Phylogenetic studies of sinipercid fish (Perciformes: Sinipercidae) based on multiple genes, with first application of an immune-related gene, the virus-induced protein (viperin) gene

Molecular Characterization and Functional Analysis of Hypoxia-Responsive Factor Prolyl Hydroxylase Domain 2 in Mandarin Fish (Siniperca chuatsi)

With increased breeding density, the phenomenon of hypoxia gradually increases in aquaculture. Hypoxia is primarily mediated by the hypoxia-inducible factor 1 (HIF-1) signaling pathway. Prolyl hydroxylase domain proteins (PHD) are cellular oxygen-sensing molecules that regulate the stability of HIF-1α through hydroxylation. In this study, the characterization of the PHD2 from mandarin fish Siniperca chuatsi (scPHD2) and its roles in the HIF-1 signaling pathway were investigated. Bioinformation analysis showed that scPHD2 had the conserved prolyl 4-hydroxylase alpha subunit homolog domains at its C-terminal and was more closely related to other Perciformes PHD2 than other PHD2. Tissue-distribution results revealed that scphd2 gene was expressed in all tissues tested and more highly expressed in blood and liver than in other tested tissues. Dual-luciferase reporter gene and RT-qPCR assays showed that scPHD2 overexpression could significantly inhibit the HIF-1 signaling pathway. Co-immunoprecipitation analysis showed that scPHD2 could interact with scHIF-1α. Protein degradation experiment results suggested that scPHD2 could promote scHIF-1α degradation through the proteasome degradation pathway. This study advances our understanding of how the HIF-1 signaling pathway is regulated by scPHD2 and will help in understanding the molecular mechanisms underlying hypoxia adaptation in teleost fish.

Molecular characterization and transcriptional conservation of N-myc-interactor, Nmi, by type I and type II IFNs in mandarin fish Siniperca chuatsi

N-myc-interactor (Nmi) belongs to interferon (IFN) stimulated genes (ISGs) and is involved in the regulation of physiological processes including viral infection, inflammatory response, apoptosis and tumorigenesis in mammals. However, the function of Nmi in teleost fish remains to be explored. In this study, an Nmi homologue was characterized from mandarin fish Siniperca chuatsi. The mandarin fish Nmi shares two conserved functional Nmi/IFP35 homology domains (NIDs) with mammalian Nmi protein in its C-terminal domain and a coiled coil region (CC) in its N-terminal domain, with its genomic DNA sequence consisting of nine exons and eight introns. Subcellular localization analysis shows that mandarin fish Nmi is a cytoplasmic protein and that its localization is dependent on the CC and NID1 regions. High and constitutive mRNA level of Nmi was observed in all examined tissues, with the highest level being observed in blood. In addition, the Nmi gene was significantly induced in various organs/tissues following the infection of infectious spleen and kidney necrosis virus (ISKNV), and its mRNA and protein level was also significantly induced in vitro after the treatment of IFNh, IFNc, as well as IFN-γ. The dual luciferase activity analysis indicated that the Nmi promoter was activated by the three type I IFNs through interferon-stimulated response element (ISRE) sites, and it can be also transcriptionally activated by IFN-γ via IRF1 which can activate the expression of Nmi through ISRE. Taken together, it is demonstrated in this study that the transcription of Nmi in mandarin fish can be regulated by type I and type II IFNs, thus confirming that Nmi in fish is also an ISG, and is involved in antiviral and IFN-induced innate immunity.

Transcriptional and subcellular characterization of interferon induced protein-35 (IFP35) in mandarin fish, Siniperca chuatsi

Interferon (IFN)-stimulated genes (ISGs) exert multiple functions in immune system, and IFN-induced protein 35 (IFP35), which is a member of ISG, has been suggested to be involved in numerous cellular activities including the regulation of antiviral immunity in mammals. However, the role of IFP35 in fish innate immunity remains largely unknown. In the present study, we characterized the IFP35 gene in mandarin fish Siniperca chuatsi, which contains two conserved Nmi/IFP35 homology domains (NIDs) at C-terminus, but no leucine zipper motif, with its genomic DNA sequence consisting of eight exons and seven introns. High and constitutive mRNA level of IFP35 was observed in all examined tissues, with the highest level being observed in gills. Moreover, the IFP35 gene was significantly induced in vivo for 120 h following the infection of infectious spleen and kidney necrosis virus (ISKNV), and its mRNA and protein level was also significantly induced in vitro following the treatment of poly I:C, IFNh, IFNc, as well as IFN-γ. The subcellular localization results indicated that exogenous IFP35 protein was mainly located in cytoplasm, while endogenous IFP35 protein was transferred into, or aggregated around, the nucleus with the induction of poly I:C or IFNs. The dual luciferase activity analysis indicated that the IFP35 promoter was activated by type I and type II IFNs through ISRE site. It is considered that IFP35 in fish is involved in antiviral, as well as in IFN-induced innate immunity.

IRF11 regulates positively type I IFN transcription and antiviral response in mandarin fish, Siniperca chuatsi

In vertebrates, a total of eleven interferon (IFN) regulatory factors (IRFs), IRF1 to IRF11 are reported, with the conserved presence of IRF1 to IRF9 in all classes of vertebrates. However, IRF10 has been reported only in fish and birds, and IRF11 seems to be a fish specific IRF member. In this study, IRF11 in mandarin fish Siniperca chuatsi was found upregulated following virus infection, and IRF11 was localized constitutively in nucleus as revealed through immunofluorescence test. The overexpression and/or luciferase reporter assays showed that IRF11 can induce transcriptionally the ISRE activity, and the expression of type I IFNs, IFNc and IFNh, as well as the IFN-stimulated gene, Mx, thus inhibiting the Siniperca chuatsi rhabdovirus (SCRV) replication as indicated in the reduced expression of virus protein genes. It is thus suggested that IRF11 in mandarin fish and probably in other teleost fish can exert its antiviral effect through the upregulation of type I IFNs and ISGs.

Myxovirus resistance (Mx) gene and its differential expression regulated by three type I and two type II IFNs in mandarin fish, Siniperca chuatsi

Interferons (IFNs) can induce the expression of IFN-stimulated genes (ISGs), such as myxovirus resistance (Mx) protein, to inhibit virus replication. In this study, the expression of Mx gene in mandarin fish, and the IFN-sensitive response elements (ISREs) and gamma-interferon activated sites (GASs) in the promoter of Mx gene were analyzed in relation to the stimulation of three distinct type I IFNs, IFNc, IFNd and IFNh, and two type II IFNs, IFN-γ and IFN-γ related molecule (IFN-γrel). A single Mx gene was found in mandarin fish, and its expression was highly and constitutively observed in all organs/tissues examined. The Mx gene was significantly induced in vivo for 120 h following infectious spleen and kidney necrosis virus (ISKNV) infection. Furthermore, the overexpression and recombinant of IFNh, IFNc, as well as IFN-γ can significantly induce Mx expression in MFF-1 cells at transcript and protein levels, although all the three type I IFNs and the two type II IFNs can activate the Mx promoter. In addition, ISRE1 which is the proximal one among the three predicted ISREs seems to be the important ISRE for the higher and efficient activation of the Mx promoter. However, the possible interaction between the GASs and type II IFN signalling molecules require further study.

Receptor complex and signalling pathway of the two type II IFNs, IFN-γ and IFN-γrel in mandarin fish or the so-called Chinese perch Siniperca chuatsi

IFN-γ, as the sole member of mammalian type II IFN, is a multifunctional cytokine which exerts its effects through two distinct IFN-γ receptors, IFNGR1 and IFNGR2. However, in teleost fish, another IFN-γ homologous gene, namely IFN-γ related gene (IFN-γrel), has been identified. Although IFN-γ and IFN-γrel genes have been described in some fish species, many important aspects remain poorly understood in relation with their signalling and function. In the present study, IFN-γ and IFN-γrel, as well as their receptors, cytokine receptor family B (CRFB) 17, CRFB13, two of which are homologous to IFNGR1 in mammals, and CRFB6, homolomous to IFNGR2, have been characterized in mandarin fish, Siniperca chuatsi. It was revealed that the two type IFN members exhibit antiviral activity, and IFN-γ transduces downstream signalling through CRFB13 and CRFB6, while IFN-γrel interacts with CRFB17 to activate downstream signalling. Moreover, IFN-γ and IFN-γrel have been shown to exert antiviral biological activity in a STAT1-dependent manner. Intracellular domain analysis of CRFB17 and CRFB13 demonstrated that the Y386 tyrosine residue of CRFB13 is required for the activation of the IFN-γ-mediated biologic response, and the Y324 and Y370 residues in CRFB17 are required to activate IFN-γrel signalling.

Characterization and Transcript Expression Analyses of Atlantic Cod Viperin

Viperin is a key antiviral effector in immune responses of vertebrates including the Atlantic cod (Gadus morhua). Using cloning, sequencing and gene expression analyses, we characterized the Atlantic cod viperin at the nucleotide and hypothetical amino acid levels, and its regulating factors were investigated. Atlantic cod viperin cDNA is 1,342 bp long, and its predicted protein contains 347 amino acids. Using in silico analyses, we showed that Atlantic cod viperin is composed of 5 exons, as in other vertebrate orthologs. In addition, the radical SAM domain and C-terminal sequences of the predicted Viperin protein are highly conserved among various species. As expected, Atlantic cod Viperin was most closely related to other teleost orthologs. Using computational modeling, we show that the Atlantic cod Viperin forms similar overall protein architecture compared to mammalian Viperins. qPCR revealed that viperin is a weakly expressed transcript during embryonic development of Atlantic cod. In adults, the highest constitutive expression of viperin transcript was found in blood compared with 18 other tissues. Using isolated macrophages and synthetic dsRNA (pIC) stimulation, we tested various immune inhibitors to determine the possible regulating pathways of Atlantic cod viperin. Atlantic cod viperin showed a comparable pIC induction to other well-known antiviral genes (e.g., interferon gamma and interferon-stimulated gene 15-1) in response to various immune inhibitors. The pIC induction of Atlantic cod viperin was significantly inhibited with 2-Aminopurine, Chloroquine, SB202190, and Ruxolitinib. Therefore, endosomal-TLR-mediated pIC recognition and signal transducers (i.e., PKR and p38 MAPK) downstream of the TLR-dependent pathway may activate the gene expression response of Atlantic cod viperin. Also, these results suggest that antiviral responses of Atlantic cod viperin may be transcriptionally regulated through the interferon-activated pathway.

Functional, signalling and transcriptional differences of three distinct type I IFNs in a perciform fish, the mandarin fish Siniperca chuatsi

Teleost fish are unique in having type I and type II interferons (IFNs) only, and the type I IFNs are classified into Group one and Group two based on the presence of two or four cysteines respectively, and are further classified into seven subgroups. In the present study, three distinct type I IFNs, IFNc, IFNd and IFNh, have been identified in the genome sequences of a perciform fish, the mandarin fish Siniperca chuatsi. These IFNs are induced following the stimulation of Polyinosinic polycytidylic acid (poly(I:C)) and Resiquimod (R848) either in vivo or in vitro. But, the infectious spleen and kidney necrosis virus (ISKNV) infection caused a delayed response of IFNs, which may be resulted from the viral inhibition of type I IFN production and related signalling. The three receptor subunits, cytokine receptor family B 1 (CRFB1), CRFB2 and CRFB5 are also expressed in a similar manner as observed for the IFNs, and IFNc, IFNd and IFNh use preferentially the receptor complex, CRFB2 and CRFB5, CRFB1 and CRFB5, CRFB1 and CRFB5 respectively for their effective signalling in the induction of IFN-stimulated genes (ISGs). Moreover, the IFNs are able to induce their own expression, and also the IRF3 and IRF7 expression, leading to the amplification of IFN cascade. It is further revealed that these three IFNs are transcribed differently by IRF7 and IRF3. The composition, function, signalling and transcription of type I IFNs have been investigated in detail in a teleost fish.

Composition and transcription of all interferon regulatory factors (IRFs), IRF1‒11 in a perciform fish, the mandarin fish, Siniperca chuatsi

Interferon regulatory factors (IRFs) are a family of mediators in various biological processes including immune modulation of interferon (IFN) and proinflammatory cytokine expression. However, the data on the complete composition of IRFs is rather limited in teleost fish. In the present study, all IRF members, i.e. IRF1‒11 with two IRF4, IRF4a and IRF4b have been characterised in an aquaculture species of fish, the mandarin fish, Siniperca chuatsi, in addition to the previous report of IRF1, IRF2, IRF3 and IRF7 from the fish. These IRFs are constitutively expressed in various organs/tissues of the fish, and their expression can be induced following the stimulation of polyinosinic:polycytidylic acid (poly(I:C)) and the infection of infectious spleen and kidney necrosis virus (ISKNV), a viral pathogen of mandarin fish in aquaculture. The ISKNV infection induced the significant increase in the expression of some IRF genes, i.e. IRF2, IRF4a, IRF7, IRF9, IRF10 at 24 or 36 h post-infection (hpi) in spleen and head-kidney, and the significant increase of some other IRF genes, e.g. IRF1, IRF3, IRF4b, IRF5, IRF6, IRF8 at later stage of infection from 72, or 96, or even 120 hpi, which may imply the inhibitory effect of ISKNV on fish immune response. It is considered that the present study provides the first detailed analysis on all IRF members in an aquaculture species of fish, and can be served as the base for further investigation on the role of IRFs in teleost fish.

Species delimitation and phylogenetic reconstruction of the sinipercids (Perciformes: Sinipercidae) based on target enrichment of thousands of nuclear coding sequences

The sinipercids are freshwater fishes endemic to East Asia, mainly in China. Phylogenetic studies on the sinipercids have made great progress in the last decades, but interspecific relationships and evolutionary history of the sinipercids remain unresolved. Lack of distinctive morphological characters leads to problems in validating of some species, such as Siniperca loona. Moreover, genetic data are needed to delimitate species pairs with explicit hypothesis testing, such as in S. chuatsi vs. S. kneri and Coreoperca whiteheadi vs. C. liui. Here we reconstructed phylogeny of the sinipercids with an unprecedented scale of data, 16,943 loci of single-copy coding sequence data from nine sinipercid species, eight putative sister taxa and two outgroups. Targeted sequences were collected using gene enrichment and Illumina sequencing, yielding thousands of protein coding sequences and single nucleotide polymorphisms (SNPs) data. Maximum likelihood and coalescent species tree analyses resulted in identical and highly supported trees. We confirmed that the centrarchids are sister to the sinipercids. A monophyletic Sinipercidae with two genera, Siniperca and Coreoperca was also supported. Different from most previous studies, S. scherzeri was found as the most basal taxon to other species of Siniperca, which consists of two clades: a clade having S. roulei sister to S. chuatsi and S. kneri, and a clade consisting S. loona sister to S. obscura and S. undulata. We found that both S. loona and C. liui are valid species using Bayes factor delimitation (BFD^∗) based on SNPs data. Species delimitation also provided decisive support for S. chuatsi and S. kneri being two distinct species. We calibrated a chronogram of the sinipercids based on 100 loci and three fossil calibration points using BEAST, and reconstructed ancestral ranges of the sinipercids using Lagrange Analysis (DEC model) and Statistical Dispersal-Vicariance Analysis (S-DIVA) implemented in RASP. Divergence time estimates and ancestral habitat reconstruction suggested a wide-ranging distribution of the common ancestor of the sinipercids in southern China at 53.1 million years ago (CI: 30.4-85.8Ma). The calibrated time tree is consistent with historical climate changes and geological events that might have shaped the current distribution of the sinipercids.

A member of the immunoglobulin superfamily, orange-spotted grouper novel immune gene EcVig, is induced by immune stimulants and type I interferon

A novel grouper immune gene, EcVig was identified in orange-spotted grouper (Epinephelus coioides). We recently determined that EcVig expression can be induced by infection with nervous necrosis virus (NNV, an RNA virus), whereas NNV replication may be suppressed when EcVig was overexpressed. Although EcVig appeared to be involved in grouper antiviral activity, its immune effects have not been well characterized. In the present study, two PAMPs (pathogen-associated molecular patterns; lipopolysaccharides [LPS] and synthetic double-stranded RNA polyriboinosinic-polyribocytidylic acid [poly(I:C)]), as well as fish DNA virus (red sea bream iridovirus, RSIV; grouper iridovirus, GIV), were used to study EcVig responses in orange-spotted grouper. In addition, groupers were given recombinant type I interferon to determine whether EcVig expression was induced. Poly(I:C) rapidly induced substantial expression of EcVig, whereas LPS stimulation did not appear to have any effect in grouper intestine. Expression levels of total EcVig and other IFN-stimulated genes (ISGs) were all significantly increased after RSIV and GIV infection. Furthermore, stimulation of recombinant type I IFN also increased EcVig expression. We conclude that EcVig may be a novel IFN-stimulated gene that demonstrates an antiviral immune response.

Disease resistance and immune-relevant gene expression in golden mandarin fish, Siniperca scherzeri Steindachner, infected with infectious spleen and kidney necrosis virus-like agent

Infectious spleen and kidney necrosis virus (ISKNV), family Iridoviridae, genus Megalocytivirus, may cause high mortality rates such as those seen in mandarin fish, Siniperca chuatsi. ISKNV has attracted much attention due to the possible environmental threat and economic losses it poses on both cultured and wild populations. We have investigated the pathogenicity of ISKNV-like agent Megalocytivirus, isolated from infected pearl gourami, in golden mandarin fish, Siniperca scherzeri - a member of the Percichthyidae family - and in another Percichthyidae species, S. chuatsi. Fish were challenged with four different doses of ISKNV-like agent Megalocytivirus (1, 10, 100 or 1000 μg per fish) over a 30-day period, and cumulative fish mortalities were calculated for each group. No significant mortality was observed for fish challenged with the lowest dose (1 μg per fish) relative to a control group. However, all other challenged groups showed 100% mortality over a 30-day period in proportion to the challenge dose. Quantitative real-time PCR was performed to measure mRNA expression levels for six immune-related genes in golden mandarin fish following ISKNV-like agent challenge. mRNA expression levels for IRF1, Mx, viperin and interleukin 8 significantly increased, while mRNA levels for IRF2 and IRF7 remained constant or declined during the challenge period.

Molecular phylogeny of weakfish species of the Stellifer group (Sciaenidae, Perciformes) of the western South Atlantic based on mitochondrial and nuclear data

The phylogenetic relationships within the Stellifer group of weakfishes (Stellifer, Odontoscion, Ophioscion, and Bairdiella) were evaluated using 2723 base pairs comprising sequences of nuclear (rhodopsin, TMO-4C4, RAG-1) and mitochondrial (16S rRNA and COI) markers obtained from specimens of nine species. Our results indicate a close relationship between Bairdiella and Odontoscion, and also that the genus Stellifer is not monophyletic, but rather that it consists of two distinct lineages, one clade containing S. microps/S. naso/S. brasiliensis and the other, S. rastrifer/S. stellifer/Stellifer sp. B, which is closer to Ophioscion than the former clade. The O. punctatissimus populations from the northern and southern Brazilian coast were also highly divergent in both nuclear (0.8% for rhodopsin and 0.9% for RAG-1) and mitochondrial sequences (2.2% for 16S rRNA and 7.3% for COI), which we conclude is consistent with the presence of two distinct species. The morphological similarities of the members of the Stellifer group is reinforced by the molecular data from both the present study and previous analyses, which have questioned the taxonomic status of the Stellifer group. If, on the one hand, the group is in fact composed of four genera (Stellifer, Ophioscion, Odontoscion, and Bairdiella), one of the two Stellifer clades should be reclassified as a new genus. However, if the close relationship and the reduced genetic divergence found within the group is confirmed in a more extensive study, including representatives of additional taxa, this, together with the morphological evidence, would support downgrading the whole group to a single genus. Obviously, these contradictory findings reinforce the need for a more systematic taxonomic revision of the Stellifer group as a whole.

EcVig, a novel grouper immune-gene associated with antiviral activity against NNV infection

VHSV-induced genes (VIGs) were first identified in rainbow trout (Oncorhynchus mykiss) and subsequently isolated in a variety of fish. Recent studies have shown that most VIGs have immunological functions against pathogenic infections. However, most research has focused on Vig1, such that our present understanding of these genes in other fish species remains limited. This study isolated a homologue of the uncharacterized O. mykiss Vig-B319 (EcVig) from orange-spotted grouper (Epinephelus coioides). Genomic organization suggests that four EcVig isoforms (EcVig A-D), are generated through alternative splicing. Due to the encoding of 2 immunoglobulin (Ig) domains, the EcVig protein can be considered a member of the immunoglobulin superfamily. The expression of EcVig increased 3 days after hatching (dph) and peaked at 9 dph. This pattern is similar to that displayed by EcMx, an important grouper antiviral gene. Additionally, a tissue tropism assay revealed that EcVig A is the major EcVig isoform present in the tissues considered by this study, with the expression of EcVig A exceeding that of EcVig B. We subsequently investigated whether EcVig expression was induced by the viral pathogen nervous necrosis virus (NNV) or the bacterial pathogen Vibrio anguillarum. Following injection with NNV, the expression levels of EcVig showed significant up-regulation. Conversely, a significant reduction was observed in EcVig expression in brain samples collected from V. anguillarum injected grouper. The overexpression of EcVig A suppressed the replication of NNV in grouper GF-1 cell lines, suggesting that EcVig is an important antiviral factor in the grouper immune responses.

The complete mitochondrial genome sequence of Siniperca undulate (Perciformes: Percichthyidae)

In this paper, the complete mitochondrial DNA (mtDNA) sequence of Siniperca undulate was determined. The complete mtDNA genome sequence of S. undulate was 16,504 bp in length. It consisted of 13 protein-coding genes, 22 transfer RNA genes, 2 rRNA genes and 2 non-coding regions. Overall base composition of mitogenome was estimated to be 28.38% for A, 29.43% for C, 16.46% for G and 25.73% for T, respectively, with a high A + T content (54.11%). The complete mitogenome of the S. undulate can provide a basic data for the studies on population history, molecular systematics, phylogeography, stock evaluation and conservation genetics. It is also helpful to the reasonable utilization and development of rational management strategies for S. undulate resource.

Characterization of tilapia (Oreochromis niloticus) viperin expression, and inhibition of bacterial growth and modulation of immune-related gene expression by electrotransfer of viperin DNA into zebrafish muscle

Viperin is an anti-viral protein, induced by viral infection. In this study, we examined whether over-expression of viperin in fish muscle could inhibit bacterial growth. We first obtained the cDNA sequence of tilapia viperin, through RT-PCR-mediated cloning and sequencing. The cDNA sequence was similar to those of several fish viperins in GenBank, and it was predicted to encode the conserved domain of radical S-adenosylmethionine superfamily proteins. Phylogenetic analysis revealed that tilapia viperin was most closely related to viperin of Sciaenops ocellatus, Coreoperca kawamebari, and C. whiteheadi. Expression of tilapia viperin was significantly up-regulated in the kidney, liver, spleen, and gills upon challenge with lipopolysaccharide (LPS) and poly(I:C) in a time- and dose-dependent manner. Injection of Vibrio vulnificus (204) and Streptococcus agalactiae (SA47) bacteria into tilapia resulted in significant induction of viperin expression in the whole body, kidney, liver, and spleen. Electrotransfer of a viperin-expressing plasmid into zebrafish muscles decreased bacterial numbers and altered expression of immune-related genes. These data indicate that such altered expression may account for the improvement in bacterial clearance following electroporation of viperin, suggesting that fish viperin has antiviral and antibacterial activities.

Positive selection drives rapid evolution of certain amino acid residues in an evolutionarily highly conserved interferon-inducible antiviral protein of fishes

Viperin, an evolutionarily highly conserved interferon-inducible multifunctional protein, has previously been reported to exhibit antiviral activity against a wide range of DNA and RNA viruses. Utilizing the complete nucleotide coding sequence data of fish viperin antiviral genes, and employing the maximum likelihood-based codon substitution models, the present study reports the pervasive role of positive selection in the evolution of viperin antiviral protein in fishes. The overall rate of nonsynonymous (dN) to synonymous (dS) substitutions (dN/dS) for the three functional domains of viperin (N-terminal, central domain and C-terminal) were 1.1, 0.12, and 0.24, respectively. Codon-by-codon substitution analyses have revealed that while most of the positively selected sites were located at the N-terminal amphipathic α-helix domain, few amino acid residues at the C-terminal domain were under positive selection. However, none of the sites in the central domain were under positive selection. These results indicate that, although viperin is evolutionarily highly conserved, the three functional domains experienced differential selection pressures. Taken together with the results of previous studies, the present study suggests that the persistent antagonistic nature of surrounding infectious viral pathogens might be the likely cause for such adaptive evolutionary changes of certain amino acids in fish viperin antiviral protein.

Phylogenetic studies of three sinipercid fishes (Perciformes: Sinipercidae) based on complete mitochondrial DNA sequences

The sinipercids are a group of 12 species of freshwater percoid fish endemic to East Asia and their phylogenetic placements have perplexed generations of taxonomists. We cloned and sequenced the complete mitochondrial DNA (mtDNA) of three sinipercid fishes (Siniperca chuatsi, S. kneri, and S. scherzeri) to characterize and compare their mitochondrial genomes. The mitochondrial genomes of S. chuatsi, S. kneri, and S. scherzeri were 16,496, 17,002, and 16,585 bp in length, respectively. The organization of the three mitochondrial genomes is similar to those reported from other fish mitochondrial genomes, which contains 37 genes (13 protein-coding genes, 2 ribosomal RNAs, and 22 transfer RNAs) and a major non-coding control region. Among the 13 protein-coding genes of all the three sinipercid fishes, three reading-frame overlaps were found on the same strand. There is an 81-bp tandem repeat cluster at the end of CSB-3 in the S. scherzeri control region. The complete mitochondrial genomes of the three sinipercids should be useful for the evolutionary studies of sinipercids and other vertebrate species.

Application of 16s rDNA and cytochrome b ribosomal markers in studies of lineage and fish populations structure of aquatic species

The most economically important form of aquaculture is fish farming, which is an industry that accounts for an ever increasing share of world fishery production. Molecular markers can be used to enhance the productivity of the aquaculture and fish industries to meet the increasing demand. Molecular markers can be identified via a DNA test regardless of the developmental stage, age or environmental challenges experienced by the organism. The application of 16s and cytochrome b markers has enabled rapid progress in investigations of genetic variability and inbreeding, parentage assignments, species and strain identification and the construction of high resolution genetic linkage maps for aquaculture fisheries. In this review, the advantages of principles and potential power tools of 16s and cytochrome b markers are discussed. Main findings in term of trend, aspects and debates on the reviewed issue made from the model of aquatic species for the benefit of aquaculture genomics and aquaculture genetics research are discussed. The concepts in this review are illustrated with various research examples and results that relate theory to reality and provide a strong review of the current status of these biotechnology topics.

Early antiviral response and virus-induced genes in fish

In fish as in mammals, virus infections induce changes in the expression of many host genes. Studies conducted during the last fifteen years revealed a major contribution of the interferon system in fish antiviral response. This review describes the screening methods applied to compare the impact of virus infections on the transcriptome in different fish species. These approaches identified a "core" set of genes that are strongly induced in most viral infections. The "core" interferon-induced genes (ISGs) are generally conserved in vertebrates, some of them inhibiting a wide range of viruses in mammals. A selection of ISGs -PKR, vig-1/viperin, Mx, ISG15 and finTRIMs - is further analyzed here to illustrate the diversity and complexity of the mechanisms involved in establishing an antiviral state. Most of the ISG-based pathways remain to be directly determined in fish. Fish ISGs are often duplicated and the functional specialization of multigenic families will be of particular interest for future studies.

The phylogenetic placement of sinipercid fishes ("Perciformes") revealed by 11 nuclear loci

Sinipercids are freshwater fishes from East Asia assigned to the genera Siniperca (8-9 species) and Coreoperca (3 species). Although supported as a monophyletic group, the phylogenetic placement of sinipercids among percomorph fishes and the identification of their closest relatives have perplexed generations of taxonomists. Here, we collect and analyze new molecular evidence from 11 nuclear genes - six of them novel markers developed for this study - sampled from seven sinipercid species and several closely-related species that have been proposed as their putative sister taxa in the past. The concatenated alignment of the 11 loci included 10,560bp that were split into 18 blocks for a partitioned analysis using Bayesian and Maximum Likelihood methods. Both approaches resulted in nearly identical topologies, in which the monophyly of the sinipercids was strongly supported (Bootstrap Support=99; Posterior Probability=1.0) with Centrarchidae as their sister taxon (BS=87; PP=1.0). Percichthyidae formed a sister group to the sinipercid-centrarchid clade (BS=100; PP=1.0). Tests for alternative hypotheses of relationships significantly rejected the placement of sinipercids within the Serranidae, Moronidae, or Centropomidae, or as sister taxon to Lateolabrax japonicus, Perca flavescens, or Pristigenys alta (SH test, p<0.001,). The contribution of individual gene genealogies to support this result was explored further using a multispecies coalescent approach (BEST) to infer the species phylogeny. The sister-group relationship with Centrarchidae also is supported by this approach but relationships among species within the genus Siniperca showed a different pattern than the results obtained with the concatenated data set. Our study supports the designation of a distinct family, Sinipercidae, for this group of fishes (Siniperca and Coreoperca).