Leureptin: a soluble, extracellular leucine-rich repeat protein from Manduca sexta that binds lipopolysaccharide

Expression characteristics and inhibitory activity of a leucine-rich repeat (LRR)-only protein in the Chinese mitten crab, Eriocheir sinensis

The leucine-rich repeat (LRR) domain is a crucial structure in a variety of immune related proteins and displays multiple immune functions. In this study, the open reading frame (ORF) of an LRR-only protein was cloned from the Chinese mitten crab, Eriocheir sinensis (EsLRRop1). The protein sequence of EsLRRop1 contained seven LRR motifs, three LRR-TYP motifs and an LRRCT motif. Tissue distribution exhibited that EsLRRop1 mainly expressed in nervous tissues including thoracic ganglion, eyestalk and brain while showed relatively lower transcriptional level in hemocyte. Based on the above expression characteristics, the responses of EsLRRop1 to the challenge of Vibrio parahaemolyticus and Staphylococcus aureus were tested. The result showed that the transcript of EsLRRop1 in thoracic ganglion and eyestalk up-regulated after being challenged with S. aureus, while it decreased post injection with V. parahaemolyticus. The transcript of EsLRRop1 in hemocytes up-regulated sharply at 3 h and decreased at 12 h and 24 h after being challenged with V. parahaemolyticus, while it decreased at 12 h and 24 h post injection with S. aureus. The recombinant protein of EsLRRop1 (His-EsLRRop1) displayed binding activities to V. alginolyticus, V. harveyi, V. parahaemolyticus, S. aureus, Corynebacterium glutamicum and Micrococcus lysodeikticus as well as lipopolysaccharide (LPS) and peptidoglycan (PGN). Moreover, the His-EsLRRop1 exhibited inhibitory activity against V. parahaemolyticus and V. harveyi with minimum inhibitory concentration (MIC) of 3.57-7.14 μM and 7.14-14.28 μM, respectively. These results provide theoretical basis for the application of EsLRRop1 in inhibiting bacteria in aquaculture practice.

The Anopheles leucine-rich repeat protein APL1C is a pathogen binding factor recognizing Plasmodium ookinetes and sporozoites

Leucine-rich repeat (LRR) proteins are commonly involved in innate immunity of animals and plants, including for pattern recognition of pathogen-derived elicitors. The Anopheles secreted LRR proteins APL1C and LRIM1 are required for malaria ookinete killing in conjunction with the complement-like TEP1 protein. However, the mechanism of parasite immune recognition by the mosquito remains unclear, although it is known that TEP1 lacks inherent binding specificity. Here, we find that APL1C and LRIM1 bind specifically to Plasmodium berghei ookinetes, even after depletion of TEP1 transcript and protein, consistent with a role for the LRR proteins in pathogen recognition. Moreover, APL1C does not bind to ookinetes of the human malaria parasite Plasmodium falciparum, and is not required for killing of this parasite, which correlates LRR binding specificity and immune protection. Most of the live P. berghei ookinetes that migrated into the extracellular space exposed to mosquito hemolymph, and almost all dead ookinetes, are bound by APL1C, thus associating LRR protein binding with parasite killing. We also find that APL1C binds to the surface of P. berghei sporozoites released from oocysts into the mosquito hemocoel and forms a potent barrier limiting salivary gland invasion and mosquito infectivity. Pathogen binding by APL1C provides the first functional explanation for the long-known requirement of APL1C for P. berghei ookinete killing in the mosquito midgut. We propose that secreted mosquito LRR proteins are required for pathogen discrimination and orientation of immune effector activity, potentially as functional counterparts of the immunoglobulin-based receptors used by vertebrates for antigen recognition.

LvCD14L Acts as a Novel Pattern Recognition Receptor and a Regulator of the Toll Signaling Pathway in Shrimp

Leucine-rich repeat (LRR) is a structural motif has important recognition function in immune receptors, such as Tolls and NOD-like receptors (NLRs). The immune-related LRR proteins can be divided into two categories, LRR-containing proteins and LRR-only proteins. The latter contain LRR motifs while they are without other functional domains. However, the functional mechanisms of the LRR-only proteins were still unclear in invertebrates. Here, we identified a gene encoding a secretory LRR-only protein, which possessed similarity with vertebrate CD14 and was designated as LvCD14L, from the Pacific whiteleg shrimp Litopenaeus vannamei. Its transcripts in shrimp hemocytes were apparently responsive to the infection of Vibrio parahaemolyticus. Knockdown of LvCD14L with dsRNA resulted in significant increase of the viable bacteria in the hepatopancreas of shrimp upon V. parahaemolyticus infection. Further functional studies revealed that LvCD14L could bind to microorganisms' PAMPs, showed interaction with LvToll1 and LvToll2, and regulated the expression of LvDorsal and LvALF2 in hemocytes. These results suggest that LvCD14L functions as a pattern recognition receptor and activates the NF-κB pathway through interaction with LvTolls. The present study reveals a shrimp LvCD14L-Tolls-NF-κB signaling pathway like the CD14/TLR4/NF-κB signaling pathway in mammalians, which enriches the functional mechanism of secretory LRR-only immune receptors during pathogens infection in invertebrates.

An LRR domain-containing membrane protein gene in rotifer Brachionus plicatilis: Sequence feature, expression pattern, and ligands binding activity

Leucine-rich repeat (LRR) domains mediate multiple innate immune responses via protein-ligand and protein-protein interactions, but their exact roles in invertebrates are poorly understood. Herein, an LRR domain-containing transmembrane protein (BpLRRm) was identified in the rotifer Brachionus plicatilis. The 1069 bp BpLRRm nucleotide sequence contains a 942 bp open reading frame (ORF) encoding a 313 amino acid polypeptide with four LRR motifs harbouring the LXXLXXLXLXXNXLXXL motif, and a transmembrane domain. Treatment with 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) decreased BpLRRm mRNA levels at 3 h, but they increased thereafter and peaked at 12 h. Lipopolysaccharide (LPS) treatment first increased BpLRRm mRNA levels at 3 h, but levels returned to normal at 12 h, then increased and peaked at 24 h. Recombinant BpLRRm protein bound pathogen-related molecular patterns (PAMPs), including LPS, peptidoglycan (PGN), glucan (GLU) and polyinosinic-polycytidylic acid (poly IC), in a dose-dependent manner. Thus, BpLRRm might function as a pattern recognition receptor (PRR) in the innate immunity of B. plicatilis, and mediate responses to environmental pollution.

Molecular characterization of an LRR-only protein gene in Pacific white shrimp Litopenaeus vannamei: Sequence feature, expression pattern, and protein activity

Leucine-rich repeat (LRR)-only proteins have been proved to be involved in the innate immune responses as they could mediate protein-protein or protein-ligand interactions. In the present study, a novel LRR-only protein (LvLRRop-1) was identified and characterized from Pacific white shrimp Litopenaeus vannamei. The complete cDNA sequence of LvLRRop-1 contains an open reading frame (ORF) of 1488 bp, which encoded a polypeptide of 495 amino acids with a predicted molecular mass of 55.67 kDa and a calculated theoretical isoelectric point of 6.435. There are five LRR motifs, six LRR_TYP motifs in the protein sequence of LvLRRop-1 with consensus signature sequences of LxxLxxLxLxxNxL. The LvLRRop-1 mRNA transcripts could be detected in all the tested tissues, including eyestalk, gill, gonad, heart, hemocytes, hepatopancreas, intestine, muscle, nerve and stomach, especially highest in hemocytes and hepatopancreas. The mRNA transcripts of LvLRRop-1 increased within the first 6 h in hemocytes and hepatopancreas after Vibrio parahaemolyticus or white spot syndrome virus (WSSV) challenges. The recombinant LvLRRop-1 could bind four typical pathogen-associated molecular patterns (PAMPs), including lipopolysaccharide (LPS), peptidoglycan (PGN), glucan (GLU) and polycytidine-polycytidylic acid (poly IC), in a dose-dependent manner, and inhibit the growth of bacteria Micrococcus luteus. These data indicated that LvLRRop-1 could play a pivotal role in the innate immune response of shrimps as a kind of pattern recognition receptor (PRR).

Comparative transcriptome analysis of the newly discovered insect vector of the pine wood nematode in China, revealing putative genes related to host plant adaptation

BACKGROUND

In many insect species, the larvae/nymphs are unable to disperse far from the oviposition site selected by adults. The Sakhalin pine sawyer Monochamus saltuarius (Gebler) is the newly discovered insect vector of the pine wood nematode (Bursaphelenchus xylophilus) in China. Adult M. saltuarius prefers to oviposit on the host plant Pinus koraiensis, rather than P. tabuliformis. However, the genetic basis of adaptation of the larvae of M. saltuarius with weaken dispersal ability to host environments selected by the adult is not well understood.

RESULTS

In this study, the free amino and fatty acid composition and content of the host plants of M. saltuarius larvae, i.e., P. koraiensis and P. tabuliformis were investigated. Compared with P. koraiensis, P. tabuliformis had a substantially higher content of various free amino acids, while the opposite trend was detected for fatty acid content. The transcriptional profiles of larval populations feeding on P. koraiensis and P. tabuliformis were compared using PacBio Sequel II sequencing combined with Illumina sequencing. The results showed that genes relating to digestion, fatty acid synthesis, detoxification, oxidation-reduction, and stress response, as well as nutrients and energy sensing ability, were differentially expressed, possibly reflecting adaptive changes of M. saltuarius in response to different host diets. Additionally, genes coding for cuticle structure were differentially expressed, indicating that cuticle may be a potential target for plant defense. Differential regulation of genes related to the antibacterial and immune response were also observed, suggesting that larvae of M. saltuarius may have evolved adaptations to cope with bacterial challenges in their host environments.

CONCLUSIONS

The present study provides comprehensive transcriptome resource of M. saltuarius relating to host plant adaptation. Results from this study help to illustrate the fundamental relationship between transcriptional plasticity and adaptation mechanisms of insect herbivores to host plants.

Comparative response of Spodoptera litura challenged per os with Serratia marcescens strains differing in virulence

Host plays an important role in influencing virulence of a pathogen and efficacy of a biopesticide. The present study was aimed to characterize the possible factors present in Spodoptera litura that influenced pathogenecity of orally ingested S. marcescens strains, differing in their virulence. Fifth instar larvae of S. litura responded differently as challenged by two Serratia marcescens strains, SEN (virulent strain, LC₅₀ 7.02 10³ cfu/ml) and ICC-4 (non-virulent strain, LC₅₀ 1.19 10¹² cfu/ml). Considerable increase in activity of lytic enzymes protease and phospholipase was recorded in the gut and hemolymph of larvae fed on diet supplemented with S. marcescens strain ICC-4 as compared to the larvae treated with S. marcescens strain SEN. However, a significant up-regulation of antioxidative enzymes SOD (in foregut and midgut), CAT (in the midgut) and GST (in the foregut and hemolymph) was recorded in larvae fed on diet treated with the virulent S. marcescens strain SEN in comparison to larvae fed on diet treated with the non-virulent S. marcescens strain ICC-4. Activity of defense related enzymes lysozyme and phenoloxidase activity were also higher in the hemolymph of larvae fed with diet treated with S. marcescens strain SEN as compared to hemolymph of S. marcescens strain ICC-4 treated larvae. More number of over-expressed proteins was observed in the gut and hemolymph of S. marcescens strains ICC-4 and SEN treated larvae, respectively. Identification of the selected differentially expressed proteins indicated induction of proteins involved in insect innate immune response (Immunoglobulin I-set domain, Apolipophorin III, leucine rich repeat and Titin) in S. marcescens strain SEN treated larvae. Over-expression of two proteins, actin related protein and mt DNA helicase, were noted in S. marcescens treated larvae with very high levels observed in the non-virulent strain. Up-regulation of homeobox protein was noted only in S. marcescens strain ICC-4 challenged larvae. This study indicated that ingestion of non-virulent S. marcescens strain ICC-4 induced strong immune response in insect gut while there was weak response to the virulent S. marcescens strain SEN which probably resulted in difference in their virulence.

Identification and functional study of an LRR domain containing membrane protein in Litopenaeus vannamei

Leucine-rich repeat (LRR) is a vital structure in some pattern recognition receptors such as TLRs, NLRs and newly reported LRR-containing proteins. Apart from some limited reported LRR-containing proteins, most of LRR proteins, especially immune-related proteins, remain uncharacterized functionally. In the present study, a transmembrane protein containing several LRR motifs, designated as LvLRRm, was identified from the shrimp Litopenaeus vannamei. LvLRRm contained a long signal peptide, one LRRNT region, 12 LRR motifs, one LRRCT region and a transmembrane region. The transcripts of LvLRRm were widely distributed in all tested tissues of shrimp and they were responsive to Vibrio parahaemolyticus infection in several immune-related tissues including Oka, intestine, gill and hemocytes. Knockdown of LvLRRm by dsRNA interference led to a decreased survival rate of shrimp infected by Vibrio parahaemolyticus and an increased in vivo Vibrio propagation. Meanwhile, knockdown of LvLRRm also down-regulated the expression levels of genes involved in antibacterial immune signaling pathways, including the transcription factors LvDorsal and LvRelish, and several antimicrobial peptides. These data suggested that LvLRRm played important roles in shrimp against Vibrio infection, which was probably functioning through activation of antibacterial immune signaling pathways. The present study provided new evidence to elucidate the immune function of LRR-containing proteins in invertebrates.

Novel Characteristics of Immune Responsive Protein IRP30 in the Bumble Bee Bombus lantschouensis (Hymenoptera: Apidae)

Immune responsive protein 30 (IRP30) is a Hymenoptera-specific protein first identified from honey bee hemolymph in response to bacterial infection. However, its function remains elusive. Here, we cloned the full-length IRP30 gene and clarified its expression pattern in the bumble bee Bombus lantschouensis (Vogt). The full-length IRP30 gene measures 1443 bp and contains two exons and one intron. The length of the cDNA is 1082 bp, including a 36-bp 5'-UTR and a 218-bp 3'-UTR, and it encodes a putative protein of 275 amino acids. As expected, the sequence of the B. lantschouensis IRP30 protein was clustered with the bumble bee group, which appeared as a single clade next to honey bees. The family shared similar conserved protein domains. Moreover, bumble bee IRP30 belongs to a recently diverged clade that has four leucine-rich repeat (LRR) conserved domains. IRP30 is highly expressed in the worker caste, during pupal developmental stages, and in the head and thorax tissues. Interestingly, its expression increases 20- to 90-fold when female bumble bees (B. lantschouensis) and honey bees (Apis mellifera L.) begin laying eggs. Overall, based on the expression of IRP30 during development and egg laying in female bumble bees, this protein not only responds to immune challenge but also may play an important role in metamorphosis and reproduction.

A novel LRR-only protein mediates bacterial proliferation in hemolymph through regulating expression of antimicrobial peptides in mollusk Chlamys farreri

Leucine-rich repeat (LRR)-only proteins are involved in innate immune responses through mediating protein-ligand or protein-protein interactions, yet the exact roles of most LRR-only proteins in invertebrates are not well documented. In the present study, a novel LRR-only protein (designated CfLRRop-7) was identified in Zhikong scallop Chlamys farreri. The full-length cDNA sequence of CfLRRop-7 was 1463 bp and contained an open reading frame of 1086 bp, which encoded a protein of 361 amino acids. Five LRR motifs with a conserved signature sequence LxxLxLxxNxL were identified in the predicted protein sequence. The expression of CfLRRop-7 was particularly high in hemocytes. The expression of CfLRRop-7 was relatively high in oocytes and embryos during the ontogenesis of scallops. CfLRRop-7 expression changed in hemocytes in response to stimulation with different microbes, including Vibrio splendidus, Staphylococcus aureus and Pichia pastoris. CfLRRop-7 recognized five kinds of ligands/agonists. CfLRRop-7 recombinant protein inhibited bacterial proliferation in hemolymph and induced lysozyme activity in serum. After knocking down CfLRRop-7, the mRNA expression of selected antimicrobial peptides was reduced. All these results indicated that CfLRRop-7 might be a potential pattern recognition receptor that recognizes various pathogen associated molecular patterns, and regulates antibacterial immunity in scallops.

Identification and Characterization of C-type Lectins in Ostrinia furnacalis (Lepidoptera: Pyralidae)

C-type lectins (CTLs) are a large family of calcium-dependent carbohydrate-binding proteins. They function primarily in cell adhesion and immunity by recognizing various glycoconjugates. We identified 14 transcripts encoding proteins with one or two CTL domains from the transcriptome from Asian corn borer, Ostrinia furnacalis (Guenée; Lepidoptera: Pyralidae). Among them, five (OfCTL-S1 through S5) only contain one CTL domain, the remaining nine (OfIML-1 through 9) have two tandem CTL domains. Five CTL-Ss and six OfIMLs have a signal peptide are likely extracellular while another two OfIMLs might be cytoplasmic. Phylogenetic analysis indicated that OfCTL-Ss had 1:1 orthologs in Lepidoptera, Diptera, Coleoptera and Hymenoptera species, but OfIMLs only clustered with immulectins (IMLs) from Lepidopteran. Structural modeling revealed that the 22 CTL domains adopt a similar double-loop fold consisting of β-sheets and α-helices. The key residues for calcium-dependent or independent binding of specific carbohydrates by CTL domains were predicted with homology modeling. Expression profiles assay showed distinct expression pattern of 14 CTLs: the expression and induction were related to the developmental stages and infected microorganisms. Overall, our work including the gene identification, sequence alignment, phylogenetic analysis, structural modeling, and expression profile assay would provide a valuable basis for the further functional studies of O. furnacalis CTLs.

The versatile functions of LRR-only proteins in mollusk Chlamys farreri

Leucine-rich repeat (LRR)-only proteins are involved in the innate immune responses as they mediate protein-ligand interactions. In the present study, three novel LRR-only proteins, CfLRRop-4, CfLRRop-5 and CfLRRop-6, were identified and characterized from Zhikong scallop Chlamys farreri. They all contained LRR motifs with consensus signature sequences of LxxLxLxxNxL or LxxLxLxxCxxL. All the mRNA transcripts of three CfLRRops were high abundant in hepatopancreas, gills and gonads, and their mRNA transcripts in hemocytes could respond to the stimulations of different microbes, including Vibrio anguillarum, Micrococcus luteus and Pichia pastoris. These three CfLRRops exhibited similar ligand binding and recognition characteristics as Toll-like receptors (TLRs) and NOD-like receptors (NLRs). The immune effectors, including tumor necrosis factor α, superoxide dismutase, catalase and lysozyme, varied significantly after the scallops were stimulated by recombinant LRR-only proteins. All these results indicated that LRR-only proteins are functionally differentiated and exhibit different immunomodulation activities on various downstream immune effectors.

Novel Pattern Recognition Receptor Protects Shrimp by Preventing Bacterial Colonization and Promoting Phagocytosis

The recognition of pathogen-associated molecular patterns is accomplished by the recognition modules of pattern recognition receptors (PRRs). Leucine-rich repeats (LRRs) and C-type lectin-like domain (CTLD) represent the two most universal categories of recognition modules. In the current study, we identified a novel soluble and bacteria-inducible PRR comprising LRRs and a CTLD from the hepatopancreas of kuruma shrimp Marsupenaeus japonicus and named it Leulectin. The module arrangement of Leulectin is unique among all organisms. Both modules, together with the whole molecule, protected shrimp against Vibrio infection. By screening the pathogen-associated molecular patterns that shrimp might encounter, Leulectin was found to sense Vibrio flagellin through the LRRs and to recognize LPS through CTLD. The LRR-flagellin interaction was confirmed by pull-down and far-Western assays and was found to rely on the fourth LRR of Leulectin and the N terminus of flagellin. The recognition of LPS was determined by the long loop region of CTLD in a calcium-independent manner. By sensing the flagellin, LRRs could prevent its attachment to shrimp cells, thereby inhibiting Vibrio colonization. With the ability to recognize LPS, CTLD could agglutinate the bacteria and promote hemocytic phagocytosis. Our study clearly showed the division of labor and the synergy between different recognition modules and provided new insights into the concept of pattern recognition and the function of soluble PRRs in the antibacterial response.

Leucine-rich repeats containing protein functions in the antibacterial immune reaction in stomach of kuruma shrimp Marsupenaeus japonicus

Leucine rich repeat (LRR) motif exists in many immune receptors of animals and plants. Most LRR containing (LRRC) proteins are involved in protein-ligand and protein-protein interaction, but the exact functions of most LRRC proteins were not well-studied. In this study, an LRRC protein was identified from kuruma shrimp Marsupenaeus japonicus, and named as MjLRRC1. MjLRRC1 was consistently expressed in different tissues of normal shrimp with higher expression in gills and stomach. At the transcriptional level, there were no significant changes of MjLRRC1 after injection of Vibrio anguillarum or Staphylococcus aureus in gills and hepatopancreas. While in V. anguillarum oral infection, MjLRRC1 was upregulated in stomach but not in intestine. The recombinant MjLRRC1 protein could bind to Gram-positive and Gram-negative bacteria, bacterial cell wall components including peptidoglycan, lipoteichoic acid, and lipopolysaccharide. MjLRRC1 regulated the expression of some antimicrobial peptide (AMP) genes and participated in bacteria clearance of stomach. All these results suggested that MjLRRC1 might play important roles in antibacterial immune response of kuruma shrimp.

Annotation of the Asian Citrus Psyllid Genome Reveals a Reduced Innate Immune System

Citrus production worldwide is currently facing significant losses due to citrus greening disease, also known as Huanglongbing. The citrus greening bacteria, Candidatus Liberibacter asiaticus (CLas), is a persistent propagative pathogen transmitted by the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). Hemipterans characterized to date lack a number of insect immune genes, including those associated with the Imd pathway targeting Gram-negative bacteria. The D. citri draft genome was used to characterize the immune defense genes present in D. citri. Predicted mRNAs identified by screening the published D. citri annotated draft genome were manually searched using a custom database of immune genes from previously annotated insect genomes. Toll and JAK/STAT pathways, general defense genes Dual oxidase, Nitric oxide synthase, prophenoloxidase, and cellular immune defense genes were present in D. citri. In contrast, D. citri lacked genes for the Imd pathway, most antimicrobial peptides, 1,3-β-glucan recognition proteins (GNBPs), and complete peptidoglycan recognition proteins. These data suggest that D. citri has a reduced immune capability similar to that observed in A. pisum, P. humanus, and R. prolixus. The absence of immune system genes from the D. citri genome may facilitate CLas infections, and is possibly compensated for by their relationship with their microbial endosymbionts.

Report of leucine-rich repeats (LRRs) from Scylla serrata: Ontogeny, molecular cloning, characterization and expression analysis following ligand stimulation, and upon bacterial and viral infections

Leucine-rich repeat (LRR) proteins are present in all living organisms, and their participation in signal transduction and defense mechanisms has been elucidated in humans and mosquitoes. LRRs possibly involve in protein-protein interactions also and show differential expression pattern upon challenge with pathogens. In the present study, a new LRR gene was identified in mud crab, Scylla serrata. LRR gene mRNA levels in different developmental stages and various tissues of S. serrata were analysed. Further, the response of the gene against different ligands, Gram-negative bacterium, and white spot syndrome virus (WSSV) was investigated in vitro and in vivo. Full-length cDNA sequence of S. serrata LRR (SsLRR) was found to be 2290 nucleotide long with an open reading frame of 1893bp. SsLRR encodes for a protein containing 630 deduced amino acids with 17 conserved LRR domains and exhibits significant similarity with crustacean LRRs so that these could be clustered into a branch in the phylogenetic tree. SsLRR mRNA transcripts were detected in all the developmental stages (egg, Zoea1-5, megalopa and crab instar), haemocytes and various tissues such as, stomach, gill, muscle, hepatopancreas, hematopoietic organ, heart, epithelial layer and testis by reverse-transcriptase PCR. SsLRR transcripts in cultured haemocytes showed a 2-fold increase in expression at 1.5 and 12h upon Poly I:C induction. WSSV challenge resulted in significant early up-regulation at 3h in-vitro and late up-regulation at 72h in-vivo. Peptidoglycan (PGN)-induction resulted in marginal up-regulation of SsLRR at timepoints, 6, 12 and 24h (fold change below 1.5) and no significant change in the expression at early timepoints. LPS-stimulation, on the other hand, showed either down-regulation or normal level of expression at all timepoints. However, a delayed 5-fold up-regulation was observed in vivo against Vibrio parahaemolyticus infection at 72hpi. The constitutive expression of the LRR gene in all the early life-stages, and its response to various ligands and to viral challenge suggest the possible role of the LRR in immune defense in mud crab. The result provides additional information which would help in future studies in understanding the innate immune pathways in crustaceans.

Two novel LRR-only proteins in Chlamys farreri: Similar in structure, yet different in expression profile and pattern recognition

Leucine-rich repeat (LRR)-only proteins could mediate protein-ligand and protein-protein interactions and be involved in the immune response. In the present study, two novel LRR-only proteins, CfLRRop-2 and CfLRRop-3, were identified and characterized from scallop Chlamys farreri. They both contained nine LRR motifs with the consensus signature sequence LxxLxLxxNxL and formed typical horseshoe structure. The CfLRRop-2 and CfLRRop-3 mRNA transcripts were constitutively expressed in haemocytes, muscle, mantle, gill, haepatopancreas and gonad, with the highest expression level in haepatopancreas and gill, respectively. During the ontogenesis of scallop, the mRNA transcripts of CfLRRop-2 were kept at a high level in oocytes and embryos, while those of CfLRRop-3 were expressed at a rather low level from oocytes to blastula. Their mRNA transcripts were significantly increased after the stimulation of lipopolysaccharide (LPS), peptidoglycan (PGN), glucan (GLU) and polyinosinic-polycytidylic acid (poly I:C), and the mRNA expression of CfLRRop-2 rose more intensely than that of CfLRRop-3. After the suppression of CfTLR (previously identified Toll-like receptor in C. farreri) via RNA interference (RNAi), CfLRRop-3 mRNA transcripts increased more intensely and lastingly than those of CfLRRop-2. The rCfLRRop-3 protein could bind LPS, PGN, GLU and poly I:C, while rCfLRRop-2 exhibited no significant binding activity to them. Additionally, rCfLRRop-2 could significantly induce the release of TNF-α from the mixed primary cultured scallop haemocytes, but rCfLRRop-3 failed. These results collectively indicated that CfLRRop-2 might act as an immune effector or pro-inflammatory factor, while CfLRRop-3 would function as a pattern recognition receptor (PRR), suggesting the function of LRR-only protein family has differentiated in scallop.

An LRR-only protein representing a new type of pattern recognition receptor in Chlamys farreri

Accumulating evidence has demonstrated that leucine-rich repeat (LRR)-only proteins could mediate protein-ligand and protein-protein interactions and were involved in the immune response. In the present study, an LRR-only protein (designed as CfLRRop-1) was cloned from Zhikong scallop Chlamys farreri. The complete cDNA sequence of CfLRRop-1 contained an open reading frame (ORF) of 1377 bp, which encoded a protein of 458 amino acids. An LRRNT motif, an LRR_7 motif and seven LRR motifs were found in the deduced amino acid sequence of CfLRRop-1. And these seven LRR motifs contained a conserved signature sequence LxxLxLxxNxL. The mRNA transcripts of CfLRRop-1 were constitutively expressed in all the tested tissues, including haemocytes, muscle, mantle, gill, hepatopancreas and gonad, with the highest expression level in hepatopancreas. After the stimulation of lipopolysaccharide (LPS), peptidoglycan (PGN), glucan (GLU) and polyinosinic-polycytidylic acid (poly I:C), the mRNA transcripts of CfLRRop-1 in haemocytes all increased firstly within the first 6 h and secondly during 12-24 h post stimulation. The mRNA expression level of CfLRRop-1 was continuously up-regulated, after the expression of CfTLR (previously identified Toll-like receptor in C. farreri) was suppressed via RNA interference (RNAi). The recombinant CfLRRop-1 protein could directly bind LPS, PGN, GLU and poly I:C, and induce the release of TNF-α in mixed primary cultured scallop haemocytes. These results collectively indicated that CfLRRop-1 would function as a powerful pattern recognition receptor (PRR) and play a pivotal role in the immune response of scallops.

Phylogenetic analysis and expression profiling of the pattern recognition receptors: Insights into molecular recognition of invading pathogens in Manduca sexta

Pattern recognition receptors (PRRs) detect microbial pathogens and trigger innate immune responses. Previous biochemical studies have elucidated the physiological functions of eleven PRRs in Manduca sexta but our understanding of the recognition process is still limited, lacking genomic perspectives. While 34 C-type lectin-domain proteins and 16 Toll-like receptors are reported in the companion papers, we present here 120 other putative PRRs identified through the genome annotation. These include 76 leucine-rich repeat (LRR) proteins, 14 peptidoglycan recognition proteins, 6 EGF/Nim-domain proteins, 5 β-1,3-glucanase-related proteins, 4 galectins, 4 fibrinogen-related proteins, 3 thioester proteins, 5 immunoglobulin-domain proteins, 2 hemocytins, and 1 Reeler. Sequence alignment and phylogenetic analysis reveal the evolution history of a diverse repertoire of proteins for pathogen recognition. While functions of insect LRR proteins are mostly unknown, their structure diversification is phenomenal: In addition to the Toll homologs, 22 LRR proteins with a signal peptide are expected to be secreted; 18 LRR proteins lacking signal peptides may be cytoplasmic; 36 LRRs with a signal peptide and a transmembrane segment may be non-Toll receptors on the surface of cells. Expression profiles of the 120 genes in 52 tissue samples reflect complex regulation in various developmental stages and physiological states, including some likely by Rel family transcription factors via κB motifs in the promoter regions. This collection of information is expected to facilitate future biochemical studies detailing their respective roles in this model insect.

Immunity-related genes in Ixodes scapularis--perspectives from genome information

Ixodes scapularis, commonly known as the deer tick, transmits a wide array of human and animal pathogens including Borrelia burgdorferi. Despite substantial advances in our understanding of immunity in model arthropods, including other disease vectors, precisely how I. scapularis immunity functions and influences persistence of invading pathogens remains largely unknown. This review provides a comprehensive analysis of the recently sequenced I. scapularis genome for the occurrence of immune-related genes and related pathways. We will also discuss the potential influence of immunity-related genes on the persistence of tick-borne pathogens with an emphasis on the Lyme disease pathogen B. burgdorferi. Further enhancement of our knowledge of tick immune responses is critical to understanding the molecular basis of the persistence of tick-borne pathogens and development of novel interventions against the relevant infections.

A comprehensive analysis of the Manduca sexta immunotranscriptome

As a biochemical model, Manduca sexta has substantially contributed to our knowledge on insect innate immunity. The RNA-Seq approach was implemented in three studies to examine tissue immunotranscriptomes of this species. With the latest and largest focusing on highly regulated process- and tissue-specific genes, we further analyzed the same set of data using BLAST2GO to explore functional aspects of the larval fat body (F) and hemocyte (H) transcriptomes with (I) or without (C) immune challenge. Using immunity-related sequences from other insects, we found 383 homologous contigs and compared them with those discovered based on relative abundance changes. The major overlap of the two lists validated our previous research designed for gene discovery and transcript profiling in organisms lacking sequenced genomes. By concatenating the contigs, we established a repertoire of 232 immunity-related genes encoding proteins for pathogen recognition (16%), signal transduction (53%), microbe killing (13%) and others (18%). We examined their transcript levels along with attribute classifications and detected prominent differences in nine of the 30 level 2 gene ontology (GO) categories. The increase in extracellular proteins (155%) was consistent with the highly induced synthesis of defense molecules (e.g., antimicrobial peptides) in fat body after the immune challenge. We identified most members of the putative Toll, IMD, MAPK-JNK-p38 and JAK-STAT pathways and small changes in their mRNA levels. Together, these findings set the stage for on-going analysis of the M. sexta immunogenome.

Cloning and characterization of the SpLRR cDNA from green mud crab, Scylla paramamosain

Infectious diseases have seriously inhibited the aquaculture of mud crab Scylla paramamosain in southeastern China. Identification of the immune molecules and characterization of the defense mechanisms will be pivotal to the reduction of these diseases. Available data show that leucine-rich repeat (LRR) proteins play a crucial role in protein-protein interactions, recognition processes or immune reactions in both invertebrates and vertebrates. In the present study, we cloned and characterized a LRR cDNA from the mud crab Scylla paramamosain (SpLRR) by using the RACE strategy. Bioinformatics analysis predicted that SpLRR contains one open reading frame of 1893 bp and encodes a LRR protein of 630 amino acids with 17 LRR domains and 5 potential N-glycosylation sites. Further, SpLRR and other arthropod LRR proteins could be clustered into one branch in a phylogenetic tree. SpLRR transcripts were detected using RT-PCR from examined tissues including heart, gill, stomach, intestine, muscle and hemocytes, whereas not from hepatopancreas. More importantly, the SpLRR mRNA expression was up-regulated after infection with Vibrio alginolyticus, Beta streptococcus or Poly I: C for 12-48 h, suggesting a novel LRR homolog in crab might be associated with the resistance to pathogens. The result could be important for future investigation of crab immune defense mechanisms.

RNA-Seq Study of Microbially Induced Hemocyte Transcripts from Larval Heliothis virescens (Lepidoptera: Noctuidae)

Larvae of the tobacco budworm are major polyphagous pests throughout the Americas. Development of effective microbial biopesticides for this and related noctuid pests has been stymied by the natural resistance mediated innate immune response. Hemocytes play an early and central role in activating and coordinating immune responses to entomopathogens. To approach this problem we completed RNA-seq expression profiling of hemocytes collected from larvae following an in vivo challenge with bacterial and fungal cell wall components to elicit an immune response. A de novo exome assembly was constructed by combination of sequence tags from all treatments. Sequence tags from each treatment were aligned separately with the assembly to measure expression. The resulting table of differential expression had >22,000 assemblies each with a distinct combination of annotation and expression. Within these assemblies >1,400 were upregulated and >1,500 downregulated by immune activation with bacteria or fungi. Orthologs to innate immune components of other insects were identified including pattern recognition, signal transduction pathways, antimicrobial peptides and enzymes, melanization and coagulation. Additionally orthologs of components regulating hemocytic functions such as autophagy, apoptosis, phagocytosis and nodulation were identified. Associated cellular oxidative defenses and detoxification responses were identified providing a comprehensive snapshot of the early response to elicitation.

Evidence of a novel immune responsive protein in the Hymenoptera

Honeybee populations are severely threatened by parasites and diseases. Recent outbreaks of Colony Collapse Disorder (CCD) has caused loss of more than 35% of bee colonies in the USA, and this is thought to at least in part be due to parasites and/or disease. Interestingly, the honeybee possesses of a limited set of immune genes compared to other insects. Non-canonical immune genes of honeybee are of interest because they may provide greater insights into the peculiar nature of the immune system of this social insect. Previous analyses of bee haemolymph upon bacterial challenge identified a novel leucine-rich repeat protein termed IRP30. Here we show that IRP30 behaves as a typical secreted immune protein. It is expressed simultaneously with carboxylesterase upon treatment with bacteria or other elicitors of immune response. Furthermore we characterize the gene and the mRNA encoding this protein and the IRP30 protein itself. Its regulation and evolution reveal that IRP30 belongs to a protein family, distributed broadly among Hymenoptera, suggesting its ancient function in immune response. We document an interesting case of a recent IRP30 loss in the ant Atta cephalotes and hypothesize that a putative IRP30 homolog of Nasonia emerged by convergent evolution rather than diverged from a common ancestor.

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.