Molecular cloning, characterization and expression analysis of cathepsin O in silkworm Bombyx mori related to bacterial response

Group V Chitin Deacetylases Influence the Structure and Composition of the Midgut of Beet Armyworm, Spodoptera exigua

Chitin deacetylase (CDA) can accelerate the conversion of chitin to chitosan, influencing the mechanical properties and permeability of the cuticle structures and the peritrophic membrane (PM) in insects. Putative Group V CDAs SeCDA6/7/8/9 (SeCDAs) were identified and characterized from beet armyworm Spodoptera exigua larvae. The cDNAs of SeCDAs contained open reading frames of 1164 bp, 1137 bp, 1158 bp and 1152 bp, respectively. The deduced protein sequences showed that SeCDAs are synthesized as preproteins of 387, 378, 385 and 383 amino acid residues, respectively. It was revealed via spatiotemporal expression analysis that SeCDAs were more abundant in the anterior region of the midgut. The SeCDAs were down-regulated after treatment with 20-hydroxyecdysone (20E). After treatment with a juvenile hormone analog (JHA), the expression of SeCDA6 and SeCDA8 was down-regulated; in contrast, the expression of SeCDA7 and SeCDA9 was up-regulated. After silencing SeCDAV (the conserved sequences of Group V CDAs) via RNA interference (RNAi), the layer of intestinal wall cells in the midgut became more compact and more evenly distributed. The vesicles in the midgut were small and more fragmented or disappeared after SeCDAs were silenced. Additionally, the PM structure was scarce, and the chitin microfilament structure was loose and chaotic. It was indicated in all of the above results that Group V CDAs are essential for the growth and structuring of the intestinal wall cell layer in the midgut of S. exigua. Additionally, the midgut tissue and the PM structure and composition were affected by Group V CDAs.

RNA Interference-Mediated Knockdown of Bombyx mori Haemocyte-Specific Cathepsin L (Cat L)-Like Cysteine Protease Gene Increases Bacillus thuringiensis kurstaki Toxicity and Reproduction in Insect Cadavers

The silkworm’s Cat L-like gene, which encodes a lysosomal cathepsin L-like cysteine protease, is thought to be part of the insect’s innate immunity via an as-yet-undetermined mechanism. Assuming that the primary function of Cat L-like is microbial degradation in mature phagosomes, we hypothesise that the suppression of the Cat L-like gene expression would increase Bacillus thuringiensis (Bt) bacteraemia and toxicity in knockdown insects. Here, we performed a functional analysis of Cat L-like in larvae that were fed mulberry leaves contaminated with a commercial biopesticide formulation based on Bt kurstaki (Btk) (i.e., Dipel) to investigate its role in insect defence against a known entomopathogen. Exposure to sublethal doses of Dipel resulted in overexpression of the Cat L-like gene in insect haemolymph 24 and 48 h after exposure. RNA interference (RNAi)-mediated suppression of Cat L-like expression significantly increased the toxicity of Dipel to exposed larvae. Moreover, Btk replication was higher in RNAi insects, suggesting that Cat L-like cathepsin may be involved in a bacterial killing mechanism of haemocytes. Finally, our results confirm that Cat L-like protease is part of the antimicrobial defence of insects and suggest that it could be used as a target to increase the insecticidal efficacy of Bt-based biopesticides.

Bombyx mori U-shaped regulates the melanization cascade and immune response via binding with the Lozenge protein

Zinc finger protein, an important transcription factor, regulates gene expression associated with various physiological and pathological processes. U-shaped, belong to the Friend of GATA (FOG) transcription factor, plays a crucial role in hematopoiesis by interacting with the GATA transcription factor as a co-factor. However, little is known about its functions in insects. In the present study, a U-shaped cDNA was identified and characterized from the silkworm Bombyx mori and its potential roles in innate immunity investigated. The predicted silkworm U-shaped amino acid sequence contained a classical nuclear localization signal (NLS) motif "GESSPKRRRR" at position 450-459, and arginine residues at position 456 and 478 are the critical sites of the NLS. U-shaped mRNA was detected in all tested tissues of the B. mori; however, the highest levels were found in the hemocytes. U-shaped mRNA expression levels were upregulated in the hemocyte after the Escherichia coli and Staphylococcus aureus challenge. Furthermore, U-shaped knockdown significantly reduced the melanization process and suppressed the expression of melanization-associated genes, including PPO1, PPO2, PPAE and BAEE. In addition, U-shaped interacts with Lozenge protein to regulate the innate immune response of the insect. Our results revealed that U-shaped binds directly to Lozenge protein to modulate the melanization process and innate immune responses in silkworm.

Molecular mechanism and potential application of bacterial infection in the silkworm, Bombyx mori

As a representative species of Lepidoptera, Bombyx mori has been widely studied and applied. However, bacterial infection has always been an important pathogen threatening the growth of silkworms. Bombyx mori can resist various pathogenic bacteria through their own physical barrier and innate immune system. However, compared with other insects, such as Drosophila melanogaster, research on the antibacterial mechanism of silkworms is still in its infancy. This review systematically summarized the routes of bacterial infection in silkworms, the antibacterial mechanism of silkworms after ingestion or wounding infection, and the intestinal bacteria and infection of silkworms. Finally, we will discuss silkworms as a model animal for studying bacterial infectious diseases and screening antibacterial drugs.

Genomic and transcriptomic identification of the cathepsin superfamily in the Mediterranean mussel Mytilus galloprovincialis

Cathepsins are lysosomal enzymes that participate in important physiological processes, such as development, tissue remodelling, senescence and innate and adaptive immunity. The description of these proteins in molluscs is fragmented and incomplete. In the present work, we identified most of the cathepsin family members in the bivalve Mytilus galloprovincialis by screening published genomic and transcriptomic information. In this specie, the cathepsin family is composed of 41 proteins showing a high diversification of cathepsins D, L and F, not previously observed in other taxonomic groups. Specific set of cathepsins are constitutively expressed in the different mussel tissues. Transcriptomic analyses suggested coordinated activity of the different cathepsins and their sequential activation during larval development. Cathepsins also play an important role in the immune response of bivalves, and different immune pathways seem to be activated in response to Vibrio splendidus infection.

Scavenger receptor C regulates antimicrobial peptide expression by activating toll signaling in silkworm, Bombyx mori

Scavenger receptor is pattern-recognition receptor (PRR) that plays a crucial function in host defense against pathogens. Scavenger receptor C (SR-C) is present only in invertebrates and its function has not been studied in detail. In this study, an SR-C homologous gene from the silkworm, Bombyx mori, was identified and characterized. SR-C was largely expressed in hemocytes and Malpighian tubules, with continuous expression in hemocytes. The peak expression was observed in hemocytes during molting and wandering stages both at mRNA and protein levels. Furthermore, immunofluorescence demonstrated it to be mainly distributed in the cell membranes of hemocytes, including oenocytoids and granulocytes. The recombinant SR-C protein (rSR-C) could bind to different types of bacteria and pathogen-associated molecular patterns (PAMPs), with strong binding to gram-positive bacteria and Lys-type peptidoglycans. The overexpression of SR-C induced the expression of genes related to the Toll pathway and antibacterial peptides. While the knockdown of SR-C reduced the expression of AMPs and inhibited the Toll pathway, it impaired the bacterial clearance ability of silkworm larvae, thus decreasing silkworm larvae's survival rate. Altogether, SR-C is a PRR that protect silkworms against bacterial pathogens by enhancing the expression of AMPs expression via the Toll pathway in hemocytes.

Functions of Bombyx mori cathepsin L-like in innate immune response and anti-microbial autophagy

Cathepsins belongs to the cysteine protease family, which are activated by an acidic environment. They play essential biological roles in the innate immunity and development of animals. Here, we identified a 62 kDa cathepsin L-like protease from the silkworm Bombyx mori. It contained putative conserved domains, including an I29 inhibitor domain and a peptidase C1A domain. The expression analysis revealed that cathepsin L-like was highly produced in the fat body, and 20-hydroxyecdysone (20 E) induced its expression. After challenge with three different types of heat-killed pathogens (Escherichia coli, Beauveria bassiana, and Bacillus cereus), the mRNA levels of cathepsin L-like significantly increased and displayed variable expression patterns in the immune tissues, suggesting its potential role in the innate immune response. The suppression of cathepsin L-like altered the expression of immune-related genes associated with the Toll and IMD pathway. Besides, autophagy-related genes such as Atg6, Atg8, VAMP2, Vps4, and syntaxin expression were also altered, indicating that cathepsin L-like regulates innate immunity and autophagy. Fluorescence microscopic analysis exhibited that cathepsin L-like was localized in the cytoplasm, and it was activated and dispersed throughout the cytoplasm and nucleus following the induction of anti-microbial autophagy. Altogether, our data suggest that cathepsin L-like may regulate the innate immune response and anti-microbial autophagy in the silkworm, B. mori.

A hemocyte-specific cathepsin L-like cysteine protease is involved in response to 20-hydroxyecdysone and microbial pathogens stimulation in silkworm, Bombyx mori

Cathepsin L protease belongs to the papain-like cysteine proteases family, plays indispensable roles in animals' pathological and physiological processes. However, little is known about Cathepsin L in silkworm, Bombyx mori. Herein, a novel Cathepsin L-like (Cat L-like) was cloned and identified from silkworm by the rapid amplification of cDNA ends (RACE). Cat L-like contains an intact open reading frame (ORF) of 1 668 bp and encodes 556 amino acid residues, consisting of a signal peptide, typical cathepsins' inhibitor_I29, and pept_C1 domain. Cat L-like is specifically and highly expressed in hemocytes. The cathepsin (including Cathepsin L, B, and H) crude extract from hemocytes had typical substrate specific catalytic activities and were sensitive to pH and temperature. Cat L-like up-regulated considerably after 20-hydroxyecdysone (20-E) administration, indicating that Cat L-like may be regulated by insect hormone. The responses of Cat L-like against bacterial infection suggest it may play essential roles in silkworm immunity. Overall, our studies provide a theoretical basis and insights to further investigate the functions of Cat L-like and in insects' innate immunity mechanisms.

20-Hydroxyecdysone regulates the transcription of the lysozyme via Broad-Complex Z2 gene in silkworm, Bombyx mori

Broad-Complex Z2 (Br-C Z2) is an ecdysone inducible transcription factor that regulates physiological, innate immune and developmental events in insects. Here, we identified an orthologue of Br-C Z2 from silkworm, Bombyx mori (BmBr-C Z2) to study its involvement in immune responses. The quantitative real-time PCR analysis revealed that BmBr-C Z2 was expressed ubiquitously in all tested tissues under normal physiological conditions. Further, developmental profile displayed that BmBr-C Z2 expression was detectable in different developmental stages, however the gene's expression was highest in the molting and pre-pupal stages. Administration of 20-hydroxyecdysone (20E) enhanced the expression levels of BmBr-C Z2 in hemocytes. The challenge with pathogens and pathogen associated molecular patterns (PAMPs) also upregulated the mRNA levels of BmBr-C Z2 in hemocytes when compared with the control. By contrast, the ectopic expression of BmBr-C Z2 remarkably increased the production of antimicrobial peptides, while the knock-down of this gene by double stranded RNA decreased their production. Dual-luciferase assay exhibited that BmBr-C Z2 induced the expression of lysozyme by directly binding to its promoter region. The treatment of Escherichia coli following the knock-down of BmBr-C Z2 strongly reduced the survival rate of silkworm larvae. These results suggest that BmBr-C Z2 plays an important biological role in the innate immune responses of silkworm by regulating immune-related genes.

20-Hydroxyecdysone-upregulated proteases involved in Bombyx larval fat body destruction

During insect larval-pupal metamorphosis, the obsolete larval organs and tissues undergo histolysis and programmed cell death to recycle cellular materials. It has been demonstrated that some cathepsins are essential for histolysis in larval tissues, but the process of tissue destruction is not well documented. Fat body, the homologous organ to mammalian liver and adipose tissue, goes through a distinct destruction process during larval-pupal transition. Herein, we found that most of the Bombyx proteases - including Bombyx cathepsin B (BmCatB) (BmCatLL-2), Bombyx cathepsin D (BmCatD), Bombyx cathepsin L like-1 (BmCatLL-1) and -2(BmCatLL-2), Bombyx fibroinase (BmBcp), Bombyx matrix metalloprotease (BmMmp), Bombyx A disintegrin and metalloproteinase with thrombospondin motifs 1 (BmAdamTS-1), Bombyx A disintegrin and metalloproteinase with thrombospondin motifs like (BmAdamTS L) and Bombyx cysteine protease inhibitor (Bmbcpi)- were expressed highly in fat body during feeding and metamorphosis, with a peak occurring during the nonfeeding moulting or prepupal stage, as well as being responsive to 20-hydroxyecdysone (20E). The aforementioned protease genes expression was upregulated by injection of 20E into the feeding larvae, while blocking 20E signalling transduction led to downregulation. Western blotting and immunofluorescent staining of BmCatB and BmBcp confirmed the coincident variation of their messenger RNA (mRNA) and protein level during the development and after the treatments. Moreover, BmCatB, BmBcp, BmMmp and BmAdamTS-1 RNA interference all led to blockage of larval fat body destruction. Taken together, we conclude that 20E regulates larval fat body destruction by upregulating related protease gene expression and protein levels during larval-pupal transition.

Demethylzeylasteral inhibits glioma growth by regulating the miR-30e-5p/MYBL2 axis

Glioma is the most common and malignant form of primary brain tumour, and is characterised by high proliferation and extensive invasion and neurological destruction. Demethylzeylasteral (T-96), which is extracted from Tripterygium wilfordii, is considered to have immunosuppressive, anti-inflammatory and anti-angiogenic effects. Here, the anti-tumour effect of T-96 on glioma was evaluated. Our results demonstrated that T-96 significantly inhibited glioma cell growth and induced cell cycle arrest in G1 phase but did not induce apoptosis. Cell invasion and migration were dramatically suppressed after treatment with T-96. Almost all genes related to cell cycle and DNA replication were downregulated after treatment with T-96. Our results showed that miR-30e-5p was noticeably upregulated after T-96 treatment, and MYBL2, which is involved in cell cycle progression and is a target gene of miR-30e-5p, was significantly reduced in synchrony. Overexpression of MYBL2 partially rescued the T-96-induced inhibition of cell growth and proliferation. Moreover, a miR-30e-5p antagomir significantly reduced the upregulation of miR-30e-5p expression induced by T-96, leading to recovery of MYBL2 expression, and partially rescued the T-96-induced inhibition of cell growth and proliferation. More important, T-96 effectively upregulated miR-30e-5p expression and downregulated MYBL2 expression, thus inhibiting LN-229 cell tumour growth in a mouse model. These results indicated that T-96 might inhibit glioma cell growth by regulating the miR-30e-5p/MYBL2 axis. Our study demonstrated that T-96 might act as a promising agent for malignant glioma therapy.

Molecular cloning and functional characterization of cathepsin B from Nile tilapia (Oreochromis niloticus)

Cathepsin B (CatB) has been widely known for its hydrolytic ability and involvement in the innate immunity. However, the mechanism of CatB from teleosts participating in immunoregulation remains poorly understood; and the sequence of CatB from Nile tilapia (NtCatB) has not been cloned and characterized. In this study, the coding sequence of NtCatB was cloned, and then characterized by bioinformatic analysis and heterologous expression. The deduced amino acid sequence (330-aa) of NtCatB contains the representative features of CatB. Quantitative real-time PCR revealed the extensive mRNA expression of NtCatB in six tissues of healthy Nile tilapia, and its transcription level was significantly up-regulated after Streptococcus agalactiae challenge. NtCatB may interact with some immunological function proteins and take part in the regulatory pathway. These results suggest that NtCatB is likely to be involved in the immune reaction. The mature region (residues 79-328, mNtCatB) of NtCatB was cloned and transferred to pET-28a for expressing the recombinant protein. The purified recombinant mNtCatB was verified with the activity of 992.34 U mg^-1 min^-1 under the optimal condition using a substrate hydrolyzing assay. The recombinant cystatin-A1-like can effectively inhibit the activity of the recombinant mNtCatB, and their binding form was predicted by molecular docking. Our results contribute to elucidating the immunological functions of NtCatB.

Transgenic characterization of two silkworm tissue-specific promoters in the haemocyte plasmatocyte cells

Haemocytes play crucial roles in insect metabolism, metamorphosis, and innate immunity. As a model of lepidopteran insects, the silkworm is a useful model to study the functions of both haematopoiesis and haemocytes. Tissue-specific promoters are excellent tools for genetic manipulation and are widely used in fundamental biological research. Herein, two haemocyte-specific genes, Integrin β2 and Integrin β3, were confirmed. Promoter activities of Integrin β2 and Integrin β3 were evaluated by genetic manipulation. Quantitative real-time PCR and western blotting suggested that both promoters can drive enhanced green fluorescent protein (EGFP) specifically expressed in haemocytes. Further evidence clearly demonstrated that the transgenic silkworm exhibited a high level of EGFP signal in plasmatocytes, but not in other detected haemocyte types. Moreover, EGFP fluorescence signals were observed in the haematopoietic organ of both transgenic strains. Thus, two promoters that enable plasmatocytes to express genes of interest were confirmed in our study. It is expected that the results of this study will facilitate advances in our understanding of insect haematopoiesis and immunity in the silkworm, Bombyx mori.

Cathepsin L-like protease can regulate the process of metamorphosis and fat body dissociation in Antheraea pernyi

Cathepsins are a group of protease, located in lysosome and play a vital role in physiological process. Here, we reported cathepsin L-like protease (Ap-cathL), which contained an open reading frame of 1155 bp and encoding 385 amino acid residues protein. The I29 inhibitor domain and peptidase C1A (clan CA of cysteine proteases, papain family C1 subfamily) putative conserved domains were detected in Ap-cathL. Quantitative real-time PCR (qRT-PCR) analysis revealed that Ap-cathL highly expressed in the fat body and midgut. The high expression during the molting stage, pupal stage and following 20E (20-hydroxyecdysone) treatment indicated that it maybe involved in the process of molting and metamorphosis. In addition, depletion of Ap-cathL influenced the expression of apoptosis pathway related genes. The protease inhibitor and RNA interference experiments showed that Ap-cathL was involved in the fat body dissociation of A. pernyi. These results suggest that Ap-cathL may involve in the process of metamorphosis and fat body dissociation of A. pernyi.

Integrin β3 plays a novel role in innate immunity in silkworm, Bombyx mori

Integrins are transmembrane receptors that play essential roles in many physiological and pathological processes through cell-to-cell and cell-to-extracellular matrix (ECM) interactions. In the current study, a 2653-bp full-length cDNA of a novel integrin β subunit (designated Bmintegrin β3) was obtained from silkworm hemocytes. Bmintegrin β3 has the typical conserved structure of the integrin β family. The qRT-PCR results showed that Bmintegrin β3 was specifically expressed in the hematological system and that its expression was significantly increased after challenge with different types of PAMPs and bacteria. The recombinant Bmintegrin β3 protein displayed increased aggregation with S. aureus, suggesting that Bmintegrin β3 might directly bind to PAMPs. Interestingly, Bmintegrin β3 knockdown promoted PPO1, PPO2, BAEE, SPH78, SPH125, and SPH127 expression and accelerated the melanization process. Unexpectedly, the expression of genes related to phagocytosis, the Toll pathway, and the IMD pathway was also up-regulated after Bmintegrin β3 knockdown. Thus, Bmintegrin β3 might be a pattern recognition protein (PRP) for PAMPs and might directly bind to bacteria and enhance the phagocytosis activity of hemocytes. Moreover, Bmintegrin β3 and its ligand might negatively regulate the expression of immune-related genes through an unknown mechanism. In summary, our studies provide new insights into the immune functions of Bmintegrin β3 from the silkworm, Bombyx mori.

Sexual dimorphism in the mast cell transcriptome and the pathophysiological responses to immunological and psychological stress

Background

Biological sex plays a prominent role in the prevalence and severity of a number of important stress-related gastrointestinal and immune-related diseases including IBS and allergy/anaphylaxis. Despite the establishment of sex differences in these diseases, the underlying mechanisms contributing to sex differences remain poorly understood. The objective of this study was to define the role of biological sex on mast cells (MCs), an innate immune cell central to the pathophysiology of many GI and allergic disorders.

Methods

Twelve-week-old C57BL/6 male and female mice were exposed to immunological stress (2 h of IgE-mediated passive systemic anaphylaxis (PSA)) or psychological stress (1 h of restraint stress (RS)) and temperature, clinical scores, serum histamine, and intestinal permeability (for RS) were measured. Primary bone marrow-derived MCs (BMMCs) were harvested from male and female mice and analyzed for MC degranulation, signaling pathways, mediator content, and RNA transcriptome analysis.

Results

Sexually dimorphic responses were observed in both models of PSA and RS and in primary MCs. Compared with male mice, female mice exhibited increased clinical scores, hypothermia, and serum histamine levels in response to PSA and had greater intestinal permeability and serum histamine responses to RS. Primary BMMCs from female mice exhibited increased release of β-hexosaminidase, histamine, tryptase, and TNF-α upon stimulation with IgE/DNP and A23187. Increased mediator release in female BMMCs was not associated with increased upstream phospho-tyrosine signaling pathways or downstream Ca²⁺ mobilization. Instead, increased mediator release in female MCs was associated with markedly increased capacity for synthesis and storage of MC granule-associated immune mediators as determined by MC mediator content and RNA transcriptome analysis.

Conclusions

These results provide a new understanding of sexual dimorphic responses in MCs and have direct implications for stress-related diseases associated with a female predominance and MC hyperactivity including irritable bowel syndrome, allergy, and anaphylaxis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-016-0113-7) contains supplementary material, which is available to authorized users.

Identification of Immunity-Related Genes in Dialeurodes citri against Entomopathogenic Fungus Lecanicillium attenuatum by RNA-Seq Analysis

Dialeurodes citri is a major pest in citrus producing areas, and large-scale outbreaks have occurred increasingly often in recent years. Lecanicillium attenuatum is an important entomopathogenic fungus that can parasitize and kill D. citri. We separated the fungus from corpses of D. citri larvae. However, the sound immune defense system of pests makes infection by an entomopathogenic fungus difficult. Here we used RNA sequencing technology (RNA-Seq) to build a transcriptome database for D. citri and performed digital gene expression profiling to screen genes that act in the immune defense of D. citri larvae infected with a pathogenic fungus. De novo assembly generated 84,733 unigenes with mean length of 772 nt. All unigenes were searched against GO, Nr, Swiss-Prot, COG, and KEGG databases and a total of 28,190 (33.3%) unigenes were annotated. We identified 129 immunity-related unigenes in transcriptome database that were related to pattern recognition receptors, information transduction factors and response factors. From the digital gene expression profile, we identified 441 unigenes that were differentially expressed in D. citri infected with L. attenuatum. Through calculated Log₂Ratio values, we identified genes for which fold changes in expression were obvious, including cuticle protein, vitellogenin, cathepsin, prophenoloxidase, clip-domain serine protease, lysozyme, and others. Subsequent quantitative real-time polymerase chain reaction analysis verified the results. The identified genes may serve as target genes for microbial control of D. citri.

The expression analysis of cysteine proteinase-like protein in wild-type and nm2 mutant silkworm (Lepidoptera: Bombyx mori)

The mutant of non-molting in the 2nd instar (nm2) is a recently discovered mutant of Bombyx mori. The mutant cannot molt and exuviate and died successively in premolting of 2nd instar. In this study, two dimensional gel electrophoresis (2-DE) was performed to screen the differential expression of epidermis proteins in pre-molting larvae of 2nd instar between the wild-type and nm2 mutant. Interestingly, a cysteine proteinase-like (BmCP-like) protein in nm2 was significantly higher than that of the wild-type. The transcription profiles of BmCP-like gene were investigated by quantitative real-time PCR (qRT-PCR), and the result revealed that BmCP-like mRNA was remarkably higher in nm2 than that of the wild-type. The transcription level of BmCP-like was high in the epidermis while low in the midgut and hemocytes, and fluctuate with development, while the highest in the newly molted larvae of 3rd and lowest in the pre-molting of the 1st and 2nd instar. The body of injected BmCP-like RNAi of 2nd larvae formed a dark spots around the injection place. These results suggested the BmCP-like gene play a key role in the degradation of the cuticle and epidermis layer during molting of 1st and 2nd instar silkworm. Furthermore, the ORF of BmCP-like gene in nm2 was the same to the wild-type. These studies give us a hint that BmCP-like gene maybe not the major gene responsible for nm2, but BmCP-like gene might participate in the immune systems of silkworm, and the upregulation of BmCP-like transcription in the nm2 mutant might be induced by the disadvantages that limit the growth and development of silkworm in order to survive.