An in vitro study of NF-κB factors cooperatively in regulation of Drosophila melanogaster antimicrobial peptide genes

Maintenance of persistent transmission of a plant arbovirus in its insect vector mediated by the Toll-Dorsal immune pathway

Throughout evolution, arboviruses have developed various strategies to counteract the host's innate immune defenses to maintain persistent transmission. Recent studies have shown that, in addition to bacteria and fungi, the innate Toll-Dorsal immune system also plays an essential role in preventing viral infections in invertebrates. However, whether the classical Toll immune pathway is involved in maintaining the homeostatic process to ensure the persistent and propagative transmission of arboviruses in insect vectors remain unclear. In this study, we revealed that the transcription factor Dorsal is actively involved in the antiviral defense of an insect vector (Laodelphax striatellus) by regulating the target gene, zinc finger protein 708 (LsZN708), which mediates downstream immune-related effectors against infection with the plant virus (Rice stripe virus, RSV). In contrast, an antidefense strategy involving the use of the nonstructural-protein (NS4) to antagonize host antiviral defense through competitive binding to Dorsal from the MSK2 kinase was employed by RSV; this competitive binding inhibited Dorsal phosphorylation and reduced the antiviral response of the host insect. Our study revealed the molecular mechanism through which Toll-Dorsal-ZN708 mediates the maintenance of an arbovirus homeostasis in insect vectors. Specifically, ZN708 is a newly documented zinc finger protein targeted by Dorsal that mediates the downstream antiviral response. This study will contribute to our understanding of the successful transmission and spread of arboviruses in plant or invertebrate hosts.

Immunological regulation by Toll-1 and Spätzle-4 in larval density-dependent prophylaxis of the oriental armyworm, Mythimna separata

High population density has been shown to alter insect prophylactic immunity. Toll-Spätzle pathway performs a key function in insect innate immune response. To determine the role of Toll and Spätzle, two main components of Toll-Spätzle pathway, in the density-dependent prophylaxis of Mythimna separata. We identified full-length cDNA encoding the Toll-1 and Spätzle-4 genes in M. separata (designed MsToll-1 and Ms Spätzle-4). Both MsToll-1 and MsSpätzle-4 were expressed throughout all developmental stages. MsToll-1 expression was highly in fat body and brain and MsSpätzle-4 was highly expressed in brain and Malpighian tubule. With increased larval density, MsToll-1 expression was markedly up-regulated. MsSpätzle-4 expression was found to be raised in larvae that were fed in high density (5 and 10 larvae per jar). Co-immunoprecipitation assays demonstrated that MsToll-1 interacted with MsSpätzle-4. Immune-related genes transcriptions were considerably reduced in high-density larvae MsToll-1 (or MsSpätzle-4) was silenced by dsRNA injection. Meanwhile, a discernible reduction in the survival rate of the larvae exposed to Bacillus thuringiensis infection with silence of MsToll-1 (or MsSpätzle-4) was observed. This study implies that prophylactic immunity was influenced by crowded larvae via modulating the Toll-Spätzle pathway in M. separata and allow for a new understanding of into density-dependent prophylaxis in insects.

Relish-facilitated lncRNA-CR11538 suppresses Drosophila Imd immune response and maintains immune homeostasis via decoying Relish away from antimicrobial peptide promoters

Innate immunity plays a crucial role in host defense against pathogen invasion and its strength and duration requires precise control. Long non-coding RNAs (lncRNAs) have become important regulators of innate immunity, yet their roles in Drosophila immune responses remain largely unknown. In this study, we identified that the overexpression of lncRNA-CR11538 inhibits the expression of antimicrobial peptides (AMPs) Dpt and AttA in Drosophila upon Escherichia coli (E. coli) infection, and influences the survival rate of flies after E. cloacae infection. Mechanically, lncRNA-CR11538 decoys Relish away from AMPs promoter region. We further revealed that Relish can promote the transcription of lncRNA-CR11538. After analyzing the dynamic expression profile of lncRNA-CR11538 during Imd immune response, we put forward a hypothesis that in the late stage of Imd immune response, lncRNA-CR11538 can be activated by Relish and further decoy Relish away from the AMPs promoter to suppress excessive immune signal and maintain immune homeostasis. This mechanism we proposed provides insights into the complex regulatory networks controlling immune responses in Drosophila and suggests potential targets for therapeutic intervention in diseases involving dysregulated immune responses.

Tea Tree Oil Improves Energy Metabolism, Non-Specific Immunity, and Microbiota Diversity via the Intestine-Hepatopancreas Axis in Macrobrachium rosenbergii under Low Fish Meal Diet Administration

Tea tree oil (TTO) is an essential plant oil with diverse antibacterial and antioxidant properties; however, whether the role played by TTO in low fish meal (LF) diets induced the observed effects in the farmed crustaceans remains unclear. Therefore, this study used Macrobrachium rosenbergii as the model crustacean, and an 8-week feeding experiment with NF (normal fish meal), LF (soybean meal replacing 40% fish meal), and LFT (LF with 200 mg/kg TTO) diets was conducted to evaluate the positive effects of TTO under the LF diet. Compared to the NF diet, the LF diet reduced hemolymph antioxidant capacity and non-specific immunity, and induced hepatopancreas apoptosis and damage. However, in comparison with LF, LTF significantly ameliorated morphological impairment in the hepatopancreas, improved hepatopancreas energy metabolism by upregulating the Bcl-2/Bax and Akt/mTOR pathways, and enhanced antioxidant and non-specific immune capacity by activating the NF-κB/NO pathway. In addition, LFT repaired intestinal barrier injury and the imbalance of intestinal microbiota induced by the LF diet. Moreover, the Pearson correlation revealed the variations of the above indicators, which were related to the abundance changes of Klebsiella, Clostridium sensu stricto 12, Thermobifida, Bifidobacterium, and Alistipes, indicating that these microbes might serve as prospective targets for the intestine-hepatopancreas axis to affect hepatopancreas apoptosis, metabolism, and non-specific immunity. In summary, 200 mg/kg TTO supplementation mediated gut microbiota and positively improved energy metabolism and non-specific immunity, thereby alleviating hepatopancreas dysplasia and damage induced by the LF diet in M. rosenbergii.

Lipids as a key element of insect defense systems

The relationship between insect pathogenic fungi and their insect hosts is a classic example of a co-evolutionary arms race between pathogen and target host: parasites evolve towards mechanisms that increase their advantage over the host, and the host increasingly strengthens its defenses. The present review summarizes the literature data describing the direct and indirect role of lipids as an important defense mechanism during fungal infection. Insect defense mechanisms comprise anatomical and physiological barriers, and cellular and humoral response mechanisms. The entomopathogenic fungi have the unique ability to digest the insect cuticle by producing hydrolytic enzymes with chitin-, lipo- and proteolytic activity; besides the oral tract, cuticle pays the way for fungal entry within the host. The key factor in insect resistance to fungal infection is the presence of certain types of lipids (free fatty acids, waxes or hydrocarbons) which can promote or inhibit fungal attachment to cuticle, and might also have antifungal activity. Lipids are considered as an important source of energy, and as triglycerides are stored in the fat body, a structure analogous to the liver and adipose tissue in vertebrates. In addition, the fat body plays a key role in innate humoral immunity by producing a range of bactericidal proteins and polypeptides, one of which is lysozyme. Energy derived from lipid metabolism is used by hemocytes to migrate to the site of fungal infection, and for phagocytosis, nodulation and encapsulation. One polyunsaturated fatty acid, arachidonic acid, is used in the synthesis of eicosanoids, which play several crucial roles in insect physiology and immunology. Apolipoprotein III is important compound with antifungal activity, which can modulate insect cellular response and is considered as important signal molecule.

Drosophila Relish Activating lncRNA-CR33942 Transcription Facilitates Antimicrobial Peptide Expression in Imd Innate Immune Response

Long noncoding RNAs (lncRNAs) are an emerging class of regulators that play crucial roles in regulating the strength and duration of innate immunity. However, little is known about the regulation of Drosophila innate immunity-related lncRNAs. In this study, we first revealed that overexpression of lncRNA-CR33942 could strengthen the expression of the Imd pathway antimicrobial peptide (AMP) genes Diptericin (Dpt) and Attacin-A (AttA) after infection, and vice versa. Secondly, RNA-seq analysis of lncRNA-CR33942-overexpressing flies post Gram-negative bacteria infection confirmed that lncRNA-CR33942 positively regulated the Drosophila immune deficiency (Imd) pathway. Mechanistically, we found that lncRNA-CR33942 interacts and enhances the binding of NF-κB transcription factor Relish to Dpt and AttA promoters, thereby facilitating Dpt and AttA expression. Relish could also directly promote lncRNA-CR33942 transcription by binding to its promoter. Finally, rescue experiments and dynamic expression profiling post-infection demonstrated the vital role of the Relish/lncRNA-CR33942/AMP regulatory axis in enhancing Imd pathway and maintaining immune homeostasis. Our study elucidates novel mechanistic insights into the role of lncRNA-CR33942 in activating Drosophila Imd pathway and the complex regulatory interaction during the innate immune response of animals.

The antiviral role of NF-κB-mediated immune responses and their antagonism by viruses in insects

The antiviral role of innate immune responses mediated by the NF-κB family of transcription factors is well established in vertebrates but was for a long time less clear in insects. Insects encode two canonical NF-κB pathways, the Toll and Imd ('immunodeficiency') pathways, which are best characterised for their role in antibacterial and antifungal defence. An increasing body of evidence has also implicated NF-κB-mediated innate immunity in antiviral responses against some, but not all, viruses. Specific pattern recognition receptors (PRRs) and molecular events leading to NF-κB activation by viral pathogen-associated molecular patterns (PAMPs) have been elucidated for a number of viruses and insect species. Particularly interesting are recent findings indicating that the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway detects viral RNA to activate NF-κB-regulated gene expression. We summarise the literature on virus-NF-κB pathway interactions across the class Insecta, with a focus on the dipterans Drosophila melanogaster and Aedes aegypti. We discuss potential reasons for differences observed between different virus-host combinations, and highlight similarities and differences between cGAS-STING signalling in insects versus vertebrates. Finally, we summarise the increasing number of known molecular mechanisms by which viruses antagonise NF-κB responses, which suggest that NF-κB-mediated immunity exerts strong evolutionary pressures on viruses. These developments in our understanding of insect antiviral immunity have relevance to the large number of insect species that impact on humans through their transmission of human, livestock and plant diseases, exploitation as biotechnology platforms, and role as parasites, pollinators, livestock and pests.

Interaction of lncRNA-CR33942 with Dif/Dorsal Facilitates Antimicrobial Peptide Transcriptions and Enhances Drosophila Toll Immune Responses

The Drosophila Toll signaling pathway mainly responds to Gram-positive (G⁺) bacteria or fungal infection, which is highly conserved with mammalian TLR signaling pathway. Although many positive and negative regulators involved in the immune response of the Toll pathway have been identified in Drosophila, the roles of long noncoding RNAs (lncRNAs) in Drosophila Toll immune responses are poorly understood to date. In this study, our results demonstrate that lncRNA-CR33942 is mainly expressed in the nucleus and upregulated after Micrococcus luteus infection. Especially, lncRNA-CR33942 not only modulates differential expressions of multiple antimicrobial peptide genes but also affects the Drosophila survival rate during response to G⁺ bacterial infection based on the transiently overexpressing and the knockdown lncRNA-CR33942 assays in vivo. Mechanically, lncRNA-CR33942 interacts with the NF-κB transcription factors Dorsal-related immunity factor/Dorsal to promote the transcriptions of antimicrobial peptides drosomycin and metchnikowin, thus enhancing Drosophila Toll immune responses. Taken together, this study identifies lncRNA-CR33942 as a positive regulator of Drosophila innate immune response to G⁺ bacterial infection to facilitate Toll signaling via interacting with Dorsal-related immunity factor/Dorsal. It would be helpful to reveal the roles of lncRNAs in Toll immune response in Drosophila and provide insights into animal innate immunity.

The Prepropalustrin-2CE2 and Preprobrevinin-2CE3 Gene from Rana Chensinensis: Gene Expression, Genomic Organization, and Functional Analysis of the Promoter Activity

BACKGROUND

Palustrin-2CE2 and brevinin-2CE3 are antimicrobial peptides from Rana chensinensis. In R. chensinensis tadpoles, the expression of prepropalustrin-2CE2 and preprobrevinin-2CE3 increased with the developmental stage. In addition, the expression of the two genes was dramatically upregulated with stimulation by Escherichia coli, Staphylococcus aureus, and the chemical lipopolysaccharide (LPS). The genomic organization of the two antimicrobial peptide genes was confirmed. Both prepropalustrin-2CE2 and preprobrevinin-2CE3 contain three exons separated by two large introns. Additionally, several presumed transcription factor binding sites were identified in the promoter sequence. Functional analysis of the promoter was performed using a luciferase reporter system, and further confirmed by yeast one-hybrid experiment and EMSA assay. The results indicated that the transcription factors NF-κB and RelA are involved in regulating the expression of prepropalustrin-2CE2 and preprobrevinin-2CE3. As amphibian populations decline globally, this study provides new data demonstrating how frogs defend against pathogens from the environment by regulating AMP expression. For amphibians, antimicrobial peptides are innate immune molecules that resist adverse external environmental stimuli. However, the regulation mechanism of antimicrobial peptide gene expression in frogs is still unclear.

OBJECTIVE

The two antimicrobial peptides, palustrin-2CE2 and brevinin-2CE3, are produced under external stimulation in Rana chensinensis. Using this model, we analyzed the gene structure and regulatory elements of the two antimicrobial peptide genes and explored the regulatory effects of related transcription factors on the two genes.

METHOD

Different stimuli such as E. coli, S. aureus, and chemical substance lipopolysaccharide (LPS) were applied to Rana chensinensis tadpoles at different developmental stages, and antimicrobial peptide expression levels were detected by RT-PCR. Bioinformatics analysis and 5'-RACE and genome walking technologies were employed to analyze the genome structure and promoter region of the antimicrobial peptide genes. With dual-luciferase reporter gene assays, yeast one-hybrid experiment and EMSA assays, we assessed the regulatory effect of the endogenous regulators of the cell on the antimicrobial peptide promoter.

RESULTS

The transcription levels of prepropalustrin-2CE2 and preprobrevinin-2CE3 were significantly upregulated after different stimulations. Genomic structure analysis showed that both genes contained three exons and two introns. Promoter analysis indicated that there are binding sites for regulatory factors of the NF-κB family in the promoter region, and experiments showed that endogenous NF-κB family regulatory factors in frog cells activate the promoters of the antimicrobial peptide genes. Yeast one-hybrid experiment and EMSA assay demonstrated that RelA and NF-κB1 might interact with specific motifs in the prepropalustrin-2CE2 promoter.

CONCLUSION

In this paper, we found that the gene expression levels of the antimicrobial peptides, palustrin-2CE2 and brevinin-2CE3, in R. chensinensis will increase under environmental stimuli, and we verified that the changes in gene expression levels are affected by the transcription factors RelA and NF-κB1. The yeast one-hybrid experiment and EMSA assay confirmed that RelA and NF-κB1 could directly interact with the frog antimicrobial peptide gene promoter, providing new data for the regulatory mechanism of antimicrobial peptides in response to environmental stimuli.

lncRNA-CR46018 positively regulates the Drosophila Toll immune response by interacting with Dif/Dorsal

The Toll signaling pathway is highly conserved from insects to mammals. Drosophila is a model species that is commonly used to study innate immunity. Although many studies have assessed protein-coding genes that regulate the Toll pathway, it is unclear whether long noncoding RNAs (lncRNAs) play regulatory roles in the Toll pathway. Here, we evaluated the expression of the lncRNA CR46018 in Drosophila. Our results showed that this lncRNA was significantly overexpressed after infection of Drosophila with Micrococcus luteus. A CR46018-overexpressing Drosophila strain was then constructed; we expected that CR46018 overexpression would enhance the expression of various antimicrobial peptides downstream of the Toll pathway, regardless of infection with M. luteus. RNA-seq analysis of CR46018-overexpressing Drosophila after infection with M. luteus showed that upregulated genes were mainly enriched in Toll and Imd signaling pathways. Moreover, bioinformatics predictions and RNA-immunoprecipitation experiments showed that CR46018 interacted with the transcription factors Dif and Dorsal to enhance the Toll pathway. During gram-positive bacterial infection, flies overexpressing CR46018 showed favorable survival compared with flies in the control group. Overall, our current work not only reveals a new immune regulatory factor, lncRNA-CR46018, and explores its potential regulatory model, but also provides a new perspective for the effect of immune disorders on the survival of Drosophila melanogaster.

An apocrine mechanism delivers a fully immunocompetent exocrine secretion

Apocrine secretion is a recently discovered widespread non-canonical and non-vesicular secretory mechanism whose regulation and purpose is only partly defined. Here, we demonstrate that apocrine secretion in the prepupal salivary glands (SGs) of Drosophila provides the sole source of immune-competent and defense-response proteins to the exuvial fluid that lies between the metamorphosing pupae and its pupal case. Genetic ablation of its delivery from the prepupal SGs to the exuvial fluid decreases the survival of pupae to microbial challenges, and the isolated apocrine secretion has strong antimicrobial effects in "agar-plate" tests. Thus, apocrine secretion provides an essential first line of defense against exogenously born infection and represents a highly specialized cellular mechanism for delivering components of innate immunity at the interface between an organism and its external environment.

Imd pathway-specific immune assays reveal NF-κB stimulation by viral RNA PAMPs in Aedes aegypti Aag2 cells

BACKGROUND

The mosquito Aedes aegypti is a major vector for the arthropod-borne viruses (arboviruses) chikungunya, dengue, yellow fever and Zika viruses. Vector immune responses pose a major barrier to arboviral transmission, and transgenic insects with altered immunity have been proposed as tools for reducing the global public health impact of arboviral diseases. However, a better understanding of virus-immune interactions is needed to progress the development of such transgenic insects. Although the NF-κB-regulated Toll and 'immunodeficiency' (Imd) pathways are increasingly thought to be antiviral, relevant pattern recognition receptors (PRRs) and pathogen-associated molecular patterns (PAMPs) remain poorly characterised in A. aegypti.

METHODOLOGY/PRINCIPLE FINDINGS

We developed novel RT-qPCR and luciferase reporter assays to measure induction of the Toll and Imd pathways in the commonly used A. aegypti-derived Aag2 cell line. We thus determined that the Toll pathway is not inducible by exogenous stimulation with bacterial, viral or fungal stimuli in Aag2 cells under our experimental conditions. We used our Imd pathway-specific assays to demonstrate that the viral dsRNA mimic poly(I:C) is sensed by the Imd pathway, likely through intracellular and extracellular PRRs. The Imd pathway was also induced during infection with the model insect-specific virus cricket paralysis virus (CrPV).

CONCLUSIONS/SIGNIFICANCE

Our demonstration that a general PAMP shared by many arboviruses is sensed by the Imd pathway paves the way for future studies to determine how viral RNA is sensed by mosquito PRRs at a molecular level. Our data also suggest that studies measuring inducible immune pathway activation through antimicrobial peptide (AMP) expression in Aag2 cells should be interpreted cautiously given that the Toll pathway is not responsive under all experimental conditions. With no antiviral therapies and few effective vaccines available to treat arboviral diseases, our findings provide new insights relevant to the development of transgenic mosquitoes as a means of reducing arbovirus transmission.

Fungal compound 1-octen-3-ol induces mitochondrial morphological alterations and respiration dysfunctions in Drosophila melanogaster

Fungal volatile organic compounds (VOCs) comprise a group of compounds commonly found in damp or water-damaged indoor places affecting air quality. Indoor fungal pollution is a severe threat to human health, contributing to the onset of allergic diseases. The compound 1-octen-3-ol, known as "mushroom alcohol", is the most abundant VOC and confers the characteristic mold odor. Exposure to 1-octen-3-ol induces inflammatory markers and episodes of allergic rhinitis and conjunctivitis; however, the effects of this compound towards mitochondria are fairly known. The present study aimed to evaluate the effects of 1-octen-3-ol on inflammatory targets and on mitochondrial morphology and bioenergetic rate in D. melanogaster. Drosophilas were exposed by inhalation to 2.5 μL/L and 5 μL/L of 1-octen-3-ol for 24 h. Observation showed a decreasing in the survival and locomotor ability of flies. Superoxide dismutase (SOD) activity was induced whereas Catalase (CAT) activity was inhibited. Analysis of the mitochondria respiration, detected inhibition of complex I and II in the electron transport chain and a decreased bioenergetic rate. Electronic microscopy provided morphological insights of the mitochondrial status in which a disarrangement in mitochondrial cristae profile was observed. 1-Octen-3-ol induced increased activity of caspase 3/7 and ERK phosphorylation. The mRNA relative steady-state levels of p38^MAPK and JNK were down-regulated, whereas NF-κB and p53 were up-regulated. In parallel, nitrite levels were induced in relation to the non-exposed group. These findings point to the mitochondria as a crucial target for the toxicity of 1-octen-3-ol in parallel with activation of pro-inflammatory factors and apoptotic signaling pathway cascade.

Survival Following Traumatic Brain Injury in Drosophila Is Increased by Heterozygosity for a Mutation of the NF-κB Innate Immune Response Transcription Factor Relish

Traumatic brain injury (TBI) pathologies are caused by primary and secondary injuries. Primary injuries result from physical damage to the brain, and secondary injuries arise from cellular responses to primary injuries. A characteristic cellular response is sustained activation of inflammatory pathways commonly mediated by nuclear factor-κB (NF-κB) transcription factors. Using a Drosophila melanogaster TBI model, we previously found that the main proximal transcriptional response to primary injuries is triggered by activation of Toll and Imd innate immune response pathways that engage NF-κB factors Dif and Relish (Rel), respectively. Here, we found by mass spectrometry that Rel protein level increased in fly heads at 4-8 hr after TBI. To investigate the necessity of Rel for secondary injuries, we generated a null allele, Reldel , by CRISPR/Cas9 editing. When heterozygous but not homozygous, the Reldel mutation reduced mortality at 24 hr after TBI and increased the lifespan of injured flies. Additionally, the effect of heterozygosity for Reldel on mortality was modulated by genetic background and diet. To identify genes that facilitate effects of Reldel on TBI outcomes, we compared genome-wide mRNA expression profiles of uninjured and injured +/+, +/Reldel , and Reldel /Reldel flies at 4 hr following TBI. Only a few genes changed expression more than twofold in +/Reldel flies relative to +/+ and Reldel /Reldel flies, and they were not canonical innate immune response genes. Therefore, Rel is necessary for TBI-induced secondary injuries but in complex ways involving Rel gene dose, genetic background, diet, and possibly small changes in expression of innate immune response genes.

Dichloroacetate-induced metabolic reprogramming improves lifespan in a Drosophila model of surviving sepsis

Sepsis is the leading cause of death in hospitalized patients and beyond the hospital stay and these long-term sequelae are due in part to unresolved inflammation. Metabolic shift from oxidative phosphorylation to aerobic glycolysis links metabolism to inflammation and such a shift is commonly observed in sepsis under normoxic conditions. By shifting the metabolic state from aerobic glycolysis to oxidative phosphorylation, we hypothesized it would reverse unresolved inflammation and subsequently improve outcome. We propose a shift from aerobic glycolysis to oxidative phosphorylation as a sepsis therapy by targeting the pathways involved in the conversion of pyruvate into acetyl-CoA via pyruvate dehydrogenase (PDH). Chemical manipulation of PDH using dichloroacetic acid (DCA) will promote oxidative phosphorylation over glycolysis and decrease inflammation. We tested our hypothesis in a Drosophila melanogaster model of surviving sepsis infected with Staphylococcus aureus. Drosophila were divided into 3 groups: unmanipulated, sham and sepsis survivors, all treated with linezolid; each group was either treated or not with DCA for one week following sepsis. We followed lifespan, measured gene expression of Toll, defensin, cecropin A, and drosomycin, and levels of lactate, pyruvate, acetyl-CoA as well as TCA metabolites. In our model, metabolic effects of sepsis are modified by DCA with normalized lactate, TCA metabolites, and was associated with improved lifespan of sepsis survivors, yet had no lifespan effects on unmanipulated and sham flies. While Drosomycin and cecropin A expression increased in sepsis survivors, DCA treatment decreased both and selectively increased defensin.

Two relish isoforms produced by alternative splicing participate in the regulation of antimicrobial peptides expression in Procambarus clarkii intestine

Nuclear factor κB (NF-κB) plays a key role in the innate immunity of invertebrates. Relish belongs to the NF-κB family. In insects, alternative splicing induces the sequence diversity of the Relish gene. However, information on the roles of various relish isoforms in crustacean innate immune response is limited. Here, two alternatively spliced Relish isoforms (designated as SPcRelish and LPcRelish) were identified from freshwater crayfish (Procambarus clarkii), and functional analysis was performed. The Relish gene has 25 exons and 24 introns. The long isoform LPcRelish is fully spliced, whereas the short isoform SPcRelish is alternatively spliced and contains exon 1-9 and a retention of intron 9. LPcRelish contains the Rel homology domain (RHD), the ig-like, plexins, transcription factors (IPT), and ankyrin-repeat (ANK) inhibitory domain. However, SPcRelish contains only the RHD and IPT domain, and does not have an ANK domain. The transcripts of SPcRelish and LPcRelish can be regulated by Vibrio parahaemolyticus. The intestinal immunological barrier and bacterial balance in the intestine play crucial roles in host health. In this study, we analyzed the connection between Relish isoforms and the transcripts of antimicrobial peptides (AMPs) in intestine. The transcripts of all the tested AMPs, except ALF-41125, were upregulated by V. parahaemolyticus. The knock down of the SPcRelish gene resulted in a significant decrease in the expression levels of ALF-7032, ALF-13162, and Crustin-42012 during V. parahaemolyticus invasion. The expression levels of four AMP genes (ALF-41125, ALF-42430, Crustin-41354, and Crustin-42993) were obviously increased in V. parahaemolyticus-challenged SPcRelish-silenced crayfish. ALF-7032, ALF-9228, ALF-13162, ALF-42430, Crustin-41354, Crustin-42012, and Crustin-42993 were evidently downregulated in V. parahaemolyticus-infected LPcRelish-silenced crayfish. Overall, generating the two Relish isoforms by alternative splicing may be an important mechanism of the host immune system to promote molecular diversity, which results in the functional diversity of the relish transcription factor.

Positive and negative regulatory effects of transcription factor activator protein 1 (AP1) on the expression of antimicrobial peptides in Macrobrachium nipponense

Transcription factor activator protein 1 (AP1) plays an irreplaceable role in the response to a variety of external stimulants, such as cellar stress, bacterial and viral infections, and inflammatory cytokines. In this study, we identified a novel AP1 gene from Macrobrachium nipponense and named it MnAP1, which has a full length of 1747 bp contains an 882 bp open reading frame, and encodes a protein with 293 amino acids. The MnAP1 protein contains Pfam and bZIP domains. MnAP1 is widely distributed in hemocytes, heart, hepatopancreas, gill, stomach, and intestinal tissues. The expression levels of MnAP1 in the gills and stomach were significantly upregulated after Vibrio parahaemolyticus and Staphylococcus aureus attacks. We studied the relationship between MnAP1 and the transcripts of antimicrobial peptides (AMPs) in gills through RNA interference. Interestingly, the regulatory effects of MnAP1 on the expression of different AMPs were different. We found that the expression levels of crustins, including Cru1, Cru3, and Cru4 in the gills were evidently decreased, whereas the synthesis of Cru5 and anti-lipopolysaccharide factors (ALF3 and ALF4) were obviously increased. We further explored the effect of MnAP1 on the expression of transcription factor relish from M. nipponense. The result showed that the knockdown of MnAP1 can remarkably upregulate the expression of MnRelish. Relish as a member of the nuclear factor κB family that regulates the expression of AMPs in the innate immunity of crustacean. Hence, we also detected the expression levels of Cru5, ALF3, and ALF4 in the gills of MnRelish-silenced prawns. The Data showed that the expression levels of these three AMPs were evidently reduced after MnRelish silencing. Our results indicated that MnAP1 plays a positive role in regulating the expression of AMPs, promotes the JNK/AP1 signaling pathway, and exerts a negative regulatory effect on the synthesis of AMPs by inhibiting the transcription of NF-κB factor in the innate immunity of M. nipponense.

Temporal changes in transcriptome profile provide insights of White Spot Syndrome Virus infection in Litopenaeus vannamei

Shrimp aquaculture is severely affected by WSSV. Despite an increasing effort to understand host/virus interaction by characterizing changes in gene expression (GE) following WSSV infection, the majority of published studies have focussed on a single time-point, providing limited insight on the development of host-pathogen interaction over the infection cycle. Using RNA-seq, we contrasted GE in gills of Litopenaeus vannamei at 1.5, 18 and 56 hours-post-infection (hpi), between WSSV-challenged and control shrimps. Time course analysis revealed 5097 differentially expressed genes: 63 DEGs were viral genes and their expression in WSSV group either peaked at 18 hpi (and decreased at 56 hpi) or increased linearly up to 56 hpi, suggesting a different role played by these genes during the course of infection. The remaining DEGs showed that WSSV altered the expression of metabolic, immune, apoptotic and cytoskeletal genes and was able to inhibit NF-κB and JAK/STAT pathways. Interestingly, GE changes were not consistent through the course of infection but were dynamic with time, suggesting the complexity of host-pathogen interaction. These data offer novel insights into the cellular functions that are affected during the course of infection and ultimately provide a valuable resource towards our understanding of the host-pathogen dynamics and its variation with time.

Ingestion of killed bacteria activates antimicrobial peptide genes in Drosophila melanogaster and protects flies from septic infection

Drosophila melanogaster possesses a sophisticated and effective immune system composed of humoral and cellular immune responses, and production of antimicrobial peptides (AMPs) is an important defense mechanism. Expression of AMPs is regulated by the Toll and IMD (immune deficiency) pathways. Production of AMPs can be systemic in the fat body or a local event in the midgut and epithelium. So far, most studies focus on systemic septic infection in adult flies and little is known about AMP gene activation after ingestion of killed bacteria. In this study, we investigated activation of AMP genes in the wild-type w¹¹¹⁸, MyD88 and Imd mutant flies after ingestion of heat-killed Escherichia coli and Staphylococcus aureus. We showed that ingestion of E. coli activated most AMP genes, including drosomycin and diptericin, in the first to third instar larvae and pupae, while ingestion of S. aureus induced only some AMP genes in some larval stages or in pupae. In adult flies, ingestion of killed bacteria activated AMP genes differently in males and females. Interestingly, ingestion of killed E. coli and S. aureus in females conferred resistance to septic infection by both live pathogenic Enterococcus faecalis and Pseudomonas aeruginosa, and ingestion of E. coli in males conferred resistance to P. aeruginosa infection. Our results indicated that E. coli and S. aureus can activate both the Toll and IMD pathways, and systemic and local immune responses work together to provide Drosophila more effective protection against infection.