Short neuropeptide F signaling regulates functioning of male reproductive system in Tenebrio molitor beetle

Differential expression of sNPF in male and female eyestalk leading to sex dimorphism of AMP expression in Procambarus clarkii intestine

Antimicrobial peptide (AMP) is an important component of crustaceans' innate immune system. In this study, a short neuropeptide F (sNPF) gene (Pc-sNPF) and a Forkhead box O (FOXO) gene (PcFOXO) from Procambarus clarkii were identified. Analysis findings showed that the expression level of AMP genes differed between male and female P. clarkii. Furthermore, Pc-sNPF and PcFOXO were related to the sex dimorphism of AMP. Knockdown of Pc-sNPF in the eyestalk significantly upregulated the expression of PcFOXO and two anti-lipopolysaccharide factors (PcALF4 and PcALFL) in the intestine of P. clarkii. The expression of PcFOXO in the intestine of female P. clarkii was higher than in that of males. Results from RNA interference revealed that PcFOXO positively regulated the expression of PcALF4 and PcALFL in the intestine of male and female P. clarkii. In summary, our study showed that differences in Pc-sNPF expression in eyestalk of male and female P. clarkii leading to sex dimorphism of AMP expression in the intestine are mediated by the sNPF-FOXO-AMP signal pathway called the eyestalk-intestine axis.

The allatotropin/orexin system as an example of immunomodulatory properties of neuropeptides

The central nervous system (CNS) plays a critical role in signal integration in animals and allows the orchestration of life processes to maintain homeostasis. Current research clearly shows that inflammatory processes can also be modulated by the CNS via the neuroendocrine system. One of the neuropeptide families that participate in vertebrates in this process is orexins (OXs). Interestingly, our previous results suggested that a similar dependency may also exist between neuropeptides and immune system activity in insects. Due to the structural homology of orexin and allatotropin receptors and the functional similarity between these two neuropeptide families, the main aim of this research was to perform a complex analysis of the relationships between allatotropin (AT) and the insect immune response. Our results revealed functional similarities between vertebrate OXs and insect ATs. Similar effects were observed in the profile of the expression level of the gene encoding the AT precursor in the Tenebrio molitor nervous system and in the general action of Tenmo-AT on selected immune parameters of the tested beetles. Moreover, for the first time in insects, we confirmed the role of cytokines in the modulation of neuroendocrine system by determining the effect of Spätzle-like protein injection on the expression of genes encoding AT precursor and receptor. All these results are important for understanding the evolutionary basis of hormonal regulation of the immune response.

Short neuropeptide F in integrated insect physiology

The short neuropeptide F (sNPF) family of peptides is a multifunctional group of neurohormones involved in the regulation of various physiological processes in insects. They have been found in a broad spectrum of species, but the number of isoforms in the precursor molecule varies from one to four. The receptor for sNPF (sNPFR), which belongs to the G protein-coupled receptor family, has been characterized in various insect orders and was shown to be an ortholog of the mammalian prolactin-releasing peptide receptor (PrPR). The sNPF signaling pathway interacts with other neurohormones such as insulin-like peptides, SIFamide, and pigment-dispersing factors (PDFs) to regulate various processes. The main physiological function of sNPF seems to be involved in the regulation of feeding, but the observed effects are species-specific. sNPF is also connected with the regulation of foraging behavior and the olfactory system. The influence of sNPF on feeding and thus energy metabolism may also indirectly affect other vital processes, such as reproduction and development. In addition, these neurohormones are involved in the regulation of locomotor activity and circadian rhythm in insects. This review summarizes the current state of knowledge about the sNPF system in insects.

Effect of short neuropeptide F signaling on larval feeding in Mythimna separata

Mythimna separata is a notorious phytophagous pest which poses serious threats to cereal crops owing to the gluttony of the larvae. Because short neuropeptide F (sNPF) and its receptor sNPFR are involved in a diversity of physiological functions, especially in functions related to feeding in insects, it is a molecular target for pest control. Herein, an sNPF and 2 sNPFRs were identified and cloned from M. separata. Bioinformatics analysis revealed that the sNPF and its receptors had a highly conserved RLRFamide C-terminus and 7 transmembrane domains, respectively. The sNPF and its receptor genes were distributed across larval periods and tissues, but 2 receptors had distinct expression patterns. The starvation-induced assay elucidated that sNPF and sNPFR expression levels were downregulated under food deprivation and recovered with subsequent re-feeding. RNA interference knockdown of sNPF, sNPFR1, and sNPFR2 by injection of double-stranded RNA into larvae not only suppressed food consumption and increased body size and weight, but also led to decrease of glycogen and total lipid contents, and increase of trehalose compared with double-stranded green fluorescent protein injection. Furthermore, molecular docking was performed on the interaction mode between sNPFR protein and its ligand sNPF based on the 3-dimensional models constructed by AlphaFold; the results indicated that both receptors were presumably activated by the mature peptide sNPF-2. These results revealed that sNPF signaling played a considerably vital role in the feeding regulation of M. separata and represents a potential control target for this pest.

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

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

Tachykinin-related peptides modulate immune-gene expression in the mealworm beetle Tenebrio molitor L

Tachykinins (TKs) are a group of conserved neuropeptides. In insects, tachykinin-related peptides (TRPs) are important modulators of several functions such as nociception and lipid metabolism. Recently, it has become clear that TRPs also play a role in regulating the insect immune system. Here, we report a transcriptomic analysis of changes in the expression levels of immune-related genes in the storage pest Tenebrio molitor after treatment with Tenmo-TRP-7. We tested two concentrations (10^-8 and 10^-6 M) at two time points, 6 and 24 h post-injection. We found significant changes in the transcript levels of a wide spectrum of immune-related genes. Some changes were observed 6 h after the injection of Tenmo-TRP-7, especially in relation to its putative anti-apoptotic action. Interestingly, 24 h after the injection of 10^-8 M Tenmo-TRP-7, most changes were related to the regulation of the cellular response. Applying 10^-6 M Tenmo-TRP-7 resulted in the downregulation of genes associated with humoral responses. Injecting Tenmo-TRP-7 did not affect beetle survival but led to a reduction in haemolymph lysozyme-like antibacterial activity, consistent with the transcriptomic data. The results confirmed the immunomodulatory role of TRP and shed new light on the functional homology between TRPs and TKs.

Corazonin signaling modulates the synthetic activity of male accessory gland in Grapholita molesta

Although neuropeptide corazonin (Crz) has been identified in numerous insect species, the research about its function in regulation of reproduction is still in its infancy. Herein, we characterized the Crz (GmolCrz) and its receptor (GmolCrzR) to investigate their reproductive function in Grapholita molesta. Both molecular docking result and cell-based receptor activity assay showed that GmolCrz could interact with GmolCrzR. Additionally, spatial expression patterns of GmolCrz and GmolCrzR in males were evaluated. Knockdown of GmolCrz or GmolCrzR significantly lengthened copulation duration and decreased fertility in males. In these males, we found that the production of sperm was normal, while the content of accessory gland proteins (Acps) in the accessory gland (AG) was strongly diminished. Furthermore, knockdown of GmolCrz or GmolCrzR in males had no effect on sperm and Acps transfer to females. RNA-seq and gene expression analyses further confirmed that genes involved in serine-type endopeptidase activity were significantly downregulated in the AG upon GmolCrzR knockdown. Finally, sperm activation assays demonstrated that this process was disrupted in the spermatophore of females mated with GmolCrz or GmolCrzR knockdown males, which may cause the decreased fertility in males. Our findings provide new insights into the functions of Crz signaling in a Lepidopteran insect.

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.

Identification of the Short Neuropeptide F and Short Neuropeptide F Receptor Genes and Their Roles of Food Intake in Dendroctonus armandi

The short neuropeptide F (sNPF) is an essential signaling molecule that is evolutionarily conserved and involved in a broad range of physiological functions in the invertebrates, by interacting with sNPF receptors, which belong to G protein-coupled receptors (GPCR). However, the function of sNPF in regulating the food intake of Dendroctonus armandi has been unclear. In this study, we cloned and characterized cDNAs encoding sNPF and sNPF receptor in the D. armandi and made bioinformatics predictions on the deduced amino acid sequences. They had a high degree of similarity to that of Dendroctonus ponderosa. Quantitative real-time reverse transcription PCR (qRT-PCR) revealed that the transcript levels of both sNPF and sNPFR varied across developmental stages and body parts. In addition, the sNPF and sNPFR expression levels were upregulated in starved beetles, and the expression levels recovered after re-feeding. Furthermore, RNAi knockdown by the injection of sNPF and sNPFR dsRNA into beetles significantly increased mortality and reduced their food intake and body weight, and also caused decrease of glycogen and free fatty acid and increase of trehalose. These results indicate that sNPF signaling pathway plays an important role in the regulation of food intake and provides a potential molecular target for the eco-friendly control strategies of this pest.

A possible role of tachykinin-related peptide on an immune system activity of mealworm beetle, Tenebrio molitor L

Tachykinin-related peptides (TRPs) are important neuropeptides. Here we show that they affect the insect immune system, especially the cellular response. We also identify and predict the sequence and structure of the tachykinin-related peptide receptor (TRPR) and confirm the presence of expression of gene encoding TRPR on Tenebrio molitor haemocytes. After application of the Tenmo-TRP-7 in T. molitor the number of circulating haemocytes increased and the number of haemocytes participating in phagocytosis of latex beads decreased in a dose- and time-dependent fashion. Also, Tenmo-TRP-7 affects the adhesion ability of haemocytes. Six hours after injection of Tenmo-TRP-7, a decrease of haemocyte surface area was observed under both tested Tenmo-TRP-7 concentrations (10^-7 and 10^-5 M). The opposite effect was reported 24 h after injection, which indicates that the influence of Tenmo-TRP-7 on modulation of haemocyte behaviour differs at different stages of stress response. Tenmo-TRP-7 application also resulted in increased phenoloxidase activity 6 and 24 h after injection. The assessment of DNA integrity of haemocytes showed that the injection of Tenmo-TRP-7 at 10^-7 M led to a decrease in DNA damage compared to control individuals. This effect was only visible 6 h after Tenmo-TRP-7 application. After 24 h, Tenmo-TRP-7 injection increased DNA damage. We also confirmed the expression of immune-related genes in nervous tissue of T. molitor. Transcripts for genes encoding receptors participating in pathogen recognition processes and antimicrobial peptides were detected in T. molitor brain, retrocerebral complex and ventral nerve cord. These results may indicate a role of the insect nervous system in pathogen recognition and modulation of immune response similar to vertebrates. Taken together, our results support the notion that tachykinin-related peptides probably play an important role in the regulation of the insect immune system. Moreover, some resemblances with action of tachykinin-related peptides and substance P showed that insects can be potential model organisms for analysis of hormonal regulation of conserved innate immune mechanisms.

G-Protein Coupled Receptors (GPCRs) in Insects-A Potential Target for New Insecticide Development

G-protein coupled receptors (GPCRs) play important roles in cell biology and insects' physiological processes, toxicological response and the development of insecticide resistance. New information on genome sequences, proteomic and transcriptome analysis and expression patterns of GPCRs in organs such as the central nervous system in different organisms has shown the importance of these signaling regulatory GPCRs and their impact on vital cell functions. Our growing understanding of the role played by GPCRs at the cellular, genome, transcriptome and tissue levels is now being utilized to develop new targets that will sidestep many of the problems currently hindering human disease control and insect pest management. This article reviews recent work on the expression and function of GPCRs in insects, focusing on the molecular complexes governing the insect physiology and development of insecticide resistance and examining the genome information for GPCRs in two medically important insects, mosquitoes and house flies, and their orthologs in the model insect species Drosophila melanogaster. The tissue specific distribution and expression of the insect GPCRs is discussed, along with fresh insights into practical aspects of insect physiology and toxicology that could be fundamental for efforts to develop new, more effective, strategies for pest control and resistance management.

G-Protein Coupled Receptors (GPCRs): Signaling Pathways, Characterization, and Functions in Insect Physiology and Toxicology

G-protein-coupled receptors (GPCRs) are known to play central roles in the physiology of many organisms. Members of this seven α-helical transmembrane protein family transduce the extracellular signals and regulate intracellular second messengers through coupling to heterotrimeric G-proteins, adenylate cyclase, cAMPs, and protein kinases. As a result of the critical function of GPCRs in cell physiology and biochemistry, they not only play important roles in cell biology and the medicines used to treat a wide range of human diseases but also in insects’ physiological functions. Recent studies have revealed the expression and function of GPCRs in insecticide resistance, improving our understanding of the molecular complexes governing the development of insecticide resistance. This article focuses on the review of G-protein coupled receptor (GPCR) signaling pathways in insect physiology, including insects’ reproduction, growth and development, stress responses, feeding, behaviors, and other physiological processes. Hormones and polypeptides that are involved in insect GPCR regulatory pathways are reviewed. The review also gives a brief introduction of GPCR pathways in organisms in general. At the end of the review, it provides the recent studies on the function of GPCRs in the development of insecticide resistance, focusing in particular on our current knowledge of the expression and function of GPCRs and their downstream regulation pathways and their roles in insecticide resistance and the regulation of resistance P450 gene expression. The latest insights into the exciting technological advances and new techniques for gene expression and functional characterization of the GPCRs in insects are provided.