Functions of a C-type lectin with a single carbohydrate-recognition domain in the innate immunity and movement of the red flour beetle, Tribolium castaneum

Characterization of temporal expression of immune genes in female locust challenged by fungal pathogen, Aspergillus sp

Introduction

The innate immune system provides defense against invading pathogens in insects and mammals.

Methods

We conducted transcriptomic analyses of the locust Locusta migratoria under Aspergillus oryzae infection to clarify temporal variation in its molecular immune response.

Results

We found that fat body cells and hemocytes play different roles in the immune response of locusts to Aspergillus infection at different time points after inoculation, and melanization was the main process underlying the immune response of female locusts. Most pattern recognition receptors (PRR) genes were up-regulated in fat body cells and down-regulated in hemocytes from 24 h to 72 h after inoculation. This means that fat body cells, but not hemocytes, would be able to precisely recognize invading pathogens. Most serine protease inhibitors (SERPINs) genes and clip domain serine proteinase (CLIP) genes were up-regulated in fat body cells. However, most SERPINs were down-regulated in hemocytes, which indicated that serine proteinases may be inhibited to activate downstream reactions involving the prophenoloxidase (PPO), peroxidase (POD), and Toll pathways. Most lysozymes, PPOs, and peroxiredoxin (PRDX) are effectors that were up-regulated in fat body cells 24 h after inoculation but down-regulated 48 h and 72 h after inoculation. Similar patterns were observed for effectors in hemocytes, which indicates that locust immune genes expression was suppressed by A. oryzae 72 h after inoculation, and might result in the weak melanization of locusts in response to Aspergillus infection.

Discussion

Our findings enhance our understanding of insect-fungi interactions, as well as have implications for the development of more effective microbial control strategies for the management of locust populations.

The dual functions of a newly identified C-type lectin (TcCTL17) in the immunity and development of Tribolium castaneum

C-type lectins (CTLs), a diverse family of pattern recognition receptors, are essential for immune recognition and pathogen clearance in invertebrates. TcCTL17 contains one carbohydrate recognition domain and three scavenger receptor Cys-rich domains. Spatial and temporal expression analysis revealed that TcCTL17 is highly expressed in early pupa, early adult stages, and the larval gut at 20 days. The recombinant TcCTL17 exhibited dose-dependent binding to lipopolysaccharides and peptidoglycans, Ca2+-dependent binding and agglutination of bacteria in vitro. Knocking down TcCTL17 before bacterial exposure reduced survival rates and increased bacterial loads in T. castaneum larvae, accompanied by decreased antimicrobial peptide expression and haemolymph phenoloxidase activity. Additionally, TcCTL17 RNA interference caused developmental abnormalities, affecting metamorphosis and fecundity, possibly by influencing the 20E, JH, and vitellogenin pathways. These findings underscore dual functions of TcCTL17 in immunity and development, making it a potential target for pest management.

A C-type lectin with dual carbohydrate recognition domains functions in innate immune response in Asian corn borer, Ostrinia furnacalis

C-type lectins (CTLs) act as pattern recognition receptors (PRRs) to initiate the innate immune response in insects. A CTL with dual carbohydrate recognition domains (CRDs) (named immulectin-4 [IML-4]) was selected from the Ostrinia furnacalis transcriptome dataset for functional studies. We cloned the full-length complementary DNA of O. furnacalis IML-4 (OfIML-4). It encodes a 328-residue protein with a Glu-Pro-Asn (EPN) and Gln-Pro-Asp (QPD) motifs in 2 CRDs, respectively. OfIML-4 messenger RNA levels increased significantly upon the bacterial and fungal infection. Recombinant OfIML-4 (rIML-4) and its individual CRDs (rCRD1 and rCRD2) exhibited the binding ability to various microorganisms including Escherichia coli, Micrococcus luteus, Pichia pastoris, and Beauveria bassiana, and the cell wall components including lipopolysaccharide from E. coli, peptidoglycan from M. luteus or Bacillus subtilis, and curdlan from Alcaligenes faecalis. The binding further induced the agglutination of E. coli, M. luteus, and B. bassiana in the presence of calcium, the phagocytosis of Staphylococcus aureus by the hemocytes, in vitro encapsulation and melanization of nickel-nitrilotriacetic acid beads, and a significant increase in phenoloxidase activity of plasma. In addition, rIML-4 significantly enhanced the phagocytosis, nodulation, and resistance of O. furnacalis to B. bassiana. Taken together, our results suggest that OfIML-4 potentially works as a PRR to recognize the invading microorganisms, and functions in the innate immune response in O. furnacalis.

C-Type Lectin S Group TcCTL4 Participates in the Immunity of Tribolium castaneum

C-type lectin S (CTL-S) plays a crucial role in pathogen recognition and the activation of immune response. In comparison, the proportion of CTL-S was relatively high in insects, but the study was much smaller than the proportion observed. In this study, we cloned and characterized one CTL-S, TcCTL4, from Tribolium castaneum. Our analysis revealed that TcCTL4 was highly expressed during the early pupal stage, with expression levels exhibiting a tendency to change with developmental stages. Additionally, tissue expression analysis showed a high expression of TcCTL4 in the central nervous system (CNS). Moreover, we observed a significant increase in TcCTL4 transcripts after bacterial challenge. The RNA interference (RNAi) of TcCTL4 before bacterial treatment resulted in a significant reduction in the transcripts of immune factors (IFs) and antimicrobial peptides (AMPs), indicating that TcCTL4 may regulate AMP expression through the activation of the immune signaling pathway. Furthermore, our investigation revealed that the recombinant protein TcCTL4 (rTcCTL4) not only recognized bacteria but also agglutinated bacteria in a Ca2+-dependent manner. Enzyme activity analysis suggested that rTcCTL4 could enhance phenoloxidase activity, implying its potential involvement in the prophenoloxidase activation pathway. In conclusion, these results indicate that TcCTL4 is involved in the immunity of T. castaneum, providing valuable insights into insect CTLs.

A novel C-type lectin protein (BjCTL5) interacts with apoptosis stimulating proteins of p53 (ASPP) to activate NF-κB signaling pathway in primitive chordate

C-type lectin proteins (CTLs), a group of pattern recognition receptors (PRRs), play pivotal roles in immune responses. However, the signal transduction and regulation of CTLs in cephalochordates have yet to be explored. In this study, we examined the composition of CTLs in Branchiostoma japonicum, identifying a total of 272 CTLs. These CTLs underwent further analysis concerning domain arrangement, tandem and segmental duplication events. A multidomain C-type lectin gene, designated as BjCTL5, encompassing CLECT, KR, CUB, MAM, and SR domains, was the focal point of our investigation. BjCTL5 exhibits ubiquitous expression across all detected tissues and is responsive to stimulation by LPS, mannose, and poly (I:C). The recombinant protein of BjCTL5 can bind to Escherichia coli and Staphylococcus aureus, inducing their agglutination and inhibiting the proliferation of S. aureus. Yeast two-hybrid, CoIP, and confocal immunofluorescence experiments revealed the interaction between BjCTL5 and apoptosis-stimulating proteins of p53, BjASPP. Intriguingly, BjCTL5 was observed to induce the luciferase activity of the NF-κB promoter in HEK293T cells. These results suggested a potential interaction between BjCTL5 and BjASPP, implicating that they involve in the activation of the NF-κB signaling pathway, which provides an evolutionary viewpoint on NF-κB signaling pathway in primitive chordate.

The combined analysis of transcriptomics and metabolomics reveals the mechanisms by which dietary quercetin regulates growth and immunity in Penaeus vannamei

As a potent antioxidant, the flavonoid compound quercetin (QUE) has been widely used in the farming of aquatic animals. However, there are fewer reports of the beneficial effects, especially in improving immunity of Penaeus vannamei by QUE. The aim of this study was to investigate the effects of dietary QUE on growth, apoptosis, antioxidant and immunity of P. vannamei. It also explored the potential mechanisms of QUE in improving the growth and immunity of P. vannamei. P. vannamei were fed diets with QUE for 60 days. The results revealed that QUE (0.5 or 1.0 g/kg) ameliorated the growth, and the expressions of genes related to apoptosis, antioxidant, and immunity. The differentially expressed genes (DEGs) and differential metabolites (DMs) obtained through transcriptomics and metabolomics, respectively, enriched in pathways related to nutritional metabolism such as lipid metabolism, amino acid metabolism, and carbohydrate metabolism. After QUE addition, especially at 0.5 g/kg, DEGs were enriched into the functions of response to stimulus and antioxidant activity, and the pathways of HIF-1 signaling pathway, C-type lectin receptor signaling pathway, Toll-like receptor signaling pathway, and FoxO signaling pathway. In conclusion, dietary QUE can ameliorate growth, apoptosis, antioxidant and immunity of P. vannamei, the appropriate addition amount was 0.5 g/kg rather than 1.0 g/kg. Regulations of QUE on nutrient metabolism and immune-related pathways, and bioactive metabolites, were important factors for improving the aforementioned abilities in P. vannamei.

A pattern recognition receptor C-type lectin TcCTL14 contributes to immune response and development in the red flour beetle, Tribolium castaneum

Evidence is accumulating that pattern recognition receptor (PRR) C-type lectins (CTL) play essential roles in recognition of pathogens. TcCTL14 (accession no. TC00871) contains the most domains among all CTL of Tribolium castaneum. Yet the biological function of TcCTL14 remains unclear. In this study, TcCTL14 exhibiting typical motif and domain of CTL was cloned from T. castaneum. The expression pattern analysis showed that TcCTL14 was highly expressed in late pupae and central nervous system, and was upregulated after treatment with Escherichia coli and Staphylococcus aureus, respectively. Analysis of binding affinity revealed that recombinant TcCTL14 not only could bind to lipopolysaccharide and peptidoglycan in a dose-dependent fashion, but possibly could bind to and agglutinate different bacteria in a Ca2+ -dependent fashion. Knockdown of TcCTL14 before injection with bacteria led to the downregulation of nuclear factor-κB transcription factors of Toll/IMD and 4 antimicrobial peptides. Knockdown of TcCTL14 also caused suppressed metamorphosis, reduced fecundity, and delayed embryogenesis of T. castaneum. Further observation discovered that knockdown of TcCTL14 inhibited the development of ovaries and embryos. The detection of signaling pathways revealed that TcCTL14 may be involved in metamorphosis and fecundity by impacting 20-hydroxyecdysone and vitellogenin, respectively. Overall, these results indicate that TcCTL14 may contribute to immune response by agglutination or regulating the expression of antimicrobial peptides by the Toll/IMD pathway, and is required for T. castaneum development including metamorphosis, fecundity, and embryogenesis. These findings will improve the functional cognition of PRR CTL in insects and provide the new strategy for pest control.

Functional Analysis of a CTL-X-Type Lectin CTL16 in Development and Innate Immunity of Tribolium castaneum

C-type lectins (CTLs) are a class of proteins containing carbohydrate recognition domains (CRDs), which are characteristic modules that recognize various glycoconjugates and function primarily in immunity. CTLs have been reported to affect growth and development and positively regulate innate immunity in Tribolium castaneum. However, the regulatory mechanisms of TcCTL16 proteins are still unclear. Here, spatiotemporal analyses displayed that TcCTL16 was highly expressed in late pupae and early adults. TcCTL16 RNA interference in early larvae shortened their body length and narrowed their body width, leading to the death of 98% of the larvae in the pupal stage. Further analysis found that the expression level of muscle-regulation-related genes, including cut, vestigial, erect wing, apterous, and spalt major, and muscle-composition-related genes, including Myosin heavy chain and Myosin light chain, were obviously down-regulated after TcCTL16 silencing in T. castaneum. In addition, the transcription of TcCTL16 was mainly distributed in the hemolymph. TcCTL16 was significantly upregulated after challenges with lipopolysaccharides, peptidoglycans, Escherichia coli, and Staphylococcus aureus. Recombinant CRDs of TcCTL16 bind directly to the tested bacteria (except Bacillus subtilis); they also induce extensive bacterial agglutination in the presence of Ca²⁺. On the contrary, after TcCTL16 silencing in the late larval stage, T. castaneum were able to develop normally. Moreover, the transcript levels of seven antimicrobial peptide genes (attacin2, defensins1, defensins2, coleoptericin1, coleoptericin2, cecropins2, and cecropins3) and one transcription factor gene (relish) were significantly increased under E. coli challenge and led to an increased survival rate of T. castaneum when infected with S. aureus or E. coli, suggesting that TcCTL16 deficiency could be compensated for by increasing AMP expression via the IMD pathways in T. castaneum. In conclusion, this study found that TcCTL16 could be involved in developmental regulation in early larvae and compensate for the loss of CTL function by regulating the expression of AMPs in late larvae, thus laying a solid foundation for further studies on T. castaneum CTLs.

Functional Analysis of a Multiple-Domain CTL15 in the Innate Immunity, Eclosion, and Reproduction of Tribolium castaneum

C-type lectin X (CTL-X) plays critical roles in immune defense, cell adhesion, and developmental regulation. Here, a transmembrane CTL-X of Tribolium castaneum, TcCTL15, with multiple domains was characterized. It was highly expressed in the early and late pupae and early adults and was distributed in all examined tissues. In addition, its expression levels were significantly induced after being challenged with pathogen-associated molecular patterns (PAMPs) and bacteria. In vitro, the recombinant TcCTL15 could recognize bacteria through binding PAMPs and exhibit agglutinating activity against a narrow range of bacteria in the presence of Ca²⁺. RNAi-mediated TcCTL15-knockdown-larvae infected with Escherichia coli and Staphylococcus aureus showed less survival, had activated immune signaling pathways, and induced the expression of antimicrobial peptide genes. Moreover, silencing TcCTL15 caused eclosion defects by impairing ecdysone and crustacean cardioactive peptide receptors (CCAPRs). Suppression of TcCTL15 in female adults led to defects in ovary development and fecundity, accompanied by concomitant reductions in the mRNA levels of vitellogenin (TcVg) and farnesol dehydrogenase (TcFDH). These findings imply that TcCTL15 has extensive functions in developmental regulation and antibacterial immunity. Uncovering the function of TcCTL15 will enrich the understanding of CTL-X in invertebrates. Its multiple biological functions endow the potential to be an attractive target for pest control.

A C-type lectin TcCTL1 is required for embryogenesis in Tribolium castaneum

C-type lectin S group (CTL-S) plays a variety of roles in invertebrate including pathogen recognition and activation of immune responses. Previous studies have shown that CTL-S subfamily of Tribolium castaneum is mainly divided into two clades, of which only TcCTL1 was separately located in one clade. However, it remains unclear whether TcCTL1 occurs the differentiation of function. Therefore, the CTL-S TcCTL1 gene was cloned and characterized from T. castaneum. Functional analysis revealed that TcCTL1 could recognize and agglutinate pathogens, as well as activate immune signaling pathways to participate in immune response, which was consistent with our previously reported for TcCTL5 and TcCTL6. Differently, RNAi of TcCTL1 discovered that the egg produced by dsTcCTL1-treated adult could not hatch into larvae. Further DAPI-straining embryo indicated that the process of embryogenesis in dsTcCTL1-treated beetle was defeated, implying that TcCTL1 is required for embryogenesis in T. castaneum except for immune response. These results will aid implications for the understanding of CTL-S in invertebrate.

RNAi-mediated silencing of an egg-specific gene Nllet1 results in hatch failure in the brown planthopper

BACKGROUND

The brown planthopper (BPH) is one of the most destructive agricultural pests in Asia. RNA interference (RNAi)-mediated pest management has been under development for years, and the selection of appropriate target genes is important for pest-targeted RNAi. C-type lectins (CTLs) are a class of genes that perform a variety of functions, such as the regulation of growth and development.

RESULTS

A CTL-S protein named Nllet1, containing a single calcium ion (Ca²⁺ )-dependent carbohydrate-binding domain (CRD) with a conserved triplet motif QPD was identified and functionally characterized in BPH. Expression profiles at both the transcriptional and translational levels show that Nllet1 accumulates during the serosal cuticle (SC) formation period. Immunofluorescence and immunogold labeling further demonstrated that Nllet1 is located in the serosal endocuticle (en-SC). Maternal RNAi-mediated silencing of Nllet1 disrupted the SC structure, accompanied by a loss of the outward barrier and 100% embryo mortality. Injection of 10 ng dsNllet1 or dsNllet1' per female adult BPH resulted in a total failure of egg hatching.

CONCLUSION

Nllet1 is essential for SC formation and embryonic development in BPH, which helps us understand the important roles of CTL-Ss. Additionally, BPH eggs show high sensitivity to the depletion of Nllet1. This study indicates that Nllet1 is a promising candidate gene that can be used to develop RNAi-based control strategies at the BPH egg stage, and it can also be used as a target for developing novel ovicides. © 2022 Society of Chemical Industry.

A Novel Ig Domain-Containing C-Type Lectin Triggers the Intestine-Hemocyte Axis to Regulate Antibacterial Immunity in Crab

The C-type lectin family with the signature C-type lectin-like domain promotes antibacterial host defense within the animal kingdom. We examined the role of Chinese mitten crab, Eriocheir sinensis (H. Milne-Edwards) (Decapoda: Grapsidae) Ig domain-containing C-type lectin (EsIgLectin), a novel and poorly understood member of the C-type lectin family. EsIgLectin was expressed primarily by both hemocytes (E sinensis) and intestines, with significantly induced mRNA expression on intestinal or hemolymph bacterial infections. As a soluble protein, both its C-type lectin-like domain and the Ig domain were required for bacterial binding, bacterial agglutination, bacterial growth inhibition, and in vivo bacterial clearance. Polymeric EsIgLectin could be constructed via the disulfide bond in the Ig domain, significantly enhancing EsIgLectin antibacterial activity. EsIgLectin promoted bacterial phagocytosis in an Ig domain-dependent manner in hemocytes, while it controlled microbial homeostasis and protected against bacteria-induced inflammation in the intestine. Protein interaction studies revealed that the EsIgLectin Ig domain bound to the first Ig domain of the polymeric Ig receptor, which was essential for EsIgLectin-induced bacterial phagocytosis. The temporal sequence of cell interactions during intestinal inflammation is only beginning to be understood. In this article, we show that hemocyte-derived EsIgLectin entered the intestinal wall at the later phase of intestinal inflammation. Moreover, EsIgLectin protected the host against intestinal and hemolymph infections in a polymeric Ig receptor-dependent manner. Therefore, the EsIgLectin promoted bacterial clearance and protected against inflammatory disease through an independent or synergistic effect of hemocytes and intestines in invertebrates.

Role of Lectin in the Response of Aedes aegypti Against Bt Toxin

Aedes aegypti is one of the world’s most dangerous mosquitoes, and a vector of diseases such as dengue fever, chikungunya virus, yellow fever, and Zika virus disease. Currently, a major global challenge is the scarcity of antiviral medicine and vaccine for arboviruses. Bacillus thuringiensis var israelensis (Bti) toxins are used as biological mosquito control agents. Endotoxins, including Cry4Aa, Cry4Ba, Cry10Aa, Cry11Aa, and Cyt1Aa, are toxic to mosquitoes. Insect eradication by Cry toxin relies primarily on the interaction of cry toxins with key toxin receptors, such as aminopeptidase (APN), alkaline phosphatase (ALP), cadherin (CAD), and ATP-binding cassette transporters. The carbohydrate recognition domains (CRDs) of lectins and domains II and III of Cry toxins share similar structural folds, suggesting that midgut proteins, such as C-type lectins (CTLs), may interfere with interactions among Cry toxins and receptors by binding to both and alter Cry toxicity. In the present review, we summarize the functional role of C-type lectins in Ae. aegypti mosquitoes and the mechanism underlying the alteration of Cry toxin activity by CTLs. Furthermore, we outline future research directions on elucidating the Bti resistance mechanism. This study provides a basis for understanding Bti resistance, which can be used to develop novel insecticides.

Functional analysis of TcCTL12 in innate immunity and development in Tribolium castaneum

C-type lectins (CTLs) play vital roles in invertebrates' innate immunity. Six CTL-X type lectins are identified in Tribolium castaneum. However, their functions and regulating mechanisms remain elusive. Here, TcCTL12, one CTL-X, was identified and cloned from T. castaneum. Spatiotemporal expression profiling revealed that TcCTL12 highly expressed in late pupa and early adult of T. castaneum in comparison with other developmental stages, and exhibited the highest expression level in the haemolymph and central nervous system (CNS). Then, the expression of TcCTL12 was remarkably induced by the stimulation of Escherichia coli and Staphylococcus aureus. Moreover, the recombinant protein TcCTL12 could bind pathogen-associated molecular patterns (PAMPs) including LPS and PGN, and displayed agglutinative activity to both Gram-positive and Gram-negative bacteria in a calcium-dependent manner in vitro. Furthermore, RNAi of TcCTL12 caused T. castaneum pupation and eclosion defected. The abnormal pupa thinned their epidermal, and appeared the abnormal development of muscle cell compared with the control group. Additionally, depletion of TcCTL12 resulted in reducing fertility of offspring and affected their fecundity. In sum, these results indicated that TcCTL12 had extensive functions in the regulation of development in T. castaneum, in addition to the immune response. It further expanded insights into CTL functions in insects.

A New C-Type Lectin Homolog SpCTL6 Exerting Immunoprotective Effect and Regulatory Role in Mud Crab Scylla paramamosain

C-type lectin (CTL), a well-known immune-related molecule, has received more and more attention due to its diverse functions, especially its important role in development and host defense of vertebrate and invertebrate. Since the research on crab CTLs is still lack, we screened a new CTL homolog, named SpCTL6 from mud crab Scylla paramamosain. The full-length cDNA sequence of SpCTL6 was 738 bp with a 486 bp of ORF, and the deduced amino acids were 161 aa. SpCTL6 was predicted to have a 17 aa signal peptide and its mature peptide was 144 aa (MW 16.7 kDa) with pI value of 5.22. It had typical CTL structural characteristics, such as a single C-type lectin-like domain, 4 conserved cysteines, similar tertiary structure to that of vertebrate CTLs and a mutated Ca²⁺ binding motif Gln-Pro-Thr (QPT), clustering into the same branch as the crustacean CTLs. SpCTL6 was highly expressed in the entire zoeal larval stages and widely distributed in adult crab tissues with the highest transcription level in testis. During the molting process of juvenile crabs, the expression level of SpCTL6 was remarkably increased after molting. SpCTL6 could be significantly upregulated in two larval stages (Z1 and megalopa) and adult crab testis under immune challenges. Recombinant SpCTL6 (rSpCTL6) was successfully obtained from eukaryotic expression system. rSpCTL6 exhibited binding activity with PAMPs (LPS, lipoteichoic acid, peptidoglycan, and glucan) and had a broad spectrum bacterial agglutination activity in a Ca²⁺-dependent manner. In addition, rSpCTL6 could enhance the encapsulation activity of hemocytes and has no cytotoxic effect on hemocytes. Although rSpCTL6 had no bactericidal activity on Vibrio alginolyticus, rSpCTL6 treatment could significantly reduce the bacterial endotoxin level in vitro and greatly improved the survival of S. paramamosain under V. alginolyticus infection in vivo. The immunoprotective effect of rSpCTL6 might be due to the regulatory role of rSpCTL6 in immune-related genes and immunological parameters. Our study provides new information for understanding the immune defense of mud crabs and would facilitate the development of effective strategies for mud crab aquaculture disease control.