Development of recombinant rabies viruses vectors with Gaussia luciferase reporter based on Chinese vaccine strain CTN181

Development of infectious clones of a wild-type Korean rabies virus and evaluation of their pathogenic potential

Most reverse genetic (RG) systems for rabies viruses (RVs) have been constructed on the genome background of laboratory-adapted strains. In this study, we developed an RG system using a Korean wild type (KGH) strain to investigate the pathogenic potential of different strains. We developed a RG system with the KGH strain for the first time. Following the complete genome sequencing of the KGH strain, pKGH infectious clones were constructed using the CMV/T7 promoter, and HamRz and HdvRz were introduced to allow self-cleavage of the synthesized RNA. We successfully recovered the rescued virus by constructing chimeric RVs in which we replaced a part of the construct with the partial gene from the fixed RC-HL strain. The rescued viruses formed clearer and countable plaques in an immunostaining plaque assay, with a distinct plaque morphology. Furthermore, compared with the chimeric RVs, the pKGH/RCinsΔ4 strain containing the KGH strain G protein exhibited a decreased efficiency of cell-to-cell spreading in BHK-21 cells and significantly reduced (100-1000 fold) replication kinetics. However, pKGH/RCinsΔ4 strain-infected mice revealed 100% morbidity at 11days post-infection, whereas other chimeric RV strains showed no mortality. Our RG system is a useful tool for studying differences in the cell-to-cell spreading efficiency and replication with respect to the different internalization patterns of street and fixed laboratory-adapted viruses.

Bacterial expression and re-engineering of Gaussia princeps luciferase and its use as a reporter protein

Bioluminescence, the generation of visible light in a living organism, is widely observed in nature, and a large variety of bioluminescent proteins have been discovered and characterized. Luciferase is a generic term for bioluminescent enzymes that catalyze the emission of light through the oxidization of a luciferin (also a generic term). Luciferase are not necessarily evolutionary related and do not share sequence or structural similarities. Some luciferases, such as those from fireflies and Renilla, have been thoroughly characterized and are being used in a wide range of applications in bio-imaging. Gaussia luciferase (GLuc) from the marine copepod Gaussia princeps is the smallest known luciferase, and it is attracting much attention as a potential reporter protein. GLuc identification is relatively recent, and its structure and its biophysical properties remain to be fully characterized. Here, we review the bacterial production of natively folded GLuc with special emphasis on its disulfide bond formation and the re-engineering of its bioluminescence properties. We also compare the bioluminescent properties under a strictly controlled in vitro condition of selected GLuc's variants using extensively purified proteins with native disulfide bonds. Furthermore, we discuss and predict the domain structure and location of the catalytic core based on literature and on bioinformatics analysis. Finally, we review some examples of GLuc's emerging use in biomolecular imaging and biochemical assay systems.

Development of a reverse genetics system for the aG strain of rabies virus in China

The aG rabies virus strain has been attenuated through multiple passages in cells and is now used as a vaccine strain in China. We attempted to develop a reverse genetics system using the aG strain. Recombinant full-length genomic cDNA was flanked by a hammerhead ribozyme and the hepatitis delta virus ribozyme. Three helper plasmids encoding the nucleoprotein, the phosphoprotein, and the large protein were produced and introduced together with a plasmid containing the full-length aG viral genome into BHK-21 cells by transfection. Recombinant virus was successfully recovered from the cloned cDNA under the control of a CMV promoter driven by RNA polymerase II. The recombinant virus was confirmed by RT-PCR, and the titer of the recombinant virus was 6.2 log LD50.