A bacteria-induced, intracellular serpin in granular hemocytes of Manduca sexta

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

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

A serpin (CvT-serpin15) of teratocytes contributes to microbial-resistance in Plutella xylostella during Cotesia vestalis parasitism

BACKGROUND

Parasitic wasps are an important group of entomophagous insects for pest control. As parasitic wasps often lay eggs on or into their associated hosts, parasitoids evolve to utilize several factors including venom, polydnavirus (PDV) to alter host physiology for successful parasitism. Some taxa of endoparasitoids produce teratocytes, which are a type of cell that is released into host insects when wasp eggs hatch. Teratocytes display multifunction in parasitism such as host nutritional exploration, immune and developmental regulation, by secreting plenty of proteins into host hemocoel.

RESULTS

A serpin (CvT-serpin15) secreted by teratocytes was characterized. QPCR results showed the expressional level of CvT-serpin15 was upregulated following bacterial challenges. Enzyme activity experiment indicated the recombinant CvT-serpin15 protein could interfere with the growth of Gram-positive bacteria Staphylococcus aureus. The survival rate assay demonstrated CvT-serpin15 increased survival rate of Plutella xylostella infected by S. aureus.

CONCLUSION

CvT-serpin15 secreted by teratocytes would boost the host immune system when pathogens invade host hemocoel during parasitism, and ultimately protect the development of wasp larva from bacterial infection. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Serpin7 controls egg diapause of migratory locust (Locusta migratoria) by regulating polyphenol oxidase

Diapause is a state of arrested growth, which allows insects to adapt to diverse environments. Serine protease inhibitors (serpins) play an important role in various physiological processes, including blood coagulation, fibrinolysis, development, complement activation and extracellular matrix remodeling. We hypothesized that serpin may affect energy metabolism and thereby control diapause of migratory locust (Locusta migratoria) embryos by regulating protease cascades. A total of seven nonredundant serpin genes (named serpin1–serpin7) of L. migratoria were obtained through transcriptomic analysis. We further performed label‐free proteomic sequencing and analysis of diapause and nondiapause eggs of L. migratoria, revealing significant differences in serpin7 expression. A significant reduction in diapause rate under the short photoperiod was observed in insects treated with serpin7 double‐stranded RNA. Furthermore, knockdown of the serpin7 gene resulted in significant upregulation of the activity of polyphenol oxidase. We therefore propose that the observed serpin7 gene plays a crucial role in diapause, suggesting that control of energy metabolism may have potential as a future strategy for the reproductive control of insect pests.

The Manduca sexta serpinome: Analysis of serpin genes and proteins in the tobacco hornworm

Members of the serpin superfamily of proteins occur in animals, plants, bacteria, archaea and some viruses. They adopt a variety of physiological functions, including regulation of immune system, modulation of apoptosis, hormone transport and acting as storage proteins. Most members of the serpin family are inhibitors of serine proteinases. In this study, we searched the genome of Manduca sexta and identified 32 serpin genes. We analyzed the structure of these genes and the sequences of their encoded proteins. Three M. sexta genes (serpin-1, serpin-15, and serpin-28) have mutually exclusive alternatively spliced exons encoding the carboxyl-terminal reactive center loop of the protein, which is the site of interaction with target proteases. We discovered that MsSerpin-1 has 14 splicing isoforms, including two undiscovered in previous studies. Twenty-eight of the 32 M. sexta serpins include a putative secretion signal peptide and are predicted to be extracellular proteins. Phylogenetic analysis of serpins in M. sexta and Bombyx mori indicates that 17 are orthologous pairs, perhaps carrying out essential physiological functions. Analysis of the reactive center loop and hinge regions of the protein sequences indicates that 16 of the serpin genes encode proteins that may lack proteinase inhibitor activity. Our annotation and analysis of these serpin genes and their transcript profiles should lead to future advances in experimental study of their functions in insect biochemistry.

Characterization and functional analysis of serpin-28 gene from silkworm, Bombyx mori

Serine protease inhibitors (Serpins) are a broadly distributed superfamily of proteins with a SERPIN domain and participate in several immune responses. In this study, a serpin-28 gene was identified in B. mori and its role in immune regulation was investigated. This gene has an open reading frame of 1065 bp that encodes a 354-amino acid residue polypeptide containing one SERPIN domain with a predicted molecular weight of 40.3 kDa. Recombinant Bmserpin-28 protein was expressed in Escherichia coli and used to raise rabbit anti-Bmserpin-28 polyclonal antibodies. Quantitative real-time PCR analysis revealed that Bmserpin-28 was expressed in all examined tissues, with maximum expression in the fat body and silk gland. Expression pattern of different developmental stages showed that the highest expression level was in the pupae, while the lowest expression level was recorded at the egg stage. After challenge with four different microorganisms (Escherichia coli, Beauveria bassiana, Micrococcus luteus and B. mori nuclear polyhedrosis virus), the expression pattern of Bmserpin-28 was investigated in fat body and haemocyte samples. A substantial upregulation of Bmserpin-28 expression level was recorded following pathogen challenge in both the tested tissues. Furthermore, RNA interference of Bmserpin-28 resulted in significant upregulation of antimicrobial peptide genes. In summary, our results indicated that Bmserpin-28 may be involved in the innate immunity of B. mori.

Cloning and characterization of serpin from red king crab Paralithodes camtschaticus

Serpins are a family of serine protease inhibitors that are involved in numerous physiological processes and are known to regulate innate immunity pathways. To advance our understanding of their role in P. camtschaticus, a commercially significant species, we cloned and characterized a serpin from this species, designated serpin PC, that has anticoagulant and anticomplement effects on human blood. We found that serpin PC is a secreted protein with a typical serpin-like primary structure that is similar to other known crustacean serpins. Recombinant serpin PC was found to have inhibitory activity against R/K-specific bovine cationic trypsin. The reaction proceeds through the formation of a stable covalent complex of peptidase with P1 residue R383 of serpin PC. This interaction is characterized by a relatively high overall inhibition constant k_ass=(2.3 ± 0.7) × 10⁶ M^-1s^-1 and an SI of 4.7 ± 0.8. Protein localization by western blotting showed that serpin PC is present in the muscles and, to a lesser extent, the heart, whereas it is transcribed predominantly in hemocytes and the heart. Through peptidase activity profiling of hemocytes and plasma, we found that serpin PC inhibits at least two R/K-specific activities and showed that it inhibits phenoloxidase (PO) activity induction in hemocytes.

Serpin-14 negatively regulates prophenoloxidase activation and expression of antimicrobial peptides in Chinese oak silkworm Antheraea pernyi

Genes encoding proteins of serpins superfamily are widely distributed in invertebrates. In insects, serpins play important roles in regulating immune responses and other physiological processes. Here, we report the cloning and characterization of cDNA of Apserpin-14 from Chinese oak silkworm (Antheraea pernyi). The Apserpin-14 gene contains 1206 bp open reading frame, encoding a predicted 401 amino acid residue protein. We expressed the recombinant Apserpin-14 protein in Escherichia coli and then purified protein was used to prepare rabbit anti-Apserpin-14 polyclonal antibodies. Quantitative real-time PCR analysis revealed that mRNA level of Apserpin-14 was highest in the fat body, whereas, among developmental stages the 5th instar and pupal stage showed greatest expression. Furthermore, Escherichia coli, Beauveria bassiana, Micrococcus luteus and nuclear polyhedrosis virus challenge enhanced Apserpin-14 transcript in both the fat body and hemocyte. Recombinant Apserpin-14 added to hemolymph inhibited spontaneous melanization and suppressed prophenoloxidase activation stimulated by M. luteus, but did not affect phenoloxidase (PO) activity. Injection of recombinant Apserpin-14 protein into A. pernyi larvae significantly reduced the transcript levels of antimicrobial peptides in the fat body, while its depletion by double stranded RNA enhanced their expression. We concluded that Apserpin-14 likely involved in regulation of proPO activation and production of antimicrobial peptides, implying its important role in the innate immune system of A. pernyi.

Melanization inhibition protein of Penaeus monodon acts as a negative regulator of the prophenoloxidase-activating system

Melanization mediated by the prophenoloxidase-activating system (proPO) is an important immune response in invertebrates. However, in addition to melanin, the proPO system produces reactive intermediates that are not only harmful to the invading microbes but also to the host cells. Thus, the proPO system must be tightly regulated by several inhibitors. Previously, a melanization inhibition protein from the black tiger shrimp Penaeus monodon, PmMIP, has been identified and preliminarily characterized. In this study, we investigate the function of PmMIP in the regulation of the proPO system in shrimp. When challenged with the bacterium Vibrio harveyi, the expression of PmMIP transcripts in gills was down-regulated dramatically at 24 h but recovered after 48 h post infection (hpi), while the PmMIP protein level in shrimp plasma was decreased at 6 hpi but recovered at 24 hpi. Double-stranded RNA-mediated gene silencing of PmMIP suppressed both PmMIP transcriptional and translational levels and resulted in increased hemolymph phenoloxidase and proteinase activities compared to controls injected with GFP dsRNA or NaCl. Furthermore, the recombinant PmMIP protein successfully expressed in Escherichia coli was able to inhibit hemolymph PO activity by 50%. These results suggested that PmMIP was involved in the proPO system by acting as a negative regulator and interfering with hemolymph proteinase activity.

Characterization and expression profiling of serine protease inhibitors in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

BACKGROUND

Serine protease inhibitors (SPIs) have been found in all living organisms and play significant roles in digestion, development and innate immunity. In this study, we present a genome-wide identification and expression profiling of SPI genes in the diamondback moth, Plutella xylostella (L.), a major pest of cruciferous crops with global distribution and broad resistance to different types of insecticides.

RESULTS

A total of 61 potential SPI genes were identified in the P. xylostella genome, and these SPIs were classified into serpins, canonical inhibitors, and alpha-2-macroglobulins based on their modes of action. Sequence alignments showed that amino acid residues in the hinge region of known inhibitory serpins from other insect species were conserved in most P. xylostella serpins, suggesting that these P. xylostella serpins may be functionally active. Phylogenetic analysis confirmed that P. xylostella inhibitory serpins were clustered with known inhibitory serpins from six other insect species. More interestingly, nine serpins were highly similar to the orthologues in Manduca sexta which have been demonstrated to participate in regulating the prophenoloxidase activation cascade, an important innate immune response in insects. Of the 61 P.xylostella SPI genes, 33 were canonical SPIs containing seven types of inhibitor domains, including Kunitz, Kazal, TIL, amfpi, Antistasin, WAP and Pacifastin. Moreover, some SPIs contained additional non-inhibitor domains, including spondin_N, reeler, and other modules, which may be involved in protein-protein interactions. Gene expression profiling showed gene-differential, stage- and sex-specific expression patterns of SPIs, suggesting that SPIs may be involved in multiple physiological processes in P. xylostella.

CONCLUSIONS

This is the most comprehensive investigation so far on SPI genes in P. xylostella. The characterized features and expression patterns of P. xylostella SPIs indicate that the SPI family genes may be involved in innate immunity of this species. Our findings provide valuable information for uncovering further biological roles of SPI genes in P. xylostella.

Serpin-15 from Bombyx mori inhibits prophenoloxidase activation and expression of antimicrobial peptides

Serine protease inhibitors (SPIs) play a key role in physiological responses by controlling protease activities. In this study, we studied the biochemical functions of serpin-15, an SPI, from Bombyx mori (Bmserpin-15). Recombinant Bmserpin-15 was expressed in Escherichia coli cells and used to raise rabbit anti-Bmserpin-15 polyclonal antibodies. Bmserpin-15 mRNA and protein expression was detected in all tested tissues, particularly in the fat body and silk gland. After challenge with four different microorganisms (Escherichia coli, Beauveria bassiana, Micrococcus luteus and B. mori nuclear polyhedrosis virus), the expressions of Bmserpin-15 mRNA and protein were induced significantly, particularly by B. bassiana and M. luteus. Recombinant Bmserpin-15 inhibited prophenoloxidase activation, but did not affect phenoloxidase activity, in B. mori hemolymph. Injection of recombinant Bmserpin-15 into B. mori larvae reduced significantly the transcript levels of antimicrobial peptides in fat body. Our results suggested that Bmserpin-15 plays an important role in the innate immunity of B. mori.

RNAi-mediated knockdown of serine protease inhibitor genes increases the mortality of Plutella xylostella challenged by destruxin A

Destruxin A is a mycotoxin that is secreted by entomopathogenic fungi which has a broad-spectrum insecticidal effect. Previous transcript and protein profiling analysis showed that destruxin A has significant effects on the expression of serine protease inhibitor genes (serpin-2, 4, 5) in the larvae of Plutella xylostella. In the current study, we aimed to understand the role of serpins under application of destruxin A. We obtained two full-length cDNA sequences of P. xylostella serpins, named serpin-4 and serpin-5, and cloned the serpin-2 gene whose full-length has already been published. Phylogenetic analysis indicated that these two serpin genes were highly clustered with other serpins associated with the immune response in other insects. The temporal and spatial expression of serpin-2, serpin-4 and serpin-5 were determined to be the highest in the fat body and hemolymph of 4^th larval stage using qRT-PCR and western blot detection techniques. RNA interference (RNAi) mediated knockdown of P. xylostella serpin genes was carried out by microinjection of double-stranded RNA (dsRNA). The expression levels of serpins decreased significantly after RNAi. Results showed that the depletion of serpins induced cecropins expression, increased phenoloxidase (PO) activity, body melanization and mortality in the larvae of P. xylostella under the same lethal concentration of destruxin A. The superimposed effects of serpins RNAi were similar with the destruxin A treatment upon mortality of P. xylostella larvae. We discovered for the first time that serpins play indispensable role in P. xylostella when challenged by destruxin A and deduced the possible function mechanism of destruxin A. Our findings are conducive to fully understanding the potential insecticidal mechanism of destruxin A and constitute a well-defined potential molecular target for novel insecticides.

Manduca sexta serpin-7, a putative regulator of hemolymph prophenoloxidase activation

Serpins regulate various physiological reactions in humans and insects, including certain immune responses, primarily through inhibition of serine proteases. Six serpins have previously been identified and characterized in the tobacco hornworm Manduca sexta. In this study, we obtained a full-length cDNA sequence of another Manduca serpin, named serpin-7. The open reading frame of serpin-7 encodes a polypeptide of 400 amino acid residues with a predicted signal peptide of the first 15 residues. Multiple protein sequence alignment of the reactive center loop region of the M. sexta serpins indicated that serpin-7 contains Arg-Ile at the position of the predicted scissile bond cleaved by protease in the serpin inhibition mechanism. The same residues occur in the scissile bond of the reactive center loop in M. sexta serpin-4 and serpin-5, which are protease inhibitors that can block prophenoloxidase activation in plasma. Serpin-7 transcript was detected in hemocytes and fat body, and its expression increased in fat body after injection of larvae with Micrococcus luteus. Recombinant serpin-7 added to larval plasma inhibited spontaneous melanization and decreased prophenoloxidase activation stimulated by bacteria. Serpin-7 inhibited prophenoloxidase-activating protease-3 (PAP3), forming a stable serpin-protease complex. Considering that serpin-3 and serpin-6 are also efficient inhibitors of PAP3, it appears that multiple serpins present in plasma may have redundant or overlapping functions. We conclude that serpin-7 has serine protease inhibitory activity and is likely involved in regulation of proPO activation or other protease-mediated aspects of innate immunity in M. sexta.

Microarray analysis of gene expression profile in resistant and susceptible Bombyx mori strains reveals resistance-related genes to nucleopolyhedrovirus

To investigate the molecular mechanism of silkworm resistance to BmNPV infection, we constructed a near-isogenic line (BC8) with BmNPV resistance using highly resistant (NB) and highly susceptible parental strains (306). We investigated variations in the gene expression in the midguts of BmNPV-infected BC8 and 306 at 12 h pi using the microarray. 92 differentially expressed genes were identified. Real-time qPCR analysis confirmed that 10 genes were significantly up-regulated or down-regulated in the midguts of BC8 and NB compared to 306. To our knowledge, we first defined the role of the amino acid transporter and 26S proteasome in insect antiviral. However, serine protease was not completely consistent with data of reported previously in insect antiviral. The role of the 5 genes (Bm123, Bm122, COP β', aquaporin, glycoside hydrolases) was also demonstrated in insect antiviral. Our results provided new insights into the molecular mechanism of the Bombyx mori immune response against BmNPV infection.

Conservation of a pair of serpin 2 genes and their expression in Amphiesmenoptera

Silk secreted by the larvae of Hydropsyche angustipennis (Trichoptera) contains serpins HaSerp2A and HaSerp2B that are homologous to serpin 2 known from several lepidopterans and some other insects. The gene HaSerp2A is 2684 bp downstream from the HaSerp2B gene. The genes possess identical exon/intron segmentation (9 exons) and their sequences are nearly identical: only 8 out of 1203 nt differ in the coding region, 4 out of 567 nt in the introns and 2 out of 52 nt in 3' UTR. Both genes are highly expressed in the silk glands whereas expression in larval carcass devoid of the silk glands is hard to detect. Translation products of the genes consist of 401 amino acids, are 98.8% identical, and are secreted as 45 kDa proteins into silk. Homologous genes in similar tandem arrangement occur on chromosome 15 of Bombyx mori (Lepidoptera). The upstream gene BmSerp2B is modified in several exons and does not seem to produce functional mRNA. The gene BmSerp2A contains two copies of exon 9, of which only the second one is used. One kind of mRNA does and the other does not include exon 1, which encodes a signal peptide. The mRNA yielding secreted BmSerp2A is expressed in the posterior, and that encoding the cytoplasmic BmSerp2A in the middle silk gland region; both kinds are strongly expressed in the anterior region. The data indicate that (1) A duplication of serpin 2 gene occurred either before Trichoptera and Lepidoptera diverged as separate orders or independently in early phylogeny of either order; (2) In the caddisfly H. angustipennis, both genes are expressed specifically in the silk glands and generate proteins deposited in the silk; (3) Only one gene seems to be functional in B. mori and is expressed in a cytoplasmic and in a secreted forms in diverse organs, including the silk glands.

Pyrosequencing-based expression profiling and identification of differentially regulated genes from Manduca sexta, a lepidopteran model insect

Although Manduca sexta has significantly contributed to our knowledge on a variety of insect physiological processes, the lack of its genome sequence hampers the large-scale gene discovery, transcript profiling, and proteomic analysis in this biochemical model species. Here we report our implementation of the RNA-Seq cDNA sequencing approach based on massively parallel pyrosequencing, which allows us to categorize transcripts based on their relative abundances and to discover process- or tissue-specifically regulated genes simultaneously. We obtained 1,821,652 reads with an average length of 289 bp per read from fat body and hemocytes of naïve and microbe-injected M. sexta larvae. After almost all (92.1%) of these reads were assembled into 19,020 contigs, we identified 528 contigs whose relative abundances increased at least 5- and 8-fold in fat body and hemocytes, respectively, after the microbial challenge. Polypeptides encoded by these contigs include pathogen recognition receptors, extracellular and intracellular signal mediators and regulators, antimicrobial peptides, and proteins with no known sequence but likely participating in defense in novel ways. We also found 250 and 161 contigs that were preferentially expressed in fat body and hemocytes, respectively. Furthermore, we integrated data from our previous study and generated a sequence database to support future gene annotation and proteomic analysis in M. sexta. In summary, we have successfully established a combined approach for gene discovery and expression profiling in organisms lacking known genome sequences.

Immunity in lepidopteran insects

Lepidopteran insects provide important model systems for innate immunity of insects, particularly for cell biology of hemocytes and biochemical analyses of plasma proteins. Caterpillars are also among the most serious agricultural pests, and understanding of their immune systems has potential practical significance. An early response to infection in lepidopteran larvae is the activation of hemocyte adhesion, leading to phagocytosis, nodule formation, or encapsulation. Plasmatocytes and granular cells are the hemocyte types involved in these responses. Infectious microorganisms are recognized by binding of hemolymph plasma proteins to microbial surface components. This "pattern recognition" triggers phagocytosis and nodule formation, activation of prophenoloxidase and melanization and the synthesis of antimicrobial proteins that are secreted into the hemolymph. Many hemolymph proteins that function in such innate immune responses of insects were first discovered in lepidopterans. Microbial proteinases and nucleic acids released from lysed host cells may also activate lepidopteran immune responses. Hemolymph antimicrobial peptides and proteins can reach high concentrations and may have activity against a broad spectrum of microorganisms, contributing significantly to clearing of infections. Serine proteinase cascade pathways triggered by microbial components interacting with pattern recognition proteins stimulate activation of the cytokine Spätzle, which initiates the Toll pathway for expression of antimicrobial peptides. A proteinase cascade also results inproteolytic activation of phenoloxidase and production of melanin coatings that trap and kill parasites and pathogens. The proteinases in hemolymph are regulated by specific inhibitors, including members of the serpin superfamily. New developments in lepidopteran functional genomics should lead to much more complete understanding of the immune systems of this insect group.

Transcriptional Expression of Serpin-6 Gene in Bombyx Mori Larval after Infection of Bacteria at Different Developmental Stages

Serpins can block different steps in the activation cascade of prophenoloxidase (proPO) system, and play an important role in immunity of insect. In this paper, Haemolymph was collected from the 4th molting, newly moulted 5th instar and day-3 fifth instar larval challenged by lipopolysaccharide (LPS) or Bacillus thuringiensis, respectively. The results revealed that the transcriptional level of Bmserpin-6 in different developmental stages showed a trend of rise first, then fall. Bmserpin-6 of the 4th molting larva expressed highest at 6h post-infection with LPS and 3h post-infection with Bacillus thuringiensis. Bmserpin-6 of newly moulted 5th instar larva expressed highest at 9h post-infection with LPS and 6h post-infection with Bacillus thuringiensis. Bmserpin-6 of day-3 fifth instar larva expressed highest at 9h post-infection with Bacillus thuringiensis. Bmserpin-6 was all highly induced and highly expressed in haemolymph of larval at different developmental stages. But The time to arrive the highest transcriptional level was different. This is inferred that the Serpin gene may play an important role in immunity of Bombyx mori.

Disk abalone (Haliotis discus discus) expresses a novel antistasin-like serine protease inhibitor: Molecular cloning and immune response against bacterial infection

A novel antistasin-like cDNA homologue named as Ab-Antistasin was isolated from the disk abalone Haliotis discus discus normalized cDNA library. The Ab-Antistasin (1398-bp) consisted of an 1185-bp open reading frame encoding 395 amino acid (aa) residues. The predicted molecular mass and isoelectric point of Ab-Antistasin was 44 kDa and 8.5, respectively, and showed highest identity (23.1%) to Hydra magnipapillata antistasin. The most striking feature of Ab-Antistasin is the 12-fold internal repeats (IR) of an antistasin-like domain. Ten of the 12 IR domains (26-27 aa) are highly conserved, with 6 cysteines and 1 glycine. Ab-Antistasin was comprised of three Bowman-Birk serine protease inhibitor family motifs. The recombinant Ab-Antistasin (rAb-Antistasin) was over-expressed in Escherichia coli and purified using a pMAL system. rAb-Antistasin (10 microM) was able to inhibit trypsin activity by 66% in a dose-dependent manner. Moreover, it exhibited low prolongation activity for coagulation in an APTT assay (86.0 s compared to control 42.0 s) with human blood. Endogenous Ab-Antistasin mRNA was found to be expressed in digestive tract, hepatopancreas, hemocytes, abductor muscle and mantle, with highest expression levels in digestive tract followed by hepatopancreas and hemocytes. Quantitative real time PCR results revealed that Ab-Antistasin transcription was significantly induced at 3 h post-infection (p.i.) after challenged by a mixture of bacteria (Vibrio alginolyticus, Vibrio parahemolyticus, and Listeria monocytogenes) in the abalone digestive tract; in the hemocytes, induction occurred at 6 and 12 h. The results indicated that Ab-Antistasin could play an important role in the immune responses of mollusks.

Purification, characterization and immunolocalization of a novel protease inhibitor from hemolymph of tasar silkworm, Antheraea mylitta

A novel serine protease inhibitor (AmPI) was purified from larval hemolymph of tasar silkworm, Antheraea mylitta by two-step process of trypsin-affinity and gel-filtration (FPLC) chromatography. AmPI was active against larval midgut and commercial bovine trypsin and chymotrypsin. The extent of purification was determined by SDS and Native PAGE. The protease inhibitor had an apparent molecular weight of approximately 14.5 kDa as determined by SDS-PAGE. Its activity was stable over a pH range of 4.5-9 and temperatures range of 4-65 degrees C. Molecular weight as determined by MALDITOF-MS was between 13241.63 and 13261.66 Da. MS profile of AmPI also suggests two isoforms of AmPI because of glycosylation by heptose (C(7)H(14)O(7)). This confirmed the result of Native PAGE showing two bands. N-terminal amino acid sequence of this protein did not show similarity to any known protease inhibitor. To study the functional implications of AmPI in insect, it was localized in insect body tissue of different larval instars by immunogold labeling technique using GAR-gold conjugate as secondary antibody. The pattern of localization suggests constitutive nature of AmPI, which may have role in insect's defense mechanism.

A genome-wide survey for host response of silkworm, Bombyx mori during pathogen Bacillus bombyseptieus infection

Host-pathogen interactions are complex relationships, and a central challenge is to reveal the interactions between pathogens and their hosts. Bacillus bombysepticus (Bb) which can produces spores and parasporal crystals was firstly separated from the corpses of the infected silkworms (Bombyx mori). Bb naturally infects the silkworm can cause an acute fuliginosa septicaemia and kill the silkworm larvae generally within one day in the hot and humid season. Bb pathogen of the silkworm can be used for investigating the host responses after the infection. Gene expression profiling during four time-points of silkworm whole larvae after Bb infection was performed to gain insight into the mechanism of Bb-associated host whole body effect. Genome-wide survey of the host genes demonstrated many genes and pathways modulated after the infection. GO analysis of the induced genes indicated that their functions could be divided into 14 categories. KEGG pathway analysis identified that six types of basal metabolic pathway were regulated, including genetic information processing and transcription, carbohydrate metabolism, amino acid and nitrogen metabolism, nucleotide metabolism, metabolism of cofactors and vitamins, and xenobiotic biodegradation and metabolism. Similar to Bacillus thuringiensis (Bt), Bb can also induce a silkworm poisoning-related response. In this process, genes encoding midgut peritrophic membrane proteins, aminopeptidase N receptors and sodium/calcium exchange protein showed modulation. For the first time, we found that Bb induced a lot of genes involved in juvenile hormone synthesis and metabolism pathway upregulated. Bb also triggered the host immune responses, including cellular immune response and serine protease cascade melanization response. Real time PCR analysis showed that Bb can induce the silkworm systemic immune response, mainly by the Toll pathway. Anti-microorganism peptides (AMPs), including of Attacin, Lebocin, Enbocin, Gloverin and Moricin families, were upregulated at 24 hours post the infection.

Cloning, expression and characterization of four serpin-1 cDNA variants from the spruce budworm, Choristoneura fumiferana

Four cDNAs (Cfserpin-1a, Cfserpin-1b, Cfserpin-1c and Cfserpin-1d) of the Choristoneura fumiferana serpin-1 gene were cloned from an epidermis cDNA library. Analysis of the deduced amino acid sequences indicated that the cloned cDNAs encode four different proteins displaying identical N- but distinct C-termini, the latter region containing the inhibitory loop. The entire CfSerpin-1 gene is transcribed while the variants are generated. Antibodies generated against the purified recombinant serpins cross-reacted with the other three. Each of the four Cfserpin-1 cDNA variants was transcribed throughout larval development, from the 4th to the 6th instar, but transcript levels during the intermolt phases were generally higher than during the molting phase. The epidermis and fat body had higher levels of Cfserpin-1 transcripts than the midgut. Cfserpin-1 proteins, detected with the Cfserpin-1a antibody, were found in the epidermis, midgut, fat body, plasma and molting fluid of 6th instar larvae and pre-pupae. Prepupal and pupal insects had higher levels of the proteins than the 6th instar feeding larvae, despite a drop in transcript levels. Cfserpin-1a could bind with the serine proteinase elastase and form a complex in vitro. We hypothesize that the cloned serpins could be involved in the regulation of cuticle degradation during the insect molting cycle.

The serpin gene family in Anopheles gambiae

Serpins (serine protease inhibitors) regulate some innate immune responses of insects by inhibiting endogenous proteases. In this study, we characterized the serpin (SRPN) gene family in the mosquito Anopheles gambiae, the major malaria vector in Sub-Saharan Africa. We identified 18 A. gambiae SRPN genes, all on chromosomes 2 and 3, through searches of genomic DNA and EST databases. In addition to SRPN10, previously documented to exhibit alternative splicing, we found three splicing isoforms of SRPN4. We completed sequencing of cDNAs for the A. gambiae serpins to obtain complete coding sequence information and to verify or improve gene predictions. The predicted SRPN9 and 15 in the initial genome annotation were determined to be a single gene (SRPN9). Sixteen of the serpins contained putative secretion signal sequences. Multiple sequence alignments showing conserved residues important in structural conformation, including the consensus pattern within the hinge region, indicated that most of the A. gambiae serpins may be inhibitory. Phylogenetic analyses confirmed that SRPN1, 2, 3, 8, 9 and 10 formed phylogenetic clusters with known inhibitory serpins from Drosophila melanogaster and Manduca sexta. Many of the A. gambiae serpins were expressed during all life stages. However, SRPN7, 8, 12, and 19 were expressed at very low levels in the adult stage. SRPN13 was expressed mostly in eggs and young larvae, whereas SRPN5 and 14 were expressed mostly in adults. Such differences in expression pattern suggest that the serpins are involved in multiple physiological processes. Determining the biological functions of the mosquito serpins will require future work to identify the proteases they inhibit in vivo.

A comparative analysis of serpin genes in the silkworm genome

Serine protease inhibitors (serpins) are a superfamily of proteins, most of which control protease-mediated processes by inhibiting their cognate enzymes. Sequencing of the silkworm genome provides an opportunity to investigate serpin structure, function, and evolution at the genome level. There are thirty-four serpin genes in Bombyx mori. Six are highly similar to their Manduca sexta orthologs that regulate innate immunity. Three alternative exons in serpin1 gene and four in serpin28 encode a variable region including the reactive site loop. Splicing of serpin2 pre-mRNA yields variations in serpin2A, 2A' and 2B. Sequence similarity and intron positions reveal the evolutionary pathway of seven serpin genes in group C. RT-PCR indicates an increase in the mRNA levels of serpin1, 3, 5, 6, 9, 12, 13, 25, 27, 32 and 34 in fat body and hemocytes of larvae injected with bacteria. These results suggest that the silkworm serpins play regulatory roles in defense responses.

Functional expression of an insect cathepsin B-like counter-defence protein

Insects are capable of readjusting their digestive regimes in response to dietary challenge. Cowpea bruchids (Callosobruchus maculatus) strongly induce C. maculatus cathepsin B-like cysteine protease 1 (CmCatB1) transcripts when fed diet containing a soybean cysteine protease inhibitor soyacystatin N (scN). CmCatB1 shares significant sequence similarity with cathepsin B-like cysteine proteases. In this study, we isolated another cDNA, namely CmCatB2 that encodes a protein sequence otherwise identical to CmCatB1, but lacking a 70-amino-acid internal section. CmCatB1 and CmCatB2 probably resulted from alternate splicing events. Only the CmCatB1 transcript, however, exhibited differential expression in response to dietary scN. Further, this expression was only detectable in larvae, which is the developmental stage associated with food ingestion. The scN-activated and developmentally regulated CmCatB1 expression pattern suggests it may have a unique function in insect counter-defence against antinutritional factors. Heterologously expressed recombinant CmCatB1 protein exhibited enzymatic activity in a pH-dependent manner. Activity of the protein was inhibited by both the cysteine protease inhibitor E-64 and the cathepsin B-specific inhibitor CA-074, verifying its cathepsin B-like cysteine protease nature. Interestingly, the enzymatic activity was unaffected by the presence of scN. Together, we have provided functional evidence suggesting that CmCatB1 confers inhibitor-insensitive enzymatic activity to cowpea bruchids, which is crucial for insect survival when challenged by dietary protease inhibitors.

Differential expansion and evolution of the exon family encoding the Serpin-1 reactive centre loop has resulted in divergent serpin repertoires among the Lepidoptera

Serpins are a unique class of serine protease inhibitors that are becoming increasingly recognized as important regulators of insect defense mechanisms and developmental processes. Previously, we identified three Mamestra configurata serpins that were similar in structure to those encoded by the Manduca sexta Serpin-1 gene. To gain insight into the evolution and function of serpins in lepidopterans, we developed a bacterial artificial chromosome library and sequenced the entire M. configurata gene. The Serpin-1 gene was 28 kbp and had the capacity to encode nine serpin isoforms via alternate splicing of exons encoding variant reactive center loops onto a common scaffold. The relative abundance of each isoform was estimated by expressed sequence tag analysis and their expression patterns examined in various developmental stages and larval tissues. The organization of the M. configurata Serpin-1 gene was very similar to that of M. sexta Serpin-1; however, only the Ms Serpin-1Z (1 of 12) and the Mc Serpin-1a isoforms exhibited a high degree of similarity. Orthologs similar to this variant were also found in other lepidopterans, namely Bombyx mori and Plutella xylostella, suggesting that they are involved in a conserved biochemical process and likely represent the ancestral serpin variant. Expansion of the exon family encoding the Serpin-1 reactive centre loop region appears to be a product of recent duplication events that has given rise to different serpin repertoires in related insect taxa.

Serpins in plants and green algae

Control of proteolysis is important for plant growth, development, responses to stress, and defence against insects and pathogens. Members of the serpin protein family are likely to play a critical role in this control through irreversible inhibition of endogenous and exogenous target proteinases. Serpins have been found in diverse species of the plant kingdom and represent a distinct clade among serpins in multicellular organisms. Serpins are also found in green algae, but the evolutionary relationship between these serpins and those of plants remains unknown. Plant serpins are potent inhibitors of mammalian serine proteinases of the chymotrypsin family in vitro but, intriguingly, plants and green algae lack endogenous members of this proteinase family, the most common targets for animal serpins. An Arabidopsis serpin with a conserved reactive centre is now known to be capable of inhibiting an endogenous cysteine proteinase. Here, knowledge of plant serpins in terms of sequence diversity, inhibitory specificity, gene expression and function is reviewed. This was advanced through a phylogenetic analysis of amino acid sequences of expressed plant serpins, delineation of plant serpin gene structures and prediction of inhibitory specificities based on identification of reactive centres. The review is intended to encourage elucidation of plant serpin functions.

Cell-mediated immunity in arthropods: Hematopoiesis, coagulation, melanization and opsonization

The functions of hemocytes in innate immune response are reviewed with emphasized on their roles in coagulation, melanization and opsonization. Also the ways in which hemocytes are produced in and released from hematopoietic tissue are discussed.

Astacin family metallopeptidases and serine peptidase inhibitors in spider digestive fluid

Digestive fluid of the araneid spider Argiope aurantia is known to contain zinc metallopeptidases. Using anion-exchange chromatography, size-exclusion chromatography, sucrose density gradient centrifugation, and gel electrophoresis, we isolated two lower-molecular-mass peptidases, designated p16 and p18. The N-terminal amino acid sequences of p16 (37 residues) and p18 (20 residues) are 85% identical over the first 20 residues and are most similar to the N-terminal sequences of the fully active form of meprin (beta subunits) from several vertebrates (47-52% and 50-60% identical, respectively). Meprin is a peptidase in the astacin (M12A) subfamily of the astacin (M12) family. Additionally, a 66-residue internal sequence obtained from p16 aligns with the conserved astacin subfamily domain. Thus, at least some spider digestive peptidases appear related to astacin of decapod crustaceans. However, important differences between spider and crustacean metallopeptidases with regard to isoelectric point and their susceptibility to hemolymph-borne inhibitors are demonstrated. Anomalous behavior of the lower-molecular-mass Argiope peptidases during certain fractionation procedures indicates that these peptidases may take part in reversible associations with each other or with other proteins. A. aurantia digestive fluid also contains inhibitory activity effective against insect digestive peptidases. Here we present evidence for at least thirteen, heat-stable serine peptidase inhibitors ranging in molecular mass from about 15 to 32 kDa.

Identification of plasma proteases inhibited by Manduca sexta serpin-4 and serpin-5 and their association with components of the prophenol oxidase activation pathway

One innate immune response pathway of insects is a serine protease cascade that activates prophenol oxidase (pro-PO) in plasma. However, details of this pathway are not well understood, including the number and order of proteases involved. Protease inhibitors from the serpin superfamily appear to regulate the proteases in the pathway. Manduca sexta serpin-4 and serpin-5 suppress pro-PO activation in plasma, apparently by inhibiting proteases upstream of the direct activator of pro-PO. To identify plasma proteases inhibited by these serpins, we used immunoaffinity chromatography with serpin antibodies to isolate serpin-protease complexes that formed after activation of the cascade by exposure of plasma to bacteria or lipopolysaccharide. Covalent complexes of serpin-4 with hemolymph proteases HP-1 and HP-6 appeared in plasma activated by Gram-positive or Gram-negative bacteria, whereas serpin-4 complexes with HP-21 and two unidentified proteases were unique to plasma treated with Gram-positive bacteria. HP-1 and HP-6 were also identified as target proteases of serpin-5, forming covalent complexes after bacterial activation of the cascade. These results suggest that HP-1 and HP-6 may be components of the pro-PO activation pathway, which are activated in response to infection and regulated by serpin-4 and serpin-5. HP-21 and two unidentified proteases may participate in a Gram-positive bacteria-specific branch of the pathway. Several plasma proteins that co-purified with serpin-protease complexes, most notably immulectins and serine protease homologs, are known to be components of the pro-PO activation pathway. Our results suggest that after activation by exposure to bacteria, components of the pro-PO pathway associate to form a large noncovalent complex, which localizes the melanization reaction to the surface of invading microorganisms.

Manduca sexta Serpin-4 and Serpin-5 Inhibit the Prophenol Oxidase Activation Pathway

Infection stimulates the innate immune responses of insects, including activation of prophenol oxidase (pro-PO) in plasma as the last step of a serine protease cascade. To investigate the roles of protease inhibitors in regulating this pathway, we cloned cDNAs for two new serpins (serpin-4 and serpin-5) from the tobacco hornworm, Manduca sexta. Serpin-4 and serpin-5 mRNAs are constitutively expressed at a low level in larval hemocytes and fat body and increased dramatically upon bacterial challenge. These serpins are present in larval plasma at approximately 3 (serpin-4) and approximately 1 mug/ml (serpin-5) and increased 3-8-fold by 24 h after injection of bacteria or fungi. Recombinant serpin-4 and serpin-5 decreased pro-PO activation when added to plasma, but they did not directly inhibit the pro-PO-activating proteases. Instead, they apparently regulate the pathway by inhibiting one or more target proteases upstream of the pro-PO-activating proteases.

Manduca sexta serpin-6 regulates immune serine proteinases PAP-3 and HP8. cDNA cloning, protein expression, inhibition kinetics, and function elucidation

Analogous to blood coagulation and complement activation in mammals, some insect defense responses (e.g. prophenoloxidase (proPO) activation and Toll pathway initiation) are mediated by serine proteinase cascades and regulated by serpins in hemolymph. We recently isolated Manduca sexta serpin-6 from hemolymph of the bacteria-challenged larvae, which selectively inhibited proPO-activating proteinase-3 (PAP-3) (Wang, Y., and Jiang, H. (2004) Insect Biochem. Mol. Biol. 34, 387-395). To further characterize its structure and function, we cloned serpin-6 from an induced fat body cDNA library using a PCR-derived probe. M. sexta serpin-6 is 55% similar in amino acid sequence to Drosophila melanogaster serpin-5, an immune-responsive protein. We produced serpin-6 in an Escherichia coli expression system and purified the soluble protein by nickel affinity and hydrophobic interaction chromatography. The recombinant protein specifically inhibited PAP-3 and blocked proPO activation in vitro in a concentration-dependent manner. Matrix-assisted laser desorption ionization-time of flight mass spectrometry indicated that the cleavage site of serpin-6 is between Arg373 and Ser374. Serpin-6 is constitutively present in hemolymph of naive larvae, and its mRNA and protein levels significantly increase after a bacterial injection. The association rate constant of serpin-6 and PAP-3 is 2.6 x 10(4) m(-1) s(-1), indicating that serpin-6 may contribute to the inhibitory regulation of PAP-3 in the hemolymph. We also identified the covalent complex of serpin-6 and PAP-3 in induced hemolymph by immunoaffinity chromatography and mass spectrometry. Furthermore, immulectin-2, serine proteinase homologs, proPO, PO, attacin-2, and a complex of serpin-6 and hemolymph proteinase-8 were also detected in the proteins eluted from the immunoaffinity column using serpin-6 antibody. These results suggest that serpin-6 plays important roles in the regulation of immune proteinases in the hemolymph.

Innate immune responses of a lepidopteran insect, Manduca sexta

Many innate immune mechanisms are conserved throughout the animal kingdom. Manduca sexta, a widely used model for insect biochemical research, employs these mechanisms to defend against invading pathogens and parasites. We have isolated from M. sexta hemolymph a group of proteins (hemolin, peptidoglycan recognition proteins, beta-1,3-glucan recognition proteins, and C-type lectins), which serve as a surveillance mechanism by binding to microbial surface molecules (e.g. peptidoglycan, lipopolysaccharide, lipoteichoic acid, and beta-1,3-glucan). The binding triggers diverse responses such as phagocytosis, nodule formation, encapsulation, melanization, and synthesis of anti-microbial peptides/proteins. Some of these responses are mediated and coordinated by serine proteinase cascades, analogous to the complement system in mammals. Our current research is focused on the proteolytic activation of prophenoloxidase (proPO)--a reaction implicated in melanotic encapsulation, wound healing, and protein cross-linking. We have isolated three proPO-activating proteinases, each of which requires serine proteinase homologs as a cofactor for generating active phenoloxidase. The proteinases and proteinase-like molecules, containing one to two clip domains at their amino-terminus, are acute-phase proteins induced upon an immune challenge. Inhibitory regulation of the proteinases by serpins and association of the proteinase homologs with a bacteria-binding lectin are important for ensuring a localized defense response. Additional serine proteinases expressed in M. sexta hemocytes and fat body have been discovered. Future research efforts will be aimed at elucidating the proteinase cascade for proPO activation and investigating the roles of proteinases in other immune responses such as processing of plasmatocyte-spreading peptide.

Isolation, characterization, and recombinant expression of multiple serpins from the cat flea, Ctenocephalides felis

Several clones encoding serine protease inhibitors were isolated from larval and adult flea cDNA expression libraries by immunoscreening and PCR amplification. Each cDNA contained an open reading frame encoding a protein of approximately 45 kDa, which had significant sequence similarity with the serpin family of serine protease inhibitors. The thirteen cDNA clones isolated to date encode serpin proteins, which share a primary structure that includes a nearly identical constant region of about 360 amino acids, followed by a C-terminal variable region of about 40-60 amino acids. The variable C-terminal sequences encode most of the reactive site loop (RSL) and are generated by mutually exclusive alternative exon splicing, which may confer unique protease selectivity to each serpin. Utilization of an alternative exon splicing mechanism has been verified by sequence analysis of a flea serpin genomic clone and adjacent genomic sequences. RNA expression patterns of the cloned genes have been examined by Northern blot analysis using variable region-specific probes. Several putative serpins have been overexpressed using the cDNA clones in Escherichia coli and baculovirus expression systems. Two purified baculovirus-expressed recombinant proteins have N-terminal amino acid sequences identical to the respective purified native mature flea serpins indicating that appropriate N-terminal processing occurred in the virus-infected insect cells.

The construction of an EST database for Bombyx mori and its application

To build a foundation for the complete genome analysis of Bombyx mori, we have constructed an EST database. Because gene expression patterns deeply depend on tissues as well as developmental stages, we analyzed many cDNA libraries prepared from various tissues and different developmental stages to cover the entire set of Bombyx genes. So far, the Bombyx EST database contains 35,000 ESTs from 36 cDNA libraries, which are grouped into approximately 11,000 nonredundant ESTs with the average length of 1.25 kb. The comparison with FlyBase suggests that the present EST database, SilkBase, covers >55% of all genes of Bombyx. The fraction of library-specific ESTs in each cDNA library indicates that we have not yet reached saturation, showing the validity of our strategy for constructing an EST database to cover all genes. To tackle the coming saturation problem, we have checked two methods, subtraction and normalization, to increase coverage and decrease the number of housekeeping genes, resulting in a 5-11% increase of library-specific ESTs. The identification of a number of genes and comprehensive cloning of gene families have already emerged from the SilkBase search. Direct links of SilkBase with FlyBase and WormBase provide ready identification of candidate Lepidoptera-specific genes.

Manduca sexta serpin-3 regulates prophenoloxidase activation in response to infection by inhibiting prophenoloxidase-activating proteinases

Many serine proteinase inhibitors of the serpin superfamily have evolved in vertebrates and invertebrates to regulate serine proteinase cascades that mediate the host defense responses. We have isolated an immune-responsive serpin from the tobacco hornworm, Manduca sexta. This inhibitor, M. sexta serpin-3, contains a reactive site loop strikingly similar to the proteolytic activation site in prophenoloxidase (pro-PO). Molecular cloning and sequence comparison indicate that serpin-3 is orthologous to Drosophila melanogaster serpin 27A, a regulator of melanization. M. sexta serpin-3 is constitutively present in hemolymph at a low concentration of 5-12 microg/ml and increases to 30-75 microg/ml after a microbial challenge. Recombinant serpin-3 efficiently blocks pro-PO activation in the hemolymph, and it forms SDS-stable acyl-enzyme complexes with purified pro-PO-activating proteinases (PAPs) from M. sexta. PAP-serpin-3 complexes were isolated by immunoaffinity chromatography from hemolymph activated by treatment with Micrococcus luteus. Kinetic analysis of PAP-serpin-3 association strongly suggests that serpin-3 is a physiological regulator of the pro-PO activation reaction.

Protein purification, cDNA cloning and characterization of a protease inhibitor from the Indian tasar silkworm, Antheraea mylitta

An inhibitor of Aspergillus oryzae fungal protease was purified to homogeneity from the hemolymph of fifth instar larvae of Antheraea mylitta by ammonium sulfate precipitation, anion exchange and gel filtration (FPLC) chromatography, and termed as AmFPI-1. The extent of purification was checked by two-dimensional gel electrophoresis, and the molecular weight of purified inhibitor was determined by SDS-PAGE as 10.4 kDa. Fifteen N-terminal amino acid sequences of this protein were determined, and degenerate oligonucleotides were synthesized on the basis of these sequences. A cDNA library of A. mylitta integument was constructed, and protease inhibitor cDNA was partially amplified by PCR using degenerate oligonucleotides and CDS primers. A full-length inhibitor cDNA clone obtained by screening the library with PCR amplified DNA as probe was sequenced. The cDNA consists of 543 nucleotides with an ORF of 315 bp and encodes a protein of 105 amino acids. The sequence exhibits similarity to several Bombyx mori ESTs, and in particular to N-terminal amino acid sequence of an inducible serine protease inhibitor (ISPI-1) from Galleria mellonella indicating its relatedness to ISPI-1 of G. mellonella. The presence of this protease inhibitor in the hemolymph may play an important role as a natural defense system against invading microorganisms.

Identification by subtractive suppression hybridization of bacteria-induced genes expressed in Manduca sexta fat body

Insect immune processes are mediated by programs of differential gene expression. To understand the molecular regulation of the immune response in the tobacco hornworm, Manduca sexta, the relevant subset of differentially expressed genes of interest must be identified, cloned and studied in detail. In this study, suppression subtractive hybridization, a PCR-based method for cDNA subtraction was performed to identify mRNAs from fat body of immunized larvae that are not present (or present at a low level) in control larvae. A subtracted cDNA library enriched in immune-inducible genes was constructed. Northern blot analysis of a sample of clones from our subtracted library indicated that >90% of the clones randomly selected from the subtracted library are immune inducible. Sequence analysis of 238 expressed sequence tags (ESTs) revealed that 120 ESTs, representing 54 distinct genes or gene families, had sequences identical or similar to previously characterized genes, some of which have been confirmed to be involved in innate immunity. These ESTs were categorized into seven groups, including pattern recognition proteins, serine proteinases and their inhibitors, and antimicrobial proteins. 112 ESTs, about 47.5% of the library, showed no significant similarity to any known genes. The sequences identified in this M. sexta library reflect our knowledge of insect immune strategies and may facilitate better understanding of insect immune responses.

Mamestra configurata serpin-1 homologues: cloning, localization and developmental regulation

A screen of a Mamestra configurata (bertha armyworm) midgut cDNA library identified three types of cDNA clones that resemble the Manduca sexta serpin-1 gene family. Two serpins, 1b and 1c, possess a common conserved serpin amino terminal scaffold domain but bear no similarity to any members of the M. sexta gene family within the reactive centre loop. These serpins differ from one another by only two amino acids in the reactive centre loop (S(363)-->P) and serpin signature (M(369)-->T) regions. The other member, denoted serpin-1a, is closely related to the M. sexta serpin-1Z. M. configurata serpins as a group were expressed in all insect developmental stages including eggs, larvae and adult moths. Within larvae, serpin gene expression was restricted to the early to middle instar developmental phase and mainly in the fat body and hemocytes. Stress imposed by starvation strongly induced expression in fat body and to a lesser degree in alimentary organs, nervous system and Malphigian tubules. Conversely, starvation decreased expression in hemocytes. Wounding or inoculation with bacteria did not induce serpin gene transcription but did lead to the formation of higher and lower molecular weight forms, presumably serpin-protease complexes and resultant truncated serpin, respectively. Two dimensional PAGE and western blotting analysis revealed at least 12 distinct serpins consisting primarily of neutral, but also highly acidic and basic isoforms, as well as additional high and low molecular weight immuno-reactive species. Serpins-1b/1c are the more prominent serpin isoforms and are expressed predominantly in the fat body and subsequently exported to the hemolymph as revealed by western blotting and immunolocalization. The serpin-1b/1c isoform was found only as the fully glycosylated species within the hemolymph. Hemolymph protease activity was comprised mostly of serine proteases whose overall activity increased dramatically at the onset of the molt concomitant with a sharp decline in serpin gene expression.

Cloning and characterization of four Anopheles gambiae serpin isoforms, differentially induced in the midgut by Plasmodium berghei invasion

The genomic locus SRPN10 of the malaria vector Anopheles gambiae codes for four alternatively spliced serine protease inhibitors of the serpin superfamily. The four 40- to 42-kDa isoforms differ only at their C terminus, which bears the reactive site loop, and exhibit protein sequence similarity with other insect serpins and mammalian serpins of the ovalbumin family. Inhibition experiments with recombinant purified SRPN10 serpins reveal distinct and specific inhibitory activity of three isoforms toward different proteases. All isoforms are mainly expressed in the midgut but also in pericardial cells and hemocytes of the mosquito. The cellular localization of SRPN10 serpins is nucleocytoplasmic in pericardial cells, in hemocytes and in a hemocyte-like mosquito cell line, but in the gut the proteins are mostly localized in the nucleus. Although the transcript levels of all SRPN10 isoforms are marginally affected by bacterial challenge, the transcripts of two isoforms (KRAL and RCM) are induced in female mosquitoes in response to midgut invasion by Plasmodium berghei ookinetes. The KRAL and RCM SRPN10 isoforms represent new potential markers to study the ookinete midgut invasion process in anopheline mosquitoes.