Diptericin expression in bacteria infected Drosophila mbn-2 cells - effect of infection dose and phagocytosis.

Drosophila haemocytes play a key role in defence against microbial aggression. Their capacity to sense and dispose of bacteria and also to signal to other immune tissues is probably vital to overcome an infection. In this work we used the haemocyte-like mbn-2 cell line to investigate how expression of the antimicrobial peptide diptericin is affected after a high dose bacterial challenge with diaminopimelic acid (DAP)-peptidoglycan Gram-positive and Gram-negative bacteria. We report that diptericin expression is negatively affected by high infection dose and rapid bacterial growth regardless of the type of infection and bacterial virulence and occurs in the absence of mbn-2 cell death. Furthermore we show that the mbn-2 cell population is heterogeneous, containing both phagocytic and nonphagocytic cells and that contact with large numbers of bacteria decreases diptericin expression in the phagocytic cell population.

Detection of genomic DNA of the crayfish plague fungus Aphanomyces astaci (Oomycete) in clinical samples by PCR.

A diagnostic procedure, based on a polymerase chain reaction method (PCR) was developed to detect infection of crayfish with the Oomycete Aphanomyces astaci. A set of oligonucleotide primers was designed to specifically amplify A. astaci DNA in the ITS region surrounding the 5.8S rDNA gene. The PCR amplifies a 115bp amplicon. The specificity of the primers was demonstrated by testing on 27 A. astaci strains and against 20 non-A. astaci Oomycetes and 5 fungal species. Most of the non-A. astaci Oomycete or fungal species included in the study are either known parasites of freshwater crayfish cuticle or can be found in their natural environment. Specificity was also tested against crayfish tissue and some known parasites and bacteria infecting crayfish. A protocol for the extraction of A. astaci DNA from infected crayfish tissue was developed. The optimised method allows the detection of two genome equivalents of purified A. astaci genomic DNA. The method was tested on noble crayfish (Astacus astacus), artificially infected with A. astaci. Detection of A. astaci was possible at the very first time of sampling, which was 2 days after the beginning of spore exposure.

Molecular characterization of the fish-pathogenic fungus Aphanomyces invadans.

Aphanomyces invadans (Saprolegniaceae) is a peronosporomycete fungus associated with the serious fish disease, epizootic ulcerative syndrome (EUS), also known as mycotic granulomatosis. In this study, interspecific relationships were examined between A. invadans isolates and other aquatic animal pathogenic Saprolegniaceae, and saprophytic Saprolegniaceae from EUS-affected areas. Restriction fragment length polymorphisms and sequences of ribosomal DNA confirmed that A. invadans is distinct from all other species studied. A sequence from the internal transcribed spacer region ITS1, unique to A. invadans, was used to design primers for a PCR-based diagnostic test. Intraspecific relationships were also examined by random amplification of polymorphic DNA using 20 isolates of A. invadans from six countries. The isolates showed a high degree of genetic homogeneity using 14 random ten-mer primers. This provides evidence that the fungus has spread across Asia in one relatively rapid episode, which is consistent with reports of outbreaks of EUS. Physiological distinctions between A. invadans and other Aphanomyces species based on a data set of 16 growth parameters showed remarkable taxonomic congruence with the molecular phylogeny.

Enteric bacteria counteract lipopolysaccharide induction of antimicrobial peptide genes.

The humoral immunity of Drosophila involves the production of antimicrobial peptides, which are induced by evolutionary conserved microbial molecules, like LPS. By using Drosophila mbn-2 cells, we found that live bacteria, including E. coli, Salmonella typhimurium, Erwinia carotovora, and Pseudomonas aeruginosa, prevented LPS from inducing antimicrobial peptide genes, while Micrococcus luteus and Streptococcus equi did not. The inhibitory effect was seen at bacterial levels from 20 per mbn-2 cell, while antimicrobial peptides were induced at lower bacterial concentrations (< or =2 bacteria per cell) also in the absence of added LPS. Gel shift experiment suggests that the inhibitory effect is upstream or at the level of the activation of the transcription factor Relish, a member of the NF-kappaB/Rel family. The bacteria have to be in physical contact with the cells, but not phagocytosed, to prevent LPS induction. Interestingly, the inhibiting mechanism is, at least for E. coli, independent of the type III secretion system, indicating that the inhibitory mechanism is unrelated to the one earlier described for YopJ from Yersinia.

Sequence analysis of the ribosomal internal transcribed spacer DNA of the crayfish parasite Psorospermium haeckeli.

Two morphotypes of the crayfish parasite Psorospermium haeckeli were isolated from 2 crayfish species of different geographical origin. The oval-shaped sporocysts were obtained from the epidermal and connective tissue beneath the carapace of the noble crayfish Astacus astacus from Sweden and Finland. Elongated spores were isolated from the abdominal muscle tissue of the red swamp crayfish Procambarus clarkii from USA. To compare genetic divergence of 2 morphotypes of the parasite, the ribosomal internal transcribed spacer (ITS) DNA (ITS 1 and ITS 2) and the 5.8S rRNA gene were cloned and sequenced. The analysed region is variable in length, with the ribosomal ITS sequence of the European morphotype longer than the North American one. Sequence diversity is found mainly in ITS 1 and ITS 2 regions, and there is 66% and 58% similarity between the 2 morphotypes, respectively. Thus, analysis of the ribosomal ITS DNA suggests that P. haeckeli forms obtained from Europe and North America are genetically diverse, which supports the previously reported morphological characteristics.

A transglutaminase involved in the coagulation system of the freshwater crayfish, Pacifastacus leniusculus. Tissue localisation and cDNA cloning.

The crayfish haemolymph can form stable and insoluble clots by a transglutaminase (TGase)-catalysed crosslinking reaction between the soluble clotting protein molecules from the plasma. The crayfish haemocytes, both semigranular and granular cells, as well as the muscle tissue, contain TGase activity, whereas the hepatopancreas and plasma have no TGase activity. A 3199 bp cDNA encoding a TGase was isolated from a crayfish haemocyte cDNA library. The deduced protein comprises 766 amino acid residues and has a calculated molecular mass of between 85,930 and 86,034 kDa due to four amino acid variations. This gene is expressed as a single 4.9 kb transcript exclusively in the haemocytes and at very low levels in muscle and the hepatopancreas. Sequence comparison shows that this TGase has significant similarities to other TGases from invertebrates and mammals.

Characterization of a pattern recognition protein, a masquerade-like protein, in the freshwater crayfish Pacifastacus leniusculus.

A multifunctional masquerade-like protein has been isolated, purified, and characterized from hemocytes of the freshwater crayfish, Pacifastacus leniusculus. It was isolated by its Escherichia coli binding property, and it binds to formaldehyde-treated Gram-negative bacteria as well as to yeast, Saccharomyces cerevisiae, whereas it does not bind to formaldehyde-fixed Gram-positive bacteria. The intact masquerade (mas)-like protein is present in crayfish hemocytes as a heterodimer composed of two subunits with molecular masses of 134 and 129 kDa. Under reducing conditions the molecular masses of the intact proteins are not changed. After binding to bacteria or yeast cell walls, the mas-like protein is processed by a proteolytic enzyme. The 134 kDa of the processed protein yields four subunits of 65, 47, 33, and 29 kDa, and the 129-kDa protein results in four subunits of 63, 47, 33, and 29 kDa in 10% SDS-PAGE under reducing conditions. The 33-kDa protein could be purified by immunoaffinity chromatography using an Ab to the C-terminal part of the mas-like protein. This subunit of the mas-like protein has cell adhesion activity, whereas the two intact proteins, 134 and 129 kDa, have binding activity to LPSs, glucans, Gram-negative bacteria, and yeast. E. coli coated with the mas-like protein were more rapidly cleared in crayfish than only E. coli, suggesting this protein is an opsonin. Therefore, the cell adhesion and opsonic activities of the mas-like protein suggest that it plays a role as an innate immune protein.

Molecular cloning and characterization of two serine proteinase genes from the crayfish plague fungus, Aphanomyces astaci.

Two novel genes encoding the serine proteinases, subtilisin (AaSP1) and trypsin (AaSP2), from Aphanomyces astaci were identified. Based on the amino acidconsensus sequences around the catalytic triad of these serine proteinases, degenerated oligonucleotides were designed for isolation of serine proteinase genes from a genomic DNA library. The AaSP1 gene encodes a full-length protein of 515 amino acids as a large precursor of 56 kDa. After cleavage of a predicted leader sequence of 18 residues and a prepeptide of 133 amino acids, the mature enzyme of 364 amino acids is generated with a calculated molecular mass of 39 kDa and a pI of 6.0. The primary sequence of AaSP1 showed similarity to both bacterial subtilisin and fungal subtilisin-like serine proteinases. Southern blot analysis of AaSP1 revealed the presence of at least two subtilisin genes in the A. astaci genome. Northern blot analysis indicated that the size of AaSP1 transcript was 1.6 kb. The AaSP2 gene encodes a prepropeptide of 276 amino acids with a molecular mass of 29 kDa. A mature protein of 237 amino acids is probably generated after cleavage of a 17-residue signal peptide and a 21-amino-acid prepeptide with a predicted molecular mass of 25 kDa and a pI of 6.0. The primary sequence of AaSP2 showed similarity to trypsin enzymes from various organisms. Southern blot analysis revealed the presence of multiple trypsin genes in the A. astaci genome. Northern blot analysis indicated that the size of AaSP2 transcript was 1.0 kb. The regulation of AaSP2 transcription was not controlled by nitrogen catabolic repression. However, the expression of AaSP2 was found to be specifically induced by crayfish plasma, implying a role in pathogenesis toward the crayfish host.

Peroxinectin, a cell adhesive protein associated with the proPO system from the black tiger shrimp, Penaeus monodon.

Upon activation of the prophenoloxidase activating system in the shrimp, Penaeus monodon, a cell adhesion activity in the haemolymph is generated. A cell adhesion assay showed that a high number of granular cells (60%) adhered to coverslips coated with a shrimp haemocyte lysate supernatant, whereas a very low number of cells adhered to coverslips coated with bovine serum albumin. Inhibition of adhesion by an antiserum against crayfish peroxinectin, a cell adhesion protein, revealed that the cell adhesion activity detected in shrimp haemocyte lysate supernatant might result from a peroxinectin-like molecule in shrimp. A cDNA clone encoding shrimp peroxinectin was isolated, which had an open reading frame of 2337 nucleotides, with a polyadenylation sequence and a poly A tail. It encodes a protein of 778 amino acids including a 20 amino acid signal peptide. The mature protein (758 amino acids) has a predicted molecular mass of 84.8kDa and an estimated pI of 9.0. Two putative integrin binding motifs, RGD (Arg-Gly-Asp) and KGD (Lys-Gly-Asp), were found in shrimp peroxinectin. Sequence comparison shows that the shrimp protein is similar to crayfish peroxinectin (69%) and to various peroxidases and putative peroxidases from invertebrates and vertebrates. The shrimp peroxinectin cDNA also shows similarity (51%) to both Drosophila peroxinectin-related protein (AAF78217) and peroxidasin (S46224), an extracellular matrix protein combining an active peroxidase domain as well as immunoglobulin domains, leucine rich repeats and procollagen-like motif. However, the sequence similarity to both Drosophila molecules are mostly within the peroxidase domain. Northern blot analysis, using a non-peroxidase region in peroxinectin as a probe, revealed that peroxinectin is constitutively expressed in shrimp haemocyte and was reduced significantly in shrimp injected with a beta-1,3-glucan, laminarin, to mimic an infection with a fungus.

Properties of the prophenoloxidase activating enzyme of the freshwater crayfish, Pacifastacus leniusculus.

The prophenoloxidase activating enzyme (ppA), a serine proteinase catalyzing the conversion of prophenoloxidase to an active phenoloxidase, has a molecular mass of about 36 kDa in its active form. This protein was cloned from a blood cell cDNA library and its corresponding cDNA of 1736 base pairs encodes a zymogenic protein (proppA) of 468 amino acids. An antibody raised against a synthetic peptide derived from a region of the cDNA sequence could efficiently inhibit the beta-1,3-glucan triggered activation of prophenoloxidase in vitro. The C-terminal half of the proppA is composed of a typical serine proteinase domain, with a sequence similar to other invertebrate and vertebrate serine proteinases. The N-terminal half contains a cationic glycine-rich domain, a cationic proline-rich domain and a clip-domain, in which the disulfide-bonding pattern is likely to be identical to those of the horseshoe crab big defensin and mammalian beta-defensins. Antibodies made against both the C- and the N-terminal halves recognize two proppAs under reducing conditions. However, under nonreducing conditions only the anti-C antibody recognized the two proppAs, which suggests that a conformational change takes place upon reduction that allows the anti-N to react with the N-terminal half of proppA. The recombinant clip-domain in crayfish proppA was overexpressed in Escherichia coli and the resulting peptide exhibited antibacterial activity against Gram-positive bacterial strains such as Micrococcus luteus Ml11 and Bacillus megaterium Bm11 with 50% growth inhibitory concentrations of 1.43 microM and 17.9 microM, respectively. These results suggest that the clip-domains in proppAs may function as antibacterial peptides.

Experimental infection of white spot syndrome virus in freshwater crayfish Pacifastacus leniusculus.

The signal freshwater crayfish Pacifastacus leniusculus was found to be susceptible to infection with white spot syndrome virus (WSSV). Histopathological observations of various tissues of virus-injected crayfish showed similar symptoms to those from WSSV-infected penaeid shrimp, but no appearance of white spots on the cuticle or reddish body colour were observed, although these are the prominent gross signs of white spot disease in shrimp. A gene probe for detecting WSSV was developed in order to detect the virus in affected cells and tissues using in situ hybridisation. Strong signals were observed in cells of virus-injected crayfish, but not in control-injected crayfish. The number of granular haemocytes in virus-injected crayfish was significantly higher than in sham-injected and non-injected crayfish from Days 5 to 8 (p < or = 0.05) and Days 3 to 8 (p < 0.01) post-injection, respectively. The proportion of granular haemocytes in virus-injected crayfish was also significantly higher than in sham-injected controls from Days 3 to 8 (p < 0.01). These results indicate that WSSV has a significant effect on the proportion of different haemocyte types in the freshwater crayfish.

A cell adhesion protein from the crayfish Pacifastacus leniusculus, a serine proteinase homologue similar to Drosophila masquerade.

A cDNA encoding a protein resembling masquerade, a serine proteinase homologue expressed during embryogenesis, larval, and pupal development in Drosophila melanogaster, was identified in hemocytes of the adult freshwater crayfish, Pacifastacus leniusculus. The crayfish protein is similar to Drosophila masquerade in the following aspects: (a) overall sequence of the serine proteinase domain, such as the position of three putative disulfide bridges, glycine in the place of the catalytic serine residue, and the presence of a substrate-lining pocket typical for trypsins; (b) the presence of several copies of a disulfide-knotted motif in the putative propeptide. This masquerade-like protein is cleaved into a 27-kDa fragment, which could be detected by immunoblot analysis using an affinity-purified antibody against a synthetic peptide in the C-terminal domain of the protein. The 27-kDa protein could be immunoaffinity-purified from hemocyte lysate supernatant and exhibited cell adhesion activity in vitro, indicating that the C-terminal domain of the crayfish masquerade-like protein mediates cell adhesion.

A lipopolysaccharide- and beta-1,3-glucan-binding protein from hemocytes of the freshwater crayfish Pacifastacus leniusculus. Purification, characterization, and cDNA cloning.

A lipopolysaccharide- and beta-1,3-glucan-binding protein (LGBP) was isolated and characterized from blood cells (hemocytes) of the freshwater crayfish Pacifastacus leniusculus. The LGBP was purified by chromatography on Blue-Sepharose and phenyl-Sepharose, followed by Sephacryl S-200. The LGBP has a molecular mass of 36 kDa and 40 kDa on 10% SDS-polyacrylamide gel electrophoresis under reducing and nonreducing conditions, respectively. The calculated mass of LGBP is 39,492 Da, which corresponds to the native size of LGBP; the estimated pI of the mature LGBP is 5.80. LGBP has binding activity to lipopolysaccharides as well as to beta-1,3-glucans such as laminarin and curdlan, but peptidoglycan could not bind to LGBP. Cloning and sequencing of LGBP showed significant homology with several putative Gram-negative bacteria-binding proteins and beta-1, 3-glucanases. Interestingly, LGBP also has a structure and functions similar to those of the coelomic cytolytic factor-1, a lipopolysaccharide- and glucan-binding protein from the earthworm Eisenia foetida. To evaluate the involvement of LGBP in the prophenoloxidase (proPO) activating system, a polyclonal antibody against LGBP was made and used for the inhibition of phenoloxidase (PO) activity triggered by the beta-1,3-glucan laminarin in the hemocyte lysate of crayfish. The PO activity was blocked completely by the anti-LGBP antibody. Moreover, the PO activity could be recovered by the addition of purified LGBP. These results suggest that the 36-kDa LGBP plays a role in the activation of the proPO activating system in crayfish and thus seems to play an important role in the innate immune system of crayfish.

Molecular cloning and characterization of prophenoloxidase in the black tiger shrimp, Penaeus monodon.

A cDNA encoding shrimp, Penaeus monodon, prophenoloxidase (proPO) was obtained by screening a hemocyte library by plaque hybridization using a proPO cDNA fragment from freshwater crayfish, Pacifastaceus leniusculus, as a probe. The 3,002 bp cDNA contains an open reading frame of 2,121 bp and a 881 bp 3'-untranslated region. The molecular mass of the deduced amino acid sequence (688 amino acids) is 78,700 Da with an estimated pI of 5.8. Two putative copper binding sites are present and they have a highly conserved sequence around these sites. No signal peptide was detected in the shrimp proPO, as has been previously shown to be the case for all arthropod proPOs cloned so far. The cleavage site of zymogen activation is likely to be between Arg 44 and Val 45. A tentative complement-like motif (GCGWPQHM) is also present. Shrimp proPO mRNA is synthesized in the hemocytes and not in the hepatopancreas. Comparison of amino acid sequences showed that shrimp proPO is more closely related to another crustacean proPO, namely crayfish, than to the insect proPOs.

Trypsin from Pacifastacus leniusculus hepatopancreas: purification and cDNA cloning of the synthesized zymogen.

Trypsin was purified from crayfish, Pacifastacus leniusculus, hepatopancreas, and the gene that encoded this enzyme was cloned from a hepatopancreas cDNA library. Crayfish trypsin is synthesized as a zymogen according to the sequence of the putative precursor peptide. The authenticity of the trypsinogen is supported by the deduced amino acid sequence and confirmed by the N-terminal amino acid sequence of the mature protein. The enzyme has features characteristic of a trypsin, such as a specific binding pocket. Sequence comparison shows that crayfish trypsin is similar to those of other species, with the exception that six cysteine residues present in vertebrates are missing. Some structural characteristics, such as the length of the signal peptide and a calcium binding site, are similar to bacterial trypsin.

The crayfish plasma clotting protein: a vitellogenin-related protein responsible for clot formation in crustacean blood.

Coagulation in crayfish blood is based on the transglutaminase-mediated crosslinking of a specific plasma clotting protein. Here we report the cloning of the subunit of this clotting protein from a crayfish hepatopancreas cDNA library. The ORF encodes a protein of 1,721 amino acids, including a signal peptide of 15 amino acids. Sequence analysis reveals that the clotting protein is homologous to vitellogenins, which are proteins found in vitellogenic females of egg-laying animals. The clotting protein and vitellogenins are all lipoproteins and share a limited sequence similarity to certain other lipoproteins (e.g., mammalian apolipoprotein B and microsomal triglyceride transfer protein) and contain a stretch with similarity to the D domain of mammalian von Willebrand factor. The crayfish clotting protein is present in both sexes, unlike the female-specific vitellogenins. Electron microscopy was used to visualize individual clotting protein molecules and to study the transglutaminase-mediated clotting reaction. In the presence of an endogenous transglutaminase, the purified clotting protein molecules rapidly assemble into long, flexible chains that occasionally branch.

An atypical iron-responsive element (IRE) within crayfish ferritin mRNA and an iron regulatory protein 1 (IRP1)-like protein from crayfish hepatopancreas.

A putative crayfish iron-responsive element (IRE) is present in the 5'-untranslated region of the crayfish ferritin mRNA. The putative crayfish IRE is in a cap-proximal position and shares most of the structural features of the consensus IRE, but the RNA stem-loop structure contains a bulge of a guanine instead of a cytosine at the expected position, so far thought to be a hallmark of IREs. By using an electromobility shift assay this IRE was shown to specifically bind purified recombinant human iron regulatory protein 1 (IRP1) as well as a factor(s) present in a homogenate of crayfish hepatopancreas, likely to be a crayfish IRP1 homologue. With mutations in the crayfish IRE, the affinity of IRP to IRE was drastically decreased. A cDNA encoding an IRP1-like protein was cloned from the hepatopancreas of crayfish. This protein has sequence similarities to IRP, and contains all the active-site residues of aconitase, two putative RNA-binding regions and a putative contact site between RNA and IRP. These results show that a crayfish IRE, lacking the bulged C, can bind IRP1 in vitro and that an IRP1-like protein present in crayfish hepatopancreas may have both aconitase and RNA-binding activities.

A cell-surface superoxide dismutase is a binding protein for peroxinectin, a cell-adhesive peroxidase in crayfish.

Peroxinectin, a cell-adhesive peroxidase (homologous to human myeloperoxidase), from the crayfish Pacifastacus leniusculus, was shown by immuno-fluorescence to bind to the surface of crayfish blood cells (haemocytes). In order to identify a cell surface receptor for peroxinectin, labelled peroxinectin was incubated with a blot of haemocyte membrane proteins. It was found to specifically bind two bands of 230 and 90 kDa; this binding was decreased in the presence of unlabelled peroxinectin. Purified 230/90 kDa complex also bound peroxinectin in the same assay. In addition, the 230 kDa band binds the crayfish beta-1,3-glucan-binding protein. The 230 kDa band could be reduced to 90 kDa, thus showing that the 230 kDa is a multimer of 90 kDa units. The peroxinectin-binding protein was cloned from a haemocyte cDNA library, using immuno-screening or polymerase chain reaction based on partial amino acid sequence of the purified protein. It has a signal sequence, a domain homologous to CuZn-containing superoxide dismutases, and a basic, proline-rich, C-terminal tail, but no membrane-spanning segment. In accordance, the 90 and 230 kDa bands had superoxide dismutase activity. Immuno-fluorescence of non-permeabilized haemocytes with affinity-purified antibodies confirmed that the crayfish CuZn-superoxide dismutase is localized at the cell surface; it could be released from the membrane with high salt. It was thus concluded that the peroxinectin-binding protein is an extracellular SOD (EC-SOD) and a peripheral membrane protein, presumably kept at the cell surface via ionic interaction with its C-terminal region. This interaction with a peroxidase seems to be a novel function for an SOD. The binding of the cell surface SOD to the cell-adhesive/opsonic peroxinectin may mediate, or regulate, cell adhesion and phagocytosis; it may also be important for efficient localized production of microbicidal substances.