Myosuppressin signaling deficiency affects ovarian development via repression of 20-hydroxyecdysone biosynthesis in Grapholita molesta

The steroid 20-hydroxyecdysone (20E) is crucial in regulating ovarian development. However, the neuropeptidergic mechanisms underlying ovarian development via 20E are underexplored. In this study, we investigated myosuppressin (MS) signaling in the dominant fruit pest Grapholita molesta and revealed that MS signaling is necessary for 20E biosynthesis during ovarian maturation. Pharmacological and molecular docking analyses confirmed that the GmMS mature peptide could activate its receptor GmMSR. Additionally, transcript expression analyses of GmMS and GmMSR showed different distribution patterns in adults. Notably, GmMSR was also detected in the ovaries of sexually mature females. RNAi-mediated dysfunction of GmMS or GmMSR specifically decreased fertility in females. Furthermore, GmMS or GmMSR knockdown decreased vitellogenin synthesis and uptake, thereby delaying ovarian development. RNA-seq, gene expression validation, and hormone quantification further revealed that GmMS signaling depletion blocked 20E biosynthesis in the ovary. Finally, exogenous MS rescued most dsGmMS- or dsGmMSR-induced ovarian defects and 20E titers. These results suggest that MS/MSR-to-20E signaling regulates ovarian development through vitellogenesis, providing a new perspective on the development of neuroendocrine targets that suppress pest field populations.

Mechanisms of feeding cessation in Helicoverpa armigera larvae exposed to Bacillus thuringiensis Cry1Ac toxin

Insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have been applied in sprayable formulations and expressed in transgenic crops for the control of pests in the field. When exposed to Bt proteins insect larvae display feeding cessation, yet the mechanism for this phenomenon remains unknown. In this study, we investigated the feeding behavior and underlying mechanisms of cotton bollworm (Helicoverpa armigera) larvae after exposure to the Cry1Ac protein from Bt. Three H. armigera strains were studied: the susceptible SCD strain, the C2/3-KO strain with HaABCC2 and HaABCC3 knocked out and high-level resistance to Cry1Ac (>15,000-fold), and the SCD-KI strain with a T92C point mutation in tetraspanin (HaTSPAN1) and medium-level resistance to Cry1Ac (125-fold). When determining the percentage of insects that continued feeding after various exposure times to Cry1Ac, we observed quick cessation of feeding in larvae from the susceptible SCD strain, whereas larvae from the C2/3-KO strain did not display feeding cessation. In contrast, larvae from the SCD-KI strain rapidly recovered from the initial feeding cessation. Histopathological analyses and qRT-PCR in midguts of SCD larvae after Cry1Ac exposure detected serious epithelial damage and significantly reduced expression of the neuropeptide F gene (NPF) and its potential receptor gene NPFR, which are reported to promote insect feeding. Neither epithelial damage nor altered NPF and NPFR expression appeared in midguts of C2/3-KO larvae after Cry1Ac treatment. The same treatment in SCD-KI larvae resulted in milder epithelial damage and subsequent repair, and a decrease followed by an initial increase in NPF and NPFR expression. These results demonstrate that the feeding cessation response to Cry1Ac in cotton bollworm larvae is closely associated with midgut epithelial damage and downregulation of NPF and NPFR expression. This information provides clues to the mechanism of feeding cessation in response to Bt intoxication and contributes to the mode of action of the Cry1Ac toxin in target pests.

The Male Reproductive System of the Kissing Bug, Rhodnius prolixus Stål, 1859 (Hemiptera: Reduviidae: Triatominae): Arrangements of the Muscles and the Myoactivity of the Selected Neuropeptides

The gross anatomy of the male reproductive structures and their associated musculature are described in the blood-gorging vector of Chagas disease, Rhodnius prolixus. The male reproductive system is composed of muscular tissues each performing contractions that aid in the movement of sperm out of the testis into the vas deferens, seminal vesicle and then into the ejaculatory duct, along with proteins and lipids from the transparent and opaque accessory glands. Phalloidin staining shows the various patterns of muscle fiber layers, from thin circular to more complex crisscross patterns, implying subtle differences in the form of the contractions and movement of each of the structures, allowing for waves of contractions or twisting patterns. The transcripts for the receptors for proctolin, myosuppressin (RhoprMS) and for the extended FMRFamides are expressed in the various regions of the reproductive system, and the nerve processes extending over the reproductive structures are positive for FMRFamide-like immunoreactivity, as are neurosecretory cells lying on the nerves. Proctolin and AKDNFIRFamide are strong stimulators for the frequency of the contractions, and RhoprMS can inhibit the proctolin-induced contractions. Taken together, this work implicates these two families of peptides in coordinating the male reproductive structures for the successful transfer of sperm and the associated accessory gland fluid to the female during copulation.

The hormonal and neural control of egg production in the historically important model insect, Rhodnius prolixus: A review, with new insights in this post-genomic era

Rhodnius prolixus, the blood gorging kissing bug, is a model insect, extensively used by Sir Vincent Wigglesworth and others, upon which the foundations of insect physiology, endocrinology, and development are built. It is also medically important, being a principal vector of Trypanosoma cruzi, the causative agent of Chagas disease in humans. The blood meal stimulates and enables egg production, and since an adult mated female can take several blood meals, each female can produce hundreds of offspring. Understanding the reproductive biology of R. prolixus is therefore of some critical importance for controlling the transmission of Chagas disease. The R. prolixus genome is available and so the post-genomic era has arrived for this historic model insect. This review focuses on the female reproductive system and coordination over the production of eggs, emphasizing the classical (neuro)endocrinological studies that led to a model describing inputs from feeding and mating, and the neural control of egg-laying. We then review recent insights brought about by molecular analyses, including transcriptomics, that confirm, support, and considerably extends this model. We conclude this review with an updated model describing the events leading to full expression of egg production, and also provide a consideration of questions for future exploration and experimentation.

Salivary and Intestinal Transcriptomes Reveal Differential Gene Expression in Starving, Fed and Trypanosoma cruzi-Infected Rhodnius neglectus

Rhodnius neglectus is a potential vector of Trypanosoma cruzi (Tc), the causative agent of Chagas disease. The salivary glands (SGs) and intestine (INT) are actively required during blood feeding. The saliva from SGs is injected into the vertebrate host, modulating immune responses and favoring feeding for INT digestion. Tc infection significantly alters the physiology of these tissues; however, studies that assess this are still scarce. This study aimed to gain a better understanding of the global transcriptional expression of genes in SGs and INT during fasting (FA), fed (FE), and fed in the presence of Tc (FE + Tc) conditions. In FA, the expression of transcripts related to homeostasis maintenance proteins during periods of stress was predominant. Therefore, the transcript levels of Tret1-like and Hsp70Ba proteins were increased. Blood appeared to be responsible for alterations found in the FE group, as most of the expressed transcripts, such as proteases and cathepsin D, were related to digestion. In FE + Tc group, there was a decreased expression of blood processing genes for insect metabolism (e.g., Antigen-5 precursor, Pr13a, and Obp), detoxification (Sult1) in INT and acid phosphatases in SG. We also found decreased transcriptional expression of lipocalins and nitrophorins in SG and two new proteins, pacifastin and diptericin, in INT. Several transcripts of unknown proteins with investigative potential were found in both tissues. Our results also show that the presence of Tc can change the expression in both tissues for a long or short period of time. While SG homeostasis seems to be re-established on day 9, changes in INT are still evident. The findings of this study may be used for future research on parasite-vector interactions and contribute to the understanding of food physiology and post-meal/infection in triatomines.

Myosuppressin influences fecundity in the Colorado potato beetle, Leptinotarsa decemlineata

Insect neuropeptides regulate various physiological processes, such as reproduction, feeding, growth and development, and have been considered as viable targets in the development of alternative strategies for pest control. Amongst these neuropeptides is myosuppressin (MS), a very conserved neuropeptide that has been reported to regulate cardiac and skeletal muscle contractility, feeding and pupal diapause in insects. In this study, we investigated the involvement of MS in fecundity in a notorious defoliator of potato and other solanaceous plants, the Colorado potato beetle (CPB), Leptinotarsa decemlineata. We identified an MS-precursor-encoding transcript in the L. decemlineata transcriptomic database and then evaluated its transcript levels in various CPB tissues. MS transcript levels were found to be highest in the central nervous system, gut and muscle of CPB males and females. To investigate the role of MS in fecundity, MS was silenced in adult CPBs through RNA interference (RNAi). This resulted in a significant reduction in oviposition (over 80%) and oocyte size (69%) in the treated beetles compared to the controls. Also, the reduction in oviposition in treated females was confirmed to be dependent on MS knockdown and independent of male fertilization. Furthermore, MS-knockdown in females resulted in decreased levels of ecdysteroid hormone titers and the transcript levels of its receptor. Interestingly, the injection of 20-hydroxyecdysone into females following MS knockdown could rescue ovary development. Altogether, this study highlights the important role played by MS in regulating fecundity in CPB.

She's got nerve: roles of octopamine in insect female reproduction

The biogenic monoamine octopamine (OA) is a crucial regulator of invertebrate physiology and behavior. Since its discovery in the 1950s in octopus salivary glands, OA has been implicated in many biological processes among diverse invertebrate lineages. It can act as a neurotransmitter, neuromodulator and neurohormone in a variety of biological contexts, and can mediate processes including feeding, sleep, locomotion, flight, learning, memory, and aggression. Here, we focus on the roles of OA in female reproduction in insects. OA is produced in the octopaminergic neurons that innervate the female reproductive tract (RT). It exerts its effects by binding to receptors throughout the RT to generate tissue- and region-specific outcomes. OA signaling regulates oogenesis, ovulation, sperm storage, and reproductive behaviors in response to the female's internal state and external conditions. Mating profoundly changes a female's physiology and behavior. The female's OA signaling system interacts with, and is modified by, male molecules transferred during mating to elicit a subset of the post-mating changes. Since the role of OA in female reproduction is best characterized in the fruit fly Drosophila melanogaster, we focus our discussion on this species but include discussion of OA in other insect species whenever relevant. We conclude by proposing areas for future research to further the understanding of OA's involvement in female reproduction in insects.

What happens after a blood meal? A transcriptome analysis of the main tissues involved in egg production in Rhodnius prolixus, an insect vector of Chagas disease

The blood-sucking hemipteran Rhodnius prolixus is a vector of Chagas disease, one of the most neglected tropical diseases affecting several million people, mostly in Latin America. The blood meal is an event with a high epidemiological impact since adult mated females feed several times, with each meal resulting in a bout of egg laying, and thereby the production of hundreds of offspring. By means of RNA-Sequencing (RNA-Seq) we have examined how a blood meal influences mRNA expression in the central nervous system (CNS), fat body and ovaries in order to promote egg production, focusing on tissue-specific responses under controlled nutritional conditions. We illustrate the cross talk between reproduction and a) lipids, proteins and trehalose metabolism, b) neuropeptide and neurohormonal signaling, and c) the immune system. Overall, our molecular evaluation confirms and supports previous studies and provides an invaluable molecular resource for future investigations on different tissues involved in successful reproductive events. These analyses serve as a starting point for new investigations, increasing the chances of developing novel strategies for vector population control by translational research, with less impact on the environment and more specificity for a particular organism.

Nitric oxide produced by periostial hemocytes modulates the bacterial infection-induced reduction of the mosquito heart rate

The circulatory and immune systems of mosquitoes are functionally integrated. An infection induces the migration of hemocytes to the dorsal vessel, and specifically, to the regions surrounding the ostia of the heart. These periostial hemocytes phagocytose pathogens in the areas of the hemocoel that experience the highest hemolymph flow. Here, we investigated whether a bacterial infection affects cardiac rhythmicity in the African malaria mosquito, Anopheles gambiae We discovered that infection with Escherichia coli, Staphylococcus aureus and Staphylococcus epidermidis, but not Micrococcus luteus, reduces the mosquito heart rate and alters the proportional directionality of heart contractions. Infection does not alter the expression of genes encoding crustacean cardioactive peptide (CCAP), FMRFamide, corazonin, neuropeptide F or short neuropeptide F, indicating that they do not drive the cardiac phenotype. Infection upregulates the transcription of two superoxide dismutase (SOD) genes, catalase and a glutathione peroxidase, but dramatically induces upregulation of nitric oxide synthase (NOS) in both the heart and hemocytes. Within the heart, nitric oxide synthase is produced by periostial hemocytes, and chemically inhibiting the production of nitric oxide using l-NAME reverses the infection-induced cardiac phenotype. Finally, infection induces the upregulation of two lysozyme genes in the heart and other tissues, and treating mosquitoes with lysozyme reduces the heart rate in a manner reminiscent of the infection phenotype. These data demonstrate an exciting new facet of the integration between the immune and circulatory systems of insects, whereby a hemocyte-produced factor with immune activity, namely nitric oxide, modulates heart physiology.

Identification and expression profiling of neuropeptides and neuropeptide receptor genes in Atrijuglans hetaohei

Atrijuglans hetaohei Yang (Lepidoptera: Gelechioidea), is one of the major pests that can seriously damage the walnut fruits. Neuropeptides and their receptors regulate most physiological functions in insects and represent new targets for the development of control agents. To identify the neuropeptides and their receptors from A. hetaohei, we sequenced and analyzed its head transcriptomic data, identified 32 neuropeptides and 39 neuropeptide receptor genes. Sequence comparisons and phylogenetic analyses suggest that A. hetaohei neuropeptides and receptor genes have high homology with those in Bombyx mori, Chilo suppressalis, Plutella xylostella and Helicoverpa armigera. Moreover, gene expression patterns revealed that neuropeptide genes such as AKH1, CP, MS and PTTH were expressed specifically in male head, while CAP3, DH, NPLP1, PBAN and SIF showed higher expression in the female head. Bur showed abdomen biased expression in both male and female. Neuropeptide receptor genes such as A8, A11, A15 and LGR were highly expressed in male head, whereas A24 and LGR2 were preferentially expressed in female head. This is the first sequencing, identification and expression analyses of neuropeptides and neuropeptide receptor genes from A. hetaohei. Our results could provide a powerful background that will facilitate the further investigations using transcriptomics to determine neuropeptides and their receptors presence, functions, and indicates potential targets in A. hetaohei for a novel pest management strategy.

Peptide Hormones in the Insect Midgut

Insects produce many peptide hormones that play important roles in regulating growth, development, immunity, homeostasis, stress, and other processes to maintain normal life. As part of the digestive system, the insect midgut is also affected by hormones secreted from the prothoracic gland, corpus allatum, and various neuronal cells; these hormones regulate the secretion and activity of insects’ digestive enzymes and change their feeding behaviors. In addition, the insect midgut produces certain hormones when it recognizes various components or pathogenic bacteria in ingested foods; concurrently, the hormones regulate other tissues and organs. In addition, intestinal symbiotic bacteria can produce hormones that influence insect signaling pathways to promote host growth and development; this interaction is the result of long-term evolution. In this review, the types, functions, and mechanisms of hormones working on the insect midgut, as well as hormones produced therein, are reviewed for future reference in biological pest control.

The Insect Circulatory System: Structure, Function, and Evolution

Although the insect circulatory system is involved in a multitude of vital physiological processes, it has gone grossly understudied. This review highlights this critical physiological system by detailing the structure and function of the circulatory organs, including the dorsal heart and the accessory pulsatile organs that supply hemolymph to the appendages. It also emphasizes how the circulatory system develops and ages and how, by means of reflex bleeding and functional integration with the immune system, it supports mechanisms for defense against predators and microbial invaders, respectively. Beyond that, this review details evolutionary trends and novelties associated with this system, as well as the ways in which this system also plays critical roles in thermoregulation and tracheal ventilation in high-performance fliers. Finally, this review highlights how novel discoveries could be harnessed for the control of vector-borne diseases and for translational medicine, and it details principal knowledge gaps that necessitate further investigation.

Function of myosuppressin in regulating digestive function in the two-spotted cricket, Gryllus bimaculatus

Myosuppressin is one of essential peptides controlling biological processes including feeding behavior. Here we identified and characterized the cDNAs that encode myosuppressin precursor and its receptor in the two-spotted cricket Gryllus bimaculatus. The presence of the mature peptide (Grybi-MS) was confirmed by direct measurement of adult brain. RT-PCR revealed the tissue distribution of these transcripts; myosuppressin is expressed predominantly in the brain and central nervous system, whereas its receptor is ubiquitously expressed in the cricket body. To address the function of Grybi-MS, we performed several bioassays to test concerning feeding behavior and digestive function upon exposure to Grybi-MS. Administration of synthetic Grybi-MS resulted in increased feeding motivation, accompanied by an increase in food intake. Meanwhile, the hemolymph lipid and carbohydrate titers were both elevated after Grybi-MS injection. As the intestinal contraction is significantly inhibited by the exposure to Grybi-MS, the upregulating feeding index might be complicated in the cricket body. The current data indicate that Grybi-MS modulates feeding behavior to control the physiological processes in the cricket.

Neuropeptide- and serotonin- cells in the brain of Rhodnius prolixus (Hemiptera) associated with the circadian clock

The neuronal pathways of the circadian clock in the brain of R. prolixus have been described in detail previously, but there is no information concerning the cells or their pathways which relay either inputs to the clock (e.g. for light entrainment), or outputs from it to driven rhythms. Here, we employ antisera to three neuropeptides (type A allatostatin-7, crustacean cardioactive peptide and FMRFamide), and serotonin in confocal laser scanning immunohistochemistry to analyze the distribution of cell bodies and their projections in relation to the principle circadian clock cells (lateral cells, LNs) for all four neuron types. LNs are revealed following labelling with anti- pigment dispersing factor in double labelled preparations. Regions of potential communication between ramifications of the LNs and each of the four other neuron types is described (identified by close superposition of their neurites in various brain regions), as is their detailed projections within the brain. Neuromodulation is sometimes suggested by close, but not intimate, proximity of varicosities of neurites. We infer that some neuron types comprise input pathways to the LNs, some are outputs to neuroendocrine or behavioral rhythms, and others participate in both input and output pathways, sometimes by the same neuron type but in different locations. For example, one retinula cell in each ommatidium is immunoreactive for allatostatin A; its axon projects to the medulla making superpositions with LNs, as do serotonin cells in the optic lobe, indicating roles of both neuron types in light input (entrainment) to the clock. But in other brain areas, these same types appear to mediate outputs from the clock. The accessory medulla has been widely reported as the principle center of integration in other insects; but we found sparse evidence of this in R. prolixus as it contains few neurites other than those from the clock cells. Rather, the importance of neural pathways involving the medulla and the superior protocerebrum is emphasized. We conclude that there is a vast and complex web of interactions in the brain with the LNs, which potentially receive multiple pathways of inputs and outputs that could drive rhythmicity in a multitude of downstream cells, rendering a host of output pathways rhythmic, notably hormone release from neurosecretory cells and behaviors.

RNAi mediated myosuppressin deficiency affects muscle development and survival in the salmon louse (Lepeophtheirus salmonis)

Muscle activity is regulated by stimulatory and inhibitory neuropeptides allowing for contraction and relaxation. In Arthropods, one of the important myoinhibitors is Myosuppressin, belonging to FMRFamide-like peptides, that was shown to have inhibitory effects on visceral muscle contraction and to regulate vital physiological processes including reproduction or feeding. We have identified myosuppressin in salmon louse Lepeophtheirus salmonis (LsalMS) and systematically characterised its function and complex abnormalities emerging after LsalMS knockdown by RNAi in all developmental stages in this species. Immunohistochemistry analysis localized the LsalMS mainly to the central nervous system, but also to the vital organs within the alimentary tract and the reproductive system. The most striking feature of LsalMS deficiency during lice development was severe reduction of the muscle content, with abnormalities detected in both the visceral and skeletal muscles. Moreover, down-regulation of LsalMS affects moulting, spermatophore deposition and feeding by affecting development of the intestinal wall and increasing its contraction frequency.

Nezara viridula (Hemiptera: Pentatomidae) transcriptomic analysis and neuropeptidomics

Stinkbugs (Hemiptera: Pentatomidae) are of major economic importance as pest of crops. Among the species composing the stinkbug complex, Nezara viridula is one of the most abundant in Brazil, Argentina and the Southern USA. However, this species has been poorly characterized at the genetic and physiological level. Here we sequenced and analyzed the complete transcriptome of N. viridula male and female adults. We identified neuropeptide precursor genes and G-protein coupled receptors for neuropeptides in this transcriptome. Mature neuropeptides were identified in N. viridula brain extracts by liquid chromatography-tandem mass spectrometry. We also analyzed the neuropeptide precursor complement in the genome sequence of Halyomorpha halys, another pentatomid of economic relevance. We compared the results in both pentatomids with the well-characterized neuropeptide repertoire from the kissing bug Rhodnius prolixus (Hemiptera: Reduviidae). We identified both group-specific features (which could be related to the different feeding habits) and similarities that could be characteristic of Heteroptera. This work contributes to a deeper knowledge of the genetic information of these pests, with a focus on neuroendocrine system characterization.

Insect heart rhythmicity is modulated by evolutionarily conserved neuropeptides and neurotransmitters

Insects utilize an open circulatory system to transport nutrients, waste, hormones and immune factors throughout the hemocoel. The primary organ that drives hemolymph circulation is the dorsal vessel, which is a muscular tube that traverses the length of the body and is divided into an aorta in the head and thorax, and a heart in the abdomen. The dorsal vessel is myogenic, but its rhythmicity is modulated by neuropeptides and neurotransmitters. This review summarizes how neuropeptides such as crustacean cardioactive peptide (CCAP), FMRFamide-like peptides, proctolin, allatotropin and allatostatin modulate the heart contraction rate and the directionality of heart contractions. Likewise, it discusses how neurotransmitters such as serotonin, octopamine, glutamate and nitric oxide influence the heart rate, and how transcriptomic and proteomic approaches are advancing our understanding of insect circulatory physiology. Finally, this review argues that the immune system may modulate heart rhythmicity, and discusses how the myotropic activity of cardioactive factors extends to the accessory pulsatile organs, such as the auxiliary hearts of the antennae.

Expression and functional characterization of tachykinin-related peptides in the blood-feeding bug, Rhodnius prolixus

Tachykinins (tachykinin-related peptides, TRPs) are multifunctional neuropeptides that have widespread distribution in the central nervous system (CNS) and in the gastrointestinal tract of many insects, and most have been shown to stimulate contractions of visceral muscles. Invertebrate TRPs carry a characteristic conserved C-terminal pentapeptide (FXGXR-amide) and most of them share some amino acid sequence similarities (approx. 45%) with the vertebrate and mammalian tachykinin family. We have functionally characterized the tachykinins in R. prolixus (Rhopr-TKs) and partially cloned the transcript that encodes for the peptide precursor. The transcript encodes 8 Rhopr-TKs, 7 of which are unique with Rhopr-TK 5 having 2 copies. The spatial distribution analysis of the Rhopr-TK transcript indicates that the highest expression levels are in the CNS, but transcript expression is also associated with salivary glands, fat body, dorsal vessel, and the various gut compartments. Rhopr-TK 1, 2 and 5 significantly increase the frequency and amplitude of peristaltic contractions of the salivary glands. Hindgut muscle also displayed a dose-dependent increase in basal tonus in response to Rhopr-TK1, 2 and 5. TK-like immunoreactivity was seen in a small group of processes that are situated on the lateral margins of the hindgut. Interestingly, kinin-like immunoreactivity is seen in immunoreactive processes on the lateral margin of the hindgut as well as fine processes covering the entire hindgut. Co-localization studies show that TK-like staining is always co-localized with kinin-like immunoreactivity, whereas kinin-like staining is seen in the fine processes that are devoid of TK-like immunoreactivity indicating that TKs are most likely released together with kinins to act on the hindgut. Rhopr-Kinin 2 is a potent stimulator of hindgut muscle contraction in R. prolixus. Addition of Rhopr-Kinin 2 and Rhopr-TK 2 to the hindgut leads to a contraction that was additive of the effects of Rhopr-Kinin 2 and Rhopr-TK 2 alone.

Cloning, localization, and physiological effects of sulfakinin in the kissing bug, Rhodnius prolixus

Sulfakinins (SKs) are a family of multifunctional neuropeptides that have been shown to have myotropic activity on muscles of the digestive system and to function as feeding satiety factors. Here, we confirm via cloning the presence of two sulfakinins (Rhopr-SK-1 and Rhopr-SK-2) in Rhodnius prolixus. Reverse transcriptase quantitative PCR demonstrates that the Rhopr-SK transcript is highly expressed in the central nervous system (CNS) of unfed fifth-instar R. prolixus. Fluorescent in situ hybridization shows transcript expression only in neurons in the brain. Immunohistochemical staining of SK-like peptides was observed in the same neurons in the brain and in processes extending throughout the CNS, as well as over the posterior midgut and anterior hindgut. Rhopr-SK-1 (sulfated form) induces contractions of the hindgut in a dose-dependent manner. Injection Rhopr-SK-1 (sulfated form) significantly decreases the overall weight of the blood meal consumed, suggesting SK's role as a satiety factor in R. prolixus.

Neuropeptides in the regulation of Rhodnius prolixus physiology

In the kissing bug Rhodnius prolixus, events such as diuresis, antidiuresis, development and reproduction are triggered by blood feeding. Hence, these events can be accurately timed, facilitating physiological experiments. This, combined with its relatively big size, makes R. prolixus an excellent model in insect neuroendocrinological studies. The importance of R. prolixus as a Chagas' disease vector as much as an insect model has motivated the sequencing of its genome in recent years, facilitating genetic and molecular studies. Most crucial physiological processes are regulated by the neuroendocrine system, composed of neuropeptides and their receptors. The identification and characterization of neuropeptides and their receptors could be the first step to find targets for new insecticides. The sequences of 41 neuropeptide precursor genes and the receptors for most of them were identified in the R. prolixus genome. Functional information about many of these molecules was obtained, whereas many neuroendocrine systems are still unstudied in this model species. This review addresses the knowledge available to date regarding the structure, distribution, expression and physiological effects of neuropeptides in R. prolixus, and points to future directions in this research field.

Neuropeptidomics in Triatoma infestans. Comparative transcriptomic analysis among triatomines

Chagas' disease, affecting up to 6-7 million people worldwide, is transmitted to humans through the feces of triatomine kissing bugs. From these, Rhodnius prolixus, Triatoma dimidiata, Triatoma infestans and Triatoma pallidipennis are important vectors distributed throughout the Latin American subcontinent. Resistance to pyrethroids has been developed by some triatomine populations, especially T. infestans, obstructing their control. Given their role in the regulation of physiological processes, neuroendocrine-derived factors have been proposed as a source of molecular targets for new-generation insecticides. However, the involvement of neuropeptides in insecticide metabolism and resistance in insects has been poorly studied. In the present work, the sequences of 20 neuropeptide precursor genes in T. infestans, 16 in T. dimidiata, and 13 in T. pallidipennis detected in transcriptomic databases are reported, and a comparative analysis in triatomines is presented. A total of 59 neuropeptides were validated by liquid chromatography-tandem mass spectrometry in brain and nervous ganglia from T. infestans, revealing the existence of differential post-translational modifications, extended and truncated forms. The results suggest a high sequence conservation in some neuropeptide systems in triatomines, whereas remarkable differences occur in several others within the core domains. Comparisons of the basal expression levels for several neuropeptide precursor genes between pyrethroid sensitive and resistant population of T. infestans are also presented here, in order to introduce a proof of concept to test the involvement of neuropeptides in insecticide resistance. From the precursors tested, NVP and ITG peptides are significantly higher expressed in the resistant population. To our knowledge, this is the first report to associate differential neuropeptide expression with insecticide resistance. The information provided here contributes to creating conditions to widely extend functional and genetic studies involving neuropeptides in triatomines.

CCAP and FMRFamide-like peptides accelerate the contraction rate of the antennal accessory pulsatile organs (auxiliary hearts) of mosquitoes

Insects rely on specialized accessory pulsatile organs (APOs), also known as auxiliary hearts, to propel hemolymph into their antennae. In most insects, this is accomplished via the pulsations of a pair of ampulla located in the head, each of which propels hemolymph across an antenna via an antennal vessel. Once at the distal end of the appendage, hemolymph returns to the head via the antennal hemocoel. Although the structure of the antennal hearts has been elucidated in various insect orders, their hormonal modulation has only been studied in cockroaches and other hemimetabolous insects within the superorder Polyneoptera, where proctolin and FMRFamide-like peptides accelerate the contraction rate of these auxiliary hearts. Here, we assessed the hormonal modulation of the antennal APOs of mosquitoes, a group of holometabolous (Endopterygota) insects within the order Diptera. We show that crustacean cardioactive peptide (CCAP), FMRFamide and SALDKNFMRFamide increase the contraction rate of the antennal APOs and the heart of Anopheles gambiae. Both antennal hearts are synchronously responsive to these neuropeptides, but their contractions are asynchronous with the contraction of the heart. Furthermore, we show that these neuropeptides increase the velocity and maximum acceleration of hemolymph within the antennal space, suggesting that each contraction is also more forceful. To our knowledge, this is the first report demonstrating that hormones of a holometabolous insect modulate the contraction dynamics of an auxiliary heart, and the first report that shows that the hormones of any insect accelerate the velocity of hemolymph in the antennal space.

Conserved molecular switch interactions in modeled cardioactive RF-NH2 peptide receptors: Ligand binding and activation

Peptides may act through G protein-coupled receptors to influence cardiovascular performance; thus, delineating mechanisms involved in signaling is a molecular-based strategy to influence health. Molecular switches, often represented by conserved motifs, maintain a receptor in an inactive state. However, once the switch is broken, the transmembrane regions move and activation occurs. The molecular switches of Drosophila melanogaster myosuppressin (MS) receptors were previously identified to include a unique ionic lock and novel 3-6 lock, as well as transmission and tyrosine toggle switches. In addition to MS, cardioactive ligands structurally related by a C-terminal RF-NH2 include sulfakinin, neuropeptide F (NPF), short NPF, and FMRF-NH2-containing peptide subfamilies. We hypothesized receptor molecular switch motifs were conserved within a RF-NH2 subfamily and across species. Thus, we investigated RF-NH2 receptor (RFa-R) molecular switches in D. melanogaster, Tribolium castaneum, Anopheles gambiae, Rhodnius prolixus, and Bombyx mori. Adipokinetic hormone (AKH), which does not contain a RF-NH2, was also examined. The tyrosine toggle switch and ionic lock showed a higher degree of conservation within a RF-NH2 subfamily than the transmission switch and 3-7 lock. AKH receptor motifs were not representative of a RF-NH2 subfamily. The motifs and interactions of switches in the RFa-Rs were consistent with receptor activation and ligand-specific binding.

Cardiac contractility structure-activity relationship and ligand-receptor interactions; the discovery of unique and novel molecular switches in myosuppressin signaling

Peptidergic signaling regulates cardiac contractility; thus, identifying molecular switches, ligand-receptor contacts, and antagonists aids in exploring the underlying mechanisms to influence health. Myosuppressin (MS), a decapeptide, diminishes cardiac contractility and gut motility. Myosuppressin binds to G protein-coupled receptor (GPCR) proteins. Two Drosophila melanogaster myosuppressin receptors (DrmMS-Rs) exist; however, no mechanism underlying MS-R activation is reported. We predicted DrmMS-Rs contained molecular switches that resembled those of Rhodopsin. Additionally, we believed DrmMS-DrmMS-R1 and DrmMS-DrmMS-R2 interactions would reflect our structure-activity relationship (SAR) data. We hypothesized agonist- and antagonist-receptor contacts would differ from one another depending on activity. Lastly, we expected our study to apply to other species; we tested this hypothesis in Rhodnius prolixus, the Chagas disease vector. Searching DrmMS-Rs for molecular switches led to the discovery of a unique ionic lock and a novel 3-6 lock, as well as transmission and tyrosine toggle switches. The DrmMS-DrmMS-R1 and DrmMS-DrmMS-R2 contacts suggested tissue-specific signaling existed, which was in line with our SAR data. We identified R. prolixus (Rhp)MS-R and discovered it, too, contained the unique myosuppressin ionic lock and novel 3-6 lock found in DrmMS-Rs as well as transmission and tyrosine toggle switches. Further, these motifs were present in red flour beetle, common water flea, honey bee, domestic silkworm, and termite MS-Rs. RhpMS and DrmMS decreased R. prolixus cardiac contractility dose dependently with EC50 values of 140 nM and 50 nM. Based on ligand-receptor contacts, we designed RhpMS analogs believed to be an active core and antagonist; testing on heart confirmed these predictions. The active core docking mimicked RhpMS, however, the antagonist did not. Together, these data were consistent with the unique ionic lock, novel 3-6 lock, transmission switch, and tyrosine toggle switch being involved in mechanisms underlying TM movement and MS-R activation, and the ability of MS agonists and antagonists to influence physiology.

Identification, characterization and expression of a receptor for the unusual myosuppressin in the blood-feeding bug, Rhodnius prolixus

Myosuppressins are a family of the FMRFamide-like peptides. They have been characterized in many insects and shown to inhibit visceral muscle contraction. Rhodnius prolixus possesses an unusual myosuppressin in that the typical FLRFamide C-terminal motif is unique and ends with FMRFamide. In the present study, we isolated the cDNA sequence for the R. prolixus receptor for this unusual myosuppressin (RhoprMSR). Quantitative PCR indicates high relative transcript expression of RhoprMSR in the central nervous system and also supports the previously described physiological effects of RhoprMS on the digestive system, with expression of the RhoprMSR transcript in the midgut and hindgut. Expression of the RhoprMSR transcript was also found in the female and male reproductive system of 5th instar nymphs, with transcript expression greater in the female reproductive tissues. No expression was found in the salivary glands or Malpighian tubules. A functional receptor expression assay confirmed that the cloned RhoprMSR is indeed activated by RhoprMS (half maximum effective concentration = 42.7 nM). Structure-activity studies based upon both functional receptor assays and physiological assays showed the importance of the HVFMRFamide moiety, as further N-terminal truncation removed all activity.

Myoinhibitors controlling oviduct contraction within the female blood-gorging insect, Rhodnius prolixus

Muscle activity can be regulated by stimulatory and inhibitory neuropeptides allowing for contraction and relaxation. There are various families of neuropeptides that can be classified as inhibitors of insect muscle contraction. This study focuses on Rhodnius prolixus and three neuropeptide families that have been shown to be myoinhibitors in insects: A-type allatostatins, myoinhibiting peptides (B-type allatostatins) and myosuppressins. FGLa/AST-like immunoreactive axons and blebs were found on the anterior of the dorsal vessel and on the abdominal nerves. FGLa/AST-like immunoreactive axons were also seen in the trunk nerves and on the bursa. The effects of RhoprAST-2 (FGLa/AST or A-type allatostatins) and RhoprMIP-4 (MIP/AST or B-type allatostatins) were similar, producing dose-dependent inhibition of R. prolixus spontaneous oviduct contractions with a maximum of 70% inhibition and an EC50 at approximately 10(-8)M. The myosuppressin of R. prolixus (RhoprMS) has an unusual FMRFamide C-terminal motif (pQDIDHVFMRFa) as compared to myosuppressins from other insects. Quantitative PCR results show that the RhoprMS receptor transcript is present in adult female oviducts; however, RhoprMS does not have an inhibitory effect on R. prolixus oviduct contractions, but does have a dose-dependent inhibitory effect on the spontaneous contraction of Locusta migratoria oviducts. SchistoFLRFamide, the myosuppressin of Schistocerca gregaria and L. migratoria, also does not inhibit R. prolixus oviduct contractions. This implies that FGLa/ASTs and MIP/ASTs may play a role in regulating egg movement within the oviducts, and that the myosuppressin although myoinhibitory on other muscles in R. prolixus, does not inhibit the contractions of R. prolixus oviducts and may play another role in the reproductive system.

Differential peptidomics highlights adipokinetic hormone as key player in regulating digestion in anautogenous flesh fly, Sarcophaga crassipalpis

Females of anautogenous flesh flies, Sarcophaga crassipalpis, need a protein meal in order to produce their first batch of eggs. This protein meal elicits an increase in midgut proteolytic activity that is under neuropeptidergic regulation. Time series of decapitation and rescue experiments of liver fed flies evidenced the need of a peptide factor released by corpora cardiaca (CC) within 4h post protein feeding in order to assure complete protein digestion. Q-Exactive quantitative differential peptidomics analysis on CC of sugar fed flies and flies 5h post protein feeding respectively, showed a unique consistent decrease in the stored amount of adipokinetic hormone (AKH) ranging between 16% up to 63%. Injection of AKH into liver fed decapitated flies as well as sugar fed intact flies resulted in dose dependent enhanced midgut proteolytic activity up to the level of intact protein fed flies. This suggests a key role of AKH in food depended reproduction.

Myotropic effects of FMRFamide containing peptides on the heart of the mosquito Anopheles gambiae

FMRFamide-like peptides (FLPs) are produced by invertebrate and vertebrate animals, and regulate diverse physiological processes. In insects, several FLPs modulate heart physiology, with some increasing and others decreasing dorsal vessel contraction dynamics. Here, we describe the FMRFamide gene structure in the mosquito, Anopheles gambiae, quantify the developmental and spatial expression of FMRFamide and its putative receptor (FMRFamideR), and show that the peptides FMRFamide and SALDKNFMRFamide have complex myotropic properties. RACE sequencing showed that the FMRFamide gene encodes eight putative FLPs and is alternatively spliced. Of the eight FLPs, only one is shared by A. gambiae, Aedes aegypti and Culex quinquefasciatus: SALDKNFMRFamide. Quantitative PCR showed that peak expression of FMRFamide and FMRFamideR occurs in second instar larvae and around eclosion. In adults, FMRFamide is primarily transcribed in the head and thorax, and FMRFamideR is primarily transcribed in the thorax. Intravital video imaging of mosquitoes injected FMRFamide and SALDKNFMRFamide revealed that at low doses these peptides increase heart contraction rates. At high doses, however, these peptides decrease heart contraction rates and alter the proportional directionality of heart contractions. Taken altogether, these data describe the FMRFamide gene in A. gambiae, and show that FLPs are complex modulators of mosquito circulatory physiology.

Cardioacceleratory function of the neurohormone CCAP in the mosquito Anopheles gambiae

Crustacean cardioactive peptide (CCAP) is a highly conserved arthropod neurohormone that is involved in ecdysis, hormone release and the modulation of muscle contractions. Here, we determined the CCAP gene structure in the malaria mosquito Anopheles gambiae, assessed the developmental expression of CCAP and its receptor and determined the role that CCAP plays in regulating mosquito cardiac function. RACE sequencing revealed that the A. gambiae CCAP gene encodes a neuropeptide that shares 100% amino acid identity with all sequenced CCAP peptides, with the exception of Daphnia pulex. Quantitative RT-PCR showed that expression of CCAP and the CCAP receptor displays a bimodal distribution, with peak mRNA levels in second instar larvae and pupae. Injection of CCAP revealed that augmenting hemocoelic CCAP levels in adult mosquitoes increases the anterograde and retrograde heart contraction rates by up to 28%, and increases intracardiac hemolymph flow velocities by up to 33%. Partial CCAP knockdown by RNAi had the opposite effect, decreasing the mosquito heart rate by 6%. Quantitative RT-PCR experiments showed that CCAP mRNA is enriched in the head region, and immunohistochemical experiments in newly eclosed mosquitoes detected CCAP in abdominal neurons and projections, some of which innervated the heart, but failed to detect CCAP in the abdomens of older mosquitoes. Instead, in older mosquitoes CCAP was detected in the pars lateralis, the subesophageal ganglion and the corpora cardiaca. In conclusion, CCAP has a potent effect on mosquito circulatory physiology, and thus heart physiology in this dipteran insect is under partial neuronal control.