Immune proteins and their gene expression in the silkworm, Bombyx mori

Hemocytin, the special aggregation factor connecting insect hemolymph immunity, a potential target of insecticidal immunosuppresant

Insects possess an effective innate immunity that enables them to adapt to their intricate living environment and fend off various pathogens (or parasites). This innate immunity comprises both humoral and cellular immunity, which synergistically orchestrate immune responses. Hemocytin, a lectin with a distinctive structure, plays a crucial role in insect hemolymph immunity. Hemocytin is involved in the early immune response, facilitating processes such as coagulation, nodulation, and encapsulation in the hemolymph. It prevents hemolymph overflow and microbial pathogens invasion resulting from epidermal damage, and also aids in the recognition and elimination of invaders. However, the research on hemocytin is still limited. Our previous findings demonstrated that destruxin A effectively inhibits insect hemolymph immunity by interacting with hemocytin, suggesting that hemocytin could be a potential target for insecticides development. Therefore, it is crucial to gain a deeper understanding of hemocytin. This review integrates recent advancements in the study of the structure and function of insect hemocytin and also explores the potential of hemocytin as a target for insecticides. This review aims to enhance our comprehension of insect innate immunity and provide innovative ideas for the development of environmentally friendly pesticides.

A new antimicrobial peptide, Pentatomicin, from the stinkbug Plautia stali

Antimicrobial peptides (AMPs) play crucial roles in the innate immunity of diverse organisms, which exhibit remarkable diversity in size, structural property and antimicrobial spectrum. Here, we describe a new AMP, named Pentatomicin, from the stinkbug Plautia stali (Hemiptera: Pentatomidae). Orthologous nucleotide sequences of Pentatomicin were present in stinkbugs and beetles but not in other insect groups. Notably, orthologous sequences were also detected from a horseshoe crab, cyanobacteria and proteobacteria, suggesting the possibility of inter-domain horizontal gene transfers of Pentatomicin and allied protein genes. The recombinant protein of Pentatomicin was effective against an array of Gram-positive bacteria but not against Gram-negative bacteria. Upon septic shock, the expression of Pentatomicin drastically increased in a manner similar to other AMPs. On the other hand, unlike other AMPs, mock and saline injections increased the expression of Pentatomicin. RNAi-mediated downregulation of Imd pathway genes (Imd and Relish) and Toll pathway genes (MyD88 and Dorsal) revealed that the expression of Pentatomicin is under the control of Toll pathway. Being consistent with in vitro effectiveness of the recombinant protein, adult insects injected with dsRNA of Pentatomicin exhibited higher vulnerability to Gram-positive Staphylococcus aureus than to Gram-negative Escherichia coli. We discovered high levels of Pentatomicin expression in eggs, which is atypical of other AMPs and suggestive of its biological functioning in eggs. Contrary to the expectation, however, RNAi-mediated downregulation of Pentatomicin did not affect normal embryonic development of P. stali. Moreover, the downregulation of Pentatomicin in eggs did not affect vertical symbiont transmission to the offspring even under heavily contaminated conditions, which refuted our expectation that the antimicrobial activity of Pentatomicin may contribute to egg surface-mediated symbiont transmission by suppressing microbial contaminants.

Characterisation of the enzyme transport path between shipworms and their bacterial symbionts

Background

Shipworms are marine xylophagus bivalve molluscs, which can live on a diet solely of wood due to their ability to produce plant cell wall-degrading enzymes. Bacterial carbohydrate-active enzymes (CAZymes), synthesised by endosymbionts living in specialised shipworm cells called bacteriocytes and located in the animal’s gills, play an important role in wood digestion in shipworms. However, the main site of lignocellulose digestion within these wood-boring molluscs, which contains both endogenous lignocellulolytic enzymes and prokaryotic enzymes, is the caecum, and the mechanism by which bacterial enzymes reach the distant caecum lumen has remained so far mysterious. Here, we provide a characterisation of the path through which bacterial CAZymes produced in the gills of the shipworm Lyrodus pedicellatus reach the distant caecum to contribute to the digestion of wood.

Results

Through a combination of transcriptomics, proteomics, X-ray microtomography, electron microscopy studies and in vitro biochemical characterisation, we show that wood-digesting enzymes produced by symbiotic bacteria are localised not only in the gills, but also in the lumen of the food groove, a stream of mucus secreted by gill cells that carries food particles trapped by filter feeding to the mouth. Bacterial CAZymes are also present in the crystalline style and in the caecum of their shipworm host, suggesting a unique pathway by which enzymes involved in a symbiotic interaction are transported to their site of action. Finally, we characterise in vitro four new bacterial glycosyl hydrolases and a lytic polysaccharide monooxygenase identified in our transcriptomic and proteomic analyses as some of the major bacterial enzymes involved in this unusual biological system.

Conclusion

Based on our data, we propose that bacteria and their enzymes are transported from the gills along the food groove to the shipworm’s mouth and digestive tract, where they aid in wood digestion.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01162-6.

Proteomics and ultrastructural analysis of Hermetia illucens (Diptera: Stratiomyidae) larval peritrophic matrix

BACKGROUND

The black soldier fly (Hermetia illucens) has significant economic potential. The larvae can be used in financially viable waste management systems, as they are voracious feeders able to efficiently convert low-quality waste into valuable biomass. However, most studies on H. illucens in recent decades have focused on optimizing their breeding and bioconversion conditions, while information on their biology is limited.

METHODS

About 200 fifth instar well-fed larvae were sacrificed in this work. The liquid chromatography-tandem mass spectrometry and scanning electron microscopy were employed in this study to perform a proteomic and ultrastructural analysis of the peritrophic matrix (PM) of H. illucens larvae.

RESULTS

A total of 565 proteins were identified in the PM samples of H. illucen, of which 177 proteins were predicted to contain signal peptides, bioinformatics analysis and manual curation determined 88 proteins may be associated with the PM, with functions in digestion, immunity, PM modulation, and others. The ultrastructure of the H. illucens larval PM observed by scanning electron microscopy shows a unique diamond-shaped chitin grid texture.

CONCLUSIONS

It is the first and most comprehensive proteomics research about the PM of H. illucens larvae to date. All the proteins identified in this work has been discussed in details, except several unnamed or uncharacterized proteins, which should not be ignored and need further study. A comparison of the ultrastructure between H. illucens larval PM and those of other insects as observed by SEM indicates that the PM displays diverse textures on an ultra-micro scale and we suscept a unique diamond-shaped chitin grid texture may help H. illucens larval to hold more food. This work deepens our understanding of the molecular architecture and ultrastructure of the H. illucens larval PM.

A Tale of Two Transcriptomic Responses in Agricultural Pests via Host Defenses and Viral Replication

Autographa californica Multiple Nucleopolyhedrovirus (AcMNPV) is a baculovirus that causes systemic infections in many arthropod pests. The specific molecular processes underlying the biocidal activity of AcMNPV on its insect hosts are largely unknown. We describe the transcriptional responses in two major pests, Spodoptera frugiperda (fall armyworm) and Trichoplusia ni (cabbage looper), to determine the host-pathogen responses during systemic infection, concurrently with the viral response to the host. We assembled species-specific transcriptomes of the hemolymph to identify host transcriptional responses during systemic infection and assessed the viral transcript abundance in infected hemolymph from both species. We found transcriptional suppression of chitin metabolism and tracheal development in infected hosts. Synergistic transcriptional support was observed to suggest suppression of immune responses and induction of oxidative stress indicating disease progression in the host. The entire AcMNPV core genome was expressed in the infected host hemolymph with a proportional high abundance detected for viral transcripts associated with replication, structure, and movement. Interestingly, several of the host genes that were targeted by AcMNPV as revealed by our study are also targets of chemical insecticides currently used commercially to control arthropod pests. Our results reveal an extensive overlap between biological processes represented by transcriptional responses in both hosts, as well as convergence on highly abundant viral genes expressed in the two hosts, providing an overview of the host-pathogen transcriptomic landscape during systemic infection.

Hemocytin facilitates host immune responses against Nosema bombycis

Invertebrates lack an adaptive immune response and thus are reliant on their innate immune response for eliminating invading pathogens. The innate immune responses of silkworms against the pathogen Nosema bombycis include: hemocyte aggregation, melanization, antimicrobial peptides, etc. In our current study, we discovered that a silkworm hemostasis-related protein, hemocytin, is up-regulated after Nosema bombycis infection. This novel finding lead to our hypothesis that hemocytin participates in immune responses against N. bombycis. We investigated this hypothesis by analyzing the adhesive effects of hemocytin to invading N. bombycis, and the hemocytin-mediated hemocyte aggregation and hemolymph melanization. We showed that hemocytin can adhere to the surface of N. bombycis, which facilitates the agglutination of N. bombycis and hemocytes as well as the subsequent melanization. Moreover, when we utilize RNAi technology to decrease in vivo hemocytin expression, we found that the proliferation of N. bombycis within the host significantly increased. These results support our hypothesis that hemocytin exerts pro-inflammatory effects by facilitating pathogen agglutination, along with hemocyte aggregation and melanization, to combat N. bombycis. Our study is the first to determine a function of hemocytin in innate immunity against N. bombycis. Moreover, our findings are of great importance to provide potential targets for developing novel strategy against microsporidia infection.

Antimicrobial peptides fromBombyx mori: a splendid immune defense response in silkworms

Bombyx mori L., a primary producer of silk, is the main tool in the sericulture industry and provides the means of livelihood to a large number of people. Silk cocoon crop losses due to bacterial infection pose a major threat to the sericulture industry. Bombyx mori L., a silkworm of the mulberry type, has a sophisticated inherent innate immune mechanism to combat such invasive pathogens. Among all the components in this defense system, antimicrobial peptides (AMPs) are notable due to their specificity towards the invading pathogens without harming the normal host cells. Bombyx mori L. so far has had AMPs identified that belong to six different families, namely cecropin, defensin, moricin, gloverin, attacin and lebocin, which are produced by the Toll and immune deficiency (IMD) pathways. Their diverse modes of action depend on microbial pathogens and are still under investigation. This review examines the recent progress in understanding the immune defense mechanism of Bombyx mori based on AMPs.

AMPs produced by B. mori induced by microbial challenge in the fat body.

Immune responses to bacterial and fungal infections in the silkworm, Bombyx mori

The silkworm Bombyx mori, an economically important insect that is usually reared indoors, is susceptible to various pathogens, including bacteria, fungi, viruses, and microsporidia. As with other insects, the silkworm lacks an adaptive immune system and relies solely on innate immunity to defend itself against infection. Compared to other intensively studied insects, such as the fruit fly and tobacco hornworm, the principal immune pathways in the silkworm remain unclear. In this article, we review the literature concerning silkworm immune responses to bacteria and fungi and present our perspectives on future research into silkworm immunity.

Identification of Secreted Proteins Involved in Nonspecific dsRNA-Mediated Lutzomyia longipalpis LL5 Cell Antiviral Response

Hematophagous insects transmit infectious diseases. Sand flies are vectors of leishmaniasis, but can also transmit viruses. We have been studying immune responses of Lutzomyia longipalpis, the main vector of visceral leishmaniasis in the Americas. We identified a non-specific antiviral response in L. longipalpis LL5 embryonic cells when treated with non-specific double-stranded RNAs (dsRNAs). This response is reminiscent of interferon response in mammals. We are investigating putative effectors for this antiviral response. Secreted molecules have been implicated in immune responses, including interferon-related responses. We conducted a mass spectrometry analysis of conditioned medium from LL5 cells 24 and 48 h after dsRNA or mock treatment. We identified 304 proteins. At 24 h, 19 proteins had an abundance equal or greater than 2-fold change, while the levels of 17 proteins were reduced when compared to control cells. At the 48 h time point, these numbers were 33 and 71, respectively. The two most abundant secreted peptides at 24 h in the dsRNA-transfected group were phospholipid scramblase, an interferon-inducible protein that mediates antiviral activity, and forskolin-binding protein (FKBP), a member of the immunophilin family, which mediates the effect of immunosuppressive drugs. The transcription profile of most candidates did not follow the pattern of secreted protein abundance.

SWATH-based quantitative proteomics reveals the mechanism of enhanced Bombyx mori nucleopolyhedrovirus-resistance in silkworm reared on UV-B treated mulberry leaves

Bombyx mori nucleopolyhedrovirus (BmNPV) is one of the most acute infectious diseases in silkworm, which has led to great economic loss in sericulture. Previous study showed that the content of secondary metabolites in mulberry leaves, particularly for moracin N, was increased after UV-B irradiation. In this study, the BmNPV resistance of silkworms reared on UV-B treated and moracin N spread mulberry leaves was improved. To uncover the mechanism of enhanced BmNPV resistance, silkworm midguts from UV-B treated mulberry leaves (BUM) and moracin N (BNM) groups were analyzed by SWATH-based proteomic technique. Of note, the abundance of ribosomal proteins in BUM and BNM groups was significantly changed to maintain the synthesis of total protein levels and cell survival. While, cytochrome c oxidase subunit II, calcium ATPase and programmed cell death 4 involved in apoptotic process were up-regulated in BNM group. Expressions of lipase-1, serine protease precursor, Rab1 protein, and histone genes were increased significantly in BNM group. These results suggest that moracin N might be the main active component in UV-B treated mulberry leaves which could improve the BmNPV-resistance of silkworm through promoting apoptotic cell death, enhancing the organism immunity, and regulating the intercellular environment of cells in silkworm. It also presents an innovative process to reduce the mortality rate of silkworms infected with BmNPV.

Serine protease Bm-SP142 was differentially expressed in resistant and susceptible Bombyx mori strains, involving in the defence response to viral infection

Bm-SP142 is a 35 kDa protease in the silkworm, but its exact functions remain unknown. In this study, sequence alignment revealed that the His-Asp-Ser catalytic triad is embedded in the TAAHC-DIAL-GDSGGP sequence motif, establishing Bm-SP142 as a serine protease. Soluble recombinant GST-BmSP142 was expressed and purified, and serine protease activity was confirmed in vitro. RT-qPCR results indicated that Bm-SP142 was mainly expressed in the middle part of the silkworm midgut, and Bm-SP142 transcripts were significantly up-regulated at 24 hours post infection (hpi) in BmBDV-resistant strains (798) inoculated with BmBDV and BmNPV-resistant strains (NB) inoculated with BmNPV, but not in BmBDV-susceptible strains (306). Surprisingly, transcripts were significantly down-regulated at 12 hpi in BmNPV-susceptible strains (HuaBa 35) inoculated with BmNPV, compared with healthy silkworms. Recombinant BmNPV treated with purified Bm-SP142 effectively impaired its ability to infect BmN cells, and Bm-SP142 decreases the efficiency of BmNPV and BmBDV propagation in silkworms. Furthermore, overexpression of Bm-SP142 in BmN cells inhibited viral propagation.

Characterization of the Bombyx mori Cecropin A1 promoter regulated by IMD pathway

Cecropin A1 (CecA1) promoter from Bombyx mori was cloned and characterized to provide insight into the transcriptional control of this antimicrobial peptide gene upon immune challenges. Reporter gene assays demonstrated that both Escherichia coli and lipopolysaccharide could induce expression in BmE cells but B. bombyseptieus or peptidoglycan failed, and the induction pattern of the reporter gene was coincident with the endogenous CecA1. Analysis of deletion and mutation constructs revealed that the regulatory region was the κB motif located between -176 and -166, and no other predicted elements on CecA1 promoter affected its inducibility. Insertion of additional κB motifs increased the activity of CecA1 promoter. Furthermore, binding of Relish to κB motif was confirmed by electrophoretic mobility shift assay. These findings indicate the regulatory mechanism of CecA1 expression in IMD pathway and suggest an approach of engineering antimicrobial peptide promoter with enhanced activities that may lead to broad applications.

Identification of a Soluble NADPH Oxidoreductase (BmNOX) with Antiviral Activites in the Gut Juice ofBombyx mori

Silkworms show high variability in silk quality and disease resistance. Attempts are on to combine the disease tolerance of multivoltine races and the silk quality of bivoltine races to generate new races with desirable phenotypic traits. We report the identification of a 26.5-kDa protein that is overexpressed in the gut juice of disease-resistant multivoltine races and that has anti-BmNPV activity. We have characterized this protein as a soluble NADH-oxidoreductase-like protein (BmNOX). Treatment of live BmNPV particles with BmNOX inhibited the capability of the viral particles to infect BmN cells in vitro.

Proteomic Studies of Lipopolysaccharide-induced Polypeptides in the Silkworm,Bombyx mori

Silkworm larvae at the 5th instar were injected with lipopolysaccharide from Escherichia coli and inducible polypeptides were examined within a pI range of 3-10 and a size range of 14-97 kDa by proteomics, including peptide mass fingerprinting. No polypeptides were induced in the midgut. FB1 and H1-4 polypeptides were significantly induced in fat body and hemolymph, respectively. FB1 and H1 were estimated to be antitrypsin and serpin-2 proteinase inhibitors respectively. H2 and H3 were novel polypeptides. H4 was estimated to be attacin antibacterial polypeptide with high coverage of sequence. The amounts of all the induced polypeptides decreased at 48 h after the injection.

Identification and analysis of genes differentially expressed in the Spodoptera litura fat body in response to the biocontrol fungus, Nomuraea rileyi

Nomuraea rileyi is an important pathogenic fungus that can successfully control Spodoptera litura. However, little is known on how S. litura responds to N. rileyi infection. A forward suppression subtractive hybridization (SSH) cDNA library was constructed from the S. litura fat body and the up-regulated genes were identified to isolate differentially expressed genes in response to N. rileyi. A total of 345/1175 random clones screened by cDNA array dot blotting were sequenced, resulting in 117 uniquely expressed sequence tags (ESTs). Potential functional genes were identified by BLAST searches and were categorized into seven groups associated with different biological processes based on the literature and gene ontologies. Among 117 genes, 74 had matches in the non-redundant (NR) protein database and were found to be involved in different biological processes, while 43 of the screened genes were classified to the "unknown function" gene group. Notably, only two genes had previously been reported in S. litura and most of the screened genes showed less similarity to known sequences based on BLASTn results, suggesting that 115 genes were found for the first time in S. litura. Semi-quantitative RT-PCR analysis of seven randomly selected genes revealed that most were differentially expressed after N. rileyi infection. qRT-PCR analysis confirmed that four genes (Hsp70, Hsp90, gallerimycin, and cysteine proteinase) were significantly up-regulated after N. rileyi infection. Taken together, the present study identified up-regulated S. litura genes in response to N. rileyi infection. Further investigations are needed to unravel the molecular mechanisms of the genes or proteins potentially involved in the S. litura innate immune defense against N. rileyi infection.

Comparative proteomic analysis reveals that caspase-1 and serine protease may be involved in silkworm resistance to Bombyx mori nuclear polyhedrosis virus

The silkworm Bombyx mori is of great economic value. The B. mori nuclear polyhedrosis virus (BmNPV) is one of the most common and severe pathogens for silkworm. Although certain immune mechanisms exist in silkworms, most silkworms are still susceptible to BmNPV infection. Interestingly, BmNPV infection resistance in some silkworm strains is varied and naturally existing. We have previously established a silkworm strain NB by genetic cross, which is highly resistant to BmNPV invasion. To investigate the molecular mechanism of silkworm resistance to BmNPV infection, we employed proteomic approach and genetic cross to globally identify proteins differentially expressed in parental silkworms NB and 306, a BmNPV-susceptible strain, and their F(1) hybrids. In all, 53 different proteins were found in direct cross group (NB♀, 306♂, F(1) hybrid) and 21 in reciprocal cross group (306♀, NB♂, F(1) hybrid). Gene ontology and KEGG pathway analyses showed that most of these different proteins are located in cytoplasm and are involved in many important metabolisms. Caspase-1 and serine protease expressed only in BmNPV-resistant silkworms, but not in BmNPV-susceptible silkworms, which was further confirmed by Western blot. Taken together, our data suggests that both caspase-1 and serine protease play a critical role in silkworm resistance against BmNPV infection.

Lipoteichoic acid and lipopolysaccharide can activate antimicrobial peptide expression in the tobacco hornworm Manduca sexta

Activation of prophenoloxidase and synthesis of antimicrobial peptides (AMPs) are two important innate immune mechanisms in insects. In the current study, we investigated immune responses activated by three major bacterial components, lipopolysaccharide (LPS) (including rough mutants of LPS), lipoteichoic acid (LTA), and peptidoglycan (PG), in the larvae of a lepidopteran insect, Manduca sexta. We found that two DAP (diaminopimelic acid)-type PGs from Escherichia coli and Bacillus subtilis were much more potent than LPS and LTA from the respective bacteria as well as a Lysine-type PG in activation of prophenoloxidase in M. sexta larval plasma in vitro. Transcription levels of AMP genes, such as Attacin, Lebocin and Moricin genes, in the hemocytes and fat body of larvae were significantly induced by smooth LPS (TLR4grade) and rough mutants of LPS (TLRgrade), synthetic lipid A, LTA, and PG. LPS from E. coli and LTA from B. subtilis activated AMP expression to significantly higher levels than PGs from the respective bacterial strains, and smooth LPS were more potent than lipid A and rough mutants of LPS in activation of AMP expression. Our results demonstrated for the first time that LTA can activate AMP expression, and different moieties of LPS may synergistically activate AMP expression in M. sexta.

Discovering microRNAs from Bombyx mori nucleopolyhedrosis virus

MicroRNAs (miRNAs) have emerged as key players in host-pathogen interaction. Recently, many virus-encoded miRNAs have been identified from different mammalian species. However, the large family of invertebrate viruses of Baculoviridae, which infects diverse species of beneficial insects and agriculture pests, has hardly been investigated for elucidating the role of miRNAs in host-pathogen interaction. In the study reported here, we have identified four Bombyx mori nucleopolyhedrosis virus (BmNPV)-encoded miRNAs using a combination of in silico and experimental methods. Unlike other reported viral miRNAs, the BmNPV-encoded miRNAs identified in the present study were found to be evolutionarily conserved among many closely related baculoviruses. Besides, we have computationally predicted 8 viral and 64 cellular targets of these virus-encoded miRNAs and the putative functions of these targets suggest a key role of viral miRNAs in insect-pathogen interactions by modulating several viral replication genes as well as those involved in host immune defense machinery.

Expression profiling of novel bacteria-induced genes from the silkworm, Bombyx mori

In this study, we have newly identified three bacteria-induced genes from the silkworm Bombyx mori by quantitative reverse transcriptase-polymerase chain reaction. One of these, eukaryotic initiation factor 4E-1 (eIF4E-1), is assumed to encode an eIF4E family, which plays a role in the initiation of translation as a mRNA cap-binding protein. The second gene is BmFOXG1, belonging to a family of forkhead transcription factors, FOXG1. The third gene is MBF2-related (MBF2-R) whose product has high homology to a co-activator protein MBF2 from B. mori. Although BmFOXG1 was up-regulated in the fat body in response to three kinds of bacteria, Escherichia coli, Staphylococcus aureus, and Bacillus subtilis, eIF4E-1 and MBF2-R were up-regulated by E. coli and B. subtilis, but not S. aureus, suggesting that bacteria possessing meso-diaminopimelic acid-containing peptidoglycan but not lysine-containing peptidoglycan activate eIF4E-1 and MBF2-R, probably through a conserved immune deficiency pathway. We further profiled the expression of three genes in different tissues and a silkworm cell line, NIAS-Bm-aff3, in response to bacteria, and at different times after bacterial challenge in the fat body.

A promising broad spectrum antimicrobial red fluorescent protein present in silkworm excreta

The purified silkworm excretory red fluorescent protein (SE-RFP) has exhibited a potent broad spectrum antimicrobial activity. The anti-microbial assays of purified SE-RFP against several pathogenic bacterial (both Gram positive and Gram negative) and fungal strains were performed by agar cup plate method. The minimum inhibitory concentration (MIC) of SE-RFP against pathogenic bacteria and fungi was evaluated by agar dilution technique. The SE-RFP has exhibited highest activity (lowest minimum inhibitory concentration and largest zone of inhibition) against Staphylococcus aureus and Candida albicans among the tested bacteria and fungi, respectively. For the first time, we are reporting here the bioactivity of a red fluorescent protein purified from the silkworm excreta against clinically important bacteria and fungi. The bioactive SE-RFP has two absorption peaks at 280 and 603 nm and, it has exhibited fluorescence emission peaks at 334 and 619 nm upon exciting at 280 and 603 nm, respectively. The SE-RFP being an aqua-soluble, economically feasible and eco-friendly protein, it can therefore be used for the practical applications as an effective antimicrobial agent.

Gene expression profiling during early response to injury and microbial challenges in the silkworm, Bombyx mori

To identify Bombyx mori genes involved in the early response to injury and microbial challenge, we performed genome-wide gene expression-profiling experiments using oligonucleotide DNA microarrays. Of approximately 23,000 genes examined, 465 displayed changes in mRNA expression levels. Of these, 306 were induced and 159 were repressed in response to injury (injection with phosphate buffer saline) or challenges by Gram-negative (Serratia marcescens), Gram-positive bacteria (Staphylococcus aureus), or fungus (Beauveria bassiana). Many of these differentially expressed genes can be assigned to specific functional groups of the innate immune response, including recognition, signaling, melanization and coagulation, and antimicrobial peptides. Seventeen percent of differentially expressed genes encode proteins with no obvious similarity to known functional domains. Of particular interest is a member of the juvenile hormone-binding protein family, which was highly induced by both injury and microbial challenges. The possible role of juvenile hormone in innate immunity is discussed.

Genomic structure and promoter analysis of pathogen-induced repat genes from Spodoptera exigua

The repat gene family encodes midgut proteins overexpressed in response to pathogen infection in the lepidopteran Spodoptera exigua. Up-regulation of repat genes has been observed after challenging the larvae with both Bacillus thuringiensis toxins and after infection with the baculovirus Autographa californica multiple nucleopolyhedrovirus. In our study, PCR amplification of the genomic region and genome walking were used to obtain the genomic structure and the sequence of the 5'-upstream region of repat1 and repat2, two of the most phylogenetically distant members of the repat family. A similar gene structure between repat1 and repat2 has been found, with conserved exon-intron positions and junction sequences, suggesting a common origin for these genes. Recombinant baculoviruses carrying the firefly luciferase gene under the control of different 5'-upstream regions of the repat1 gene were constructed to elucidate the influence of these regions in gene expression. Infection of Helicoverpa zea gut-derived cells with the recombinant baculoviruses revealed the upstream regions of the repat1 gene which are involved in gene transcription and demonstrated the role of an intron located in the 5'-untranslated region in the enhancement of gene expression.

Lipopolysaccharide elicits expression of immune-related genes in the silkworm, Bombyx mori

Lipopolysaccharide (LPS), a major cell wall component of gram-negative bacteria, was found to be unable to activate immune-related genes in Drosophila melanogaster. In contrast, highly purified LPS elicited immune-related gene expression in the fat body of Bombyx mori. However, the level of activation by highly purified LPS was lower than crude LPS and peptidoglycan. Furthermore, synthetic lipid A also activated these genes, suggesting that B. mori possesses unknown signal pathways to activate immune-related genes by LPS. Up-regulation of antimicrobial peptide genes by highly purified LPS was not confirmed in the immune-responsive cell line, NIAS-Bm-aff3, suggesting that some factors necessary for signal transduction activated by LPS are deficient in this cell line.

Sequence structure and expression pattern of a novel anionic defensin-like gene from silkworm (Bombyx mori)

A defensin-like gene, BmdefA, was rediscovered in the silkworm genome and expressed sequence tags databases. The open reading frame of BmdefA encodes a prepropeptide consisting of a 22-residue signal peptide, a 34-residue propeptide, and a 36-residue mature peptide with a molecular mass of 4.0 kDa. The mature peptide possesses the characteristic six-cysteine motif of insect defensins, and its predicted isoelectric point is 4.12, indicating it is a novel anionic defensin. An intron is present in BmdefA and several cis-regulatory elements are in the regulating region. It is transcribed constitutively at a high level in the hemocyte, silk gland, head, and ovary of the silkworm larvae, and in the fat body of early-stage pupae and moth. BmdefA is also strongly induced by immune challenge. These results suggest that BmdefA plays an important role in both immunity and metamorphosis.

Detection of genes encoding antimicrobial peptides in Mexican strains of Trichoplusia ni (Hübner) exposed to Bacillus thuringiensis

The systemic immune response of Trichoplusia ni after Bacillus thuringiensis (Bt) exposure was evaluated by comparing the expression of genes encoding antimicrobial peptides (AMPs) in Bt-susceptible and -resistant T. ni strains that were either exposed or not to XenTari (Bt-XT). AMP genes were detected by RT-PCR using primers for attacin, gloverin, lebocin, lysozyme, and peptidoglycan recognition peptide (PGRP). In general, AMP genes were detected more frequently in Mexican field strains previously exposed to Bt (SALX and GTOX) than in a Mexican laboratory strain (NL), but expression was similar to the AMP expression in USA laboratory strains (US and USX). Among the AMPs, transcripts for lebocin were the least detected (11.7%) and those for lysozyme were the most detected (84.8%) in all samples. Lebocin was detected only in 2nd instar and pupa. All untreated controls expressed attacin. Attacin and gloverin were not detected in any midgut sample, and their highest detection was in pupa. Lysozyme was rarely detected in 2nd instar larvae from any strain or treatment but was detected in almost all midgut and hemolymph samples. Overall, AMPs were found more in T. ni strains previously exposed to Bt-XT, especially lebocin and globerin (1.8-fold increase) and PGRP (3.8-fold increase). The data suggest that the expression of AMPs in T. ni correlates to previous Bt exposure.

Prominent down-regulation of storage protein genes after bacterial challenge in eri-silkworm, Samia cynthia ricini

We constructed two independent cDNA libraries from the fat body of Escherichia coli- or Candida albicans-challenged eri-silkworm Samia cynthia ricini larvae. We performed comparative expressed sequence tag (EST) analysis of the two cDNA libraries and found that two putative storage protein genes, ScSP1 and ScSP2, were markedly repressed by E. coli injection as compared with C. albicans injection. By quantitative real-time RT-PCR analysis, we showed that ScSP1 mRNA significantly reduced to 1/32-1/3 in the fat body of the female larvae, and ScSP2 mRNA reduced to 1/7-1/3 and 1/22-1/5 in the females and males, respectively, 12-36 h after E. coli injection as compared with PBS injection. In addition, SDS-PAGE analysis revealed that the accumulation of both the ScSP proteins in the larval hemolymph apparently decreased up to 36 h after E. coli injection. However, the amounts of the two ScSP proteins returned to the same level as those in the larvae injected with PBS by 48 h after injection, showing that the reduction in ScSPs caused by the bacterial challenge was transient. Moreover, potential binding sites for the Drosophila Rel/NF-kappaB protein Dorsal were found in the 5' upstream regulatory regions of ScSP1 and ScSP2, suggesting the participation of the Rel/NF-kappaB proteins in controlling the bacterial suppression of the ScSP genes. These results suggested the hypothesis that S. c. ricini has a genetic program to shut down temporarily dispensable gene expression in order to induce an acute and efficient expression of immune-related genes. These findings may provide new insight into the innate immune system in lepidopteran insects.

Expression of antimicrobial peptide genes encoding Enbocin and Gloverin isoforms in the silkworm, Bombyx mori

Antimicrobial peptides, Enbocin and Gloverin isoforms from the silkworm Bombyx mori, were analyzed for expression of these peptide genes. Tissue-specific expression of Enbocin and Bmgloverin isoform genes was observed mainly in the fat body upon injection of Escherichia coli. Peptidoglycan and lipopolysaccharide triggered expression of these genes in vivo. On the other hand, lipid A activated Bmgloverin isoform genes but not Enbocin isoform genes. These results illustrate the fact that expression of Enbocin and Bmgloverin isoform genes is inducible by bacteria and that the effects of bacterial cell wall components on the activation of these peptide genes are not necessarily the same. In addition, selective activation of the Enbocin2, Bmgloverin2, and Bmgloverin4 genes by BmRelB rather than BmRelA was observed, providing additional evidence for the occurrence of selective activation of antimicrobial peptide genes by a Rel protein. These results suggest complex regulatory mechanisms in insect antimicrobial peptide genes by bacterial cell wall components.

Immune upregulation of novel antibacterial proteins from silkmoths (Lepidoptera) that resemble lysozymes but lack muramidase activity

Study on immune proteins in domesticated and wild silkmoths Bombyx mori and Antheraea mylitta, respectively, led to identification of a new class of antimicrobial proteins. We designated them as lysozyme-like proteins (LLPs) owing to their partial similarity with lysozymes. However, lack of characteristic catalytic amino acid residues essential for muramidase activity in LLPs puts them functionally apart from classical lysozymes. Two LLPs, one from B. mori (BLLP1) and the other from A. mylitta (ALLP1) expressed in a recombinant system, exhibited a broad-spectrum antibacterial action. Further investigation of the antibacterial mechanism revealed that BLLP1 is bacteriostatic rather than bactericidal against Escherichia coli and Micrococcus luteus. Substantial increase in hemolymph bacterial load was observed in B. mori upon RNA interference mediated in vivo knockdown of BLLP1. We demonstrate that the antibacterial mechanism of this protein depends on peptidoglycan binding unlike peptidoglycan hydrolysis or membrane permeabilization as observed with lysozymes and most other antimicrobial peptides. To our knowledge, this is the first report on functional analysis of novel, non-catalytic lysozyme-like family of antibacterial proteins that are quite apart functionally from classical lysozymes. The present analysis holds promise for functional annotation of similar proteins from other organisms.

Purification and characterization of eight peptides from Galleria mellonella immune hemolymph

Defense peptides play a crucial role in insect innate immunity against invading pathogens. From the hemolymph of immune-challenged greater wax moth, Galleria mellonella (Gm) larvae, eight peptides were isolated and characterized. Purified Gm peptides differ considerably in amino acid sequences, isoelectric point values and antimicrobial activity spectrum. Five of them, Gm proline-rich peptide 2, Gm defensin-like peptide, Gm anionic peptides 1 and 2 and Gm apolipophoricin, were not described earlier in G. mellonella. Three others, Gm proline-rich peptide 1, Gm cecropin D-like peptide and Galleria defensin, were identical with known G. mellonella peptides. Gm proline-rich peptides 1 and 2 and Gm anionic peptide 2, had unique amino acid sequences and no homologs have been found for these peptides. Antimicrobial activity of purified peptides was tested against gram-negative and gram-positive bacteria, yeast and filamentous fungi. The most effective was Gm defensin-like peptide which inhibited fungal and sensitive bacteria growth in a concentration of 2.9 and 1.9 microM, respectively. This is the first report describing at least a part of defense peptide repertoire of G. mellonella immune hemolymph.

Effect of superoxide dismutase gene inactivation on virulence of Pseudomonas aeruginosa PAO1 toward the silkworm, Bombyx mori

To investigate the role of superoxide dismutase (SOD) in virulence against the silkworm, Bombyx mori, mutants of Pseudomonas aeruginosa PAO1 lacking manganese-SOD (PAO1sodM), iron-SOD (PAO1sodB), or both (PAO1sodMB) were generated. The mutants were injected into the hemocoel of B. mori. The virulence decreased in the order PAO1=PAO1sodM>PAO1sodB>PAO1sodMB. In particular, PAO1sodMB was avirulent at a dose of 10(5) cells or less. The sod double mutant PAO1sodMB was then complemented with either pSodM or pSodB in trans. In both the complemented strains, the virulence was partially restored. Of the two plasmids, pSodB contributed more to the virulence of P. aeruginosa against B. mori. The results of growth in B. mori hemolymph broth and microscopic analysis suggested that a longer lag phase and superoxide sensitivity correlated with decreased virulence in sod mutants. In conclusion, the SODs are required for full virulence of P. aeruginosa against B. mori and Fe-SOD is more important than Mn-SOD in the infection process.

Two-component signaling in the virulence of Staphylococcus aureus: a silkworm larvae-pathogenic agent infection model of virulence

Staphylococcus aureus is a pathogenic bacterium that causes abscesses, pneumonia, endocarditis, and food poisoning. S. aureus is also one of the resident flora of the endotherm and colonizes the host by skillfully evading its defense mechanism. Identification of attenuated mutants of S. aureus in an animal infection model is useful for investigating its adaptability and pathogenesis. This chapter describes a staphylococcal two-component SA0614-SA0615 system, which was identified using a silkworm larvae infection model.

Gene expression profiling of Spodoptera frugiperda hemocytes and fat body using cDNA microarray reveals polydnavirus-associated variations in lepidopteran host genes transcript levels

Background

Genomic approaches provide unique opportunities to study interactions of insects with their pathogens. We developed a cDNA microarray to analyze the gene transcription profile of the lepidopteran pest Spodoptera frugiperda in response to injection of the polydnavirus HdIV associated with the ichneumonid wasp Hyposoter didymator. Polydnaviruses are associated with parasitic ichneumonoid wasps and are required for their development within the lepidopteran host, in which they act as potent immunosuppressive pathogens. In this study, we analyzed transcriptional variations in the two main effectors of the insect immune response, the hemocytes and the fat body, after injection of filter-purified HdIV.

Results

Results show that 24 hours post-injection, about 4% of the 1750 arrayed host genes display changes in their transcript levels with a large proportion (76%) showing a decrease. As a comparison, in S. frugiperda fat body, after injection of the pathogenic JcDNV densovirus, 8 genes display significant changes in their transcript level. They differ from the 7 affected by HdIV and, as opposed to HdIV injection, are all up-regulated. Interestingly, several of the genes that are modulated by HdIV injection have been shown to be involved in lepidopteran innate immunity. Levels of transcripts related to calreticulin, prophenoloxidase-activating enzyme, immulectin-2 and a novel lepidopteran scavenger receptor are decreased in hemocytes of HdIV-injected caterpillars. This was confirmed by quantitative RT-PCR analysis but not observed after injection of heat-inactivated HdIV. Conversely, an increased level of transcripts was found for a galactose-binding lectin and, surprisingly, for the prophenoloxidase subunits. The results obtained suggest that HdIV injection affects transcript levels of genes encoding different components of the host immune response (non-self recognition, humoral and cellular responses).

Conclusion

This analysis of the host-polydnavirus interactions by a microarray approach indicates that the presence of HdIV induces, directly or indirectly, variations in transcript levels of specific host genes, changes that could be responsible in part for the alterations observed in the parasitized host physiology. Development of such global approaches will allow a better understanding of the strategies employed by parasites to manipulate their host physiology, and will permit the identification of potential targets of the immunosuppressive polydnaviruses.

Bombyx mori cell line as a model of immune-system organs

We tested 11 Bombyx mori cell lines for induction of cecropin B gene (CecB) expression. After the immune challenge, CecB expression was induced in seven cell lines. A mixture of the cell-free supernatant from the immune-responsive cell lines and lipopolysaccharide activated a promoter of CecB in the non-immune-responsive cell line, indicating that secreted factor(s) is involved in CecB activation. The expressed sequence tags of one of the immune-responsive cell lines, NISES-BoMo-Cam1, contained genes encoding proteins similar to Relish, Cactus, clip-domain serine protease, serpin, lectin, peptidoglycan recognition protein, 6tox and gloverin, in addition to seven known B. mori immune-inducible genes. These results show that NISES-BoMo-Cam1 cells can be used as an in vitro model of the immune system organs of B. mori.

Structures, regulatory regions, and inductive expression patterns of antimicrobial peptide genes in the silkworm Bombyx mori

Antimicrobial peptides (AMPs) are a group of immune proteins that protect the host from infection. In Drosophila, seven groups of inducible AMPs have been identified, with activities against fungi and gram-positive and gram-negative bacteria. On the basis of the silkworm genome sequence and expressed sequence tags, we identified 35 AMP genes, mostly belonging to the cecropin, moricin, and gloverin gene families. We predicted the core promoters required for gene transcription and the cis-regulatory elements for NF-kappaB/Rel and GATA transcription factors. The expression profiles of these genes after an immune challenge with lipopolysaccharide were examined by reverse transcription PCR. Members of the cecropin B and gloverin A subfamilies were intensely expressed in the fat body after induction. In contrast, those of the moricin B subfamily were not expressed under the same conditions. Such results suggest that these regulatory elements and their positions in the upstream regions play an important role in regulating the transcription of these defense genes.

Discovery of immune-related genes expressed in hemocytes of the tarantula spider Acanthoscurria gomesiana

The present study reports the identification of immune related transcripts from hemocytes of the spider Acanthoscurria gomesiana by high throughput sequencing of expressed sequence tags (ESTs). To generate ESTs from hemocytes, two cDNA libraries were prepared: one by directional cloning (primary) and the other by the normalization of the first (normalized). A total of 7584 clones were sequenced and the identical ESTs were clustered, resulting in 3723 assembled sequences (AS). At least 20% of these sequences are putative novel genes. The automatic functional annotation of AS based on Gene Ontology revealed several abundant transcripts related to the following functional classes: hemocyanin, lectin, and structural constituents of ribosome and cytoskeleton. From this annotation, 73 transcripts possibly involved in immune response were also identified, suggesting the existence of several molecular processes not previously described for spiders, such as: pathogen recognition, coagulation, complement activation, cell adhesion and intracellular signaling pathway for the activation of cellular defenses.

RS1, a discoidin domain-containing retinal cell adhesion protein associated with X-linked retinoschisis, exists as a novel disulfide-linked octamer

RS1, also known as retinoschisin, is an extracellular protein that plays a crucial role in the cellular organization of the retina. Mutations in RS1 are responsible for X-linked retinoschisis, a common, early-onset macular degeneration in males that results in a splitting of the inner layers of the retina and severe loss in vision. RS1 is assembled and secreted from photoreceptors and bipolar cells as a homo-oligomeric protein complex. Each subunit consists of a 157-amino acid discoidin domain flanked by two small segments of 39 and 5 amino acids. To begin to understand how the structure of RS1 relates to its role in retinal cell adhesion and X-linked retinoschisis, we have determined the subunit organization and disulfide bonding pattern of RS1 by SDS gel electrophoresis, velocity sedimentation, and mass spectrometry. Our results indicate that RS1 exists as a novel octamer in which the eight subunits are joined together by Cys(59)-Cys(223) intermolecular disulfide bonds. Subunits within the octamer are further organized into dimers mediated by Cys(40)-Cys(40) bonds. These cysteines lie just outside the discoidin domain indicating that these flanking segments primarily function in the octamerization of RS1. Within the discoidin domain, two cysteine pairs (Cys(63)-Cys(219) and Cys(110)-Cys(142)) form intramolecular disulfide bonds that are important in protein folding, and one cysteine (Cys(83)) exists in its reduced state. Because mutations that disrupt subunit assembly cause X-linked retinoschisis, the assembly of RS1 into a disulfide-linked homo-octamer appears to be critical for its function as a retinal cell adhesion protein.

Immune stimulation in the silkworm, Bombyx mori L., by CpG oligodeoxynucleotides

Synthetic ODNs containing unmethylated CpG dinucleotides are known to stimulate immune responses in vertebrates, but so far the effect has not been studied in insects. In this report, we describe an induction of immune response following injection of oligodeoxynucleotides (ODNs) into the insect hemocoel. The fifth instar silkworm (Bombyx mori L.) larvae were injected with several synthetic ODNs containing variable number of unmethylated CpG motifs, heat-denatured genomic DNA of B. mori itself, or intact genomic DNA to observe a new induction pattern in the insect immune mechanism. When the induction of immune response was examined based on the expression rates of genes for antibacterial peptides such as attacin and cecropin, we could confirm that it was triggered upon injection of ODNs. The expression was, however, neither dependent on numbers of CpG motifs nor methylation of CpGs in ODNs. Furthermore, it was confirmed that the presence of CpG in ODN was not involved in the induction pattern of insect immunity caused by ODNs, although it has been reported that vertebrates respond in a specific manner against invading ODNs containing CpG dinucleotides. In addition, insect immunity was not stimulated by injection of intact DNA from host. In contrast, the injection of denatured genomic DNA provoked the host immune reaction. Taken together, our data suggest that foreignness of ODNs or DNA might be a key factor in the induction of insect immunity.

Scarabaecin, a novel cysteine-containing antifungal peptide from the rhinoceros beetle, Oryctes rhinoceros

A novel antifungal peptide, scarabaecin (4080Da), was isolated from the coconut rhinoceros beetle, Oryctes rhinoceros. Scarabaecin cDNA was cloned by reverse transcriptase-polymerase chain reactions (RT-PCR) using a primer based on the N-terminal amino acid sequence. The amino acid sequence deduced from scarabaecin cDNA showed no significant similarity to those of reported proteins. Chemically synthesized scarabaecin indicated antifungal activity against phytopathogenic fungi such as Pyricularia oryzae, Rhizoctonia solani, and Botrytis cinerea, but not against phytopathogenic bacteria. It showed weak activity against Bauberia bassiana, an insect pathogenic fungus, and Staphylococcus aureus, a pathogenic bacterium. Scarabaecin showed chitin binding property and its K(d) was 1.315 microM. A comparison of putative chitin-binding domains among scarabaecin, invertebrate, and plant chitin-binding proteins suggests that scarabaecin is a new member of chitin-binding antimicrobial proteins.

Genomic structure and expression analysis of the gene encoding a silkworm basic Kunitz-type chymotrypsin inhibitor

Kunitz-type chymotrypsin inhibitor CIb1 of silkworm Bombyx mori is a basic peptide consisting of 62 amino acid residues. To elucidate the mechanisms of transcriptional regulation of CIb1 gene expression, we cloned it for genomic structure analysis. CIb1 cDNA was used as a probe to screen a BAC sub-library. One positive clone containing the upstream sequences was isolated and the sequence result showed that CIb1 gene consists of three exons spaced by two introns. In the 5'-flanking region, consensus TATA and CCAAT boxes were identified. Other binding sites for transcription factors such as NF-kappaB, GATA, C/EBP, COUP-TF/HNF-4, RORalpha1, SRY, and HOXA3 were also detected. Southern blot analysis suggested a single copy of CIb1 gene in the silkworm genome. Northern blot analysis indicated that the expression of CIb1 gene is transcriptionally regulated during development and is apparently tissue-specific. The CIb1 mRNA was detected in fat body, ovary, trachea, and skin. We furthermore investigated the CIb1 expression profiles after LPS and E. coli injection. The fluctuations of CIb1 transcript in challenged larvae confirm our proposal that CIb1 is an immune responsible gene. According to our data, we discussed the transcriptional factors putatively responsible for the physiological role of CIb1 in the silkworm hemolymph.

A molecular analysis of ascidian metamorphosis reveals activation of an innate immune response

Ascidian metamorphosis represents a powerful model for comparative work on chordate development that has remained largely unexplored. We isolated transcripts differentially expressed during metamorphosis in the ascidian Boltenia villosa by suppressive PCR subtractions of staged larval and juvenile cDNAs. We employed a series of three subtractions to dissect gene expression during metamorphosis. We have isolated 132 different protein coding sequences, and 65 of these transcripts show significant matches to GenBank proteins. Some of these genes have putative functions relevant to key metamorphic events including the differentiation of smooth muscle, blood cells, heart tissue and adult nervous system from larval rudiments. In addition, a significant fraction of the differentially expressed transcripts match identified genes from the innate immune system. Innate immunity confers a rapid response to pathogen-specific molecules and/or compromised self-tissues. The activation of innate immunity genes during metamorphosis may represent the programmed maturation of the adult immune system. In addition, this immune response may be necessary for phagocytosis and re-structuring of larval tissues. An innate immune-related inflammatory response may also underlie two waves of trans-epidermal blood cell migration that occur during the swimming larval period and immediately upon settlement. We characterized these trans-epidermal migrations and discovered that some migratory cells leave the animal entirely through an anterior tunnel in the tunic. We show that these cells are positioned to detect external settlement cues and hypothesize that the innate immune system may also be employed to detect and rapidly respond to environmental settlement cues.

Solution structure of moricin, an antibacterial peptide, isolated from the silkworm Bombyx mori

A novel antibacterial peptide, moricin, isolated from the silkworm Bombyx mori, consists of 42 amino acids. It is highly basic and the amino acid sequence has no significant similarity to those of other antibacterial peptides. The 20 structures of moricin in methanol have been determined from two-dimensional 1H-nuclear magnetic resonance spectroscopic data. The solution structure reveals an unique structure comprising of a long alpha-helix containing eight turns along nearly the full length of the peptide except for four N-terminal residues and six C-terminal residues. The electrostatic surface map shows that the N-terminal segment of the alpha-helix, residues 5-22, is an amphipathic alpha-helix with a clear separation of hydrophobic and hydrophilic faces, and that the C-terminal segment of the alpha-helix, residues 23-36, is a hydrophobic alpha-helix except for the negatively charged surface at the position of Asp30. The results suggest that the amphipathic N-terminal segment of the alpha-helix is mainly responsible for the increase in permeability of the membrane to kill the bacteria.

Bass hepcidin is a novel antimicrobial peptide induced by bacterial challenge

We report the isolation of a novel antimicrobial peptide, bass hepcidin, from the gill of hybrid striped bass, white bass (Morone chrysops) x striped bass (M. saxatilis). After the intraperitoneal injection of Micrococcus luteus and Escherichia coli, the peptide was purified from HPLC fractions with antimicrobial activity against Escherichia coli. Sequencing by Edman degradation revealed a 21-residue peptide (GCRFCCNCCPNMSGCGVCCRF) with eight putative cysteines. Molecular mass measurements of the native peptide and the reduced and alkylated peptide confirmed the sequence with four intramolecular disulfide bridges. Peptide sequence homology to human hepcidin and other predicted hepcidins, indicated that the peptide is a new member of the hepcidin family. Nucleotide sequences for cDNA and genomic DNA were determined for white bass. A predicted prepropeptide (85 amino acids) consists of three domains: a signal peptide (24 amino acids), prodomain (40 amino acids) and a mature peptide (21 amino acids). The gene has two introns and three exons. A TATA box and several consensus-binding motifs for transcription factors including C/EBP, nuclear factor-kappaB, and hepatocyte nuclear factor were found in the region upstream of the transcriptional start site. In white bass liver, hepcidin gene expression was induced 4500-fold following challenge with the fish pathogen, Streptococcus iniae, while expression levels remained low in all other tissues tested. A novel antimicrobial peptide from the gill, bass hepcidin, is predominantly expressed in the liver and highly inducible by bacterial exposure.

A novel lipopolysaccharide response element in the Bombyx mori cecropin B promoter

Cecropin B is one of the major antibacterial peptides in the silkworm, Bombyx mori. Transcription of the cecropin B gene (CecB) occurs rapidly after bacterial invasion. Using 235 base pairs (bp) of the CecB promoter region, a kappaB-related protein and two additional DNA-binding complexes (designated F2BPI and F4BP) were identified in nuclear extracts from immunized larval fat body by the electrophoretic mobility shift assay (EMSA) (1). Further EMSA analyses indicated that the F2BPI-binding site was CATTA, and that F2BPI translocated from the cytoplasm to the nucleus after infection. In a recently established B. mori cell line, NISES-BoMo-DZ, 235 bp of CecB promoter linked to a reporter luciferase was activated 6-fold by stimulation with lipopolysaccharide (LPS), which is a major trigger of CecB expression in larvae. Truncation of the F2BPI-binding site from the promoter reduced the activation 2-fold. Deletion of either of two kappaB motifs also reduced promoter activation 2-fold. Elimination of both the F2BPI-binding site and the kappaB motifs resulted in the complete loss of LPS inducibility. These results indicate that the F2BPI-binding site is an LPS-responsive cis-element that is necessary for full activation of CecB.

Trichoplusia ni lebocin, an inducible immune gene with a downstream insertion element

A cDNA clone encoding a lebocin-like protein was obtained from the cabbage looper Trichoplusia ni by using differential display PCR. Northern blot analysis showed that lebocin gene expression was inducible upon bacterial challenge. Transcripts were mainly found in fat body but were also observed in hemocytes. Expression reached its highest level at 20 h and continued at least until 60 h after bacterial injection. The deduced protein is proline-rich and contains 143 amino acid residues. At position 128, a possible O-glycosylation site is observed. The whole protein shows 35% identity to Bombyx mori lebocin. The mature peptide displays an N-terminus similar to that of lebocin and a C-terminus to that of Drosophila metchnikowin. A 39-bp repetitive element is located downstream of the coding region.