Tlr22 structure and expression characteristic of barbel chub, Squaliobarbus curriculus provides insights into antiviral immunity against infection with grass carp reovirus.

Grass carp reovirus (GCRV) is the most virulent agent to Grass carp, Ctenopharyngodon idella, and causes a severe infectious disease called hemorrhagic disease of grass carp. Generally, barbel chub, Squaliobarbus curriculus, a genetically closely related species to grass carp, exhibits significant resistance against GCRV infection compared to grass carp. To investigate whether the Toll-like receptor 22 (tlr22) has got a vital role against the GCRV infection, the full cDNA sequence of tlr22 from barbel chub (Sctlr22) was cloned by RACE-PCR, and the structure and expression feature were studied. The complete cDNA sequence of Sctlr22 has a size of 3504 bp, encoding for 960 amino acid residues. Sctlr22 possesses typical structural features of the tlrs family, including 19 leucine rich repeats (LRRs), a transmembrane (TM) and a Toll/interleukin-1 receptor (TIR) domain. Phylogenetic analysis revealed that barbel chub Tlr22 was clustered together with the Tlr22 of grass carp (Citlr22). Structurally, barbel chub Tlr22 have two different structure in LRRs domain and TIR domain with grass carp (Susceptible to GCRV), but was similar to that of Danio rerio and Cyprinus carpio (Resistance to GCRV). Quantitative RT-PCR analysis has shown that Sctlr22 is prominently expressed in immune relevant tissues such as head kidney and spleen. After GCRV infection, Sctlr22 expression level was up-regulated in four tested tissues and the highest expression of Sctlr22 appeared fast and higher than Citlr22. The interferon-ß (ifn-ß) expression level in CIK cells over-expressing fused cDNA encoding the LRR domain of Sctlr22 to the transmembrane and TIR domain of Citlr22 was significantly higher than that cells overexpressing Citlr22 after GCRV infection. The virus titer was significantly reduced compared to Citlr22 over-expressing cells. These results suggested that Sctlr22 seems to play a vital role in the immune response against GCRV.

De novo annotation of the immune-enriched transcriptome provides insights into immune system genes of Chinese sturgeon (Acipenser sinensis).

Chinese sturgeon (Acipenser sinensis), one of the oldest extant actinopterygian fishes with very high evolutionary, economical and conservation interest, is considered to be one of the critically endangered aquatic animals in China. Up to date, the immune system of this species remains largely undetermined with little sequence information publicly available. Herein, the first comprehensive transcriptome of immune tissues for Chinese sturgeon was characterized using Illumina deep sequencing. Over 67 million high-quality reads were generated and de novo assembled into the final set of 91,739 unique sequences. The annotation pipeline revealed that 25,871 unigenes were successfully annotated in the public databases, of which only 2002 had significant match to the existing sequences for the genus Acipenser. Overall 22,827 unigenes were categorized into 52 GO terms, 12,742 were classified into 26 KOG categories, and 4968 were assigned to 339 KEGG pathways. A more detailed annotation search showed the presence of a notable representation of immune-related genes, which suggests that this non-teleost actinopterygian fish harbors the same intermediates as in the well known immune pathways from mammals and teleosts, such as pattern recognition receptor (PRR) signaling pathway, JAK-STAT signaling pathway, complement and coagulation pathway, T-cell receptor (TCR) and B-cell receptor (BCR) signaling pathways. Additional genetic marker discovery led to the retrieval of 20,056 simple sequence repeats (SSRs) and 327,140 single nucleotide polymorphisms (SNPs). This immune-enriched transcriptome of Chinese sturgeon represents a rich resource that adds to the currently nascent field of chondrostean fish immunogenetics and furthers the conservation and management of this valuable fish.

Construction of a recombinant eukaryotic vector for a grass carp reovirus VP6 gene and its expression in vitro and in vivo.

A recombinant plasmid expressing the VP6 inner capsid coding gene of grass carp reovirus (GCRV) was constructed and expressed in a Ctenopharyngodon idellus kidney (CIK) cell line and grass carps. The VP6 gene was amplified by RT-PCR, cloned into a pEGFP-N1 eukaryotic expression vector and transfected into CIK cells. Results from enhanced green fluorescent protein (EGFP) experiments and flow cytometry showed highest protein expression at 48 h. The immunoreactivity of fusion protein was confirmed using an indirect immunofluorescent assay. The specific binding between the fusion protein and polyclonal mouse GCRV VP6-specific antiserum indicated that the fusion protein was translated in vitro and had good immunogenicity. An antiviral activity assay showed that the virus titer was 100-fold lower in the GCRV VP6 expressed cells than in the pEGFP-N1 transfected cells. The expression levels of three immune genes in the head kidney of grass carps injected with the recombinant plasmid were used. Mx, TLR3 and IgM mRNA expression increased sharply at the 1st and 15th days post-injection (dpi). Specific antibodies were detected 30 days after vaccination. Neutralizing titers of the antibodies in vaccinated fish detected ranged from 160 to 320. Intramuscular injection of grass carps with 1 µg of pEGFP-N1-VP6 was found to provide strong protection against GCRV. These results suggested that the VP6 gene was a good candidate for the design of GCRV-DNA vaccines and to investigate the use of cytokines as co-stimulatory molecules.

[Highly efficient inhibition on replication of grass carp reovirus mediated by chemically synthesized small interfering RNAs].

Two short interfering RNAs (siRNA-RdRp1286, siRNA-RdRp1441) and one short interfering RNA (siRNA-OCP117), targeted to the RNA dependent RNA polymerase (RdRp) gene and outer capsid protein (OCP) gene of Grass carp reovirus (GCRV) respectively, were chemically synthesized and transfected into the CIK cells by lipofectamine 2000. 6 hours after transfection, the transfected CIK cells were challenged with GCRV. The culture media were collected at 48h post challenge and the virus was titrated in microculture system to evaluate the inhibition effect on GCRV replication mediated by siRNAs. Referring to the mRNA level of housekeeping gene beta-actin, RT-PCR was applied to detect the level of GCRV mRNA in transfected and challenged CIK cells. The results showed that the viral titer (lgTCID50/0. 1mL) in siRNA-RdRp1286, siRNA-RdRp1441 and siRNA-OCP117 transfected CIK cells were 4.41 +/- 0.16, 3.83 +/- 0.44 and 1.94 +/- 0.42 respectively, which were significantly lower than that in virus infection positive control (7.92 +/- 0.52) (P < 0.01). No significant change in viral titer was observed in the group transfected with siRNA negative control after challenged with GCRV (7.50 +/- 0.17, P > 0.05). Compared with the mRNA transcriptional level of beta-actin gene in virus infection positive control, the mRNA levels of GCRV in siRNA-RdRpl 286, siRNA-RdRp1 441 and siRNA-OCP117 transfected CIK cells were reduced significantly and the inhibition rate reached to (82.08 +/- 2.15)%, (89.19 +/- 1.14).% and (92.62 +/- 0.17)%, respectively. The mRNA level of GCRV in the siRNA negative control group had no noticeable change (P > 0 05).

[Isolation and identification of channel catfish (Ictalurus punctatus) hemorrhage reovirus].

By using cell culture and virus infection methods, a new reovirus had been isolated from channel catfish (Ictalurus punctatus) suffered with severe hemorrhage and had been identified as channel catfish reovirus (CCRV) after artificial infection in fish, electron microscopy observation, physical-chemical tests, genomic SDS-PAGE analysis and sequencing. In artificial infection test, the typical symptoms of channel catfish hemorrhage as naturally occurred could be reproduced. The isolated virus could cause typical cytopathic effect in CCO and CCK cell lines. Electron microscopy observation of ultra-thin section samples of CCRV infected CCO and CCK cells revealed that the virus replicated in cytoplasm, arrayed in crystalline, and had a non-enveloped double capsid with a diameter of 60-70 nm. Frozen-thawed, 56 degrees C 1 h, chloroform and ether had no significant effects on CCRV titer, 65 degrees C 1 h could significantly inactivated the viral infectivity. The CCRV genome SDS-PAGE analysis and nuclease sensitivity test showed that the virus genome was the same as that of viruses in Aquareovirudae and consisted of 11 segments of dsRNA assigned into three classes L1, L2, L3; M1, M2, M3 and S1, S2, S3, S4, S5 with a range of size from 0.9 to 4.4 kb. The Cloning and sequencing of the CCRV S4 segment indicated the nucleic acid number of CCRV S4 was 909 bp in length, which was exactly the same as that of GCRV S4 (AF403396) and GSRV S4 (AF403407) segments. The BLAST of CCRV S4 sequence in NCBI GenBank showed that it had a 99% and 90% similarity in sequence to the GCRV S4 and GSRV S4 segments, respectively.