Molecular cloning and functional characterization of interferon regulatory factor 7 of the barbel chub, Squaliobarbus curriculus

The regulatory mechanisms of IRF7 mediated by the type I IFN signalling pathway against Streptococcus iniae in yellowfin seabream, Acanthopagrus latus (Hottuyn, 1782)

Interferon regulatory factor 7 (IRF7) regulates type I interferon (IFN) genes via combining to the ISRE region in the immune response against bacteria. Streptococcus iniae is one of the dominant pathogenic bacteria of yellowfin seabream, Acanthopagrus latus. However, the regulatory mechanisms of A. latus IRF7 (AlIRF7) mediated by the type I IFN signalling pathway against S. iniae was ambiguously. In the present study, IRF7, and two IFNa3s (IFNa3 and IFNa3-like) were authenticated from A. latus. The total length of AlIRF7 cDNA is 2142 bp, containing a 1314 bp open reading frame (ORF) encoding an inferred 437 amino acids (aa). Three typical regions, a serine-rich domain (SRD), a DNA-binding domain (DBD), and an IRF association domain (IAD), are conserved in AlIRF7. Furthermore, AlIRF7 is fundamentally expressed in various kinds of organs, with high levels in the spleen and liver. Additionally, S. iniae challenge promoted AlIRF7 expression in the spleen, liver, kidney, and brain. AlIRF7 is confirmed to be located at the nucleus and cytoplasm by overexpression of AlIRF7. Moreover, truncation mutation analyses shows that the regions, -821 bp to +192 bp and -928 bp to +196 bp, were known as core promoters from AlIFNa3 and AlIFNa3-like, respectively. The point mutation analyses and electrophoretic mobile shift assay (EMSA) verified that AlIFNa3 and AlIFNa3-like transcriptions are depended on the M2/5 and M2/3/4 binding sites with AlIRF7 regulation, respectively. Additionally, an overexpression experiment showed that AlIRF7 can dramatically decrease the mRNA levels of two AlIFNa3s and interferon signalling molecules. These results suggest that two IFNa3s may mediate the regulation of AlIRF7 in the immune responses of A. latus against S. iniae infection.

Interferon regulatory factor 7 contributes to the host response during Vibrio harveyi infection in the golden pompano Trachinotus ovatus

Vibrio harveyi is regarded as serious pathogen for marine fishes. However, host defense mechanisms involved in V. harveyi infection remain incompletely defined. The transcription factor IFN regulatory factor 7 (IRF7) is largely associated with host defense against viral infections, and the role of IRF7 during V. harveyi infection in fish has not been well illuminated previously. In this study, IRF7 from golden pompano (Trachinotus ovatus) was characterized (TroIRF7). The TroIRF7 gene is 1323 bp, which encodes 440 amino acid residues. Multiple amino acid alignments of TroIRF7 shows 30.37%-80.18% identity with other fish IRF7s, including Epinephelus coioides (80.18%), Larimichthys crocea (79.72%), Collichthys lucidus (79.26%), Miichthys miiuy (79.26%), Channa argus (78.77%), Cynoglossus semilaevis (72.67%), and Gadus morhua (65.23%). Like other IRF7s, TroIRF7 also contains 3 conserved domains: an N-terminal DNA-binding domain (DBD), an IRF association domain (IAD), and a C-terminal serine-rich domain (SRD). In the DBD, 4-5 conserved tryptophans were observed, which is a characteristic unique to all fish IRF7 members. TroIRF7 was constitutively expressed, with high levels in gill, head kidney, spleen, skin, and intestine. V. harveyi infection-induced TroIRF7 transcripts significantly up-regulation and translocation to the nucleus. TroIRF7 overexpression promote the fish to inhibit the replication of V. harveyi. And TroIRF7 knockdown led to decreased bacterial clearance in fish tissue. Furthermore, over-expression of TroIRF7 resulted in an increased production of interferon a3 and IFN signaling molecule in the spleen, suggesting that V. harveyi activates the IRF7- IFN pathway. These results suggest that TroIRF7 is an important component of immune responses against V. harveyi infection.

Molecular characterization of yellow catfish (Pelteobagrus fulvidraco) IRF7 suggests involvement in innate immune response

Interferon regulatory factor 7 (IRF7) serves as a critical mediator in the regulation of type Ι interferon (IFN) response to invading pathogens. Here, an ortholog of IRF7 was characterized in yellow catfish (Pelteobagrus fulvidraco). The full-length cDNA of PfIRF7 consisted of 1516 bp encoding a polypeptide of 425 amino acids. PfIRF7 protein comprised a typical IRF structural architecture, including a DNA binding domain (DBD), an IRF association domain (IAD) and a serine-rich domain (SRD). PfIRF7 was expressed predominantly in the immune-related tissues and transcriptionally upregulated by PolyI:C, LPS, and Edwardsiella ictaluri. Ectopic expression of PfIRF7 led to activation of fish type I IFN promoters and induction of IFN and Vig1, thereby conferring a strong antiviral effect against spring viremia of carp virus (SVCV). Overall, the present data suggest that PfIRF7 may play an essential role in type I IFN response of yellow catfish.

GH and GHR gene cloning, expression and their associations with growth-related traits of the barbel chub (Squaliobarbus curriculus)

Growth hormone (ScGH) and growth hormone receptor (ScGHR) genes from the barbel chub (Squaliobarbus curriculus), in addition to their cDNAs, were cloned. The associations between their mRNA expression levels and growth-related traits were analysed, and the differences in the levels of expression of growth regulation-related genes between the largest and smallest individuals were compared. The full-length 1182-bp cDNA of ScGH contained a 633-bp open reading frame (ORF), and the length of the gene had 2492 bp. The full-length 2825-bp cDNA of ScGHRa contained a 1818-bp ORF, and the gene had 6970 bp. The full-length 2822-bp cDNA of ScGHRb contained a 1737-bp ORF, and the gene had 8149 bp. Quantitative real-time PCR revealed that ScGH was only expressed in the pituitary. ScGHRa was expressed predominantly in muscle, and the expression level of ScGHRb was the highest in the liver. The ScGHRa mRNA levels in the muscle were significantly negatively correlated with the caudal peduncle length. However, no correlation between growth-related traits and ScGH and ScGHRb expression levels were found. Pituitary ScGH, liver GHRb and liver insulin-like growth factor I (igf-1) expression levels were significantly higher in the largest individuals than those in the smallest S. curriculus individuals. Contrarily, the largest individuals had significantly lower expression levels of muscle igf-1 and liver myog than the smallest individuals. Overall, our results provide novel molecular information for growth-regulation study of S. curriculus.

Sequence and expression analysis of the cytoplasmic pattern recognition receptor melanoma differentiation-associated gene 5 from the barbel chub Squaliobarbus curriculus

MDA5 is a cytoplasmic viral double-stranded RNA recognition receptor that plays a pivotal role in the aquatic animal innate immune system. To decipher the role of MDA5 of Squaliobarbus curriculus (ScMDA5) in the immune response, full-length cDNA of ScMDA5 was cloned using the RACE technology, mRNA and protein expression levels of ScMDA5 signalling pathway members in response to stimulation were detected and effects of overexpression of ScMDA5 on the immune response were investigated. ScMDA5 comprises 3597 bp and is composed of an open reading frame (2958 nucleotides long) that translates into a putative peptide of 985 amino acid residues. ScMDA5 possesses two N-terminal caspase-recruiting domains, DEAD-like helicases superfamily, helicase superfamily C-terminal and RIG-I_C-RD domains, and differences in these domains among species were mainly observed with respect to their length and location. ScMDA5 was closely clustered with those of Carassius auratus, Ctenopharyngodon idellus and Mylopharyngodon piceus. ScMDA5 transcripts were most abundant in the spleen and the lowest in the liver. Expression levels of ScMDA5 in healthy tissues were significantly correlated with those of ScIRF3, ScIRF7 and ScIFN. Besides, mRNA expression levels of ScIRF3 were significantly correlated with those of ScIRF7 (0.956, P < 0.01). Expression level changes, including downregulation, upregulation and initial upregulation followed by downregulation, were found in ScMDA5 signalling pathway molecules in tissues after grass carp reovirus infection. Protein levels of ScMDA5 were the highest in the liver and the lowest in the spleen in detected healthy tissues. Overexpression of ScMDA5 led to significantly enhanced CiIRF7 and CiMx transcription in grass carp ovary cells (P < 0.05). The results of this study helped to clarify the role of ScMDA5 in the immune reaction against grass carp reovirus and provided fundamental information for fish breeding to achieve strong resistance to infection.

Functional characterization of dark sleeper (Odontobutis obscura) IRF3 in IFN regulation

The dark sleeper, Odontobutis obscura (O. obscura), is a commercially important species of freshwater sleeper native to East Asia. However, its molecular biology system is unexplored, including the interferon (IFN) signaling pathway, which is crucial to the antiviral response. In this study, we characterised the IFN regulation pattern of dark sleeper interferon regulatory factor 3 (OdIRF3), supplementing evidence of the conservation of this classical pathway in fish. First, the open reading frame (ORF) of OdIRF3 was cloned from the liver tissue by Rapid amplification of cDNA ends (RACE). Amino acid sequence analysis suggested that OdIRF3 is homologous with other fish IRF3 and that the N-terminal DNA-binding domain (DBD) and the C-terminal IRF-association domain (IAD) are conserved. Then, the cellular distribution demonstrated that OdIRF3 is located in the cytoplasm region and transfers into the nuclear region under stimulation. For the function identification, OdIRF3 activated several types of IFN promoters and induced downstream interferon stimulated genes (ISGs) expression. Finally, the overexpression of OdIRF3 significantly decreased viral proliferation. Taken together, these data systematically characterised the sequence, cellular location, and function in IFN expression of OdIRF3, shedding light on the molecular biology mechanism of the dark sleeper.

Molecular characterization and expression of TLR7 and TLR8 in barbel chub (Squaliobarbus curriculus): Responses to stimulation of grass carp reovirus and lipopolysaccharide

The barbel chub (Squaliobarbus curriculus) is a kind of small size commercial fish species that is widely spread in Asia and has shown significant resistance to disease. In this study, the full-length cDNA sequences of Toll-like receptor (TLR) 7 and 8 from S. curriculus, designated as ScTLR7 and ScTLR8, were cloned, and their differences in the structure and the responses to the grass carp (GCRV) infection and lipopolysaccharide stimulation were investigated. The full-length 3715 base pair (bp) cDNA of ScTLR7 contained a complete open reading frame of 3162 bp and encoded a putative polypeptide of 1053 amino acid residues. The full-length 4624 base pair (bp) cDNA of ScTLR8 contained a complete open reading frame of 3072 bp and encoded a putative polypeptide of 1023 amino acid residues. ScTLR7 and ScTLR8 consisted of N-terminal signal peptide, leucine-rich repeats (LRRs), and Toll/IL-1 Receptors domain. LRR motifs of ScTLR7 and ScTLR8 bend into horseshoe-like solenoid structure, while the number of LRRs between the two genes is different. Phylogenetic analysis showed that both the ScTLR7 and ScTLR8 were closely clustered with Ctenopharyngodon idellus and Megalobrama amblycephala. Quantitative real-time polymerase chain reaction analysis showed that the expression levels of ScTLR7 in S. curriculus were most abundant in the brain followed by the spleen and heart, and the lowest in the intestine. The highest expression level of ScTLR8 was observed in spleen and the lowest in the liver. After LPS stimulation, the relative expression levels of both ScTLR7 and ScTLR8 exhibited an overall trend of up-regulation. The expression levels of type I-IFN showed an overall trend of down-regulation at time points of 12, 24, 72 and 168 h compared to that of 6 h after LPS stimulation. Compared to 6 h post GCRV infection, the transcription level of ScTLR7 was up-regulated from 12 to 168 h, and transcription levels of ScTLR8, MyD88, and type I-IFN were firstly up-regulated from 12 to 72 h, and then down-regulated from 72 to 168 h. Correlation analysis showed that expression level of ScTLR7 in the spleen was significantly positively correlated with that of MyD88 (Pearson correlation coefficient: 0.909, P: 0.033), and a significantly positive correlation was also observed between expression levels of MyD88 and type I IFN (Pearson correlation coefficient: 0.962, P: 0.009), after GCRV stimulation. These results indicate that ScTLR7 and ScTLR8 may play important roles in the responses to the grass carp (GCRV) infection and lipopolysaccharide stimulation and trigger different downstream immune signal pathways.

Duck interferon regulatory factor 7 (IRF7) can control duck Tembusu virus (DTMUV) infection by triggering type I interferon production and its signal transduction pathway

Human interferon regulatory factor 7 (IRF7) plays an important role in the innate antiviral immune response. To date, the characteristics and functions of waterfowl IRF7 have not been clarified. This study reports the cDNA sequence, tissue distribution, and antiviral function of duck IRF7. The duck IRF7 gene has a 1536-bp open read frame (ORF) and encodes a 511-amino acid polypeptide. IRF7 is highly expressed in the blood and pancreas of 5-day-old ducklings and in the small intestine, large intestine and liver of 60-day-old adult ducks. Indirect immunofluorescence assay (IFA) showed that over-expressed duck IRF7 was located in both the cytoplasm and nucleus of transfected duck embryo fibroblasts (DEFs), which was also observed in poly(I:C)-stimulated or duck Tembusu virus (DTMUV)-infected DEFs. Titres and copies of DTMUV were significantly reduced in DEFs overexpressing IRF7. Moreover, overexpression of duck IRF7 significantly induced IFNα/β, but not IFNγ, mRNA expression, and transcription of downstream interferon-stimulated genes (ISGs), such as MX, OASL and IL-6, which were significantly induced by poly(I:C) co-stimulation, was enhanced. Additionally, duck IRF7 overexpression can significantly activate the IFNβ promoter in DEFs. Collectively, duck IRF7 plays an important role in host anti-DTMUV immune regulation, which depends on type I interferons and associated signal transduction pathway(s).

Lysine 39 of IKKε of black carp is crucial for its regulation on IRF7-mediated antiviral signaling

Interferon regulatory factor 7 (IRF7) plays a crucial role in the interferon (IFN) signaling in mammals, in which it is activated by the TBK1/IKKε complex during host antiviral innate immune response. There are few reports about the relation between IRF7 and IKKε in teleost fishes. In this study, the IRF7 homologue (bcIRF7) of black carp (Mylopharyngodon Piceus) has been cloned and characterized. The transcription of bcIRF7 gene increased in host cells in response to the stimulation of LPS, poly (I:C) and viral infection. bcIRF7 migrated around 56 KDa in immunoblot assay and was identified as a predominantly cytosolic protein by immunofluorescent staining. bcIRF7 showed IFN-inducing ability in reporter assay and EPC cells expressing bcIRF7 showed enhanced antiviral ability against both grass carp reovirus (GCRV) and spring viremia of carp virus (SVCV). IKKε of black carp (bcIKKε) was found to be recruited into host innate immune response initiated by SVCV and GCRV in the previous work; in this paper, the kinase dead mutant of bcIKKε, bcIKKε-K39A was constructed and showed no IFN-inducing activity. The data of reporter assay and plaque assay demonstrated that bcIKKε but not bcIKKε-K39A obviously enhanced bcIRF7-mediated IFN production and antiviral activity. Our data support the conclusion that bcIKKε upregulates bcIRF7-mediated antiviral signaling, which most likely depends on its kinase activity.