Immunohistochemical mapping and transcript expression of the GPA2/GPB5 receptor in tissues of the adult mosquito, Aedes aegypti

Membrane Protein Fractionation and Analysis through Western Blot in Aedes aegypti Malpighian Tubules

Western blot analysis is a well-known and dependable technique used to quantify protein abundance in a wide variety of samples. A major consideration for running a successful western blot is ensuring that the protein to be analyzed is purified appropriately. For work with membrane-bound proteins, traditional methods of protein processing such as the use of high-frequency sonication and ultracentrifugation to separate proteins from the membrane are being replaced with less time-consuming approaches. The use of a membrane fractionation kit, which involves the separation of membrane proteins from soluble (cytosolic) proteins, is effective in allowing for the quantification and analysis of membrane-bound proteins. In this protocol, we describe use of the membrane fractionation kit to isolate membrane-bound proteins, followed by western blot analysis, to observe protein abundance. The protocol involves methods that require organ (or tissue) collection, followed by protein processing, and a 2-d western blot procedure.

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.

Functional characterization of CCHamides and deorphanization of their receptors in the yellow fever mosquito, Aedes aegypti

As a widely distributed anthropophilic mosquito species and vector of various arboviruses, Aedes aegypti poses a significant threat to human health on a global scale. Investigating mosquito neuropeptides allows us to better understand their physiology. The neuropeptides CCHamide1 (CCHa1) and CCHamide2 (CCHa2) along with their associated G protein-coupled receptors (CCHa1R and CCHa2R) were recently identified and studied across insects. However, expression profiles and physiological roles of CCHamides and their receptors in many other insects, including A. aegypti, remain unclear. This research aimed to quantify and localize the expression of CCHamides along with their receptors and gain insight on their physiological function in the yellow fever mosquito. RT-qPCR analysis revealed transcript abundance of CCHamides and receptors changes over development. Differential expression was also observed in tissues/organs of adult mosquitoes indicating CCHa1 and CCHa2 transcripts are enriched in the midgut, while receptors are expressed across various tissues. CCHamide immunoreactivity was observed in neurons in the brain and ventral nerve cord along with enteroendocrine cells in the posterior midgut adjacent to the midgut-hindgut junction, corroborating their transcript expression profiles. Using different mass spectrometrical approaches, presence of CCHamides were confirmed in the brain of both sexes, including the pars intercerebralis of female mosquitoes, as well as in the gut of adult mosquitoes. For chemical identification of predicted CCHamides, we analyzed brain and gut extracts by ESI-Q Exactive Orbitrap MS and resulting fragmentations confirmed CCHa1 and CCHa2 in brain and midgut samples of both male and female mosquitoes. A heterologous functional assay was used to confirm the specificity and sensitivity of the two CCHamide receptors by assessing their activation in response to diverse mosquito peptides, which confirmed CCHa1 and CCHa2 as natural ligands. Finally, using a capillary feeder (CAFE) bioassay, our results suggest that CCHa2 modulates feeding behaviour in female mosquitoes.

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 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.

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.

Investigating the role of glycoprotein hormone GPA2/GPB5 signaling in reproduction in adult female Rhodnius prolixus

Glycoprotein hormones are essential for regulating various physiological activities in vertebrates and invertebrates. In vertebrates, the classical glycoprotein hormones include follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH) and chorionic gonadotropin (CG), which have crucial roles in growth, development, metabolism, and reproduction. In female mammals, FSH stimulates egg production in the ovaries, whereas LH and CG act as the triggers for follicular ovulation. The more recently discovered heterodimeric glycoprotein hormone GPA2/GPB5 (called thyrostimulin in vertebrates) is suggested to be involved in reproductive processes in arthropods. Here, we focus on understanding the role of GPA2/GPB5 and its receptor, LGR1, in the reproductive success of adult female Rhodnius prolixus, a vector of Chagas disease. qPCR was used to monitor the expression of GPA2 and GPB5 transcripts and their receptor in different tissues. Immunohistochemistry was used to show the distribution of GPB5 in the nervous system and reproductive system, and RNA interference was used to disrupt the glycoprotein hormone signaling pathway. Both subunit transcripts, GPA2 and GPB5, are present in a variety of tissues, with the greatest expression in the central nervous system; whereas the LGR1 transcript is present in peripheral tissues, including the fat body and the reproductive system of adult females. In the adult female, GPB5-like immunoreactive axonal projections are present in the trunk nerves extending onto the reproductive tissues, with processes overlaying the ovaries, oviducts, spermatheca, and bursa, indicating the possibility of neural control by neurons containing GPA2/GPB5. In addition, GPB5-like immunostaining is present in muscles encircling the ovarioles, and in the cytoplasm of trophocytes (nurse cells) located in the tropharium. GPB5-like immunoreactive processes and blebs are also localized to the previtellogenic follicles, suggesting an involvement of this glycoprotein hormone signaling in oocyte development. LGR1 transcript expression increases in the adult female reproductive system post-feeding, a stimulus that initiates reproductive development, adding further support to an involvement in reproduction. We have investigated the effect of LGR1 downregulation on reproductive processes, monitoring the number and the quality of eggs laid, hatching ratio, and production of vitellogenin (Vg), the major yolk protein for developing eggs. Downregulation of LGR1 leads to increases in transcript expression of vitellogenin, RhoprVg1, in the fat body and the vitellogenin receptor, RhoprVgR, in the ovaries. Total protein in the fat body and hemolymph of dsLGR1-injected insects increased compared to controls and associated with this effect was a significant increase in vitellogenin in these tissues. dsLGR1-injection leads to accelerated oogenesis, an increase in the number of eggs produced and laid, an increase in egg size and a reduction in hatching rate. Our results indicate that GPA2/GPB5 signaling acts to delay egg production in adult female R. prolixus.

Antibody-Based Methods Reveal the Protein Expression Properties of Glucosinolate Sulfatase 1 and 2 in Plutella xylostella

The glucosinolates (GLs) and myrosinase defensive systems in cruciferous plants were circumvented by Plutella xylostella using glucosinolate sulfatases (PxGSSs) during pest-plant interaction. Despite identifying three duplicated GSS-encoding genes in P. xylostella, limited information regarding their spatiotemporal and induced expression is available. Here, we investigated the tissue- and stage-specific expression and induction in response to GLs of PxGSS1 and PxGSS2 (PxGSS1/2) at the protein level, which shares a high degree of similarity in protein sequences. Western blotting (WB) analysis showed that PxGSS1/2 exhibited a higher protein level in mature larvae, their guts, and gut content. A significantly high protein and transcript levels of PxGSS1/2 were also detected in the salivary glands using WB and qRT-PCR. The immunofluorescence (IF) and immunohistochemistry (IHC) results confirmed that PxGSS1/2 is widely expressed in the larval body. The IHC was more appropriate than IF when autofluorescence interference was present in collected samples. Furthermore, the content of PxGSS1/2 did not change significantly under treatments of GL mixture from Arabidopsis thaliana ecotype Col-0, or commercial ally (sinigrin), 4-(methylsulfinyl)butyl, 3-(methylsulfinyl)propyl, and indol-3-ylmethyl GLs indicating that the major GLs from leaves of A. thaliana Col-0 failed to induce the expression of proteins for both PxGSS1 and PxGSS2. Our study systemically characterized the expression properties of PxGSS1/2 at the protein level, which improves our understanding of PxGSS1/2-center adaptation in P. xylostella during long-term insect-plant interaction.

Genes Encoding the Glycoprotein Hormone GPA2/GPB5 and the Receptor LGR1 in a Female Prawn

In vertebrate reproduction, metabolism, growth and development, essential roles are played by glycoprotein hormones, such as follicle-stimulating hormone (FSH), luteinizing hormone (LH) and thyroid-stimulating hormone (TSH), all of which are heterodimers consisting of two subunits, a structurally identical alpha subunit, and a variable beta subunit, which provides specificity. A 'new' glycoprotein hormone heterodimer identified in both vertebrates and invertebrates, including decapod crustaceans, was shown to be composed of the glycoprotein alpha 2 (GPA2) and glycoprotein beta 5 (GPB5) subunits. The putative receptor for GPA2/GPB5 in invertebrates is the leucine-rich repeat-containing G protein-coupled receptor 1 (LGR1). In this study in the giant freshwater prawn, Macrobrachium rosenbergii, we identified and characterized the GPA2 (MrGPA2), GPB5 (MrGPB5) and LGR1 (MrLGR1) encoding genes and revealed their spatial expression patterns in female animals. Loss-of-function RNA interference (RNAi) experiments in M. rosenbergii females demonstrated a negative correlation between MrGPA2/MrGPB5 silencing and MrLGR1 transcript levels, suggesting a possible ligand-receptor interaction. The relative transcript levels of M. rosenbergii vitellogenin (MrVg) in the hepatopancreas were significantly reduced following MrGPA2/MrGPB5 knockdown. MrLGR1 loss-of-function induced MrVg receptor (MrVgR) transcript levels in the ovary and resulted in significantly larger oocytes in the silenced group compared to the control group. Our results provide insight into the possible role of GPA2/GPB5-LGR1 in female reproduction, as shown by its effect on MrVg and MrVgR expression and on the oocyte development. Here, we suggest that the GPA2/GPB5 heterodimer act as a gonad inhibiting factor in the eyestalk-hepatopancreas-ovary endocrine axis in M. rosenbergii.

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.

Temporal groups of lineage-related neurons have different neuropeptidergic fates and related functions in the Drosophila melanogaster CNS

The central nervous system (CNS) of Drosophila is comprised of the brain and the ventral nerve cord (VNC), which are the homologous structures of the vertebrate brain and the spinal cord, respectively. Neurons of the CNS arise from neural stem cells called neuroblasts (NBs). Each neuroblast gives rise to a specific repertory of cell types whose fate is unknown in most lineages. A combination of spatial and temporal genetic cues defines the fate of each neuron. We studied the origin and specification of a group of peptidergic neurons present in several abdominal segments of the larval VNC that are characterized by the expression of the neuropeptide GPB5, the GPB5-expressing neurons (GPB5-ENs). Our data reveal that the progenitor NB that generates the GPB5-ENs also generates the abdominal leucokinergic neurons (ABLKs) in two different temporal windows. We also show that these two set of neurons share the same axonal projections in larvae and in adults and, as previously suggested, may both function in hydrosaline regulation. Our genetic analysis of potential specification determinants reveals that Klumpfuss (klu) and huckebein (hkb) are involved in the specification of the GPB5 cell fate. Additionally, we show that GPB5-ENs have a role in starvation resistance and longevity; however, their role in desiccation and ionic stress resistance is not as clear. We hypothesize that the neurons arising from the same neuroblast lineage are both architecturally similar and functionally related.

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.

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

Insect CAPA neuropeptides are homologs of mammalian neuromedin U and are known to influence ion and water balance by regulating the activity of the Malpighian 'renal' tubules (MTs). Several diuretic hormones are known to increase primary fluid and ion secretion by insect MTs and, in adult female mosquitoes, a calcitonin-related peptide (DH31) called mosquito natriuretic peptide, increases sodium secretion to compensate for the excess salt load acquired during blood-feeding. An endogenous mosquito anti-diuretic hormone was recently described, having potent inhibitory activity against select diuretic hormones, including DH31. Herein, we functionally deorphanized, both in vitro and in vivo, a mosquito anti-diuretic hormone receptor (AedaeADHr) with expression analysis indicating highest enrichment in the MTs where it is localized within principal cells. Characterization using a heterologous in vitro system demonstrated the receptor was highly sensitive to mosquito CAPA neuropeptides while in vivo, AedaeADHr knockdown abolished CAPA-induced anti-diuretic control of DH31-stimulated MTs. CAPA neuropeptides are produced within a pair of neurosecretory cells in each of the abdominal ganglia, whose axonal projections innervate the abdominal neurohaemal organs, where these neurohormones are released into circulation. Lastly, pharmacological inhibition of nitric oxide synthase (NOS) and protein kinase G (PKG) signaling eliminated anti-diuretic activity of CAPA, highlighting the role of the second messenger cGMP and NOS/PKG in this anti-diuretic signaling pathway.

Expression Profiling, Downstream Signaling, and Inter-subunit Interactions of GPA2/GPB5 in the Adult Mosquito Aedes aegypti

GPA2/GPB5 and its receptor constitute a glycoprotein hormone-signaling system native to the genomes of most vertebrate and invertebrate organisms. Unlike the well-studied gonadotropins and thyrotropin, the exact function of GPA2/GPB5 remains elusive, and whether it elicits its functions as heterodimers, homodimers or as independent monomers remains unclear. Here, the glycoprotein hormone signaling system was investigated in adult mosquitoes, where GPA2 and GPB5 subunit expression was mapped and modes of its signaling were characterized. In adult Aedes aegypti mosquitoes, GPA2 and GPB5 transcripts co-localized to bilateral pairs of neuroendocrine cells, positioned within the first five abdominal ganglia of the central nervous system. Unlike GPA2/GPB5 homologs in human and fly, GPA2/GPB5 subunits in A. aegypti lacked evidence of heterodimerization. Rather, cross-linking analysis to determine subunit interactions revealed A. aegypti GPA2 and GPB5 subunits may form homodimers, although treatments with independent subunits did not demonstrate receptor activity. Since mosquito GPA2/GPB5 heterodimers were not evident by heterologous expression, a tethered fusion construct was generated for expression of the subunits as a single polypeptide chain to mimic heterodimer formation. Our findings revealed A. aegypti LGR1 elicited constitutive activity with elevated levels of cAMP. However, upon treatment with recombinant tethered GPA2/GPB5, an inhibitory G protein (Gi/o) signaling cascade is initiated and forskolin-induced cAMP production is inhibited. These results further support the notion that heterodimerization is a requirement for glycoprotein hormone receptor activation and provide novel insight to how signaling is achieved for GPA2/GPB5, an evolutionary ancient neurohormone.

Cytoplasmic sharing through apical membrane remodeling

Multiple nuclei sharing a common cytoplasm are found in diverse tissues, organisms, and diseases. Yet, multinucleation remains a poorly understood biological property. Cytoplasm sharing invariably involves plasma membrane breaches. In contrast, we discovered cytoplasm sharing without membrane breaching in highly resorptive Drosophila rectal papillae. During a six-hour developmental window, 100 individual papillar cells assemble a multinucleate cytoplasm, allowing passage of proteins of at least 62 kDa throughout papillar tissue. Papillar cytoplasm sharing does not employ canonical mechanisms such as incomplete cytokinesis or muscle fusion pore regulators. Instead, sharing requires gap junction proteins (normally associated with transport of molecules < 1 kDa), which are positioned by membrane remodeling GTPases. Our work reveals a new role for apical membrane remodeling in converting a multicellular epithelium into a giant multinucleate cytoplasm.

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

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

Anti-diuretic action of a CAPA neuropeptide against a subset of diuretic hormones in the disease vector Aedes aegypti

The mosquito Aedes aegypti is a vector responsible for transmitting various pathogens to humans, and their prominence as chief vectors of human disease is largely due to their anthropophilic blood feeding behaviour. Larval stage mosquitoes must deal with the potential dilution of their haemolymph in freshwater, whereas the haematophagus A. aegypti female faces the challenge of excess ion and water intake after a blood meal. The excretory system, composed of the Malpighian tubules (MTs) and hindgut, is strictly controlled by neuroendocrine factors, responsible for the regulation of diuresis across all developmental stages. The highly studied insect MTs are influenced by a variety of diuretic hormones and, in some insects, anti-diuretic factors. In the present study, we investigated the effects of AedaeCAPA-1 neuropeptide on larval and adult female A. aegypti MTs stimulated with various diuretic factors including serotonin (5-HT), a corticotropin-related factor (CRF) diuretic peptide, a calcitonin-related diuretic hormone (DH₃₁) and a kinin-related diuretic peptide. Overall, our findings establish that AedaeCAPA-1 specifically inhibits secretion of larval and adult MTs stimulated by 5-HT and DH₃₁, whilst having no activity on MTs stimulated by other diuretic factors. Furthermore, although AedaeCAPA-1 acts as an anti-diuretic, it does not influence the relative proportions of cations transported by adult MTs, thus maintaining the kaliuretic activity of 5-HT and natriuretic activity of DH₃₁ In addition, we tested the effects of the second messenger cGMP in adult MTs. We established that cGMP has similar effects to AedaeCAPA-1, strongly inhibiting 5-HT- and DH₃₁-stimulated fluid secretion, but with only minor effects on CRF-stimulated diuresis. Interestingly, although AedaeCAPA-1 has no inhibitory activity on kinin-stimulated fluid secretion, cGMP strongly inhibited fluid secretion by this diuretic hormone, which targets stellate cells specifically. Collectively, these results support that AedaeCAPA-1 inhibits select diuretic factors acting on the principal cells and this probably involves cGMP as a second messenger. Kinin-stimulated diuresis, which targets stellate cells, is also inhibited by cGMP, suggesting that another anti-diuretic factor in addition to AedaeCAPA-1 exists and may utilize cGMP as a second messenger.

Functional characterization and quantitative expression analysis of two GnRH-related peptide receptors in the mosquito, Aedes aegypti

To cope with stressful events such as flight, organisms have evolved various regulatory mechanisms, often involving control by endocrine-derived factors. In insects, two stress-related factors include the gonadotropin-releasing hormone-related peptides adipokinetic hormone (AKH) and corazonin (CRZ). AKH is a pleiotropic hormone best known as a substrate liberator of proteins, lipids, and carbohydrates. Although a universal function has not yet been elucidated, CRZ has been shown to have roles in pigmentation, ecdysis or act as a cardiostimulatory factor. While both these neuropeptides and their respective receptors (AKHR and CRZR) have been characterized in several organisms, details on their specific roles within the disease vector, Aedes aegypti, remain largely unexplored. Here, we obtained three A. aegypti AKHR transcript variants and further identified the A. aegypti CRZR receptor. Receptor expression using a heterologous functional assay revealed that these receptors exhibit a highly specific response for their native ligands. Developmental quantitative expression analysis of CRZR revealed enrichment during the pupal and adult stages. In adults, quantitative spatial expression analysis revealed CRZR transcript in a variety of organs including head, thoracic ganglia, primary reproductive organs (ovary and testis), as well as male carcass. This suggest CRZ may play a role in ecdysis, and neuronal expression of CRZR indicates a possible role for CRZ within the nervous system. Quantitative developmental expression analysis of AKHR identified significant transcript enrichment in early adult stages. AKHR transcript was observed in the head, thoracic ganglia, accessory reproductive tissues and the carcass of adult females, while it was detected in the abdominal ganglia and enriched significantly in the carcass of adult males, which supports the known function of AKH in energy metabolism. Collectively, given the enrichment of CRZR and AKHR in the primary and secondary sex organs, respectively, of adult mosquitoes, these neuropeptides may play a role in regulating mosquito reproductive biology.

Molecular identification, transcript expression, and functional deorphanization of the adipokinetic hormone/corazonin-related peptide receptor in the disease vector, Aedes aegypti

The recently discovered adipokinetic hormone/corazonin-related peptide (ACP) is an insect neuropeptide structurally intermediate between corazonin (CRZ) and adipokinetic (AKH) hormones, which all demonstrate homology to the vertebrate gonadotropin-releasing hormone (GnRH). To date, the function of the ACP signaling system remains unclear. In the present study, we molecularly identified the complete open reading frame encoding the Aedes aegypti ACP receptor (ACPR), which spans nine exons and undergoes alternative splicing giving rise to three transcript variants. Only a single variant, AedaeACPR-I, yielding a deduced 577 residue protein, contains all seven transmembrane domains characteristic of rhodopsin-like G protein-coupled receptors. Functional deorphanization of AedaeACPR-I using a heterologous cell culture-based system revealed highly-selective and dose-dependent receptor activation by AedaeACP (EC₅₀ = 10.25 nM). Analysis of the AedaeACPR-I and AedaeACP transcript levels in all post-embryonic developmental stages using quantitative RT-PCR identified enrichment of both transcripts after adult eclosion. Tissue-specific expression profiling in adult mosquitoes reveals expression of the AedaeACPR-I receptor transcript in the central nervous system, including significant enrichment within the abdominal ganglia. Further, the AedaeACP transcript is prominently detected within the brain and thoracic ganglia. Collectively, these results indicate a neuromodulator or neurotransmitter role for ACP and suggest this neuropeptide may function in regulation of post-ecdysis activities.