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Wen J, Wu J, Cao T, Zhi S, Chen Y, Aagaard L, Zhen P, Huang Y, Zhong J, Huang J. Methylation silencing and reactivation of exogenous genes in lentivirus-mediated transgenic mice. Transgenic Res 2021; 30:63-76. [PMID: 33394315 DOI: 10.1007/s11248-020-00224-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Accepted: 11/24/2020] [Indexed: 12/27/2022]
Abstract
Taking advantage of their ability to integrate their genomes into the host genome, lentiviruses have been used to rapidly produce transgenic mice in biomedical research. In most cases, transgenes delivered by lentiviral vectors have resisted silencing mediated by epigenetic modifications in mice. However, some studies revealed that methylation caused decreased transgene expression in mice. Therefore, there is conflicting evidence regarding the methylation-induced silencing of transgenes delivered by lentiviral transduction in mice. In this study, we present evidence that the human TTR transgene was silenced by DNA methylation in the liver of a transgenic mouse model generated by lentiviral transduction. The density of methylation on the transgene was increased during reproduction, and the expression of the transgene was completely silenced in mice of the F2 generation. Interestingly, 5-azacytidine (5-AzaC), a methyltransferase inhibitor, potently reactivated the silenced genes in neonatal mice whose hepatocytes were actively proliferating and led to stable transgene expression during development. However, 5-AzaC did not rescue liver transgene expression when administered to adult mice. Moreover, 5-AzaC at the given dose had low developmental toxicity in the newborn mice. In summary, we demonstrate the methylation-induced silencing of an exogenous gene in the liver of a mouse model generated by lentiviral transduction and show that the silenced transgene can be safely and efficiently reactivated by 5-AzaC treatment, providing an alternative way to obtain progeny with stable transgene expression in the case of the methylation of exogenous genes in transgenic mice generated by lentiviral transduction.
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Affiliation(s)
- Jinkun Wen
- Department of Neurology, Jiangmen Central Hospital, Affiliated Jiangmen Hospital of Sun Yat-Sen University, Jiangmen, 529030, China.,MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Jinni Wu
- MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Tianqi Cao
- MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Shengyao Zhi
- MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Yuxi Chen
- MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Lars Aagaard
- Department of Biomedicine, Aarhus University, 8000, Aarhus C, Denmark
| | - Peilin Zhen
- Department of Infectious Diseases, Jiangmen Central Hospital, Affiliated Jiangmen Hospital of Sun Yat-Sen University, Jiangmen, 529030, China
| | - Yanming Huang
- Clinical Experimental Center, Jiangmen Central Hospital, Affiliated Jiangmen Hospital of Sun Yat-Sen University, Jiangmen, 529030, China
| | - Jianxin Zhong
- Department of Neurology, Jiangmen Central Hospital, Affiliated Jiangmen Hospital of Sun Yat-Sen University, Jiangmen, 529030, China
| | - Junjiu Huang
- MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China. .,Clinical Experimental Center, Jiangmen Central Hospital, Affiliated Jiangmen Hospital of Sun Yat-Sen University, Jiangmen, 529030, China. .,Key Laboratory of Reproductive Medicine of Guangdong Province, First Affiliated Hospital and School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China.
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New Transgenic Technologies. Mov Disord 2015. [DOI: 10.1016/b978-0-12-405195-9.00003-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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Ma J, Chai J, Shang Y, Li Y, Chen R, Jia J, Jiang S, Peng J. Swine PPAR-γ2 expression upregulated in skeletal muscle of transgenic mice via the swine Myozenin-1 gene promoter. Transgenic Res 2014; 24:409-20. [PMID: 25421932 DOI: 10.1007/s11248-014-9849-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2014] [Accepted: 11/05/2014] [Indexed: 10/24/2022]
Abstract
Myozenin-1 (Myoz1) gene-encoded calsarcin-2 protein was expressed exclusively in fast-twitch muscles. Peroxisome proliferator-activated receptor γ2 (PPAR-γ2) is a key regulator of adipocyte differentiation, fatty acid uptake and storage in mammals. In this study, transgenic (TG) mice were generated by injecting linearized DNA that contained mouse creatine kinase M-type enhancer, Myoz1 core promoter, swine PPAR-γ2 (sPPAR-γ2) and SV40 polyadenylation sequences into pronuclei of fertilized FVB/NJ mouse embryos using microinjection technology. Then, the TG mice were used to identify whether swine Myoz1 (sMyoz1) promoter could upregulate sPPAR-γ2 expression in skeletal muscle in a TG mouse model. The results showed that the sMyoz1 promoter indeed upregulated sPPAR-γ2 expression on both the RNA and protein levels. The target genes of PPAR-γ in fat formation pathways, such as fatty acid-binding protein 4 (FABP4) and lipoprotein lipase (LPL), were also overexpressed on the RNA level. Meanwhile, the level of skeletal muscle triacylglycerol in TG mice was increased (P < 0.05), and the result of Oil Red-O staining in the skeletal muscle sections also showed that the number of lipid droplets was significantly increased in TG mice compared to wild-type mice, which might improve the intramuscular fat (IMF) content. For pork, the quality was mostly influenced by the IMF; the identification of swine muscle-specific promoter, sMyoz1, could further serve to develop transgenic pigs with higher intramuscular fat contents and improve pork quality.
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Affiliation(s)
- Juanjuan Ma
- Agricultural Ministry Key Laboratory of Swine Breeding and Genetics and Key Laboratory of Agricultural Animal Genetics, Breeding, and Reproduction of the Ministry of Education, College of Animal Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China
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4
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Construction and quantitative evaluation of a dual specific promoter system for monitoring the expression status of Stra8 and c-kit genes. Mol Biotechnol 2014; 56:1100-9. [PMID: 25260891 DOI: 10.1007/s12033-014-9790-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Applications of genetic constructs with multiple promoters, which are fused with reporter genes and simultaneous monitoring of various events in cells, have gained special attention in recent years. Lentiviral vectors, with their distinctive characteristics, have been considered to monitor the developmental changes of cells in vitro. In this study, we constructed a novel lentiviral vector (FUM-M), containing two germ cell-specific promoters (Stra8 and c-kit), fused with ZsGreen and DsRed2 reporter genes, and evaluated its efficiency in different cells following treatments with retinoic acid and DMSO. Several cell lines (P19, GC-1 spg and HEK293T) were transduced with this vector, and functional capabilities of the promoters were verified by flow cytometry and quantitative RT-PCR. Our results indicate that FUM-M shows dynamic behavior in the presence and absence of extrinsic factors. A correlation was also observed between the function of promoters, present in the lentiviral construct and the endogenous level of the Stra8 and c-kit mRNAs in the cells. In conclusion, we recommend this strategy, which needs further optimization of the constructs, as a beneficial and practical way to screen chemical inducers involved in cellular differentiation toward germ-like cells.
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Lentiviral vector transduction of spermatozoa as a tool for the study of early development. FEBS Open Bio 2014; 4:266-75. [PMID: 24918038 PMCID: PMC4048842 DOI: 10.1016/j.fob.2014.02.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2013] [Revised: 02/13/2014] [Accepted: 02/19/2014] [Indexed: 01/25/2023] Open
Abstract
Sperm are mature cell types that can be transduced by lentiviral vectors. Lentiviral integration in sperm has been demonstrated. Lentivirally transduced sperm is useful for the study of early development.
Spermatozoa and lentiviruses are two of nature’s most efficient gene delivery vehicles. Both can be genetically modified and used independently for the generation of transgenic animals or gene transfer/therapy of inherited disorders. Here we show that mature spermatozoa can be directly transduced with various pseudotyped lentiviral vectors and used in in vitro fertilisation studies. Lentiviral vectors encoding Green Fluorescent Protein (GFP) were shown to be efficiently processed and expressed in sperm. When these transduced sperm were used in in vitro fertilisation studies, GFP expression was observed in arising blastocysts. This simple technique of directly transducing spermatozoa has potential to be a powerful tool for the study of early and pre-implantation development and could be used as a technique in transgenic development and vertical viral transmission studies.
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Key Words
- 293T, Human embryonic kidney cells
- 7-AAD, 7-Aminoactinomycin D
- AZT, azidodeoxythimidine
- CMV, Cytomegalovirus promoter
- Development
- EF-1, Elongation factor 1 alpha promoter
- GFP, Green Fluorescent Protein
- IVF, in vitro fertilisation
- In vitro fertilisation
- LTR, Long Terminal Repeat
- Lentiviral vectors
- PGK, Phosphoglycerate kinase promoter
- Spermatozoa
- Transduction
- Transgenics
- UCOE, ubiquitous chromatin opening element promoter
- VSV-g, vesicular stomatitis virus
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Chandrashekran A, Sarkar R, Thrasher A, Fraser SE, Dibb N, Casimir C, Winston R, Readhead C. Efficient generation of transgenic mice by lentivirus‐mediated modification of spermatozoa. FASEB J 2013; 28:569-76. [DOI: 10.1096/fj.13-233999] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Anil Chandrashekran
- Department of Surgery and CancerDivision of CancerInstitute of Reproductive and Developmental Biology (IRDB)Imperial College LondonLondonUK
| | - Rupa Sarkar
- Department of Surgery and CancerDivision of CancerInstitute of Reproductive and Developmental Biology (IRDB)Imperial College LondonLondonUK
| | - Adrian Thrasher
- Molecular Immunology UnitUniversity College London Institute of Child HealthLondonUK
| | - Scott E. Fraser
- Biological Imaging CenterBeckman InstituteCalifornia Institute of TechnologyPasadenaCaliforniaUSA
| | - Nicholas Dibb
- Department of Surgery and CancerDivision of CancerInstitute of Reproductive and Developmental Biology (IRDB)Imperial College LondonLondonUK
| | - Colin Casimir
- Department of Natural SciencesSchool of Science and TechnologyMiddlesex UniversityLondonUK
| | - Robert Winston
- Department of Surgery and CancerDivision of CancerInstitute of Reproductive and Developmental Biology (IRDB)Imperial College LondonLondonUK
| | - Carol Readhead
- Biological Imaging CenterBeckman InstituteCalifornia Institute of TechnologyPasadenaCaliforniaUSA
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Lu P, Zhang GR, Cai YZ, Heng BC, Ren H, Wang LL, Ji J, Zou XH, Ouyang HW. Lentiviral-encoded shRNA silencing of proteoglycan decorin enhances tendon repair and regeneration within a rat model. Cell Transplant 2013; 22:1507-17. [PMID: 23295185 DOI: 10.3727/096368912x661292] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Injured tendons often heal with scar tissue formation, resulting in uniformly smaller collagen fibrils and poor mechanical properties. The small leucine-rich proteoglycan decorin is well known to regulate fusion of collagen fibrils. Rat patellar tendon cells were transfected with lentiviral-encoded shRNA that specifically targets decorin. Silencing of decorin expression resulted in decreased cell growth. Three types of scaffold-free engineered tendons with different mix ratios of anti-decorin shRNA-treated cells to untreated cells at 1:0 (DCN), 1:1 (MIX), and 0:1 (CON) were utilized for repair of injured patellar tendons. Four weeks after implantation in situ, the MIX group manifested the best results (best coordination of histology, more mature collagen deposition, and larger collagen fibril diameter). Although the DCN group exhibited the largest collagen fibril diameter, this was associated with abnormal shape. Hence, regulation of decorin expression to an appropriate level is crucial for tendon repair with gene therapy.
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Affiliation(s)
- Ping Lu
- Center for Stem Cells and Tissue Engineering, School of Medicine, Zhejiang University, Hangzhou, China
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Cho YS, Lee SY, Kim YK, Kim DS, Nam YK. Functional ability of cytoskeletal β-actin regulator to drive constitutive and ubiquitous expression of a fluorescent reporter throughout the life cycle of transgenic marine medaka Oryzias dancena. Transgenic Res 2011; 20:1333-55. [PMID: 21437716 DOI: 10.1007/s11248-011-9501-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2010] [Accepted: 02/20/2011] [Indexed: 01/16/2023]
Abstract
Marine medaka Oryzias dancena, a candidate model organism, represents many attractive merits as a material for experimental transgenesis and/or heterologous expression assay particularly in the field of ecotoxicology and developmental biology. In this study, cytoskeletal β-actin gene was characterized from O. dancena and the functional capability of its promoter to drive constitutive expression of foreign reporter protein was evaluated. The O. dancena β-actin gene possessed a conserved genomic organization of vertebrate major cytoplasmic actin genes and the bioinformatic analysis of its 5'-upstream regulatory region predicted various transcription factor binding motifs. Heterologous expression assay using a red fluorescent protein (RFP) reporter construct driven by the O. dancena β-actin regulator resulted in stunningly bright expression of red fluorescence signals in not only microinjected embryos but also grown-up transgenic adults. Although founder transgenics exhibited mosaic patterns of RFP expression, transgenic offspring in subsequent generations displayed a vivid and uniform expression of RFP continually from embryos to adults. Based on the blot hybridization assays, two transgenic lines established in this study were proven to possess high copy numbers of transgene integrants (approximately 240 and 34 copies, respectively), and the transgenic genotype in both lines could successfully be passed stably up to three generations, although the rate of transgene transmission in one of the two transgenic lines was significantly lower than expected Mendelian ratio. Significant red fluorescence color could be ubiquitously observable in all the tissues or organs of the transgenics. Quantitative real-time RT-PCR represented that the expression pattern of transgene under the regulation of β-actin promoter would resemble, in overall, the regulation of endogenous β-actin gene in adult tissues, although putative mechanism for competitive or independent regulation between transgene and endogenous gene could also be found in several tissues. Results from this study undoubtedly indicate that the O. dancena β-actin promoter would be powerful enough to fluorescently visualize most cell types in vivo throughout its whole lifespan. This study could be a useful start point for a variety of transgenic experiments with this species concerning the constitutive expression of living fluorescent color reporters and other foreign proteins.
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MESH Headings
- Actins/genetics
- Actins/metabolism
- Animal Structures/cytology
- Animal Structures/metabolism
- Animals
- Animals, Genetically Modified/genetics
- Animals, Genetically Modified/metabolism
- Blotting, Southern
- Cloning, Molecular
- Computational Biology
- Cytoskeleton/genetics
- Cytoskeleton/metabolism
- Embryo, Nonmammalian/cytology
- Embryo, Nonmammalian/embryology
- Embryo, Nonmammalian/metabolism
- Embryonic Development
- Female
- Fish Proteins/genetics
- Fish Proteins/metabolism
- Gene Dosage
- Gene Expression Regulation, Developmental
- Gene Library
- Genes, Reporter
- Genetic Vectors/genetics
- Genetic Vectors/metabolism
- Inheritance Patterns
- Luminescent Proteins/genetics
- Luminescent Proteins/metabolism
- Male
- Microinjections
- Microscopy, Fluorescence
- Oryzias/embryology
- Oryzias/genetics
- Oryzias/metabolism
- Promoter Regions, Genetic
- Reverse Transcriptase Polymerase Chain Reaction/methods
- Transcription Factors/genetics
- Transcription Factors/metabolism
- Transgenes
- Red Fluorescent Protein
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Affiliation(s)
- Young Sun Cho
- Institute of Marine Living Modified Organisms, Pukyong National University, Busan 608-737, Korea
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9
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From genome-wide association studies to etiology: probing autoimmunity genes by RNAi. Trends Mol Med 2011; 17:634-40. [DOI: 10.1016/j.molmed.2011.06.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 06/08/2011] [Accepted: 06/13/2011] [Indexed: 11/20/2022]
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10
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KONG QR, LIU ZH. Inheritance and expression stability of transgene in transgenic animals. YI CHUAN = HEREDITAS 2011; 33:504-11. [DOI: 10.3724/sp.j.1005.2011.00504] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Faster generation of hiPSCs by coupling high-titer lentivirus and column-based positive selection. Nat Protoc 2011; 6:701-14. [PMID: 21637193 DOI: 10.1038/nprot.2011.320] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The protocols described here address methods used in two crucial stages in the retroviral reprogramming of somatic cells to produce human induced pluripotent stem cell (hiPSC) lines. The first is an optimized method for producing lentivirus at an efficiency 600-fold greater than previously published, and it includes conjugation of the lentivirus to streptavidin superparamagnetic particles; this process takes 8 d. The second method enables the isolation of true hiPSCs immediately after somatic cell reprogramming and involves column-based positive selection of cells expressing the pluripotency marker TRA-1-81. This process takes 2 h and, as it is directly compatible with feeder-free culture, the time burden of manually identifying and mechanically propagating hiPSC colonies is reduced drastically. Taken together, these methods accelerate the production of hiPSCs and enable lines to be isolated, expanded to approxiamtely 10⁷ cells and cryopreserved within 6-8 weeks.
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Bressan FF, Dos Santos Miranda M, Perecin F, De Bem TH, Pereira FTV, Russo-Carbolante EM, Alves D, Strauss B, Bajgelman M, Krieger JE, Binelli M, Meirelles FV. Improved production of genetically modified fetuses with homogeneous transgene expression after transgene integration site analysis and recloning in cattle. Cell Reprogram 2011; 13:29-36. [PMID: 21241190 DOI: 10.1089/cell.2010.0022] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Animal cloning by nuclear transfer (NT) has made the production of transgenic animals using genetically modified donor cells possible and ensures the presence of the gene construct in the offspring. The identification of transgene insertion sites in donor cells before cloning may avoid the production of animals that carry undesirable characteristics due to positional effects. This article compares blastocyst development and competence to establish pregnancies of bovine cloned embryos reconstructed with lentivirus-mediated transgenic fibroblasts containing either random integration of a transgene (random integration group) or nuclear transfer derived transgenic fibroblasts with known transgene insertion sites submitted to recloning (recloned group). In the random integration group, eGFP-expressing bovine fetal fibroblasts were selected by fluorescence activated cell sorting (FACS) and used as nuclei donor cells for NT. In the recloned group, a fibroblast cell line derived from a transgenic cloned fetus was characterized regarding transgene insertion and submitted to recloning. The recloned group had higher blastocyst production (25.38 vs. 14.42%) and higher percentage of 30-day pregnancies (14.29 vs. 2.56%) when compared to the random integration group. Relative eGFP expression analysis in fibroblasts derived from each cloned embryo revealed more homogeneous expression in the recloned group. In conclusion, the use of cell lines recovered from transgenic fetuses after identification of the transgene integration site allowed for the production of cells and fetuses with stable transgene expression, and recloning may improve transgenic animal yields.
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Dick E, Matsa E, Bispham J, Reza M, Guglieri M, Staniforth A, Watson S, Kumari R, Lochmüller H, Young L, Darling D, Denning C. Two new protocols to enhance the production and isolation of human induced pluripotent stem cell lines. Stem Cell Res 2010; 6:158-67. [PMID: 21095172 DOI: 10.1016/j.scr.2010.10.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/20/2010] [Revised: 10/12/2010] [Accepted: 10/14/2010] [Indexed: 12/31/2022] Open
Abstract
There are two critical stages in the retroviral reprogramming of somatic cells to produce human induced pluripotent stem cell (hiPSC) lines. One is the production of high titer virus required to reprogram somatic cells; the other is identification of true hiPSC colonies from heterogeneous cell populations, and their isolation and expansion to generate a sustainable, pluripotent stem cell line. Here we describe simple, time-saving methods to address the current difficulties at these two critical junctures. First, we have developed a method to increase the number of infectious viral units 600-fold. Second, we have developed a TRA-1-81-based positive selection column method for isolating "true" hiPSCs from the heterogeneous cell populations, which overcomes the labor-intensive and highly subjective method of manual selection of hiPSC colonies. We have used these techniques to produce 8 hiPSC lines from human fibroblasts and we believe that they are of considerable utility to researchers in the hiPSC field.
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Affiliation(s)
- Emily Dick
- Wolfson Centre for Stem Cells, Tissue Engineering & Modelling, Centre for Biomolecular Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
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Abstract
We have taken a synthetic biology approach to the generation and screening of transcription factor binding sites for activity in human cells. All possible 10-mer DNA sequences were printed on microarrays as 100-mers containing 10 repeats of the same sequence in tandem, yielding an oligonucleotide library of 52,429 unique sequences. This library of potential enhancers was introduced into a retroviral vector and screened in multiple cell lines for the ability to activate GFP transcription from a minimal CMV promoter. With this method, we isolated 100 bp synthetic enhancer elements that were as potent at activating transcription as the WT CMV immediate early enhancer. The activity of the recovered elements was strongly dependent on the cell line in which they were recovered. None of the elements were capable of achieving the same levels of transcriptional enhancement across all tested cell lines as the CMV enhancer. A second screen, for enhancers capable of synergizing with the elements from the original screen, yielded compound enhancers that were capable of twofold greater enhancement activity than the CMV enhancer, with higher levels of activity than the original synthetic enhancer across multiple cell lines. These findings suggest that the 10-mer synthetic enhancer space is sufficiently rich to allow the creation of synthetic promoters of all strengths in most, if not all, cell types.
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