Serpins in arthropod biology

Functional analysis of serine protease EfSP1 in Eocanthecona furcellata Wolff (Hemiptera: Pentatomidae)

BACKGROUND

Serine protease is an important digestive enzyme involved in many physiological and biochemical reactions, including digestion of insect food protein, blood coagulation, signal transduction, immune response, and hormone activation. The physiological functionality of salivary gland serine protease EfSP1 in the predatory natural enemy Eocanthecona furcellata is unknown. As a salivary gland protein, EfSP1 may have insecticidal activity against the prey Spodoptera frugiperda.

RESULTS

The expression of the EfSP1 gene was interfered with microinjection. After RNAi, the molting of the 5th instar nymphs of E. furcellata was blocked, and the survival rate and daily predation of male and female adults were reduced. The prokaryotic expression of EfSP1 protein was injected into the 4th instar larvae of S. frugiperda, causing difficulty in molting to death of the 4th instar larvae, and the dead larvae showed melanization, softening, and liquefaction. The development duration of the 4th instar larvae was prolonged, the survival rate was decreased, the pupal weight was decreased, the pupal period was prolonged, and the pupal eclosion rate was decreased. This inhibited the chitin and trehalose metabolism of S. frugiperda larvae, hemolymph melanization, and phenoloxidase activity, affecting the transcription of antimicrobial peptide genes.

CONCLUSION

These findings indicate that EfSP1 is involved in the growth, development, and predation of E. furcellata. As a salivary gland protein, EfSP1 also has insecticidal activity, affecting the growth and development, chitin metabolism, trehalose metabolism, and humoral immunity of S. frugiperda. These findings reveal the physiological function of EfSP1. © 2025 Society of Chemical Industry.

Mosquito immune responses to Plasmodium parasites that limit malaria transmission

The mosquito immune system is a major barrier that malaria parasites must overcome for their successful development and disease transmission. At each developmental stage in the vector, Plasmodium parasites can be potentially targeted by the mosquito innate immune responses, which involve epithelial, humoral, and cellular components. The immune response to Plasmodium ookinetes can be powerful and some of the underlying effector mechanisms are well characterized. However, the defense responses to oocysts and sporozoites appear to be less effective and are less well understood. Plasmodium parasites are under constant pressure to avoid elimination by evading and/or manipulating the mosquito immune system. Understanding the intricate interaction between Plasmodium parasites and the mosquito immune system is fundamental to understand the epidemiology of malaria transmission and to devise innovative control strategies.

A venom serpin from the assassin bug Sycanus croceovittatus exhibiting inhibitory effects on melanization, development, and insecticidal activity towards its prey

Serine protease inhibitors (SPIs) have been identified as main common components in the venom of the predatory bugs, while their functional roles remain unexplored. In this study, we identified 35 SPI genes belonging to three subfamilies of serpin, canonical SPI, and A2M in genome of the assassin bug, Sycanus croceovittatus. The amino acid sequences of these SPI genes reveal conserved functional regions, albeit with mutations or deletions at certain active site residues. Transcriptomic and qPCR analyses of gene expression patterns in various tissues across developmental stages indicate that most SPI genes exhibit high expression levels in venom apparatus, suggesting their role as venom proteins. Notably, the ScSPI5 gene from the serpin class was found to be most abundantly expressed in all three distinct venom glands, indicating its significant role as a venomous protein. Functional characterization demonstrated that this venom serpin effectively inhibits trypsin activity in vitro and suppresses phenoloxidase activity, thereby blocking hemolymph melanization in preys, including Spodoptera frugiperda, Achelura yunnanensis, and Tenebrio molitor. When ingested, it reduces the larval and pupal weight of the fall armyworm by impeding trypsin activity in the midgut. Upon injection, ScSPI5 exhibits a dose-dependent insecticidal effect against T. molitor, with an LD50 of 5.6 ± 1.1 μg/g. These findings elucidate the specific functions of SPIs in the venom of predatory bugs, enhancing our understanding of their predation efficiency, and highlighting the potential application of venomous SPIs as protease inhibitors in pest management strategies.

Molecular evolution of dietary shifts in ladybird beetles (Coleoptera: Coccinellidae): from fungivory to carnivory and herbivory

BACKGROUND

Dietary shifts are major evolutionary steps that shape ecological niches and biodiversity. The beetle family Coccinellidae, commonly known as ladybirds, first transitioned from a fungivorous to an insectivorous and subsequently a plant diet. However, the molecular basis of this dietary diversification remained unexplored.

RESULTS

We investigated the molecular evolution of dietary shifts in ladybirds, focusing on the transitions from fungivory to carnivory (Coccinellidae) and from carnivory to herbivory (Epilachnini), by comparing 25 genomes and 62 transcriptomes of beetles. Our analysis shows that chemosensory gene families have undergone significant expansions at both nodes of diet change and were differentially expressed in feeding experiments, suggesting that they may be related to foraging. We found expansions of digestive and detoxifying gene families and losses of chitin-related digestive genes in the herbivorous ladybirds, and absence of most plant cell wall-degrading enzymes in the ladybirds dating from the transition to carnivory, likely indicating the effect of different digestion requirements on the gene repertoire. Immunity effector genes tend to emerge or have specific amino acid sequence compositions in carnivorous ladybirds and are downregulated under suboptimal dietary treatments, suggesting a potential function of these genes related to microbial symbionts in the sternorrhynchan prey.

CONCLUSIONS

Our study provides a comprehensive comparative genomic analysis to address evolution of chemosensory, digestive, detoxifying, and immune genes associated with dietary shifts in ladybirds. Ladybirds can be considered a ubiquitous example of dietary shifts in insects, and thus a promising model system for evolutionary and applied biology.

Innate Immunity in Insects: The Lights and Shadows of Phenoloxidase System Activation

Melanogenesis and melanin deposition are processes essential for the effective immune response of insects to various invaders. Phenoloxidase (PO), produced in specialized cells as an inactive precursor prophenoloxidase (proPO), is the key enzyme for melanin formation. The precursor is activated via limited proteolysis by a dedicated serine proteinase, which is the final element in the cascade of serine proteinases (SPs) that make up the PO system. Melanogenesis provides different cytotoxic molecules active in fighting infections, as well as melanin, which is important for sequestration of invaders. However, since the cytotoxic reactive compounds generated during melanization also pose a threat to host cells, strict control of the PO system is necessary for host self-protection. Different pathogens and parasites influence the PO system and melanization through various strategies, which allow them to survive and develop in the host insect body. In this review, we characterize "the lights and shadows" of PO system activation, indicating, on one hand, its advantages as an efficient and effective mechanism of the insect immune response and, on the other hand, the dangers for the insect host associated with the improper functioning of this system and selected strategies for regulating its activity by entomopathogenic organisms.

Systematic review of innate immune responses against Mycobacterium tuberculosis complex infection in animal models

Background

Mycobacterium tuberculosis (Mtb) complex (MTBC) includes ten species that affect mammals and pose a significant global health concern. Upon infection, Mtb induces various stages in the host, including early bacterial elimination, which may or may not involve memory responses. Deciphering the role of innate immune responses during MTBC infection is crucial for understanding disease progression or protection. Over the past decade, there has been growing interest in the innate immune response to Mtb, with new preclinical models emerging.

Methods

We conducted a systematic review following PRISMA guidelines, focused on innate immune mediators linked to protection or disease progression in animal models of MTBC infection. We searched two databases: National Library of Medicine and Web of Science. Two researchers independently extracted data based on specific inclusion and exclusion criteria.

Results

Eighty-three articles were reviewed. Results were categorized in four groups: MTBC species, animal models, soluble factors and innate pathways, and other molecules (metabolites and drugs). Mtb and M. bovis were the only species studied. P2X7R receptor's role in disease progression and higher macrophage recruitment were observed differentially after infection with hypervirulent Mtb strains. Mice and non-human primates (NHPs) were the most used mammals, with emerging models like Galleria mellonella and planarians also studied. NHPs provided insights into age-dependent immunity and markers for active tuberculosis (ATB). Key innate immune factors/pathways identified included TNF-α, neutrophil recruitment, ROS/RNS responses, autophagy, inflammasomes, and antimicrobial peptides, with homologous proteins identified in insects. Metabolites like vitamin B5 and prostaglandin E2 were associated with protection. Immunomodulatory drugs targeting autophagy and other mechanisms were studied, exhibiting their potential as therapeutic alternatives.

Conclusion

Simpler, physiologically relevant, and ethically sound models, such as G. mellonella, are needed for studying innate responses in MTBC infection. While insects lack adaptive immunity, they could provide insights into "pure" innate immune responses. The dissection of "pure," "sustained" (later than 7 days post-infection), and trained innate immunity presents additional challenges that require high-resolution temporospatial analytical methods. Identifying early innate immune mediators and targetable pathways in the blood and affected tissues could identify biomarkers for immunization efficiency, disease progression, and potential synergistic therapies for ATB.

The OnSPN2 from the nipa palm hispid beetle Octodonta nipae is a multipurpose defense tool against proteases from different peptidase families

Serpins (serine protease inhibitors) constitute a superfamily of proteins with functional diversity and unusual conformational flexibility. In insects, serpins act as multiple inhibitors, by forming inactive acyl-enzyme complexes, in regulating Spätzles activation, phenoloxidases (POs) activity, and other cytokines. In this study, we present the cloning and characterization of Octodonta nipae serpin2 (OnSPN2), a 415 residues protein homologous to Tenebrio molitor 42Dd-like. Notably, OnSPN2 features an arginine residue (R364) at the P1 position, and additional arginine residues (R362, R367) at the P3 and P3' positions, respectively which is crucial for protease inhibition. Immunohistochemistry (IHC) and Western blot analyses revealed that OnSPN2 is primarily synthesized in plasmatocytes and then released into the plasma to exert its function. RNA interference results indicated that OnSPN2 knockdown may depress serine protease in melanization and remarkably increase the transcript level of Attacin in hemolymph, but its messenger RNA levels were not changed upon immune induction. Reciprocal co-immunoprecipitation assay results confirmed that OnSPN2 binds to OnPPAF1 and OnSP8, indicating its role as a negative regulator in the PO and AMP pathway. Intriguingly, several cathepsin-L isoforms were identified in the OnSPN2 immunoprecipitated samples. The cathepsin-L inhibition assays and protein-protein docking results, identified cathepsin-L as a potential target of OnSPN2. These results indicate that OnSPN2 is produced as an intracellular resident and additionally is associated with the PO and AMP pathway. OnSPN2 represents a multiple defense tool that may provide multiple antiproteolytic functions.

Comparative proteotranscriptomic analysis of four carpenter moth species reveals key salivary proteins related to feeding adaptations

Salivary proteins play a crucial role in insects, facilitating nutrient acquisition and regulating complex interactions with host plants. However, most research has focused on pierce-sucking insects, leaving chewing insects, such as caterpillars largely unexplored. Carpenter moths (Cossidae) are important destructive wood bores whose larvae cause significant damage to forestry. Here, we present the first comparative morphological and proteotranscriptomic analysis of the salivary glands of four cossid species, namely Cossus cossus, Deserticossus arenicola, Streltzoviella insularis and Yakudza vicarious. Despite the conserved structure of their salivary glands, we identified a complex composition of salivary proteins involved in digestion, feeding regulation and silk production. Notably, proteins related to immunity and detoxification were enriched in sialome, indicating their essential roles in insect-plant interactions. Furthermore, our analysis revealed that cossid species with similar feeding habits exhibited convergent patterns in major protein groups and expression. Specifically, serpins were the most expressed in root feeders, while odorant-binding proteins dominated in stem feeders, likely contributing to their specific feeding preferences. Our findings highlight the essentiality of salivary proteins in feeding adaptations of carpenter moths and provide valuable insights for developing targeted pest management strategies against these wood-boring pests.

Expressions of Immune Prophenoloxidase (proPO) System-Related Genes Under Oxidative Stress in the Gonads and Stomach of the Mud Crab (Macrophthalmus japonicus) Exposed to Endocrine-Disrupting Chemicals

Endocrine-disrupting chemicals (EDCs) significantly damage biological systems related to reproductive, neurological, and metabolic functions. Approximately 1000 chemicals are known to possess endocrine-acting properties, including bisphenol A (BPA) and di(2-ethylhexyl) phthalate (DEHP). This study primarily focuses on the potential effects of EDCs on the transcriptional levels of innate immune prophenoloxidase (proPO) system-related genes under oxidative stress in the gonads and stomach of the mud crab Macrophthalmus japonicus, an indicator species for assessing coastal benthic environments, when exposed to 1 µg L-1, 10 µg L-1, and 30 µg L-1 BPA or DEHP. After EDC exposure, the expression of lipopolysaccharide and β-1,3-glucan-binding protein (LGBP), a pattern recognition protein that activates the proPO system, was upregulated in the stomach of M. japonicus, whereas LGBP gene expression was downregulated in the gonads. In the gonads, which is a reproductive organ, EDC exposure mainly induced the transcriptional upregulation of trypsin-like serine protease (Tryp) at relatively low concentrations. In the stomach, which is a digestive organ, LGBP expression was upregulated at relatively low concentrations of EDCs over 7 days, whereas all proPO system-related genes (LGBP, Tryp, serine protease inhibitor (Serpin), and peroxinectin (PE)) responded to all concentrations of EDCs. These results suggest that the antioxidant and immune defense responses of the proPO system to EDC toxicity may vary, causing different degrees of damage depending on the tissue type in the mud crab.

Bombyx mori serpin 3 is involved in innate immunity by interacting with serine protease 7 to regulate prophenoloxidase activation

A subfamily of conserved proteins called serpins plays crucial roles in various physiological functions, particularly in the activation pathway of the serine protease cascade, an essential component of insect innate immunity. Here, we found Bombyx mori serpin 3 (BmSerpin3) was most highly expressed in the fat body, and was up-regulated after exposure to bacteria, fungus and virus. Further, the expression of BmSerpin3 in the hemocytes, fat body, midgut of silkworm larvae, and BmN cells was up-regulated upon Bombyx mori nucleopolyhedrovirus (BmNPV) infection. Through Bac-to-Bac expression system, we obtained the active protein of BmSerpin3, and the enzyme activity assay showed that BmSerpin3 significantly inhibited the activity of both subtilisin and trypsin. In addition, BmSerpin3 could inhibit the activation of prophenoloxidase (PPO) in larvae. The knockdown of BmSerpin3 showed increased phenoloxidase (PO) activity compared to control after BmNPV infection. Ultimately, we confirmed that BmSerpin3 interacts with B. mori Serine Protease 7 (BmSP7). Hence, we hypothesize that BmSerpin3 is involved in innate immunity by interacting with BmSP7 to regulate the PPO activation cascade. Taken together, these results showed that BmSerpin3 play a role in silkworm innate immunity and lay a foundation for studying its functions.

Hemolymph protease-17b activates proHP6 to stimulate melanization and Toll signaling in Manduca sexta

Manduca sexta hemolymph protease-6 (HP6) plays a central role in coordinating antimicrobial responses, such as prophenoloxidase (PPO) activation and Toll signaling. Our previous studies indicated that HP5 and GP6 activate proHP6 in larval hemolymph and extraembryonic tissues, respectively. Here, we report the characterization of HP17b as another HP6 activating enzyme and its regulation by multiple serpins in hemolymph. The precursor of HP17b expressed in baculovirus infected Sf9 cells became spontaneously cleaved at two sites, and these products were purified together in one preparation named HP17b', a mixture of proHP17b, a 35 kDa intermediate, and HP17b. HP17b' converted proHP6 to HP6. As reported before, HP6 converted precursors of PPO activating protease-1 (PAP1) and HP8 to their active forms. HP8 activates proSpӓtzle-1 to turn on Toll signaling. We found HP17b' directly activated proSPHI and II to form a cofactor for PPO activation by PAP1. Supplementation of larval hemolymph with HP17b', HP17b, or proHP17b significantly increased PPO activation. Adding Micrococcus luteus to the reactions did not enhance PPO activation in the reactions containing HP17b', HP17b, or proHP17b. Using HP17b antibodies, we isolated from induced plasma HP17b fragments and associated proteins (e.g., serpin-4). Serpin-1A, 1J, 1J', 4, 5, or 6 reduced the activation of proHP6 by HP17b' through formation of covalent complexes with active HP17b. We detected an activity for proHP17b cleavage in hemolymph from bar-stage pharate pupae but failed to purify the protease due to its high instability. Other known HPs did not activate proHP17b in vitro. Together, these results suggest that HP17b is a clip-domain protease activated by an unknown endopeptidase in response to a danger signal and regulated by multiple serpins.

Transcriptomic Analysis of the Response of the Dioryctria abietella Larva Midgut to Bacillus thuringiensis 2913 Infection

Dioryctria abietella Denis Schiffermuller (Lepidoptera: Pyralidae) is an oligophagous pest that mainly damages Pinaceae plants. Here, we investigated the effects of the Bacillus thuringiensis 2913 strain (Bt 2913), which carries the Cry1Ac, Cry2Ab, and Vip3Aa genes, on the D. abietella midgut transcriptome at 6, 12, and 24 h after infection. In total, 7497 differentially expressed genes (DEGs) were identified from the midgut transcriptome of D. abietella larvae infected with Bt 2913. Among these DEGs, we identified genes possibly involved in Bt 2913-induced perforation of the larval midgut. For example, the DEGs included 67 genes encoding midgut proteases involved in Cry/Vip toxin activation, 74 genes encoding potential receptor proteins that bind to insecticidal proteins, and 19 genes encoding receptor NADH dehydrogenases that may bind to Cry1Ac. Among the three transcriptomes, 88 genes related to metabolic detoxification and 98 genes related to immune defense against Bt 2913 infection were identified. Interestingly, 145 genes related to the 60S ribosomal protein were among the DEGs identified in the three transcriptomes. Furthermore, we performed bioinformatic analysis of zonadhesin, GST, CYP450, and CarE in the D. abietella midgut to determine their possible associations with Bt 2913. On the basis of the results of this analysis, we speculated that trypsin and other serine proteases in the D. abietella larval midgut began to activate Cry/Vip prototoxin at 6 h to 12 h after Bt 2913 ingestion. At 12 h after Bt 2913 ingestion, chymotrypsin was potentially involved in degrading the active core fragment of Vip3Aa toxin, and the detoxification enzymes in the larvae contributed to the metabolic detoxification of the Bt toxin. The ABC transporter and several other receptor-protein-related genes were also downregulated to increase resistance to Bt 2913. However, the upregulation of 60S ribosomal protein and heat shock protein expression weakened the resistance of larvae to Bt 2913, thereby enhancing the expression of NADH dehydrogenase and other receptor proteins that are highly expressed in the larval midgut and bind to activating toxins, including Cry1Ac. At 24 h after Bt 2913 ingestion, many activated toxins were bound to receptor proteins such as APN in the larval midgut, resulting in membrane perforation. Here, we clarified the mechanism of Bt 2913 infection in D. abietella larvae, as well as the larval immune defense response to Bt 2913, which provides a theoretical basis for the subsequent control of D. abietella using B. thuringiensis.

Genome resequencing and genome-wide polymorphisms in mosquito vectors Aedes aegypti and Aedes albopictus from south India

Aedes aegypti and Aedes albopictus mosquitoes spread major vector-borne viral diseases in tropical and sub-tropical regions of the globe. In this study, we sequenced the genome of Indian Ae. aegypti and Ae. albopictus and mapped to their reference genomes. Comparative genomics were performed between our strain and the reference strains. A total of 14,416,484 single nucleotide polymorphisms (SNPs) and 156,487 insertions and deletions (InDels) were found in Ae. aegypti, and 28,940,433 SNPs and 188,987 InDels in Ae. albopictus. Particular emphasis was given to gene families involved in mosquito digestion, development, and innate immunity, which could be putative candidates for vector control. Serine protease cascades and their inhibitors called serpins, play a central role in these processes. We extracted high-impact variants in genes associated with serine proteases and serpins. This study reports for the first time a high coverage genome sequence data of an Indian Ae. albopictus mosquito. The results from this study will provide insights into Indian Aedes specific polymorphisms and the evolution of immune related genes in mosquitoes, which can serve as a resource for future comparative genomics and those pursuing the development of targeted biopesticides for effective mosquito control strategies.

Microsporidia secretory effectors and their roles in pathogenesis

Microsporidia, a group of unicellular eukaryotic parasites, rely intensely on secretory effectors for successful invasion and proliferation within host cells. This review focuses on the identification, characterization, and functional roles of effectors, including secretory proteins and microRNAs. The adhesion proteins like the Ricin-B-lectin facilitate initial invasion, which binds to the host cell surface. Once inside, microsporidia deploy a range of effectors to modulate host immune responses, such as serpin proteins, and redirect host cell metabolism to meet the parasite's nutritional needs through hexokinase. Some effectors such as microRNAs, alter the host gene expression to create a more favorable intracellular parasitic environment. In conclusion, the secretory effectors of microsporidia play a pivotal role spanning from host cell invasion to intracellular establishment. In the future, more effectors secreted by microsporidia will be studied, which will not only help to elucidate the molecular mechanism of pathogenic manipulation of the host but also help to provide the potential targets for anti-parasitic treatments.

The serine protease inhibitor HAMpin-1 produced by the ectoparasite Hyalomma anatolicum salivary gland modulates the host complement system

Ticks are notable vectors of diseases affecting both humans and animals, with Hyalomma anatolicum being of particular significance due to its wide distribution and capability to transmit a variety of pathogens, including Theileriaannulata and Crimean-Congo haemorrhagic fever virus. This study aimed to investigate the inhibitory effects of H. anatolicum salivary gland extract (HaSGE) and the identification of its key component on the complement system of the host's innate immune defense. We demonstrated that HaSGE exerts a dose-dependent inhibition on the complement activation in a host-specific manner. Mechanistic studies revealed that HaSGE interferes with deposition and cleavage of complement proteins C3 and C5, thus preventing the formation of the membrane attack complex. Further, we identified a serine protease inhibitor, Hyalomma anatolicum serpin-1 (HAMpin-1), from the HaSGE through proteomic analysis and characterized its structure, function, and interaction with complement proteins. HAMpin-1 exhibited potent inhibitory activity against chymotrypsin and cathepsin-G, and notably, it is the first serpin from ticks shown to inhibit the classical and lectin pathways of the complement system. The expression of HAMpin-1 was highest in the salivary glands, suggesting its crucial role in blood feeding and immune evasion. Our findings revealed one of the potential mechanisms used by H. anatolicum to modulate host immune responses at the interface, offering new insights into tick-host interactions.

The Crystal Structure of the Michaelis-Menten Complex of C1 Esterase Inhibitor and C1s Reveals Novel Insights into Complement Regulation

The ancient arm of innate immunity known as the complement system is a blood proteolytic cascade involving dozens of membrane-bound and solution-phase components. Although many of these components serve as regulatory molecules to facilitate controlled activation of the cascade, C1 esterase inhibitor (C1-INH) is the sole canonical complement regulator belonging to a superfamily of covalent inhibitors known as serine protease inhibitors (SERPINs). In addition to its namesake role in complement regulation, C1-INH also regulates proteases of the coagulation, fibrinolysis, and contact pathways. Despite this, the structural basis for C1-INH recognition of its target proteases has remained elusive. In this study, we present the crystal structure of the Michaelis-Menten (M-M) complex of the catalytic domain of complement component C1s and the SERPIN domain of C1-INH at a limiting resolution of 3.94 Å. Analysis of the structure revealed that nearly half of the protein/protein interface is formed by residues outside of the C1-INH reactive center loop. The contribution of these residues to the affinity of the M-M complex was validated by site-directed mutagenesis using surface plasmon resonance. Parallel analysis confirmed that C1-INH-interfacing residues on C1s surface loops distal from the active site also drive affinity of the M-M complex. Detailed structural comparisons revealed differences in substrate recognition by C1s compared with C1-INH recognition and highlight the importance of exosite interactions across broader SERPIN/protease systems. Collectively, this study improves our understanding of how C1-INH regulates the classical pathway of complement, and it sheds new light on how SERPINs recognize their cognate protease targets.

Effect of acute exposure of Hg on physiological parameters and transcriptome expression in silkworms (Bombyx mori)

Mercury (Hg) contamination poses a global threat to the environment, given its elevated ecotoxicity. Herein, we employed the lepidopteran model insect, silkworm (Bombyx mori), to systematically investigate the toxic effects of Hg-stress across its growth and development, histomorphology, antioxidant enzyme activities, and transcriptome responses. High doses of Hg exposure induced evident poisoning symptoms, markedly impeding the growth of silkworm larvae and escalating mortality in a dose-dependent manner. Under Hg exposure, the histomorphology of both the midgut and fat body exhibited impairments. Carboxylesterase (CarE) activity was increased in both midgut and fat body tissues responding to Hg treatment. Conversely, glutathione S-transferase (GST) levels increased in the fat body but decreased in the midgut. The transcriptomic analysis revealed that the response induced by Hg stress involved multiple metabolism processes. Significantly differently expressed genes (DEGs) exhibited strong associations with oxidative phosphorylation, nutrient metabolisms, insect hormone biosynthesis, lysosome, ribosome biogenesis in eukaryotes, and ribosome pathways in the midgut or the fat body. The findings implied that exposure to Hg might induce the oxidative stress response, attempting to compensate for impaired metabolism. Concurrently, disruptions in nutrient metabolism and insect hormone activity might hinder growth and development, leading to immune dysfunction in silkworms. These insights significantly advance our theoretical understanding of the potential mechanisms underlying Hg toxicity in invertebrate organisms.

Comprehensive Proteomics Analysis of the Hemolymph Composition of Sugar-Fed Aedes aegypti Female and Male Mosquitoes

In arthropods, hemolymph carries immune cells and solubilizes and transports nutrients, hormones, and other molecules that are involved in diverse physiological processes including immunity, metabolism, and reproduction. However, despite such physiological importance, little is known about its composition. We applied mass spectrometry-based label-free quantification approaches to study the proteome of hemolymph perfused from sugar-fed female and male Aedes aegypti mosquitoes. A total of 1403 proteins were identified, out of which 447 of them were predicted to be extracellular. In both sexes, almost half of these extracellular proteins were predicted to be involved in defense/immune response, and their relative abundances (based on their intensity-based absolute quantification, iBAQ) were 37.9 and 33.2%, respectively. Interestingly, among them, 102 serine proteases/serine protease-homologues were identified, with almost half of them containing CLIP regulatory domains. Moreover, proteins belonging to families classically described as chemoreceptors, such as odorant-binding proteins (OBPs) and chemosensory proteins (CSPs), were also highly abundant in the hemolymph of both sexes. Our data provide a comprehensive catalogue of A. aegypti hemolymph basal protein content, revealing numerous unexplored targets for future research on mosquito physiology and disease transmission. It also provides a reference for future studies on the effect of blood meal and infection on hemolymph composition.

Shared Transcriptomic Signatures of Inflammaging Among Diverse Strains of Drosophila melanogaster

Background

A prominent hallmark of aging is inflammaging-the increased expression of innate immune genes without identifiable infection. Model organisms with shorter lifespans, such as the fruit fly, provide an essential platform for probing the mechanisms of inflammaging. Multiple groups have reported that, like mammalian models, old flies have significantly higher levels of expression of anti-microbial peptide genes. However, whether some of these genes-or any others-can serve as reliable markers for assessing and comparing inflammaging in different strains remains unclear.

Methods and Results

We compared RNA-Seq datasets generated by different groups. Although the fly strains used in these studies differ significantly, we found that they share a core group of genes with strong aging-associated expression. In addition to anti-microbial peptide genes, we identified other genes that have prominently increased expression in old flies, especially SPH93. We further showed that machine learning models can be used to predict the "inflammatory age" of the fruit y.

Conclusion

A core group of genes may serve as markers for studying inflammaging in Drosophila. RNA-Seq profiles, in combination with machine-learning models, can be applied to measure the acceleration or deceleration of inflammaging.

Immune protection of three serine protease inhibitors vaccine in mice against Rhipicephalus sanguineus

Bioactive molecules in tick saliva are considered to be key to successful feeding and further the transmission of tick-borne pathogens. Problems such as pathogen transmission and animal weight loss result in tick infestation can cause tremendous economic losses to the livestock industry. Therefore, the development of a universal tick vaccine is urgently needed. In this paper, three serine protease inhibitor (serpin) proteins RMS-3, L7LRK7 and L7LTU1 were analyzed with bioinformatics methods. Subsequently the proteins were expressed and purified, and inoculated into Kunming mice for immune protection analysis. The amino acid sequence similarities between RMS-3, L7LRK7 and L7LTU1 were up to 90% in Rhipicephalus sanguineus. The recombinant RMS-3 + L7LRK7 + L7LTU1 showed anticoagulant reaction function and could inhibit the activity of CD4+ lymphocytes, when inoculated into Kunming mice. Additionally, After the immunized mice were challenged with Rhipicephalus sanguineus, the percentage of larvae and nymphs that were fully engorged dropped to 40.87% (P < 0.05) and 87.68% (P > 0.05) in the RmS-3 + L7LRK7 immune group, 49.57% (P < 0.01) and 52.06% (P < 0.05) in the RmS-3 + L7LTU1 group, and 45.22% (P < 0.05) and 60.28% (P < 0.05) in the RmS-3 + L7LRK7 + L7LTU1 immune group, in comparison with the control group. These data indicate that RmS-3 + L7LRK7 + L7LTU1 has good immune protection and has the potential to be developed into a vaccine against the larvae and nymphs of R. sanguineus.

MicroRNA Targets PAP1 to Mediate Melanization in Plutella xylostella (Linnaeus) Infected by Metarhizium anisopliae

MicroRNAs (miRNAs) play a pivotal role in important biological processes by regulating post-transcriptional gene expression and exhibit differential expression patterns during development, immune responses, and stress challenges. The diamondback moth causes significant economic damage to crops worldwide. Despite substantial advancements in understanding the molecular biology of this pest, our knowledge regarding the role of miRNAs in regulating key immunity-related genes remains limited. In this study, we leveraged whole transcriptome resequencing data from Plutella xylostella infected with Metarhizium anisopliae to identify specific miRNAs targeting the prophenoloxidase-activating protease1 (PAP1) gene and regulate phenoloxidase (PO) cascade during melanization. Seven miRNAs (pxy-miR-375-5p, pxy-miR-4448-3p, pxy-miR-279a-3p, pxy-miR-3286-3p, pxy-miR-965-5p, pxy-miR-8799-3p, and pxy-miR-14b-5p) were screened. Luciferase reporter assays confirmed that pxy-miR-279a-3p binds to the open reading frame (ORF) and pxy-miR-965-5p to the 3' untranslated region (3' UTR) of PAP1. Our experiments demonstrated that a pxy-miR-965-5p mimic significantly reduced PAP1 expression in P. xylostella larvae, suppressed PO activity, and increased larval mortality rate. Conversely, the injection of pxy-miR-965-5p inhibitor could increase PAP1 expression and PO activity while decreasing larval mortality rate. Furthermore, we identified four LncRNAs (MSTRG.32910.1, MSTRG.7100.1, MSTRG.6802.1, and MSTRG.22113.1) that potentially interact with pxy-miR-965-5p. Interference assays using antisense oligonucleotides (ASOs) revealed that silencing MSTRG.7100.1 and MSTRG.22113.1 increased the expression of pxy-miR-965-5p. These findings shed light on the potential role of pxy-miR-965-5p in the immune response of P. xylostella to M. anisopliae infection and provide a theoretical basis for biological control strategies targeting the immune system of this pest.

An evolutionarily conserved serine protease network mediates melanization and Toll activation in Drosophila

Melanization and Toll pathway activation are essential innate immune mechanisms in insects, which result in the generation of reactive compounds and antimicrobial peptides, respectively, to kill pathogens. These two processes are mediated by phenoloxidase (PO) and Spätzle (Spz) through an extracellular network of serine proteases. While some proteases have been identified in Drosophila melanogaster in genetic studies, the exact order of proteolytic activation events remains controversial. Here, we reconstituted the serine protease framework in Drosophila by biochemical methods. This system comprises 10 proteases, i.e., ModSP, cSP48, Grass, Psh, Hayan-PA, Hayan-PB, Sp7, MP1, SPE and Ser7, which form cascade pathways that recognize microbial molecular patterns and virulence factors, and generate PO1, PO2, and Spz from their precursors. Furthermore, the serpin Necrotic negatively regulates the immune response progression by inhibiting ModSP and Grass. The biochemical approach, when combined with genetic analysis, is crucial for addressing problems that long stand in this important research field.

Parasitoid Serpins Evolve Novel Functions to Manipulate Host Homeostasis

Parasitoids introduce various virulence factors when parasitism occurs, and some taxa generate teratocytes to manipulate the host immune system and metabolic homeostasis for the survival and development of their progeny. Host-parasitoid interactions are extremely diverse and complex, yet the evolutionary dynamics are still poorly understood. A category of serpin genes, named CvT-serpins, was discovered to be specifically expressed and secreted by the teratocytes of Cotesia vestalis, an endoparasitoid of the diamondback moth Plutella xylostella. Genomic and phylogenetic analysis indicated that the C. vestalis serpin genes are duplicated and most of them are clustered into 1 monophyletic clade. Intense positive selection was detected at the residues around the P1-P1' cleavage sites of the Cv-serpin reactive center loop domain. Functional analyses revealed that, in addition to the conserved function of melanization inhibition (CvT-serpins 1, 16, 18, and 21), CvT-serpins exhibited novel functions, i.e. bacteriostasis (CvT-serpins 3 and 5) and nutrient metabolism regulation (CvT-serpins 8 and 10). When the host-parasitoid system is challenged with foreign bacteria, CvT-serpins act as an immune regulator to reprogram the host immune system through sustained inhibition of host melanization while simultaneously functioning as immune effectors to compensate for this suppression. In addition, we provided evidence that CvT-serpin8 and 10 participate in the regulation of host trehalose and lipid levels by affecting genes involved in these metabolic pathways. These findings illustrate an exquisite tactic by which parasitoids win out in the parasite-host evolutionary arms race by manipulating host immune and nutrition homeostasis via adaptive gene evolution and neofunctionalization.

A Genome-Wide Analysis of Serine Protease Inhibitors in Cydia pomonella Provides Insights into Their Evolution and Expression Pattern

Serine protease inhibitors (serpins) appear to be ubiquitous in almost all living organisms, with a conserved structure and varying functions. Serpins can modulate immune responses by negatively regulating serine protease activities strictly and precisely. The codling moth, Cydia pomonella (L.), a major invasive pest in China, can cause serious economic losses. However, knowledge of serpin genes in this insect remain largely unknown. In this study, we performed a systematic analysis of the serpin genes in C. pomonella, obtaining 26 serpins from the C. pomonella genome. Subsequently, their sequence features, evolutionary relationship, and expression pattern were characterized. Comparative analysis revealed the evolution of a number of serpin genes in Lepidoptera. Importantly, the evolutionary relationship and putative roles of serpin genes in C. pomonella were revealed. Additionally, selective pressure analysis found amino acid sites with strong evidence of positive selection. Interestingly, the serpin1 gene possessed at least six splicing isoforms with distinct reactive-center loops, and these isoforms were experimentally validated. Furthermore, we observed a subclade expansion of serpins, and these genes showed high expression in multiple tissues, suggesting their important roles in C. pomonella. Overall, this study will enrich our knowledge of the immunity of C. pomonella and help to elucidate the role of serpins in the immune response.

Ixodes scapularis nymph saliva protein blocks host inflammation and complement-mediated killing of Lyme disease agent, Borrelia burgdorferi

Tick serine protease inhibitors (serpins) play crucial roles in tick feeding and pathogen transmission. We demonstrate that Ixodes scapularis (Ixs) nymph tick saliva serpin (S) 41 (IxsS41), secreted by Borrelia burgdorferi (Bb)-infected ticks at high abundance, is involved in regulating tick evasion of host innate immunity and promoting host colonization by Bb. Recombinant (r) proteins were expressed in Pichia pastoris, and substrate hydrolysis assays were used to determine. Ex vivo (complement and hemostasis function related) and in vivo (paw edema and effect on Bb colonization of C3H/HeN mice organs) assays were conducted to validate function. We demonstrate that rIxsS41 inhibits chymase and cathepsin G, pro-inflammatory proteases that are released by mast cells and neutrophils, the first immune cells at the tick feeding site. Importantly, stoichiometry of inhibition analysis revealed that 2.2 and 2.8 molecules of rIxsS41 are needed to 100% inhibit 1 molecule of chymase and cathepsin G, respectively, suggesting that findings here are likely events at the tick feeding site. Furthermore, chymase-mediated paw edema, induced by the mast cell degranulator, compound 48/80 (C48/80), was blocked by rIxsS41. Likewise, rIxsS41 reduced membrane attack complex (MAC) deposition via the alternative and lectin complement activation pathways and dose-dependently protected Bb from complement killing. Additionally, co-inoculating C3H/HeN mice with Bb together with rIxsS41 or with a mixture (rIxsS41 and C48/80). Findings in this study suggest that IxsS41 markedly contributes to tick feeding and host colonization by Bb. Therefore, we conclude that IxsS41 is a potential candidate for an anti-tick vaccine to prevent transmission of the Lyme disease agent.

Serpin-1a and serpin-6 regulate the Toll pathway immune homeostasis by synergistically inhibiting the Spätzle-processing enzyme CLIP2 in silkworm, Bombyx mori

The Toll receptor signaling pathway is an important innate immune response of insects to pathogen infection; its extracellular signal transduction involves serine protease cascade activation. However, excessive or constitutive activation of the Toll pathway can be detrimental. Hence, the balance between activation and inhibition of the extracellular protease cascade must be tightly regulated to achieve favorable outcomes. Previous studies have shown that serpins-serine protease inhibitors-negatively regulate insect innate immunity by inhibiting extracellular protease cascade signaling. Although the roles of serpins in insect innate immunity are well described, the physiological mechanisms underlying their synergistic effects remain poorly understand. Here, we characterize the molecular mechanism by which serpin-1a and serpin-6 synergistically maintain immune homeostasis of the silkworm Toll pathway under physiological and pathological conditions. Through in vitro biochemical assays and in vivo bioassays, we demonstrate that clip-domain serine protease 2 (CLIP2), as the Toll cascade-activating terminal protease, is responsible for processing proSpätzle1 to induce the expression of antimicrobial peptides. Further biochemical and genetic analyses indicate that constitutively expressed serpin-1a and inducible serpin-6 synergistically target CLIP2 to maintain homeostasis of the silkworm Toll pathway under physiological and pathological conditions. Taken together, this study provides new insights into the precise regulation of Toll cascade activation signals in insect innate immune responses and highlights the importance and complexity of insect immune homeostasis regulation.

A serpin gene from a parasitoid wasp disrupts host immunity and exhibits adaptive alternative splicing

Alternative splicing (AS) is a major source of protein diversity in eukaryotes, but less is known about its evolution compared to gene duplication (GD). How AS and GD interact is also largely understudied. By constructing the evolutionary trajectory of the serpin gene PpSerpin-1 (Pteromalus puparum serpin 1) in parasitoids and other insects, we found that both AS and GD jointly contribute to serpin protein diversity. These two processes are negatively correlated and show divergent features in both protein and regulatory sequences. Parasitoid wasps exhibit higher numbers of serpin protein/domains than nonparasitoids, resulting from more GD but less AS in parasitoids. The potential roles of AS and GD in the evolution of parasitoid host-effector genes are discussed. Furthermore, we find that PpSerpin-1 shows an exon expansion of AS compared to other parasitoids, and that several isoforms are involved in the wasp immune response, have been recruited to both wasp venom and larval saliva, and suppress host immunity. Overall, our study provides an example of how a parasitoid serpin gene adapts to parasitism through AS, and sheds light on the differential features of AS and GD in the evolution of insect serpins and their associations with the parasitic life strategy.

Transcriptomic Analysis Reveals the Impact of the Biopesticide Metarhizium anisopliae on the Immune System of Major Workers in Solenopsis invicta

The red imported fire ant (Solenopsis invicta Buren, 1972) is a globally significant invasive species, causing extensive agricultural, human health, and biodiversity damage amounting to billions of dollars worldwide. The pathogenic fungus Metarhizium anisopliae (Metchnikoff) Sorokin (1883), widely distributed in natural environments, has been used to control S. invicta populations. However, the interaction between M. anisopliae and the immune system of the social insect S. invicta remains poorly understood. In this study, we employed RNA-seq to investigate the effects of M. anisopliae on the immune systems of S. invicta at different time points (0, 6, 24, and 48 h). A total of 1313 differentially expressed genes (DEGs) were identified and classified into 12 expression profiles using short time-series expression miner (STEM) for analysis. Weighted gene co-expression network analysis (WGCNA) was employed to partition all genes into 21 gene modules. Upon analyzing the statistically significant WGCNA model and conducting Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis on the modules, we identified key immune pathways, including the Toll and Imd signaling pathways, lysosomes, autophagy, and phagosomes, which may collectively contribute to S. invicta defense against M. anisopliae infection. Subsequently, we conducted a comprehensive scan of all differentially expressed genes and identified 33 immune-related genes, encompassing various aspects such as recognition, signal transduction, and effector gene expression. Furthermore, by integrating the significant gene modules derived from the WGCNA analysis, we constructed illustrative pathway diagrams depicting the Toll and Imd signaling pathways. Overall, our research findings demonstrated that M. anisopliae suppressed the immune response of S. invicta during the early stages while stimulating its immune response at later stages, making it a potential biopesticide for controlling S. invicta populations. These discoveries lay the foundation for further understanding the immune mechanisms of S. invicta and the molecular mechanisms underlying its response to M. anisopliae.

Crude saliva of Amblyomma cajennense sensu stricto (Acari: Ixodidae) reduces locomotor activity and increases the hemocyte number in the females of Aedes aegypti (Diptera: Culicidae)

Aedes aegypti are vector insects of arboviruses such as dengue, Zika, and chikungunya. All available vector control methods have limited efficacy, highlighting the urgent need to find alternative ones. Evidence shows that arachnids like ticks are sources of biologically active compounds. Moreover, chemical modulation of the locomotor and immune systems of vector insects can be used to control arbovirus transmission. The present study evaluated the effectiveness of crude saliva of female Amblyomma cajennense sensu stricto (s.s.) ticks in reducing locomotor activity and inducing an immune response in Ae. aegypti females. Additionally, the study evaluated the protein constitution of tick saliva. For this purpose, the crude saliva obtained from several semi-engorged A. cajennense females was used. A volume of 0.2 nL of crude tick saliva was administered to mosquitoes by direct intrathoracic microinjection. The effect of the tick's saliva on the locomotor activity of the mosquito was observed using Flybox, a video-automated monitoring system, and the hemolymph hemocyte levels were quantified by reading slides under a light microscope. The protein concentration of the crude tick saliva was 1.27 μg/μL, and its electrophoretic profile indicates the presence of proteins with a molecular weight ranging between ∼17 and 95 kDa. Microplusins, ixodegrins, cystatin, actins, beta-actin, calponin, albumin, alpha-globulins, and hemoglobin were the main proteins identified by proteomics in the saliva of A. cajennense. The microinjected saliva had low toxicity for Ae. aegypti females and significantly reduced their locomotor activity, especially in the transition between the light and dark phases. The crude tick saliva did not change the period and rhythmicity of the circadian cycle. The tick saliva significantly increased the number of hemocytes two days after injection and reduced it after five days. These results suggest that further evaluation of the biological properties of tick saliva proteins against Ae. aegypti would be of interest.

The tracheal immune system of insects - A blueprint for understanding epithelial immunity

The unique design of respiratory organs in multicellular organisms makes them prone to infection by pathogens. To cope with this vulnerability, highly effective local immune systems evolved that are also operative in the tracheal system of insects. Many pathogens and parasites (including viruses, bacteria, fungi, and metazoan parasites) colonize the trachea or invade the host via this route. Currently, only two modules of the tracheal immune system have been characterized in depth: 1) Immune deficiency pathway-mediated activation of antimicrobial peptide gene expression and 2) local melanization processes that protect the structure from wounding. There is an urgent need to increase our understanding of the architecture of tracheal immune systems, especially regarding those mechanisms that enable the maintenance of immune homeostasis. This need for new studies is particularly exigent for species other than Drosophila.

Vaccination with a cocktail vaccine elicits significant protection against Sarcoptes scabiei in rabbits, whereas the multi-epitope vaccine offers limited protection

Sarcoptes scabiei cause scabies in humans or sarcoptic mange in animals. Currently, information regarding vaccines against S. scabiei is limited and no commercial vaccine is available. In present study, we expressed and mixed recombinant S. scabiei serpin (rSs-serpin), recombinant S. scabiei chitinase-like protein-5 [rSs-CLP5] and -12 [rSs-CLP12] as a cocktail vaccine (three proteins mixed), and also a multi-epitope protein derived from these three S. scabiei genes was expressed as a vaccine candidate to evaluate the effects of two vaccine strategies. Four test groups (n = 12 per group) and a control group (n = 12 per group) were involved in this vaccination trial. The results showed that 91.67% (11/12) and 83.33% (10/12) of rabbits exhibited no detectable skin lesions from S. scabiei infestation in cocktail vaccine groups, whereas two multi-epitope groups produced only a few rabbits (5/12, 6/12) having no detectable skin lesions. Four test groups displayed significant increases in specific IgG antibodies (Abs) and total IgE Abs after immunized with recombinant proteins. Taken together, our data demonstrated a mixture of rSs-serpin, rSs-CLP5 and rSs-CLP12 was a promising vaccine candidate that induced robust immune protection and could significantly decrease mite populations to reduce the direct transmission between rabbits. However, vaccination with the multi-epitope protein showed limited protection in rabbits.

Two venom serpins from the parasitoid wasp Microplitis mediator inhibit the host prophenoloxidase activation and antimicrobial peptide synthesis

Endoparasitoid wasps inject venom proteins into the hemocoel of host insects to ensure survival, growth, and development of their progenies by blocking host immunity. We previously identified ten serine protease inhibitors of the serpin superfamily in venom of the endoparasitoid wasp, Microplitis mediator, but it is unclear how these inhibitors may interact with host immune serine proteases. In this study, we investigated the functions of two serpins, MmvSPN-1 and MmvSPN-2, in the regulation of humoral immune responses in two hosts, the oriental armyworm Pseudaletia separate and the cotton bollworm Helicoverpa armigera, by dsRNA knockdown and biochemical assays using recombinant proteins. Knockdown of the two serpins resulted in increases in prophenoloxidase (PPO) activation and antimicrobial peptide (AMP) production in the hosts. After injection into the host hemocoel, the recombinant serpins inhibited PPO activation and AMP transcription. Mass spectrometry analysis of the pull-downs and in vitro reconstitution experiments revealed that HacSP29, a clip-domain serine protease in H. armigera, is the target of these two serpins. Therefore, these two inhibitors in the wasp venom may protect eggs from attacks by melanization and AMPs in the host insects.

Characterization and expression profiling of serine protease inhibitors in the yellow mealworm Tenebrio molitor

Serine protease inhibitors (SPIs) act in diverse biological processes in insects such as immunity, development, and digestion by preventing the unwanted proteolysis. So far, the repertoire of genes encoding SPIs has been identified from few insect species. In this study, 62 SPI genes were identified from the genome of the yellow mealworm, Tenebrio molitor. According to their modes of action, they were classified into three families, serpin (26), canonical SPI (31), and α-macroglobulins (A2M) (5). These SPIs feature eight domains including serpin, Kazal, TIL, Kunitz, WAP, Antistasin, pacifastin, and A2M. In total, 39 SPIs contain a single SPI domain, while the others encode at least two inhibitor units. Based on the amino acids in the cleaved reactive sites, the abilities of these SPIs to inhibit trypsin, chymotrypsin, or elastase-like enzymes are predicted. The expression profiling based on the RNA-seq data showed that these genes displayed stage-specific expression patterns during development, suggesting to us their significance in development. Some of the SPI genes were exclusively expressed in particular tissues such as hemocyte, fat body, gut, ovary, and testis, which may be involved in biological processes specific to the indicated tissues. These findings provide necessary information for further investigation of insect SPIs.

Unprocessed wheat γ-gliadin reduces gluten accumulation associated with the endoplasmic reticulum stress and elevated cell death

Along with increasing demands for high yield, elite processing quality and improved nutrient value in wheat, concerns have emerged around the effects of gluten in wheat-based foods on human health. However, knowledge of the mechanisms regulating gluten accumulation remains largely unexplored. Here we report the identification and characterization of a wheat low gluten protein 1 (lgp1) mutant that shows extremely low levels of gliadins and glutenins. The lgp1 mutation in a single γ-gliadin gene causes defective signal peptide cleavage, resulting in the accumulation of an excessive amount of unprocessed γ-gliadin and a reduced level of gluten, which alters the endoplasmic reticulum (ER) structure, forms the autophagosome-like structures, leads to the delivery of seed storage proteins to the extracellular space and causes a reduction in starch biosynthesis. Physiologically, these effects trigger ER stress and cell death. This study unravels a unique mechanism that unprocessed γ-gliadin reduces gluten accumulation associated with ER stress and elevated cell death in wheat. Moreover, the reduced gluten level in the lgp1 mutant makes it a good candidate for specific diets for patients with diabetes or kidney diease.

Proteomic analysis of pharate pupal molting fluid from the tobacco hornworm, Manduca sexta

The insect cuticle is a key component of their success, being important for protection, communication, locomotion, and support. Conversely, as an exoskeleton, it also limits the size of the insect and must be periodically molted and a new one synthesized, to permit growth. To achieve this, the insect secretes a solution of chitinases, proteases and other proteins, known collectively as molting fluid, during each molting process to break down and recycle components of the old cuticle. Previous research has focused on the degradative enzymes in molting fluid and offered some characterization of their biochemical properties. However, identification of the specific proteins involved remained to be determined. We have used 2D SDS-PAGE and LC/MS-based proteomic analysis to identify proteins in the molting fluid of the tobacco hornworm, Manduca sexta, undergoing the larval to pupal molt. We categorized these proteins based on their proposed functions including chitin metabolism, proteases, peptidases, and immunity. This analysis complements previous reported work on M. sexta molting fluid and identifies candidate genes for enzymes involved in cuticle remodeling. Proteins classified as having an immune function highlight potential for molting fluid to act as an immune barrier to prevent infections during the cuticle degradation and ecdysis processes. Several proteins known to function in melanin synthesis as an immune response in hemolymph were present in molting fluid. We demonstrated that the bacterium Micrococcus luteus and the entomopathogenic fungus Beauveria bassiana can stimulate activation of phenoloxidase in molting fluid, indicating that the recognition proteins, protease cascade, and prophenoloxidase needed for melanin synthesis are present as a defense against infection during cuticle degradation. This analysis offers insights for proteins that may be important not only for molting in M. sexta but for insects in general.

Pre-exposure to Candida albicans induce trans-generational immune priming and gene expression of Musca domestica

Insects have the phenomenon of immune priming by which they can have enhanced protection against reinfection with the same pathogen, and this immune protection can be passed on to their offspring, which is defined as “trans-generational immune priming (TGIP).” But whether housefly possesses TGIP is still unclear. Therefore, we used the housefly as the insect model and Candida albicans as the pathogen to explore whether the housefly is capable of eliciting TGIP, and RNA sequencing (RNA-seq) was performed to explore the molecular mechanism of TGIP of the housefly. We found that the housefly possesses TGIP, and adults pre-exposed to heat-killed C. albicans could confer protection to itself and its offspring upon reinfection with a lethal dose of C. albicans. RNA-seq results showed that 30 and 154 genes were differentially expressed after adults were primed with heat-killed C. albicans (CA-A) and after offspring larvae were challenged with a lethal dose of C. albicans (CA-CA-G), respectively. Among the differentially expressed genes (DEGs), there were 23 immune genes, including 6 pattern recognition receptors (PRRs), 7 immune effectors, and 10 immunoregulatory molecules. More importantly, multiple DEGs were involved in the Toll signaling pathway and phagosome signaling pathway, suggesting that the Toll signaling pathway and phagocytosis might play important roles in the process of TGIP of housefly to C. albicans. Our results expanded on previous studies and provided parameters for exploring the mechanism of TGIP.

A mechanistic analysis of bacterial recognition and serine protease cascade initiation in larval hemolymph of Manduca sexta

Serine protease cascades have evolved in vertebrates and invertebrates to mediate rapid defense responses. Previous biochemical studies showed that in hemolymph of a caterpillar, Manduca sexta, recognition of fungi by β-1,3-glucan recognition proteins (βGRP1 and βGRP2) or recognition of bacteria by peptidoglycan recognition protein-1 (PGRP1) and microbe binding protein (MBP) results in autoactivation of hemolymph protease-14 precursor (proHP14). HP14 then activates downstream members of a protease cascade leading to the melanization immune response. ProHP14 has a complex domain architecture, with five low-density lipoprotein receptor class A repeats at its amino terminus, followed by a Sushi domain, a Sushi domain variant called Wonton, and a carboxyl-terminal serine protease catalytic domain. Its zymogen form is activated by specific proteolytic cleavage at the amino-terminal end of the protease domain. While a molecular mechanism for recognition and triggering the response to β-1,3-glucan has been delineated, it is unclear how bacterial recognition stimulates proHP14 activation. To fill this knowledge gap, we expressed the two domains of M. sexta MBP and found that the amino-terminal domain binds to diaminopimelic acid-peptidoglycan (DAP-PG). ProHP14 bound to both the carboxyl-terminal domain (MBP-C) and amino-terminal domain (MBP-N) of MBP. In the mixture of DAP-PG, MBP, and larval plasma, inclusion of an HP14 fragment composed of LDLa repeats 2-5 (LDLa2-5) or MBP-C significantly reduced prophenoloxidase activation, likely by competing with the interactions of the full-length proteins, and suggesting that molecular interactions involving these regions of proHP14 and MBP take part in proHP14 activation in response to peptidoglycan. Using a series of N-terminally truncated versions of proHP14, we found that autoactivation required LDLa2-5. The optimal ratio of PGRP1, MBP, and proHP14 is close to 3:2:1. In summary, proHP14 autoactivation by DAP-type peptidoglycan requires binding of DAP-PG by PGRP1 and the MBP N-terminal domain and association of the LDLa2-5 region of proHP14 with the MBP C-terminal domain. These interactions may concentrate the proHP14 zymogen at the bacterial cell wall surface and promote autoactivation.

Ovi-protective mothers: exploring the proteomic profile of weevil (Gonipterus) egg capsules

Insects of different orders produce elaborate structures to protect their eggs from the many threats they may face from the environment and natural enemies. In the weevil genus Gonipterus, their dark, hardened egg capsule is possibly generated by a mixture of the insects' excrement and glandular substances. To test this hypothesis, this study focused on the elucidation of protein components present in the egg capsule cover and interrogated them through comparative analysis and gene expression to help infer potential functions. First, female Gonipterus sp. n. 2 reproductive and alimentary tissues were isolated to establish a reference transcriptome-derived protein database. Then, proteins from weevil frass (excrement) and egg capsule cover were identified through mass spectrometry proteomics. We found that certain egg capsule cover proteins were both exclusive and shared between frass and egg capsule cover, including those of plant origin (e.g. photosystem II protein) and others secreted by the weevil, primarily from reproductive tissue. Among them, a mucin/spidroin-like protein and novel proteins with repetitive units that likely play a structural role were identified. We have confirmed the dual origin of the egg capsule cover substance as a blend of the insects’ frass and secretions. Novel proteins secreted by the weevils are key candidates for holding the egg case cover together.

An endoparasitoid uses its egg surface proteins to regulate its host immune response

With proteomic analysis, we identified 379 egg surface proteins from an endoparasitoid, Cotesia chilonis. Proteins containing conserved enzymatic domains constitute a large proportion of egg surface components. Some proteins, such as superoxidase dismutase, homolog of C. rubecula 32-kDa protein, and immunoevasive protein-2A, are classical parasitism factors that have known functions in host immunity regulation. Melanization assays revealed that a novel egg surface protein, C. chilonis egg surface serpin domain-containing protein had the same function as a C. chilonis venom serpin, as both suppressed host melanization in a dose-dependent manner. C. chilonis egg surface serpin domain-containing protein is mainly transcribed in C. chilonis oocytes with follicular cells, and it is located on both the anterior and posterior sides of the mature egg surface. Additionally, we used LC-MS/MS to identify 586 binding proteins sourced from C. suppressalis plasma located on the eggshell surface of C. chilonis, which included some immunity-related proteins. These results not only indicate that C. chilonis uses its egg surface proteins to reduce the immune response of its host but also imply that endoparasitoid egg surface proteins might be a new parasitism factor involved in host immune regulation.

Serpin-4 Facilitates Baculovirus Infection by Inhibiting Melanization in Asian Corn Borer, Ostrinia furnacalis (Guenée)

Phenoloxidase (PO)-catalyzed melanization is a vital immune response in insects for defense against pathogen infection. This process is mediated by clip domain serine proteases and regulated by members of the serpin superfamily. We here revealed that the infection of Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) significantly inhibited the PO activity in Ostrinia furnacalis hemolymph and induced the expression of O. furnacalis serpin-4. Addition of recombinant serpin-4 protein to O. furnacalis hemolymph resulted in a great increase of AcMNPV copies. Serpin-4 significantly suppressed the PO activity and the amidase activity in cleaving colorimetric substrate IEARpNA (IEARase activity) of hemolymph. Further experiments indicated it formed covalent complexes with three serine proteases (SP1, SP13 and SP105) and prevented them from cleaving their cognate downstream proteases in vitro. Altogether, O. furnacalis melanization restricted AcMNPV replication and serpin-4 facilitated AcMNPV infection by inhibiting serine proteases, SP1, SP13, and SP105 which were all involved in the melanization response.

KPI5 Is Involved in the Regulation of the Expression of Antibacterial Peptide Genes and Hemolymph Melanization in the Silkworm, Bombyx mori

Kunitz-type protease inhibitors (KPIs) are ubiquitously found in many organisms, and participate in various physiological processes. However, their function in insects remains to be elucidated. In the present study, we characterized and functionally analyzed silkworm KPI5. Sequence analysis showed that KPI5 contains 85 amino acids with six conserved cysteine residues, and the P1 site is a phenylalanine residue. Inhibitory activity and stability analyses indicated that recombinant KPI5 protein significantly inhibited the activity of chymotrypsin and was highly tolerant to temperature and pH. The spatio-temporal expression profile analysis showed that KPI5 was synthesized in the fat body and secreted into the hemolymph. In vivo induction analysis showed that the expression of KPI5 in the fat body was significantly upregulated by pathogen-associated molecular patterns (PAMPs). Binding assays suggested that KPI5 can bind to pathogens and PAMPs. In vitro pathogen growth inhibition assay and encapsulation analysis indicated that KPI5 can neither kill pathogenic bacteria directly nor promote the encapsulation of agarose beads by silkworm hemocytes. Recombinant protein injection test and CRISPR/Cas9-mediated knockdown showed that KPI5 promotes the expression of antimicrobial peptides (AMPs) in the fat body. Moreover, the survival rate of individuals in the KPI5 knockdown group was significantly lower than that of the control group after pathogen infection. Phenoloxidase (PO) activity assays showed that KPI5 significantly inhibited the hemolymph PO activity and melanization induced by PAMPs. These findings suggested that KPI5 plays a dual regulatory role in innate immunity by promoting the expression of antimicrobial peptides in the fat body and inhibiting hemolymph melanization. Our study furthers the understanding of the function of insect KPIs and provides new insights into the regulatory mechanism of insect immune homeostasis.

Serpins in Tick Physiology and Tick-Host Interaction

Tick saliva has been extensively studied in the context of tick-host interactions because it is involved in host homeostasis modulation and microbial pathogen transmission to the host. Accumulated knowledge about the tick saliva composition at the molecular level has revealed that serine protease inhibitors play a key role in the tick-host interaction. Serpins are one highly expressed group of protease inhibitors in tick salivary glands, their expression can be induced during tick blood-feeding, and they have many biological functions at the tick-host interface. Indeed, tick serpins have an important role in inhibiting host hemostatic processes and in the modulation of the innate and adaptive immune responses of their vertebrate hosts. Tick serpins have also been studied as potential candidates for therapeutic use and vaccine development. In this review, we critically summarize the current state of knowledge about the biological role of tick serpins in shaping tick-host interactions with emphasis on the mechanisms by which they modulate host immunity. Their potential use in drug and vaccine development is also discussed.

Potential Mechanisms of Transmission of Tick-Borne Viruses at the Virus-Tick Interface

Ticks (Acari; Ixodidae) are the second most important vector for transmission of pathogens to humans, livestock, and wildlife. Ticks as vectors for viruses have been reported many times over the last 100 years. Tick-borne viruses (TBVs) belong to two orders (Bunyavirales and Mononegavirales) containing nine families (Bunyaviridae, Rhabdoviridae, Asfarviridae, Orthomyxovirida, Reoviridae, Flaviviridae, Phenuviridae, Nyamiviridae, and Nairoviridae). Among these TBVs, some are very pathogenic, causing huge mortality, and hence, deserve to be covered under the umbrella of one health. About 38 viral species are being transmitted by <10% of the tick species of the families Ixodidae and Argasidae. All TBVs are RNA viruses except for the African swine fever virus from the family Asfarviridae. Tick-borne viral diseases have also been classified as an emerging threat to public health and animals, especially in resource-poor communities of the developing world. Tick-host interaction plays an important role in the successful transmission of pathogens. The ticks' salivary glands are the main cellular machinery involved in the uptake, settlement, and multiplication of viruses, which are required for successful transmission into the final host. Furthermore, tick saliva also participates as an augmenting tool during the physiological process of transmission. Tick saliva is an important key element in the successful transmission of pathogens and contains different antimicrobial proteins, e.g., defensin, serine, proteases, and cement protein, which are key players in tick-virus interaction. While tick-virus interaction is a crucial factor in the propagation of tick-borne viral diseases, other factors (physiological, immunological, and gut flora) are also involved. Some immunological factors, e.g., toll-like receptors, scavenger receptors, Janus-kinase (JAK-STAT) pathway, and immunodeficiency (IMD) pathway are involved in tick-virus interaction by helping in virus assembly and acting to increase transmission. Ticks also harbor some endogenous viruses as internal microbial faunas, which also play a significant role in tick-virus interaction. Studies focusing on tick saliva and its role in pathogen transmission, tick feeding, and control of ticks using functional genomics all point toward solutions to this emerging threat. Information regarding tick-virus interaction is somewhat lacking; however, this information is necessary for a complete understanding of transmission TBVs and their persistence in nature. This review encompasses insight into the ecology and vectorial capacity of tick vectors, as well as our current understanding of the predisposing, enabling, precipitating, and reinforcing factors that influence TBV epidemics. The review explores the cellular, biochemical, and immunological tools which ensure and augment successful evading of the ticks' defense systems and transmission of the viruses to the final hosts at the virus-vector interface. The role of functional genomics, proteomics, and metabolomics in profiling tick-virus interaction is also discussed. This review is an initial attempt to comprehensively elaborate on the epidemiological determinants of TBVs with a focus on intra-vector physiological processes involved in the successful execution of the docking, uptake, settlement, replication, and transmission processes of arboviruses. This adds valuable data to the existing bank of knowledge for global stakeholders, policymakers, and the scientific community working to devise appropriate strategies to control ticks and TBVs.

Hemocyte Clusters Defined by scRNA-Seq in Bombyx mori: In Silico Analysis of Predicted Marker Genes and Implications for Potential Functional Roles

Within the hemolymph, insect hemocytes constitute a heterogeneous population of macrophage-like cells that play important roles in innate immunity, homeostasis and development. Classification of hemocytes in different subtypes by size, morphology and biochemical or immunological markers has been difficult and only in Drosophila extensive genetic analysis allowed the construction of a coherent picture of hemocyte differentiation from pro-hemocytes to granulocytes, crystal cells and plasmatocytes. However, the advent of high-throughput single cell technologies, such as single cell RNA sequencing (scRNA-seq), is bound to have a high impact on the study of hemocytes subtypes and their phenotypes in other insects for which a sophisticated genetic toolbox is not available. Instead of averaging gene expression across all cells as occurs in bulk-RNA-seq, scRNA-seq allows high-throughput and specific visualization of the differentiation status of individual cells. With scRNA-seq, interesting cell types can be identified in heterogeneous populations and direct analysis of rare cell types is possible. Next to its ability to profile the transcriptomes of individual cells in tissue samples, scRNA-seq can be used to propose marker genes that are characteristic of different hemocyte subtypes and predict their functions. In this perspective, the identities of the different marker genes that were identified by scRNA-seq analysis to define 13 distinct cell clusters of hemocytes in larvae of the silkworm, Bombyx mori, are discussed in detail. The analysis confirms the broad division of hemocytes in granulocytes, plasmatocytes, oenocytoids and perhaps spherulocytes but also reveals considerable complexity at the molecular level and highly specialized functions. In addition, predicted hemocyte marker genes in Bombyx generally show only limited convergence with the genes that are considered characteristic for hemocyte subtypes in Drosophila.

A teratocyte-specific serpin from the endoparasitoid wasp Cotesia vestalis inhibits the prophenoloxidase-activating system of its host Plutella xylostella

Many endoparasitoids adopt several parasitic factors, such as venom, polydnavirus and teratocytes, to suppress the immune response of their associated hosts including melanization for successful parasitism. A teratocyte-specific expressed serpin gene, designated as CvT-serpin6, was identified from the parasitoid Cotesia vestalis. The immunoblot result suggested that CvT-serpin6 was secreted into extracellular space. qPCR results showed that CvT-serpin6 was mainly transcribed at later stages of parasitism, and the transcriptional abundance of CvT-serpin6 in teratocytes was significantly increased in response to the challenge of bacteria. Inhibitory assay indicated that recombinant CvT-serpin6 (rCvT-serpin6) could inhibit the activation of Plutella xylostella prophenoloxidase and ultimately resulted in the inhibition of melanization in P. xylostella haemolymph. Furthermore, we confirmed that rCvT-serpin6 could form SDS-stable complexes with activated PxPAP1 and PxPAP3 in a dose-dependent manner. Altogether, our results further shed insight into the molecular mechanisms that teratocytes involved in controlling host immune response.

Novel proteinase inhibitor from the hemolymph of soybean pest Anticarsia gemmatalis (lepidóptera: Noctuidae): Structural modeling and enzymatic kinetic

New approaches are needed to reduce risks to the environment and natural enemies and to avoid or delay the onset of insecticide resistance. The use of insecticides based on proteinase inhibitors of hemolymph is an alternative for the control of Lepidoptera pests primarily by having low toxicity and short persistence in the environment. Thus, in this study, we describe the purification process and identification of protease inhibitors from hemolymph Anticarsia gemmatalis and their activities against trypsin enzymes. Furthermore, the three-dimensional (3D) structure of the inhibitor and binding mode to trypsin enzymes was determined, and the stability of the inhibitory activity in several pHs and temperature values was evaluated. The inhibitor was characterized as a serpin family inhibitor and named A. gemmatalis hemolymph serpin inhibitor (AHSI), with an approximate mass of 38 ± 2 kDa, highly stable to temperature and pH variations, and with inhibitory capacity on bovine trypsin and gut trypsin of A. gemmatalis demonstrated by calculated Ki values and affinity energy through molecular docking, being a reversible competitive inhibitor that binds to the active site of trypsin-like enzymes. We conclude that the AHSI inhibitor identified from the hemolymph of the soybean pest A. gemmatalis preserves the original structure of the serpin family with a good overall stereochemical quality confirmed from molecular modeling. The docking analysis showed that the reactive site of the inhibitor is in contact with the catalytic cavity of the trypsin with high-affinity energy.

Segmental pairs of dermal secretory cells release proteins into the hemolymph at the larval-pupal molt

At each molt of Manduca, the large dermal secretory cells expel the protein contents of their vacuoles into the hemocoel. The constellation of proteins expelled at the last larval-pupal molt, however, differs qualitatively from those proteins released at earlier larval-larval molts. Secretory cells at the two stages not only have different lectin staining properties but also have different proteins that separate on two-dimensional gels. Numerous physiological changes accompany the termination of the last larval instar, including increased chitin synthesis, diminished oxygen delivery, and reduced humoral immunity. Secretion of trehalase that is essential for chitin synthesis and the release of hypoxia up-regulated protein to ameliorate oxygen deprivation help ensure normal transition from larva to pupa. Proteins released by dermal secretory cells at this last molt could supplement the diminished immune defenses mediated by fat body and hemocytes at the end of larval life. Additional immune defenses provided by dermal secretory cells could help ensure a safe transition during a period of increased vulnerability for the newly molted pupa with its soft, thin cuticle and reduced mobility.

Transcriptome of the Maize Leafhopper (Dalbulus maidis) and Its Transcriptional Response to Maize Rayado Fino Virus (MRFV), Which It Transmits in a Persistent, Propagative Manner

The corn leafhopper (Dalbulus maidis) is an important vector of maize rayado fino virus (MRFV), a positive-strand RNA (+ssRNA) marafivirus which it transmits in a persistent propagative manner. The interaction of D. maidis with MRFV, including infection of the insect and subsequent transmission to new plants, is not well understood at the molecular level. To examine the leafhopper-virus interaction, a D. maidis transcriptome was assembled and differences in transcript abundance between virus-exposed and naive D. maidis were examined at two time points (4 h and 7 days) post exposure to MRFV. The D. maidis transcriptome contained 56,116 transcripts generated from 1,727,369,026 100-nt paired-end reads from whole adult insects. The transcriptome of D. maidis shared highest identity and most orthologs with the leafhopper Graminella nigrifrons (65% of transcripts had matches with E values of <10^-5) versus planthoppers Sogatella furcifera (with 23% of transcript matches below the E value cutoff) and Peregrinus maidis (with 21% transcript matches below the E value cutoff), as expected based on taxonomy. D. maidis expressed genes in the Toll, Imd, and Jak/Stat insect immune signaling pathways, RNA interference (RNAi) pathway genes, prophenoloxidase-activating system pathways, and immune recognition protein-encoding genes such as peptidoglycan recognition proteins (PGRPs), antimicrobial peptides, and other effectors. Statistical analysis (performed by R package DESeq2) identified 72 transcripts at 4 h and 67 at 7 days that were significantly responsive to MRFV exposure. Genes expected to be favorable for virus propagation, such as protein synthesis-related genes and genes encoding superoxide dismutase, were significantly upregulated after MRFV exposure. IMPORTANCE The transcriptome of the corn leafhopper, D. maidis, revealed conserved biochemical pathways for immunity and discovered transcripts responsive to MRFV-infected plants at two time points, providing a basis for functional identification of genes that either limit or promote the virus-vector interaction. Compared to other hopper species and the propagative plant viruses they transmit, D. maidis shared 15 responsive transcripts with S. furcifera (to southern rice black-streaked dwarf virus [SRBSDV]), one with G. nigrifrons (to maize fine streak virus [MFSV]), and one with P. maidis (to maize mosaic virus [MMV]), but no virus-responsive transcripts identified were shared among all four hopper vector species.

rDromaserpin: A Novel Anti-Hemostatic Serpin, from the Salivary Glands of the Hard Tick Hyalomma dromedarii

Hemostatic disorders are caused either by platelet-related dysfunctions, defective blood coagulation, or by a combination of both, leading to an increased susceptibility to cardiovascular diseases (CVD) and other related illnesses. The unique specificity of anticoagulants from hematophagous arthropods, such as ticks, suggests that tick saliva holds great promise for discovering new treatments for these life-threatening diseases. In this study, we combined in silico and in vitro analyses to characterize the first recombinant serpin, herein called Dromaserpin, from the sialotranscriptome of the Hyalomma dromedarii tick. Our in silico data described Dromaserpin as a secreted protein of ~43 kDa with high similarities to previously characterized inhibitory serpins. The recombinant protein (rDromaserpin) was obtained as a well-structured monomer, which was tested using global blood coagulation and platelet aggregation assays. With this approach, we confirmed rDromaserpin anticoagulant activity as it significantly delayed plasma clotting in activated partial thromboplastin time and thrombin time assays. The profiling of proteolytic activity shows its capacity to inhibit thrombin in the micromolar range (0.2 to 1 μM) and in the presence of heparin this inhibition was clearly increased. It was also able to inhibit Kallikrein, FXIa and slightly FXIIa, with no significant effect on other factors. In addition, the rDromaserpin inhibited thrombin-induced platelet aggregation. Taken together, our data suggest that rDromaserpin deserves to be further investigated as a potential candidate for developing therapeutic compounds targeting disorders related to blood clotting and/or platelet aggregation.

Seminal fluid proteins induce transcriptome changes in the Aedes aegypti female lower reproductive tract

BACKGROUND

Mating induces behavioral and physiological changes in the arbovirus vector Aedes aegypti, including stimulation of egg development and oviposition, increased survival, and reluctance to re-mate with subsequent males. Transferred seminal fluid proteins and peptides derived from the male accessory glands induce these changes, though the mechanism by which they do this is not known.

RESULTS

To determine transcriptome changes induced by seminal proteins, we injected extract from male accessory glands and seminal vesicles (MAG extract) into females and examined female lower reproductive tract (LRT) transcriptomes 24 h later, relative to non-injected controls. MAG extract induced 87 transcript-level changes, 31 of which were also seen in a previous study of the LRT 24 h after a natural mating, including 15 genes with transcript-level changes similarly observed in the spermathecae of mated females. The differentially-regulated genes are involved in diverse molecular processes, including immunity, proteolysis, neuronal function, transcription control, or contain predicted small-molecule binding and transport domains.

CONCLUSIONS

Our results reveal that seminal fluid proteins, specifically, can induce gene expression responses after mating and identify gene targets to further investigate for roles in post-mating responses and potential use in vector control.