Regulation of feeding by Neuropeptide F in the desert locust, Schistocerca gregaria

Characterization of Neuropeptides from Spodoptera litura and Functional Analysis of NPF in Diet Intake

Neuropeptides are involved in many biological processes in insects. However, it is unclear what role neuropeptides play in Spodoptera litura adaptation to phytochemical flavone. In this study, 63 neuropeptide precursors from 48 gene families were identified in S. litura, including two neuropeptide F genes (NPFs). NPFs played a positive role in feeding regulation in S. litura because knockdown of NPFs decreased larval diet intake. S. litura larvae reduced flavone intake by downregulating NPFs. Conversely, the flavone intake was increased if the larvae were treated with NPF mature peptides. The NPF receptor (NPFR) was susceptible to the fluctuation of NPFs. NPFR mediated NPF signaling by interacting with NPFs to regulate the larval diet intake. In conclusion, this study suggested that NPF signaling regulated diet intake to promote S. litura adaptation to flavone, which contributed to understanding insect adaptation mechanisms to host plants and provide more potential pesticidal targets for pest control.

Starvation-Induced Changes to the Midgut Proteome and Neuropeptides in Manduca sexta

Starvation is a complex physiological state that induces changes in protein expression to ensure survival. The insect midgut is sensitive to changes in dietary content as it is at the forefront of communicating information about incoming nutrients to the body via hormones. Therefore, a DIA proteomics approach was used to examine starvation physiology and, specifically, the role of midgut neuropeptide hormones in a representative lepidopteran, Manduca sexta. Proteomes were generated from midguts of M. sexta fourth-instar caterpillars, starved for 24 h and 48 h, and compared to fed controls. A total of 3047 proteins were identified, and 854 of these were significantly different in abundance. KEGG analysis revealed that metabolism pathways were less abundant in starved caterpillars, but oxidative phosphorylation proteins were more abundant. In addition, six neuropeptides or related signaling cascade proteins were detected. Particularly, neuropeptide F1 (NPF1) was significantly higher in abundance in starved larvae. A change in juvenile hormone-degrading enzymes was also detected during starvation. Overall, our results provide an exploration of the midgut response to starvation in M. sexta and validate DIA proteomics as a useful tool for quantifying insect midgut neuropeptide hormones.

Transcriptome wide identification of neuropeptides and G protein-coupled receptors (GPCRs) in Sunn pest, Eurygaster integriceps Puton

Sunn pest (Eurygaster integriceps Puton) is major wheat pest causing economic damage. Neuropeptides and their receptors, G protein-coupled receptors (GPCRs), are involved in the regulation of insect physiology and behavior. Herein, a transcriptome-wide analysis was conducted in order to identify genes encoding neuropeptides, and putative GPCRs to gain insight into neuropeptide-modulated processes. De novo transcriptome assembly was undertaken using paired-end sequence reads derived from RNA samples collected from whole adults and yielded 582,398 contigs. In total, 46 neuropeptides have been identified, encompassing various known insect neuropeptide families. In addition, we discovered four previously uncharacterized neuroparsin peptides, which contributes to our understanding of the neuropeptide landscape. Furthermore, 85 putative neuropeptide GPCRs were identified, comprising three classes of GPCRs, A, B, C, and LGR, of which class C is not widely reported in insects. In addition, the identified GPCRs exhibited a remarkable 80% homology with the GPCRs found in the brown marmorated stink bug. It is noteworthy that these GPCRs displayed only a 20% homology to GPCRs from many other insect species. This information may be used to understand the neuropeptide-modulated physiology and behavior of Eurygaster integriceps, and to develop specific neuropeptide-based pest management strategies.

The cholinergic pathway transmits signals of neuropeptide F to regulate feeding of Ostrinia furnacalis larvae

BACKGROUND

Feeding is the basis of animal survival and reproduction. In insects, the neuropeptide F (NPF), a homologous polypeptide of NPY in vertebrates, plays an important role in regulation of feeding behavior. However, relatively little has been known about the molecular mechanism of feeding.

RESULTS

In this study, we show that the cholinergic pathway is very important in signaling transmission of NPF feeding regulation in Ostrinia furnacalis larvae, in which the choline acetyltransferase (ChAT), the vesicular acetylcholine transporter (vAChT) in presynaptic membrane and the nicotinic acetylcholine receptor (nAChR) in postsynaptic membrane are positively regulated by NPF, while the ace1 and ace2 encoding the acetylcholinesterase (AChE) are negatively regulated by NPF, leading to a balance of acetylcholine (ACh)-the excitatory transmitter. More, the cholinergic pathway further transmits signaling to the downstream pathways of the phosphoInositide-3 kinase (PI3K) and the cAMP responsive element binding protein (CREB), respectively.

CONCLUSION

The cholinergic transmission, positively regulated by NPF, is involved in feeding of O. furnacalis larvae via downstream PI3K and the CREB pathways, respectively. The deexcitation of cell cholinergic pathway or inhibition of PI3K and CREB lead to decreases of larval feeding amount. © 2023 Society of Chemical Industry.

Nicotine-mediated dopamine regulates short neuropeptide F to inhibit brown planthopper feeding behavior in tobacco-rice rotation cropping

BACKGROUND

The tobacco-rice rotation cropping (TRRC) is an ecologically friendly system that can both alleviate soil nicotine pollution and decrease the brown planthopper (BPH, Nilaparvata lugens Stål) fitness on rice. However, few studies on this green and effective rotational cropping system have been reported. In particular, the underlying mechanisms of TRRC on the significant reduction of field pest population at the molecular level is still unknown.

RESULTS

Field investigation showed that BPH population decreased significantly in TRRC than in rice-rice successive cropping (RRSC) field. In addition, the short neuropeptide F (NlsNPF) and its receptor NlA7 of BPH had half-times lower levels in the TRRC field. Behavioral bioassay indicated a 1.93-fold increase in the number of salivary flanges of the dsNlsNPF group, while BPH fitness parameters, such as honeydew, weight gain, and mortality decreased significantly. Dopamine (DA) content in BPH decreased by ~11.1% under the influence of nicotine, and its presence increased the expression levels of NlsNPF and NlA7. Exogenous DA application eliminated the inhibitory effects of nicotine on BPH feeding and restored the fitness levels of its parameters. Independent application of either a mixture of dsNlsNPF with a nanocarrier or nicotine to the normal rice field revealed that the latter could produce better effects in combination with dsRNA.

CONCLUSION

These findings confirmed that DA regulated NlsNPF to inhibit the BPH feeding behavior in TRRC. The results not only provided novel findings on the mechanism of pest-host interactions, but also presented new method for integrated pest management. © 2023 Society of Chemical Industry.

What Are the Functional Roles of Piwi Proteins and piRNAs in Insects?

Research on Piwi proteins and piRNAs in insects has focused on three experimental models: oogenesis and spermatogenesis in Drosophila melanogaster, the antiviral response in Aedes mosquitoes and the molecular analysis of primary and secondary piRNA biogenesis in Bombyx mori-derived BmN4 cells. Significant unique and complementary information has been acquired and has led to a greater appreciation of the complexity of piRNA biogenesis and Piwi protein function. Studies performed in other insect species are emerging and promise to add to the current state of the art on the roles of piRNAs and Piwi proteins. Although the primary role of the piRNA pathway is genome defense against transposons, particularly in the germline, recent findings also indicate an expansion of its functions. In this review, an extensive overview is presented of the knowledge of the piRNA pathway that so far has accumulated in insects. Following a presentation of the three major models, data from other insects were also discussed. Finally, the mechanisms for the expansion of the function of the piRNA pathway from transposon control to gene regulation were considered.

Piwi/piRNAs control food intake by promoting neuropeptide F expression in locusts

Animal feeding, which directly affects growth and metabolism, is an important physiological process. However, the contribution of PIWI proteins and PIWI‐interacting RNAs (piRNAs) to the regulatory mechanism of animal feeding is unknown. Here, we report a novel function of Piwi and piRNAs in regulating food intake in locusts. Our study shows that the locust can serve as a representative species for determining PIWI function in insects. Knockdown of Piwi1 expression suppresses anabolic processes and reduces food consumption and body weight. The reduction in food intake by knockdown of Piwi1 expression results from decreased expression of neuropeptide NPF1 in a piRNA‐dependent manner. Mechanistically, intronic piRNAs might enhance RNA splicing of NPF1 by preventing hairpin formation at the branch point sites. These results suggest a novel nuclear PIWI/piRNA‐mediated mechanism that controls food intake in the locust nervous system.

The short neuropeptide F (sNPF) promotes the formation of appetitive visual memories in honey bees

Motivation can critically influence learning and memory. Multiple neural mechanisms regulate motivational states, among which signalling via specific neuropeptides, such as NPY in vertebrates and NPF and its short variant sNPF in invertebrates, plays an essential role. The honey bee (Apis mellifera) is a privileged model for the study of appetitive learning and memory. Bees learn and memorize sensory cues associated with nectar reward while foraging, and their learning is affected by their feeding state. However, the neural underpinnings of their motivational states remain poorly known. Here we focused on the short neuropeptide F (sNPF) and studied if it modulates the acquisition and formation of colour memories. Artificially increasing sNPF levels in partially fed foragers with a reduced motivation to learn colours resulted in significant colour learning and memory above the levels exhibited by starved foragers. Our results thus identify sNPF as a critical component of motivational processes involved in foraging and in the cognitive processes associated with this activity in honey bees.

Neuropeptide F from endocrine cells in Plutella xylostella midgut modulates feeding and synergizes Cry1Ac action

With the wide cultivation of transgenic plants throughout the world and the rising risk of resistance to Bacillus thuringiensis crystal (Cry) toxins, it is essential to design an adaptive resistance management strategy for continued use. Neuropeptide F (NPF) of insects has proven to be valuable for the production of novel-type transgenic plants via its important role in the control of feeding behavior. In this study, the gene encoding NPF was cloned from the diamondback moth, Plutella xylostella, an important agricultural pest. Real-time quantitative reverse transcription-polymerase chain reaction and in situ hybridization showed a relatively high expression of P. xylostella-npf (P. x-npf) in endocrine cells of the midgut of fourth instar larvae, and it was found to participate in P. xylostella feeding behavior and Cry1Ac-induced feeding inhibition. Prokaryotic expression and purification provided structure unfolded P. x-npf from inclusion bodies for diet surface overlay bioassays and the results demonstrated a significant synergistic effect of P. x-npf on Cry1Ac toxicity by increasing intake of noxious food which contains Cry toxins, especially quick death at an early stage of feeding. Our findings provided a potential new way to efficiently control pests by increasing intake of lower dose Cry toxins and a novel hint for the complex Cry toxin mechanism.

NPF activates a specific NPF receptor and regulates food intake in Pacific abalone Haliotis discus hannai

Neuropeptides function through G protein-coupled receptors (GPCRs) with high specificity, implying a significant degree of neuropeptide-GPCR coevolution. However, potential neuropeptide signaling systems in non-chordates are relatively elusive. We determined the specificity of the neuropeptide F (Hdh-NPF) signaling system with a cognate receptor (Hdh-NPFR) in the Pacific abalone, Haliotis discus hannai. Phylogenetic and exon–intron arrangement analyses of bilaterian NPF and the chordate ortholog NPY with their receptor sequences revealed a likely common ancestor, and Hdh-NPFR was similar to the NPYR2 subtype among the NPYR1, NPYR2, and NPYR5 subtypes. Among four Hdh-NPFR-related receptors, Hdh-NPFR specifically responded to Hdh-NPF peptide, supported by the dose–response luciferase reporter curve, intracellular Ca²⁺ mobilization, and phosphorylation of ERK1/2 and its inhibition with a protein kinase C inhibitor. Peptide fragmentations and shuffling of Hdh-NPF with human NPY could not activate the cellular response of Hdh-NPFR. Three-dimensional in silico modeling suggested that interaction of Hdh-NPF C-terminal amino acids with the extracellular loops of Hdh-NPFR is critical for Hdh-NPFR activation. In vivo injection of Hdh-NPF peptide increased food consumption, and knockdown of Hdh-NPF expression decreased food consumption in Pacific abalone. These findings provide evidence for co-evolution of the NPF/Y ligand-receptor system, enabling further research on mollusk orexigenic neuropeptides.

Insects as a New Complex Model in Hormonal Basis of Obesity

Nowadays, one of the biggest problems in healthcare is an obesity epidemic. Consumption of cheap and low-quality energy-rich diets, low physical activity, and sedentary work favor an increase in the number of obesity cases within many populations/nations. This is a burden on society, public health, and the economy with many deleterious consequences. Thus, studies concerning this disorder are extremely needed, including searching for new, effective, and fitting models. Obesity may be related, among other factors, to disrupting adipocytes activity, disturbance of metabolic homeostasis, dysregulation of hormonal balance, cardiovascular problems, or disorders in nutrition which may lead to death. Because of the high complexity of obesity, it is not easy to find an ideal model for its studies which will be suitable for genetic and physiological analysis including specification of different compounds’ (hormones, neuropeptides) functions, as well as for signaling pathways analysis. In recent times, in search of new models for human diseases there has been more and more attention paid to insects, especially in neuro-endocrine regulation. It seems that this group of animals might also be a new model for human obesity. There are many arguments that insects are a good, multidirectional, and complex model for this disease. For example, insect models can have similar conservative signaling pathways (e.g., JAK-STAT signaling pathway), the presence of similar hormonal axis (e.g., brain–gut axis), or occurrence of structural and functional homologues between neuropeptides (e.g., neuropeptide F and human neuropeptide Y, insulin-like peptides, and human insulin) compared to humans. Here we give a hint to use insects as a model for obesity that can be used in multiple ways: as a source of genetic and peptidomic data about etiology and development correlated with obesity occurrence as well as a model for novel hormonal-based drug activity and their impact on mechanism of disease occurrence.

Genome-Wide Identification of Neuropeptides and Their Receptors in an Aphid Endoparasitoid Wasp, Aphidius gifuensi

In insects, neuropeptides and their receptors not only play a critical role in insect physiology and behavior but also are the potential targets for novel pesticide discoveries. Aphidius gifuensis is one of the most important and widespread aphid parasitoids, and has been successfully used to control aphid. In the present work, we systematically identified neuropeptides and their receptors from the genome and head transcriptome of A. gifuensis. A total of 35 neuropeptide precursors and 49 corresponding receptors were identified. The phylogenetic analyses demonstrated that 35 of these receptors belong to family-A, four belong to family-B, two belong to leucine-rich repeat-containing GPCRs, four belong to receptor guanylyl cyclases, and four belong to receptor tyrosine kinases. Oral ingestion of imidacloprid significantly up-regulated five neuropeptide precursors and four receptors whereas three neuropeptide precursors and eight receptors were significantly down-regulated, which indicated that these neuropeptides and their receptors are potential targets of some commercial insecticides. The RT-qPCR results showed that dopamine receptor 1, dopamine receptor 2, octopamine receptor, allatostatin-A receptor, neuropeptides capa receptor, SIFamide receptor, FMRFamide receptor, tyramine receptor and short neuropeptide F predominantly were expressed in the head whilst the expression of ion transport peptide showed widespread distribution in various tissues. The high expression levels of these genes suggest their important roles in the central nervous system. Taken together, our study provides fundamental information that may further our understanding of neuropeptidergic signaling systems in the regulation of the physiology and behavior of solitary wasps. Furthermore, this information could also aid in the design and discovery of specific and environment-friendly insecticides.

The sugar-responsive enteroendocrine neuropeptide F regulates lipid metabolism through glucagon-like and insulin-like hormones in Drosophila melanogaster

The enteroendocrine cell (EEC)-derived incretins play a pivotal role in regulating the secretion of glucagon and insulins in mammals. Although glucagon-like and insulin-like hormones have been found across animal phyla, incretin-like EEC-derived hormones have not yet been characterised in invertebrates. Here, we show that the midgut-derived hormone, neuropeptide F (NPF), acts as the sugar-responsive, incretin-like hormone in the fruit fly, Drosophila melanogaster. Secreted NPF is received by NPF receptor in the corpora cardiaca and in insulin-producing cells. NPF-NPFR signalling resulted in the suppression of the glucagon-like hormone production and the enhancement of the insulin-like peptide secretion, eventually promoting lipid anabolism. Similar to the loss of incretin function in mammals, loss of midgut NPF led to significant metabolic dysfunction, accompanied by lipodystrophy, hyperphagia, and hypoglycaemia. These results suggest that enteroendocrine hormones regulate sugar-dependent metabolism through glucagon-like and insulin-like hormones not only in mammals but also in insects.

Effects of NPF on larval taste responses and feeding behaviors in Ostrinia furnacalis

The insect taste system regulates insect feeding behavior and patterns of food consumption. In this study, we showed that the medial and lateral sensilla styloconica in the mouthparts of 5th-instar Asian corn borer larvae are sensitive to fructose and sucrose in a concentration-dependent way. The two sensilla produced significant electrophysiological responses (greater than100 spikes/s) by exposure to 10 mM fructose or sucrose. However, electrophysiological responses and feeding preferences to fructose or sucrose were inhibited by neuropeptide F double-stranded RNA (dsNPF). Additionally, the medial sensilla styloconica are sensitive to low concentrations of the deterrents caffeine and nicotine. However, starvation, followed by increases in larval npf expression plus feeding, led to increases in spike frequencies of related sensilla to fructose, sucrose, and deterrents. In contrast, these responses were reduced on the dsNPF treatment. Our results suggest that NPF plays an important role influencing caterpillar feeding behavior through regulating the taste neurons of the sensilla styloconica.

Expression patterns and functional analysis of the short neuropeptide F and NPF receptor genes in Rhopalosiphum padi

The short neuropeptide F (sNPF) and NPF receptor (NPFR) genes play important roles in many physiological processes. However, information on the survival-related functions of sNPF and NPFR under different stress conditions is lacking in aphids. In this study, we cloned sNPF and NPFR, and investigated the expression levels of these genes in different developmental stages, wing morphs, and stress conditions of the bird cherry-oat aphid (Rhopalosiphum padi L.), an important agricultural pest. The sNPF and NPFR transcript levels varied among developmental stages, and their expression levels in alate females were significantly higher than those in apterous females. In addition, starvation resulted in significantly increased sNPF expression, which then recovered after refeeding. Heat stress and insecticides significantly affected transcription of both genes. sNPF and NPFR knockdown in R. padi using RNA interference revealed optimal interference efficiency at 48 h post-injection. sNPF knockdown significantly decreased adult longevity, 15-d fecundity, and food intake. Additionally, mortality under starvation, insecticides, and heat stress conditions was significantly higher after injection with double-stranded sNPF in R. padi. NPFR knockdown significantly affected food intake and starvation resistance in R. padi. These results strongly indicate that sNPF plays vital roles in food intake, longevity, and reproduction in R. padi, and it can significantly affect the pest's response to stress conditions.

Cloning and Expression of the Neuropeptide F and Neuropeptide F Receptor Genes and Their Regulation of Food Intake in the Chinese White Pine Beetle Dendroctonus armandi

Neuropeptide F (NPF) is an important signaling molecule that acts as a neuromodulator to regulate a diversity of physiological and behavioral processes from vertebrates to invertebrates by interaction with NPF receptors, which are G protein-coupled receptors (GPCR). However, nothing is known about NPF in Chinese white pine beetle, Dendroctonus armandi, a destructive pest of natural and coniferous forests in the middle Qinling Mountains of China. We have cloned and characterized cDNAs encoding one NPF precursor and two NPF receptors in D. armandi and made bioinformatics predictions according to the deduced amino acid sequences. They were highly similar to that of Dendroctonus ponderosa. The transcription levels of these genes were different between larvae and adults of sexes, and there were significant differences among the different developmental stages and tissues and between beetles under starvation and following re-feeding states. Additionally, downregulation of NPF and NPFR by injecting dsRNA into beetles reduced their food intake, caused increases of mortality and decreases of body weight, and also resulted in a decrease of glycogen and free fatty acid and an increase of trehalose. These results indicate that the NPF signaling pathway plays a significant positive role in the regulation of food intake and provides a potential target for the sustainable management of this pest.

Involvement of clathrin-dependent endocytosis in cellular dsRNA uptake in aphids

RNAi is an essential technology for studying gene function in eukaryotes, and is also considered to be a potential strategy for pest control. However, the mechanism behind the cellular uptake of dsRNA in aphids, a group of important agricultural sucking pests, remains unknown. Here, using the pea aphid Acyrthosiphon pisum as model for aphids, we identified two core genes of clathrin-dependent endocytosis (CDE), Apchc and Apvha16. We confirmed that expression of Apchc, Apvha16 and RNAi core component genes (ApAgo2, ApDcr2 and ApR2d2) were simultaneously induced at 12 h after feeding dsRNA. By using an RNAi-of-RNAi approach, we demonstrated that suppression of Apchc and Apvha16 transcripts by RNAi significantly impaired RNAi efficiency of selected reporter genes (RGs), including ApGNBP1, Apmts and Aphb, suggesting the involvement of CDE in cellular dsRNA uptake in aphids. Further confirmation was also provided using two inhibitors, chlorpromazine (CPZ) and bafilomycin A1 (BafA1). Administration of CPZ and of BafA1 both led to an impaired silencing efficiency of the RGs in the pea aphid. Finally, these RNAi-of-RNAi results were reconfirmed in the peach aphid Myzus persicae. Taking these findings together, we conclude that CDE is involved in cellular dsRNA uptake in aphids.

The Role of Peptide Hormones in Insect Lipid Metabolism

Lipids are the primary storage molecules and an essential source of energy in insects during reproduction, prolonged periods of flight, starvation, and diapause. The coordination center for insect lipid metabolism is the fat body, which is analogous to the vertebrate adipose tissue and liver. The fat body is primarily composed of adipocytes, which accumulate triacylglycerols in intracellular lipid droplets. Genomics and proteomics, together with functional analyses, such as RNA interference and CRISPR/Cas9-targeted genome editing, identified various genes involved in lipid metabolism and elucidated their functions. However, the endocrine control of insect lipid metabolism, in particular the roles of peptide hormones in lipogenesis and lipolysis are relatively less-known topics. In the current review, the neuropeptides that directly or indirectly affect insect lipid metabolism are introduced. The primary lipolytic and lipogenic peptide hormones are adipokinetic hormone and the brain insulin-like peptides (ILP2, ILP3, ILP5). Other neuropeptides, such as insulin-growth factor ILP6, neuropeptide F, allatostatin-A, corazonin, leucokinin, tachykinins and limostatin, might stimulate lipolysis, while diapause hormone-pheromone biosynthesis activating neuropeptide, short neuropeptide F, CCHamide-2, and the cytokines Unpaired 1 and Unpaired 2 might induce lipogenesis. Most of these peptides interact with one another, but mostly with insulin signaling, and therefore affect lipid metabolism indirectly. Peptide hormones are also involved in lipid metabolism during reproduction, flight, diapause, starvation, infections and immunity; these are also highlighted. The review concludes with a discussion of the potential of lipid metabolism-related peptide hormones in pest management.

Role of the neuropeptide F 1 in regulating the appetite for food in Locusta migratoria

BACKGROUND

Neuropeptide F (NPF) is an intercellular signaling molecule that mediates many physiological and behavioral processes. However, the function of neuropeptide F in mediating the feeding behavior of Locusta migratoria has been unclear.

RESULTS

The neuropeptide F 1 precursor cDNA from L. migratoria was obtained and analyzed, and its amino acid sequence deduced. Mature LmiNPF1 was composed of 36 amino acids and was similar to that of Schistocerca gregaria. The spatial and temporal expression profiles of LmiNPF1 were investigated. LmiNPF1 was primarily expressed in the central nervous system, especially in the brain, and the expression levels were higher during the day than during the night. However, starvation activated LmiNPF1 expression increases, and downregulation of LmiNPF1 inhibited locust feeding behavior.

CONCLUSION

LmiNPF1 promotes the feeding behavior of the locust and is a potential molecular target to control locust feeding. © 2018 Society of Chemical Industry.

Distribution of neuropeptide F in the ventral nerve cord and its possible role on testicular development and germ cell proliferation in the giant freshwater prawn, Macrobrachium rosenbergii

Neuropeptide F in invertebrates is a homolog of neuropeptide Y in mammals and it is a member of FMRFamide-related peptides. In arthropods, such as insects, there are two types of neuropeptide F comprising long neuropeptide F (NPF) and short neuropeptide F (sNPF). Both NPFs are known to play a crucial role in the regulations of foraging, feeding-related behaviors, circadian rhythm, stress responses, aggression and reproduction in invertebrates. We have earlier found that in the giant freshwater prawn, Macrobrachium rosenbergii, there are three isoforms of NPF and four isoforms of sNPF and that NPFs are expressed in the eyestalks and brain. In the present study, we investigate further the tissue distribution of NPF-I in the ventral nerve cord (VNC) and its role in the development of testes in small male (SM) Macrobrachium rosenbergii. By immunolocalization, using the rabbit polyclonal antibody against NPF-I as a probe, we could detect NPF-I immunoreactivity in the neuropils and neuronal clusters of the subesophageal ganglia (SEG), thoracic ganglia (TG) and abdominal ganglia (AG) of the SM prawns. In functional assays, the administrations of synthetic NPF-I (KPDPTQLAAMADALKYLQELDKYYSQVSRPRFamide) and sNPF (APALRLRFamide) peptides significantly increased the growth rates of SM prawns and significantly increased the gonadosomatic index (GSI) and proliferations of early germ cells in the seminiferous tubules of their testes. It is, therefore, suggestive that NPFs may play critical roles in energy homeostasis towards promoting growth as well as testicular development in prawns that could be applied in the aquaculture of this species.

Regulation of Feeding and Metabolism by Neuropeptide F and Short Neuropeptide F in Invertebrates

Numerous neuropeptide systems have been implicated to coordinately control energy homeostasis, both centrally and peripherally. However, the vertebrate neuropeptide Y (NPY) system has emerged as the best described one regarding this biological process. The protostomian ortholog of NPY is neuropeptide F, characterized by an RXRF(Y)amide carboxyterminal motif. A second neuropeptide system is short NPF, characterized by an M/T/L/FRF(W)amide carboxyterminal motif. Although both short and long NPF neuropeptide systems display carboxyterminal sequence similarities, they are evolutionary distant and likely already arose as separate signaling systems in the common ancestor of deuterostomes and protostomes, indicating the functional importance of both. Both NPF and short-NPF systems seem to have roles in the coordination of feeding across bilaterian species, but during chordate evolution, the short NPF system appears to have been lost or evolved into the prolactin releasing peptide signaling system, which regulates feeding and has been suggested to be orthologous to sNPF. Here we review the roles of both NPF and sNPF systems in the regulation of feeding and metabolism in invertebrates.

Molecular Evidence for the Fitness of Cotton Aphid, Aphis gossypii in Response to Elevated CO2 From the Perspective of Feeding Behavior Analysis

Rising atmospheric carbon dioxide (CO2) concentration is likely to influence insect-plant interactions. Aphid, as a typical phloem-feeding herbivorous insect, has shown consistently more positive responses in fitness to elevated CO2 concentrations than those seen in leaf-chewing insects. But, little is known about the mechanism of this performance. In this study, the foliar soluble constituents of cotton and the life history of the cotton aphid Aphis gossypii and its mean relative growth rate (MRGR) and feeding behavior were measured, as well as the relative transcript levels of target genes related appetite, salivary proteins, molting hormone (MH), and juvenile hormone, to investigate the fitness of A. gossypii in response to elevated CO2 (800 ppm vs. 400 ppm). The results indicated that elevated CO2 significantly stimulated the increase in concentrations of soluble proteins in the leaf and sucrose in seedlings. Significant increases in adult longevity, lifespan, fecundity, and MRGR of A. gossypii were found under elevated CO2 in contrast to ambient CO2. Furthermore, the feeding behavior of A. gossypii was significantly affected by elevated CO2, including significant shortening of the time of stylet penetration to phloem position and significant decrease in the mean frequency of xylem phase. It is presumed that the fitness of A. gossypii can be enhanced, resulting from the increases in nutrient sources and potential increase in the duration of phloem ingestion under elevated CO2 in contrast to ambient CO2. In addition, the qPCR results also demonstrated that the genes related to appetite and salivary proteins were significantly upregulated, whereas, the genes related to MH were significantly downregulated under elevated CO2 in contrast to ambient CO2, this is in accordance with the performance of A. gossypii in response to elevated CO2. In conclusion, rise in atmospheric CO2 concentration can enhance the fitness of A. gossypii by increasing their ingestion of higher quantity and higher quality of host plant tissues and by simultaneously upregulating the transcript expression of the genes related to appetite and salivary proteins, and then this may increase the control risk of A. gossypii under conditions of climate change in the future.

Comparison of RNAi knockdown effect of tyramine receptor 1 induced by dsRNA and siRNA in brains of the honey bee, Apis mellifera

RNA interference (RNAi) is a powerful tool for artificially manipulating gene expression in diverse organisms. In the honey bee, Apis mellifera, both long double stranded RNA (dsRNA) and small interference RNA (siRNA) have been successfully used to reduce targeted gene expression and induce specific phenotypes. However, whether dsRNA and siRNA have different effects and efficiencies in gene silencing has never been investigated in honey bees. Thus, we tested the effect of dsRNA and siRNA on the tyramine receptor 1 (tyr1), which encodes a receptor of neurotransmitter tyramine, in honey bee brains at mRNA and protein levels over time. We found that both dsRNA and siRNA achieved successful gene knockdown. The siRNA mixes affected tyr1 gene expression faster than dsRNA, and the duration of the knockdown between dsRNA and siRNA varied. We also found that the turnover rate of TYR1 protein was relatively fast, which is consistent with its role as a neurotransmitter receptor. Our study reveals the different efficiencies of dsRNA and siRNA in honey bee brains. We show that consideration of the gene regions targeted by RNAi, prior screening for RNAi molecules and combing siRNAs are important strategies to enhance RNAi efficiency.

Characterization and expression of a long neuropeptide F (NPF) receptor in the Chagas disease vector Rhodnius prolixus

In this study, a long neuropeptide F receptor of the blood-feeding hemipteran, Rhodnius prolixus (RhoprNPFR) has been cloned and characterized. Approximately 70% of the RhoprNPFR deduced protein sequence is identical to that of other hemipteran NPFRs. RhoprNPFR has seven highly-conserved transmembrane domains, two cysteine residues in the 2nd and 3rd extracellular loops that likely form a disulfide bond integral for maintaining the structure of the receptor, and a conserved DRY motif after the third transmembrane domain. All of these characteristics are typical of class A rhodopsin-like GPCRs. The receptor transcript is predominantly expressed in the central nervous system (CNS) and gut of both fifth instar and adult R. prolixus. Using fluorescent in situ hybridization (FISH), we identified six bilaterally-paired large median neurosecretory cells (approximately 30μm in diameter) in the brain that express the RhoprNPFR mRNA transcript. We also found RhoprNPFR transcript expression in endocrine cells in the anterior midgut of fifth instars, as well as in putative pre-follicular cells present in the germarium and between developing oocytes, and in the nutritive cord. These results suggest that RhoprNPFR may play a role within the CNS, and in digestion and possibly egg production and/or egg development in R. prolixus.

Glucose, some amino acids and a plant secondary metabolite, chlorogenic acid induce the secretion of a regulatory hormone, tachykinin-related peptide, from the silkworm midgut

Enteroendocrine cells in the insect midgut are thought to secrete peptide hormones in response to the nutritional state. However, the role of dietary compounds in inducing peptide hormone secretion from enteroendocrine cells in insects remains unknown. In the present study, we demonstrated that several dietary compounds from mulberry leaves, including glucose, amino acids, and the secondary metabolite chlorogenic acid, induced significant secretion of tachykinin-related peptides from isolated silkworm midguts at the luminal concentrations measured in fed larvae. This study provides evidence that the insect midgut senses a non-nutritious secondary metabolite in addition to nutrient metabolites to monitor luminal food status and secretes a feeding regulatory hormone, suggesting that a unique dietary sensory system modulates insect feeding via enteroendocrine control.

Autophagy-Associated Shrinkage of the Hepatopancreas in Fasting Male Macrobrachium rosenbergii Is Rescued by Neuropeptide F

Invertebrate neuropeptide F-I (NPF-I), much alike its mammalian homolog neuropeptide Y, influences several physiological processes, including circadian rhythms, cortical excitability, stress response, and food intake behavior. Given the role of autophagy in the metabolic stress response, we investigated the effect of NPF-1 on autophagy during fasting and feeding conditions in the hepatopancreas and muscle tissues of the male giant freshwater prawn Macrobrachium rosenbergii. Starvation up-regulated the expression of the autophagy marker LC3 in both tissues. Yet, based on the relative levels of the autophagosome-associated LC3-II isoform and of its precursor LC3-I, the hepatopancreas was more responsive than the muscle to starvation-induced autophagy. Injection of NPF-I inhibited the autophagosome formation in the hepatopancreas of fasting prawns. Relative to the body weight, the muscle weight was not affected, while that of the hepatopancreas decreased upon starvation and NPF-1 treatment could largely prevent such weight loss. Thus, the hepatopancreas is the reserve organ for the nutrient homeostasis during starvation and NPF-I plays a crucial role in the balancing of energy expenditure and energy intake during starvation by modulating autophagy.

Functional characterization of mosquito short neuropeptide F receptors

Mosquito blood feeding transiently inhibits sugar- and host seeking through neuropeptide signaling. Short neuropeptide F (sNPF) is one of the neuromodulators involved in this regulation. Here, we identified the genes for the sNPF precursor and the sNPF receptor in the southern house mosquito, Culex quinquefasciatus. Comparative analyses are made with the genes of the sNPF precursor and receptor from two other important vectors, Aedes aegypti and Anopheles coluzzii. We functionally characterized the receptors in all three species using endogenous neuropeptides, and quantified their transcript expression following a blood meal and a sugar meal. Our analysis reveals several Cx. quinquefasciatus-specific duplications of the sNPF-3 isoform on the sNPF precursor, which are not reflected in the precursors of the other two species. In contrast, the structure of the sNPF receptors is highly conserved within mosquitoes, and a putative ligand binding region is proposed and discussed. Reflecting the high structural conservation, the sNPF receptor sensitivity to endogenous sNPF isoforms is conserved across mosquito species. Using quantitative real time PCR, we demonstrate that transcript abundance of the sNPF receptor and precursor is regulated following feeding, only in Cx. quinquefasciatus. We discuss our findings in relation to previous work on sNPF signaling and its role in feeding regulation.

Expression of Neuropeptide F Gene and Its Regulation of Feeding Behavior in the Pea Aphid, Acyrthosiphon pisum

Neuropeptide F (NPF) signaling systems are widespread and highly evolutionarily conserved from vertebrates to invertebrates. In fact, NPF has been identified in many insect species and plays regulatory roles in diverse physiological processes, such as feeding, learning, reproduction and stress responses. NPF operates by interacting with the NPF receptor (NPFR). Here, we characterized and determined the presumed role of NPF signaling in the wingless parthenogenetic pea aphid, Acyrthosiphon pisum. Quantitative real-time reverse transcription-PCR (qRT-PCR) revealed that the expression levels of both NPF and NPFR transcripts varied across developmental stages, which implies that the NPF signaling system might participate in the developmental regulation of aphid physiological processes or behaviors. The NPF transcript was mainly detected in the head but not in the gut, whereas the NPFR transcript was mainly detected in both the gut and head. In addition, the NPF transcript levels were markedly up-regulated in starved aphids compared with satiated aphids, and the transcript levels recovered after re-feeding. In contrast, the NPFR transcript levels remained stable in starved and re-fed aphids. Furthermore, RNAi knockdown by the injection of NPF dsRNA into wingless adult aphids significantly reduced their food intake. Further analysis of the modification of aphid feeding behavior on broad bean plants using electrical penetration graphs (EPGs) revealed that both the probing time and the total duration of phloem activity decreased significantly in the NPF treatment group. These results indicated a lower appetite for food after NPF knockdown, which could explain the reduction in aphid food intake. NPF silencing was also shown to reduce reproduction but not survival in aphids. Overall, the results of these experiments suggest that NPF plays an important role in regulation of feeding in A. pisum.

Calcitonin-like peptide hormone (CT/DH) in the frontal ganglia as a feeding regulatory peptide of the silkworm, Bombyx mori

The frontal ganglion (FrG) in insects contributes to the modulation of feeding behavior via the regulation of foregut contraction and other neural networks. Profiling the peptides of the FrG is important to understand endocrine regulation of feeding behavior in insects. High-resolution spiral matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) identified an ion peak, corresponding to calcitonin-like diuretic hormone 31 (CT/DH) in the FrG of silkworm Bombyx mori larvae. RT-PCR confirmed that CT/DH is expressed in the FrG, as are other peptide hormones, including allatoregulatory peptides. A feeding latency assay using synthetic CT/DH revealed that it increases the time to the initiation of feeding in a dose-dependent manner. These data indicate that CT/DH is a candidate regulatory peptide that modulates the feeding behavior of B. mori.

Molecular insights into reproduction regulation of female Oriental River prawns Macrobrachium nipponense through comparative transcriptomic analysis

The oriental river prawn, Macrobrachium nipponense, is an important commercial aquaculture resource in China. During breeding season, short ovary maturation cycles of female prawns cause multi-generation reunions in ponds and affect the growth of females representing individual miniaturization (known as autumn -propagation). These reproductive characteristics pose problems for in large - scale farming. To date, the molecular mechanisms of reproduction regulation of M. nipponense remain unclear. To address this issue, we performed transcriptome sequencing and gene expression analyses of eyestalk and cerebral ganglia of female M. nipponense during breeding and non-breeding seasons. Differentially expressed gene enrichment analysis results revealed several important reproduction related terms and signaling pathways, such as "photoreceptor activity", "structural constituent of cuticle" and "G-protein coupled receptor activity". The following six key genes from the transcriptome were predicted to mediate environmental factors regulating reproduction of M. nipponense: neuroparsin, neuropeptide F II, orcokinin II, crustacean cardioactive peptide, pigment-dispersing hormone 3 and tachykinin. These results will contribute to a better understanding of the molecular mechanisms of reproduction of oriental river prawns. Further detailed functional analyses of the candidate reproduction regulation related neuropeptides are needed to shed light on the mechanisms of reproduction of crustacean.

The short neuropeptide F modulates olfactory sensitivity of Bactrocera dorsalis upon starvation

The insect short neuropeptide F (sNPF) family has been shown to modulate diverse physiological processes, such as feeding, appetitive olfactory behavior, locomotion, sleep homeostasis and hormone release. In this study, we identified the sNPF (BdsNPF) and its receptor (BdsNPFR) in an important agricultural pest, the oriental fruit fly Bactrocera dorsalis (Hendel). Afterwards, the receptor cDNA was functionally expressed in Chinese hamster ovary cell lines. Activation of BdsNPFR by sNPF peptides caused an increase in intracellular calcium ions, with a 50% effective concentration values at the nanomolar level. As indicated by qPCR, the BdsNPF and BdsNPFR transcripts were mainly detected in the central nervous system and antennae, and they showed significantly starvation-induced expression patterns. Furthermore, we found that the starved flies had an increased electroantennogram response compared to the normally fed flies. However, this enhanced olfactory sensitivity was reversed when we decreased the expression of BdsNPF by double-stranded RNA injection in adults. We concluded that sNPF plays an important role in modulating the olfactory sensitivity of B. dorsalis upon starvation. Our results will facilitate the understanding of the regulation of early olfactory processing in B. dorsalis.

The neuropeptide F/nitric oxide pathway is essential for shaping locomotor plasticity underlying locust phase transition

Behavioral plasticity is widespread in swarming animals, but little is known about its underlying neural and molecular mechanisms. Here, we report that a neuropeptide F (NPF)/nitric oxide (NO) pathway plays a critical role in the locomotor plasticity of swarming migratory locusts. The transcripts encoding two related neuropeptides, NPF1a and NPF2, show reduced levels during crowding, and the transcript levels of NPF1a and NPF2 receptors significantly increase during locust isolation. Both NPF1a and NPF2 have suppressive effects on phase-related locomotor activity. A key downstream mediator for both NPFs is nitric oxide synthase (NOS), which regulates phase-related locomotor activity by controlling NO synthesis in the locust brain. Mechanistically, NPF1a and NPF2 modify NOS activity by separately suppressing its phosphorylation and by lowering its transcript level, effects that are mediated by their respective receptors. Our results uncover a hierarchical neurochemical mechanism underlying behavioral plasticity in the swarming locust and provide insights into the NPF/NO axis.

DOI:http://dx.doi.org/10.7554/eLife.22526.001

Migratory locusts are widespread throughout the Eastern Hemisphere, especially in Asia, Australia and Africa. Although usually solitary insects, locusts can also form swarms made up of millions of individuals, which can devastate crops. Swarming can be studied on a smaller scale in the laboratory by forcing locusts to crowd together. This causes the locusts to enter a so-called gregarious state in which they are more active and sociable, which in turn promotes swarming. Isolating individual locusts has the opposite effect, causing the insects to enter a solitary state in which they are less active.

Chemicals in the locust brain called neuropeptides control phase transitions between solitary and gregarious behavior. Neuropeptides bind to specific proteins called receptors in the outer membranes of neurons and initiate unique signaling cascades inside cells. However, exactly how neuropeptides regulate the changes in locust behavior that affect swarming was not clear.

Hou et al. now reveal the role that two related neuropeptides, NPF1a and NPF2, play in this process. Crowding causes the levels of NPF1a and NPF2 in the locust brain to decrease, whereas isolating individual locusts causes the levels of two NPF receptors to increase. Both neuropeptides reduce levels of a molecule called nitric oxide in the brain. NPF1a does this by reducing the activity of the enzyme that produces nitric oxide, whereas NPF2 reduces the production of this enzyme. The reduction in nitric oxide in turn makes the locusts less active.

Similar NPF neuropeptides had previously been shown to affect activity levels in other invertebrates, such as roundworms and fruit flies. This, combined with the results now presented by Hou et al., suggests that the NPF/nitric oxide pathway may regulate activity in insects in general. Future work should investigate this possibility, as well as whether the NPF/nitric oxide pathway controls changes in other insect behaviors such as feeding and mating.

DOI:http://dx.doi.org/10.7554/eLife.22526.002

RNAi Efficiency, Systemic Properties, and Novel Delivery Methods for Pest Insect Control: What We Know So Far

In recent years, the research on the potential of using RNA interference (RNAi) to suppress crop pests has made an outstanding growth. However, given the variability of RNAi efficiency that is observed in many insects, the development of novel approaches toward insect pest management using RNAi requires first to unravel factors behind the efficiency of dsRNA-mediated gene silencing. In this review, we explore essential implications and possibilities to increase RNAi efficiency by delivery of dsRNA through non-transformative methods. We discuss factors influencing the RNAi mechanism in insects and systemic properties of dsRNA. Finally, novel strategies to deliver dsRNA are discussed, including delivery by symbionts, plant viruses, trunk injections, root soaking, and transplastomic plants.

Characterization of a neuropeptide F receptor in the tsetse fly, Glossina morsitans morsitans

Neuropeptides related to mammalian neuropeptide Y (NPY) and insect neuropeptide F (NPF) are conserved throughout Metazoa and intimately involved in a wide range of biological processes. In insects NPF is involved in regulating feeding, learning, stress and reproductive behavior. Here we identified and characterized an NPF receptor of the tsetse fly, Glossina morsitans morsitans, the sole transmitter of Trypanosoma parasites causing sleeping sickness. We isolated cDNA sequences encoding tsetse NPF (Glomo-NPF) and its receptor (Glomo-NPFR), and examined their spatial and temporal expression patterns using quantitative PCR. In tsetse flies, npfr transcripts are expressed throughout development and most abundantly in the central nervous system, whereas low expression is found in the flight muscles and posterior midgut. Expression of npf, by contrast, shows low transcript levels during development but is strongly expressed in the posterior midgut and brain of adult flies. Expression of Glomo-npf and its receptor in the brain and digestive system suggests that NPF may have conserved neuromodulatory or hormonal functions in tsetse flies, such as in the regulation of feeding behavior. Cell-based activity studies of the Glomo-NPFR showed that Glomo-NPF activates the receptor up to nanomolar concentrations. The molecular data of Glomo-NPF and Glomo-NPFR paves the way for further investigation of its functions in tsetse flies.

Cloning and expression of long neuropeptide F and the role of FMRFamide-like peptides in regulating egg production in the Chagas vector, Rhodnius prolixus

Long neuropeptide F (NPF) is a neuropeptide implicated in the control of feeding, digestion and reproduction in various insect species. Here we have isolated the cDNA sequence encoding NPF in Rhodnius prolixus (RhoprNPF). The RhoprNPF gene is composed of 3 exons and 2 introns, one of which is present in the peptide coding region. RhoprNPF is 42 amino acids long and has the characteristic RFamide C-terminus, which is common of FMRFamide-like peptides (FLPs). Quantitative PCR (qPCR) shows that RhoprNPF mRNA is present in higher amounts in fifth instars than in adults, implying that it may play a role in growth and development. In situ hybridization shows that the RhoprNPF transcript is present in median neurosecretory cells (MNSCs) in the brain, cells in the fifth instar hindgut and cells along the longitudinal muscle fibers of the adult female lateral oviducts. Injection of the last 8 amino acids of RhoprNPF (truncated RhoprNPF, AVAGRPRFa), which is considered to be the active core sequence for biological activity, into mated, fed, female adult R. prolixus decreased the number of eggs found in the ovaries as well as increased the number of eggs laid. This suggests that RhoprNPF may play a role in accelerating the process of ovulation from the ovary of the female R. prolixus. An increase in oogenesis was observed following the injection of other FLPs such as RhoprShortNPF, GNDNFMRFamide and AKDNFIRFamide, whereas the FLP, RhoprMS, and the allatostatin, RhoprAST-2, inhibited egg production.

Neuropeptides in the cerebral ganglia of the mud crab, Scylla paramamosain: transcriptomic analysis and expression profiles during vitellogenesis

Neuropeptides play a critical role in regulating animal reproduction. In vertebrates, GnRH, GnIH and kisspeptin are the key neuropeptide hormones of the reproductive axis, however, the reproductive axis for invertebrates is vague. Knowledge on ovarian development of the mud crab, Scylla paramamosain, is critical for aquaculture and resources management of the commercially important species. This study employed Illumina sequencing, reverse transcription-polymerase chain reaction and quantitative real-time PCR techniques to identify neuropeptides that may be involved in ovarian development of S. paramamosain. A total of 32 neuropeptide transcripts from two dozen neuropeptide families, 100 distinct mature peptides were predicted from the transcriptome data of female S. paramamosain cerebral ganglia. Among them, two families, i.e. GSEFLamide and WXXXRamide, were first identified from the cerebral ganglia of crustaceans. Of these neuropeptides, 21 transcripts of interest were selected for further confirmation and all of them were detected in the cerebral ganglia, as well as in other nervous tissues and the ovary. Most of them also had differential expression in the cerebral ganglia during various vitellogenic stages, suggesting their likely involvement in regulating vitellogenesis and ovarian maturation. Overall, these findings provide an important basis for subsequent studies on peptide function in reproduction of S. paramamosain.

Chemical identity, function and regulation of enteroendocrine peptides in insects

How animals allocate energy and metabolic decisions are coordinated is a fundamental physiological question. Metabolic research is strongly driven by an increasing obesity rate in humans. For insects-which contain many pest species and disease vectors-the control of feeding is of agroeconomical and medical importance. Regulatory peptides have since long been in focus of metabolic research. In insects, major advances have been made recently, mostly due to research in the genetically tractable Drosophila melanogaster with focus on the central nervous system as a source of neuropeptides. Research on peptides produced by enteroendocrine cells remained peripheral, but this situation is about to change. This review highlights current knowledge and advances on the identity and role of enteroendocrine insect peptides.

Vitellogenin-RNAi and ovariectomy each increase lifespan, increase protein storage, and decrease feeding, but are not additive in grasshoppers

Reduced reproduction has been shown to increase lifespan in many animals, yet the mechanisms behind this trade-off are unclear. We addressed this question by combining two distinct, direct means of life-extension via reduced reproduction, to test whether they were additive. In the lubber grasshopper, Romalea microptera, ovariectomized (OVX) individuals had a ~20% increase in lifespan and a doubling of storage relative to controls (Sham operated). Similarly, young female grasshoppers treated with RNAi against vitellogenin (the precursor to egg yolk protein) had increased fat body mass and halted ovarian growth. In this study, we compared VgRNAi to two control groups that do not reduce reproduction, namely buffer injection (Buffer) and injection with RNAi against a hexameric storage protein (Hex90RNAi). Each injection treatment was tested with and without ovariectomy. Hence, we tested feeding, storage, and lifespans in six groups: OVX and Buffer, OVX and Hex90RNAi, OVX and VgRNAi, Sham and Buffer, Sham and Hex90RNAi, and Sham and VgRNAi. Ovariectomized grasshoppers and VgRNAi grasshoppers each had similar reductions in feeding (~40%), increases in protein storage in the hemolymph (150-300%), and extensions in lifespan (13-21%). Ovariectomized grasshoppers had higher vitellogenin protein levels than did VgRNAi grasshoppers. Last but not least, when ovariectomy and VgRNAi were applied together, there was no greater effect on feeding, protein storage, or longevity. Hence, feeding regulation, and protein storage in insects, may be conserved components of life-extension via reduced reproduction.

Molecular characterization and expression profiles of neuropeptide precursors in the migratory locust

Neuropeptides serve as the most important regulatory signals in insects. Many neuropeptides and their precursors have been identified in terms of the contig sequences of whole genome information of the migratory locust (Locusta migratoria), which exhibits a typical phenotypic plasticity in morphology, behavior and physiology. However, functions of these locust neuropeptides are largely unknown. In this study, we first revised the 23 reported neuropeptide precursor genes and identified almost all the neuropeptide precursors and corresponding products in L. migratoria. We further revealed the significant expansion profiles (such as AKH) and alternative splicing of neuropeptide genes (Lom-ITP, Lom-OK and Lom-NPF1). Transcriptomic analysis indicated that several neuropeptides, such as Lom-ACP and Lom-OK, displayed development-specific expression patterns. qRT-PCR data confirmed that most neuropeptide precursors were strongly expressed in the central nervous system. Fifteen neuropeptide genes displayed different expression levels between solitarious and gregarious locusts. These findings provide valuable clues to understand neuropeptide evolution and their functional roles in basic biology and phase transition in locusts.

In silico Neuropeptidome of Female Macrobrachium rosenbergii Based on Transcriptome and Peptide Mining of Eyestalk, Central Nervous System and Ovary

Macrobrachium rosenbergii is the most economically important of the cultured freshwater crustacean species, yet there is currently a deficiency in genomic and transcriptomic information for research requirements. In this study, we present an in silico analysis of neuropeptide genes within the female M. rosenbergii eyestalk, central nervous system, and ovary. We could confidently predict 37 preproneuropeptide transcripts, including those that encode bursicons, crustacean cardioactive peptide, crustacean hyperglycemic hormones, eclosion hormone, pigment-dispersing hormones, diuretic hormones, neuropeptide F, neuroparsins, SIFamide, and sulfakinin. These transcripts are most prominent within the eyestalk and central nervous system. Transcript tissue distribution as determined by reverse transcription-polymerase chain reaction revealed the presence of selected neuropeptide genes of interest mainly in the nervous tissues while others were additionally present in the non-nervous tissues. Liquid chromatography-mass spectrometry analysis of eyestalk peptides confirmed the presence of the crustacean hyperglycemic hormone precursor. This data set provides a strong foundation for further studies into the functional roles of neuropeptides in M. rosenbergii, and will be especially helpful for developing methods to improve crustacean aquaculture.

Drosha, Dicer-1 and Argonaute-1 in the desert locust: phylogenetic analyses, transcript profiling and regulation during phase transition and feeding

In this article, we identify and characterise the miRNA machinery components Drosha, Dicer-1 and Argonaute-1 of the desert locust. By means of phylogenetic analyses, we reveal important insights in the evolutionary context of these components. Our data illustrate that insect Argonaute-1 proteins form a monophyletic group with ALG-1 and ALG-2 of Caenorhabditis elegans and with the four (non-Piwi) Argonaute proteins present in humans. On the other hand, humans apparently lack clear homologues of the insect Argonaute-2 proteins. In addition, we demonstrate that drosha, dicer-1 and argonaute-1 display wide transcript tissue-distribution in adult desert locusts, and that during locust phase transition and feeding of starved locusts the expression levels of the miRNA pathway are regulated at the transcript level.

Systemic RNA interference in locusts: reverse genetics and possibilities for locust pest control

RNA interference (RNAi) is a biological process triggered by double stranded (ds)RNA that results in sequence-dependent mRNA degradation. Because of its high specificity, this post-transcriptional gene silencing mechanism is a widely used tool for reverse genetics in several insect species. In particular, locusts possess a very robust and sensitive RNAi response that has already been exploited to investigate a diverse range of important physiological processes. These orthopteran insects constitute important model organisms in several areas of entomology, but they can also become voracious swarming pests that threaten the agricultural production in large parts of the world. In comparison to the widely applied chemical insecticides, the RNAi-technology could contribute to the development of a novel generation of insecticides, with high species-specificity. In this article, we discuss the potential of the RNAi-technology in loss of function studies in locusts, as well as to control locust populations.

The contribution of the genomes of a termite and a locust to our understanding of insect neuropeptides and neurohormones

The genomes of the migratory locust Locusta migratoria and the termite Zootermopsis nevadensis were mined for the presence of genes encoding neuropeptides, neurohormones, and their G-protein coupled receptors (GPCRs). Both species have retained a larger number of neuropeptide and neuropeptide GPCRs than the better known holometabolous insect species, while other genes that in holometabolous species appear to have a single transcript produce two different precursors in the locust, the termite or both. Thus, the recently discovered CNMa neuropeptide gene has two transcripts predicted to produce two structurally different CNMa peptides in the termite, while the locust produces two different myosuppressin peptides in the same fashion. Both these species also have a calcitonin gene, which is different from the gene encoding the calcitonin-like insect diuretic hormone. This gene produces two types of calcitonins, calcitonins A and B. It is also present in Lepidoptera and Coleoptera and some Diptera, but absent from mosquitoes and Drosophila. However, in holometabolous insect species, only the B transcript is produced. Their putative receptors were also identified. In contrast, Locusta has a highly unusual gene that codes for a salivation stimulatory peptide. The Locusta genes for neuroparsin and vasopressin are particularly interesting. The neuroparsin gene produces five different transcripts, of which only one codes for the neurohormone identified from the corpora cardiaca. The other four transcripts code for neuroparsin-like proteins, which lack four amino acid residues, and that for that reason we called neoneuroparsins. The number of transcripts for the neoneuroparsins is about 200 times larger than the number of neuroparsin transcripts. The first exon and the putative promoter of the vasopressin genes, of which there are about seven copies in the genome, is very well-conserved, but the remainder of these genes is not. The relevance of these findings is discussed.

In silico characterization of the peptidome of the sea louse Caligus rogercresseyi (Crustacea, Copepoda)

Copepods of the order Siphonostomatoida are a major concern for commercial aquaculture as many farmed fish serve as hosts for these parasitic crustaceans. Caligus rogercresseyi, a member of the Siphonostomatoida, is a significant problem for salmonid aquaculture in the Southern Hemisphere, and as such, a search for methods for controlling infestations of it is ongoing. One possibility for biological control of this and other copepod ectoparasites is endocrine manipulation. However, little is known about the native endocrine signaling systems in these animals. As part of an ongoing effort to characterize crustacean ectoparasite peptidergic systems, the publicly accessible C. rogercresseyi transcriptome shotgun assembly (TSA) was mined for peptide-encoding transcripts. Using the identified TSA sequences, precursor proteins were deduced and their mature peptides predicted. Thirty-three peptide-encoding transcripts were identified within the Caligus TSA dataset, with the structures of 131 distinct peptides characterized from the deduced pre/preprohormones. The predicted peptides included isoforms of allatostatin A, allatostatin B, bursicon α, bursicon β, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone, diuretic hormone 31, DXXRLamide, FLRFamide, FXGGXamide, GSEFLamide, insulin-like peptide (ILP), intocin, leucokinin, molt-inhibiting hormone, myosuppressin, neuroparsin, neuropeptide F (NPF), orcokinin and tachykinin-related peptide. The predicted ILPs are of particular note as they are the first members of this peptide family identified from a copepod. Similarly, the predicted complement of four distinct NPFs is larger than that known from other crustaceans. Taken collectively, these data greatly expand the known C. rogercresseyi peptidome and provide a foundation for initiating studies of peptidergic control in this species.

Peptide discovery in the ectoparasitic crustacean Argulus siamensis: identification of the first neuropeptides from a member of the Branchiura

Recent advances in high-throughput sequencing have facilitated the generation of large transcriptomic datasets for an ever-growing number of crustaceans, one being the carp louse Argulus siamensis. This and other members of the subclass Branchiura are obligate fish ectoparasites, and as such, are a major concern for commercial aquaculture. Using the extant transcriptome shotgun assembly (TSA) sequences for A. siamensis, 27 transcripts encoding putative neuropeptide precursors were identified, and their pre/preprohormones deduced and characterized using a well-established bioinformatics workflow. The structures of 105 distinct peptides were predicted from the deduced proteins, including isoforms of adipokinetic hormone (AKH), allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon α, bursicon β, crustacean cardioactive peptide (CCAP), diuretic hormone 31, diuretic hormone 44, eclosion hormone, myosuppressin, neuroparsin, neuropeptide Y, orcokinin, pigment dispersing hormone, proctolin, short neuropeptide F, SIFamide, sulfakinin and tachykinin-related peptide. While several of the predicted peptides are known from other crustacean and/or insect species, e.g. RYLPT, a broadly conserved arthropod proctolin isoform, and PFCNAFTGCamide (disulfide bridging between the two cysteines), the stereotypical crustacean CCAP, the vast majority of them are described here for the first time, e.g. pQVNFSTKWamide, a new AKH/red pigment concentrating hormone superfamily member, pQEGLDHMFMRFamide, a novel myosuppressin, and SYKSKPPFNGSIFamide, a new member of the SIFamide family. As the peptides presented here are the only ones thus far described from A. siamensis, or for that matter, any branchiuran, they represent a new resource to begin investigations of peptidergic control of physiology and behavior in this and other related aquacultural pests.

ER type I signal peptidase subunit (LmSPC1) is essential for the survival of Locusta migratoria manilensis and affects moulting, feeding, reproduction and embryonic development

The endoplasmic reticulum type I signal peptidase complex (ER SPC) is a conserved enzyme that cleaves the signal peptides of secretory or membrane preproteins. The deletion of this enzyme leads to the accumulation of uncleaved proteins in biomembranes and cell death. However, the physiological functions of ER SPC in insects are not fully understood. Here, a catalytic subunit gene of ER SPC, LmSPC1, was cloned from Locusta migratoria manilensis and its physiological functions were analysed by RNA interference (RNAi). The LmSPC1 open reading frame encoded a protein of 178 amino acids with all five conserved regions of signal peptidases. RNAi-mediated knockdown of LmSPC1 resulted in high mortality. Sixty-nine per cent of dead nymphs died of abnormal moulting, corresponding to decreased activity of moulting fluid protease. Moreover, insects in the RNAi group experienced a decline in food intake, and a decrease in the secretion of total protein and digestive enzymes from midgut tissues to the midgut lumen. Furthermore, the females produced fewer eggs and eggs with disrupted embryogenesis. These results indicate that LmSPC1 is required for the secretion of secretory proteins, affects physiological functions, including moulting, feeding, reproduction and embryonic development, and is essential for survival. Therefore, LmSPC1 may be a potential target for locust control.