CAPA neuropeptides and their receptor form an anti-diuretic hormone signaling system in the human disease vector, Aedes aegypti

The Integrative Physiology of Hormone Signaling: Insights from Insect Models

Hormones orchestrate virtually all physiological processes in animals and enable them to adjust internal responses to meet diverse physiological demands. Studies in both vertebrates and insects have uncovered many novel hormones and dissected the physiological mechanisms they regulate, demonstrating a remarkable conservation in endocrine signaling across the tree of life. In this review, we focus on recent advances in insect research, which have provided a more integrative view of the conserved interorgan communication networks that control physiology. These new insights have been driven by experimental advantages inherent to insects, which over the past decades have aligned with new technologies and sophisticated genetic tools, to transform insect genetic models into a powerful testbed for posing new questions and exploring longstanding issues in endocrine research. Here, we illustrate how insect studies have addressed classic questions in three main areas, hormonal control of growth and development, neuroendocrine regulation of ion and water balance, and hormonal regulation of behavior and metabolism, and how these discoveries have illuminated our fundamental understanding of endocrine signaling in animals. The application of integrative physiology in insect systems to questions in endocrinology and physiology is expanding and is poised to be a crucible of discovery, revealing fundamental mechanisms of hormonal regulation that underlie animal adaptations to their environments.

Neuropeptides from a praying mantis: what the loss of pyrokinins and tryptopyrokinins suggests about the endocrine functions of these peptides

Background

Neuropeptides play important roles in insects, but in many cases their functions remain obscure. Comparative neuropeptidome analyses may provide clues to what these functions might be. Praying mantises are predators and close relatives of cockroaches that are scavengers. Cockroach neuropeptidomes are well established, but little is known about mantis neuropeptides. The recently published genome assembly of the praying mantis Tenodera sinensis makes it Possible to change that.

Methods

The genome assembly from T. sinensis was analyzed for the presence of genes coding neuropeptides. For comparison, publicly available short read archives from this and other mantis species were also examined for the presence and expression of neuropeptides.

Results

As a rule, the neuropeptidomes of the Mantodea and Blattodea are almost identical; praying mantises and cockroaches use very similar neuropeptides. However, there is one surprising exception. Praying mantises lack the receptors for pyrokinins, including those for the tryptopyrokinins. No typical pyrokinin genes were found, but some species do have a tryptopyrokinin gene, in others this has also been lost and, in one species it is a speudogene. For most praying mantises there is no information where tryptopyrokinin is expressed, but in Deroplatys truncata it is in the thorax and thus not in the suboesophageal ganglion, as in other insects. In the genomic short read archives of two species-out of 52-sequences were found for a tryptopyrokinin specific receptor. The phylogenetic position of those two species implies that the receptor gene was independently lost on multiple occasions. The loss of the tryptopyrokinin gene also happened more than once.

Discussion

The multiple independent losses of the pyrokinin receptors in mantises suggests that these receptors are irrelevant in praying mantises. This is very surprising, since expression of tryptopyrokinin is very strongly conserved in two neuroendocrine cells in the suboeosphageal ganglion. In those species for which this is known, the expression of its receptor is in the salivary gland. As a neuroendocrine, tryptopyrokinin is unlikely to acutely regulate salivation, which in other insects is regulated by well characterized neurons. If the action of tryptopyrokinin were to prime the salivary gland for subsequent salivation, it would make perfect sense for a praying mantis to lose this capacity, as they can not anticipate when they will catch their next prey. Priming the salivary gland days before it is actually needed would be energetically costly. The other pyrokinins are known to facilitate feeding and may in a similar fashion prime muscles needed for moving to the food source and digesting it. This hypothesis provides a good explanation as to why praying mantises do not need pyrokinins, and also what the function of these ubiquitous arthropod neuropeptides may be.

Examining Protein Localization in Aedes aegypti Cells, Tissues, and Organs: Whole-Mount Immunohistochemistry

Immunohistochemistry (IHC) is a powerful technique used for visualizing cellular components and determining the presence and/or location of proteins or other macromolecules in tissue samples. The classical IHC process involves the detection of epitopes using a highly specific primary antibody. This is followed by a secondary antibody that is coupled to a reporter molecule or fluorophore and capable of binding to the primary antibody and allowing for protein immunodetection. Although IHC does not routinely provide quantitative results compared to an enzyme-linked immunoassay or western blotting, it permits the localization of the proteins in intact tissues. This protocol describes an IHC assay for whole-body Aedes aegypti mosquito tissues that is used to detect small proteins, specifically neuropeptide hormones. This method is useful for protein detection in whole-mount preparations; however, cross-section IHC is recommended to determine if a protein is localized in the apical versus basolateral membrane of tissues/organs or to visualize immunological distribution in larger, more complex preparations.

Examining Apical or Basolateral Protein Localization in Aedes aegypti Tissues: Cross-Section Immunohistochemistry

Immunohistochemistry (IHC) is an important technique that permits visualization of cellular components and for determining the presence and/or distribution of proteins or other macromolecules in tissue samples. Normally, IHC involves the detection of epitopes using an antigen-specific primary antibody and a secondary antibody coupled with a reporter molecule or fluorophore that can bind to the primary antibody, allowing for the spatial distribution of a protein of interest to be detected. Although normally IHC does not provide quantitative results compared to techniques such as enzyme-linked immunoassay or western blotting, it permits the localization, expression mapping, and distribution of target proteins in intact tissues. Here, we describe an IHC protocol for examining apical versus basolateral protein staining through sectioning tissue samples from fixed, embedded tissues (e.g., IHC-paraffin) and adding primary antibodies against a target protein. This IHC protocol provides a guide for tissue fixation, sectioning, and staining of tissue samples.

Examining Cell-Specific Localization in Aedes aegypti Tissues with Fluorescence In Situ Hybridization

Fluorescence in situ hybridization (FISH) is a macromolecular recognition tool that uses RNA or DNA fragments combined with fluorophore- or digoxigenin-coupled nucleotides as probes to examine transcript localization through the presence or absence of complementary sequences in fixed tissues or samples under a fluorescent microscope. FISH technology has been highly effective for mapping genes and constructing a visual map of animal genomes. Here, we describe the application of FISH technology in the Aedes aegypti mosquito, where it is specifically used to localize receptor transcripts in gut tissues/organs. The methods presented highlight the synthesis of RNA probes and describe the 2-d process of incubating the tissues/organs with the RNA probes. We also describe tyramide signal amplification for improved signal detection.

Mapping Transcript Cell-Specific Localization and Protein Subcellular Localization in the Adult Mosquito Aedes aegypti

This introduction reviews techniques used to examine the distribution and expression of gene transcripts and proteins in a variety of tissues/organs in the medically important global disease vector mosquito, Aedes aegypti Specifically, these methods allow the detection of cell-specific transcript expression by fluorescent in situ hybridization; facilitate immunohistochemical mapping of a protein of interest in whole-mount small tissue/organ samples; examine the subcellular localization of proteins, such as membrane transporters, through sectioning of paraffin-embedded tissue/organ samples; and finally, enable the efficient separation of cytosolic and membrane proteins for western blot analysis without the need for specialized equipment (e.g., ultracentrifuge) in the mosquito Ae. aegypti Such techniques are useful to help answer fundamental questions in mosquito scientific research including (but not limited to) the identification of specific cells in an organ responsible for expressing a receptor of particular interest and necessary for eliciting a response to exogenous signals, including hormones. Moreover, changes in the subcellular localization of specific targets of interest can be assessed both qualitatively and quantitatively, providing insight into transient or long-term physiologically relevant regulation necessary for activity under experimental treatments or varied internal (e.g., development) or external (e.g., environmental stress) factors that might be normally experienced by the organism.

Another fly diuretic hormone: tachykinins increase fluid and ion transport by adult Drosophila melanogaster Malpighian 'renal' tubules

Insects such as the model organism Drosophila melanogaster must modulate their internal physiology to withstand changes in temperature and availability of water and food. Regulation of the excretory system by peptidergic hormones is one mechanism by which insects maintain their internal homeostasis. Tachykinins are a family of neuropeptides that have been shown to stimulate fluid secretion from the Malpighian 'renal' tubules (MTs) in some insect species, but it is unclear if that is the case in the fruit fly, D. melanogaster. A central objective of the current study was to examine the physiological role of tachykinin signaling in the MTs of adult D. melanogaster. Using the genetic toolbox available in this model organism along with in vitro and whole-animal bioassays, our results indicate that Drosophila tachykinins (DTKs) function as diuretic hormones by binding to the DTK receptor (DTKR) localized in stellate cells of the MTs. Specifically, DTK activates cation and anion transport across the stimulated MTs, which impairs their survival in response to desiccation because of their inability to conserve water. Thus, besides their previously described roles in neuromodulation of pathways controlling locomotion and food search, olfactory processing, aggression, lipid metabolism and metabolic stress, processing of noxious stimuli and hormone release, DTKs also appear to function as bona fide endocrine factors regulating the excretory system and appear essential for the maintenance of hydromineral balance.

Functional expression and characterization of CAPA receptor in the digestive tract and life stages of Drosophila suzukii, and differential activities with insect PRXamide peptides

Spotted-wing drosophila, Drosophila suzukii (Matsumura), is an invasive vinegar fly that is a major threat to the small fruits industries globally. Insect capa genes encode multiple neuropeptides, including CAPA-periviscerokinin (CAPA-PVK) peptides, that are specifically known to cause diuresis or anti-diuresis in various organisms. Here we identified and characterized a corresponding G protein-coupled receptor (GPCR) of the D. suzukii CAPA-PVK peptides: CAPA receptor (CAPA-R). To better characterize the behavior of D. suzukii CAPA-R, we used insect cell-based functional expression assays to evaluate responses of CAPA-R against D. suzukii CAPA-PVKs, CAPA-PVKs from five species in Insecta, one species from Mollusca, modified CAPA-PVK peptides, and some PRXamide family peptides: pyrokinin (PK), diapause hormone (DH), and ecdysis-triggering hormone (ETH). Functional studies revealed that the D. suzukii CAPA-R is strongly activated by both of its own natural D. suzukii CAPA-PVKs, and interestingly, it was strongly activated by other CAPA-PVK peptides from Frankliniella occidentallis (Thysanoptera), Solenopsis invicta (Hymenoptera), Helicoverpa zea (Lepidoptera) and Plutella xylostella (Lepidoptera). However, D. suzukii CAPA-R was not activated by Mollusca CAPA-PVK or the other PRXamide peptides. Gene expression analyses showed that the CAPA-R was highly expressed in the Malpighian tubules and moderately in hindgut compared to other digestive organs or the rest of body, supporting diuretic/antidiuretic functionality. When compared across life stages of D. suzukii, expression of CAPA-R was approximately 1.5x greater in the third instar than the other stages and minimally detected in the eggs, 4-day old pupae and 3-day old adults. Our results functionally characterized the D. suzukii CAPA-R and a few short peptides were identified as potential biological targets to exploit the CAPA-R for D. suzukii management.

Molecular characterization, localization, and physiological roles of ITP and ITP-L in the mosquito, Aedes aegypti

The insect ion transport peptide (ITP) and its alternatively spliced variant, ITP-like peptide (ITP-L), belong to the crustacean hyperglycemic hormone family of peptides and are widely conserved among insect species. While limited, studies have characterized the ITP/ITP-L signaling system within insects, and putative functions including regulation of ion and fluid transport, ovarian maturation, and thirst/excretion have been proposed. Herein, we aimed to molecularly investigate Itp and Itp-l expression profiles in the mosquito, Aedes aegypti, examine peptide immunolocalization and distribution within the adult central nervous system, and elucidate physiological roles for these neuropeptides. Transcript expression profiles of both AedaeItp and AedaeItp-l revealed distinct enrichment patterns in adults, with AedaeItp expressed in the brain and AedaeItp-l expression predominantly within the abdominal ganglia. Immunohistochemical analysis within the central nervous system revealed expression of AedaeITP peptide in a number of cells in the brain and in the terminal ganglion. Comparatively, AedaeITP-L peptide was localized solely within the pre-terminal abdominal ganglia of the central nervous system. Interestingly, prolonged desiccation stress caused upregulation of AedaeItp and AedaeItp-l levels in adult mosquitoes, suggesting possible functional roles in water conservation and feeding-related activities. RNAi-mediated knockdown of AedaeItp caused an increase in urine excretion, while knockdown of both AedaeItp and AedaeItp-l reduced blood feeding and egg-laying in females as well as hindered egg viability, suggesting roles in reproductive physiology and behavior. Altogether, this study identifies AedaeITP and AedaeITP-L as key pleiotropic hormones, regulating various critical physiological processes in the disease vector, A. aegypti.

The functional assay identified authentic interactions between CAPA peptides and the CAPA receptor isoforms in Bemisia tabaci (Gennadius)

CAPA neuropeptides regulate the diuresis/ antidiuresis process in insects by activating specific cognate receptor, CAPAr. In this study, we characterized the CAPAr gene (BtabCAPAr) in the whitefly, Bemisia tabaci Asia II 1. The two alternatively spliced isoforms of BtabCAPAr gene, BtabCAPAr-1 and BtabCAPAr-2, having six and five exons, respectively, were identified. The BtabCAPAr gene expression was highest in adult whitefly as compared to gene expression in egg, nymphal and pupal stages. Among the three putative CAPA peptides, CAPA-PVK1 and CAPA-PVK2 strongly activated the BtabCAPAr-1 with very low EC50 values of 0.067 nM and 0.053 nM, respectively, in heterologous calcium mobilization assays. None of the peptide activated the alternatively spliced isoform BtabCAPAr-2 that has lost the transmembrane segments 3 and 4. Significant levels of mortality were observed when whiteflies were fed with CAPA-PVK1 at 1.0 μM (50.0%), CAPA-PVK2 at 100.0 nM (43.8%) and CAPA-tryptoPK 1.0 μM (40.0%) at the 96 h after the treatment. This study provides valuable information to design biostable peptides to develop a class of insecticides.

The V-type H+-ATPase is targeted in antidiuretic hormone control of the Malpighian "renal" tubules

Like other insects, secretion by mosquito Malpighian tubules (MTs) is driven by the V-type H+-ATPase (VA) localized in the apical membrane of principal cells. In Aedes aegypti, the antidiuretic neurohormone CAPA inhibits secretion by MTs stimulated by select diuretic hormones; however, the cellular effectors of this inhibitory signaling cascade remain unclear. Herein, we demonstrate that the VA inhibitor bafilomycin selectively inhibits serotonin (5HT)- and calcitonin-related diuretic hormone (DH31)-stimulated secretion. VA activity increases in DH31-treated MTs, whereas CAPA abolishes this increase through a NOS/cGMP/PKG signaling pathway. A critical feature of VA activation involves the reversible association of the cytosolic (V1) and membrane (Vo) complexes. Indeed, higher V1 protein abundance was found in membrane fractions of DH31-treated MTs, whereas CAPA significantly decreased V1 abundance in membrane fractions while increasing it in cytosolic fractions. V1 immunolocalization was observed strictly in the apical membrane of DH31-treated MTs, whereas immunoreactivity was dispersed following CAPA treatment. VA complexes colocalized apically in female MTs shortly after a blood meal consistent with the peak and postpeak phases of diuresis. Comparatively, V1 immunoreactivity in MTs was more dispersed and did not colocalize with the Vo complex in the apical membrane at 3 h post blood meal, representing a time point after the late phase of diuresis has concluded. Therefore, CAPA inhibition of MTs involves reducing VA activity and promotes complex dissociation hindering secretion. Collectively, these findings reveal a key target in hormone-mediated inhibition of MTs countering diuresis that provides a deeper understanding of this critical physiological process necessary for hydromineral balance.

Diuretic hormone 31 activates two G protein-coupled receptors with differential second messengers for diuresis in Drosophila suzukii

Diuretic hormones (DHs) bind to G protein-coupled receptors (GPCRs), regulating water and ion balance to maintain homeostasis in animals. Two distinct DHs are known in insects: calcitonin (CT)-like DH31 and corticotropin-releasing factor (CRF)-like DH44. In this study, we identified and characterized DH31 and two DH31 GPCR variants, DH31-Ra and DH31-Rb, from spotted-wing drosophila, Drosophila suzukii, a globally prevalent vinegar fly causing severe damage to small fruits. Both GPCRs are active, but DH31-Ra is the dominant receptor based on gene expression analyses and DH31 peptide binding affinities. A notable difference between the two variants lies in 1) the GPCR structures of their C-termini and 2) the utilization of second messengers, and the amino acid sequences of the two variants are identical. DH31-Ra contains 12 additional amino acids, providing different intracellular C-terminal configurations. DH31-Ra utilizes both cAMP and Ca2+ as second messengers, whereas DH31-Rb utilizes only cAMP; this is the first time reported for an insect CT-like DH31 peptide. DH31 stimulated fluid secretion in D. suzukii adults, and secretion increased in a dose-dependent manner. However, when the fly was injected with a mixture of DH31 and CAPA, an anti-diuretic hormone, fluid secretion was suppressed. Here, we discuss the structures of the DH31 receptors and the differential signaling pathways, including second messengers, involved in fly diuresis. These findings provide fundamental insights into the characterization of D. suzukii DH31 and DH31-Rs, and facilitate the identification of potential biological targets for D. suzukii management.

Managing fuels and fluids: Network integration of osmoregulatory and metabolic hormonal circuits in the polymodal control of homeostasis in insects

Osmoregulation in insects is an essential process whereby changes in hemolymph osmotic pressure induce the release of diuretic or antidiuretic hormones to recruit individual osmoregulatory responses in a manner that optimizes overall homeostasis. However, the mechanisms by which different osmoregulatory circuits interact with other homeostatic networks to implement the correct homeostatic program remain largely unexplored. Surprisingly, recent advances in insect genetics have revealed several important metabolic functions are regulated by classic osmoregulatory pathways, suggesting that internal cues related to osmotic and metabolic perturbations are integrated by the same hormonal networks. Here, we review our current knowledge on the network mechanisms that underpin systemic osmoregulation and discuss the remarkable parallels between the hormonal networks that regulate body fluid balance and those involved in energy homeostasis to provide a framework for understanding the polymodal optimization of homeostasis in insects.

Insect PRXamides: Evolutionary Divergence, Novelty, and Loss in a Conserved Neuropeptide System

The PRXamide neuropeptides have been described in both protostome and deuterostome species, including all major groups of the Panarthropoda. Best studied are the insect PRXamides consisting of three genes: pk/pban, capa, and eth, each encoding multiple short peptides that are cleaved post-translationally. Comparisons of genome and transcriptome sequences reveal that while retaining its fundamental ancestral organization, the products of the pk/pban gene have undergone significant change in the insect Order Diptera. Basal dipteran pk/pban genes are much like those of other holometabolous insects, while more crown species have lost two peptide coding sequences including the otherwise ubiquitous pheromone biosynthesis activating neuropeptide (PBAN). In the genomic model species Drosophila melanogaster, one of the remaining peptides (hugin) plays a potentially novel role in feeding and locomotor regulation tied to circadian rhythms. Comparison of peptide coding sequences of pk/pban across the Diptera pinpoints the acquisition or loss of the hugin and PBAN peptide sequences respectively, and provides clues to associated changes in life history, physiology, and/or behavior. Interestingly, the neural circuitry underlying pk/pban function is highly conserved across the insects regardless of the composition of the pk/pban gene. The rapid evolution and diversification of the Diptera provide many instances of adaptive novelties from genes to behavior that can be placed in the context of emerging selective pressures at key points in their phylogeny; further study of changing functional roles of pk/pban may then be facilitated by the high-resolution genetic tools available in Drosophila melanogaster.

Functional insight and cell-specific expression of the adipokinetic hormone/corazonin-related peptide in the human disease vector mosquito, Aedes aegypti

The adipokinetic hormone/corazonin-related peptide (ACP) is an insect neuropeptide structurally intermediate between corazonin (CRZ) and adipokinetic hormone (AKH). Unlike the AKH and CRZ signaling systems that are widely known for their roles in the mobilization of energy substrates and stress responses, respectively, the main role of ACP and its receptor (ACPR) remains unclear in most arthropods. The current study aimed to localize the distribution of ACP in the nervous system and provide insight into its physiological roles in the disease vector mosquito, Aedes aegypti. Immunohistochemical analysis and fluorescence in situ hybridization localized the ACP peptide and transcript within a number of cells in the central nervous system, including two pairs of laterally positioned neurons in the protocerebrum of the brain and a few ventrally localized neurons within the pro- and mesothoracic regions of the fused thoracic ganglia. Further, extensive ACP-immunoreactive axonal projections with prominent blebs and varicosities were observed traversing the abdominal ganglia. Given the prominent enrichment of ACPR expression within the abdominal ganglia of adult A. aegypti mosquitoes as determined previously, the current results indicate that ACP may function as a neurotransmitter and/or neuromodulator facilitating communication between the brain and posterior regions of the nervous system. In an effort to elucidate a functional role for ACP signaling, biochemical measurement of energy substrates in female mosquitoes revealed a reduction in abdominal fat body in response to ACP that matched the actions of AKH, but interestingly, a corresponding hypertrehalosaemic effect was only found in response to AKH since ACP did not influence circulating carbohydrate levels. Comparatively, both ACP and AKH led to a significant increase in haemolymph carbohydrate levels in male mosquitoes while both peptides had no influence on their glycogen stores. Neither ACP nor AKH influenced circulating or stored lipid levels in both male and female mosquitoes. Collectively, these results reveal ACP signaling in mosquitoes may have complex sex-specific actions, and future research should aim to expand knowledge on the role of this understudied neuropeptide.

Periviscerokinin (Cap2b; CAPA) receptor silencing in females of Rhipicephalus microplus reduces survival, weight and reproductive output

BACKGROUND

The cattle fever tick, Rhipicephalus (Boophilus) microplus, is a vector of pathogens causative of babesiosis and anaplasmosis, both highly lethal bovine diseases that affect cattle worldwide. In Ecdysozoa, neuropeptides and their G-protein-coupled receptors play a critical integrative role in the regulation of all physiological processes. However, the physiological activity of many neuropeptides is still unknown in ticks. Periviscerokinins (CAP2b/PVKs) are neuropeptides associated with myotropic and diuretic activities in insects. These peptides have been identified only in a few tick species, such as Ixodes ricinus, Ixodes scapularis and R. microplus, and their cognate receptor only characterized for the last two.

METHODS

Expression of the periviscerokinin receptor (Rhimi-CAP2bR) was investigated throughout the developmental stages of R. microplus and silenced by RNA interference (RNAi) in the females. In a first experiment, three double-stranded (ds) RNAs, named ds680-805, ds956-1109 and ds1102-1200, respectively, were tested in vivo. All three caused phenotypic effects, but only the last one was chosen for subsequent experiments. Resulting RNAi phenotypic variables were compared to those of negative controls, both non-injected and dsRNA beta-lactamase-injected ticks, and to positive controls injected with beta-actin dsRNA. Rhimi-CAP2bR silencing was verified by quantitative reverse-transcriptase PCR in whole females and dissected tissues.

RESULTS

Rhimi-CAP2bR transcript expression was detected throughout all developmental stages. Rhimi-CAP2bR silencing was associated with increased female mortality, decreased weight of surviving females and of egg masses, a delayed egg incubation period and decreased egg hatching (P < 0.05).

CONCLUSIONS

CAP2b/PVKs appear to be associated with the regulation of female feeding, reproduction and survival. Since the Rhimi-CAP2bR loss of function was detrimental to females, the discovery of antagonistic molecules of the CAP2b/PVK signaling system should cause similar effects. Our results point to this signaling system as a promising target for tick control.

Efficacy and biosafety assessment of neuropeptide CAPA analogues against the peach-potato aphid (Myzus persicae)

Insect CAPA neuropeptidesare considered to affect water and ion balance by mediating the physiological metabolism activities of the Malpighian tubules. In previous studies, the CAPA-PK analogue 1895 (2Abf-Suc-FGPRLamide) was reported to decrease aphid fitness when administered through microinjection or via topical application. However, a further statistically significant decrease in the fitness of aphids and an increased mortality could not be established with pairwise combinations of 1895 with other CAPA analogue. In this study, we assessed the topical application of new combinations of 1895 with five CAPA-PVK analogues on the fitness of aphids. We found that 1895 and CAPA-PVK analogue 2315 (ASG-[β³ L]-VAFPRVamide) was statistically the most effective combination to control the peach potato aphid Myzus persicae nymphs via topical application, leading to 72% mortality. Additionally, the combination (1895+2315) was evaluated against a selection of beneficial insects, that is, a pollinator (Bombus terrestris) and three natural enemies (Chrysoperla carnea, Nasonia vitripennis, and Adalia bipunctata). We found no significant influence on food intake, weight increase, and survival for the pollinator and the three representative natural enemies. These results could facilitate to further establish and generate CAPA analogues as alternatives to broad spectrum and less friendly insecticides.

The Peptide Hormone CNMa Influences Egg Production in the Mosquito Aedes aegypti

Mosquito reproduction is regulated by a suite of hormones, many acting through membrane-bound receptor proteins. The Aedes aegypti G protein-coupled receptors AAEL024199 (AeCNMaR-1a) and AAEL018316 (AeCNMaR-1b) were identified as orthologs of the Drosophila melanogaster CNMa receptor (DmCNMaR). The receptor was duplicated early in the evolution of insects, and subsequently in Culicidae, into what we refer to as CNMaR-1a and CNMaR-1b. AeCNMaR-1a is only detected in male mosquito antennae while AeCNMaR-1b is expressed at high levels in mosquito ovaries. Using a heterologous cell assay, we determined that AeCNMa activates AeCNMaR-1a with a ~10-fold lower concentration than it does AeCNMaR-1b, though both receptors displayed half maximal effective concentrations of AeCNMa in the low nanomolar range. Finally, we show that injections of AeCNMa into blood-fed mated female Ae. aegypti resulted in fewer eggs laid.

G protein-coupled receptors that influence lifespan of human and animal models

Humanity has always sought to live longer and for this, multiple strategies have been tried with varying results. In this sense, G protein-coupled receptors (GPCRs) may be a good option to try to prolong our life while maintaining good health since they have a substantial participation in a wide variety of processes of human pathophysiology and are one of the main therapeutic targets. In this way, we present the analysis of a series of GPCRs whose activity has been shown to affect the lifespan of animal and human models, and in which we put a special interest in describing the molecular mechanisms involved. Our compilation of data revealed that the mechanisms most involved in the role of GPCRs in lifespan are those that mimic dietary restriction, those related to insulin signaling and the AMPK and TOR pathways, and those that alter oxidative homeostasis and severe and/or chronic inflammation. We also discuss the possibility of using agonist or antagonist drugs, depending on the beneficial or harmful effects of each GPCR, in order to prolong people's lifespan and healthspan.

Hormonal regulation and functional role of the "renal" tubules in the disease vector, Aedes aegypti

The Aedes aegypti mosquito is a vector responsible for transmitting various arboviruses including dengue and yellow fever. Their ability to regulate the ionic and water composition of their hemolymph is a major physiological phenomenon, allowing the mosquito to adapt to a range of ecological niches. Hematophagus insects, including the female A. aegypti, face the challenge of excess salt and water intake after a blood meal. Post-prandial diuresis is under rigorous control by neuroendocrine factors, acting on the Malpighian "renal" tubules (MTs), to regulate primary urine production. The MTs are made up of two cell types; mitochondria-rich principal cells, which facilitate active transport of Na⁺ and K⁺ cations across the membrane, and thin stellate cells, which allows for transepithelial Cl^- secretion. The active driving force responsible for ion transport is the apical V-type H⁺ ATPase, which creates a proton gradient allowing for Na⁺ and/or K⁺ cation exchange through cation/H⁺ antiporters. Additionally, the basolaterally localized Na⁺-K⁺-2Cl^- cotransporter (NKCC) is responsible for the transport of these ions from the hemolymph into the principal cells. Numerous studies have examined hormonal regulation of the mosquito MTs and identified several diuretics including serotonin (5HT), a calcitonin-related diuretic hormone 31 (DH₃₁), a corticotropin-related factor like diuretic peptide (DH₄₄), a kinin-related diuretic peptide, as well as anti-diuretic factors including CAPA peptides, all of which are known to regulate fluid and ion transport by the MTs. This review therefore focuses on the control of ionic homeostasis in A. aegypti mosquitoes, emphasizing the importance of the MTs, the channels and transporters involved in maintaining hydromineral balance, and the neuroendocrine regulation of both diuresis and anti-diuresis.

A neuroendocrine pathway modulating osmotic stress in Drosophila

Environmental factors challenge the physiological homeostasis in animals, thereby evoking stress responses. Various mechanisms have evolved to counter stress at the organism level, including regulation by neuropeptides. In recent years, much progress has been made on the mechanisms and neuropeptides that regulate responses to metabolic/nutritional stress, as well as those involved in countering osmotic and ionic stresses. Here, we identified a peptidergic pathway that links these types of regulatory functions. We uncover the neuropeptide Corazonin (Crz), previously implicated in responses to metabolic stress, as a neuroendocrine factor that inhibits the release of a diuretic hormone, CAPA, and thereby modulates the tolerance to osmotic and ionic stress. Both knockdown of Crz and acute injections of Crz peptide impact desiccation tolerance and recovery from chill-coma. Mapping of the Crz receptor (CrzR) expression identified three pairs of Capa-expressing neurons (Va neurons) in the ventral nerve cord that mediate these effects of Crz. We show that Crz acts to restore water/ion homeostasis by inhibiting release of CAPA neuropeptides via inhibition of cAMP production in Va neurons. Knockdown of CrzR in Va neurons affects CAPA signaling, and consequently increases tolerance for desiccation, ionic stress and starvation, but delays chill-coma recovery. Optogenetic activation of Va neurons stimulates excretion and simultaneous activation of Crz and CAPA-expressing neurons reduces this response, supporting the inhibitory action of Crz. Thus, Crz inhibits Va neurons to maintain osmotic and ionic homeostasis, which in turn affects stress tolerance. Earlier work demonstrated that systemic Crz signaling restores nutrient levels by promoting food search and feeding. Here we additionally propose that Crz signaling also ensures osmotic homeostasis by inhibiting release of CAPA neuropeptides and suppressing diuresis. Thus, Crz ameliorates stress-associated physiology through systemic modulation of both peptidergic neurosecretory cells and the fat body in Drosophila.

Receptor Characterization and Functional Activity of Pyrokinins on the Hindgut in the Adult Mosquito, Aedes aegypti

Pyrokinins are structurally related insect neuropeptides, characterized by their myotropic, pheromonotropic and melanotropic roles in some insects, but their function is unclear in blood-feeding arthropods. In the present study, we functionally characterized the pyrokinin-1 and pyrokinin-2 receptors (PK1-R and PK2-R, respectively), in the yellow fever mosquito, Aedes aegypti, using a heterologous cell system to characterize their selective and dose-responsive activation by members of two distinct pyrokinin subfamilies. We also assessed transcript-level expression of these receptors in adult organs and found the highest level of PK1-R transcript in the posterior hindgut (rectum) while PK2-R expression was enriched in the anterior hindgut (ileum) as well as in reproductive organs, suggesting these to be prominent target sites for their peptidergic ligands. In support of this, PRXa-like immunoreactivity (where X = V or L) was localized to innervation along the hindgut. Indeed, we identified a myoinhibitory role for a PK2 on the ileum where PK2-R transcript was enriched. However, although we found that PK1 did not influence myoactivity or Na⁺ transport in isolated recta, the PRXa-like immunolocalization terminating in close association to the rectal pads and the significant enrichment of PK1-R transcript in the rectum suggests this organ could be a target of PK1 signaling and may regulate the excretory system in this important disease vector species.