In vivo and in vitro studies using larval and adult antigens from Neobenedenia melleni on immune response in yellowtail (Seriola lalandi)

Neobenedenia melleni is a monogenean parasite that causes significant mortality and economic losses in fish aquaculture. Changes in the antigenic composition of this parasite occur during its developmental stages. In this study, we evaluated humoral parameters in serum and transcriptional immune responses of yellowtail naturally infected with N. melleni. In addition, in vitro assays were performed to study the stimulatory effects of antigens from larvae and adults on spleen leucocytes from non-infected fish at 6 and 24 h post-stimulation. The results showed enhanced total protein, myeloperoxidase and antiprotease activities in N. melleni-infected fish compared with non-infected ones. The induction of Toll-like receptors (TLRs) and pro-inflammatory cytokines in spleen leucocytes during natural infection with N. melleni suggests that these immune-related genes play an important role in the initiation of the immune defence mechanism for controlling parasite infection. Interestingly, the magnitude of in vitro responses of spleen leucocytes was dependent on the parasitic stage. An important stimulation of gene expression by adult antigens on spleen leucocytes was observed. Differential expression patterns of TLRs and target cytokines in yellowtail leucocytes in both in vivo and in vitro studies suggest that the quality of yellowtail immune response is conditioned by N. melleni development.

Virulence of acute hepatopancreatic necrosis disease PirAB-like relies on secreted proteins not on gene copy number

AIMS

To investigate the virulence of the Vp_PirAB-like genes in Vibrio parahaemolyticus- acute hepatopancreatic necrosis disease (AHPND)-causing strain and the factors that are associated with the virulence level.

METHODS AND RESULTS

The virulence of Vp_PirAB-like was examined using a non-virulent strain FP11 of V. parahaemolyticus transformed with a plasmid harbouring Vp_PirAB-like genes and then it was used to challenge shrimp Litopenaeus vannamei and Marsupenaeus japonicus. Both species experienced 100% mortality at 10 days post infection. Analysis of a mutant strain (E1M), that was originally identified as virulent strain (E1) but lost its virulence to L. vannamei, revealed that it lacked a part of the Vp_PirA-like gene and all of the Vp_PirB-like gene. The copy numbers of Vp_PirA-like and Vp_PirB-like genes varied among virulent strains and were not correlated with their virulence. In Western blotting, Vp_PirA-like and Vp_PirB-like proteins were detected in both the cell lysate and the culture supernatant. The strongest intensity of detecting band in the culture supernatant was observed in the strain that caused the highest mortality. The V. parahaemolyticus AHPND-causing strain, unlike the human tdh-positive strain, did not show any enterotoxicity.

CONCLUSION

Vibrio parahaemolyticus AHPND-causing strains secrete the Vp_PirA-like and Vp_PirB-like proteins during the growing phase. The amount of secreted proteins affects the shrimp mortality.

SIGNIFICANCE AND IMPACT OF THE STUDY

The secreted proteins of Vp_PirAB-like are key factors of virulence in the V. parahaemolyticus AHPND-causing strain, but not gene copy.

Inhibition of Hirame rhabdovirus growth by RNA aptamers

RNA aptamers are artificial nucleic acids that specifically bind to a wide variety of targets. They are an effective tool for pharmaceutical research and development of antiviral agents. Here, we describe four Hirame rhabdovirus (HIRRV)-RNA aptamers (H1, H2, H3 and H4) that we obtained from an in vitro process called the systematic evolution of ligands by exponential enrichment (SELEX). The HIRRV-RNA aptamers specifically bind to HIRRV. Hirame natural embryo (HINAE) cells treated with virus and the RNA aptamer showed a decrease in appearance of cytopathic effect when compared with control (treated only with virus). Rhodovulum sulfidophilum was transformed with genes for the RNA aptamers, and the aptamers were detected in the culture medium, indicating that they were secreted from the cells. Thus, the recombinant R. sulfidophilum might be a powerful tool for the prevention of HIRRV in aquaculture.

Drug resistance mechanism of the fish-pathogenic bacterium Lactococcus garvieae

The minimum inhibitory concentrations (MICs) of 15 chemotherapeutic agents were tested against 146 Lactococcus garvieae strains isolated from 1999 to 2006 in Japan. The agents used included chloramphenicol, ciprofloxacin, erythromycin (EM), enoxacin, fleroxacin, florfenicol, kanamycin, lincomycin (LCM), norfloxacin, oxolinic acid, orbifloxacin, ofloxacin, benzylpenicillin, streptomycin and tetracycline (TC). Of the tested strains, 46 showed high levels of resistance to EM, LCM and TC. Twelve of these strains were detected to be carrying transferable R-plasmids using a conjugation experiment and, using Southern hybridization, were shown to have the same structure as the R-plasmid. The remaining 34 resistant strains had a similar DNA structure to that of the R-plasmid as confirmed by polymerase chain reaction (PCR) using primers designed from sites in the transferable R-plasmid. The EM and TC resistance genes were classified into the ermB and tetS groups using PCR. We also detected gyrA and/or parC mutants that are highly resistant to old and new generation quinolones. This study revealed that transferable R-plasmids encoding EM, LCM and TC are widely distributed and are conserved regardless of the area and/or time of collection.

Cloning and characterization of Photobacterium damselae ssp. piscicida phospholipase: an enzyme that shows haemolytic activity

A phospholipase gene of Photobacterium damselae ssp. piscicida (ppp) was cloned from a genomic library and its nucleotide sequence was determined. The open reading frame consisted of 1218 bp encoding a protein of 405 amino acids with a predicted molecular mass of 46 kDa. The PPP had identities (53-55%) with phospholipase and haemolysin of Vibrio spp., while it showed low identities (23-26%) with glycerophospholipid cholesterol acyltransferase of Aeromonas spp. A recombinant PPP (rPPP) with a His tag at the C-terminus expressed in Escherichia coli and purified showed phospholipase activity. The rPPP also showed lecithin-dependent haemolytic activity against mammalian erythrocytes and direct haemolytic activity against fish erythrocytes. The culture supernatant of wild-type P. damselae ssp. piscicida showed phospholipase activity, while that of a PPP gene knockout mutant did not.

Immune modulation and expression of cytokine genes in rainbow trout Oncorhynchus mykiss upon probiotic feeding

This study elucidates the immune modulation including the expression of cytokine genes following dietary administration of three selected probiotic bacteria--Lactobacillus rhamnosus, Enterococcus faecium and Bacillus subtilis to fish, rainbow trout Oncorhynchus mykiss. They were fed for 45 days on either a basal control diet or one of the three probiotic diets containing the specific bacteria in freeze-dried form at a density of 10(9)CFUgfeed-1. The non-specific immune parameters examined--superoxide anion production by the head kidney leukocytes and the alternate complement activity of serum was improved by probiotic feeding. Besides this, the relative gene expressions of interleukin-1beta1, tumor necrosis factor 1 and 2 and transforming growth factor-beta were up regulated in the spleen and the head kidney. The comparatively better performance of E. faecium could possibly be linked to their suitable ambient temperature conditions. Thus, probiotic bacteria delivered in feed exerts its influence on the immune system of fish, both at cellular and molecular levels.

Putative virulence-related genes in Vibrio anguillarum identified by random genome sequencing

The genome of Vibrio anguillarum strain H775-3 was partially determined by a random sequencing procedure. A total of 2,300 clones, 2,100 from a plasmid library and 200 from a cosmid library, were sequenced and subjected to homology search by the BLAST algorithm. The total length of the sequenced clones is 1.5 Mbp. The nucleotide sequences were classified into 17 broad functional categories. Forty putative virulence-related genes were identified, 36 of which are novel in V. anguillarum, including a repeat in toxin gene cluster, haemolysin genes, enterobactin gene, protease genes, lipopolysaccharide biosynthesis genes, capsule biosynthesis gene, flagellar genes and pilus genes.

Detection of quinolone-resistance genes in Photobacterium damselae subsp. piscicida strains by targeting-induced local lesions in genomes

Quinolone-resistant strains of the fish-pathogenic bacterium, Photobacterium damselae subsp. piscicida are distributed widely in cultured yellowtail, Seriola quinqueradiata (Temminck & Schlegel), in Japan. The quinolone resistance-determining region (QRDR) was amplified with degenerate primers, followed by cassette ligation-mediated PCR. Open reading frames encoding proteins of 875 and 755 amino acid residues were detected in the gyrA and parC genes, respectively. Resistant strains of P. damselae subsp. piscicida carried a point mutation only in the gyrA QRDR leading to a Ser-to-Ile substitution at residue position 83. No amino acid alterations were discovered in the ParC sequence. A mutation in the gyrA gene was also detected in nalidixic acid-resistant mutants of strain SP96002 obtained from agar medium containing increased levels of quinolone. These results suggest that GyrA, as in other Gram-negative bacteria, is a target of quinolone in P. damselae subsp. piscicida. Furthermore, we attempted to detect a point mutation using targeting-induced local lesions in genomes (TILLING), which is a general strategy used for the detection of a variety of induced point mutations and naturally occurring polymorphisms. We developed a new detection method for the rapid and large-scale identification of quinolone-resistant strains of P. damselae subsp. piscicida using TILLING.

Molecular cloning and functional analysis of Photobacterium damselae subsp. piscicida haem receptor gene

A haem receptor gene from Photobacterium damselae subsp. piscicida (formerly known as Pasteurella piscicida) has been cloned, sequenced and analysed for its function. The gene, designated as pph, has an open reading frame consisting of 2154 bp, a predicted 718 amino acid residues and exists as a single copy. It is homologous with the haem receptors of Vibrio anguillarum hupA, V. cholerae hutA, V. mimicus mhuA and V. vulnificus hupA at 32.7, 32.7, 45.6 and 30.9%, respectively, and is highly conserved, consisting of a Phe-Arg-Ala-Pro sequence (FRAP), an iron transport related molecule (TonB) and a Asn-Pron-Asn-Leu sequence (NPNL), binding motifs associated with haem receptors. As a single gene knockout mutant P. damselae subsp. piscicida was able to bind haem in the absence of pph, suggesting that other receptors may be involved in its iron transport system. This study shows that the P. damselae subsp. piscicida pph belongs to the haem receptor family, is conserved and that its iron-binding system may involve more than one receptor.

Genetic diversity and molecular markers of the tropical abalone (Haliotis asinina) in Thailand

Genetic diversity of abalone in Thailand, Haliotis asinina, H. ovina, and H. varia, was analyzed by polymerase chain reaction (PCR) of 18S and 16S rDNAs, with randomly amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP). Species-specific RAPD markers were found in each abalone species. Restriction analysis of 18S (nuclear) ribosomal DNA with Alu I, Taq I, and Hae III and 16S (mitochondrial) rDNA with Bam HI, Eco RI, Hae III, and Alu I gave 12 and 13 digestion patterns, respectively. A total of 49 composite haplotypes were found. A dendogram obtained by the unweighted pair-group method with arithmetic mean, constructed from divergence between pairs of composite haplotypes, revealed reproductively isolated gene pools of these abalone and indicated that H. asinina and H. ovina are genetically closer than H. varia. When H. varia was discovered owing to small sample sizes, geographic heterogeneity analysis and FST estimate indicated clear genetic differentiation between H. ovina originating from the Andaman Sea (west) and the Gulf of Thailand (east, P<0.0001), whereas partial differentiation was observed between the Philippines and the remaining H. asinina samples (P<0.0021). The amplified 16S rDNAs of individuals representing composite haplotypes found in this study were cloned and sequenced. A neighbor-joining tree constructed from sequence divergence of 16S rDNA accurately allocated those sequences according to species origins of abalone. Species-specific PCR based on 16S rDNA polymorphism was successfully developed in H. asinina and H. varia but not in H. ovina.

Inhibition of N-ethyl-N'-nitro-N-nitrosoguanidine-induced Duodenal Tumorigenesis in Mice by Whole-leaf Aloe arborescens Miller var. natalensis Berger

We examined the modifying effects of freeze-dried whole-leaf Aloe arborescens Miller var. natalensis Berger (designated as 'ALOE') on N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG)-induced duodenal tumorigenesis in C57BL/6 mice. Experiment 1: Male mice were given ENNG in drinking water for the first 4 weeks, and then 10% ALOE in basal diet for 16 weeks. Experiment 2: Female mice were given ENNG for 5 weeks, and then 5%, 1% or 0.2% ALOE in the diet were given for 15 weeks. In Experiment 1, the tumor incidence and tumor multiplicity (tumors per mouse) of the duodenum in the ENNG + 10% ALOE group were significantly decreased compared with that in the ENNG alone group. Erythrocyte polyamine levels in the ENNG + 10% ALOE group were also significantly decreased. In Experiment 2, the incidence of duodenal tumors in the ENNG + 5% ALOE group were significantly decreased compared with that in the ENNG alone group. These results indicated that ALOE, especially at 10% in the diet, inhibits ENNG-induced duodenal tumorigenesis in mice.

Differential expression of two tumor necrosis factor genes in rainbow trout, Oncorhynchus mykiss

A second TNF gene (TNF2) has been cloned and sequenced in rainbow trout. In common with the first TNF gene isolated (TNF1), this gene is more TNF alpha-like than TNF beta-like. The full length cDNA is 1519bp, containing a 765bp open reading frame. The gene has four exons, of 380, 49, 60 and 1030bp, respectively. Analysis of the 5' flanking regions of TNF1 and TNF2 reveals several interesting differences in identified transcriptional regulatory elements, with a CATAAA box present 26bp upstream of the transcription start in both genes. Expression analysis in LPS stimulated macrophages has shown a much stronger expression of TNF2 relative to TNF1, with expression being detected earlier and lasting longer.

Construction and characterization of BAC libraries for three fish species; rainbow trout, carp and tilapia

Bacterial artificial chromosome (BAC) libraries are important tools for genomic research. We have constructed seven genomic BAC libraries from three fish species, rainbow trout (Oncorhynchus mykiss), carp (Cyprinus carpio) and tilapia (Oreochromis niloticus). The two rainbow trout BAC libraries have average insert sizes of 58 and 110 kb. The average size of inserts in the carp BAC library is 160 kb. The average insert sizes of the four tilapia BAC libraries are 65, 105, 145 and 194 kb, respectively. These libraries represent good coverage of each genome (2-64 x coverage). The libraries can be screened by conventional colony hybridization and provide a starting point for the construction of high-density filtres or polymerase chain reaction (PCR) screening approaches. These BAC libraries will facilitate the positional cloning of quantitative trait loci (QTLs) for a variety of economically important traits in these species.

Molecular cloning, expression and evolution of the Japanese flounder goose-type lysozyme gene, and the lytic activity of its recombinant protein

In this study, we cloned the goose-type (g-type) lysozyme gene from the Japanese flounder genomic DNA library, the first such data in fish and only the second after the chicken g-type lysozyme gene. The Japanese flounder g-type lysozyme gene was 1252 bp in length from the transcription site to the polyadenylation site, coded for 758 bp of mRNA and 195 deduced amino acids, which contain five exons and four introns. A phylogenetic analysis based on amino acid sequences showed that the flounder gene was closer to g-type lysozyme, followed by phage-type lysozyme and then chicken-type (c-type) lysozyme. Although exon 1 of the flounder gene differs from exons 1 and 2 of the chicken g-type lysozyme gene, three catalytic residues, as well as their neighboring amino acids were conserved between the Japanese flounder and the four avian g-type lysozymes. In a Southern blot analysis using the genomic DNA of homo-cloned Japanese flounder, the flounder g-type lysozyme gene showed a simple pattern, suggesting that it is encoded by a single copy gene. A Northern blot analysis showed that this gene was expressed in all tissues of Japanese flounder that we examined in this study and showed major differences from those expressed tissues of the chicken g-type gene. Japanese flounder g-type lysozyme mRNA levels in the intestine, heart and whole blood increased after injecting the fish with Edwardsiella tarda. Recombinant flounder g-type lysozyme, which has an optimal pH and temperature of pH 6.0 and 25 degrees C, possessed lytic activity against Micrococcus lysodeikticus and several fish pathogenic bacteria. This is the first report of a g-type lysozyme gene other than for reported avian species.

Expression of Japanese flounder c-type lysozyme cDNA in insect cells

Lysozyme is a widely distributed hydrolase which likely plays an important role in bio-defense systems. In the current study, we constructed a baculovirus expression system for the c-type lysozyme cDNA of Japanese flounder (Paralichthys olivaceus) and evaluated the activity of the recombinant protein. This activity was estimated, by turbidimetric assay, to be 7.7U/mg, a value five times higher than that of hen egg white (HEW) c-type lysozyme examined under the same conditions. The optimum pH and temperature for the lytic activity of the Japanese flounder c-type recombinant lysozyme were found to be 5.0-6.5 and 40 degrees C, respectively. Two groupings for fish lysozyme activity are proposed; the first has an optimum pH of approximately 6.0 and the second an optimum pH of above 8.0. Flounder c-type lysozyme was found to possess little lytic activities against Edwardsiella tarda and Streptococcus sp. This latter characteristic may help explain the fact that these two bacterial species are responsible for significant disease problems in cultured Japanese flounder.

Cloning of Japanese flounder Paralichthys olivaceus CD3 cDNA and gene, and analysis of its expression

Two distinct CD3 homologue cDNAs, CD3-1 and CD3-2, were isolated from a Japanese flounder leukocyte cDNA library. CD3-1 consisted of 961 bp encoding 178 amino acid residues, and CD3-2 consisted of 927 bp encoding 182 amino acid residues. The two deduced amino acid sequences had an identity of 95.1%, and neither had N-linked glycosylation sites. The identities between the Japanese flounder CD3s and previously reported CD3s (CD3 epsilon, CD3 gamma, or CD3 delta) of Xenopus laevis, chicken, and various mammals were approximately 25%. The Japanese flounder CD3s had an extracellular domain, a CXXCXE motif, and an immunoreceptor tyrosine-based activation motif (ITAM), each of which are important characteristics of CD3 chains. Furthermore, the positions of four cysteine residues in the extracellular domain were preserved in both of the Japanese flounder CD3s. A phylogenetic tree based on the amino acid sequences confirmed that the Japanese flounder CD3s are closer to CD3 epsilon than to CD3 gamma and CD3 delta. However, the gene structure of Japanese flounder CD3 is identical to the chicken and Xenopus CD3 gamma/delta genes and the mammalian CD3 delta gene. Southern blot hybridization and the DNA sequence of the CD3 gene of homocloned Japanese flounder indicated that the CD3 gene exists as a single copy. Southern blot hybridization also showed the presence of a polymorphic variant of Japanese flounder CD3. An RT-PCR analysis detected Japanese flounder CD3 mRNA in several organs that contained lymphocytes. The proportion of CD3-positive cells in the peripheral blood leukocytes was 34.9%.

Cloning and expression analysis of rainbow trout Oncorhynchus mykiss tumour necrosis factor-alpha

A rainbow trout (Oncorhynchus mykiss) gene for tumor necrosis factor (TNF) has been cloned and sequenced. The cDNA contains an open reading frame of 738 nucleotides that translate into a 246 amino-acid putative peptide, with a 5' untranslated region (UTR) of 140 bp and a 3' UTR of 506 bp. Two potential N-linked glycosylation sites exist in the translation. The genomic sequence measures 2007 bp and contains three introns that intercept four coding exons. Expression studies using RT-PCR have shown that the trout TNF gene is constitutively expressed in the gill and kidney of unstimulated fish. Trout TNF expression could be up-regulated by stimulation of isolated head kidney leucocytes with lipopolysaccharide (LPS). Similarly, stimulation of a trout macrophage cell line (RTS11) with LPS resulted in an increased transcript level, as did incubation with recombinant trout interleukin (IL)-1 beta. The optimal timing for induction of TNF expression in trout macrophages was determined using recombinant trout IL-1 beta, where a clear induction was apparent by 2 h and peaked at 4 h. Evidence that this TNF gene is equivalent to mammalian TNF-alpha is discussed.

Assessment of DNA vaccine potential for juvenile Japanese flounder Paralichthys olivaceus, through the introduction of reporter genes by particle bombardment and histopathology

Genetic immunisation potential, following DNA bombardment for juvenile Japanese flounder, Paralichthys olivaceus was examined. GFP plasmids bombarded at two pressures, 150 and 300psi were sampled at 1, 7, 14 and 28 days, greater immunofluorescence was observed at the higher bombardment pressure. Histopathology, at 3 h post bombardment showed considerable damage to fish epithelial and dermal tissues when bombarded at pressures greater than 200 psi, with many DNA-coated gold particles present. At 150psi there was little pathology and no DNA-coated particles. Histopathology, up to 28 days again showed little pathology at 150 psi with few DNA-coated particles, whereas at 300 psi there was significant pathology observed with many DNA-coated particles seen in conjunction with the cytoplasm of inflammatory cells. By day 28 epithelial coverage was observed with tissue damage restricted to the dermal layer. Chloramphenicol acetyltransferase (CAT) assay showed long term and stable expression of the CAT protein from day 1 to day 60. The transcription activity of two promoters; pCMV-CAT and pSV2-CAT showed greater activity in the former. It was concluded that DNA vaccination potential for juvenile flounder is a viable option.

Genomic bacterial artificial chromosome library of the Japanese flounder Paralichthys olivaceus

We have constructed a genomic bacterial artificial chromosome (BAC) library from homozygous cloned Japanese flounder Paralichthys olivaceus using the pBAC- lac vector. This BAC library consists of about 49,100 clones and is deposited in 128 microtiter plates with 384 wells. The average size of inserted DNA was calculated to be 165 kb. The BAC library was determined to cover 9 times the Japanese flounder haploid genome. The Japanese flounder genomic BAC library will be useful for gene isolation as well as quantitative trait loci (QTL) analysis.

Molecular cloning, characterization, and expression of TNF cDNA and gene from Japanese flounder Paralychthys olivaceus

We cloned a cDNA and the gene for Japanese flounder TNF. The TNF cDNA consisted of 1217 bp, which encoded 225 amino acid residues. The identities between Japanese flounder TNF and members of the mammalian TNF family were approximately 20-30%. The positions of cysteine residues that are important for disulfide bonds were conserved with respect to those in mammalian TNF-alpha. The Japanese flounder TNF gene has a length of approximately 2 kbp and consists of four exons and three introns. The positions of the exon-intron junction positions of Japanese flounder TNF gene are similar to those of human TNF-alpha. However, the length of the first intron of Japanese flounder is much shorter than that of the human TNF-alpha gene. There are simple CA or AT dinucleotide repeats in the 5'-upstream and 3'-downstream regions of the Japanese flounder TNF gene. Southern blot hybridization indicted that Japanese flounder TNF exists as a single copy. Expression of Japanese flounder TNF mRNA is greatly induced after stimulation of PBLs with LPS, Con A, or PMA. These results indicated that Japanese flounder TNF is more like mammalian TNF-alpha than mammalian lymphotoxin-alpha, with respect to its gene structure, length of amino acid sequence, number and position of cysteine residues, and regulation of gene expression.

Identification of viral induced genes in Ig+ leucocytes of Japanese flounder Paralichthys olivaceus, by differential hybridisation with subtracted and un-subtracted cDNA probes

Up-regulated genes of leucocytes expressing immunoglobulin (Ig+ leucocytes) of hirame rhabdovirus (HRV)-infected Japanese flounder were identified by differential hybridisation, using subtracted and un-subtracted cDNA probes. Ig+ leucocytes were separated from apparently healthy and HRV-infected Japanese flounder by the magnetic beads antibody method using mouse anti-Japanese flounder Ig monoclonal antibody (mab). A cDNA library was constructed from HRV-infected Japanese flounder leucocytes, and was screened with subtracted cDNA probes enriched in genes up-regulated by HRV infection. Fifty cDNAs were isolated for further analysis. These included cDNAs coding for homologues of interferon-inducible 56K protein (IFI56), Stat3, CEF-10, RGS5, inducible poly(A) binding protein, prolylcarboxylpeptidase, basigin III (Ig superfamily), MUC-18 (Ig superfamily), proteasome-nexin 1 (SERPIN), herpes virus entry mediator (TNFR family), collagenase III, gelatinase-b, megakaryocyte stimulating factor, Rab8-interacting protein, IgM, IgD and 20 unknown cDNA clones. The majority of these identified genes are reported for the first time in fish. From leucocytes mRNA for homologues of IFI56, CEF-10, Stat3, SERPIN and inducible poly (A) binding protein expression was shown to increase following HRV infection.

Cloning and analysis of expression of Mx cDNA in Japanese flounder, Paralichthys olivaceus

Myxovirus resistance (Mx) is an interferon (IFN)-induced protein that specifically prevents growth, in vivo and in vitro, of certain classes of virus. We isolated the Mx cDNA from a leukocyte cDNA library obtained from a Japanese flounder infected with Hirame rhabdovirus (HRV). The Mx cDNA was found to contain 2385 bp coding for 620 amino acids. The amino acid sequence had approximately 51 and 78% identities to the sequences of human and rainbow trout Mx cDNAs, respectively. We propose that the amino acid sequence encoded by this cDNA clone contains a tripartite guanosine-5'-triphosphate (GTP)-binding motif, GXXXSGKS/T, DXXG and T/NKXD, and a signature of the dynamin family, LPRG(S/K)GIVTR, which are conserved in all IFN-induced Mx proteins of vertebrates. In addition, the C-terminal region of the Japanese flounder Mx protein, like those of other Mx proteins, contains a highly conserved leucine zipper motif. Japanese flounder infected with the HRV showed increased expression of Mx mRNA in the leukocytes starting at 48 h and peaking at 72 h. An RT-PCR (reverse transcription-polymerase chain-reaction) analysis of Mx mRNA from a healthy fish showed that the Mx mRNA was predominantly expressed in the kidney, spleen, intestine, brain, peritoneal cavity fluid and gill, and only minimally expressed in leukocytes, liver, muscle and mucus.

Molecular Cloning and Novel Repeated Sequences of a C-type Lysozyme Gene in Japanese Flounder (Paralichthys olivaceus)

A clone of a DNA fragment of approximately 10 kb that included a c-type lysozyme gene of Japanese flounder (Paralichthys olivaceus) was isolated from a Japanese flounder genomic DNA library. This clone was subcloned, and the nucleotide sequence of the c-type lysozyme gene was determined. The flounder c-type lysozyme gene, which consisted of 3,617 bp, was found to be composed of four exons and three introns. The transcription start site was determined to be 44 bp upstream of the ATG codon by primer extension analysis. The number of exons and introns and the positions of the catalytic residues of the flounder gene were the same as those of the human and chicken c-type lysozyme genes. However, introns 1 and 3 of the flounder gene were shorter, and intron 2 was longer, than those in the other reported vertebrates genes. There were no Alu repeated sequences in the flounder lysozyme gene, as determined for the human lysozyme gene, but 45 repeated sequences were found in the second intron of the flounder lysozyme gene. We suggest that the length of intron 2 in the Japanese flounder c-type lysozyme gene depends on the presence of this repeated sequence. Furthermore, Southern blot analysis revealed that the c-type lysozyme gene was probably a single copy in the genomic DNA of homo-cloned Japanese flounder.

Stable Expression of a Foreign Gene, Delivered by Gene Gun, in the Muscle of Rainbow Trout Oncorhynchus mykiss

We report the efficient delivery of a foreign gene into muscle of rainbow trout Oncorhynchus mykiss with a gene gun. The foreign gene was a reporter gene, chloramphenicol acetyltransferase (CAT). Two CAT-containing plasmids were used: pCMV-CAT, which contains cytomegalovirus immediate early promoter, and pSV2-CAT, which contains the simian virus 40 early promoter. All plasmids were introduced by particle bombardment using a gene gun. During the 90-day sampling period following bombardment, CAT was strongly and stably expressed in the muscle of all the fish bombarded with pCMV-CAT and pSV2-CAT. No CAT expression was detected in the blood samples until 90 days after introduction, when it was found in only one fish from the pCMV-CAT group and one from the pSV2-CAT group. The stable and long-term expression of plasmid DNA in muscle makes muscle an attractive target tissue for the introduction of viral DNA for the purpose of DNA vaccination.

Virulence properties of motile aeromonads isolated from farmed frogs Rana tigerina and R. rugulosa

Virulence factors were compared in Aeromonas species isolated from clinically normal and septicaemic farmed frogs from Thailand. Haemolysin activities against frog erythrocytes were significantly different within the collection of aeromonads. Groups of high haemolytic activity (unspeciated Aeromonas, Au), moderate haemolytic activity (A. hydrophila), and low haemolytic activity (A. veronii biovar sobria, A. veronii biovar veronii, A. caviae, A. schubertii) were noted. DNA colony hybridisation studies revealed that Au isolates possessed a haemolysin gene (ASH1) which was not present in any of the other Thai aeromonads or type strains tested. Elastinolytic activity was demonstrated in 90% of the Au isolates, 60% of the A. hydrophila isolates and in none of the other motile aeromonads. The cytotoxic activity of the Aeromonas isolates varied according to the source of cells used in the assays. Cells from rainbow trout were extremely sensitive to Au toxins but less so to toxins produced by other species. In contrast mammalian cells showed very little sensitivity to Au toxins but were more sensitive to toxins produced by A. hydrophila. Selection of suitable assay substrates is therefore important.

A survey of expressed genes in the leukocytes of Japanese flounder, Paralichthys olivaceus, infected with Hirame rhabdovirus

We constructed a cDNA library of Japanese flounder, Paralichthys olivaceus, leukocytes that were infected with Hirame rhabdovirus (HRV) in order to analyze some of the genes that are induced and expressed by virus infection in the immune system. Four hundred and fifty-two partial sequences representing 300 cDNA clones were obtained from the 5' and/or 3' ends of inserts derived from the Japanese flounder leukocyte cDNA library. About three-quarters of the 300 cDNA clones (217 clones, 72.3%) represented known genes in the public databases, whereas the remaining 83 (27.7%) of the clones did not show any significant homology with the sequences in the public databases. Clones matching known genes were classified into 12 categories according to their function or distribution. Only 40 (18.4%) of the 217 known genes showed homology with fish genes deposited in the database. Thirty (10%) of the clones, encoding 21 different sequences, and representing several categories, were identified as putative biodefense genes or genes associated with the immune response. Nineteen of the 21 putative biodefense or immune response-related cDNAs have not been previously reported in fish genes or cDNAs.

Identification of genes in a KG- phenotype of Lactococcus garvieae, a fish pathogenic bacterium, whose proteins react with antiKG- rabbit serum

Five different clones (SA1B05, SA1B10, SA2F01, SA8A11 and SA9H10) were isolated from the gene library of the Lactococcus garvieae SA8201 (KG-) strain by immunological screening using rabbit serum against L. garvieae (KG-) phenotype cells. A Western blot analysis indicated that the molecular sizes of immunologically detected proteins of SA1B05, SA1B10, SA2F01, SA8A11 and SA9H10, which were fused with LacZ protein, were 25, 30, 28, 26 and 13 kDa, respectively. The amino acid sequences of the immunologically detected proteins of SA1B05, SA1B10, SA2F01 and SA8A11 were homologous to a processing protease of Bacillus subtilis (36.6%), dihydropteroate synthase of Escherichia coli (34.6%), trigger factor of B. subtilis (45.8%) and N-acetylglucosamine-6-phosphate deacetylase of Vibrio furnissii (37.1%), respectively. There was no significant homologous sequence of SA9H10 in DDBJ/EMBL/GenBank and SwissProt. We cloned and sequenced a longer DNA fragment (SA9H10L) of SA9H10 from the gene library. The predicted amino acid sequence of this clone was weak homology to M protein of Streptococcus pyogenes (22.7%). Five genes were specifically expressed in the KG- phenotype strains. However, SA8A11 and SA9H10 was expressed in the mutated strain SA8201-TTC, whose serological phenotype was changed from KG- to KG+ by 2,3,5-triphenyltetrazolium chloride.

Molecular analysis of complement component C8beta and C9 cDNAs of Japanese flounder, Paralichthys olivaceus

The amino acid sequences of the human terminal complement components show extensive structural similarity to each other. In this study the C8beta and C9 cDNAs of Japanese flounder, Paralichthys olivaceus, were cloned and analyzed. The derived deduced amino acid sequences of the two terminal components were homologous to those of humans, in that the sequences of both species contained LDL receptor, EGF precursor, and two thrombospondin domains. Japanese flounder C9 was found to have a second thrombospondin region in the C-terminus, similar to that reported for rainbow trout and pufferfish. Moreover, these two complement component cDNAs of Japanese flounder had partial similarity to human perforin. These findings show that Japanese flounder C8beta and C9 have similar structures, which supports the hypothesis that the terminal complement genes originated from the same ancestral gene. Collectively, these features emphasize the strong similarity among the members of the terminal complement family.

Sequences of 596 cDNA Clones (565,977 bp) of Japanese Flounder (Paralichthys olivaceus) Leukocytes Infected with Hirame Rhabdovirus

: We have partially sequenced 785 sequences of 596 independent complementary DNA clones isolated from a cDNA library of Japanese flounder leukocytes infected with hirame rhabdovirus. These sequences consist of a total of 565,977 base pairs. The average size of the sequenced lengths was 721 bp. Of 596 clones, 386 (64.8%) were identified as previously reported genes by the BLASTN and BLASTX programs. About 30% of the identified clones could be recognized by only the BLASTX program. A total of 251 distinct genes were identified, and 181 of these genes are the first such genes reported from the teleostei. Approximately 27% of the identified Japanese flounder genes appear to be associated with cell division, cell structure or motility, and basic energy metabolism, 29% with gene or protein expression, and 17% with cell signaling, cell communication, and cell or organism defense. The most frequently identified expressed sequence tags of leukocytes of Japanese flounder were gelatinase b and ribosomal protein L23, which both had 1.34% prevalence.

Molecular cloning and evolution of transferrin cDNAs in salmonids

Transferrin complementary DNAs were cloned from the livers of seven species in three genera of salmonids (kokanee salmon Oncorhynchus nerka, amago salmon Oncorhynchus masou ishikawa, masu salmon Oncorhynchus masou masou, Japanese char Salvelinus pluvius, brook trout Salvelinus fontinalis, lake trout Salvelinus namaycush, and brown trout Salmo trutta) subsequent to polymerase chain reaction amplification with primers derived from conserved regions of transferrin cDNA sequences. The transferrin cDNAs of the seven species of salmonids had sizes of 2.2 to 2.4 kb and encoded an open reading frame consisting of 691 amino acids with a putative signal peptide of 18 amino acids. The alignment of salmonid transferrin cDNAs showed a duplicated structure and conserved anion-binding residues, iron-binding residues, and cysteine residues for disulfide bridges. The deduced amino acid sequences of the seven salmonid transferrin cDNAs share 85% to 99% homology. A phylogenetic tree of amino acid sequences of transferrin cDNAs from salmonids showed that the relationship among the three genera of salmonids (Oncorhynchus, Salvelinus, and Salmo) is well correlated with that derived from classic morphologic and genetic analyses.

DNA sequencing of the gene encoding Salmonella typhimurium-derived T-cell inhibitor (STI) and characterization of the gene product, cloned STI

In a previous study, we found a novel protein which inhibited T-cell responsiveness to interleukin-2 (IL-2) in Salmonella typhimurium and called it S. typhimurium-derived T-cell inhibitor (STI). In this study, we analyzed the DNA sequence of the gene encoding STI. The STI gene was cloned into a plasmid vector, pUC118, and expressed in Escherichia coli JM109. Like native STI, the cloned STI inhibited IL-2-dependent CTLL-2 cell growth. Furthermore, this growth inhibition involved down-regulation of IL-2 receptor expression. These results indicate that the cloned STI expressed in E. coli was identical to native STI. Sequencing revealed that the STI gene contained an open reading frame of 2298 base pairs encoding a precursor form of 765 amino acid residues (molecular mass 83605) that is processed into a mature form of 745 amino acid residues with molecular mass 81 548. Homology analysis revealed that its amino acid sequence was highly homologous with that of the beta-glucosidase of E. coli K-12. We designated the gene encoding STI sti.

Histogenetic stereological reconstruction of rat basophilic, clear, and oncocytic neoplastic renal cell lesions using carbonic anhydrase type II-PAS double-stained sections

The histogenesis of 3 types of rat renal cell tumors (basophilic cell, clear cell, and oncocytic) was stereologically analyzed, with particular attention paid to transitions from normal tubules. Early nitrosamine-induced preneoplastic lesions, including dysplastic tubules (altered tubules), epithelial hyperplasias, and small adenomas, were reconstructed using serially sectioned specimens processed for carbonic anhydrase type II (CA) and periodic acid-Schiff (PAS) (CA-PAS) double staining to allow easier distinction of the nephron segments: Proximal tubules had a PAS-positive brush border and were weakly positive for CA in the cytoplasm; distal tubules were PAS negative and weakly positive for CA; collecting ducts were PAS negative and strongly positive for CA. Similarly, cytochrome c oxidase (CytOx) and CytOx-PAS double staining was also applied to confirm the character of oncocytic lesions. All basophilic lesions (7 of 7) showed transition to proximal tubules. Clear cell lesions positive for CA, on the other hand, showed transition to distal tubules in 4 of 9 (44.4%) lesions and to collecting ducts in 4 of 9 (44.4%) lesions, but in only 1 of 9 (11%) to a proximal tubule. All oncocytic lesions (16 of 16), characterized by positivity for both CA and CytOx, showed transition to collecting ducts. The results indicate that the origins of renal cell neoplasia are proximal tubules for the basophilic cell lesions, either proximal or distal tubules for their clear cell counterparts, and collecting ducts for oncocytic lesions.

Note: molecular cloning of chitinase genes from Vibrio anguillarum and V. parahaemolyticus

Chitinase genes from Vibrio anguillarum KV9001 and V. parahaemolyticus ATCC17802 were cloned into Escherichia coli. Open reading frames of chitinase genes from V. anguillarum (vac) and V. parahaemolyticus (vpc) are 1755 bp and 1890 bp, respectively. The deduced amino acid sequences of these genes have 71.6% identity. There are two consensus sequence regions in the VAC and VPC proteins. The vac gene was highly prevalent in V. anguillarum, and the DNA probe of the vac gene hybridized to V. alginolyticus and Beneckea proteolytica DNA. The DNA probe of the upc gene hybridized to V. alginolyticus, V. harveyi and V. ordalii DNA.

Molecular cloning of a novel interferon regulatory factor in Japanese flounder, Paralichthys olivaceus

A complementary DNA library was constructed in lambda ZAP II using messenger RNA from the leukocytes of some heterocloned Japanese flounder, Paralichthys olivaceus, that had been artificially infected with Hirame rhabdovirus (HRV). A cloned flounder interferon regulatory factor (designated fIRF) cDNA was found to be 1746 bp in length, with an open reading frame of 297 amino acids. The overall amino acid sequence of fIRF had approximately 40% identity with the previously reported avian and mammalian IRF-1s and IRF-2s. The fIRF sequence was most similar to that recorded for the chicken IRF-1. Amino acid sequence identities between the DNA-binding domain of the fIRF and that of both chicken IRF-1 and chicken IRF-2 were 72.3%. The DNA-binding domain of fIRF contained the repeated tryptophan motif that is characteristic of members of the IRF family. The mRNA of fIRF was detected in various tissues by reverse transcription-polymerase chain reaction (RT-PCR). The fIRF was transcribed mainly in the intestine, ovary, muscle, liver, heart and spleen, while it was minimally transcribed in the brain and kidney. When Japanese flounder were injected with HRV, the relative expression of fIRF mRNA was found to increase and peak 3 days after injection. The quantities of the fIRF mRNA increased to levels that were 7.5-fold higher than those of noninjected fish. In addition, when Japanese flounder were injected with Edwardsiella tarda, the expression of fIRF mRNA showed increases 2, 3, and 4 days after injection. The quantities of the fIRF mRNA on those days represented approximately 6-, 15-, and 14-fold increases, respectively, over the levels in noninjected fish.

Rapid diagnosis of red sea bream iridovirus infection using the polymerase chain reaction

A simple and sensitive polymerase chain reaction (PCR) based assay is described for detection of the red sea bream iridovirus (RSIV) in infected fish. The assay involves amplification of a portion of the ribonucleotide reductase small subunit (RNRS) gene of the virus from DNA isolated from the spleen. The system was tested on red sea bream following an experimental infection. In our infection model, disease signs first became apparent 5 to 6 d post-infection, and mortality commenced at Day 6 and reached 90% by Day 9. No amplified product was detected from fish at 1 or 2 d post-infection, but 3 of 5 fish tested positive at Day 3, and all fish tested positive at Days 5 and 8. Thus, infection could be detected prior to the appearance of overt symptoms. This PCR method should be of considerable value for aquaculture to detect RSIV infection.

Structure and expression of activin genes in rainbow trout

Activins are dimeric members of the transforming growth factor-beta (TGF-beta) superfamily. By using the polymerase chain reaction (PCR), we have cloned and sequenced activin beta A and beta B genes encoding the mature region of the peptides from the rainbow trout genomic DNA. Two forms of beta A and a single form of beta B-subunits were found. There is high identity with mammalian counterparts; the two rainbow trout beta A-subunits have more than 75% nucleotide sequence identity with the human beta A-subunit, and the beta B-subunit had 82% sequence identity with the human beta B-subunit. Expression of rainbow trout activin genes was examined by reverse transcription-PCR (RT-PCR). The major expression tissue of rainbow trout activin was ovary and brain at the messenger RNA level, and the major expression subunit of rainbow trout activin was the beta B subunit.

A survey of expressed genes in Japanese flounder (Paralichthys olivaceus) liver and spleen

Expressed sequence tags (ESTs) were obtained from Japanese flounder (Paralichthys olivaceus). We present the results of single-pass sequencing of 493 ESTs from 350 clones from liver cDNA and 57 ESTs from 41 clones from spleen cDNA. Sequences of the cDNA clones were compared with sequences in the GenBank database. Two hundred and two clones (51.7%) appeared to be completely unknown and are likely to represent newly described genes, whereas 189 clones (48.3%) were identified based on matches to sequences in the databases. Three of the unidentified sequences were isolated from both the liver and spleen cDNA libraries. However, there were no identical sequences between liver and spleen clones.

Identification of major antigenic proteins of Pasteurella piscicida

Two different antigenic protein-coding clones (PPA1 and PPA2) were isolated using anti-Pasteurella piscicida rabbit serum from a genomic DNA library of P. piscicida strain KP9038. The PPA1 and PPA2 expressed 7 kDa and 45 kDa proteins in Escherichia coli, respectively, and the molecular sizes of these expressed proteins are the same as these of the major antigenic proteins of P. piscicida. PPA1 encodes a protein of 83 amino acids residues, which is similar to the bacterial lipoprotein. Comparison of the predicted amino acid sequence of the PPA1-encoded 7 kDa protein of P. piscicida with previously reported bacterial lipoprotein sequence data revealed that it shares about 40% amino acid sequence identity. PPA2 has two large open reading frame (ORFs). The larger ORF (encoding 452 amino acid residues) encodes a homolog of DegQ protease, and the smaller ORF (371 amino acid residues) encodes a homolog of DegS protease. The antibodies reacted with the larger ORF-encoded 45 kDa DegQ homolog protein. The DegQ and DegS homolog proteins contain an export signal and a serine protease active site. The structural features of the PPA2-coding locus are similar to those of the loci in E. coli for the degQ and degS serine protease genes. A sequence in the 3' non-coding region of Vibrio hollisae thermostable hemolysin gene that is highly homologous with a similar located sequence in the Pseudomonas putida p-cresol methylhydroxylase gene is also found in the 3' non-coding region of the degS homolog gene of the PPA2.

Expressed sequence tags of medaka (Oryzias latipes) liver mRNA

A medaka liver cDNA library was constructed in lambda ZAPII. The number of clones in this library is approximately 5 x 10(6). Three hundred sixty-one clones were randomly selected and, of these, 33 clones with over 1 kb were sequenced. These sequences were compared with GenBank and the dbEST (Re.96.0). Twenty-five clones of these 33 clones encoded 18 different genes and 2 different expressed sequence tags (ESTs). Sequences of 10 of the 18 clones had not previously been reported in fish. The codon usage of medaka genes is similar to that of Xenopus, mouse, and human genes, but not similar to that of yeast and Escherichia coli genes.

Characterization and expression of c-type lysozyme cDNA from Japanese flounder (Paralichthys olivaceus)

Lysozyme is a widely distributed enzyme located in the serum, skin mucus, and other organs of fish, which is responsible for catalyzing the hydrolysis of the cell walls of most bacteria. A c-type of lysozyme cDNA was cloned from a kidney cDNA library of the Japanese flounder (Paralichthys olivaceus). The cDNAs consisted of 612 bp, which coded for 143 amino acid residues. The deduced amino acid sequence of Japanese flounder c-type lysozyme possessed 72.9%, 57.4%, and 65.4% identities with rainbow trout, chicken, and human c-type lysozymes, respectively. Comparison of the c-type lysozymes showed that the catalytic residues, the residues binding to sugar chains, and cysteine residues were completely conserved. Northern blot analysis indicated that the c-type lysozyme gene is apparently transcribed in the head kidney, posterior kidney, spleen, brain, and ovary of healthy flounder. When flounder were experimentally infected with Edwardsiella tarda, quantities of the c-type lysozyme mRNA increased in the head kidney, spleen, and ovary of the flounder.