Rapid and Sparse Labeling of Neurons Based on the Mutant Virus-Like Particle of Semliki Forest Virus / 神经科学通报·英文版

Sparse labeling of neurons contributes to uncovering their morphology, and rapid expression of a fluorescent protein reduces the experiment range. To achieve the goal of rapid and sparse labeling of neurons in vivo, we established a rapid method for depicting the fine structure of neurons at 24 h post-infection based on a mutant virus-like particle of Semliki Forest virus. Approximately 0.014 fluorescent focus-forming units of the mutant virus-like particle transferred enhanced green fluorescent protein into neurons in vivo, and its affinity for neurons in vivo was stronger than for neurons in vitro and BHK21 (baby hamster kidney) cells. Collectively, the mutant virus-like particle provides a robust and convenient way to reveal the fine structure of neurons and is expected to be a helper virus for combining with other tools to determine their connectivity. Our work adds a new tool to the approaches for rapid and sparse labeling of neurons in vivo.

Semliki Forest Virus: un vector viral con múltiples aplicaciones / Semliki Forest Virus: a viral vector with multiple applications

Se han utilizado los alfavirus como vectores de expresión, entre estos se encuentra el Semliki Forest virus (SFV), que es un virus envuelto, el cual, además de replicarse en el citoplasma, tiene la propiedad de expresar por separado las proteínas estructurales de las no estructurales, permitiendo un mayor control de la expresión. Los vectores derivados del SFV pueden tener una gama amplia de aplicaciones. Se pueden obtener altos títulos virales para la expresión eficiente de proteínas en diferentes líneas celulares. Pueden infectar un espectro amplio de células de mamíferos, así como de tejidos. Son prometedores para ser usados en la terapia génica como vehículos para el envío de genes específicos in vivo o in vitro, tanto en la terapia contra el cáncer como en la neuronal, especialmente cuando sólo sea necesaria una expresión a corto plazo. Sus aplicaciones en la producción de vacunas profilácticas o terapéuticas, es otro aspecto estudiado; se ha demostrado la generación de respuestas inmunes importantes contra diferentes enfermedades virales y tumorales. El desarrollo de nuevos vectores no citopáticos, de otros regulados por temperatura, así como también de otros con replicación persistente; permitirán la prolongación de la expresión. Debido a estas nuevas ventajas y a las ya conocidas, gradualmente se podrían ampliar los usos para los vectores derivados del SFV a medida que se controlen sus efectos no deseados.

Recently, Alphavirus have been used as expression vectors, among these, Semliki Forest virus (SFV), an enveloped virus, besides replicating itself in the cytoplasm, has the property to express structural proteins separately from nonstructural proteins, allowing a greater expression control. Vectors derived from SFV can have a broad range of applications. High viral titers can be obtained to efficiently express proteins in different cell lines. They can infect a wide spectrum of mammalian cells, as well as tissues. They are promising to be used on gene therapy as vehicles for specific gene delivery in vivo or in vitro, as much as in therapy against cancer as neuronal therapy, especially when a short term expression is necessary. Another studied aspect is SFV vectors applications in prophylactic or therapeutic vaccine production; the generation of important immune responses against different viral and tumor diseases is still been discussed. Development of new non-cytopathic vectors, temperature-regulated vectors, as well as others with persistent replication, will allow prolongation of expression. Due to these new advantages and to others already known, uses for vectors derived from SFV could be extended gradually, as long as undesired effects are controlled.

High-level Expression of Foreign Genes In vivo and In vitro by Improved DNA-Based Replicon Vector Derived From Semliki Forest Virus / 生物化学与生物物理进展

The design of DNA-based alphavirus vectors significantly improves the utility of these replicon vectors. The DNA-based replicon vectors can be used in expressing foreign genes and preparing RVP in virto efficiently, also in developing replicon vaccines and gene therapy vectors in vivo. The approach involved the conversion a RNA-based replicon vector into a layered DNA-based replicon vector by the RNA polymerase Ⅱ promoter and transcription termination/polyadenylation signal transcribed replicon RNA from DNA. When DNA-based alphavirus vector tranfected into cells, the first layer includes a eukaryotic RNA polymerase Ⅱ expression cassette that initiates transcription of RNA in nucleus. Following transport of this RNA from the nucleus to the cytoplasm, the second layer, autocatalytic amplification of the RNA vector corresponds to virus RNA replication cycle and results in high level expression of foreign gene. DNA and RNA-based bifunctional replicon expression vector pSCTA and helper vector pSHCTA were successfully constructed by replacing the SP6 promoter used in the original system pSFV1 and pSFV-helper2 derived from Semliki Forest virus (SFV) with CMV promoter and T7 promoter, and inserting BGH transcription termination and polyadenylation signal downstream 3′-untranslated region (UTR). In order to obtain DNA-based highly efficient replicon vectors, they were further modified to construct additional three DNA-based SFV replicon expression vectors and corresponding helper vectors. To investigate the efficiency of foreign gene expression level by the four different DNA-based SFV expression vectors and recombinant virus particle (RVP) prepared by cotranfecting with corresponding helper vectors, improved DNA-based replicon vectors pSCAR and pSHCAR derived from SFV were developed. high level protein could be generated using the new vector system by transfecting DNA into BHK21 cells and High titer of RVP produced by cotranfecting with helper vector. Antigen genes were also expressed in cells by the replicon expression vector. Additionally, reporter gene expression was observed in mice muscle following injection with SFV DNA vector. Anti-?-Gal antibody response and cell-mediated immune response were induced after intramuscular inoculation of the ?-Gal-encoding SFV replicon DNA. The results suggested that highly efficient DNA-based replicon vectors pSCAR and pSHCAR were constructed by modifying the SFV vectors. The improved DNA-based replicon vectors enhance the utility of them, and can be developed as potentially replicon vaccines and gene therapy vectors.

Expression of Open Reading Frame 5 Protein of Porcine Reproductive and Respiratory Syndrome Virus Using Semliki Forest Virus Expression System

The ORF5 gene encodes a major envelope glycoprotein (GP5), which is one of the three major proteins of porcine reproductive and respiratory syndrome virus (PRRSV). The GP5 protein has been known to be a 24.5-26kDa N-glycosylated envelope protein. The GP5 is involved in inducing neutralizing antibodies. For this reason, the GP5 is primary candidate for the PRRSV subunit vaccine. To produce the native form of GP5 in mammalian cells, we have cloned the ORF5 gene from PRRSV CNV-1 into the Semliki Forest virus (SFV)-based expression vector, resulting in recombinant pSFV-ORF5. By the infection with recombinant pSFV-ORF5 to BHK-21 cells, the GP5 expression was confirmed by immunocytochemistry and immunoblotting assay. The recombinant virus particle harboring ORF5 gene was infectious to BHK-21 and MARC-145. The RNA synthesis and expression of GP5 in the infected cell was also confirmed by RT-PCR.