Identification and properties of a receptor for the invertebrate cytokine astakine, involved in hematopoiesis

Toxicological mechanism of ammonia-N on haematopoiesis and apoptosis of haemocytes in Litopenaeus vannamei

Ammonia, as an important pollutant, contributed to the reduction of immunity, disruption of physiology in animals. RNA interference (RNAi) was performed to understand the function of astakine (AST) in haematopoiesis and apoptosis in Litopenaeus vannamei under ammonia-N exposure. Shrimps were exposed to 20 mg/L ammonia-N from 0 to 48 h with injection of 20 μg AST dsRNA. Further, shrimps were exposed to 0, 2, 10 and 20 mg/L ammonia-N also from 0 to 48 h. The results showed that the total haemocytes count (THC) decreased under ammonia-N stress and the knockdown of AST resulted in a further decrease of THC, suggesting that 1) the proliferation was decreased through the reduction of AST and Hedgehog, the differentiation was interfered by Wnt4, Wnt5 and Notch, and the migration was inhibited by the decrease of VEGF; 2) oxidative stress was induced under ammonia-N stress, leading to the increase of DNA damage with the up-regulated gene expression of death receptor, mitochondrial and endoplasmic reticulum stress pathways; 3) the changes of THC resulted from the decrease of proliferation, differentiation and migration of haematopoiesis cells and the increase of apoptosis of haemocytes. This study helps to deepen our understanding of risk management in shrimp aquaculture.

The sORF-Encoded Peptides, ATP Synthase Subunits, Facilitate WSSV Duplication in Shrimp

Short open reading frames (sORFs) are a newly identified family of genes, and the functions of most sORF genes and their encoded peptides (SEPs) are still unknown. In this study, two ATP synthase subunits were identified in kuruma shrimp (Marsupenaeus japonicus) as SEPs, namely MjATP5I and MjATP5L. They were widely distributed in all of the tested tissues of shrimp and upregulated in hemocytes and intestines in response to WSSV challenge. The injection of recombinant proteins (rMjATP5I and rMjATP5L) increased the expression of Ie1 and Vp28, while the knockdown of MjATP5I and MjATP5L decreased the expression of Ie1 and Vp28. All of the results suggest that MjATP5I and MjATP5L were beneficial for WSSV replication. Further exploration found that MjATP5I and MjATP5L RNAi significantly improved the shrimp survival rates, reduced ATP production, and upregulated the expression of antimicrobial peptide genes post viral challenge, and the two ATPase subunits and Relish negatively regulated each other. These results reveal that MjATP5I and MjATP5L facilitated WSSV duplication by regulating the production of ATP contents and the expression of antimicrobial peptide genes in shrimp.

CgATP synthase β subunit involved in the regulation of haemocytes proliferation as a CgAstakine receptor in Crassostrea gigas

Astakine is considered as an endogenous cytokine-like factor of prokineticin homologue in invertebrate. Recently, an astakine homologue (CgAstakine) has been identified and characterized in oyster Crassostrea gigas. In the present study, a CgATP synthase β subunit was identified as the receptor of CgAstakine in C. gigas. There was an ATP-synt_ab_N domain and an AAA domain in the CgATP synthase β subunit protein. The mRNA transcripts of CgATP synthase β subunit were detected in all tested tissues, with the highest expression level in hepatopancreas and gills, which was 109.11-fold (p < 0.01) and 97.21-fold (p < 0.01) of that in labial palps, respectively. After rCgAstakine stimulation, the mRNA transcripts of CgATP synthase β subunit in agranulocytes and semi-granulocytes were significantly increased at 24 h (2.44-fold, and 9.01-fold of that in control group, p < 0.01), and those in granulocytes were significantly increased at 6 h (1.83-fold, p < 0.01), 12 h (1.92-fold, p < 0.01) and 24 h (3.47-fold, p < 0.01). The expression level of CgATP synthase β subunit protein in agranulocytes and granulocytes was also significantly increased after rCgAstakine stimulation, which was 1.64-fold (p < 0.05) and 1.85-fold (p < 0.05) of that in control group, respectively, while there were no significant changes in semi-granulocytes. The immunofluorescence assay showed that CgATP synthase β subunit positive signals were mainly located on the membrane of haemocytes. The number of haemocytes with EdU positive signals was significantly increased after rCgAstakine stimulation (2.04-fold of seawater group, p < 0.01), while significantly decreased after the RNA interference (RNAi) of CgATP synthase β subunit, which was 0.28-fold of that in NC group (p < 0.01). Bio-layer interferometry (BLI) assay confirmed in vitro interaction between rCgAstakine and rCgATP synthase β subunit. There results suggested that CgATP synthase β subunit acts as the receptor of CgAstakine and plays important roles in CgAstakine induced renewal of haemocytes in C. gigas.

Transcriptome Profiling of the Pacific Oyster Crassostrea gigas Visceral Ganglia over a Reproduction Cycle Identifies Novel Regulatory Peptides

The neuropeptides involved in the regulation of reproduction in the Pacific oyster (Crassostrea gigas) are quite diverse. To investigate this diversity, a transcriptomic survey of the visceral ganglia (VG) was carried out over an annual reproductive cycle. RNA-seq data from 26 samples corresponding to VG at different stages of reproduction were de novo assembled to generate a specific reference transcriptome of the oyster nervous system and used to identify differentially expressed transcripts. Transcriptome mining led to the identification of novel neuropeptide precursors (NPPs) related to the bilaterian Eclosion Hormone (EH), crustacean female sex hormone/Interleukin 17, Nesfatin, neuroparsin/IGFBP, prokineticins, and urotensin I; to the protostome GNQQN, pleurin, prohormones 3 and 4, prothoracotropic hormones (PTTH), and QSamide/PXXXamide; to the lophotrochozoan CCWamide, CLCCY, HFAamide, and LXRX; and to the mollusk-specific NPPs CCCGS, clionin, FYFY, GNamide, GRWRN, GSWN, GWE, IWMPxxGYxx, LXRYamide, RTLFamide, SLRFamide, and WGAGamide. Among the complete repertoire of NPPs, no sex-biased expression was observed. However, 25 NPPs displayed reproduction stage-specific expression, supporting their involvement in the control of gametogenesis or associated metabolisms.

A Comprehensive Review on Crustaceans' Immune System With a Focus on Freshwater Crayfish in Relation to Crayfish Plague Disease

Freshwater crayfish immunity has received great attention due to the need for urgent conservation. This concern has increased the understanding of the cellular and humoral defense systems, although the regulatory mechanisms involved in these processes need updating. There are, however, aspects of the immune response that require clarification and integration. The particular issues addressed in this review include an overall description of the oomycete Aphanomyces astaci, the causative agent of the pandemic plague disease, which affects freshwater crayfish, and an overview of crustaceans' immunity with a focus on freshwater crayfish. It includes a classification system of hemocyte sub-types, the molecular factors involved in hematopoiesis and the differential role of the hemocyte subpopulations in cell-mediated responses, including hemocyte infiltration, inflammation, encapsulation and the link with the extracellular trap cell death pathway (ETosis). In addition, other topics discussed include the identity and functions of hyaline cells, the generation of neoplasia, and the emerging topic of the role of sessile hemocytes in peripheral immunity. Finally, attention is paid to the molecular execution of the immune response, from recognition by the pattern recognition receptors (PRRs), the role of the signaling network in propagating and maintaining the immune signals, to the effector elements such as the putative function of the Down syndrome adhesion molecules (Dscam) in innate immune memory.

F1 ATP synthase β subunit is a putative receptor involved in white spot syndrome virus infection in shrimp by binding with viral envelope proteins VP51B and VP150

White spot syndrome virus (WSSV) is highly virulent toward shrimp, and F1 ATP synthase β subunit (ATPsyn-β) has been suggested to be involved in WSSV infection. Therefore, in this study, interactions between Penaeus monodon ATPsyn-β (PmATPsyn-β) and WSSV structural proteins were characterized. Based on the results of yeast two-hybrid, co-immunoprecipitation, and protein pull-down assays, WSSV VP51B and VP150 were identified as being able to interact with PmATPsyn-β. Membrane topology assay results indicated that VP51B and VP150 are envelope proteins with large portions exposed outside the WSSV virion. Cellular localization assay results demonstrated that VP51B and VP150 co-localize with PmATPsyn-β on the membranes of transfected cells. Enzyme-linked immunosorbent assay (ELISA) and competitive ELISA results demonstrated that VP51B and VP150 bound to PmATPsyn-β in a dose-dependent manner, which could be competitively inhibited by the addition of WSSV virions. In vivo neutralization assay results further showed that both recombinant VP51B and VP150 could delay mortality in shrimp challenged with WSSV.

Silencing of ATP synthase β reduces phytoplasma multiplication in a leafhopper vector

The leafhopper Euscelidius variegatus is a natural vector of the chrysanthemum yellows phytoplasma (CYp) and a laboratory vector of the Flavescence dorée phytoplasma (FDp). Previous studies indicated a crucial role for insect ATP synthase α and β subunits during phytoplasma infection of the vector species. Gene silencing of ATP synthase β was obtained by injection of specific dsRNAs in E. variegatus. Here we present the long-lasting nature of such silencing, its effects on the small RNA profile, the significant reduction of the corresponding protein expression, and the impact on phytoplasma acquisition capability. The specific transcript expression was silenced at least up to 37 days post injection with an average reduction of 100 times in insects injected with dsRNAs targeting ATP synthase β (dsATP) compared with those injected with dsRNAs targeting green fluorescent protein (dsGFP), used as negative controls. Specific silencing of this gene was also confirmed at protein level at 15 days after the injection. Total sRNA reads mapping to dsATP and dsGFP sequences in analysed libraries showed in both cases a peak of 21 nt, a length consistent with the generation of dsRNA-derived siRNAs by RNAi pathway. Reads mapped exclusively to the fragment corresponding to the injected dsATPs, probably indicating the absence of a secondary machinery for siRNA synthesis. Insects injected either with dsATP or dsGFP successfully acquired CYp and FDp during feeding on infected plants. However, the average phytoplasma amount in dsATP insects was significantly lower than that measured in dsGFP specimens, indicating a probable reduction of the pathogen multiplication when ATP synthase β was silenced. The role of the insect ATP synthase β during phytoplasma infection process is discussed.

The N-terminal peptide generated after activation of prophenoloxidase affects crayfish hematopoiesis

The circulating hemocytes of invertebrates are important mediators of immunity, and hemocyte homeostasis is of high importance for survival and health of crustaceans. The prophenoloxidase (proPO)-activating system is one of the most essential immune reactions, which can be activated by pattern recognition proteins from microorganisms. Activation of proPO by the proPO activating enzyme generates an N-terminal peptide, with cleavage site after Arg176, as well as the active enzyme phenoloxidase, which is the key enzyme for melanization. In the present study we demonstrate a role for the N-terminal proPO-peptide in hematopoiesis. Injection of this proPO-peptide increased the number of circulating hemocytes and especially granular hemocytes. We also show that the reactive oxygen species (ROS) production in the anterior proliferative center was enhanced after proPO peptide injection, which is a prerequisite for rapid hemocyte release from the hematopoietic tissue. Moreover, this peptide had an effect on ROS production in in vitro cultured hematopoietic cells and induced spreading of these cells within 72 h. Taken together, our findings show a role of the N-terminal proPO peptide in stimulation of hematopoiesis in crayfish, Pacifastacus leniusculus.

The Prokineticins: Neuromodulators and Mediators of Inflammation and Myeloid Cell-Dependent Angiogenesis

The mammalian prokineticins family comprises two conserved proteins, EG-VEGF/PROK1 and Bv8/PROK2, and their two highly related G protein-coupled receptors, PKR1 and PKR2. This signaling system has been linked to several important biological functions, including gastrointestinal tract motility, regulation of circadian rhythms, neurogenesis, angiogenesis and cancer progression, hematopoiesis, and nociception. Mutations in PKR2 or Bv8/PROK2 have been associated with Kallmann syndrome, a developmental disorder characterized by defective olfactory bulb neurogenesis, impaired development of gonadotropin-releasing hormone neurons, and infertility. Also, Bv8/PROK2 is strongly upregulated in neutrophils and other inflammatory cells in response to granulocyte-colony stimulating factor or other myeloid growth factors and functions as a pronociceptive mediator in inflamed tissues as well as a regulator of myeloid cell-dependent tumor angiogenesis. Bv8/PROK2 has been also implicated in neuropathic pain. Anti-Bv8/PROK2 antibodies or small molecule PKR inhibitors ameliorate pain arising from tissue injury and inhibit angiogenesis and inflammation associated with tumors or some autoimmune disorders.

A Prokineticin (PK)-like cytokine from Chinese mitten crab Eriocheir sinensis promotes the production of hemocytes via reactive oxygen species

Astakine is a cytokine-like factor containing a prokineticin domain, which directly participates in hematopoiesis and blood cell differentiation. In the present study, a novel Astakine gene was identified from Chinese mitten crab Eriocheir sinensis (designated as EsAst). The full-length cDNA of EsAst was of 1163 bp, consisting of a 5' untranslated region (UTR) of 120 bp, a 3' UTR of 656 bp, and an open reading frame (ORF) of 387 bp encoding a polypeptide of 128 amino acids. There were a signal peptide and a prokineticin domain with nine conserved cysteine residues in the deduced amino acid sequence of EsAst. EsAst shared higher similarity with Astakines from Penaeus monodon and Pacifastacus leniusculus, and it was closely clustered with the Astakine from shrimp P. monodon in the phylogenetic tree. The EsAst mRNA transcript was higher expressed in hemocytes and hepatopancreas. The relative expression level of EsAst in hemocytes was continuously increased from 1.5 to 48 h after Vibro anguillarum challenge compared that in the untreated control group. After Pichia pastoris GS115 challenge, the relative expression level of EsAst in hemocytes was also up-regulated. After rEsAst injection, ROS levels in HPT cells were also increased at 12 and 24 h, and the total hemocyte counts were also significantly increased at 6, 9, 12, and 24 h post rEsAst injection. The interference of EsAst expression with dsRNA injection could delay the recovery of hemocytes production post A. hydrophila stimulation. When mitochondrial complexes I was knock down by dsRNA, ROS levels were decreased and THCs were also decreased. Recovery of hemocyte production inducing by A. hydrophila stimulation and rEsAst injection were delayed with dsEsbc1 injection. When ROS levels were increased after RNAi of Lon protease, THCs were also increased. The expression levels of five genes (EsJNK, EsSTAT, EsPI3K, EsAKT1, EsP70S6K) involved in SAPK-JNK and mTOR signaling pathways were up-regulated at 12 and 24 h in rEsAst group and EsLon dsRNA group compared with that in EGFP dsRNA group, and were similar to the trend of ROS levels. These results collectively suggested that EsAst should be a novel Astakine to promote the production of hemocytes in a ROS-dependent way in E. sinensis.

Brain gene expression analyses in virgin and mated queens of fire ants reveal mating-independent and socially regulated changes

Transcriptomes of dissected brains from virgin alate and dealate mated queens from polygyne fire ants (Solenopsis invicta) were analyzed and compared. Thirteen genes were upregulated in mated queen brain, and nine were downregulated. While many of the regulated genes were either uncharacterized or noncoding RNAs, those annotated genes included two hexamerin proteins, astakine neuropeptide, serine proteases, and serine protease inhibitors. We found that for select differentially expressed genes in the brain, changes in gene expression were most likely driven by the changes in physiological state (i.e., age, nutritional status, or dominance rank) or in social environment (released from influence of primer pheromone). This was concluded because virgins that dealated after being separated from mated queens showed similar patterns of gene expression in the brain as those of mated queens for hexamerin 1, astakine, and XR_850909. Abaecin (XR_850725), however, appears upregulated only after mating. Therefore, our findings contribute to distinguish how specific gene networks, especially those influenced by queen primer pheromone, are regulated in queen ants. Additionally, to identify brain signaling pathways, we mined the fire ant genome and compiled a list of G-protein-coupled receptors (GPCRs). The expression level of GPCRs and other genes in the "genetic toolkit" in the brains of virgin alates and mated dealate queens is reported.

Astakines in arthropods-phylogeny and gene structure

Astakine1 was isolated as a hematopoietic cytokine in the freshwater crayfish Pacifastacus leniusculus. In this study we detect and compare 79 sequences in GenBank, which we consider to be possible astakine orthologs, among which eleven are crustacean, sixteen are chelicerate and 52 are from insect species. Available arthropod genomes are searched for astakines, and in conclusion all astakine sequences in the current study have a similar exon containing CCXX(X), thus potentially indicating that they are homologous genes with the structure of this exon highly conserved. Two motifs, RYS and YP(N), are also conserved among the arthropod astakines. A phylogenetic analysis reveals that astakine1 and astakine2 from P. leniusculus and Procambarus clarkii are distantly related, and may have been derived from a gene duplication occurring early in crustacean evolution. Moreover, a structural comparison using the Mamba intestinal toxin (MIT1) from Dendroaspis polylepis as template indicates that the overall folds are similar in all crustacean astakines investigated.

PDGF/VEGF-Related Receptor Affects Transglutaminase Activity to Control Cell Migration During Crustacean Hematopoiesis

The platelet-derived growth factor (PDGF) receptor, a tyrosine kinase (TK) receptor whose ligand is PDGF, is crucial in the transduction of extracellular signals into cells and mediates numerous processes, such as cell proliferation, differentiation, survival, and migration. We demonstrate the important roles of a receptor TK related to the PDGF/VEGF family protein (PVR) in controlling hematopoietic progenitor cell migration by affecting extracellular transglutaminase (TGase) activity. Pl_PVR1, GenBank accession No. KY444650, is highly expressed in hemocytes and the hematopoietic tissue (HPT). Sunitinib malate was used to block the PVF/PVR downstream pathway in HPT cell culture. The addition of Sunitinib also caused the HPT cells to increase in size and begin spreading. An increase in extracellular TGase activity on the HPT cell membrane was observed in a dose-dependent manner after treatment with Sunitinib malate. The presence of crude Ast1 provided a combinatorial beneficial effect that enhanced the number of spreading cells after inhibition of the Pl_PVR downstream signaling cascade. In addition, an increased immunoreactivity for β-tubulin and elongation of β-tubulin filaments were found in Pl_PVR signaling-inhibited cells. The potential roles of PVF/PVR signaling in controlling progenitor cell activity during hematopoiesis in crayfish were investigated and discussed.

A Pacifastacus leniusculus serine protease interacts with WSSV

Serine proteases are involved in many critical physiological processes including virus spread and replication. In the present study, we identified a new clip-domain serine protease (PlcSP) in the crayfish Pacifastacus leniusculus hemocytes, which can interact with the White Spot Syndrome Virus (WSSV) envelope protein VP28. It was characterized by a classic clip domain with six strictly conserved Cys residues, and contained the conserved His-Asp-Ser (H-D-S) motif in the catalytic domain. Furthermore, signal peptide prediction revealed that it has a 16-residue secretion signal peptide. Tissue distribution showed that it was mainly located in P. leniusculus hemocytes, and its expression was increased in hemocytes upon WSSV challenge. In vitro knock down of PlcSP decreased both the expression of VP28 and the WSSV copy number in hematopoietic stem (HPT) cells. Accordingly, these data suggest that the new serine protease may be of importance for WSSV infection into hematopoietic cells.

Identification of β-chain of Fo F1 -ATPase in apoptotic cell population induced by Microplitis bicoloratus bracovirus and its role in the development of Spodoptera litura

Two physiological changes of Spodoptera litura parasitized by Microplitis bicoloratus are hemocyte-apoptosis and retarded immature development. β-Chain of F_o F₁ -ATPase was found from a S. litura transcriptome. It belongs to a conserved P-loop NTPase superfamily, descending from a common ancestor of Lepidopteran clade. However, the characterization of β-chain of ATPase in apoptotic cells and its involvement in development remain unknown. Here, the ectopic expression and endogenous F_o F₁ -ATPase β-chain occurred on S. litura cell membrane: in vivo, at the late stage of apoptotic hemocyte, endogenous F_o F₁ -ATPase β-chain was stably expressed during M. bicoloratus larva development from 4 to 7 days post-parasitization; in vitro, at an early stage of pre-apoptotic Spli221 cells by infecting with M. bicoloratus bracovirus particles, the proteins were speedily recover expression. Furthermore, endogenous F_o F₁ -ATPase β-chain was localized on the apoptotic cell membrane. RNA interference (RNAi) of F_o F₁ -ATPase β-chain led to significantly decreased head capsule width. This suggested that F_o F₁ -ATPase β-chain positively regulated the development of S. litura. The RNAi effect on the head capsule width was enhanced with parasitism. Our research found that F_o F₁ -ATPase β-chain was expressed and localized on the cell membrane in the apoptotic cells, and involved in the development of S. litura.

Lipids in Insect Oocytes: From the Storage Pathways to Their Multiple Functions

In insect physiology, the mechanisms involved in the buildup and regulation of yolk proteins in developing oocytes have been thoroughly researched during the last three decades. Comparatively, the study of lipid metabolism in oocytes had received less attention. The importance of this issue lies in the fact that lipids make up to 40% of the dry weight of an insect egg, being the most important supply of energy for the developing embryo. Since the oocyte has a very limited capacity to synthesize lipids de novo, most of the lipids in the mature eggs arise from the circulation. The main lipid carriers in the insect circulatory system are the lipoproteins lipophorin and vitellogenin. In some species, the endocytosis of lipophorin and vitellogenin may account for about 10% of the lipids present in mature eggs. Thus, most of the lipids are transferred by a lipophorin-mediated pathway, in which the lipoprotein unloads its lipid cargo at the surface of oocytes without internalization. This chapter recapitulates the current status on lipid storage and its utilization in insect oocytes and discusses the participation of key factors including lipoproteins, transfer proteins, lipolytic enzymes, and dynamic organelles such as lipid droplets. The new findings in the field of lipophorin receptors are presented in the context of lipid accumulation during egg maturation, and the roles of lipids beyond energy source are summarized from the perspective of oogenesis and embryogenesis. Finally, prospective and fruitful areas of future research are suggested.

A mitochondrial membrane protein is a target for rice ragged stunt virus in its insect vector

Rice ragged stunt virus (RRSV; Reoviridae) is exclusively transmitted by the brown planthopper Nilaparvata lugens in a persistent-propagative manner. It is understood that RNA viral proliferation is associated with the intracellular membranes of the insect host cells. However, the molecular mechanisms of the interaction between the RRSV proliferation and the intracellular membranes remain essentially unknown. It will be of great interest to determine whether RRSV protein(s) directly interact with intracellular membrane components of its host cells. In this study, we identified a RRSV nonstructural protein Pns10 interacting with a host oligomycin-sensitivity conferral protein (OSCP) using yeast two-hybrid system. The interaction between RRSV Pns10 and N. lugens OSCP was verified by a glutathione S-transferase pull-down assay. Confocal miscopy revealed colocalization of these two proteins in the cytoplasm of the salivary gland cells during the viral infection. The virions were further detected in the mitochondria under confocal miscopy and transmission electron microscopy combined with western blotting assay. This is the first observation that RRSV protein has a direct link with mitochondria. Suppressing OSCP gene expression by RNA interference notably decreased the viral loads in RRSV-infected insects. These findings revealed novel aspects of a viral protein in targeting the host mitochondrial membrane and provide insights concerning the mitochondrial membrane protein-based virus proliferation mode in the insect vector.

White shrimp Litopenaeus vannamei that have received fucoidan exhibit a defense against Vibrio alginolyticus and WSSV despite their recovery of immune parameters to background levels

White shrimp Litopenaeus vannamei receiving fucoidan at 2, 6, and 10 μg g^-1 after 0-144 h or 0-120 h were examined for immune parameters (haemograms, phenoloxidase activity, respiratory burst, and superoxide dismutase activity), proliferation of haemocyte in the haematopoietic tissue (HPT), gene expression, and phagocytic activity and clearance efficiency to Vibrio alginolyticus. Immune parameters and mitotic index of HPT increased after 3-24 h, reached their maxima after 48-72 h, and returned to background values after 144 h. Transcripts of lipopolysaccharide and β-1,3-glucan binding protein (LGBP), peroxinectin (PX), prophenoloxidase (proPO) I, proPO II, astakine, and haemocyte homeostasis-associated protein (HHAP) were up-regulated to a maximum after 48-72 h and returned to background values after 144 h. Phagocytic activity and clearance efficiency to V. alginolyticus increased after 12 h, reached its maximum after 48 h, and continued to remain higher after 120 h. In another experiment, shrimp receiving fucoidan after 48 h and 144 h were respectively challenged with V. alinolyticus at 6 × 10⁶ colony-forming units (cfu) shrimp^-1 or challenged with WSSV at 1.2 × 10⁵ copies shrimp^-1 and then placed in seawater. The survival rate of shrimp receiving fucoidan was significantly higher than in controls. In conclusion, shrimp receiving fucoidan showed a proliferation of HPT, increased immune parameters, and up-regulated transcripts of LGBP, PX, proPO I, proPO II, astakine, and HHAP after 48 h. Shrimp receiving fucoidan exhibited a defense against V. alginolyticus and WSSV, even after immune parameters recovered to background levels.

Immunodominant membrane proteins of phytoplasmas

Phytoplasmas are plant-pathogenic, phloem-colonizing, cell wall-less microorganisms that are primarily dependent on insect transmission for their spread and survival. The life cycle of phytoplasmas involves replication in insects and host plants. Until recently, phytoplasmas have resisted all attempts at cultivation in cell-free media, making these pathogens poorly characterized on a physiological and biochemical basis. However, host-pathogen relationships can be studied by investigating immunodominant membrane proteins (IDPs), which are located on the exterior surfaces of phytoplasma cells and are the most abundant proteins of the cell membrane. These membrane proteins come in direct contact with both insect and plant hosts and are thought to play a crucial role in phytoplasma spread both within the plant and by insect vectors. Therefore, there is great interest in studying this class of proteins. We summarize and discuss important investigations about these membrane proteins, which have already provided a better understanding of the host-phytoplasma relationship.

A cytokine-like factor astakine accelerates the hemocyte production in Pacific oyster Crassostrea gigas

Astakine has been reported to be a hematopoietic growth factor of prokineticin homolog firstly found in arthropods freshwater crayfish Pacifastacus leniusculus. In the present study, an astakine homologous gene was identified from Pacific oyster Crassostrea gigas (designated CgAstakine). The full length cDNA of CgAstakine encoded a polypeptide of 103 amino acids containing a prokineticin (PK) domain homologous to that in astakine from freshwater crayfish P. leniusculus. The deduced amino acid sequence of CgAstakine shared higher similarity with those of other invertebrate astakines than prokineticins from vertebrates. The mRNA of CgAstakine was highly expressed in hepatopancreas and adductor muscle of oyster, while the CgAstakine protein was mainly distributed in hepatopancreas, gill and hemocytes. The mRNA expression of CgAstakine in hemocytes was significantly increased (p < 0.01) and maintained at a high level from 3 h to 9 h after Vibrio anguillarum challenge. After the oyster hemocytes were incubated with 5 μg/mL recombinant CgAstakine protein (rCgAstakine) for 24 h in vitro, the proliferation of hemocytes was significantly increased to 1.89 fold of that in control group (p < 0.05). Moreover, the total count of oyster hemocytes was significantly upregulated (2.45 fold of that in control group, p < 0.05) at 12 h after the oysters were received an injection of rCgAstakine (0.5 μg/g). These results collectively indicated that CgAstakine could modulate the hemocytes proliferation both in vitro and in vivo, and probably involved in the hematopoietic process fighting against the invasion of foreign pathogens.

Antimicrobial proteins: From old proteins, new tricks

This review describes the main types of antimicrobial peptides (AMPs) synthesised by crustaceans, primarily those identified in shrimp, crayfish, crab and lobster. It includes an overview of their range of microbicidal activities and the current landscape of our understanding of their gene expression patterns in different body tissues. It further summarises how their expression might change following various types of immune challenges. The review further considers proteins or protein fragments from crustaceans that have antimicrobial properties but are more usually associated with other biological functions, or are derived from such proteins. It discusses how these unconventional AMPs might be generated at, or delivered to, sites of infection and how they might contribute to crustacean host defence in vivo. It also highlights recent work that is starting to reveal the extent of multi-functionality displayed by some decapod AMPs, particularly their participation in other aspects of host protection. Examples of such activities include proteinase inhibition, phagocytosis, antiviral activity and haematopoiesis.

ATP synthesis is active on the cell surface of the shrimp Litopenaeus vannamei and is suppressed by WSSV infection

BACKGROUND

Over the past a few years, evidences indicate that adenosine triphosphate (ATP) is an energy source for the binding, maturation, assembly, and budding process of many enveloped viruses. Our previous studies suggest that the F1-ATP synthase beta subunit (ATPsyn β, BP53) of the shrimp Litopenaeus vannamei (L. vannamei) might serve as a potential receptor for white spot syndrome virus (WSSV)'s infection.

METHODS

BP53 was localized on the surface of shrimp hemocytes and gill epithelial cells by immunofluorescence assay and immunogold labeling technique. Cell surface ATP synthesis was demonstrated by an in vitro bioluminescent luciferase assay. Furthermore, the expression of bp53 after WSSV infection was investigated by RT-PCR test. In addition, RNAi was developed to knock down endogenous bp53.

RESULTS

BP53 is present on shrimp cell surface of hemocytes and gill epithelia. The synthesized ATP was detectable in the extracellular supernatant by using a bioluminescence assay, and the production declined post WSSV binding and infection. Knocking down endogenous bp53 resulted in a 50% mortality of L. vannamei.

CONCLUSION

These results suggested that BP53, presenting on cell surface, likely served as one of the receptors for WSSV infection in shrimp. Correspondingly, WSSV appears to disturb the host energy metabolism through interacting with host ATPsyn β during infection. This work firstly showed that host ATP production is required and consumed by the WSSV for binding and proceeds with infection process.

Astakine LvAST binds to the β subunit of F1-ATP synthase and likely plays a role in white shrimp Litopeneaus vannamei defense against white spot syndrome virus

Cytokines play a critical role in innate and adaptive immunity. Astakines represent a group of invertebrate cytokines that are related to vertebrate prokineticin and function in promoting hematopoiesis in crustaceans. We have identified an astakine from the white shrimp Litopeneaus vannamei and named it LvAST in a previous research. In the present research, we investigated the interactions among LvAST, the envelope protein VP37 of white spot syndrome virus (i.e., WSSV), and the β subunit of F1-ATP synthase (ATPsyn-β) of the white shrimp (i.e., BP53) using binding assays and co-precipitations. We also examined the effects of LvAST on shrimp susceptibility to WSSV. We found that LvAST and VP37 competitively bound to BP53, but did not bind to each other. Shrimps that had been injected with recombinant LvAST exhibited significantly lower mortality and longer survival time in experimental infections by WSSV. In contrast, shrimps whose LvAST gene expression had been inhibited by RNA interference showed significantly higher WSSV infection intensity and shorter survival time following viral challenges. These results suggested that LvAST and WSSV both likely use ATPsyn-β as a receptor and LvAST plays a role in shrimp defense against WSSV infection. This represented the first research showing the involvement of astakines in host antiviral immunity.

β-chain of ATP synthase as a lipophorin binding protein and its role in lipid transfer in the midgut of Panstrongylus megistus (Hemiptera: Reduviidae)

Lipophorin, the main lipoprotein in the circulation of the insects, cycles among peripheral tissues to exchange its lipid cargo at the plasma membrane of target cells, without synthesis or degradation of its apolipoprotein matrix. Currently, there are few characterized candidates supporting the functioning of the docking mechanism of lipophorin-mediated lipid transfer. In this work we combined ligand blotting assays and tandem mass spectrometry to characterize proteins with the property to bind lipophorin at the midgut membrane of Panstrongylus megistus, a vector of Chagas' disease. We further evaluated the role of lipophorin binding proteins in the transfer of lipids between the midgut and lipophorin. The β subunit of the ATP synthase complex (β-ATPase) was identified as a lipophorin binding protein. β-ATPase was detected in enriched midgut membrane preparations free of mitochondria. It was shown that β-ATPase partially co-localizes with lipophorin at the plasma membrane of isolated enterocytes and in the sub-epithelial region of the midgut tissue. The interaction of endogenous lipophorin and β-ATPase was also demonstrated by co-immunoprecipitation assays. Blocking of β-ATPase significantly diminished the binding of lipophorin to the isolated enterocytes and to the midgut tissue. In vivo assays injecting the β-ATPase antibody significantly reduced the transfer of [(3)H]-diacylglycerol from the midgut to the hemolymph in insects fed with [9,10-(3)H]-oleic acid, supporting the involvement of lipophorin-β-ATPase association in the transfer of lipids. In addition, the β-ATPase antibody partially impaired the transfer of fatty acids from lipophorin to the midgut, a less important route of lipid delivery to this tissue. Taken together, the findings strongly suggest that β-ATPase plays a role as a docking lipophorin receptor at the midgut of P. megistus.

β-thymosins and hemocyte homeostasis in a crustacean

Thymosin proteins are well known for their actin-binding activity. Thymosin beta 4 (Tβ4) has been associated with biological activities in tissue repair and cell migration via interaction with ATP-synthase in vertebrates, while the information of similar thymosin functions in invertebrates is limited. We have shown previously that ATP-synthase is present on the surface of crayfish hematopoietic tissue (HPT) cells, and that astakine 1 (Ast1, an invertebrate cytokine) was found to interact with this β-subunit of ATP synthase. Here, we identified five different β-thymosins from Pacifastacus leniusculus, designated Pl-β-thymosin1-5. The two dominant isoforms in brain, HPT and hemocytes, Pl-β-thymosin1 and 2, were chosen for functional studies. Both isoforms could bind to the β-subunit of ATP-synthase, and Pl-β-thymosin1, but not Pl-β-thymosin2, significantly increased extracellular ATP formation. Moreover, Pl-β-thymosin1 stimulated HPT cell migration in vitro and Ast1 blocked this effect. Pl-β-thymosin2 increased the circulating hemocyte number at an early stage after injection. Additionally, in vivo injection of Pl-β-thymosin1 resulted in significant reduction of reactive oxygen species (ROS) production in crayfish HPT whereas Pl-β-thymosin2 had a similar but transient effect. Both Pl-β-thymosins induced the expression of Ast1 and superoxide dismutase (SOD) transcripts, while silencing of endogenous Pl-β-thymosin 1 and 2 by RNAi resulted in significant reduction of the Ast1 and SOD transcripts. The diverse effects exhibited by Pl-β-thymosin1 and Pl-β-thymosin2 indicates that these proteins are involved in a complex interaction that regulates the hematopoietic stem cell proliferation and differentiation.

Reprint of: Virus-binding proteins and their roles in shrimp innate immunity

Disease outbreaks caused by viral pathogens constitute a major limitation to development of the shrimp aquaculture industry. Many research have been conducted to better understand how host shrimp respond to viral infections with the aim of using the gained knowledge to develop better strategies for disease management and control. One approach has been to study the interactions between host and viral proteins, and particularly host virus-binding proteins that might play an important role in the viral infection process. Within the past five years, increasing numbers of virus-binding proteins (VBPs) have been reported in shrimp. Characterization of these molecules has emphasized on their potential therapeutic applications by demonstrating their activities in inhibition of viral replication via in vivo neutralization assay. However, signaling to induce innate antiviral immune responses as a consequence of binding between viral proteins and VBPs remain to be fully elucidated.

The VP37-binding protein F1ATP synthase β subunit involved in WSSV infection in shrimp Litopenaeus vannamei

To investigate the interaction between white spot syndrome virus (WSSV)-VP37 and gill membrane proteins (GMPs) of Pacific white shrimp (Litopenaeus vannamei), the VP37 protein was expressed and purified, and a distinct 53 kDa VP37-binding protein band was identified in GMPs by virus overlay protein binding assay and GST pull-down assay. By electroelution, the VP37 binding protein was purified and identified as F(1)ATP synthase β (F(1)ATPase β) subunit by Mass Spectrometry. The purified F(1)ATPase β subunit was used to immunize BALB/C mice to produce monoclonal antibodies (Mabs). After cell fusion, sixteen hybridomas secreting Mabs against F(1)ATPase β subunit of L. vannamei were screened by enzyme-linked immunosorbant assay (ELISA), three of which designated as 1D5, 1E8 and 2H4 were cloned by limiting dilution and further characterized by indirect immunofluorescence assay (IIFA) and western blotting. The results of IIFA showed that specific fluorescence signals located at the peripheral zone of the gills of L. vannamei. Western blotting demonstrated that three Mabs reacted specifically with the 53 kDa protein band in GMPs of L. vannamei. By IIFA, the Mabs could also cross-react with the gill cells of three other WSSV-susceptible shrimps Fenneropenaeus chinensis, Penaeus monodon and Marsupenaeus japonicus. Furthermore, the three anti-F(1)ATPase β subunit Mabs could partially block the binding of WSSV to GMPs by ELISA in vitro, and also exhibited direct anti-WSSV activity in shrimp by neutralization assay in vivo. These findings suggested that F(1)ATPase β subunit involved in WSSV infection in L. vannamei.

Virus-binding proteins and their roles in shrimp innate immunity

Disease outbreaks caused by viral pathogens constitute a major limitation to development of the shrimp aquaculture industry. Many research have been conducted to better understand how host shrimp respond to viral infections with the aim of using the gained knowledge to develop better strategies for disease management and control. One approach has been to study the interactions between host and viral proteins, and particularly host virus-binding proteins that might play an important role in the viral infection process. Within the past five years, increasing numbers of virus-binding proteins (VBPs) have been reported in shrimp. Characterization of these molecules has emphasized on their potential therapeutic applications by demonstrating their activities in inhibition of viral replication via in vivo neutralization assay. However, signaling to induce innate antiviral immune responses as a consequence of binding between viral proteins and VBPs remain to be fully elucidated.

The major antigenic membrane protein of "Candidatus Phytoplasma asteris" selectively interacts with ATP synthase and actin of leafhopper vectors

Phytoplasmas, uncultivable phloem-limited phytopathogenic wall-less bacteria, represent a major threat to agriculture worldwide. They are transmitted in a persistent, propagative manner by phloem-sucking Hemipteran insects. Phytoplasma membrane proteins are in direct contact with hosts and are presumably involved in determining vector specificity. Such a role has been proposed for phytoplasma transmembrane proteins encoded by circular extrachromosomal elements, at least one of which is a plasmid. Little is known about the interactions between major phytoplasma antigenic membrane protein (Amp) and insect vector proteins. The aims of our work were to identify vector proteins interacting with Amp and to investigate their role in transmission specificity. In controlled transmission experiments, four Hemipteran species were identified as vectors of “Candidatus Phytoplasma asteris”, the chrysanthemum yellows phytoplasmas (CYP) strain, and three others as non-vectors. Interactions between a labelled (recombinant) CYP Amp and insect proteins were analysed by far Western blots and affinity chromatography. Amp interacted specifically with a few proteins from vector species only. Among Amp-binding vector proteins, actin and both the α and β subunits of ATP synthase were identified by mass spectrometry and Western blots. Immunofluorescence confocal microscopy and Western blots of plasma membrane and mitochondrial fractions confirmed the localisation of ATP synthase, generally known as a mitochondrial protein, in plasma membranes of midgut and salivary gland cells in the vector Euscelidius variegatus. The vector-specific interaction between phytoplasma Amp and insect ATP synthase is demonstrated for the first time, and this work also supports the hypothesis that host actin is involved in the internalization and intracellular motility of phytoplasmas within their vectors. Phytoplasma Amp is hypothesized to play a crucial role in insect transmission specificity.

Crustacean hematopoiesis and the astakine cytokines

Major contributions to research in hematopoiesis in invertebrate animals have come from studies in the fruit fly, Drosophila melanogaster, and the freshwater crayfish, Pacifastacus leniusculus. These animals lack oxygen-carrying erythrocytes and blood cells of the lymphoid lineage, which participate in adaptive immune defense, thus making them suitable model animals to study the regulation of blood cells of the innate immune system. This review presents an overview of crustacean blood cell formation, the role of these cells in innate immunity, and how their synthesis is regulated by the astakine cytokines. Astakines are among the first invertebrate cytokines shown to be involved in hematopoiesis, and they can stimulate the proliferation, differentiation, and survival of hematopoietic tissue cells. The astakines and their vertebrate homologues, prokineticins, share similar functions in hematopoiesis; thus, studies of astakine-induced hematopoiesis in crustaceans may not only advance our understanding of the regulation of invertebrate hematopoiesis but may also provide new evolutionary perspectives about this process.

An ancient cytokine, astakine, mediates circadian regulation of invertebrate hematopoiesis

Invertebrate circulating hemocytes are key players in the innate immune defense and their continuous renewal from hematopoietic tissues is tightly regulated in crustaceans by astakine, a new family of cytokines sharing a prokineticin (PROK) domain. In vertebrates, brain PROKs function as transmitters of circadian rhythms and we present evidence that hemocyte release from hematopoietic tissues in crayfish is under circadian regulation, a direct result of rhythmic expression of astakine. We demonstrate that the observed variation in astakine expression has an impact on innate immunity assessed as susceptibility to a pathogenic Pseudomonas species. These findings enlighten the importance of comparing immune responses at fixed times not to neglect circadian regulation of innate immunity. Moreover, our results entail an evolutionary conserved function for prokineticins as mediators of circadian rhythm, and for the first time show a role for this domain in circadian regulation of hematopoiesis that may have implications also in vertebrates.

The role of F1 ATP synthase beta subunit in WSSV infection in the shrimp, Litopenaeus vannamei

Background

Knowledge of the virus-host cell interaction could inform us of the molecular pathways exploited by the virus. Studies on viral attachment proteins (VAPs) and candidate receptor proteins involved in WSSV infection, allow a better understanding of how these proteins interact in the viral life cycle. In this study, our aim was to find some host cellular membrane proteins that could bind with white spot syndrome virus (WSSV).

Results

Two proteins were evident by using a virus overlay protein binding assay (VOPBA) with WSSV. A protein with molecular weight 53 kDa, named BP53, was analyzed in this study, which was homologous with the F₁-ATP synthase beta subunit by mass spectrometry analysis. Rapid amplification of cDNA ends (RACE) PCR was performed to identify the full-length cDNA of the bp53 gene. The resulting full-length gene consisted of 1836 bp, encoding 525 amino acids with a calculated molecular mass of 55.98 kDa. The deduced amino acid sequence contained three conserved domains of the F₁-ATP synthase beta subunit. BP53 was therefore designated the F₁-ATP synthase beta subunit of L. vannamei. The binding of WSSV to BP53 were also confirmed by competitive ELISA binding assay and co-immunoprecipitation on magnetic beads. To investigate the function of BP53 in WSSV infection, it was mixed with WSSV before the mixture was injected intramuscularly into shrimp. The resulting mortality curves showed that recombinant (r) BP53 could attenuate WSSV infection.

Conclusions

The results revealed that BP53 is involved in WSSV infection. Here is the first time showed the role of shrimp F₁-ATP synthase beta subunit in WSSV infection.

Ancient cytokines, the role of astakines as hematopoietic growth factors

Hematopoiesis is the process by which hemocytes mature and subsequently enter the circulation. Vertebrate prokineticins (PKs) are known to take part in this process, as are the invertebrate prokineticin domain proteins, astakines. In Pacifastacus leniusculus, astakine 1 is essential for the release of new hemocytes into the open circulatory system of these animals. In addition to astakine 1, we have now cloned a homologue of astakine 1 with an insert of 13 amino acids, named as astakine 2. Both crustacean astakines lack the N-terminal AVIT motif, which is present in vertebrate PKs, and hence receptor binding differs from that of vertebrate PKs. We have found astakine-like sequences in 19 different invertebrate species, and the sequences show that some motifs are conserved among invertebrate groups. Previously we showed that astakine 1 is directly involved in hematopoiesis, and now we show that astakine 1 and astakine 2 have different roles in hemocyte lineage differentiation. Astakine 1 can stimulate proliferation of hematopoietic tissue (Hpt) cells (precursor of hemocytes) as well as specifically induce differentiation of Hpt cells along the semigranular cell lineage, whereas astakine 2 plays a role in granular cell differentiation. Moreover, we discuss the impact of the putative structures of different astakines in comparison with the vertebrate prokineticins.

A novel viral responsive protein is involved in hemocyte homeostasis in the black tiger shrimp, Penaeus monodon

A novel viral responsive protein, namely hemocyte homeostasis-associated protein (HHAP), was characterized for its role in the response of shrimp to white spot syndrome virus infection. The full-length cDNAs of HHAP from the black tiger shrimp (PmHHAP), Penaeus monodon, and the fresh water crayfish (PlHHAP), Pacifastacus leniusculus, were obtained and showed high sequence identity to a hypothetical protein from various organisms, with the highest identity to the hypothetical protein TcasGA2_TC006773 from the red flour beetle, Tribolium castaneum (54% amino acid sequence identity). Transcripts of PmHHAP were expressed in various shrimp tissues with the highest expression in hematopoietic tissue, whereas the transcripts of PlHHAP were found in the hematopoietic and nerve tissues. Upon white spot syndrome virus infection, a high up-regulation level of shrimp hemocytic HHAP mRNA and protein was observed by real-time reverse transcription-PCR and immunofluorescence microscopy, respectively. Gene silencing of PmHHAP by RNA interference resulted in a significant decrease in the number of circulating hemocytes and 100% shrimp mortality within 30 h of the double-stranded PmHHAP RNA injection (but not in control shrimp), indicating that HHAP is essential for shrimp survival. Interestingly, severe damage of hemocytes was observed in vivo in the PmHHAP knockdown shrimp and in vitro in shrimp primary hemocyte cell culture, suggesting that PmHHAP plays an important role in hemocyte homeostasis. Thus, it is speculated that the up-regulation of PmHHAP is an important mechanism to control circulating hemocyte levels in crustaceans during viral infection.