Exploring the role of RNASET2 in the immune response of black soldier fly larvae.

T2 RNases are transferase-type enzymes distributed across phyla, crucial for breaking down single-stranded RNA molecules. In addition to their canonical function, several T2 enzymes exhibit pleiotropic roles, contributing to various biological processes, such as the immune response in invertebrates and vertebrates. This study aims at characterizing RNASET2 in the larvae of black soldier fly (BSF), Hermetia illucens, which are used for organic waste reduction and the production of valuable insect biomolecules for feed formulation and other applications. Given the exposure of BSF larvae to pathogens present in the feeding substrate, it is likely that the mechanisms of their immune response have undergone significant evolution and increased complexity. After in silico characterization of HiRNASET2, demonstrating the high conservation of this T2 homolog, we investigated the expression pattern of the enzyme in the fat body and hemocytes, two districts mainly involved in the insect immune response, in larvae challenged with bacterial infection. While no variation in HiRNASET2 expression was observed in the fat body following infection, a significant upregulation of HiRNASET2 synthesis occurred in hemocytes shortly after the injection of bacteria in the larva. The intracellular localization of HiRNASET2 in lysosomes of plasmatocytes, its extracellular association with bacteria, and the presence of a putative antimicrobial domain in the molecule, suggest its potential role in RNA clean-up and as an alarm molecule promoting phagocytosis activation by hemocytes. These insights contribute to the characterization of the immune response of Hermetia illucens larvae and may facilitate the development of animal feedstuff enriched with highly valuable BSF bioactive compounds.

Time- and tissue-specific antimicrobial activity of the common bed bug in response to blood feeding and immune activation by bacterial injection.

Unlike almost all hematophagous insects, common bed bugs, Cimex lectularius, are not known to transmit pathogens to humans. To help unravel the reasons for their lack of vector competence, we studied the time- and tissue-dependent expression of innate immune factors after blood feeding or immune activation through the intrathoracic injection of bacteria. We used minimum inhibitory concentration (MIC1) bioassays and the Kirby-Bauer protocol to evaluate antimicrobial peptide (AMP2) activity in tissue extracts from the midguts or 'rest of body' (RoB3) tissues (containing hemolymph and fat body AMPs) against Gram-positive and Gram-negative bacteria. We compared AMP activity between blood-fed female bed bugs and yellow fever mosquitoes, Aedes aegypti and determined how female and male bed bugs respond to immune challenges, and how long AMP gene expression remains elevated in bed bugs following a blood meal. Blood meal-induced AMP activity is 4-fold stronger in female bed bugs than in female mosquitoes. Male bed bugs have elevated AMP activity within 8 h of a blood meal or an intrathoracic injection with bacteria, with the strongest activity expressed in RoB tissue 24 h after the immune challenge. Female bed bugs have a stronger immune response than males within 24 h of a blood meal. The effects of blood meal-induced elevated AMP activity lasts longer against the Gram-positive bacterium, Bacillus subtilis, than against the Gram-negative bacterium Escherichia coli. Unravelling the specific immune pathways that are activated in the bed bugs' immune responses and identifying the bed bug-unique AMPs might help determine why these insects are not vectors of human parasites.

The mode of expression divergence in Drosophila fat body is infection-specific.

Transcription is controlled by interactions of cis-acting DNA elements with diffusible trans-acting factors. Changes in cis or trans factors can drive expression divergence within and between species, and their relative prevalence can reveal the evolutionary history and pressures that drive expression variation. Previous work delineating the mode of expression divergence in animals has largely used whole-body expression measurements in one condition. Because cis-acting elements often drive expression in a subset of cell types or conditions, these measurements may not capture the complete contribution of cis-acting changes. Here, we quantify the mode of expression divergence in the Drosophila fat body, the primary immune organ, in several conditions, using two geographically distinct lines of D. melanogaster and their F1 hybrids. We measured expression in the absence of infection and in infections with Gram-negative S. marcescens or Gram-positive E. faecalis bacteria, which trigger the two primary signaling pathways in the Drosophila innate immune response. The mode of expression divergence strongly depends on the condition, with trans-acting effects dominating in response to Gram-negative infection and cis-acting effects dominating in Gram-positive and preinfection conditions. Expression divergence in several receptor proteins may underlie the infection-specific trans effects. Before infection, when the fat body has a metabolic role, there are many compensatory effects, changes in cis and trans that counteract each other to maintain expression levels. This work shows that within a single tissue, the mode of expression divergence varies between conditions and suggests that these differences reflect the diverse evolutionary histories of host-pathogen interactions.

Integrative analysis of circRNA/miRNA/mRNA regulatory network reveals the potential immune function of circRNAs in the Bombyx mori fat body.

Bombyx mori nucleopolyhedrosis virus (BmNPV) is one of the greatest threats to sustainable development of the sericulture industry. Circular RNA (circRNA), a type of non-coding RNA, has been shown to play important roles in gene expression regulation, immune response, and diseases. The fat body is a tissue with both metabolic and immune functions. To explore the potential immune function of circRNAs, we analyzed differentially expressed (DE)circRNAs, microRNAs(miRNAs), and mRNAs in the B. mori fat body in response to BmNPV infection using high-throughput RNA sequencing. A total of 77 DEcircRNAs, 32 DEmiRNAs, and 730 DEmRNAs that are associated with BmNPV infection were identified. We constructed a DEcircRNA/DEmiRNA/DEmRNA and DEcircRNA/DEmiRNA/BmNPV gene regulatory network and validated the differential expression of circ_0001432 and its corresponding miRNA (miR-2774c and miR-3406-5p) and mRNA (778467 and 101745232) in the network. Tissue-specific expression of circ_0001432 and its expression at different time points were also examined. KEGG pathway analysis of DEmRNAs, target genes of DEmiRNAs, and host genes of DEcircRNAs in the network showed that these genes were enriched in several metabolic pathways and signaling pathways, which could play important roles in insect immune responses. Our results suggest that circRNA could be involved in immune responses of the B. mori fat body and help in understanding the molecular mechanisms underlying silkworm-pathogen interactions.

A Pattern Recognition Receptor C-type Lectin-S6 (CTL-S6) is Involved in the Immune Response in the Silkworm (Lepidoptera: Bombycidae).

Insect innate immunity is initiated by the special recognition and binding of the foreign pathogens, which is accomplished by the pattern recognition receptors (PRRs). As an important type of PRRs, C-type lectins (CTLs) play various roles in insect innate immunity, including pathogen recognition, stimulation of prophenoloxidase, regulation of cellular immunity and so on. In this study, we have cloned the full-length cDNA of a CTL gene named CTL-S6 from the silkworm, Bombyx mori. The open reading frame (ORF) of B. mori CTL-S6 encodes 378 amino acids, which contain a secretion signal peptide. The mRNA of CTL-S6 exhibited the highest transcriptional level in the midgut. Its transcriptional level increased dramatically in fat body and hemocytes upon Escherichia coli or Micrococcus luteus challenge. Purified recombinant CTL-S6 could bind to bacterial cell wall components, including peptidoglycan (PGN, from Bacillus subtilis) and lipopolysaccharide (LPS, from E. coli 0111:B4), and recombinant CTL-S6 was involved in the encapsulation and melanization of hemocytes. Furthermore, the addition of recombinant CTL-S6 to the hemolymph of silkworm resulted in a significant increase in phenoloxidase activity. Overall, our results indicated that B. mori CTL-S6 may serve as a PRR for the recognition of foreign pathogens, prophenoloxidase pathway stimulation and involvement in the innate immunity.

Endocrine regulation of immunity in insects.

Organisms have constant contact with potentially harmful agents that can compromise their fitness. However, most of the times these agents fail to cause serious disease by virtue of the rapid and efficient immune responses elicited in the host that can range from behavioural adaptations to immune system triggering. The immune system of insects does not comprise the adaptive arm, making it less complex than that of vertebrates, but key aspects of the activation and regulation of innate immunity are conserved across different phyla. This is the case for the hormonal regulation of immunity as a part of the broad organismal responses to external conditions under different internal states. In insects, depending on the physiological circumstances, distinct hormones either enhance or suppress the immune response integrating individual (and often collective) responses physiologically and behaviourally. In this review, we provide an overview of our current knowledge on the endocrine regulation of immunity in insects, its mechanisms and implications on metabolic adaptation and behaviour. We highlight the importance of this multilayered regulation of immunity in survival and reproduction (fitness) and its dependence on the hormonal integration with other mechanisms and life-history traits.

Innate immune signaling in Drosophila shifts anabolic lipid metabolism from triglyceride storage to phospholipid synthesis to support immune function.

During infection, cellular resources are allocated toward the metabolically-demanding processes of synthesizing and secreting effector proteins that neutralize and kill invading pathogens. In Drosophila, these effectors are antimicrobial peptides (AMPs) that are produced in the fat body, an organ that also serves as a major lipid storage depot. Here we asked how activation of Toll signaling in the larval fat body perturbs lipid homeostasis to understand how cells meet the metabolic demands of the immune response. We find that genetic or physiological activation of fat body Toll signaling leads to a tissue-autonomous reduction in triglyceride storage that is paralleled by decreased transcript levels of the DGAT homolog midway, which carries out the final step of triglyceride synthesis. In contrast, Kennedy pathway enzymes that synthesize membrane phospholipids are induced. Mass spectrometry analysis revealed elevated levels of major phosphatidylcholine and phosphatidylethanolamine species in fat bodies with active Toll signaling. The ER stress mediator Xbp1 contributed to the Toll-dependent induction of Kennedy pathway enzymes, which was blunted by deleting AMP genes, thereby reducing secretory demand elicited by Toll activation. Consistent with ER stress induction, ER volume is expanded in fat body cells with active Toll signaling, as determined by transmission electron microscopy. A major functional consequence of reduced Kennedy pathway induction is an impaired immune response to bacterial infection. Our results establish that Toll signaling induces a shift in anabolic lipid metabolism to favor phospholipid synthesis and ER expansion that may serve the immediate demand for AMP synthesis and secretion but with the long-term consequence of insufficient nutrient storage.

TmPGRP-SA regulates Antimicrobial Response to Bacteria and Fungi in the Fat Body and Gut of Tenebrio molitor.

Antimicrobial immune response is mediated by a signal-transducing sensor, peptidoglycan recognition protein-SA (PGRP-SA), that can recognize non-self molecules. Although several studies have focused on the involvement of Drosophila PGRP-SA in antimicrobial peptide (AMP) expression in response to infections, studies on its role in Tenebrio molitor are lacking. Here, we present a functional analysis of T. molitor PGRP-SA (TmPGRP-SA). In the absence of microbes, TmPGRP-SA was highly expressed in the late-larval fat body, followed by hemocytes, and gut. Interestingly, following Escherichia coli, Staphylococcus aureus, and Candida albicans infections, the mRNA level of TmPGRP-SA was significantly upregulated in both the fat body and gut. TmPGRP-SA silencing had a significant effect on the mortality rates for all the microbes tested. Moreover, TmPGRP-SA is required for regulating the expression of eight AMP genes namely TmTenecin-1, -2, and -4; TmDefensin-1 and -2; TmColeoptericin-1; and TmAttacin-1b and -2 in the fat body in response to E. coli and S. aureus infections. TmPGRP-SA is essential for the transcription of TmTenecin-2, -4; TmDefensin-2; TmColeoptericin-1, -2; and TmAttacin-1a, -1b, and -2 in the gut upon E. coli and C. albicans infections. However, TmPGRP-SA does not regulate AMP expression in the hemocytes. Additionally, TmDorsal isoform X2, a downstream Toll transcription factor, was downregulated in TmPGRP-SA-silenced larval fat body following E. coli and S. aureus challenges, and in the gut following E. coli and C. albicans challenges.

TmDorX2 positively regulates antimicrobial peptides in Tenebrio molitor gut, fat body, and hemocytes in response to bacterial and fungal infection.

Dorsal, a member of the nuclear factor-kappa B (NF-κB) family of transcription factors, is a critical downstream component of the Toll pathway that regulates the expression of antimicrobial peptides (AMPs) against pathogen invasion. In this study, the full-length ORF of Dorsal was identified from the RNA-seq database of the mealworm beetle Tenebrio molitor (TmDorX2). The ORF of TmDorX2 was 1,482 bp in length, encoding a polypeptide of 493 amino acid residues. TmDorX2 contains a conserved Rel homology domain (RHD) and an immunoglobulin-like, plexins, and transcription factors (IPT) domain. TmDorX2 mRNA was detected in all developmental stages, with the highest levels observed in 3-day-old adults. TmDorX2 transcripts were highly expressed in the adult Malpighian tubules (MT) and the larval fat body and MT tissues. After challenging the larvae with Staphylococcus aureus and Escherichia coli, the TmDorX2 mRNA levels were upregulated 6 and 9 h post infection in the whole body, fat body, and hemocytes. Upon Candida albicans challenge, the TmDorX2 mRNA expression were found highest at 9 h post-infection in the fat body. In addition, TmDorX2-knockdown larvae exposed to E. coli, S. aureus, or C. albicans challenge showed a significantly increased mortality rate. Furthermore, the expression of 11 AMP genes was downregulated in the gut and fat body of dsTmDorX2-injected larvae upon E. coli challenge. After C. albicans and S. aureus challenge of dsTmDorX2-injected larvae, the expression of 11 and 10 AMPs was downregulated in the gut and fat body, respectively. Intriguingly, the expression of antifungal transcripts TmTenecin-3 and TmThaumatin-like protein-1 and -2 was greatly decreased in TmDorX2-silenced larvae in response to C. albicans challenge, suggesting that TmDorX2 regulates antifungal AMPs in the gut in response to C. albicans infection. The AMP expression profiles in the fat body, hemocytes, gut, and MTs suggest that TmDorX2 might have an important role in promoting the survival of T. molitor larvae against all mentioned pathogens.

An IMD-like pathway mediates the intestinal immunity to modulate the homeostasis of gut microbiota in Rhynchophorus ferrugineus Olivier (Coleoptera: Dryophthoridae).

Most animals have established the mutualistic interactions with their intestinal microbes which provide multiple benefits to their host physiology. However, the mechanisms behind hosts determine the load and composition of gut microbiota are still poorly understood outside dipteran insects. Here, the gene, encoding the NF-κB-like transcription factor Relish, being designated as RfRelish, was identified and analyzed in red palm weevil (RPW), Rhynchophorus ferrugineus Olivier. We revealed that the abundance of RfRelish transcripts in the fat body, hemolymph and gut are significantly higher than that in non-immunity-related tissues, and its expression level can be markedly induced by bacterial challenges. When RfRelish was silenced, the ability of individuals to clear the pathogenic bacteria in body cavity and gut was significantly compromised, suggesting that both the systemic and gut local immunity were impaired dramatically by RfRelish knockdown. Additionally, the silenced insects exhibited increased gut bacterial load, and the relative abundance of some gut bacteria was changed as compared to controls. Collectively, our findings demonstrate that the IMD-like pathway restricts the proliferation of gut bacteria and shapes the commensal community structure in the intestine of R. ferrugineus by mediating the secretion of antimicrobial peptides. We provide a striking example on how an insect pest maintains the homeostasis of gut microbiota via a conserved immune pathway without compromising the advantages of the mutualistic relationships.

Transcriptomic insight into antimicrobial peptide factors involved in the prophylactic immunity of crowded Mythimna separata larvae.

Similar to pathogenic infection, a high population density alters insect prophylactic immunity. Antimicrobial peptides (AMPs) are known to play critical roles in an insect's humoral immune response to microbial infection. We applied RNA sequencing to investigate differential gene expression levels in fat body and hemocyte samples from larvae reared in high- (10 larvae per jar) and low-density (1 larva per jar) conditions; the samples exhibited density-dependent prophylaxis. A number of AMP molecule-related proteins were annotated for the first time from 145,439 assembled unigenes from M. separata larvae. The transcript levels of AMP molecules such as gloverin-, defensin-, cecropin-, lebocin- and attacin-related unigenes were increased with the prophylactic immunity of high-density larvae. The pattern recognition receptor peptidoglycan recognition protein (PGRP), a key protein in the synthesis of AMPs in IMD- and Toll pathway-related unigenes, was also upregulated in the larvae from the high-density group. The resultant transcriptomic database was validated by the transcript levels of four selected AMP genes quantified from the high- and low-density larval groups with quantitative real-time PCR. The antimicrobial activity against gram-positive Staphylococcus aureus and Bacillus subtilis and gram-negative Edwardsiella ictaluri and Vibrio anguillarum in the hemolymph of larvae from the high-density group was significantly higher than that of larvae from the low-density group. Our findings provide the first insight into the role of AMP genes in the mechanisms of density-dependent prophylaxis in M. separata and provide new insight into the control of M. separata with biopesticides.

Manduca sexta hemolymph protease-2 (HP2) activated by HP14 generates prophenoloxidase-activating protease-2 (PAP2) in wandering larvae and pupae.

Melanization is a universal defense mechanism of insects against microbial infection. During this response, phenoloxidase (PO) is activated from its precursor by prophenoloxidase activating protease (PAP), the terminal enzyme of a serine protease (SP) cascade. In the tobacco hornworm Manduca sexta, hemolymph protease-14 (HP14) is autoactivated from proHP14 to initiate the protease cascade after host proteins recognize invading pathogens. HP14, HP21, proHP1*, HP6, HP8, PAP1-3, and non-catalytic serine protease homologs (SPH1 and SPH2) constitute a portion of the extracellular SP-SPH system to mediate melanization and other immune responses. Here we report the expression, purification, and functional characterization of M. sexta HP2. The HP2 precursor is synthesized in hemocytes, fat body, integument, nerve and trachea. Its mRNA level is low in fat body of 5th instar larvae before wandering stage; abundance of the protein in hemolymph displays a similar pattern. HP2 exists as an active enzyme in plasma of the wandering larvae and pupae in the absence of an infection. HP14 cleaves proHP2 to yield active HP2. After incubating active HP2 with larval hemolymph, we detected higher levels of PO activity, i.e. an enhancement of proPO activation. HP2 cleaved proPAP2 (but not proPAP3 or proPAP1) to yield active PAP2, responsible for a major increase in IEARpNA hydrolysis. PAP2 activates proPOs in the presence of a cofactor of SPH1 and SPH2. In summary, we have identified a new member of the proPO activation system and reconstituted a pathway of HP14-HP2-PAP2-PO. Since high levels of HP2 mRNA were present in integument and active HP2 in plasma of wandering larvae, HP2 likely plays a role in cuticle melanization during pupation and protects host from microbial infection in a soil environment.

Dietary restriction alters the fatbody transcriptome during immune responses in Bombyx mori.

Dietary restriction (DR) leads to extended lifespan in many species ranging from yeasts to mammal, and it can also affect the immune system to some extent. Herein, we investigated whether DR can enhance the immunity of Bombyx mori suffering from acute pathogenic microorganism infection. The results showed that DR could accelerate the melanisation reaction, delay the early death in silkworms, meanwhile Staphylococcus aureus (SA) load was lower in the early stage of infection. Moreover, more immune-related genes were identified to be down-regulated in the DR group infected with SA compared with the ad libitum - fed (AL) group infected with SA through mRNA deep sequencing (RNAseq) and quantitation PCR. We speculate that rapid melanization may beneficial to the lower SA load and delay the time point of the early death, and the lower SA load may lead to many immune-related DEGs were down-regulated. These results may help us to understand the mechanisms by which DR affects the immune system in insects and other animals.

Interorgan Molecular Communication Strategies of "Local" and "Systemic" Innate Immune Responses in Mosquito Anopheles stephensi.

Mosquitoes that transmit many deadly infectious diseases also need to keep fighting against many microbial infections. Constitutive expression of multiple antimicrobial peptides (AMPs) in almost all body tissues is believed to facilitate the effective management of these local infections. When any infection breaches the local barrier, AMPs are induced rapidly in non-target tissues such as hemocytes (HCs) and establish their co-ordination with systemic immune effectors to clear off the body infection. But how interorgan immune communication is managed during local and systemic infections remain largely unknown. To understand this interorgan molecular relationship, we identified, extensively profiled and compared the expression of AMPs in three important mosquito tissues viz. midgut, fat body (FB), and HCs. dsRNA-mediated AMPs silencing suggests that mosquito tissues are able to manage an optimal expression of AMPs at the physiological level. We also examined the possible contribution of two important immune regulator genes relish (REL) and nitric oxide synthase, controlling AMPs expression in these tissues during local or systemic infections. We show that each tissue has a unique ability to respond to local/systemic challenges, but HCs are more specialized to recognize and discriminate-specific antigens than gut and FB. Our investigation also revealed that both REL and NO participate in the overall management of the interorgan immune responses, but at the same time each tissue also has its own ability to maintain the interorgan flow of signals. In our knowledge, this is the first large-scale study examining the interorgan immune relationship in the mosquito.

Comparative transcriptomics reveals CrebA as a novel regulator of infection tolerance in D. melanogaster.

Host responses to infection encompass many processes in addition to activation of the immune system, including metabolic adaptations, stress responses, tissue repair, and other reactions. The response to bacterial infection in Drosophila melanogaster has been classically described in studies that focused on the immune response elicited by a small set of largely avirulent microbes. Thus, we have surprisingly limited knowledge of responses to infection that are outside the canonical immune response, of how the response to pathogenic infection differs from that to avirulent bacteria, or even of how generic the response to various microbes is and what regulates that core response. In this study, we addressed these questions by profiling the D. melanogaster transcriptomic response to 10 bacteria that span the spectrum of virulence. We found that each bacterium triggers a unique transcriptional response, with distinct genes making up to one third of the response elicited by highly virulent bacteria. We also identified a core set of 252 genes that are differentially expressed in response to the majority of bacteria tested. Among these, we determined that the transcription factor CrebA is a novel regulator of infection tolerance. Knock-down of CrebA significantly increased mortality from microbial infection without any concomitant change in bacterial number. Upon infection, CrebA is upregulated by both the Toll and Imd pathways in the fat body, where it is required to induce the expression of secretory pathway genes. Loss of CrebA during infection triggered endoplasmic reticulum (ER) stress and activated the unfolded protein response (UPR), which contributed to infection-induced mortality. Altogether, our study reveals essential features of the response to bacterial infection and elucidates the function of a novel regulator of infection tolerance.

Tissue-dependent induction of antimicrobial peptide genes after body wall injury in house fly (Musca domestica) larvae.

Injury of the insect body wall, which enables environmental microorganisms to invade into insect tissues, induces innate immune responses including the induction of antimicrobial peptides (AMPs) in flies and silkworms. Here, house fly (Musca domestica) larvae and pupae were injured using a needle and the effects on the expression of genes encoding AMPs were examined. The expression of AMP genes including defensin, attacin, diptericin, and sarcotoxin II dramatically increased in both larvae and pupae after injury of the body wall, indicating that innate immune responses were induced. Furthermore, the injury-dependent expression of AMP genes was examined in larval tissues including fat bodies, hemocytes, salivary glands, and digestive tracts. Injury-dependent AMP gene expression was observed in salivary glands, hemocytes, and fat bodies, but not in digestive tracts. The degree of the transcriptional induction of each gene differed among tissues, suggesting that their expression is governed by complex regulatory machinery and that AMPs have tissue-specific functions. To further examine the properties of the AMPs, we examined the antimicrobial activities of partial synthetic peptides corresponding to portions of the predicted AMP proteins deduced from the AMP genes. A synthetic peptide exhibited antimicrobial activity, indicating that these injury-inducible genes are potential medicinal resources.

A Complex Relationship between Immunity and Metabolism in Drosophila Diet-Induced Insulin Resistance.

Both systemic insulin resistance and tissue-specific insulin resistance have been described in Drosophila and are accompanied by many indicators of metabolic disease. The downstream mediators of insulin-resistant pathophysiology remain unclear. We analyzed insulin signaling in the fat body studying loss and gain of function. When expression of the sole Drosophila insulin receptor (InR) was reduced in larval fat bodies, animals exhibited developmental delay and reduced size in a diet-dependent manner. Fat body InR knockdown also led to reduced survival on high-sugar diets. To look downstream of InR at potential mediators of insulin resistance, transcriptome sequencing (RNA-seq) studies in insulin-resistant fat bodies revealed differential expression of genes, including those involved in innate immunity. Obesity-associated insulin resistance led to increased susceptibility of flies to infection, as in humans. Reduced innate immunity was dependent on fat body InR expression. The peptidoglycan recognition proteins (PGRPs) PGRP-SB2 and PGRP-SC2 were selected for further study based on differential expression studies. Downregulating PGRP-SB2 selectively in the fat body protected animals from the deleterious effects of overnutrition, whereas downregulating PGRP-SC2 produced InR-like phenotypes. These studies extend earlier work linking the immune and insulin signaling pathways and identify new targets of insulin signaling that could serve as potential drug targets to treat type 2 diabetes.

Engineered Aedes aegypti JAK/STAT Pathway-Mediated Immunity to Dengue Virus.

We have developed genetically modified Ae. aegypti mosquitoes that activate the conserved antiviral JAK/STAT pathway in the fat body tissue, by overexpressing either the receptor Dome or the Janus kinase Hop by the blood feeding-induced vitellogenin (Vg) promoter. Transgene expression inhibits infection with several dengue virus (DENV) serotypes in the midgut as well as systemically and in the salivary glands. The impact of the transgenes Dome and Hop on mosquito longevity was minimal, but it resulted in a compromised fecundity when compared to wild-type mosquitoes. Overexpression of Dome and Hop resulted in profound transcriptome regulation in the fat body tissue as well as the midgut tissue, pinpointing several expression signatures that reflect mechanisms of DENV restriction. Our transcriptome studies and reverse genetic analyses suggested that enrichment of DENV restriction factor and depletion of DENV host factor transcripts likely accounts for the DENV inhibition, and they allowed us to identify novel factors that modulate infection. Interestingly, the fat body-specific activation of the JAK/STAT pathway did not result in any enhanced resistance to Zika virus (ZIKV) or chikungunya virus (CHIKV) infection, thereby indicating a possible specialization of the pathway's antiviral role.

The Toll Signaling Pathway in the Chinese Oak Silkworm, Antheraea pernyi: Innate Immune Responses to Different Microorganisms.

The Toll pathway is one of the most important signaling pathways regulating insect innate immunity. Spatzle is a key protein that functions as a Toll receptor ligand to trigger Toll-dependent expression of immunity-related genes. In this study, a novel spatzle gene (ApSPZ) from the Chinese oak silkworm Antheraea pernyi was identified. The ApSPZ cDNA is 1065 nucleotides with an open reading frame (ORF) of 777 bp encoding a protein of 258 amino acids. The protein has an estimated molecular weight of 29.71 kDa and an isoelectric point (PI) of 8.53. ApSPZ is a nuclear and secretory protein with no conserved domains or membrane helices and shares 40% amino acid identity with SPZ from Manduca sexta. Phylogenetic analysis indicated that ApSPZ might be a new member of the Spatzle type 1 family, which belongs to the Spatzle superfamily. The expression patterns of several genes involved in the Toll pathway were examined at different developmental stages and various tissues in 5th instar larvae. The examined targets included A. pernyi spatzle, GNBP, MyD88, Tolloid, cactus and dorsalA. The RT-PCR results showed that these genes were predominantly expressed in immune-responsive fat body tissue, indicating that the genes play a crucial role in A. pernyi innate immunity. Moreover, A. pernyi infection with the fungus Nosema pernyi and the gram-positive bacterium Enterococcus pernyi, but not the gram-negative bacterium Escherichia coli, activated the Toll signaling pathway. These results represent the first study of the Toll pathway in A. pernyi, which provides insight into the A. pernyi innate immune system.

Remote Control of Intestinal Stem Cell Activity by Haemocytes in Drosophila.

The JAK/STAT pathway is a key signaling pathway in the regulation of development and immunity in metazoans. In contrast to the multiple combinatorial JAK/STAT pathways in mammals, only one canonical JAK/STAT pathway exists in Drosophila. It is activated by three secreted proteins of the Unpaired family (Upd): Upd1, Upd2 and Upd3. Although many studies have established a link between JAK/STAT activation and tissue damage, the mode of activation and the precise function of this pathway in the Drosophila systemic immune response remain unclear. In this study, we used mutations in upd2 and upd3 to investigate the role of the JAK/STAT pathway in the systemic immune response. Our study shows that haemocytes express the three upd genes and that injury markedly induces the expression of upd3 by the JNK pathway in haemocytes, which in turn activates the JAK/STAT pathway in the fat body and the gut. Surprisingly, release of Upd3 from haemocytes upon injury can remotely stimulate stem cell proliferation and the expression of Drosomycin-like genes in the intestine. Our results also suggest that a certain level of intestinal epithelium renewal is required for optimal survival to septic injury. While haemocyte-derived Upd promotes intestinal stem cell activation and survival upon septic injury, haemocytes are dispensable for epithelium renewal upon oral bacterial infection. Our study also indicates that intestinal epithelium renewal is sensitive to insults from both the lumen and the haemocoel. It also reveals that release of Upds by haemocytes coordinates the wound-healing program in multiple tissues, including the gut, an organ whose integrity is critical to fly survival.