A bicistronic lentiviral vector based on the 1D/2A sequence of foot-and-mouth disease virus expresses proteins stoichiometrically

Double-Gene Copromoting Expression Analysis in tPA/GH Transgenic Goat Mammary Epithelial Cells and Thrombolytic Activity of tPA In Vitro

Human tissue-plasminogen activator (tPA) is a thrombolytic drug widely used in the treatment of stroke, pulmonary thrombosis, acute myocardial infarction, and other thrombotic diseases. The double genes cointegrated into the organisms and cells can produce a synergistic effect, which will improve the expression level of the target gene. However, the study of the integration of the GH and tPA genes to improve the expression level of tPA has not yet been reported. In order to elucidate this, we generated monoclonal goat mammary epithelial cell lines with tPA/GH double-gene integration and analyzed the tPA expression level in single- and double-gene integrated cells. We selected the mammary gland-specific expressing vectors BLC14/tPA and BLC14/GH with the β-lactoglobulin gene as a regulatory sequence in our previous research. The tPA and GH genes were electronically cotransfected into goat mammary epithelial cells. Resistant cell lines were screened by G418, and transgenic monoclonal cell lines were confirmed by PCR. The tPA expression was induced by prolactin and detected in the cell induction solution after 48 h by ELISA and Western blotting. We detected the tPA biological activity in vitro by fibrin agarose plate assay (FAPA). The results showed that a total of 207 resistant monoclonal cells were obtained, including 126 cell lines with tPA monogenic integration and 51 cell lines with tPA/GH double-gene integration. The rate of double-gene integration was 24.6% (51/207). A total of 48 cells expressed tPA, of which 25.3% (19/75) cells expressed single gene, and 56.9% (29/51) cells expressed double genes. The concentration of tPA in single-gene-expressing cells was 8.0-64.0 μg/mL, and the tPA level in double-gene-expressing cells was significantly higher (200-7200 μg/mL). In addition, the tPA had a relatively strong in vitro thrombolytic activity determined by FAPA. The results showed that goat mammary epithelial cell lines with tPA/GH gene integration were successfully established by electrotransfection, and the expression level of tPA in double-gene integrated cell lines was significantly increased. This study provided a new way for the preparation of a transgenic goat and other animal with high tPA expression by somatic cell nuclear transfer. The findings also laid a foundation for efficient production of pharmaceutical proteins in transgenic animal mammary gland bioreactors in the future.

[Preparation of GH/tPA double transgenic mice and gene expression analysis]

OBJECTIVE

To obtain GH/tPA double transgenic mice, analyze the expression level of tissue plasminogen activator (tPA) in the mammary glands and observe the growth and development of the transgenic mice.

METHODS

We obtained the offspring mice of 2 tPA single transgenic mice (P03 and P05) mated with a female nontransgenic mouse by microinjection of linearized GH plasmid into the fertilized eggs and embryo transfer. PCR was used to detect the gene integration. The expression levels of tPA in single gene and double gene transgenic mice were compared using ELISA and Western blotting. We assessed the effects of GH gene transduction on the growth and development of the transgenic mice by observing body weight changes of the mice at each developmental stage.

RESULTS

A total of 286 fertilized eggs were collected from P03 mice, and after embryo transfer, 77 offspring mice were obtained, including 16 tPA single transgenic mice (7 male, 9 female) and 13 GH/tPA double transgenic mice (8 male, 5 female) as confirmed by PCR. The integration rate of the double genes was 16.9%. A total of 175 fertilized eggs were collected from P05 mice, and 34 offspring mice were obtained including 12 tPA single transgenic mice (5 male, 7 female) and 7 GH/tPA double transgenic mice (3 male, 4 female), in which the integration rate of the double genes was 20.6%. The highest expression level of tPA in the mammary gland was significantly higher in double than in single transgenic mice (674 μg/mL vs 82.5 μg/mL, P < 0.05). In the whole growth cycle of the mice, no significant difference in weight gain was observed in the single or double transgenic mice as compared with the na?ve mice (P>0.05).

CONCLUSION

We successfully prepared GH/tPA double transgenic mice, in which GH gene transduction significantly increases the expression level of target gene tPA without affecting the growth and development of the transgenic mice. This success suggests a promising approach to preparing transgenic animals for producing pharmaceutical proteins and the breeding of the transgenic animals.

Design and Derivation of Multi-Reporter Pluripotent Stem Cell Lines via CRISPR/Cas9n-Mediated Homology-Directed Repair

During the past decade, RNA-guided Cas9 nuclease from microbial clustered regularly interspaced short palindromic repeats (CRISPR/Cas9) has become a powerful tool for gene editing of human pluripotent stem cells (PSCs). Using paired CRISPR/Cas9 nickases (CRISPR/Cas9n) it is furthermore possible to reduce off-target effects that may typically occur with traditional CRISPR/Cas9 systems while maintaining high on-target efficiencies. With this technology and a well-designed homology-directed repair vector (HDR), we are now able to integrate transgenes into specific gene loci of PSCs in an allele conserving way. In this protocol we describe CRISPR/Cas9n design and homology directed repair vector design, transfection of human pluripotent stem cells and selection and expansion of generated cell clones. © 2020 The Authors. Basic Protocol 1: Repair template design and CRISPR/Cas9n construction Basic Protocol 2: Transfection of human pluripotent stem cells by electroporation Basic Protocol 3: Genotyping of generated cell clones.

Generation of GTKO Diannan Miniature Pig Expressing Human Complementary Regulator Proteins hCD55 and hCD59 via T2A Peptide-Based Bicistronic Vectors and SCNT

Pig-to-human organ transplantation has drawn attention in recent years due to the potential use of pigs as an alternative source of human donor organs. While GGTA1 knockout (GTKO) can protect xenografts from hyperacute rejection, complement-dependent cytotoxicity might still contribute to this type of rejection. To prolong the xenograft survival, we utilized a T2A-mediated pCMV-hCD55-T2A-hCD59-Neo vector and transfected the plasmid into GTKO Diannan miniature pig fetal fibroblasts. After G418 selection combined with single-cell cloning culture, four colonies were obtained, and three of these were successfully transfected with the hCD55 and hCD59. One of the three colonies was selected as donor cells for somatic cell nuclear transfer (SCNT). Then, the reconstructed embryos were transferred into eight recipient gilts, resulting in four pregnancies. Three of the pregnant gilts delivered, yielding six piglets. Only one piglet carried hCD55 and hCD59 genetic modification. The expression levels of the GGTA1, hCD55, and hCD59 in the tissues and fibroblasts of the piglet were determined by q-PCR, fluorescence microscopy, immunohistochemical staining, and western blotting analyses. The results showed the absence of GGTA1 and the coexpression of the hCD55 and hCD59. However, the mRNA expression levels of hCD55 and hCD59 in the GTKO/hCD55/hCD59 pig fibroblasts were lower than that in human 293T cells, which may be caused by low copy number and/or CMV promoter methylation. Furthermore, we performed human complement-mediated cytolysis assays using human serum solutions from 0 to 60%. The result showed that the fibroblasts of this triple-gene modified piglet had greater survival rates than that of wild-type and GTKO controls. Taken together, these results indicate that T2A-mediated polycistronic vector system combined with SCNT can effectively generate multiplex genetically modified pigs, additional hCD55 and hCD59 expression on top of a GTKO genetic background markedly enhance the protective effect towards human serum-mediated cytolysis than those of GTKO alone. Thus, we suggest that GTKO/hCD55/hCD59 triple-gene-modified Diannan miniature pig will be a more eligible donor for xenotransplantation.

Simulation and Reconstruction of Metabolite-Metabolite Association Networks Using a Metabolic Dynamic Model and Correlation Based Algorithms

Biological networks play a paramount role in our understanding of complex biological phenomena, and metabolite-metabolite association networks are now commonly used in metabolomics applications. In this study we evaluate the performance of several network inference algorithms (PCLRC, MRNET, GENIE3, TIGRESS, and modifications of the MRNET algorithm, together with standard Pearson's and Spearman's correlation) using as a test case data generated using a dynamic metabolic model describing the metabolism of arachidonic acid (consisting of 83 metabolites and 131 reactions) and simulation individual metabolic profiles of 550 subjects. The quality of the reconstructed metabolite-metabolite association networks was assessed against the original metabolic network taking into account different degrees of association among the metabolites and different sample sizes and noise levels. We found that inference algorithms based on resampling and bootstrapping perform better when correlations are used as indexes to measure the strength of metabolite-metabolite associations. We also advocate for the use of data generated using dynamic models to test the performance of algorithms for network inference since they produce correlation patterns that are more similar to those observed in real metabolomics data.

Coexpression of cellulases in Pichia pastoris as a self-processing protein fusion

The term cellulase refers to any component of the enzymatic complex produced by some fungi, bacteria and protozoans which act serially or synergistically to catalyze the cleavage of cellulosic materials. Cellulases have been widely used in many industrial applications ranging from food industry to the production of second generation ethanol. In an effort to develop new strategies to minimize the costs of enzyme production we describe the development of a Pichia pastoris strain able to coproduce two different cellulases. For that purpose the eglII (endoglucanase II) and cbhII (cellobiohydrolase II) genes from Trichoderma reesei were fused in-frame separated by the self-processing 2A peptide sequence from the foot-and-mouth disease virus. The protein fusion construct was placed under the control of the strong inducible AOX1 promoter. Analysis of culture supernatants from methanol-induced yeast transformants showed that the protein fusion was effectively processed. Enzymatic assay showed that the processed enzymes were fully functional with the same catalytic properties of the individual enzymes produced separately. Furthermore, when combined both enzymes acted synergistically on filter paper to produce cellobiose as the main end-product. Based on these results we propose that P. pastoris should be considered as an alternative platform for the production of cellulases at competitive costs.

TransgeneOmics--A transgenic platform for protein localization based function exploration

The localization of a protein is intrinsically linked to its role in the structural and functional organization of the cell. Advances in transgenic technology have streamlined the use of protein localization as a function discovery tool. Here we review the use of large genomic DNA constructs such as bacterial artificial chromosomes as a transgenic platform for systematic tag-based protein function exploration.

Construction of bicistronic lentiviral vectors for tracking the expression of CDNF in transduced cells

CDNF is a recently described evolutionary conserved neurotrophic factor reported to be of relevance for the treatment of Parkinson's disease. Treatment with recombinant CDNF showed neurorestorative and neuroprotective effects on dopaminergic neurons in Parkinsonian animal models. Similar results are obtained using adeno-associated viral (AAV) vectors for CDNF expression in these animal models; however, the extent of the transduced brain tissue is difficult to assess due to the lack of reporter genes in the vectors used. Here, we describe two bicistronic lentiviral plasmids based on the Δ1D/2A and IRES elements for the expression of EGFP and rat CDNF, in order to track the transduced cells expressing CDNF with EGFP fluorescence. Transfected heterologous cells or transduced neurons with these vectors are easily identified by EGFP fluorescence and CDNF expression results in its recruitment to the endoplasmic reticulum (ER) by both bicistronic vectors. CDNF immunostaining is also observed in the Golgi apparatus when expressed in heterologous cells or hippocampal neuronal cultures; however, colocalization with a dense core secretory vesicle marker was scarce. Additionally, we showed that the expression of CDNF inhibited dendrite formation in hypothalamic neurons, suggesting that CDNF expressed by these bicistronic lentiviral vectors is functional and could have a role in neuronal morphology. The bicistronic lentiviral plasmids developed here could be of use to study the effect of rat CDNF at the cellular level or to better delineate the perikarya of neurons transduced with lentiviral vectors in animal models of Parkinson's disease.

Simultaneous expression of multiple proteins under a single promoter in Caenorhabditis elegans via a versatile 2A-based toolkit

Caenorhabditis elegans is a powerful in vivo model in which transgenesis is highly developed. However, while the analysis of biological phenomena often require the expression of more than one protein of interest, no reliable tool exists to ensure efficient concomitant and equivalent expression of more than two polypeptides from a single promoter. We report the use of viral 2A peptides, which trigger a "ribosomal-skip" or "STOP&GO" mechanism during translation, to express multiple proteins from a single vector in C. elegans. Although none of the viruses known to infect C. elegans contain 2A-like sequences, our results show that 2A peptides allow the production of separate functional proteins in all cell types and at all developmental stages tested in the worm. In addition, we constructed a toolkit including a 2A-based polycistronic plasmid and reagents to generate 2A-tagged fosmids. 2A peptides constitute an important tool to ensure the delivery of multiple polypeptides in specific cells, enabling several novel applications such as the reconstitution of multi-subunit complexes.

Metabolic engineering of the flavone-C-glycoside pathway using polyprotein technology

C-Glycosylated flavonoids are biologically active plant natural products linked to dietary health benefits. We have used polyprotein expression technology to reconstruct part of the respective biosynthetic pathway in tobacco and yeast, such that dihydrochalcone and flavanone precursors are directly converted to C-glycosides. The polyprotein system developed facilitated the simple and efficient co-expression of pathway enzymes requiring different sub-cellular localization in both plants and yeast. The pathway to flavone-C-glucosides comprised a flavanone 2-hydroxylase (F2H), co-expressed with a C-glucosyltransferase (CGT). While pathway engineering in tobacco resulted in only minor C-glycoside formation, when fed with the flavanone naringenin, yeast transformed with the F2H-CGT polyprotein construct produced high concentrations of 2-hydroxynaringenin-C-glucoside in the medium. These fermentation products could then be readily chemically converted to the respective flavone-C-glucosides. The efficiency of the biosynthesis was optimal when both the F2H and CGT were obtained from the same species (rice). These results confirm the coupled roles of the F2H and CGT in producing C-glucosides in vivo, with the use of the polyprotein expression system in yeast offering a useful system to optimize the synthesis of these natural products in quantities suitable for dietary studies.

Construction of Foot-and-mouth disease virus 2A-based bicistronic expression vector and coexpression of two genes in goat mammary epithelial cells

Using animal mammary glands as bioreactors for producing commercially important proteins is a cutting-edge direction in the field of biotechnology development and application. Dairy goats are an important dairy livestock, with roughage-resistance, fast propagation, long lactation periods and high milk production per bodyweight; these characteristics make dairy goats ideal for use as mammary gland bioreactors. Foot-and-mouth disease virus 2A (FMDV 2A) is an efficient viral cleavage element that mediates proteolytic cleavage independent of the presence of other FMDV sequences. It is often incorporated into recombinant vectors to generate cleavage in the presence of heterologous sequences. To achieve specific co-expression of two heterologous genes in goat mammary gland epithelial (GMGE) cells, a mammary gland-specific bicistronic expression vector, pFIEβ, containing the β-casein 5′ flanking sequence and FMDV 2A, was successfully constructed and the specific expression of human interleukin 2 (hIL-2) and enhanced green fluorescent protein (EGFP) was conducted in primary GMGE cells. Another bicistronic expression vector, pFIEC, driven by the cytomegalovirus promoter, was constructed as a positive control. In cells transfected with pFIEβ and pFIEC, RT-PCR verified the existence of recombinant fusion mRNA of hIL-2 upstream of EGFP within the FMDV 2A cassette fragment and western blot analysis showed the existence of the fusion between hIL-2 and EGFP. It is concluded that FMDV 2A generated specific co-expression of multiple genes for the first time in primary GMGE cells driven by the β-casein promoter.

Towards optimising the production of and expression from polycistronic vectors in embryonic stem cells

Polycistronic vectors linked by self-processing 2A peptides have been successfully used in cellular reprogramming. The expression of these vectors has yet to be well documented in embryonic stem cells. In the present study, we generated expression cassettes containing combinatorial arrangements of 3 pancreatic transcriptions factors (Pdx1, Nkx2.2 and Ngn3) together with an eGFP reporter, all linked by self-processing 2A peptides. The study tested the utility of constructing complex expression cassettes by ligating multiple components, each flanked by unique restriction sites. This approach allowed flexible and efficient design and construction of a combinatorial array of polycistronic constructs, which were expressed after transient transfection into embryonic stem cells. The inclusion of EGFP provided for a convenient proxy measure of expression and showed that expression was similar regardless of EGFP's position within a 2A polycistronic construct. Expression of terminal EGFP was 51% and 24% more efficient when linked by T2A compared to F2A or E2A peptides, respectively. The highest level of expression was achieved when all genes in a construct were linked exclusively by T2A peptides. This effect of T2A was independent of the type of promoter used, as a similar increase in terminal EGFP expression was observed when the polycistronic constructs were under the control of a CAG promoter compared to the CMV promoter, even though the GAG promoter was more efficient in this model than the CMV promoter. The study provides guidance on design strategies and methods for the efficient generation and expression of 2A polycistronic constructs in embryonic stem cells.

Generation of healthy mice from gene-corrected disease-specific induced pluripotent stem cells

Using the murine model of tyrosinemia type 1 (fumarylacetoacetate hydrolase [FAH] deficiency; FAH^−/− mice) as a paradigm for orphan disorders, such as hereditary metabolic liver diseases, we evaluated fibroblast-derived FAH^−/−-induced pluripotent stem cells (iPS cells) as targets for gene correction in combination with the tetraploid embryo complementation method. First, after characterizing the FAH^−/− iPS cell lines, we aggregated FAH^−/−-iPS cells with tetraploid embryos and obtained entirely FAH^−/−-iPS cell–derived mice that were viable and exhibited the phenotype of the founding FAH^−/− mice. Then, we transduced FAH cDNA into the FAH^−/−-iPS cells using a third-generation lentiviral vector to generate gene-corrected iPS cells. We could not detect any chromosomal alterations in these cells by high-resolution array CGH analysis, and after their aggregation with tetraploid embryos, we obtained fully iPS cell–derived healthy mice with an astonishing high efficiency for full-term development of up to 63.3%. The gene correction was validated functionally by the long-term survival and expansion of FAH-positive cells of these mice after withdrawal of the rescuing drug NTBC (2-(2-nitro-4-fluoromethylbenzoyl)-1,3-cyclohexanedione). Furthermore, our results demonstrate that both a liver-specific promoter (transthyretin, TTR)-driven FAH transgene and a strong viral promoter (from spleen focus-forming virus, SFFV)-driven FAH transgene rescued the FAH-deficiency phenotypes in the mice derived from the respective gene-corrected iPS cells. In conclusion, our data demonstrate that a lentiviral gene repair strategy does not abrogate the full pluripotent potential of fibroblast-derived iPS cells, and genetic manipulation of iPS cells in combination with tetraploid embryo aggregation provides a practical and rapid approach to evaluate the efficacy of gene correction of human diseases in mouse models.

Pluripotent stem cells have unlimited self-renewing capability and the potential to differentiate into virtually all cell types of the body. Pluripotent stem cells are therefore of great interest for future cell-based therapies and are already in use today for studying diseases “in a dish” and screening for new drugs. After the seminal discovery that induced pluripotent stem cells (iPS cells) can be generated by the delivery of four transcription factors into non-pluripotent cells, a tremendous amount of enthusiasm arose about the idea that patient-derived pluripotent stem cells could be obtained and genetically corrected in order to develop customized therapies for regenerative medicine. Here, we present a mouse model of acute metabolic liver failure that fulfills such criteria. First, we demonstrated by stringent assays that disease-specific iPS cells exhibited full cellular and developmental potential and the iPS cell–derived mice reproduced the phenotypes of the founding FAH^−/− mice faithfully. Then, we genetically repaired the disease-specific iPS cells by lentiviral delivery of an intact gene copy, and we investigated the impact of this additional genetic manipulation on these cells. With our analyses, we ruled out major, and even minor, chromosomal aberrations in the gene-corrected iPS cells. Most importantly, we demonstrated that the gene-corrected cells maintained their full potential and we generated viable mice that were completely derived from these repaired cells via tetraploid complementation approach, and these mice were healthy, without any signs of the metabolic liver disease.