A zebrafish model for subgenomic hepatitis C virus replication.

Persistent infection with hepatitis C virus (HCV) is a major risk factor in the development of hepatocellular carcinoma. The elucidation of the pathogenesis of HCV-associated liver disease is hampered by the absence of an appropriate small animal model. Zebrafish exhibits high genetic homology to mammals, and is easily manipulated experimentally. In this study, we describe the use of a zebrafish model for the analysis of HCV replication mechanisms. As the 5' untranslated region (UTR), the core protein, the non-structural protein 5B (NS5B) and the 3'UTR are essential for HCV replication, we constructed a HCV sub-replicon gene construct including the 4 gene sequences and the enhanced green fluorescent protein (EGFP) reporter gene; these genes were transcribed through the mouse hepatocyte nuclear factor 4 (mHNF4) promoter. By microinjection of the subgenomic replicon vector into zebrafish larvae, the virus was easily detected by observing EGFP fluorescence in the liver. The positive core and NS5B signals showed positive expression of the HCV gene construct in zebrafish by reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis. Importantly, the negative strand sequence of the HCV subgenomic RNA was detected by RT-PCR and hybridization in situ, demonstrating that the HCV sub-replicon has positive replication activity. Furthermore, the hybridization signal mainly appeared in the liver region of larvae, as detected by the sense probe of the core protein or NS5B, which confirmed that the sub-replicon amplification occurred in the zebrafish liver. The amplification of the sub-replicon caused alterations in the expression of certain genes, which is similar to HCV infection in human liver cells. To verify the use of this zebrafish model in drug evaluation, two drugs against HCV used in clinical practice, ribavirin and oxymatrine, were tested and these drugs showed significant inhibition of replication of the HCV sub-replicon in the larvae. In conclusion, this zebrafish model of HCV may prove to be a novel and simple in vivo model for the study of the mechanisms of HCV replication and may also prove useful in the disovery of new anti-HCV drugs.

HCV IRES-mediated core expression in zebrafish.

The lack of small animal models for hepatitis C virus has impeded the discovery and development of anti-HCV drugs. HCV-IRES plays an important role in HCV gene expression, and is an attractive target for antiviral therapy. In this study, we report a zebrafish model with a biscistron expression construct that can co-transcribe GFP and HCV-core genes by human hepatic lipase promoter and zebrafish liver fatty acid binding protein enhancer. HCV core translation was designed mediated by HCV-IRES sequence and gfp was by a canonical cap-dependent mechanism. Results of fluorescence image and in situ hybridization indicate that expression of HCV core and GFP is liver-specific; RT-PCR and Western blotting show that both core and gfp expression are elevated in a time-dependent manner for both transcription and translation. It means that the HCV-IRES exerted its role in this zebrafish model. Furthermore, the liver-pathological impact associated with HCV-infection was detected by examination of gene markers and some of them were elevated, such as adiponectin receptor, heparanase, TGF-ß, PDGF-α, etc. The model was used to evaluate three clinical drugs, ribavirin, IFNα-2b and vitamin B12. The results show that vitamin B12 inhibited core expression in mRNA and protein levels in dose-dependent manner, but failed to impact gfp expression. Also VB12 down-regulated some gene transcriptions involved in fat liver, liver fibrosis and HCV-associated pathological process in the larvae. It reveals that HCV-IRES responds to vitamin B12 sensitively in the zebrafish model. Ribavirin did not disturb core expression, hinting that HCV-IRES is not a target site of ribavirin. IFNα-2b was not active, which maybe resulted from its degradation in vivo for the long time. These findings demonstrate the feasibility of the zebrafish model for screening of anti-HCV drugs targeting to HCV-IRES. The zebrafish system provides a novel evidence of using zebrafish as a HCV model organism.

Zebrafish as a potential model organism for drug test against hepatitis C virus.

Screening and evaluating anti- hepatitis C virus (HCV) drugs in vivo is difficult worldwide, mainly because of the lack of suitable small animal models. We investigate whether zebrafish could be a model organism for HCV replication. To achieve NS5B-dependent replication an HCV sub-replicon was designed and created with two vectors, one with HCV ns5b and fluorescent rfp genes, and the other containing HCV's 5'UTR, core, 3'UTR and fluorescent gfp genes. The vectors containing sub-replicons were co-injected into zebrafish zygotes. The sub-replicon amplified in liver showing a significant expression of HCV core RNA and protein. The sub-replicon amplification caused no abnormality in development and growth of zebrafish larvae, but induced gene expression change similar to that in human hepatocytes. As the amplified core fluorescence in live zebrafish was detectable microscopically, it rendered us an advantage to select those with replicating sub-replicon for drug experiments. Ribavirin and oxymatrine, two known anti-HCV drugs, inhibited sub-replicon amplification in this model showing reduced levels of HCV core RNA and protein. Technically, this method had a good reproducibility and is easy to operate. Thus, zebrafish might be a model organism to host HCV, and this zebrafish/HCV (sub-replicon) system could be an animal model for anti-HCV drug screening and evaluation.

Characterization of a cDNA coding for an extracellular calmodulin-binding protein from suspension-cultured cells of Angelica dahurica.

In order to characterize a specific extracellular 21-kDa calmodulin-binding protein (named: ECBP21) from Angelica dahurica L. suspension-cultured cells, the cDNA coding for the protein has been cloned. Here, Southern blot analysis shows that there are at least two copies of ECBP21 gene in Angelica genome. Using truncated versions of ECBP21 and synthetic peptide in CaM binding assays, we mapped the calmodulin-binding domain to a 16-amino acid stretch (residues 200-215) at the C-terminal region. The ECBP21 was localized in the cell wall area by the immunogold electron microscopy and by GFP labeling method. These results define ECBP21 as a kind of an extracellular calmodulin-binding protein (CaMBP). Furthermore, using Northern blot analysis, we examined the expression dynamics of ecbp21 during the incubation of Angelica suspension-cultured cells and the treatments with some growth regulators. The above studies further provide the molecular evidence for the existence of the gene coding for extracellular CaMBPs and imply a possible role for ECBP21.

[Immunohistochemical analysis and immuno-gold localization of ECBP21 in Angelica dahurica].

ECBP21 is a calmodulin binding protein (CaMBP) purified from extracellular extracts of suspension-cultured cells of Angelica dahurica, and it is the first reported extracellular CaMBP in plant kingdom. We have recently cloned the full-length cDNA for ECBP21. In this work, using recombinant ECBP21 we prepared rabbit antiserum with high specificity and high titer against ECBP21, and investigated the organ-specific distribution of ECBP21 in Angelica dahurica. ECBP21 was found in all organs examined, particularly abundant in the leaves flowers, and raches, and less in the roots. It was also found in all cells examined, and particularly enriched in the cell wall. These data support the notion that ECBP21 is specifically localized extracellularly, and imply that it may be involved in plant growth and development. In addition, using immunogold transmission electron microscopy method, we studied the subcellular localization of ECBP21 in rachis cells of Angelica dahurica. The results indicated that the ECBP21 was mainly localized in cell wall; this provided a direct evidence of the extracellular existence of ECBP21.