Gene structure and polymorphism of an invertebrate nitric oxide synthase gene

Effects of L-arginine on Nitric Oxide Synthesis and Larval Metamorphosis of Mytilus coruscus

To investigate the regulatory functions of L-arginine and nitric oxide (NO) on Mytilus coruscus metamorphosis, M. coruscus larvae were exposed to an inhibitor of nitric oxide synthase (NOS), aminoguanidine hemisulfate (AGH), and a substrate for NO synthesis, L-arginine. We observed that NO levels showed a significant increase, and this trend continued with L-arginine treatment. When NOS activity was inhibited, the larvae could not synthesize NO, and metamorphosis was not inhibited even in the presence of L-arginine. On transfecting pediveliger larvae with NOS siRNA followed by L-arginine exposure, we found that the larvae did not produce NO and that the larval metamorphosis rate was significantly increased, suggesting that L-arginine regulates M. coruscus larval metamorphosis by promoting NO synthesis. Our findings improve our understanding of the effects of marine environmental factors on larval metamorphosis of mollusks.

Non-immune Traits Triggered by Blood Intake Impact Vectorial Competence

Blood-feeding arthropods are considered an enormous public health threat. They are vectors of a plethora of infectious agents that cause potentially fatal diseases like Malaria, Dengue fever, Leishmaniasis, and Lyme disease. These vectors shine due to their own physiological idiosyncrasies, but one biological aspect brings them all together: the requirement of blood intake for development and reproduction. It is through blood-feeding that they acquire pathogens and during blood digestion that they summon a collection of multisystemic events critical for vector competence. The literature is focused on how classical immune pathways (Toll, IMD, and JAK/Stat) are elicited throughout the course of vector infection. Still, they are not the sole determinants of host permissiveness. The dramatic changes that are the hallmark of the insect physiology after a blood meal intake are the landscape where a successful infection takes place. Dominant processes that occur in response to a blood meal are not canonical immunological traits yet are critical in establishing vector competence. These include hormonal circuitries and reproductive physiology, midgut permeability barriers, midgut homeostasis, energy metabolism, and proteolytic activity. On the other hand, the parasites themselves have a role in the outcome of these blood triggered physiological events, consistently using them in their favor. Here, to enlighten the knowledge on vector-pathogen interaction beyond the immune pathways, we will explore different aspects of the vector physiology, discussing how they give support to these long-dated host-parasite relationships.

Mosquito Innate Immunity

Mosquitoes live under the endless threat of infections from different kinds of pathogens such as bacteria, parasites, and viruses. The mosquito defends itself by employing both physical and physiological barriers that resist the entry of the pathogen and the subsequent establishment of the pathogen within the mosquito. However, if the pathogen does gain entry into the insect, the insect mounts a vigorous innate cellular and humoral immune response against the pathogen, thereby limiting the pathogen's propagation to nonpathogenic levels. This happens through three major mechanisms: phagocytosis, melanization, and lysis. During these processes, various signaling pathways that engage intense mosquito⁻pathogen interactions are activated. A critical overview of the mosquito immune system and latest information about the interaction between mosquitoes and pathogens are provided in this review. The conserved, innate immune pathways and specific anti-pathogenic strategies in mosquito midgut, hemolymph, salivary gland, and neural tissues for the control of pathogen propagation are discussed in detail.

Interorgan Molecular Communication Strategies of "Local" and "Systemic" Innate Immune Responses in Mosquito Anopheles stephensi

Mosquitoes that transmit many deadly infectious diseases also need to keep fighting against many microbial infections. Constitutive expression of multiple antimicrobial peptides (AMPs) in almost all body tissues is believed to facilitate the effective management of these local infections. When any infection breaches the local barrier, AMPs are induced rapidly in non-target tissues such as hemocytes (HCs) and establish their co-ordination with systemic immune effectors to clear off the body infection. But how interorgan immune communication is managed during local and systemic infections remain largely unknown. To understand this interorgan molecular relationship, we identified, extensively profiled and compared the expression of AMPs in three important mosquito tissues viz. midgut, fat body (FB), and HCs. dsRNA-mediated AMPs silencing suggests that mosquito tissues are able to manage an optimal expression of AMPs at the physiological level. We also examined the possible contribution of two important immune regulator genes relish (REL) and nitric oxide synthase, controlling AMPs expression in these tissues during local or systemic infections. We show that each tissue has a unique ability to respond to local/systemic challenges, but HCs are more specialized to recognize and discriminate-specific antigens than gut and FB. Our investigation also revealed that both REL and NO participate in the overall management of the interorgan immune responses, but at the same time each tissue also has its own ability to maintain the interorgan flow of signals. In our knowledge, this is the first large-scale study examining the interorgan immune relationship in the mosquito.

Quantitative real-time PCR analysis of Anopheles dirus TEP1 and NOS during Plasmodium berghei infection, using three reference genes

Quantitative reverse transcription PCR (qRT-PCR) has been an integral part of characterizing the immunity of Anopheles mosquitoes towards Plasmodium invasion. Two anti-Plasmodium factors of Anopheles, thioester-containing protein 1 (TEP1) and nitric oxide synthase (NOS), play a role in the refractoriness of Anopheles towards Plasmodium infection and are generally expressed during infection. However, these are less studied in Anopheles dirus, a dominant malaria vector in Southeast Asia. Furthermore, most studies used a single reference gene for normalization during gene expression analysis without proper validation. This may lead to erroneous quantification of expression levels. Therefore, the present study characterized and investigated the expression profiles of TEP1 and NOS of Anopheles dirus during P. berghei infection. Prior to that, the elongation factor 1-alpha (EF1), actin 1 (Act) and ribosomal protein S7 (S7) genes were validated for their suitability as a set of reference genes. TEP1 and NOS expressions in An. dirus were found to be significantly induced after P. berghei infection.

Evolution of Cell-Autonomous Effector Mechanisms in Macrophages versus Non-Immune Cells

Specialized adaptations for killing microbes are synonymous with phagocytic cells including macrophages, monocytes, inflammatory neutrophils, and eosinophils. Recent genome sequencing of extant species, however, reveals that analogous antimicrobial machineries exist in certain non-immune cells and also within species that ostensibly lack a well-defined immune system. Here we probe the evolutionary record for clues about the ancient and diverse phylogenetic origins of macrophage killing mechanisms and how some of their properties are shared with cells outside the traditional bounds of immunity in higher vertebrates such as mammals.

Evolutionary roots of arginase expression and regulation

Two main types of macrophage functions are known: classical (M1), producing nitric oxide, NO, and M2, in which arginase activity is primarily expressed. Ornithine, the product of arginase, is a substrate for synthesis of polyamines and collagen, important for growth and ontogeny of animals. M2 macrophages, expressing high level of mitochondrial arginase, have been implicated in promoting cell division and deposition of collagen during ontogeny and wound repair. Arginase expression is the default mode of tissue macrophages, but can also be amplified by signals, such as IL-4/13 or transforming growth factor-β (TGF-β) that accelerates wound healing and tissue repair. In worms, the induction of collagen gene is coupled with induction of immune response genes, both depending on the same TGF-β-like pathway. This suggests that the main function of M2 “heal” type macrophages is originally connected with the TGF-β superfamily of proteins, which are involved in regulation of tissue and organ differentiation in embryogenesis. Excretory–secretory products of metazoan parasites are able to induce M2-type of macrophage responses promoting wound healing without participation of Th2 cytokines IL-4/IL-13. The expression of arginase in lower animals can be induced by the presence of parasite antigens and TGF-β signals leading to collagen synthesis. This also means that the main proteins, which, in primitive metazoans, are involved in regulation of tissue and organ differentiation in embryogenesis are produced by innate immunity. The signaling function of NO is known already from the sponge stage of animal evolution. The cytotoxic role of NO molecule appeared later, as documented in immunity of marine mollusks and some insects. This implies that the M2-wound healing promoting function predates the defensive role of NO, a characteristic of M1 macrophages. Understanding when and how the M1 and M2 activities came to be in animals is useful for understanding how macrophage immunity, and immune responses operate.

Injury and immune response: applying the danger theory to mosquitoes

The insect immune response can be activated by the recognition of both non-self and molecular by-products of tissue damage. Since pathogens and tissue damage usually arise at the same time during infection, the specific mechanisms of the immune response to microorganisms, and to tissue damage have not been unraveled. Consequently, some aspects of damage caused by microorganisms in vector-borne arthropods have been neglected. We herein reassess the Anopheles-Plasmodium interaction, incorporating Matzinger's danger/damage hypothesis and George Salt's injury assumptions. The invasive forms of the parasite cross the peritrophic matrix and midgut epithelia to reach the basal lamina and differentiate into an oocyst. The sporozoites produced in the oocyst are released into the hemolymph, and from there enter the salivary gland. During parasite development, wounds to midgut tissue and the basement membrane are produced. We describe the response of the different compartments where the parasite interacts with the mosquito. In the midgut, the response includes the expression of antimicrobial peptides, production of reactive oxygen species, and possible activation of midgut regenerative cells. In the basal membrane, wound repair mainly involves the production of molecules and the recruitment of hemocytes. We discuss the susceptibility to damage in tissues, and how the place and degree of damage may influence the differential response and the expression of damage associated molecular patterns (DAMPs). Knowledge about damage caused by parasites may lead to a deeper understanding of the relevance of tissue damage and the immune response it generates, as well as the origins and progression of infection in this insect-parasite interaction.

Protein kinase C-dependent signaling controls the midgut epithelial barrier to malaria parasite infection in anopheline mosquitoes

Anopheline mosquitoes are the primary vectors of parasites in the genus Plasmodium, the causative agents of malaria. Malaria parasites undergo a series of complex transformations upon ingestion by the mosquito host. During this process, the physical barrier of the midgut epithelium, along with innate immune defenses, functionally restrict parasite development. Although these defenses have been studied for some time, the regulatory factors that control them are poorly understood. The protein kinase C (PKC) gene family consists of serine/threonine kinases that serve as central signaling molecules and regulators of a broad spectrum of cellular processes including epithelial barrier function and immunity. Indeed, PKCs are highly conserved, ranging from 7 isoforms in Drosophila to 16 isoforms in mammals, yet none have been identified in mosquitoes. Despite conservation of the PKC gene family and their potential as targets for transmission-blocking strategies for malaria, no direct connections between PKCs, the mosquito immune response or epithelial barrier integrity are known. Here, we identify and characterize six PKC gene family members--PKCδ, PKCε, PKCζ, PKD, PKN, and an indeterminate conventional PKC--in Anopheles gambiae and Anopheles stephensi. Sequence and phylogenetic analyses of the anopheline PKCs support most subfamily assignments. All six PKCs are expressed in the midgut epithelia of A. gambiae and A. stephensi post-blood feeding, indicating availability for signaling in a tissue that is critical for malaria parasite development. Although inhibition of PKC enzymatic activity decreased NF-κB-regulated anti-microbial peptide expression in mosquito cells in vitro, PKC inhibition had no effect on expression of a panel of immune genes in the midgut epithelium in vivo. PKC inhibition did, however, significantly increase midgut barrier integrity and decrease development of P. falciparum oocysts in A. stephensi, suggesting that PKC-dependent signaling is a negative regulator of epithelial barrier function and a potential new target for transmission-blocking strategies.

The JAK-STAT pathway controls Plasmodium vivax load in early stages of Anopheles aquasalis infection

Malaria affects 300 million people worldwide every year and 450,000 in Brazil. In coastal areas of Brazil, the main malaria vector is Anopheles aquasalis, and Plasmodium vivax is responsible for the majority of malaria cases in the Americas. Insects possess a powerful immune system to combat infections. Three pathways control the insect immune response: Toll, IMD, and JAK-STAT. Here we analyze the immune role of the A. aquasalis JAK-STAT pathway after P. vivax infection. Three genes, the transcription factor Signal Transducers and Activators of Transcription (STAT), the regulatory Protein Inhibitors of Activated STAT (PIAS) and the Nitric Oxide Synthase enzyme (NOS) were characterized. Expression of STAT and PIAS was higher in males than females and in eggs and first instar larvae when compared to larvae and pupae. RNA levels for STAT and PIAS increased 24 and 36 hours (h) after P. vivax challenge. NOS transcription increased 36 h post infection (hpi) while this protein was already detected in some midgut epithelial cells 24 hpi. Imunocytochemistry experiments using specific antibodies showed that in non-infected insects STAT and PIAS were found mostly in the fat body, while in infected mosquitoes the proteins were found in other body tissues. The knockdown of STAT by RNAi increased the number of oocysts in the midgut of A. aquasalis. This is the first clear evidence for the involvement of a specific immune pathway in the interaction of the Brazilian malaria vector A. aquasalis with P. vivax, delineating a potential target for the future development of disease controlling strategies.

Mosquito immunity

Throughout their lifetime, mosquitoes are exposed to pathogens during feeding, through breaks in their cuticle and following pathogen-driven cuticular degradation. To resist infection, mosquitoes mount innate cellular and humoral immune responses that are elicited within minutes of exposure and can lead to pathogen death via three broadly defined mechanisms: lysis, melanization and hemocyte-mediated phagocytosis. This chapter reviews our current understanding of the mosquito immune system, with an emphasis on the physical barriers that prevent pathogens from entering the body, the organs and tissues that regulate immune responses and the mechanistic and molecular bases of immunity.

Immune homeostasis to microorganisms in the guts of triatomines (Reduviidae)--a review

Bacteria, fungi and parasites are in constant contact with the insect gut environment and can influence different aspects of the host gut physiology. Usually, some of these microorganisms develop and survive in the digestive tract. Therefore, the gut environment must be able to tolerate certain populations of these organisms for the establishment of interactions between non-pathogenic bacteria, parasites and the gut. This review provides a brief overview of the biological and molecular mechanisms that microorganisms use to interact with the gut epithelia in mosquitoes and speculates on their significances for the development of bacteria and Trypanosoma cruzi in the guts of triatomines.

The effect of nitric oxide and hydrogen peroxide in the activation of the systemic immune response of Anopheles albimanus infected with Plasmodium berghei

The expression of genes encoding the antimicrobial peptides (AMPs) attacin, cecropin and gambicin, as well as the effects of NO and H(2)O(2) on their expression was investigated in midguts and fat bodies of Anopheles albimanus during the midgut infection with Plasmodium berghei. Midgut infection induced an increase in the expression of the three AMPs in both tissues; while NO and H(2)O(2) were present in haemolymph. Treatment with L-NAME and vitamin C reduced the effect of P. berghei infection on the AMP's expression, and exogenous NO and H(2)O(2) induced their expression in the mosquito fat body. The induction of AMPs in abdominal tissues, while the malaria parasites are in the mosquito midgut, suggests communication between the midgut epithelial cells and the abdominal tissue which has not yet had direct contact with the parasites. Free radical production in mosquito midgut and haemolymph during Plasmodium infection and their inductive effect on AMPs in abdominal tissues indicates the possible participation of these radicals in mediating a systemic immune response in this mosquito.

Molecular cloning and characterization of the nitric oxide synthase gene from kuruma shrimp, Marsupenaeus japonicus

Nitric oxide (NO) signaling is involved in many physiological processes in vertebrates and invertebrates. In crustaceans, nitric oxide synthase (NOS) plays a significant role in the regulation of the nervous system and in innate immunity. Here, we describe the entire cDNA sequence (4616 bp) of the kuruma shrimp Marsupenaeus japonicus NOS (Mj NOS) generated using the reverse transcriptase-polymerase chain reaction (RT-PCR) and 5'- and 3'- rapid amplification PCRs of cDNA ends from brain and gill mRNAs. The open reading frame of Mj NOS encoded a protein of 1187 amino acids with an estimated mass of 134 kDa, and had an 82.3% sequence homology with the NOS gene of the land crab Gecarcinus lateralis. Highly conserved amino acid sequences in heme and tetrahydrobiopterin were observed in the oxygenase domain. FMN, FAD and NADPH were found in the reductase domain. Mj NOS mRNA was constitutively expressed in the brain, gill, intestine, thoracic ganglion and testis of the kuruma shrimp. When Vibrio penaeicida was injected into the kuruma shrimp, Mj NOS was expressed in the brain, gill, heart, lymphoid organ, intestine and thoracic ganglion. Mj NOS expression in the gill reached its peak 12 h and decreased to its normal level 24 h after V. penaeicida injection.

NO synthase: structures and mechanisms

Production of NO from arginine and molecular oxygen is a complex chemical reaction unique to biology. Our understanding of the chemical and regulation mechanisms of the NO synthases has developed over the past two decades, uncovering some extraordinary features. This article reviews recent progress and highlights current issues and controversies. The structure of the enzyme has now been determined almost in entirety, although it is as a selection of fragments, which are difficult to assemble unambiguously. NO synthesis is driven by electron transfer through FAD and FMN cofactors, which is controlled by calmodulin binding in the constitutive mammalian enzymes. Many of the unique structural features involved have been characterised, but the mechanics of calmodulin-dependent activation are largely unresolved. Ultimately, NO is produced in the active site by the reaction of arginine with activated heme-bound oxygen in two distinct cycles. The unique role of the tetrahydrobiopterin cofactor as an electron donor in this process has now been established, but the subsequent chemical events are currently a matter of intense speculation and debate.

Nitric oxide is an essential component of the hemocyte-mediated mosquito immune response against bacteria

Nitric oxide is a signaling and immune effector molecule synthesized by the enzyme nitric oxide synthase. In mosquitoes, nitric oxide functions as a parasite antagonist in the midgut but little is known about its function in the hemocoel. Here, we characterized the temporal and spatial expression of the Anopheles gambiae nitric oxide synthase gene and explored the role nitric oxide plays in the antibacterial response in the mosquito hemocoel. Quantitative PCR and Western blot analyses showed that nitric oxide synthase is expressed in hemocytes and fat body, and is upregulated in response to systemic infection with Escherichia coli and Micrococcus luteus. Diaphorase staining and immunofluorescence showed that nitric oxide synthase is abundant in the granulocyte subpopulation of hemocytes, and both the staining intensity and the percentage of cells that stain for nitric oxide synthase significantly increase after a bacterial challenge. When nitric oxide production was inhibited, the mosquito's ability to kill E. coli was significantly reduced. Accordingly, inhibiting nitric oxide production increased the mortality rate of mosquitoes with systemic E. coli infections. Taken altogether, these data show that nitric oxide is a crucial player in the antibacterial immune response in the mosquito hemocoel.

An ancient immunity gene duplication in Daphnia magna: RNA expression and sequence analysis of two nitric oxide synthase genes

NO (nitric oxide) is a highly reactive free radical gas thought to play a major role in the invertebrate immune response by harming pathogens and limiting their growth. Here we report on studies of nitric oxide synthase (NOS) genes in the crustacean Daphnia, one of the few non-insect arthropod models used to study host-pathogen interactions. While the NOS gene is found as a single copy in other invertebrates, we found two copies (NOS1 and NOS2), which a phylogenetic reconstruction showed to be the result of an ancient duplication event. Both genes bear features commonly found in invertebrate NOS, however, the two genes differ in their rate of evolution, intraspecific polymorphism and expression level. We tested whether the more rapid evolution of NOS2 could be due to positive selection, but found the rate of amino-acid substitutions between Daphnia species to be compatible with a neutral model. To associate NOS or NO activity with infection, we performed infection experiments with Daphnia magna and one of its natural pathogens (the bacterium Pasteuria ramosa). In one set of experimental infections, we supplemented D. magna with L-arginine, the NOS substrate, or with L-NAME, a NOS antagonist, and found this to result in lower and higher infection levels, respectively, which is at least compatible with the notion that NO may aid defence against Pasteuria. A second experiment indicated that NOS transcription does not increase following exposure to Pasteuria. Thus, the function of NOS in Daphnia immunity remains uncertain, but the pattern of gene duplication and subsequent divergence suggests evolution via neo- or subfunctionalization.

The STAT pathway mediates late-phase immunity against Plasmodium in the mosquito Anopheles gambiae

The STAT family of transcription factors activates expression of immune system genes in vertebrates. The ancestral STAT gene (AgSTAT-A) appears to have duplicated in the mosquito Anopheles gambiae, giving rise to a second intronless STAT gene (AgSTAT-B), which we show regulates AgSTAT-A expression in adult females. AgSTAT-A participates in the transcriptional activation of nitric oxide synthase (NOS) in response to bacterial and plasmodial infection. Activation of this pathway, however, is not essential for mosquitoes to survive a bacterial challenge. AgSTAT-A silencing reduces the number of early Plasmodium oocysts in the midgut, but nevertheless enhances the overall infection by increasing oocyst survival. Silencing of SOCS, a STAT suppressor, has the opposite effect, reducing Plasmodium infection by increasing NOS expression. Chemical inhibition of mosquito NOS activity after oocyte formation increases oocyte survival. Thus, the AgSTAT-A pathway mediates a late-phase antiplasmodial response that reduces oocyst survival in A. gambiae.

Determination of nitric oxide metabolites, nitrate and nitrite, in Anopheles culicifacies mosquito midgut and haemolymph by anion exchange high-performance liquid chromatography: plausible mechanism of refractoriness

Background

The diverse physiological and pathological role of nitric oxide in innate immune defenses against many intra and extracellular pathogens, have led to the development of various methods for determining nitric oxide (NO) synthesis. NO metabolites, nitrite (NO₂^-) and nitrate (NO₃^-) are produced by the action of an inducible Anopheles culicifacies NO synthase (AcNOS) in mosquito mid-guts and may be central to anti-parasitic arsenal of these mosquitoes.

Method

While exploring a plausible mechanism of refractoriness based on nitric oxide synthase physiology among the sibling species of An. culicifacies, a sensitive, specific and cost effective high performance liquid chromatography (HPLC) method was developed, which is not influenced by the presence of biogenic amines, for the determination of NO₂^- and NO₃^- from mosquito mid-guts and haemolymph.

Results

This method is based on extraction, efficiency, assay reproducibility and contaminant minimization. It entails de-proteinization by centrifugal ultra filtration through ultracel 3 K filter and analysis by high performance anion exchange liquid chromatography (Sphereclone, 5 μ SAX column) with UV detection at 214 nm. The lower detection limit of the assay procedure is 50 pmoles in all midgut and haemolymph samples. Retention times for NO₂^- and NO₃^- in standards and in mid-gut samples were 3.42 and 4.53 min. respectively. Assay linearity for standards ranged between 50 nM and 1 mM. Recoveries of NO₂^- and NO₃^- from spiked samples (1–100 μM) and from the extracted standards (1–100 μM) were calculated to be 100%. Intra-assay and inter assay variations and relative standard deviations (RSDs) for NO₂^- and NO₃^- in spiked and un-spiked midgut samples were 5.7% or less. Increased levels NO₂^- and NO₃^- in midguts and haemolymph of An. culicifacies sibling species B in comparison to species A reflect towards a mechanism of refractoriness based on AcNOS physiology.

Conclusion

HPLC is a sensitive and accurate technique for identification and quantifying pmole levels of NO metabolites in mosquito midguts and haemolymph samples that can be useful for clinical investigations of NO biochemistry, physiology and pharmacology in various biological samples.

Low levels of mammalian TGF-beta1 are protective against malaria parasite infection, a paradox clarified in the mosquito host

Nitric oxide (NO), derived from catalysis of inducible NO synthase (iNOS), limits malaria parasite growth in mammals. Transforming growth factor (TGF)-beta1 suppresses iNOS in cells in vitro as well as in vivo in mice, but paradoxically severe malaria in humans is associated with low levels of TGF-beta1. We hypothesized that this paradox is a universal feature of infection and occurs in the mosquito Anopheles stephensi, an invertebrate host for Plasmodium that also regulates parasite development with inducible NO synthase (AsNOS). We show that exogenous human TGF-beta1 dose-dependently regulates mosquito AsNOS expression and that parasite killing by low dose TGF-beta1 depends on AsNOS catalysis. Furthermore, induction of AsNOS expression by TGF-beta1 is regulated by NO synthesis. These results suggest that TGF-beta1 plays similar roles during parasite infection in mammals and mosquitoes and that this role is linked to the effects of TGF-beta1 on inducible NO synthesis.

Distribution and characterization of nitric oxide synthase in the nervous system of Triatoma infestans (Insecta: Heteroptera)

The biochemical characterization of nitric oxide synthase (NOS) and its distribution in the central nervous system (CNS) were studied in the heteropteran bug Triatoma infestans. NOS-like immunoreactivity was found in the brain, subesophageal ganglion, and thoracic ganglia by using immunocytochemistry. In the protocerebrum, NOS-immunoreactive (IR) somata were detected in the anterior, lateral, and posterior soma rinds. In the optic lobe, numerous immunostained somata were observed at the level of the first optic chiasma, around the lobula, and in the proximal optic lobe. In the deutocerebrum, NOS-IR perikarya were mainly observed in the lateral soma rind, surrounding the sensory glomeruli, and a few cell bodies were seen in association with the antennal mechanosensory and motor neuropil. No immunostaining could be detected in the antennal nerve. The subesophageal and prothoracic ganglia contained scattered immunostained cell bodies. NOS-IR somata were present in all the neuromeres of the posterior ganglion. Western blotting showed that a universal NOS antiserum recognized a band at 134 kDa, in agreement with the expected molecular weight of the protein. Analysis of the kinetics of nitric oxide production revealed a fully active enzyme in tissue samples of the CNS of T. infestans.

A standard cytogenetic photomap for the mosquito Anopheles stephensi (Diptera: Culicidae): application for physical mapping

To facilitate physical genome mapping, we have developed a new cytogenetic photomap for Anopheles stephensi (Liston) (Diptera: Culicidae), an important malaria vector in Asia. The high-resolution images of the ovarian polytene chromosomes have been straightened and divided by numbered divisions and lettered subdivisions. The exact chromosomal locations of eight DNA probes have been determined by fluorescent in situ hybridization. Using the DNA sequences, we have established correspondence between chromosomal arms among An. stephensi, Anopheles gambiae (Patton), and Anopheles funestus (Giles). The results support previous cytogenetic observations of arm translocations taking place during diversification of the species. To make the cytogenetic map useful for population genetics studies, we have indicated the chromosomal positions for the breakpoints of 19 polymorphic inversions.

Nitric oxide: an antiparasitic molecule of invertebrates

Since Furchgott, Ignarro and Murad won the Nobel prize in 1998 for their work on the role of nitric oxide (NO) as a signaling molecule, many reports have shown the seemingly limitless range of body functions controlled by this compound. In vertebrates, the role of NO as a defense against infection caused by viruses, bacteria, and protozoan and metazoan parasites has been known for several years. New evidence, however, shows that NO is also important in defending invertebrates against parasites. This discovery is a breakthrough in the understanding of how the invertebrate immune system works, and it has implications for the emerging field of invertebrate ecological immunology.

A mosquito 2-Cys peroxiredoxin protects against nitrosative and oxidative stresses associated with malaria parasite infection

Malaria parasite infection in anopheline mosquitoes induces nitrosative and oxidative stresses that limit parasite development, but also damage mosquito tissues in proximity to the response. Based on these observations, we proposed that cellular defenses in the mosquito may be induced to minimize self-damage. Specifically, we hypothesized that peroxiredoxins (Prxs), enzymes known to detoxify reactive oxygen species (ROS) and reactive nitrogen oxide species (RNOS), protect mosquito cells. We identified an Anopheles stephensi 2-Cys Prx ortholog of Drosophila melanogaster Prx-4783, which protects fly cells against oxidative stresses. To assess function, AsPrx-4783 was overexpressed in D. melanogaster S2 and in A. stephensi (MSQ43) cells and silenced in MSQ43 cells with RNA interference before treatment with various ROS and RNOS. Our data revealed that AsPrx-4783 and DmPrx-4783 differ in host cell protection and that AsPrx-4783 protects A. stephensi cells against stresses that are relevant to malaria parasite infection in vivo, namely nitric oxide (NO), hydrogen peroxide, nitroxyl, and peroxynitrite. Further, AsPrx-4783 expression is induced in the mosquito midgut by parasite infection at times associated with peak nitrosative and oxidative stresses. Hence, whereas the NO-mediated defense response is toxic to both host and parasite, AsPrx-4783 may shift the balance in favor of the mosquito.

Studies on nitric oxide synthase activity in haemocytes of shrimps Fenneropenaeus chinensis and Marsupenaeus japonicus after white spot syndrome virus infection

The nitric oxide synthase (NOS) activity in the haemocytes of shrimps Fenneropenaeus chinensis (Osbeck) and Marsupenaeus japonicus (Bate) was studied after white spot syndrome virus (WSSV) infection to determine its characteristics in response to virus infection. First, the NOS activity in haemocytes of shrimps was determined by the means of NBT reduction and changes in cell conformation. And the variations of NOS activity in shrimps after challenge with WSSV intramuscularly were evaluated through the analysis of l-citrulline and total nitrite/nitrate (both as NO derivates) concentrations. The result showed that NOS activity in the haemocytes of F. chinensis increased slightly from 0 to 12 h postchallenge, indicated by the variations of l-citrulline (from 11.15 ± 0.10 to 12.08 ± 0.64 μM) and total nitrite/nitrate concentrations (from 10.45 ± 0.65 to 12.67 ± 0.52 μM). Then it decreased sharply till the end of the experiment (84 h postchallenge), the concentrations of l-citrulline and total nitrite/nitrate at 84 h were 1.58 ± 0.24 and 2.69 ± 0.70 μM, respectively. The LPS-stimulated NOS activity kept constant during the experiment. However, in M. japonicus, the NOS activity kept increasing during the first 72 h postchallenge, the concentrations of l-citrulline and total nitrite/nitrate increased from 7.82 ± 0.77 at 0 h to 10.79 ± 0.50 μM at 72 h, and from 8.98 ± 0.43 at 0 h to 11.20 ± 0.37 μM at 72 h, respectively. Then it decreased till the end of the experiment (216 h postchallenge), and the concentrations of l-citrulline and total nitrite/nitrate at 216 h were 5.66 ± 0.27 and 4.68 ± 0.16 μM, respectively. More importantly, an apparent increase of LPS-stimulated NOS activity was observed in M. japonicus at 48 h postchallenge, which was about 4 times higher than that in the control group of health shrimps. In correspondence with the difference of NOS activity between the two species of shrimps, the cumulative mortalities of the shrimps were also different. All shrimps of F. chinensis in the mortality experiment died in 66 h, much more quickly than M. japonicus, whose accumulative mortality reached 100% after 240 h. Data here reported let us hypothesize that NOS activity in the haemocytes of shrimps F. chinensis and M. japonicus responses to WSSV infection differently, and this might be one of the reasons for the different susceptibility of F. chinensis and M. japonicus to WSSV infection.

Nitric oxide production by nurse shark (Ginglymostoma cirratum) and clearnose skate (Raja eglanteria) peripheral blood leucocytes

Reactive nitrogen intermediates, such as nitric oxide (NO), are important immunomodulators in vertebrate immune systems, but have yet to be identified as mediators of host defence in any member of class Chondrichthyes, the cartilaginous fishes. In the present study, production of NO by nurse shark (Ginglymostoma cirratum) peripheral blood leucocytes (PBL) stimulated with bacterial cell wall lipopolysaccharide (LPS) was investigated. PBL were cultured for 24 to 96 h following stimulation with LPS at concentrations ranging from 0 to 25 microg ml(-1), in both serum-supplemented and serum-free culture conditions. Production of NO was measured indirectly using the Griess reaction, with maximal NO production occurring after 72 h using 10% FBS and 10 microg LPS ml(-1). Application of these culture conditions to PBL from another cartilaginous fish (clearnose skate, Raja eglanteria) resulted in a similar NO response. Addition of a specific inhibitor of inducible nitric oxide synthase (iNOS), L-N(6)-(1-iminoethyl)lysine (L-NIL), resulted in a significant decrease in the production of NO by PBL from both species.

Nitric oxide production in blowfly hemolymph after yeast inoculation

Although insects lack the adaptive immune response of the mammalians, they manifest effective innate immune responses that include both cellular and humoral components. Cellular responses are mediated by hemocytes and humoral responses include the activation of proteolytic cascades that initiate many events, including NO production. In this work, we determined NO production in Chrysomya megacephala hemolymph and hemocytes after yeast inoculation. Assays were performed with non-infected controls (NIL), saline-injected larvae (SIL) or larvae injected with Saccharomyces cerevisiae (YIL). The hemolymph of injected groups was collected 0.5, 1, 2, 4, 12, 24 or 48h post-injection. NO levels in SIL were comparable to those measured in NIL until 12h, which might be considered the basal production, increasing at 24 and 48h post-injection, probably in response to the increased larval fragility after cuticle rupture. YIL exhibited significantly higher levels of NO than were found in other groups, peaking at 24h. l-NAME and EDTA caused a significant reduction of NO production in YIL at this time, suggesting the activity of a Ca(2+)-dependent NOS. Plasmatocytes and granular cells phagocytosed the yeasts. Plasmatocytes initiated the nodule formation and granular cells were the only hemocyte type to produce NO. These results permit us to conclude that yeasts induced augmented NO production in C. megacephala hemolymph and granular cells are the hemocyte type involved with the generation of this molecule.

Nitric oxide synthase in the nervous system and ink gland of the cuttlefish Sepia officinalis: molecular cloning and expression

Nitric oxide (NO) signaling is involved in numerous physiological processes in mollusks, e.g., learning and memory, feeding behavior, neural development, and defence response. We report the first molecular cloning of NOS mRNA from a cephalopod, the cuttlefish Sepia officinalis (SoNOS). SoNOS was cloned using a strategy that involves hybridization of degenerate PCR primers to highly conserved NOS regions, combined with RACE procedure. Two splicing variants of SoNOS, differing by 18 nucleotides, were found in the nervous system and the ink gland of Sepia. In situ hybridization shows that SoNOS is expressed in the immature and mature cells of the ink gland and in the regions of the nervous system that are related to the ink defence system.

Anti-inflammatory effects of specific cyclooxygenase 2,5-lipoxygenase, and inducible nitric oxide synthase inhibitors on experimental autoimmune anterior uveitis (EAAU)

PURPOSE

Inflammation, in general, causes the release of a variety of inflammatory mediators that in turn induce cyclooxygenase (COX) 2, nitric oxide synthase (iNOS) and 5-lipoxygense (LP) synthesis, producing large amounts of inflammatory prostaglandins (PG), nitric oxide (NO), and leukotriene (LT) B4. Therefore, inhibition of these enzymes may abrogate intraocular inflammation in experimental autoimmune anterior uveitis (EAAU).

METHODS

Lewis rats were immunized with melanin-associated antigen (MAA) isolated from bovine iris and ciliary body. These animals were divided into three groups. The first group of rats received subcutaneous injection of COX 2 inhibitor CS 236 at different time points. The second and third groups of animals received subcutaneous aminoguanidine (AG), an iNOS inhibitor, and nordihydroguaiaretic acid (NDGA), a 5-LP inhibitor, respectively. Control animals received vehicle. Rat eyes were examined daily by slit-lamp biomicroscopy from Day 7 to 30 post injection for uveitis. Animals were also sacrificed at various time points for histologic analysis.

RESULTS

Control animals developed severe EAAU in both eyes. The disease started in these animals on Day 12 post immunization and lasted for ten days. Interestingly, CS 236, a potent COX 2 inhibitor, completely abrogated EAAU when the animals were treated daily from the Day 0 to 14 or Day 0 to 20 after MAA injection. Furthermore, daily CS 236 treatment after the onset of EAAU (Day 14-20) significantly reduced the severity (both clinical and histologic) of EAAU and shortened the duration of disease. iNOS inhibitor (AG) and 5-LP inhibitor (NDGA) partially attenuated EAAU.

CONCLUSIONS

Our results show that EAAU was partially attenuated by AG and NDGA. Interestingly, CS 236, a potent COX 2 inhibitor, completely inhibited EAAU in male Lewis rats most likely by inhibiting the initial phase and onset of the disease.

Transposable elements in mosquitoes

We describe the current state of knowledge about transposable elements (TEs) in different mosquito species. DNA-based elements (class II elements), non-LTR retrotransposons (class I elements), and MITEs (Miniature Inverted Repeat Transposable Elements) are found in the three genera, Anopheles, Aedes and Culex, whereas LTR retrotransposons (class I elements) are found only in Anopheles and Aedes. Mosquitoes were the first insects in which MITEs were reported; they have several LTR retrotransposons belonging to the Pao family, which is distinct from the Gypsy-Ty3 and Copia-Ty1 families. The number of TE copies shows huge variations between classes of TEs within a given species (from 1 to 1000), in sharp contrast to Drosophila, which shows only relatively minor differences in copy number between elements (from 1 to 100). The genomes of these insects therefore display major differences in the amount of TEs and therefore in their structure and global composition. We emphasize the need for more population genetic data about the activity of TEs, their distribution over chromosomes and their frequencies in natural populations of mosquitoes, to further the current attempts to develop a transgenic mosquito unable to transmit malaria that is intended to replace the natural populations.

Induction of nitric oxide synthase in Anopheles stephensi by Plasmodium falciparum: mechanism of signaling and the role of parasite glycosylphosphatidylinositols

Malaria parasite (Plasmodium spp.) infection in the mosquito Anopheles stephensi induces significant expression of A. stephensi nitric oxide synthase (AsNOS) in the midgut epithelium as early as 6 h postinfection and intermittently thereafter. This induction results in the synthesis of inflammatory levels of nitric oxide (NO) in the blood-filled midgut that adversely impact parasite development. In mammals, P. falciparum glycosylphosphatidylinositols (PfGPIs) can induce NOS expression in immune and endothelial cells and are sufficient to reproduce the major effects of parasite infection. These effects are mediated in part by mimicry of insulin signaling by PfGPIs. In this study, we demonstrate that PfGPIs can induce AsNOS expression in A. stephensi cells in vitro and in the midgut epithelium in vivo. Signaling by P. falciparum merozoites and PfGPIs is mediated through A. stephensi Akt/protein kinase B and a pathway involving DSOR1, a mitogen-activated protein kinase kinase, and an extracellular signal-regulated kinase. However, despite the involvement of kinases that are also associated with insulin signaling in A. stephensi cells, signaling by P. falciparum and by PfGPIs is distinctively different from signaling by insulin. Therefore, although mimicry of insulin by PfGPIs appears to be restricted to mammalian hosts of P. falciparum, the conservation of PfGPIs as a prominent parasite-derived signal of innate immunity can now be extended to include Anopheles mosquitoes, indicating that parasite signaling of innate immunity is conserved in mosquito and mammalian cells.

Localization of nitric oxide synthase in the central complex and surrounding midbrain neuropils of the locust Schistocerca gregaria

Nitric oxide (NO), generated enzymatically by NO synthase (NOS), acts as an important signaling molecule in the nervous systems of vertebrates and invertebrates. In insects, NO has been implicated in development and in various aspects of sensory processing. To understand better the contribution of NO signaling to higher level brain functions, we analyzed the distribution of NOS in the midbrain of a model insect species, the locust Schistocerca gregaria, by using NADPH diaphorase (NADPHd) histochemistry after methanol/formalin fixation; results were validated by NOS immunohistochemistry. NADPHd yielded much higher sensitivity and resolution, but otherwise the two techniques resulted in corresponding labeling patterns throughout the brain, except for intense immunostaining but only weak NADPHd staining in median neurosecretory cells. About 470 neuronal cell bodies in the locust midbrain were NADPHd-positive positive, and nearly all major neuropil centers contained dense, sharply stained arborizations. We report several novel types of NOS-expressing neurons, including small ocellar interneurons and antennal sensory neurons that bypass the antennal lobe. Highly prominent labeling occurred in the central complex, a brain area involved in sky-compass orientation, and was analyzed in detail. Innervation by NOS-expressing fibers was most notable in the central body upper and lower divisions, the lateral accessory lobes, and the noduli. About 170 NADPHd-positive neurons contributed to this innervation, including five classes of tangential neuron, two systems of pontine neuron, and a system of columnar neurons. The results provide new insights into the neurochemical architecture of the central complex and suggest a prominent role for NO signaling in this brain area.

Melanogenesis and associated cytotoxic reactions: applications to insect innate immunity

Insects transmit the causative agents for such debilitating diseases as malaria, lymphatic filariases, sleeping sickness, Chagas' disease, leishmaniasis, river blindness, Dengue, and yellow fever. The persistence of these diseases provides testimony to the genetic capacity of parasites to evolve strategies that ensure their successful development in two genetically diverse host species: insects and mammals. Current efforts to address the problems posed by insect-borne diseases benefit from a growing understanding of insect and mammalian immunity. Of considerable interest are recent genomic investigations that show several similarities in the innate immune effector responses and associated regulatory mechanisms manifested by insects and mammals. One notable exception, however, is the nearly universal presence of a brown-black pigment accompanying cellular innate immunity in insects. This response, which is unique to arthropods and certain other invertebrates, has focused attention on the elements involved in pigment synthesis as causing or contributing to the death of the parasite, and has even prompted speculation that the enzyme cascade mediating melanogenesis constitutes an ill-defined recognition mechanism. Experimental evidence defining the role of melanin and its precursors in insect innate immunity is severely lacking. A great deal of what is known about melanogenesis comes from studies of the process occurring in mammalian systems, where the pigment is synthesized by such diverse cells as those comprising portions of the skin, hair, inner ear, brain, and retinal epithelium. Fortunately, many of the components in the metabolic pathways leading to the formation of melanin have been found to be common to both insects and mammals. This review examines some of the factors that influence enzyme-mediated melanogenic responses, and how these responses likely contribute to blood cell-mediated, target-specific cytotoxicity in immune challenged insects.

Cross-talk between nitric oxide and transforming growth factor-beta1 in malaria

Malaria has re-emerged as a global health problem, leading to an increased focus on the cellular and molecular biology of the mosquito Anopheles and the parasite Plasmodium with the goal of identifying novel points of intervention in the parasite life cycle. Anti-parasite defenses mounted by both mammalian hosts and Anopheles can suppress the growth of Plasmodium. Nonetheless, the parasite is able to escape complete elimination in vivo, perhaps by thwarting or co-opting these mechanisms for its own survival, as do numerous other pathogens. Among the defense systems used by the mammalian host against Plasmodium is the synthesis of nitric oxide (NO), catalyzed by an inducible NO synthase (iNOS). Nitric oxide produced by the action of an inducible Anopheles stephensi NO synthase (AsNOS) may be central to the anti-parasitic arsenal of this mosquito. In mammals, iNOS can be modulated by members of the transforming growth factor-beta (TGF-beta) cytokine superfamily. Transforming growth factor-beta is produced as an inactive precursor that is activated following dissociation of certain inhibitory proteins, a process that can be promoted by reaction products of NO as well as by hemin. Ingestion by Anopheles of blood containing Plasmodium initiates parasite development, blood digestion which results in the accumulation of hematin (hemin) in the insect midgut, and induction of both AsNOS and TGF-beta-like (As60A) gene expression in the midgut epithelium. Active mammalian TGF-beta1 can be detected in the A. stephensi midgut up to 48h post-ingestion and latent TGF-beta1 can be activated by midgut components in vitro, a process that is potentiated by NO and that may involve hematin. Further, mammalian TGF-beta1 is perceived as a cytokine by A. stephensi cells in vitro and can alter Plasmodium development in vivo. Bloodfeeding by Anopheles, therefore, results in a juxtaposition of evolutionarily conserved mosquito and mammalian TGF-beta superfamily homologs that may influence transmission dynamics of Plasmodium in endemic regions.

NO means 'yes' in the squid-vibrio symbiosis: nitric oxide (NO) during the initial stages of a beneficial association

During colonization of the Euprymna scolopes light organ, symbiotic Vibrio fischeri cells aggregate in mucus secreted by a superficial ciliated host epithelium near the sites of eventual inoculation. Once aggregated, symbiont cells migrate through ducts into epithelium-lined crypts, where they form a persistent association with the host. In this study, we provide evidence that nitric oxide synthase (NOS) and its product nitric oxide (NO) are active during the colonization of host tissues by V. fischeri. NADPH-diaphorase staining and immunocytochemistry detected NOS, and the fluorochrome diaminofluorescein (DAF) detected its product NO in high concentrations in the epithelia of the superficial ciliated fields, ducts, and crypt antechambers. In addition, both NOS and NO were detected in vesicles within the secreted mucus where the symbionts aggregate. In the presence of NO scavengers, cells of a non-symbiotic Vibrio species formed unusually large aggregates outside of the light organ, but these bacteria did not colonize host tissues. In contrast, V. fischeri effectively colonized the crypts and irreversibly attenuated the NOS and NO signals in the ducts and crypt antechambers. These data provide evidence that NO production, a defense response of animal cells to bacterial pathogens, plays a role in the interactions between a host and its beneficial bacterial partner during the initiation of symbiotic colonization.

Plasmodium berghei ookinetes induce nitric oxide production in Anopheles pseudopunctipennis midguts cultured in vitro

The Anopheles pseudopunctipennis nitric oxide synthase gene (ApNOS) was identified and its partial sequence showed high homology with NOS from A. stephensi, A. gambiae (putative sequence), and Drosophila melanogaster. ApNOS was mainly expressed in male and female adult mosquitoes and was induced by a blood meal. Nitric oxide (NO) was produced by in vitro-cultured mosquito midguts inoculated by enema with Plasmodium berghei ookinetes, Saccharomyces cerevisiae, Gram-positive bacteria (Micrococcus luteus), but not with Gram-negative bacteria (Klebsiella pneumoniae, Escherichia coli or Serratia marcescens). Dihydroxyphenylalanine (L-DOPA) oxidation induced the generation of NO in midguts in vitro, and hydrogen peroxide generated during its oxidation induced ApNOS expression. P. berghei ookinetes exposed in vitro to L-DOPA and sodium nitroprusside (a NO generator) were killed. These observations demonstrate that reactive oxygen and nitrogen intermediates constitute a part of the cytotoxic arsenal employed by Anopheles mosquitoes against microbial pathogens and Plasmodium ookinetes.

Genomic structure and differential expression of two tandem-arranged GSTZ genes in rice

Glutathione S-transferases (GSTs) are scavenging enzymes that detoxify cellular xenobiotics and toxins by catalyzing the conjugation of these substrates with a tripeptide glutathione. GSTs are classified depending on gene organization and sequence similarity. The sequence analysis of genomic DNA for zeta class GST (GSTZ) locus in rice indicated that two homologous GSTZ genes lay in a tandem orientation with a short (0.4 kb) intergenic spacer. The upstream OsGSTZ1 and downstream OsGSTZ2 spanned 3.5 and 3.2 kb with nine coding exons, respectively. The transcript of OsGSTZ1 had a long 3' untranslated region (3' UTR) that was mostly encoded by a 10th noncoding exon, whereas OsGSTZ2 mRNA contained a long 5' UTR. Northern blot analysis showed that OsGSTZ1/2 messages were strongly expressed in leaf blades, while transcripts from roots were low level. Because OsGSTZ1/2 messages in leaf tissues were strongly induced only by water treatment, it was difficult to assay for the induction of OsGSTZ1/2 transcripts by various stress treatments. Thus, using rice culture cells, we analyzed the respective responses of OsGSTZ1 and OsGSTZ2 genes against various treatments by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). The results showed that OsGSTZ1 was expressed at a level ca. 1000-fold higher than OsGSTZ2 in suspension cells without stress treatment. OsGSTZ1 was expressed constitutively under various stress conditions. In contrast, the expression of OsGSTZ2 gene was strongly enhanced to 30-fold by treatment with jasmonic acid. These observations suggested that the expression of OsGSTZ1 and OsGSTZ2 genes are differentially regulated in the culture cell of rice.

A crustacean nitric oxide synthase expressed in nerve ganglia, Y-organ,gill and gonad of the tropical land crab,Gecarcinus lateralis

NO signaling is involved in many physiological processes in invertebrates. In crustaceans, it plays a role in the regulation of the nervous system and muscle contraction. Nested reverse transcription-polymerase chain reaction(RT-PCR) and 5′ and 3′ rapid amplification of cDNA ends (RACE) PCR generated a full-length cDNA sequence (3982 bp) of land crab NO synthase(Gl-NOS) from molting gland (Y-organ) and thoracic ganglion mRNA. The open reading frame encoded a protein of 1199 amino acids with an estimated mass of 135 624 Da. Gl-NOS had the highest sequence identity with insect NOS. The amino acid sequences for binding heme and tetrahydrobiopterin in the oxygenase domain, binding calmodulin and binding FMN, FAD and NADPH in the reductase domain were highly conserved. Gl-NOS had single amino acid differences in all three highly conserved FAD-binding sequences, which distinguished it from other NOS sequences. RT-PCR showed that the Gl-NOS mRNA was present in testis,ovary, gill, eyestalk neural ganglia, thoracic ganglion and Y-organ. NOS mRNA varied between preparations of Y-organ, thoracic ganglion and gill, while NOS mRNA was at consistently high levels in the ovary, testis and eyestalk ganglia. Immunohistochemistry confirmed that the Gl-NOS protein was expressed in Y-organ, ovary and gill. These results suggest that NOS has functions in addition to neuromodulation in adults, such as regulating or modulating ecdysteroid synthesis in the Y-organ.

Mosquito transposable elements

The completion of the genome assembly for the African malaria mosquito, Anopheles gambiae, and continuing genomic efforts for the yellow fever mosquito, Aedes aegypti, have allowed the use of bioinformatics tools to identify and characterize a diverse array of transposable elements (TEs) in these and other mosquito genomes. An overview of the types and number of both RNA-mediated and DNA-mediated TEs that are found in mosquito genomes is presented. A number of novel and interesting TEs from these species are discussed in more detail. These findings have significant implications for our understanding of mosquito genome evolution and for future modifications of natural mosquito populations through the use of TE-mediated genetic transformation.

The energetic budget of Anopheles stephensi infected with Plasmodium chabaudi: is energy depletion a mechanism for virulence?

Evidence continues to accumulate showing that the malaria parasites (Plasmodium spp.) reduce the survival and fecundity of their mosquito vectors (Anopheles spp.). Our ability to identify the possible epidemiological and evolutionary consequences of these parasite-induced fitness reductions has been hampered by a poor understanding of the physiological basis of these shifts. Here, we explore whether the reductions in fecundity and longevity are the result of a parasite-mediated depletion or reallocation of the energetic resources of the mosquito. Mosquitoes infected with Plasmodium chabaudi were expected to have less energetic resources than uninfected mosquitoes, and energy levels were predicted to be lowest in mosquitoes infected with the most virulent parasite genotypes. Not only was there no evidence of a parasite-mediated reduction in the overall energetic budget of mosquitoes, but Plasmodium was actually associated with increased levels of glucose, a key insect nutritional and energetic resource. The data strongly suggest the existence of an increase in sugar feeding in mosquitoes infected with Plasmodium. We suggest different adaptive explanations for an enhanced sugar uptake in infected mosquitoes and call for more studies to investigate the physiological role of glucose in the Plasmodium-mosquito interaction.