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Comparison of recombinant barramundi and human insulin-like growth factor (IGF)-I in juvenile barramundi (Lates calcarifer): in vivo metabolic effects, association with circulating IGF-binding proteins, and tissue localisation.

The in vivo actions of human and fish insulin-like growth factor (IGF)-I have been compared to extend the understanding of the metabolism of IGFs in fish and to identify potential differences in their actions. The effects of acute administration of these proteins on the incorporation of glucose into muscle glycogen and leucine into liver protein in juvenile barramundi were investigated. In these in vivo metabolic assays, both baramundi IGF-I (bIGF-I) and human IGF-I (hIGF-I) increase the incorporation of D-[14C]glucose into muscle glycogen and [14C]leucine into liver protein. The distribution of radio-labeled human and barramundi IGF-I in the circulation and their uptake by tissue was also compared in juvenile barramundi (Lates calcarifer). Analysis of trichloroacetic acid-precipitable radioactivity in sequential samples following bolus injection of radiolabeled IGFs revealed that hIGF-I was degraded faster than bIGF-I. Neutral gel chromatography of these samples suggested that this difference is due to reduced affinity of hIGF-I, compared to bIGF-I, for the IGF-binding proteins (IGFBPs) present in the barramundi. Tissue uptake of [125I]-labeled hIGF-I and bIGF-I was similar except that [ 125I]bIGF-I uptake by the kidney exceeded that of hIGF-I. It is suggested that while some of the in vivo actions of IGFs in fish are conserved, functional differences between mammalian and teleostean IGFs exist, particularly with respect to their interactions with fish IGFBPs.

Animals↗

A minisatellite polymorphism in intron III of the barramundi (Lates calcarifer) growth hormone gene.

This paper describes the detection of a polymorphism within the growth hormone (GH) gene of the fish barramundi (Lates calcarifer). PCR amplification of barramundi genomic DNA generated three different sized products: A, 409 bp; B, 478 bp; and H, 520 bp. Each barramundi isolate displayed one of four different types of profiles, which contained specific combinations of these PCR products. Sequence analysis confirmed that products A and B are different forms of the barramundi GH gene, and studies showed that product H was an artifact due to heteroduplex formation between the two smaller-sized molecules. The polymorphic nature of these PCR products was due to differences in the number of repeat monomers within the 5' end of the barramundi decaminisatellite, an AT-rich repetitive sequence that was identified within intron III of this gene. The barramundi decaminisatellite consisted of 24 or 28 10-nucleotide imperfect direct repeat monomers in a tandem array. The monomers were grouped into one of three different families and evidence for monomer homogenization by crossover fixation was presented. The barramundi decaminisatellite differed from previously reported AT- or GC-rich minisatellites, although a similar decaminisatellite has been identified in intron III of the tilapia GH gene.

Animals↗

Barramundi as an indicator species for environmental monitoring in North Queensland, Australia: laboratory versus field studies.

The dose-response relationship for hepatic 7-ethoxyresorufin-O-deethylase (EROD) induction in barramundi (Lates calcarifer) was examined under controlled laboratory conditions for 15 d using farm-reared barramundi. These results were compared with EROD activity measured in barramundi collected from two rivers catchments (impacted and nonimpacted) in northern Queensland, Australia. Barramundi were dosed by intraperitoneal injection with a known cytochrome P4501A (CYP1A) inducer, beta-naphthoflavone (beta-NF), at 5, 10, and 50 mg kg(-1) using two controls: A vehicle control (corn-oil injected) and an experimental control (no injection). The EROD induction occurred within 4 h in the 5, 10, and 50 mg beta-NF kg(-1) exposures, reaching mean maximum activities of 88.6 (+/-51.9), 85.5 (+/-91.7), and 149.1 (+/-106.4) pmol min(-1) mg protein(-1), respectively. Mean EROD activities remained low in the corn-oil controls (2.1+/-1.8 pmol min(-1) mg protein(-1)) and experimental controls (5.3+/-4.4 pmol min(-1) mg protein(-1)) throughout the study. Barramundi demonstrated a rapid response curve, which was dose dependent (50 > 10 > 5 mg beta-NF kg(-1)) and decreased progressively over time from induction. Measurement of total cytochrome P450 content (nmol mg protein(-1)) was not dose dependent. The EROD activities from field-collected barramundi from the Johnstone River (impacted) and Olive River (nonimpacted) suggest exposure to low-level contaminants in the Johnstone River fish only. With more controlled laboratory and field studies, barramundi have the potential to become a major indicator species in assessing exposure to environmental contaminants in coastal areas throughout northern Queensland, Australia.

Animals↗

Insulin-like growth factor mRNA in Barramundi (Lates calcarifer): alternative splicing and nonresponsiveness to growth hormone.

Barramundi (Lates calcarifer) is a teleost of the superorder Acanthopterygii. Barramundi IGF-I cDNA was cloned and the distribution of alternative transcripts in various barramundi tissues was investigated using rt-PCR and RPA. It was demonstrated that in barramundi tissues, IGF-I mRNAs were represented by two transcripts corresponding to the reported salmonid Ea-2 and Ea-4. The acute effect of GH on hepatic IGF-I mRNA levels was investigated. Seven hours after intraperitonal administration of either 6 micrograms of recombinant bream GH/g body weight or saline, no significant increase in the levels of either of the two transcripts could be observed. The presence of GH receptors in the barramundi liver was demonstrated in binding assays using recombinant bream GH and liver membrane preparations. An analysis of a barramundi IGF-I genomic sequence encompassing the three exons that encode the E domain suggested that the pattern of splice site utilization is determined by the degree of homology of the splicing signals to the consensus splice site sequences.

Alternative Splicing↗

Molecular evidence for association of chlamydiales bacteria with epitheliocystis in leafy seadragon (Phycodurus eques), silver perch (Bidyanus bidyanus), and barramundi (Lates calcarifer).

Epitheliocystis in leafy seadragon (Phycodurus eques), silver perch (Bidyanus bidyanus), and barramundi (Lates calcarifer), previously associated with chlamydial bacterial infection using ultrastructural analysis, was further investigated by using molecular and immunocytochemical methods. Morphologically, all three species showed epitheliocystis cysts in the gills, and barramundi also showed lymphocystis cysts in the skin. From gill cysts of all three species and from skin cysts of barramundi 16S rRNA gene fragments were amplified by PCR and sequenced, which clustered by phylogenetic analysis together with other chlamydia-like organisms in the order Chlamydiales in a lineage separate from the family Chlamydiaceae. By using in situ RNA hybridization, 16S rRNA Chlamydiales-specific sequences were detected in gill cysts of silver perch and in gill and skin cysts of barramundi. By applying immunocytochemistry, chlamydial antigens (lipopolysaccharide and/or membrane protein) were detected in gill cysts of leafy seadragon and in gill and skin cysts of barramundi, but not in gill cysts of silver perch. In conclusion, this is the first time epitheliocystis agents of leafy seadragon, silver perch and barramundi have been undoubtedly identified as belonging to bacteria of the order Chlamydiales by molecular methods. In addition, the results suggested that lymphocystis cysts, known to be caused by iridovirus infection, could be coinfected with the epitheliocystis agent.

Animals↗

Anti-immunoglobulin antisera used in an ELISA to detect antibodies in barramundi Lates calcarifer to Cryptocaryon irritans.

Immunoglobulins (Ig) in serum from barramundi vaccinated with bovine serum albumin (BSA) were purified by ammonium sulphate precipitation and affinity chromatography using BSA as the ligand. The BSA-binding activity of eluted putative Ig fractions was assessed by enzyme-linked immunosorbent assay (ELISA) before being pooled and characterised by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Double affinity purification did not improve the purity of the Ig preparation compared to single affinity purification. Barramundi Ig were injected into sheep to produce anti-Ig antisera which were assessed in an indirect ELISA as the secondary antibody to detect serum Ig in barramundi vaccinated with Cryptocaryon irritans theronts. Affinity-purified Ig induced a more specific reagent for use as secondary antibody in ELISA than did normal whole-barramundi sera. The heavy (H) chain of barramundi Ig had an apparent molecular weight of 70 kDa while that of the light (L) chain was 27 kDa in SDS-PAGE studies. Under non-reducing conditions 2 putative populations of Ig were identified, at 768 and 210 kDa. The N-terminal sequence of the barramundi Ig H chain showed 78% homology with channel catfish Ictalurus punctatus Ig H chain sequence.

Amino Acid Sequence↗

Localization of insulin-like growth factor-I immunoreactivity in larval and juvenile barramundi (Lates calcarifer).

Antisera to mammalian IGFs cross-react with several fish species, suggesting a long phylogenetic history of IGF-like peptides and their functional importance to all vertebrates. In this study, the tissue distribution of IGF-I-immunoreactivity (IGF-I-IR) was studied at various larval and juvenile stages of the life cycle of barramundi (Lates calcarifer). It was shown that the distribution of IGF-I-IR in this species was tissue-specific and age-dependent. In newly hatched larvae, presumptive musculature in the trunk and the pectoral fin rudiments reacted positively for IGF-I. As specimen age increased, however, IGF-I-IR in these tissues became less evident. In the retinas of barramundi 42 hr and older, a distinct band of IGF-I-IR was consistently detected between the presumptive outer nuclear and bacillary layers. Examination of sections from specimens 9 days and older revealed strong reactivity for IGF-I in a large proportion of renal tubule epithelial cells. In sections from larvae 13 to 28 days old, diffuse cytoplasmic IGF-I-IR was identified in cells lining the gill structures. At these same developmental stages, IGF-I reactive cells were also observed in the islets of Langerhans. In young juveniles (22 to 28 days posthatching), sparsely scattered clusters of neurons in the lower brain were observed which exhibited granular IGF-I-IR in perikarya. In all instances reported, IGF-I-IR in barramundi tissue was abolished by replacing antisera with normal rabbit serum or by preabsorption of antisera with purified IGF-I peptide, indicating the specificity of the reactions obtained. The distribution patterns of IGF-I-IR in barramundi tissues were broadly consistent with the reported distributions of IGF-I-like peptides and transcripts in other teleost species. The findings of this study are in general agreement with the hypothesis that IGF-I-like peptides may be involved in the regulation of tissue growth, differentiation, and function during early barramundi development.

Aging↗

Organization, sequence, and expression of the gene encoding IGFII from barramundi (Teleosteii; Lates calcarifer).

We have characterized the gene encoding IGFII from the teleost fish species barramundi, Lates calcarifer. The barramundi gene spans 5.5 kb of DNA and comprises four exons and three introns. The barramundi and salmon IGFII genes share > 85% sequence similarity across all the exons and also share some regions of high sequence identity within the promoter regions and the introns. The mature barramundi IGFII peptide comprises 70 amino acid residues and shares 84 and 96% similarity with salmonid and seabream IGFII, respectively, with the majority of replacements located in regions cleaved from the mature peptide. IGFII mRNA transcripts were detected in liver, muscle, intestine, gill, heart, and brain from juvenile barramundi. This distribution mirrors that seen in the rainbow trout and seabream and extends the tissue types which synthesize IGFII in fish to include the intestine.

Amino Acid Sequence↗

Streptococcus iniae, a bacterial infection in barramundi Lates calcarifer.

The cause of ongoing mortality in barramundi Lates calcarifer (Bloch) in seawater culture was identified as Streptococcus iniae by biochemical and physiological tests. This is the first published record of this bacterial species in Australia and the first confirmed report of S. iniae causing mortality in barramundi. The bacterium was highly pathogenic for barramundi when challenged by bath exposure. The pathogen was found to have a LD50 of 2.5 x 10(5) and 3.2 x 10(4) colony-forming units at 48 h and 10 d respectively. Experimental challenge of barramundi resulted in high levels of mortality (> 40%) within a 48 h period. Ten days after the challenge, S. iniae could not be isolated from kidney, spleen, liver or eye of surviving fish. However, the organism was easily isolated from the brain of both moribund and healthy fish, indicating that barramundi can carry the bacterium asymptomatically.

Animals↗

Production, in vitro characterisation, in vivo clearance, and tissue localisation of recombinant barramundi (Lates calcarifer) insulin-like growth factor II.

Recombinant barramundi insulin-like growth-factor-II (bIGF-II) has been produced in Escherichia coli after modification of an expression plasmid that coded for a chicken IGF-II fusion protein. The bIGF-II fusion protein, deposited in bacterial inclusion bodies, was dissolved under reducing conditions, desalted, and refolded. The protein was then released from the fusion protein by cleavage with subtilisin BPN'. Finally the protein was purified to homogeneity with a number of HPLC steps. In vitro analysis of recombinant bIGF-II demonstrated decreased potency in stimulating protein synthesis when compared to human and barramundi IGF-I (bIGF-I). The in vivo distribution of radiolabeled bIGF-II and bIGF-I in the circulation and tissue uptake of radiolabeled bIGF-II was also compared in juvenile barramundi (Lates calcarifer). Analysis of trichloroacetic acid-precipitable radioactivity in sequential samples following bolus injection of radiolabeled IGFs revealed that bIGF-II was degraded faster than bIGF-I. Moreover, neutral gel chromatography of these samples suggested this difference may be due to reduced affinity of bIGF-II, compared to blGF-I, for the IGF-binding proteins (IGFBPs) present in the barramundi circulation. Based on these results, it would appear that elements important in the function of IGFs have been well conserved during vertebrate evolution. However, to clearly define the IGF system in fish it will be necessary to characterise the IGFBPs present and to determine how they influence the biological actions of native IGFs.

Amino Acid Sequence↗

Testing the ecotoxicology of vegetable versus mineral based lubricating oils: 2. Induction of mixed function oxidase enzymes in barramundi, Lates calcarifer, a tropical fish species.

An increasing number of vegetable-based oils are being developed as environmentally friendly alternatives to petroleum products. However, toxicity towards key tropical marine species has not been investigated. In this study we used laboratory-based biomarker induction experiments to compare the relative stress of a vegetable-based lubricating oil for marine 2-stroke engines with its mineral oil-based counterpart on tropical fish. The sub-lethal stress of 2-stoke outboard lubricating oils towards the fish Lates calcarifer (barramundi) was examined using liver microsomal mixed function oxidase (MFO) induction assays. This study is the first investigation into the use of this key commercial species in tropical North Queensland, Australia in stress assessment of potential hydrocarbon pollution using ethoxyresorufin O-deethylase (EROD) induction. Our results indicated that barramundi provide a wide range of inducible rates of EROD activity in response to relevant organic stressors. The vegetable- and mineral-based lubricants induced significant EROD activity at 1.0 mg kg(-1) and there was no significant difference between the two oil treatments at that concentration. At increasing concentrations of 2 and 3 mg kg(-1), the mineral-based lubricant resulted in slightly higher EROD activity than the vegetable-based lubricant. The EROD activity of control and treated barramundi are found to be within ranges for other species from temperate and tropical environments. These results indicate that vegetable-based lubricants may be less stressful to barramundi than their mineral counterparts at concentrations of lubricant > or =2 mg kg(-1). There is great potential for this species to be used in the biomonitoring of waterways around tropical North Queensland and SE Asia.

Animals↗

Cloning and analysis of antiviral activity of a barramundi (Lates calcarifer) Mx gene.

We obtained a full-length cDNA clone for the Mx gene of barramundi (Lates calcarifer), using RACE (rapid amplification of cDNA ends) polymerase chain reaction (PCR) amplification of RNA extracted from a barramundi brain cell line cBB. The Mx cDNA of 2.2kb contains an open reading frame (ORF) of 1875 nucleotides encoding a protein of 624 amino acids. The predicted barramundi Mx protein is 71.4 kDa and contains a tripartite guanosinetriphosphate (GTP)-binding motif at the amino terminal and a leucine zipper at the carboxyl terminal, characteristic of all known Mx proteins. Poly I:C-transfection induced the expression of Mx gene in cBB cells, and the induction level at 28 degrees C was higher than that at 20 degrees C. Moreover, Mx gene expression was also induced by viral infection, including fish nodavirus, birnavirus, and iridovirus. Among these, nodavirus was a stronger inducer than the other two viruses. Using an antiviral activity assay, we revealed that poly I:C-transfected cBB cells had antiviral activity against fish nodavirus and birnavirus, but not iridovirus. Furthermore, the replication of nodavirus and birnavirus could be restored after the expression of Mx gene was down-regulated by siRNA. Therefore, these results indicated that the expression of barramundi Mx gene was able to inhibit the proliferation of fish nodavirus and birnavirus.

Amino Acid Sequence↗

Cloning of the barramundi growth hormone-encoding gene: a comparative analysis of higher and lower vertebrate GH genes.

In this work the growth hormone-encoding gene (GH) from the fish barramundi (Lates calcarifer) was characterized by nucleotide (nt) sequence analysis and comparative studies on higher and lower vertebrate GH were performed. The barramundi GH contains six exons and five introns. A putative transcription start point 21 nt downstream from a potential TATAAA box was determined, with a modified primary transcript size of 1615 nt predicted. cis-Acting elements potentially important for transcriptional regulation at the basal, hormone-responsive and pituitary gland-specific levels were identified. Several microsatellite and minisatellite repetitive sequences were shown to be present within noncoding portions of this gene. Repeat sequences similar to the deca- and undeca-minisatellites of the barramundi GH were observed in the corresponding introns of the tilapia, but not other teleost GH. Comparative studies on the Osteichthyes, Mammalia and Aves vertebrate class GH promoters suggested that the TATAAA box was the only conserved region between these sequences. Conserved sequences, however, were identified within the GH promoters of different species from the Osteichthyes or Mammalia classes. The Osteichthyes A + T-rich sequence (consensus GATRMATYWAAWCA, where R = A or G; M = A or C, Y = C or T and W = A or T) is the only conserved region identified between teleost GH promoters, and is most likely involved in the pituitary gland-specific expression of these genes.

Amino Acid Sequence↗

A microsatellite linkage map of Barramundi, Lates calcarifer.

Barramundi (Lates calcarifer) is an important farmed marine food fish species. Its compact genome (approximately 700 Mb) is among the smallest genomes of food fish species. We established a first-generation genetic linkage map of Barramundi with a mapping panel containing three parents (two males and one female) and 93 progeny. A total of 240 microsatellite markers were mapped into 24 linkage groups. Among these markers, 10 were located in ESTs and known genes. The total lengths of the female and male maps were 873.8 and 414.5 cM with an average marker spacing of 6.20 and 4.70 cM, respectively. Comparing the flanking sequences of the 240 Barramundi microsatellites with the assembled whole-genome sequences of Tetraodon nigrovidiris revealed 55 homologous sequences located in 19 of the 21 chromosomes of T. nigrovidiris. The map will not only enable the mapping of quantitative trait loci, but also provide new resources for understanding the evolution of fish genomes.

Animals↗

Immune responses of barramundi, Lates calcarifer (Bloch), after administration of an experimental Vibrio harveyi bacterin by intraperitoneal injection, anal intubation and immersion.

Barramundi, Lates calcarifer (Bloch), were immunized with an experimental Vibrio harveyi bacterin via intraperitoneal injection, immersion and anal intubation. Both specific and non-specific immune parameters were measured to compare responses to bacterin after delivery by various methods. Elevated antibody activities in sera were found in all treatment groups with barramundi injected intraperitoneally displaying significantly higher antibody activity than the other groups. In addition, there was evidence of memory induction with a heightened antibody response in the intraperitoneally injected group only. Bacteriostatic assays indicated activity against V. harveyi in the sera of all bacterin-treated groups; again this activity was significantly higher in the intraperitoneally injected groups. There was no enhancement noted in head kidney macrophage phagocytic activity or in serum lysozyme levels.

Analysis of Variance↗

Isolation, characterization, and linkage analyses of 74 novel microsatellites in Barramundi (Lates calcarifer).

Barramundi (Lates calcarifer) is an important marine food fish species in Southeast Asia and Australia. Seventy-four novel microsatellites were isolated from a genomic DNA library enriched for CA repeats and were characterized in 24 unrelated individuals. Among the 74 microsatellites, 71 were polymorphic, with an average allele number of 7.0 +/- 3.6/locus. The average expected heterozygosity of these polymorphic markers was 0.66. Sixty-three of the 71 polymorphic microsatellites conformed to Hardy-Weinberg equilibrium. Linkage analyses were conducted in a reference family, leading to the assignment of 34 novel microsatellites and 16 published markers in 16 linkage groups. The novel microsatellites developed in this study will contribute significantly to the construction of a first-generation linkage map for mapping of quantitative trait loci in Barramundi, and supply a large choice of markers for studies on population genetics, stock management, and pedigree reconstruction.

Animals↗

Nutritional regulation of insulin-like growth factor-I mRNA expression in barramundi, Lates calcarifer.

The effect of nutritional status on IGF-I mRNA expression in the liver and brain of juvenile barramundi (Lates calcarifer) was investigated. Fish were either fed a satiety ration (SAT) or starved (STV) for 6 weeks. Starved fish demonstrated significantly lower condition factor and hepatic IGF-I mRNA expression at 3 and 6 weeks, when compared with the SAT group. IGF-I mRNA expression in the brain was 10 fold lower than the liver and was not affected by ration size. These results suggest the liver is the major site of IGF-I mRNA synthesis and hepatic but not brain IGF-I mRNA expression is regulated by food availability in juvenile barramundi.

Animals↗

Infection of barramundi Lates calcarifer with Streptococcus iniae: effects of different routes of exposure.

The use of various challenge techniques has allowed the formation of a hypothesis for the mode of infection of Streptococcus iniae in barramundi. A bacterial dose of 1 x 10(3) colony forming units (cfu), corresponding to the LD50, delivered orally to barramundi could initiate the sub-acute form of the disease observed at the farms. The acute form of the disease could be initiated through bath exposure to the pathogen. S. iniae was equally as infective in freshwater, saltwater or when fish were subject to skin trauma prior to exposure, with LD50 values of 3.2 x 10(4), 2.0 x 10(4), 3.2 x 10(4) cfu, respectively, when observed over a 10 d period. It is suggested that sub-acute infection occurs orally, with mass mortalities occurring through the increased presence of the bacterium in the environment.

Acute Disease↗