelial cells may explain the toxicity of manganese at the blood-CSF barrier.

Morphological and enzymatic analysis of the midgut of Anopheles darlingi during blood digestion

The midgut of adult female Anopheles darlingi is comprised of narrow anterior and dilated posterior regions, with a single layered epithelium composed by cuboidal digestive cells. Densely packed apical microvilli and an intricate basal labyrinth characterize each cell pole. Before blood feeding, apical cytoplasm contains numerous round granules and whorled profiles of rough endoplasmic reticulum. Engorgement causes a great distension of midgut. This provokes the flattening of digestive cells and their nuclei. Simultaneously, apical granules disappear, the whorls of endoplasmic reticulum disassemble and 3h post bloodmeal (PBM), nucleoli enlarge manyfold. An intense absorptive process takes place during the first 24 h PBM, with the formation of large glycogen inclusions, which persist after the end of the digestive process. Endoproteases activities are induced after bloodmeal and attain their maximum values between 10 and 36 h PBM. At least two different aminopeptidases seem to participate in the digestive process, with their maximum activity values at 36 and 48 h PBM, respectively. Coarse electrondense aggregates, possibly debris from digested erythrocytes, begin to appear on the luminal face of the peritrophic membrane from 18 h PBM and persist during all the digestive process, and are excreted at its end. We suggest that these aggregates could contain some kind of insoluble form of haem, in order of neutralize its toxicity.

Regulation of the ferritin heavy-chain homologue gene in the yellow fever mosquito, Aedes aegypti

In the yellow fever mosquito Aedes aegypti, the ferritin heavy-chain homologue (HCH) gene is induced by blood feeding. This suggests that ferritin may serve as a cytotoxic protector against the oxidative challenge of the blood meal and may be essential for the survival of the insect. In this study, various cis-acting elements for the gene were identified and mapped. Transfection assays showed that the strength and activity of a subset of these elements are orientation-dependent. The shift observed for the ferritin HCH cis-acting elements is unique among known ferritin genes. DNase I footprinting data together with Transfac analyses identified a number of putative sites known for their involvement in developmental and cell proliferation processes.

The ferritin light-chain homologue promoter in Aedes aegypti

Promoters that direct the expression of antipathogenic molecules to primary sites of pathogenic invasions provide a means to interfere with these invasions. Thus, they have the potential to be used in mosquito control. However, exogenous elements are known to lower the fitness of most insects, and given the ability of insects to evolve rapidly, all currently known promoters could be rendered useless. As transgenic mosquitoes may be a major component in the fight against mosquito-borne diseases, the identification of new mosquito promoters is needed. The promoter of the Aedes aegypti ferritin light-chain homologue (LCH) gene, a gene whose expression is induced in gut tissues during blood feeding has been identified and mapped. Transfection data indicate that the ferritin LCH promoter is a strong promoter. DNase I footprinting data and Transfac analyses suggest that the ferritin LCH promoter contains putative GATA, E2F, NIT2, TATA and DPE sites. These data together provide the first detailed map of a known ferritin LCH gene.

Midgut and salivary gland transcriptomes of the arbovirus vector Culicoides sonorensis (Diptera: Ceratopogonidae)

Numerous Culicoides spp. are important vectors of livestock or human disease pathogens. Transcriptome information from midguts and salivary glands of adult female Culicoides sonorensis provides new insight into vector biology. Of 1719 expressed sequence tags (ESTs) from adult serum-fed female midguts harvested within 5 h of feeding, twenty-eight clusters of serine proteases were derived. Four clusters encode putative iron binding proteins (FER1, FERL, PXDL1, PXDL2), and two clusters encode metalloendopeptidases (MDP6C, MDP6D) that probably function in bloodmeal catabolism. In addition, a diverse variety of housekeeping cDNAs were identified. Selected midgut protease transcripts were analysed by quantitative real-time PCR (q-PCR): TRY1_115 and MDP6C mRNAs were induced in adult female midguts upon feeding, whereas TRY1_156 and CHYM1 were abundant in midguts both before and immediately after feeding. Of 708 salivary gland ESTs analysed, clusters representing two new classes of protein families were identified: a new class of D7 proteins and a new class of Kunitz-type protease inhibitors. Additional cDNAs representing putative immunomodulatory proteins were also identified: 5' nucleotidases, antigen 5-related proteins, a hyaluronidase, a platelet-activating factor acetylhydrolase, mucins and several immune response cDNAs. Analysis by q-PCR showed that all D7 and Kunitz domain transcripts tested were highly enriched in female heads compared with other tissues and were generally absent from males. The mRNAs of two additional protease inhibitors, TFPI1 and TFPI2, were detected in salivary glands of paraffin-embedded females by in situ hybridization.

Molecular cloning, expression and characterization of cDNAs encoding the ferritin subunits from the beetle, Apriona germari

Insect secreted ferritins are composed of subunits, which resemble heavy and light chains of vertebrate cytosolic ferritins. We describe here the cloning, expression and characterization of cDNAs encoding the ferritin heavy-chain homologue (HCH) and light-chain homologue (LCH) from the mulberry longicorn beetle, Apriona germari (Coleoptera, Cerambycidae). The A. germari ferritin LCH and HCH cDNA sequences were comprised of 672 and 636 bp encoding 224 and 212 amino acid residues, respectively. The A. germari ferritin HCH subunit contained the conserved motifs for the ferroxidase center typical of vertebrate ferritin heavy chains and the iron-responsive element (IRE) sequence with a predicted stem-loop structure was present in the 5'-untranslated region (UTR) of ferritin HCH mRNA. However, the A. germari ferritin LCH subunit had no IRE at its 5'-UTR and ferroxidase center residues. Phylogenetic analysis confirmed the deduced protein sequences of A. germari ferritin HCH and LCH being divided into two types, G type (LCH) and S type (HCH). Southern blot analysis suggested the possible presence of each A. germari ferritin subunit gene as a single copy and Northern blot analysis confirmed a higher expression pattern in midgut than fat body. The cDNAs encoding the A. germari ferritin subunits were expressed as approximately 30 kDa (LCH) and 26 kDa (HCH) polypeptides in baculovirus-infected insect cells. Western blot analysis and iron staining assay confirmed that A. germari ferritin has a native molecular mass of approximately 680 kDa.

Stress and transcriptional regulation of tick ferritin HC

We previously identified a partial Dermacentor variabilis cDNA encoding ferritin HC (HC) subunit homolog (DVFER) that was differentially upregulated in Rickettsia montanensis infected ticks (Mulenga et al., 2003a). We have used rapid amplification of cDNA ends to clone full-length DVFER cDNA and its apparent ortholog from the wood tick, D. andersoni (DAFER), both of which show high sequence similarity to vertebrate than insect ferritin. Both DVFER and DAFER contain the stem-loop structure of a putative iron responsive element in the 5' untranslated region (nucleotide positions, 16-42) and the feroxidase centre loop typical for vertebrate ferritin HC subunits. Quantitative Western and Northern blotting analyses of protein and RNA from unfed and partially fed whole tick as well as dissected tick tissues demonstrated that DVFER is constitutively and ubiquitously expressed. Based on densitometric analysis of detected protein and mRNA bands, DVFER is predominantly expressed in the midgut, and to a lesser extent in the salivary glands, ovary and fatbody. Sham treatment (mechanical injury) and Escherichia coli challenge of D. variabilis ticks stimulated statistically significant (approximately 1.5- and approximately 3.0-fold, respectively) increases in DVFER mRNA abundance over time point matched naive control ticks. These data suggest that DVFER mRNA is nonspecifically up regulated in response to mechanical injury or bacterial infection induced stress.