The effectiveness of adenoviral vectors to deliver and express genes in rainbow trout, Oncorhynchus mykiss (Walbaum)

Development of a recombinant adenovirus-vectored vaccine against both infectious hematopoietic necrosis virus and infectious pancreatic necrosis virus in rainbow trout (Oncorhynchus mykiss)

Infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) are typical pathogens of rainbow trout Oncorhynchus mykiss, and the concurrent infection of the two viruses is very common among modern trout hatcheries, which has caused huge economic losses to the rainbow trout farming industry. To prevent and control the spread of IHNV and IPNV in juvenile trout simultaneously, in this study a bivalent recombinant adenovirus vaccine with IHNV Glycoprotein (G) and IPNV VP2 genes was developed. After immunizing juvenile trout with this bivalent vaccine via the immersion route, the expression levels of IHNV G and IPNV VP2 and the representative immune genes in vaccinated and control rainbow trout were tested to evaluate the correlation of immune responses with the expression of viral genes. The neutralizing antibody level induced by this bivalent vaccine as well as the protection efficacy of the vaccine against IHNV and IPNV was also evaluated. The results showed that IHNV G and IPNV VP2 were successfully expressed in juvenile trout, and all the innate and adaptive immune genes were up-regulated. This indicated that the level of the innate and adaptive immune responses were significantly increased, which might be induced by the high expression of the two viral proteins. Compared with the controls, high levels of neutralizing antibodies against IHNV and IPNV were induced in the vaccinated trout. Besides, the bivalent recombinant adenovirus vaccine showed high protection rate against IHNV, with the relative percent survival (RPS) of 81.25%, as well as against IPNV, with the RPS of 78.95%. Taken together, our findings clearly demonstrated that replication-defective adenovirus can be developed as a qualified vector for fish vaccines and IHNV G and IPNV VP2 were two suitable antigenic genes that could induce effective immune protection against these two pathogens. This study provided new insights into developing bivalent vectored vaccines and controlling the spread of IHNV and IPNV simultaneously in juvenile trout.

In vitro and in vivo gene transfer in the cloudy catshark Scyliorhinus torazame

Cartilaginous fishes have various unique physiological features such as a cartilaginous skeleton and a urea-based osmoregulation strategy for adaptation to their marine environment. Also, because they are a sister group of bony vertebrates, understanding their unique features is important from an evolutionary perspective. However, genetic engineering based on gene functions as well as cellular behavior has not been effectively utilized in cartilaginous fishes. This is partly because their reproductive strategy involves internal fertilization, which results in difficulty in microinjection into fertilized eggs at the early developmental stage. Here, to identify efficient gene transfer methods in cartilaginous fishes, we examined the effects of various methods both in vitro and in vivo using the cloudy catshark, a candidate model cartilaginous fish species. In all methods, green fluorescent protein (GFP) expression was used to evaluate exogenous gene transfer. First, we examined gene transfer into primary cultured cells from cloudy catshark embryos by lipofection, polyethylenimine (PEI) transfection, adenovirus infection, baculovirus infection, and electroporation. Among the methods tested, lipofection, electroporation, and baculovirus infection enabled the successful transfer of exogenous genes into primary cultured cells. We then attempted in vivo transfection into cloudy catshark embryos by electroporation and baculovirus infection. Although baculovirus-injected groups did not show GFP fluorescence, electroporation successfully introduced GFP into muscle cells. Furthermore, we succeeded in GFP transfer into adult tissues by electroporation. The in vitro and in vivo gene transfer methods that worked in this study may open ways for genetic manipulation including knockout experiments and cellular lineage analysis in cartilaginous fishes.

A Confocal Microscopic Study of Gene Transfer into the Mesencephalic Tegmentum of Juvenile Chum Salmon, Oncorhynchus keta, Using Mouse Adeno-Associated Viral Vectors

To date, data on the presence of adenoviral receptors in fish are very limited. In the present work, we used mouse recombinant adeno-associated viral vectors (rAAV) with a calcium indicator of the latest generation GCaMP6m that are usually applied for the dorsal hippocampus of mice but were not previously used for gene delivery into fish brain. The aim of our work was to study the feasibility of transduction of rAAV in the mouse hippocampus into brain cells of juvenile chum salmon and subsequent determination of the phenotype of rAAV-labeled cells by confocal laser scanning microscopy (CLSM). Delivery of the gene in vivo was carried out by intracranial injection of a GCaMP6m-GFP-containing vector directly into the mesencephalic tegmentum region of juvenile (one-year-old) chum salmon, Oncorhynchus keta. AAV incorporation into brain cells of the juvenile chum salmon was assessed at 1 week after a single injection of the vector. AAV expression in various areas of the thalamus, pretectum, posterior-tuberal region, postcommissural region, medial and lateral regions of the tegmentum, and mesencephalic reticular formation of juvenile O. keta was evaluated using CLSM followed by immunohistochemical analysis of the localization of the neuron-specific calcium binding protein HuCD in combination with nuclear staining with DAPI. The results of the analysis showed partial colocalization of cells expressing GCaMP6m-GFP with red fluorescent HuCD protein. Thus, cells of the thalamus, posterior tuberal region, mesencephalic tegmentum, cells of the accessory visual system, mesencephalic reticular formation, hypothalamus, and postcommissural region of the mesencephalon of juvenile chum salmon expressing GCaMP6m-GFP were attributed to the neuron-specific line of chum salmon brain cells, which indicates the ability of hippocampal mammal rAAV to integrate into neurons of the central nervous system of fish with subsequent expression of viral proteins, which obviously indicates the neuronal expression of a mammalian adenoviral receptor homolog by juvenile chum salmon neurons.

Efficient CRISPR/Cas9 genome editing in a salmonid fish cell line using a lentivirus delivery system

BACKGROUND

Genome editing is transforming bioscience research, but its application to non-model organisms, such as farmed animal species, requires optimisation. Salmonids are the most important aquaculture species by value, and improving genetic resistance to infectious disease is a major goal. However, use of genome editing to evaluate putative disease resistance genes in cell lines, and the use of genome-wide CRISPR screens is currently limited by a lack of available tools and techniques.

RESULTS

In the current study, we developed an optimised protocol using lentivirus transduction for efficient integration of constructs into the genome of a Chinook salmon (Oncorhynchus tshwaytcha) cell line (CHSE-214). As proof-of-principle, two target genes were edited with high efficiency in an EGFP-Cas9 stable CHSE cell line; specifically, the exogenous, integrated EGFP and the endogenous RIG-I locus. Finally, the effective use of antibiotic selection to enrich the successfully edited targeted population was demonstrated.

CONCLUSIONS

The optimised lentiviral-mediated CRISPR method reported here increases possibilities for efficient genome editing in salmonid cells, in particular for future applications of genome-wide CRISPR screens for disease resistance.

Introduction of a foreign gene into zebrafish and medaka cells using adenoviral vectors

Viral vectors represent a tractable system that can efficiently introduce an exogenous gene into different target cells and are thus a potentially powerful genetic manipulation tool. In our current study, we investigated the infection efficiency of mammalian virus vectors, adenoviruses (Ads), adeno-associated viruses, and lentiviruses to the Sertoli cell line and the newly established cell line from a single embryo in zebrafish. Among the viral vectors tested, Ads showed the highest infection efficiency of 10(7)-10(8) green fluorescent protein-transducing units (gtu)/mL in zebrafish cells. In addition, the adenoviral vector was also infected at 10(5) gtu/mL in the medaka testicular somatic cell line that was established from the testes of p53-deficient mutant. Further, we found that Ads could successfully infect cultured male zebrafish germ cells. Our results thus indicate that the adenoviral vector could be used as a chromosomally nonintegrating vector system in zebrafish.

Expression of an adenovirus encoded reporter gene and its reactivation following UVC and oxidative damage in cultured fish cells

PURPOSE

Recombinant human adenovirus, AdCA35lacZ, was used to examine expression of a reporter gene and its reactivation following UVC (200-280 nm) and oxidative damage in fish cells.

MATERIALS AND METHODS

AdCA35lacZ is a recombinant nonreplicating human adenovirus, which expresses the beta-galactosidase (beta-gal) reporter gene. UVC light produces DNA damage repaired by nucleotide excision repair (NER). In contrast, methylene blue plus visible light (MB+VL) produces oxidative DNA damage, mainly 8-oxoguanine, that is repaired by base excision repair (BER). We examined expression of the reporter gene and host cell reactivation (HCR) of the UVC-treated and MB+VL-treated reporter gene in fish cells.

RESULTS

AdCA35lacZ infection of Chinook salmon cells (CHSE-214), eel cells (PBLE) and four rainbow trout cell lines (RTG-2, RT-Gill, RTS-34st and RTS-pBk), but not zebrafish (ZEB) or carp (EPC) cells resulted in expression of beta-gal. HCR of UVC-treated AdCA35lacZ in fish cells varied from that obtained in NER-deficient xeroderma pigmentosum group A fibroblasts to greater than that for NER-proficient normal human fibroblasts. HCR of UVC-treated AdCA35lacZ correlated with beta-gal expression levels for untreated AdCA35lacZ. Exposure of cells to fluorescent light (400-700 nm) increased expression of the undamaged reporter gene in normal human fibroblasts and in all fish cells except PBLE and increased HCR of the UVC-damaged reporter gene in fish cells but not in human fibroblasts. HCR of the MB + VL-treated reporter gene was similar to that in human cells for PBLE, CHSE-214, RTG-2 and RTS-pBk, but was reduced in RT-Gill and RTS-34st cells.

CONCLUSIONS

These results indicate the detection of functional photoreactivation (PR) of UVC-induced DNA damage in fish cells but not in normal human fibroblasts and a link between NER and transcription of the reporter gene in the fish cells in the absence of PR. We show also efficient BER of the reporter gene in several fish cell lines.