Peptides in insect oogenesis

RNAi-Mediated FoxO Silencing Inhibits Reproduction in Locusta migratoria

FoxO is a downstream target gene of cellular nutrient and growth factors, oxidative stress responses, and insulin signaling pathways. It play a crucial role in insect growth, development, and reproduction. Locusta migratoria is a significant agricultural pest; therefore, the identification of novel control targets for its management is of significant importance. After injecting dsRNA to interfere with FoxO expression, we observed changes in the reproduction-related gene expression and ovary development through RT-qPCR and morphological observation. Simultaneously, the trehalose and glycogen contents were measured following RNAi. The results demonstrate that interference with FoxO significantly downregulates key genes in the Hippo pathway and Notch gene expression. In terms of carbohydrate metabolism, the trehalose content decreases significantly while the glycogen content increases markedly after FoxO silencing. Additionally, FoxO silencing considerably inhibits reproductive-related gene expression, resulting in delayed ovarian development. These findings indicate that FoxO regulates L. migratoria reproduction through the Hippo signaling pathway: when impaired, the reproductive capacity function declines. In addition, FoxO-mediated energy mobilization is involved in the regulation of egg production. These results indicate that the RNAi of FoxO may be a useful control strategy against L. migratoria.

Endocrine factors modulating vitellogenesis and oogenesis in insects: An update

The endocrine system plays a pivotal role in shaping the mechanisms that ensure successful reproduction. With over a million known insect species, understanding the endocrine control of reproduction has become increasingly complex. Some of the key players include the classic insect lipid hormones juvenile hormone (JH) and ecdysteroids, and neuropeptides such as insulin-like peptides (ILPs). Individual endocrine factors not only modulate their own target tissue but also play crucial roles in crosstalk among themselves, ensuring successful vitellogenesis and oogenesis. Recent advances in omics, gene silencing, and genome editing approaches have accelerated research, offering both fundamental insights and practical applications for studying in-depth endocrine signaling pathways. This review provides an updated and integrated view of endocrine factors modulating vitellogenesis and oogenesis in insect females.

Elucidating the ecophysiology of soybean pod-sucking stinkbug Riptortus pedestris (Hemiptera: Alydidae) based on de novo genome assembly and transcriptome analysis

Food security is important for the ever-growing global population. Soybean, Glycine max (L.) Merr., is cultivated worldwide providing a key source of food, protein and oil. Hence, it is imperative to maintain or to increase its yield under different conditions including challenges caused by abiotic and biotic stresses. In recent years, the soybean pod-sucking stinkbug Riptortus pedestris has emerged as an important agricultural insect pest in East, South and Southeast Asia. Here, we present a genomics resource for R. pedestris including its genome assembly, messenger RNA (mRNA) and microRNA (miRNA) transcriptomes at different developmental stages and from different organs. As insect hormone biosynthesis genes (genes involved in metamorphosis) and their regulators such as miRNAs are potential targets for pest control, we analyzed the sesquiterpenoid (juvenile) and ecdysteroid (molting) hormone biosynthesis pathway genes including their miRNAs and relevant neuropeptides. Temporal gene expression changes of these insect hormone biosynthesis pathways were observed at different developmental stages. Similarly, a diet-specific response in gene expression was also observed in both head and salivary glands. Furthermore, we observed that microRNAs (bantam, miR-14, miR-316, and miR-263) of R. pedestris fed with different types of soybeans were differentially expressed in the salivary glands indicating a diet-specific response. Interestingly, the opposite arms of miR-281 (-5p and -3p), a miRNA involved in regulating development, were predicted to target Hmgs genes of R. pedestris and soybean, respectively. These observations among others highlight stinkbug's responses as a function of its interaction with soybean. In brief, the results of this study not only present salient findings that could be of potential use in pest management and mitigation but also provide an invaluable resource for R. pedestris as an insect model to facilitate studies on plant-pest interactions.

Cluster-Enhanced Nanopore Sensing of Ovarian Cancer Marker Peptides in Urine

The development of novel methodologies that can detect biomarkers from cancer or other diseases is both a challenge and a need for clinical applications. This partly motivates efforts related to nanopore-based peptide sensing. Recent work has focused on the use of gold nanoparticles for selective detection of cysteine-containing peptides. Specifically, tiopronin-capped gold nanoparticles, trapped in the cis-side of a wild-type α-hemolysin nanopore, provide a suitable anchor for the attachment of cysteine-containing peptides. It was recently shown that the attachment of these peptides onto a nanoparticle yields unique current signatures that can be used to identify the peptide. In this article, we apply this technique to the detection of ovarian cancer marker peptides ranging in length from 8 to 23 amino acid residues. It is found that sequence variability complicates the detection of low-molecular-weight peptides (<10 amino acid residues), but higher-molecular-weight peptides yield complex, high-frequency current fluctuations. These fluctuations are characterized with chi-squared and autocorrelation analyses that yield significantly improved selectivity when compared to traditional open-pore analysis. We demonstrate that the technique is capable of detecting the only two cysteine-containing peptides from LRG-1, an emerging protein biomarker, that are uniquely present in the urine of ovarian cancer patients. We further demonstrate the detection of one of these LRG-1 peptides spiked into a sample of human female urine.

Functional characterisation of Fe (II) and 2OG-dependent dioxygenase TcALKBH4 in the red flour beetle, Tribolium castaneum

Alpha-ketoglutarate-dependent dioxygenase ALKB homologue 4 (ALKBH4) is a member of the Fe (II) and 2-oxoglutarate-dependent ALKB homologue family that plays important roles in epigenetic regulation by alkyl lesions removal in mammals. However, the roles of ALKBH4 in insects are not clear. Here, TcALKBH4 was cloned and functionally characterised in Tribolium castaneum. Temporal expression revealed that TcALKBH4 was highly expressed in early embryos and early pupae. Spatial expression showed that TcALKBH4 was highly expressed in the adult testis, and followed by the ovary. RNA interference targeting TcALKBH4 at different developmental stages in T. castaneum led to apparent phenotypes including the failure of development in larvae, the reduction of food intake and the deficiency of fertility in adult. However, further dot blot analyses showed that TcALKBH4 RNAi does not seem to influence 6 mA levels in vivo. qRT-PCR was used to further explore the underlying molecular mechanisms; the result showed that TcALKBH4 mediates the development of larvae possibly through 20E signalling pathway, and the fertility of female and male adult might be regulated by the expression of vitellogenesis and JH signalling pathway, respectively. Altogether, these findings will provide new insights into the potential function of ALKBH4 in insects.

Azadirachtin exposure inhibit ovary development of Spodoptera litura (Lepidoptera: Noctuidae) by altering lipids metabolism event and inhibiting insulin signaling pathways

Lipids are main energy source for insects reproduction, which are becoming emerging target for pest management. Azadirachtin (AZA) is a multi-targeted and promising botanical insecticide, but its reproduction toxicity mechanism related to lipids metabolism is poorly understood. Here, we applied lipidomic and transcriptomic to provide a comprehensive resource for describing the effect of AZA on lipids remodeling in ovary of Spodoptera litura. The results showed that AZA exposure obviously altered the contents of 130 lipids subclasses (76 upregulated and 54 downregulated). In detail, AZA exposure changed the length and saturation degrees of fatty acyl chain of most glycerolipid, phospholipid and sphingolipid as well as the expression of genes related to biosynthesis of unsaturated fatty acids and fatty acids elongation. Besides, following the abnormal lipids metabolism, western blot analysis suggested that AZA induce insulin resistance-like phenotypes by inhibiting insulin receptor substrates (IRS) /PI3K/AKT pathway, which might be responsible for the ovary abnormalities of S. litura. Collectively, our study provided insights into the lipids metabolism event in S. litura underlying AZA exposure, these key metabolites and genes identified in this study would also provide important reference for pest control in future.

Recent Progress in Microencapsulation of Active Peptides-Wall Material, Preparation, and Application: A Review

Being a natural active substance with a wide variety of sources, easy access, significant curative effect, and high safety, active peptides have gradually become one of the new research directions in food, medicine, agriculture, and other fields in recent years. The technology associated with active peptides is constantly evolving. There are obvious difficulties in the preservation, delivery, and slow release of exposed peptides. Microencapsulation technology can effectively solve these difficulties and improve the utilization rate of active peptides. In this paper, the commonly used materials for embedding active peptides (natural polymer materials, modified polymer materials, and synthetic polymer materials) and embedding technologies are reviewed, with emphasis on four new technologies (microfluidics, microjets, layer-by-layer self-assembly, and yeast cells). Compared with natural materials, modified materials and synthetic polymer materials show higher embedding rates and mechanical strength. The new technology improves the preparation efficiency and embedding rate of microencapsulated peptides and makes the microencapsulated particle size tend to be controllable. In addition, the current application of peptide microcapsules in different fields was also introduced. Selecting active peptides with different functions, using appropriate materials and efficient preparation technology to achieve targeted delivery and slow release of active peptides in the application system, will become the focus of future research.

The LIM Domain Protein BmFHL2 Inhibits Egg Production in Female Silkworm, Bombyx mori

The female Bombyx mori accumulates a large amount of egg proteins, mainly Vg and 30K, during egg formation to provide nutrition for embryo development. The synthesis and transport of Vg have been extensively studied, particularly the regulation of Vg transcription induced by 20E; however, the mechanism of 30K protein synthesis is poorly studied. As a model organism of the order Lepidoptera, B. mori has high reproduction potential. In the present study, we found that the FHL2 homologous gene (BmFhl2) in B. mori is involved in inhibiting female egg formation by influencing the synthesis of 30K protein. Interference of BmFhl2 expression in silkworm females increased 30K protein synthesis, accelerated ovarian development, and significantly increased the number of eggs produced and laid; however, the 20E pathway was inhibited. The transcription levels of Vg and 30Kc19 were significantly downregulated following BmFhl2 overexpression in the silkworm ovarian cell line BmN. The Co-IP assay showed that the potential binding protein of BmFHL2 included three types of 30K proteins (30Kc12, 30Kc19, and 30Kc21). These results indicate that BmFHL2 participates in egg formation by affecting 30K protein in female B. mori.

A critical role for ecdysone response genes in regulating egg production in adult female Rhodnius prolixus

Ecdysteroids control ovary growth and egg production through a complex gene hierarchy. In the female Rhodnius prolixus, a blood-gorging triatomine and the vector of Chagas disease, we have identified the ecdysone response genes in the ovary using transcriptomic data. We then quantified the expression of the ecdysone response gene transcripts (E75, E74, BR-C, HR3, HR4, and FTZ-F1) in several tissues, including the ovary, following a blood meal. These results confirm the presence of these transcripts in several tissues in R. prolixus and show that the ecdysone response genes in the ovary are mostly upregulated during the first three days post blood meal (PBM). Knockdown of E75, E74, or FTZ-F1 transcripts using RNA interference (RNAi) was used to understand the role of the ecdysone response genes in vitellogenesis and egg production. Knockdown significantly decreases the expression of the transcripts for the ecdysone receptor and Halloween genes in the fat body and the ovaries and reduces the titer of ecdysteroid in the hemolymph. Knockdown of each of these transcription factors typically alters the expression of the other transcription factors. Knockdown also significantly decreases the expression of vitellogenin transcripts, Vg1 and Vg2, in the fat body and ovaries and reduces the number of eggs produced and laid. Some of the laid eggs have an irregular shape and smaller volume, and their hatching rate is decreased. Knockdown also influences the expression of the chorion gene transcripts Rp30 and Rp45. The overall effect of knockdown is a decrease in number of eggs produced and a severe reduction in number of eggs laid and their hatching rate. Clearly, ecdysteroids and ecdysone response genes play a significant role in reproduction in R. prolixus.

Crosstalk between Nutrition, Insulin, Juvenile Hormone, and Ecdysteroid Signaling in the Classical Insect Model, Rhodnius prolixus

The rigorous balance of endocrine signals that control insect reproductive physiology is crucial for the success of egg production. Rhodnius prolixus, a blood-feeding insect and main vector of Chagas disease, has been used over the last century as a model to unravel aspects of insect metabolism and physiology. Our recent work has shown that nutrition, insulin signaling, and two main types of insect lipophilic hormones, juvenile hormone (JH) and ecdysteroids, are essential for successful reproduction in R. prolixus; however, the interplay behind these endocrine signals has not been established. We used a combination of hormone treatments, gene expression analyses, hormone measurements, and ex vivo experiments using the corpus allatum or the ovary, to investigate how the interaction of these endocrine signals might define the hormone environment for egg production. The results show that after a blood meal, circulating JH levels increase, a process mainly driven through insulin and allatoregulatory neuropeptides. In turn, JH feeds back to provide some control over its own biosynthesis by regulating the expression of critical biosynthetic enzymes in the corpus allatum. Interestingly, insulin also stimulates the synthesis and release of ecdysteroids from the ovary. This study highlights the complex network of endocrine signals that, together, coordinate a successful reproductive cycle.

Modeling Obesity-Associated Ovarian Dysfunction in Drosophila

We perform quantitative studies to investigate the effect of high-calorie diet on Drosophila oogenesis. We use the central composite design (CCD) method to obtain quadratic regression models of body fat and fertility as a function of the concentrations of protein and sucrose, two major macronutrients in Drosophila diet, and treatment duration. Our results reveal complex interactions between sucrose and protein in impacting body fat and fertility when they are considered as an integrated physiological response. We verify the utility of our quantitative modeling approach by experimentally confirming the physiological responses-including increased body fat, reduced fertility, and ovarian insulin insensitivity-expected of a treatment condition identified by our modeling method. Under this treatment condition, we uncover a Drosophila oogenesis phenotype that exhibits an accumulation of immature oocytes and a halt in the production of mature oocytes, a phenotype that bears resemblance to key aspects of the human condition of polycystic ovary syndrome (PCOS). Our analysis of the dynamic progression of different aspects of diet-induced pathophysiology also suggests an order of the onset timing for obesity, ovarian dysfunction, and insulin resistance. Thus, our study documents the utility of quantitative modeling approaches toward understanding the biology of Drosophila female reproduction, in relation to diet-induced obesity and type II diabetes, serving as a potential disease model for human ovarian dysfunction.

Gonadulin: A newly discovered insulin-like peptide involved in ovulation and oviposition in Rhodnius prolixus, a vector of Chagas disease

Insulin-like peptides (ILPs) are vital hormones involved in a wide range of physiological processes in all organisms. In insects, insulin signaling has a key role in detecting and interpreting nutrient levels for egg production. Based on publicly available transcriptomes, a new ILP named gonadulin has been reported and suggested to be expressed by the gonads (hence its name). Although the identification of gonadulin establishes its existence, its physiological relevance remains poorly understood. Rhodnius prolixus is an obligate hematophagous insect and a primary vector of Trypanosoma cruzi, the etiological agent of Chagas disease. In this study, we report for the first time the participation of gonadulin in reproductive performance of an hemipteran. By quantitative PCR and fluorescence in situ hybridization (FISH), we find that the R. prolixus gonadulin transcript is highly expressed in the reproductive system, particularly in the calyx, a structure through which eggs move into the lumen of the lateral oviducts during ovulation. The putative gonadulin receptor, a member of the leucine-rich repeat-containing G protein-coupled receptor subfamily (LGR3), is most highly expressed in the central nervous system with lower levels in the reproductive tissue and other tissues. Interestingly, when the gonadulin signaling cascade is impaired using RNA interference (RNAi), eggs are retained primarily in the ovarioles and calyx, indicating that ovulation and oviposition are inhibited. Understanding the physiological processes involved in reproduction in R. prolixus will shed light on potential targets for effective production of biopesticides by translational research, thereby controlling insect populations and transmission of the disease.

Wolbachia pipientis modulates metabolism and immunity during Aedes fluviatilis oogenesis

Wolbachia pipientis is a maternally transmitted bacterium that mostly colonizes arthropods, including the mosquito Aedes fluviatilis, potentially affecting different aspects of host physiology. This intracellular bacterium prefers gonadal tissue cells, interfering with the reproductive cycle of insects, arachnids, crustaceans, and nematodes. Wolbachia's ability to modulate the host's reproduction is related to its success in prevalence and frequency. Infecting oocytes is essential for vertical propagation, ensuring its presence in the germline. The mosquito Ae. fluviatilis is a natural host for this bacterium and therefore represents an excellent experimental model in the effort to understand host-symbiont interactions and the mutual metabolic regulation. The aim of this study was to comparatively describe metabolic changes in naturally Wolbachia-infected and uninfected ovaries of Ae. fluviatilis during the vitellogenic period of oogenesis, thus increasing the knowledge about Wolbachia parasitic/symbiotic mechanisms.

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

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

Nutritional and Physiological Regulation of Glassy-Winged Sharpshooter Oogenesis

The glassy-winged sharpshooter (Homalodisca vitripennis (Germar); Hemiptera: Cicadellidae: Cicadellinae) is an invasive insect that transmits the plant pathogenic bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadacae). While adult glassy-winged sharpshooter must feed to produce eggs, the role of nutritional status on initiating oogenesis is poorly understood. To determine the effects of glassy-winged sharpshooter nutrition on nymphal development, oogenesis, and fecundity, glassy-winged sharpshooter were reared on cowpea, sunflower, sorghum, and a mixture of the three plant species. Adults emerging from cowpea, sunflower, or plant mixture treatments had shorter development times, attained larger size, and had greater estimated lipid reserves than females reared on sorghum. In choice tests, nymphs avoided sorghum and preferentially fed on cowpea and sunflower. Adult females provisioned with a single plant species during the nymphal stage were provided with either the same host plant species or a mixture of host plant species (cowpea, sunflower, sorghum) for a 9-wk oviposition period, with 37% of females initiating oogenesis. Ovipositing females had greater juvenile hormone and octopamine levels than reproductively inactive females, although topical application of the juvenile hormone analog Methoprene did not promote oogenesis. Across nymphal diets, reproductively active females produced more eggs when held on plant mixtures than on single plant species. In choice tests, adult females were observed most frequently on cowpea, although most eggs were deposited on sorghum, the host least preferred by nymphs. Results suggest that fecundity is largely determined by the quality of the adult diet, although the stimulus that initiates oogenesis does not appear to be related to nutrition.

Dynamic transcriptome analysis of Bombyx mori embryonic development

Bombyx mori has been extensively studied but the gene expression control of its embryonic development is unclear. In this study, we performed transcriptome profiling of six stages of B. mori embryonic development using RNA sequencing (RNA-seq). A total of 12 894 transcripts were obtained from the embryos. Of these, 12 456 transcripts were shared among the six stages, namely, fertilized egg, blastoderm, germ-band, organogenesis, reversal period, and youth period stages. There were 111, 48, 41, 54, 77, and 107 transcripts specifically expressed during the six stages, respectively. By analyzing weighted gene correlation networks and differently expressed genes, we found that during embryonic development, many genes related to DNA replication, transcription, protein synthesis, and epigenetic modifications were upregulated in the early embryos. Genes of cuticle proteins, chitin synthesis-related proteins, and neuropeptides were more abundant in the late embryos. Although pathways of juvenile hormone and the ecdysteroid 20-hydroxyecdysone, and transcription factors were expressed throughout the embryonic development stages, more regulatory pathways were highly expressed around the organogenesis stage, suggesting more gene expression for organogenesis. The results of RNA-seq were confirmed by quantitative real-time polymerase chain reaction of 16 genes of different pathways. Nucleic acid methylation and seven sites in histone H3 modifications were confirmed by dot blot and western blot. This study increases the understanding of the molecular mechanisms of the embryonic developmental process and information on the regulation of B. mori development.

Neuroendocrine Regulation of Reproductive Dormancy in the Fruit Fly Drosophila melanogaster: A Review of Juvenile Hormone-Dependent Regulation

Animals can adjust their physiology, helping them survive and reproduce under a wide range of environmental conditions. One of the strategies to endure unfavorable environmental conditions such as low temperature and limited food supplies is dormancy. In some insect species, this may manifest as reproductive dormancy, which causes their reproductive organs to be severely depleted under conditions unsuitable for reproduction. Reproductive dormancy in insects is induced by a reduction in juvenile hormones synthesized in the corpus allatum (pl. corpora allata; CA) in response to winter-specific environmental cues, such as low temperatures and short-day length. In recent years, significant progress has been made in the study of dormancy-inducing conditions dependent on CA control mechanisms in Drosophila melanogaster. This review summarizes dormancy control mechanisms in D. melanogaster and discusses the implications for future studies of insect dormancy, particularly focusing on juvenile hormone-dependent regulation.

Immunoreactive Response of Plast-MIPs to Fasting and Their Functional Role in the Reduction of Hemolymph Reducing Sugars in the Brown-Winged Green Bug, Plautia stali

Animals survive nutrient deficiency by controlling their physiology, such as sugar metabolism and energy-consuming developmental events. Although research on the insect neural mechanisms of the starvation-induced modulation has progressed, the mechanisms have not been fully understood due to their complexity. Myoinhibitory peptides are known to be neuropeptides involved in various physiological activities, development, and behavior. Here, we analyzed the responsiveness of Plautia stali myoinhibitory peptides (Plast-MIPs) to starvation and their physiological role in the brown-winged green bug, P. stali. First, we performed immunohistochemical analyses to investigate the response of Plast-MIP neurons in the cephalic ganglion to fasting under long day conditions. Fasting significantly enhanced the immunoreactivity to Plast-MIPs in the pars intercerebralis (PI), which is known to be a brain region related to various endocrine regulations. Next, to analyze the physiological role of Plast-MIPs, we performed RNA interference-mediated knockdown of Plast-Mip and injection of synthetic Plast-MIP in normally fed and fasted females. The knockdown of Plast-Mip did not have significant effects on the body weight or proportions of ovarian development in each feeding condition. On the other hand, the knockdown of Plast-Mip increased the gonadosomatic index of normally fed females whereas it did not have a significant effect on food intake. Notably, the knockdown of Plast-Mip diminished the fasting-induced reduction of hemolymph reducing sugar levels. Additionally, injection of synthetic Plast-MIP acutely decreased the hemolymph reducing sugar level. Our results suggested responsiveness of Plast-MIPs in the PI to fasting and their functional role in reduction of the hemolymph reducing sugar level.

Identification of G protein-coupled receptors required for vitellogenesis and egg development in an insect with panoistic ovary

G protein-coupled receptors (GPCRs), a superfamily of integral transmembrane proteins regulate a variety of physiological processes in insects. Juvenile hormone (JH) is known to stimulate Vitellogenin (Vg) synthesis in the fat body, secretion into the hemolymph and uptake by developing oocytes. However, the role of GPCRs in JH-dependent insect vitellogenesis and oocyte maturation remains elusive. In the present study, we performed transcriptomic analysis and RNA interference (RNAi) screening in vitellogenic females of the migratory locust Locusta migratoria. Of 22 GPCRs identified in ovarian transcriptome, LGR4, OR-A1, OR-A2, Mthl1, Mthl5 and Smo were most abundant in the ovary. By comparison, mAChR-C expressed at higher levels in the fat body, whereas Oct/TyrR, OARβ, AdoR and ADGRA3 were at higher expression levels in the brain. Our RNAi screening demonstrated that knockdown of six GPCRs resulted in defective phenotypes of Vg accumulation in developing oocytes, accompanied by blocked ovarian development and impaired oocyte maturation. While LGR4 and Oct/TyrR appeared to control Vg synthesis in the fat body, OR-A1, OR-A2, mAChR-C and CirlL regulated Vg transportation and uptake. The findings provide fundamental evidence for deciphering the regulatory mechanisms of GPCRs in JH-stimulated insect reproduction.

Physiological Alterations in Deletion Mutants of Two Insulin-Like Peptides Encoded in Maruca vitrata Using CRISPR/Cas9

Most insect species encode multiple insulin-like peptides (ILPs) that exhibit functional overlaps in mediating physiological processes such as development and reproduction. Why do they need multiple ILPs? To address this question, we tested a hypothesis of the requirement of multiple ILPs by generating mutants lacking individual ILP genes using the CRISPR/Cas9 technology. Two ILPs (ILP1 and ILP2) in the legume pod borer, Maruca vitrata, mediate similar physiological processes such as hemolymph sugar level, larval development, and adult reproduction. Individual knock-out mutants (ΔILP1 and ΔILP2) were generated. They showed successful development from larvae to adults. However, they suffered from high hemolymph sugar levels by enhancing trehalose titers in the hemolymph. The hyperglycemic effect was more evident in ΔILP2 mutants than in ΔILP1 mutants. Both mutants showed increased expression of trehalose-6-phosphate synthase but suppressed expression of trehalase. These mutants also showed altered expression patterns of insulin signaling components. Expression levels of insulin receptor and Akt genes were upregulated, while those of FOXO and Target of rapamycin genes were downregulated in these mutants. These alterations of signal components resulted in significant retardation of immature development and reduced body sizes. ΔILP1 or ΔILP2 females exhibited poor oocyte development. Bromo-uridine incorporation was much reduced at the germarium of ovarioles of these mutants compared with wild females. Expression of the vitellogenin gene was also reduced in these mutants. Furthermore, males of these deletion mutants showed impaired reproductive activities when they mated with wild-type females. These results suggest that both ILPs are required for mediating larval development and adult reproduction in M. vitrata.

Cell-specific expression and individual function of prohormone convertase PC1/3 in Tribolium larval growth highlights major evolutionary changes between beetle and fly neuroendocrine systems

Background

The insect neuroendocrine system acts in the regulation of physiology, development and growth. Molecular evolution of this system hence has the potential to allow for major biological differences between insect groups. Two prohormone convertases, PC1/3 and PC2, are found in animals and both function in the processing of neuropeptide precursors in the vertebrate neurosecretory pathway. Whereas PC2-function is conserved between the fly Drosophila and vertebrates, ancestral PC1/3 was lost in the fly lineage and has not been functionally studied in any protostome.

Results

In order to understand its original functions and the changes accompanying the gene loss in the fly, we investigated PC1/3 and PC2 expression and function in the beetle Tribolium castaneum. We found that PC2 is broadly expressed in the nervous system, whereas surprisingly, PC1/3 expression is restricted to specific cell groups in the posterior brain and suboesophageal ganglion. Both proteases have parallel but non-redundant functions in adult beetles’ viability and fertility. Female infertility following RNAi is caused by a failure to deposit sufficient yolk to the developing oocytes. Larval RNAi against PC2 produced moulting defects where the larvae were not able to shed their old cuticle. This ecdysis phenotype was also observed in a small subset of PC1/3 knockdown larvae and was strongest in a double knockdown. Unexpectedly, most PC1/3-RNAi larvae showed strongly reduced growth, but went through larval moults despite minimal to zero weight gain.

Conclusions

The cell type-specific expression of PC1/3 and its essential requirement for larval growth highlight the important role of this gene within the insect neuroendocrine system. Genomic conservation in most insect groups suggests that it has a comparable individual function in other insects as well, which has been replaced by alternative mechanisms in flies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13227-021-00179-w.

Regulation of a Trehalose-Specific Facilitated Transporter (TRET) by Insulin and Adipokinetic Hormone in Rhodnius prolixus, a Vector of Chagas Disease

Using the blood-sucking kissing bug, Rhodnius prolixus as an experimental model, we have studied the involvement of insulin-like peptides (ILPs) and adipokinetic hormone (AKH) signaling in carbohydrate metabolism, focusing on the regulation of the trehalose-specific facilitated transporter (Rhopr-TRET), particularly in the ovaries. We find that trehalose stores in ovaries increase after feeding, synchronously with the beginning of vitellogenesis, but that the transcript expression of enzymes involved in trehalose synthesis show no changes between unfed and blood-fed animals. However, an eightfold increase in Rhopr-TRET transcript expression is observed in the ovaries post-blood meal. In vivo and ex vivo assays using exogenous insulins and Rhopr-AKH, reveal that Rhopr-TRET is up-regulated in ovaries by both peptide families. In accordance with these results, when ILP and AKH signaling cascades are impaired using RNA interference, Rhopr-TRET transcript is down-regulated. In addition, trehalose injection induces an up-regulation of Rhopr-TRET transcript expression and suggests an activation of insulin signaling. Overall, the results support the hypothesis of a direct trehalose uptake by ovaries from the hemolymph through Rhopr-TRET, regulated by ILP and/or AKH. We also show that Rhopr-TRET may work cooperatively with AKH signaling to support the release of trehalose from the ovaries into the hemolymph during the unfed (starved) condition. In conclusion, the results indicate that in females of R. prolixus, trehalose metabolism and its hormonal regulation by ILP and AKH play critical roles in adapting to different nutritional conditions and physiological states.

Crucial Role of Juvenile Hormone Receptor Components Methoprene-Tolerant and Taiman in Sexual Maturation of Adult Male Desert Locusts

Currently (2020), Africa and Asia are experiencing the worst desert locust (Schistocerca gregaria) plague in decades. Exceptionally high rainfall in different regions caused favorable environmental conditions for very successful reproduction and population growth. To better understand the molecular mechanisms responsible for this remarkable reproductive capacity, as well as to fill existing knowledge gaps regarding the regulation of male reproductive physiology, we investigated the role of methoprene-tolerant (Scg-Met) and Taiman (Scg-Tai), responsible for transducing the juvenile hormone (JH) signal, in adult male locusts. We demonstrated that knockdown of these components by RNA interference strongly inhibits male sexual maturation, severely disrupting reproduction. This was evidenced by the inability to show mating behavior, the absence of a yellow-colored cuticle, the reduction of relative testes weight, and the drastically reduced phenylacetonitrile (PAN) pheromone levels of the treated males. We also observed a reduced relative weight, as well as relative protein content, of the male accessory glands in Scg-Met knockdown locusts. Interestingly, in these animals the size of the corpora allata (CA), the endocrine glands where JH is synthesized, was significantly increased, as well as the transcript level of JH acid methyltransferase (JHAMT), a rate-limiting enzyme in the JH biosynthesis pathway. Moreover, other endocrine pathways appeared to be affected by the knockdown, as evidenced by changes in the expression levels of the insulin-related peptide and two neuroparsins in the fat body. Our results demonstrate that JH signaling pathway components play a crucial role in male reproductive physiology, illustrating their potential as molecular targets for pest control.

Regulatory Mechanisms of Vitellogenesis in Insects

Vitellogenesis is pre-requisite to insect egg production and embryonic development after oviposition. During insect vitellogenesis, the yolk protein precursor vitellogenin (Vg) is mainly synthesized in the fat body, transported by the hemolymph through the intercellular spaces (known as patency) in the follicular epithelium to reach the membrane of maturing oocytes, and sequestered into the maturing oocytes via receptor-mediated endocytosis. Insect vitellogenesis is governed by two critical hormones, the sesquiterpenoid juvenile hormone (JH) and the ecdysteriod 20-hydroxyecdysone (20E). JH acts as the principal gonadotropic hormone to stimulate vitellogenesis in basal hemimetabolous and most holometabolous insects. 20E is critical for vitellogenesis in some hymenopterans, lepidopterans and dipterans. Furthermore, microRNA (miRNA) and nutritional (amino acid/Target of Rapamycin and insulin) pathways interplay with JH and 20E signaling cascades to control insect vitellogenesis. Revealing the regulatory mechanisms underlying insect vitellogenesis is critical for understanding insect reproduction and helpful for developing new strategies of insect pest control. Here, we outline the recent research progress in the molecular action of gonadotropic JH and 20E along with the role of miRNA and nutritional sensor in regulating insect vitellogenesis. We highlight the advancements in the regulatory mechanisms of insect vitellogenesis by the coordination of hormone, miRNA and nutritional signaling pathways.

Identification of Gonadulin and Insulin-Like Growth Factor From Migratory Locusts and Their Importance in Reproduction in Locusta migratoria

Many insect species have several genes coding for insulin-related peptides (IRPs), but so far only a single IRP gene has been identified in migratory locusts. Here, we report and characterize two other genes coding for peptides that are related to insulin, namely gonadulin and arthropod insulin-like growth factor (aIGF); peptides postulated to be orthologs of Drosophila melanogaster insulin-like peptides 8 and 6 respectively. In Locusta migratoria the aIGF transcript is expressed in multiple tissues as was previously reported for IRP in both L. migratoria and Schistocerca gregaria, but there are significant differences in expression patterns between the two species. The gonadulin transcript, however, seems specific to the ovary, whereas its putative receptor transcript is expressed most abundantly in the ovary, fat body and the central nervous system. Since the central nervous system-fat body-ovary axis is essential for successful reproduction, we studied the influence of gonadulin on vitellogenesis and oocyte growth. A reduction in the gonadulin transcript (via RNA interference) led to a significant reduction in vitellogenin mRNA levels in the fat body and a strong oocyte growth inhibition, thus suggesting an important role for gonadulin in reproduction in this species.

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

Neuropeptides of short neuropeptides F family (sNPF) have been identified in various arthropods. They are pleiotropic neuromolecules which so far have been mainly associated with regulation of feeding and metabolism, as well as growth and development, locomotion, circadian rhythm or learning and memory. Here, we describe the effects of Tenebrionid sNPF peptide (SGRSPSLRLRFa) on various aspects of the male reproductive physiology in the Tenebrio molitor beetle. We identified in silico the putative sNPF receptor Tenmo-sNPFR. Based on RT-PCR technique, it was shown that the receptor might be present in the male reproductive tissues of this beetle. The analysis of receptor amino acid sequence showed that it is similar to other beetle sNPFRs, as well as other insect species, and belongs rhodopsin-like G-protein-coupled receptors (GPCRs). Injections of Trica-sNPF and its shorter form Trica-sNPF_(4–11) caused differentiated effects in T. molitor male reproductive tissues. After 24 h post injections, the peptides decreased the concentration of the soluble protein fraction in testes of 4- and 8-day-old beetles as well as the dry mass of these organs but only in 8-day-old individuals. The same effects were shown with regard to accessory glands. Both peptides decrease the concentration of the soluble protein fraction but do not affect the dry mass of this organ. Furthermore, injections of Trica-sNPF at the 10^–7 M concentration decrease the total sperm number in the reproductive system. Surprisingly, the same concentration of the shorter form, Trica-sNPF_(4–11) increased the sperm number. It was also shown that both peptides in different manner influence contractions of ejaculatory duct. The data presented in this article give new evidence that sNPFs are involved in the regulation of reproductive events in beetles, which might be the part of a larger neuropeptide network combining feeding, growth and development with the physiology of reproduction.

Transcriptomic analysis of regulatory pathways involved in female reproductive physiology of Rhodnius prolixus under different nutritional states

The triatomine Rhodnius prolixus, a vector of the etiological agent of Chagas disease, has long been used as model to understand important aspects of insect physiology. Despite this history, the impact of the nutritional state on regulatory pathways associated with reproductive performance in triatomines has never been studied. The insulin-like peptide/target of rapamycin (ILP/ToR) signaling pathway is typically responsible for detecting and interpreting nutrient levels. Here, we analyzed transcriptomes from the central nervous system, fat bodies and ovaries of adult females in unfed and fed conditions, with a focus on the ILP/ToR signaling. The results show an up-regulation of transcripts involved in ILP/ToR signaling in unfed insects. However, we demonstrate that this signaling is only activated in tissues from fed insects. Moreover, we report that FoxO (forkhead box O) factor, which regulates longevity via ILP signaling, is responsible for the up-regulation of transcripts related with ILP/ToR signaling in unfed insects. As a consequence, we reveal that unfed females are in a sensitized state to respond to an increase of ILP levels by rapidly activating ILP/ToR signaling. This is the first analysis that correlates gene expression and protein activation of molecules involved with ILP/ToR signaling in R. prolixus females in different nutritional states.

Genome-wide characterization and transcriptomic analyses of neuropeptides and their receptors in an endoparasitoid wasp, Pteromalus puparum

In insects, neuropeptides constitute a group of signaling molecules that act in regulation of multiple physiological and behavioral processes by binding to their corresponding receptors. On the basis of the bioinformatic approaches, we screened the genomic and transcriptomic data of the parasitoid wasp, Pteromalus puparum, and annotated 36 neuropeptide precursor genes and 33 neuropeptide receptor genes. Compared to the number of precursor genes in Bombyx mori (Lepidoptera), Chilo suppressalis (Lepidoptera), Drosophila melanogaster (Diptera), Nilaparvata lugens (Hemiptera), Apis mellifera (Hymenoptera), and Tribolium castaneum (Coleoptera), P. puparum (Hymenoptera) has the lowest number of neuropeptide precursor genes. This lower number may relate to its parasitic life cycle. Transcriptomic data of embryos, larvae, pupae, adults, venom glands, salivary glands, ovaries, and the remaining carcass revealed stage-, sex-, and tissue-specific expression patterns of the neuropeptides, and their receptors. These data provided basic information about the identity and expression profiles of neuropeptides and their receptors that are required to functionally address their biological significance in an endoparasitoid wasp.

Deletion mutant of sPLA2 using CRISPR/Cas9 exhibits immunosuppression, developmental retardation, and failure of oocyte development in legume pod borer, Maruca vitrata

Phospholipase A₂ (PLA₂) catalyzes release of free fatty acids linked to phospholipids at sn-2 position. Some of these released free fatty acids are used to synthesize eicosanoids that mediate various physiological processes in insects. Although a large number of PLA₂s form a superfamily consisting of at least 16 groups, few PLA₂s have been identified and characterized in insects. Furthermore, physiological functions of insect PLA₂s remain unclear. Clustered regularly interspaced short parlindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) has been a useful research tool to validate gene function. This study identified and characterized a secretory PLA₂ (sPLA₂) from legume pod borer, Maruca vitrata (Lepidoptera: Crambidae), and validated its physiological functions using CRISPR/Cas9. An open reading frame of M. vitrata sPLA₂ (Mv-sPLA₂) encoding 192 amino acids contained signal peptide, calcium-binding domain, and catalytic site. Phylogenetic analysis indicated that Mv-sPLA₂ was related to other Group III sPLA₂s. Mv-sPLA₂ was expressed in both larval and adult stages. It was inducible by immune challenge. RNA interference (RNAi) of Mv-sPLA₂ significantly suppressed cellular immunity and impaired larval development. Furthermore, RNAi treatment in female adults prevented oocyte development. These physiological alterations were also observed in a mutant line of M. vitrata with Mv-sPLA₂ deleted by using CRISPR/Cas9. Mv-sPLA₂ was not detected in the mutant line from western blot analysis. Addition of an eicosanoid, PGE₂, significantly rescued oocyte development of females of the mutant line. These results suggest that Mv-sPLA₂ plays crucial role in immune, developmental, and reproductive processes of M. vitrata.

Juvenile Hormone receptor Met is essential for ovarian maturation in the Desert Locust, Schistocerca gregaria

Juvenile hormones (JH) are key endocrine regulators produced by the corpora allata (CA) of insects. Together with ecdysteroids, as well as nutritional cues, JH coordinates different aspects of insect postembryonic development and reproduction. The function of the recently characterized JH receptor, Methoprene-tolerant (Met), appears to be conserved in different processes regulated by JH. However, its functional interactions with other hormonal signalling pathways seem highly dependent on the feeding habits and on the developmental and reproductive strategies employed by the insect species investigated. Here we report on the effects of RNA interference (RNAi) mediated SgMet knockdown during the first gonadotrophic cycle in female desert locusts (Schistocerca gregaria). This voracious, phytophagous pest species can form migrating swarms that devastate field crops and harvests in several of the world’s poorest countries. A better knowledge of the JH signalling pathway may contribute to the development of novel, more target-specific insecticides to combat this very harmful swarming pest. Using RNAi, we show that the JH receptor Met is essential for ovarian maturation, vitellogenesis and associated ecdysteroid biosynthesis in adult female S. gregaria. Interestingly, knockdown of SgMet also resulted in a significant decrease of insulin-related peptide (SgIRP) and increase of neuroparsin (SgNP) 3 and 4 transcript levels in the fat body, illustrating the existence of an intricate regulatory interplay between different hormonal factors. In addition, SgMet knockdown in females resulted in delayed display of copulation behaviour with virgin males, when compared with dsGFP injected control animals. Moreover, we observed an incapacity of adult dsSgMet injected female locusts to oviposit during the time of the experimental setup. As such, SgMet is an essential gene playing crucial roles in the endocrine communication necessary for successful reproduction of the desert locust.