The human cytomegalovirus immediate-early promoter is transcriptionally active in undifferentiated mouse embryonic stem cells

Characterization of promoters for adeno-associated virus mediated efficient Cas9 activation in adult Cas9 knock-in murine cochleae

CRISPR/Cas9 gene editing enables the treatment of hearing loss in congenitally deaf neonatal mice via both viral and non-viral delivery. While adeno-associated virus (AAV)-mediated gene delivery systems have been shown to be effective tools for gene replacement in the inner ear, application of the AAV-mediated CRISPR/Cas9 gene-editing approach for this purpose is yet to be documented. Based on our previous findings, we focused on the effects of several AAVs delivered via canalostomy injection in adult mice. Among the AAVs examined, AAV8 showed the greatest efficiency and specificity in transducing inner hair cells (IHC). The ability of Cre-expressing AAV8 to activate Cas9 in floxed-Cas9 knock-in (Cas9 KI) mice was further evaluated. We compared the effects of six different promoters (CMV, CAG, hSyn, CaMKIIa, GFAP, and ALB) of AAV8 delivered to the inner ear of adult Cas9 KI mice. Our findings showed that three AAV groups (CMV, CAG and hSyn promoters) infected the inner ear efficiently with different tropisms. Notably, AAVs with CMV, CAG, and hSyn promoters infected diverse cell types in mature murine cochleae, including IHCs. In particular, AAV8-hSyn showed high affinity to IHCs and spiral ganglion neurons (SGN). Neither the AAV8 virus itself (except AAV8-CAG) nor the surgical procedures used caused damage to HCs or impaired normal hearing. Our findings indicated that injection of AAV-Cre into mature inner ear efficiently induces Cas9 activation to achieve safe and efficient gene editing and different constituent promoters confer diverse infection patterns in cochlea, expanding the repertoire of gene-editing tools for regulating gene expression in target cells of the inner ear as part of the collective effort to rescue genetic hearing loss and develop effective gene therapy techniques.

An Efficient Transfection Method for Differentiation and Cell Proliferation of Mouse Embryonic Stem Cells

Embryonic stem (ES) cells are an important source of stem cells in tissue engineering and regenerative medicine because of their high self-renewal capacities and differentiation potentials. However, the detailed molecular mechanisms controlling the differentiation and renewal programs in ES cells remained unclear. One of the difficulties in understanding these mechanisms substantially results from the low efficacies of gene manipulation by delivering exogenous gene expression or knockdown of endogenous gene expression with small interfering RNA (siRNA) in ES cells. Here we describe an optimized protocol for efficiently transfecting mouse ES cells by Effectene, a liposome-based method. The high transfection efficiency in mouse ES cells is demonstrated in this chapter by (1) achieving a percentage of enhanced green fluorescence protein (EGFP) expression in >98% embryoid bodies after introducing plasmids encoding the protein; (2) decreased SOX-2 and Oct-3/4 expression and subsequent morphological evidences of cell differentiation after introducing siRNA expression for suppressing SOX-2 and Oct-3/4, which are known to be essential for maintenance of stem cell properties in mouse ES cells; and (3) overexpression or attenuated expression of 14-3-3σ to regulate cell proliferation of mouse ES cells.

An Adeno-Associated Virus-Based Toolkit for Preferential Targeting and Manipulating Quiescent Neural Stem Cells in the Adult Hippocampus

Quiescent neural stem cells (qNSCs) with radial morphology are the only proven source of new neurons in the adult mammalian brain. Our understanding of the roles of newly generated neurons depends on the ability to target and manipulate adult qNSCs. Although various strategies have been developed to target and manipulate adult hippocampal qNSCs, they often suffer from prolonged breeding, low recombination efficiency, and non-specific labeling. Therefore, developing a readily manufactured viral vector that allows flexible packaging and robust expression of various transgenes in qNSCs is a pressing need. Here, we report a recombinant adeno-associated virus serotype 4 (rAAV4)-based toolkit that preferentially targets hippocampal qNSCs and allows for lineage tracing, functional analyses, and activity manipulation of adult qNSCs. Importantly, targeting qNSCs in a non-Cre-dependent fashion opens the possibility for studying qNSCs in less genetically tractable animal species and may have translational impact in gene therapy by preferentially targeting qNSCs.

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rAAV4 vectors preferentially target quiescent NSCs in the adult hippocampus

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rAAV4 vectors with distinct promoters reveal differential selectivity for radial NSCs

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rAAV4 allows for genetic manipulation and lineage tracing of quiescent NSCs

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rAAV4 allows for calcium imaging and activity manipulation of quiescent NSCs

Neural Development by Transplanted Human Embryonal Carcinoma Stem Cells Expressing Green Fluorescent Protein

For many years, researchers have investigated the fate and potential of neuroectodermal cells during the development of the central nervous system. Although several key factors that regulate neural differentiation have been identified, much remains unknown about the molecular mechanisms that control the fate and specification of neural subtypes, especially in humans. Human embryonal carcinoma (EC) stem cells are valuable research tools for the study of neural development; however, existing in vitro experiments are limited to inducing the differentiation of EC cells into only a handful of cell types. In this study, we developed and characterized a novel EC cell line (termed TERA2.cl.SP12-GFP) that carries the reporter molecule, green fluorescent protein (GFP). We demonstrate that TERA2.cl.SP12-GFP stem cells and their differentiated neural derivatives constitutively express GFP in cells grown both in vitro and in vivo. Cellular differentiation does not appear to be affected by insertion of the transgene. We propose that TERA2.cl.SP12-GFP cells provide a valuable research tool to track the fate of cells subsequent to transplantation into alternative environments and that this approach may be particularly useful to investigate the differentiation of human neural tissues in response to local environmental signals.

Forced expression of Hnf4a induces hepatic gene activation through directed differentiation

Embryonic stem (ES) cells are capable of unlimited self-renewal and have a diverse differentiation potential. These unique features make ES cells as an attractive source for developmental biology studies. Having the mature hepatocyte in the lab with functional activities is valuable in drug discovery studies. Overexpression of hepatocyte lineage-specific transcription factors (TFs) becomes a promising approach in pluripotent cell differentiation toward liver cells. Many studies generate transgenic ES cell lines to examine the effects of specific TFs overexpression in cell differentiation. In the present report, we have addressed whether a suspension or adherent model of differentiation is an appropriate way to study the role of Hnf4a overexpression. We generated ES cells that carried a doxycycline (Dox)-inducible Hnf4a using lentiviral vectors. The transduced cells were subjected to induced Hnf4a overexpression through both spontaneous and directed differentiation methods. Gene expression analysis showed substantially increased expression of hepatic gene markers, particularly Ttr and endogenous Hnf4a, in transduced cells differentiated by the directed approach. These results demonstrated that forced expression of TFs during directed differentiation would be an appropriate way to study relevant gene activation and the effects of overexpression in the context of hepatic differentiation.

Enhancement of Transgene Expression by HDAC Inhibitors in Mouse Embryonic Stem Cells

Embryonic stem (ES) cells can self-renew and differentiate to various cells depending on the culture condition. Although ES cells are a good model for cell type specification and can be useful for application in clinics in the future, studies on ES cells have many experimental restraints including low transfection efficiency and transgene expression. Here, we observed that transgene expression after transfection was enhanced by treatment with histone deacetylse (HDAC) inhibitors such as trichostatin A, sodium butyrate, and valproic acid. Transfection was performed using conventional transfection reagents with a retroviral vector encoding GFP under the control of CMV promoter as a reporter. Treatment of ES cells with HDAC inhibitors after transfection increased population of GFP positive cells up to 180% compared with untreated control. ES cells showed normal expression of stem cell markers after treatment with HDAC inhibitors. Transgene expression was further enhanced by modifying transfection procedure. GFP positive cells selected after transfection were proved to have the stem cell properties. Our improved protocol for enhanced gene delivery and expression in mouse ES cells without hampering ES cell properties will be useful for study and application of ES cells.

Exploiting the power of LINE-1 retrotransposon mutagenesis for identification of genes involved in embryonic stem cell differentiation

Identifying the genes or epigenetic factors that control the self-renewal and differentiation of stem cells is critical to understanding the molecular basis of cell commitment. Although a number of insertional mutagenesis vectors have been developed for identifying gene functions in animal models, the L1 retrotransposition system offers additional advantages as a tool to disrupt genes in embryonic stem cells in order to identify their functions and the phenotypes associated with them. Recent advances in producing synthetic versions of L1 retrotransposon vector system and the optimization of techniques to accurately identify retrotransposon integration sites have increased their utility for gene discovery applications. We have developed a novel episomal, nonviral L1 retrotransposon vector using scaffold/matrix attachment regions that provides stable, sustained levels of retrotransposition in cell cultures without being affected by epigenetic silencing or from some of the common problems of vector integration. This modified vector contains a GFP marker whose expression occurs only after successful gene disruption events and thus the cells with disrupted genes can be easily picked for functional analysis. Here we present a method to disrupt gene function in embryonic stem cells that aid in the identification of genes involved in stem cell differentiation processes. The methods presented here can be easily adapted to the study of other types of cancer stem cells or induced pluripotent stem cells using the L1 retrotransposon as an insertional mutagen.

Epigenetic changes of lentiviral transgenes in porcine stem cells derived from embryonic origin

Because of the physiological and immunological similarities that exist between pigs and humans, porcine pluripotent cell lines have been identified as important candidates for preliminary studies on human disease as well as a source for generating transgenic animals. Therefore, the establishment and characterization of porcine embryonic stem cells (pESCs), along with the generation of stable transgenic cell lines, is essential. In this study, we attempted to efficiently introduce transgenes into Epiblast stem cell (EpiSC)-like pESCs. Consequently, a pluripotent cell line could be derived from a porcine-hatched blastocyst. Enhanced green fluorescent protein (EGFP) was successfully introduced into the cells via lentiviral vectors under various multiplicities of infection, with pluripotency and differentiation potential unaffected after transfection. However, EGFP expression gradually declined during extended culture. This silencing effect was recovered by in vitro differentiation and treatment with 5-azadeoxycytidine. This phenomenon was related to DNA methylation as determined by bisulfite sequencing. In conclusion, we were able to successfully derive EpiSC-like pESCs and introduce transgenes into these cells using lentiviral vectors. This cell line could potentially be used as a donor cell source for transgenic pigs and may be a useful tool for studies involving EpiSC-like pESCs as well as aid in the understanding of the epigenetic regulation of transgenes.

Small interfering RNA-mediated knockdown of chicken interferon-γ expression

Interferon (IFN)-γ is a cytokine with a variety of functions, including direct antiviral activities and the capacity to polarize T-cells. However, there is limited information available about the function of this cytokine in the avian immune system. To gain a better understanding of the biological relevance of IFN-γ in chicken immunity, gain-of-function (upregulation) and loss-of-function (downregulation) studies need to be conducted. RNA interference (RNAi), a technique employed for downregulating gene expression, is mediated by small interfering RNA (siRNA), which can trigger sequence-specific gene silencing. In this regard, sequence specificity and delivery of siRNA molecules remain critical issues, especially to cells of the immune system. Various direct and indirect approaches have been employed to deliver siRNA, including the use of viral vectors. The objectives of the present study were to determine whether RNAi could effectively downregulate expression of chicken IFN-γ in vitro, and investigate the feasibility of recombinant adeno-associated virus to deliver siRNA in vitro as well. Three 27-mer Dicer substrate RNAs were selected based on the chicken IFN-γ coding sequence and transfected into cells or delivered using a recombinant avian adeno-associated virus (rAAAV) into a chicken fibroblast cell line expressing chIFN-γ. The expression of chIFN-γ transcripts was significantly downregulated when a cocktail containing all three siRNAs was used. Expression of endogenous IFN-γ was also significantly downregulated in primary cells after stimulation with a peptide. Further, significant suppression of IFN-γ transcript was also observed in vitro in cells that were treated with rAAAV, expressing siRNA targeting IFN-γ. Off-target effects in the form of triggering IFN responses by RNAi, including expression of chicken 2',5'-oligoadenylate synthetase and IFN-α, were also examined. Our results suggest that siRNAs selected were effective at downregulating IFN-γ in vitro both when delivered directly as well as when expressed by an rAAAV-based vector.

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.

I-SceI-mediated double-strand break does not increase the frequency of homologous recombination at the Dct locus in mouse embryonic stem cells

Targeted induction of double-strand breaks (DSBs) at natural endogenous loci was shown to increase the rate of gene replacement by homologous recombination in mouse embryonic stem cells. The gene encoding dopachrome tautomerase (Dct) is specifically expressed in melanocytes and their precursors. To construct a genetic tool allowing the replacement of Dct gene by any gene of interest, we generated an embryonic stem cell line carrying the recognition site for the yeast I-SceI meganuclease embedded in the Dct genomic segment. The embryonic stem cell line was electroporated with an I-SceI expression plasmid, and a template for the DSB-repair process that carried sequence homologies to the Dct target. The I-SceI meganuclease was indeed able to introduce a DSB at the Dct locus in live embryonic stem cells. However, the level of gene targeting was not improved by the DSB induction, indicating a limited capacity of I-SceI to mediate homologous recombination at the Dct locus. These data suggest that homologous recombination by meganuclease-induced DSB may be locus dependent in mammalian cells.

A novel dual-color reporter for identifying insulin-producing beta-cells and classifying heterogeneity of insulinoma cell lines

Many research studies use immortalized cell lines as surrogates for primary beta- cells. We describe the production and use of a novel "indirect" dual-fluorescent reporter system that leads to mutually exclusive expression of EGFP in insulin-producing (INS(+)) beta-cells or mCherry in non-beta-cells. Our system uses the human insulin promoter to initiate a Cre-mediated shift in reporter color within a single transgene construct and is useful for FACS selection of cells from single cultures for further analysis. Application of our reporter to presumably clonal HIT-T15 insulinoma cells, as well as other presumably clonal lines, indicates that these cultures are in fact heterogeneous with respect to INS(+) phenotype. Our strategy could be easily applied to other cell- or tissue-specific promoters. We anticipate its utility for FACS purification of INS(+) and glucose-responsive beta-like-cells from primary human islet cell isolates or in vitro differentiated pluripotent stem cells.

A comparison of exogenous promoter activity at the ROSA26 locus using a ΦiC31 integrase mediated cassette exchange approach in mouse ES cells

The activities of nine ubiquitous promoters (ROSA26, CAG, CMV, CMVd1, UbC, EF1α, PGK, chicken β-actin and MC1) have been quantified and compared in mouse embryonic stem cells. To avoid the high variation in transgene expression which results from uncontrolled copy number and chromosomal position effects when using random insertion based transgenic approaches, we have adopted a PhiC31 integrase mediated cassette exchange method for the efficient insertion of transgenes at single copy within a defined and well characterized chromosomal position, ROSA26. This has enabled the direct comparison of constructs from within the same genomic context and allows a systematic and quantitative assessment of the strengths of the promoters in comparison with the endogenous ROSA26 promoter. The behavior of these exogenous promoters, when integrated at ROSA26 in both sense and antisense orientations, reveals a large variation in their levels of activity. In addition, a subset of promoters, EF1α, UbC and CAG, show an increased activity in the sense orientation as a consequence of integration. Transient transfection experiments confirmed these observations to reflect integration dependent effects and also revealed significant differences in the behaviour of these promoters when delivered transiently or stably. As well as providing an important reference which will facilitate the choice of an appropriate promoter to achieve the desired level of expression for a specific research question, this study also demonstrates the suitability of the cassette exchange methodology for the robust and reliable expression of multiple variant transgenes in ES cells.

Genetically modified mesenchymal stem cells for improved islet transplantation

The use of adult stem cells for therapeutic purposes has met with great success in recent years. Among several types of adult stem cells, mesenchymal stem cells (MSCs) derived from bone marrow (BM) and other sources have gained popularity for basic research and clinical applications because of their therapeutic potential in treating a variety of diseases. Because of their tissue regeneration potential and immune modulation effect, MSCs were recently used as cell-based therapy to promote revascularization, increase pancreatic β-cell proliferation, and avoid allograft rejection in islet transplantation. Taking advantage of the recent progress in gene therapy, genetically modified MSCs can further enhance and expand the therapeutic benefit of primary MSCs while retaining their stem-cell-like properties. This review aims to gain a thorough understanding of the current obstacles to successful islet transplantation and discusses the potential role of primary MSCs before or after genetic modification in islet transplantation.

A bidirectional promoter architecture enhances lentiviral transgenesis in embryonic and extraembryonic stem cells

The two main challenges facing retroviral transgenesis are variable expression and epigenetic silencing. Although modern lentiviral vectors incorporate several elements to increase transgene expression and reduce position effect variegation and silencing, therapeutic research in stem cells, as well as production of transgenic animals, is still hampered by these two key problems. On the basis of recent studies demonstrating the chromatin insulating properties of divergent promoters, we sought to develop a bidirectional lentiviral vector with which to conduct RNA interference (RNAi)-based genetic screens in embryonic and extraembryonic stem cells. To this end, we designed and tested a series of synthetic bidirectional promoters, combining the mouse phosphoglycerate kinase 1 (Pgk1) promoter with other strong mammalian and viral promoters. Here, we demonstrate that a back-to-back configuration of the mouse Pgk1 and human eukaryotic translation elongation factor 1 alpha 1 promoters provided a substantive increase in both transgene expression and RNAi-based transcript depletion as compared with previous designs and other promoter combinations. Using this vector, we were able to achieve stable and robust depletion of a transfected luciferase reporter, as well as an endogenous non-coding RNA. The described constructs are an improved transgene delivery system capable of conducting RNAi screens in stem cells at single copy.

An efficient transfection method for mouse embryonic stem cells

Embryonic stem (ES) cells are an important source of stem cells in tissue engineering and regenerative medicine because of their high self-renewal capacities and differentiation potentials. However, the detailed molecular mechanisms controlling the differentiation and renewal programs in ES cells remained unclear. One of the difficulties in understanding these mechanisms substantially results from the low efficacies of gene manipulation by delivering exogenous gene expression or knockdown of endogenous gene expression with small interfering RNA (siRNA) in ES cells. Here we describe an optimized protocol for efficiently transfecting mouse ES cells by Effectene, a liposome-based method. The high transfection efficiency in mouse ES cells is demonstrated in this chapter by (1) achieving a percentage of enhanced green fluorescence protein (EGFP) expression in >98% embryoid bodies after introducing plasmids encoding the protein and (2) decreased SOX-2 and Oct-3/4 expression and subsequent morphological evidence of cell differentiation after introducing siRNA expression for suppressing SOX-2 and Oct-3/4, which are known to be essential for maintenance of stem cell properties in mouse ES cells.

Hypoxia activates constitutive luciferase reporter constructs

Hypoxia has been identified as a contributing factor in the pathophysiology of several diseases and oxygen regulation is important during stem cell development, particularly in early embryogenesis. One aspect that has emerged is the role of hypoxia-inducible factors, or HIFs in regulating the effect of hypoxia. Studies in our laboratory sought to examine the hypoxic regulation of HIF activity in placental trophoblast cells, through the use of dual-reporter luciferase assays. Our study demonstrates that hypoxic conditions cause a significant increase in the level of constitutive luciferase reporter activity. We also show that this induction is not a cell type or species-specific phenomenon and provides an alternative method for normalizing transfection efficiency in luciferase assays under hypoxic conditions. Our results suggest that in studies dealing with hypoxic conditions, caution should be used when interpreting measurements of transcriptional activity by traditional dual-reporter assays.

Epigenetic regulation of promiscuous gene expression in thymic medullary epithelial cells

Thymic central tolerance comprehensively imprints the T-cell receptor repertoire before T cells seed the periphery. Medullary thymic epithelial cells (mTECs) play a pivotal role in this process by virtue of promiscuous expression of tissue-restricted autoantigens. The molecular regulation of this unusual gene expression, in particular the involvement of epigenetic mechanisms is only poorly understood. By studying promiscuous expression of the mouse casein locus, we report that transcription of this locus proceeds from a delimited region ("entry site") to increasingly complex patterns along with mTEC maturation. Transcription of this region is preceded by promoter demethylation in immature mTECs followed upon mTEC maturation by acquisition of active histone marks and local locus decontraction. Moreover, analysis of two additional gene loci showed that promiscuous expression is transient in single mTECs. Transient gene expression could conceivably add to the local diversity of self-antigen display thus enhancing the efficacy of central tolerance.

Evaluation of combinatorial cis-regulatory elements for stable gene expression in chicken cells

Background

Recent successes in biotechnological application of birds are based on their unique physiological traits such as unlimited manipulability onto developing embryos and simple protein constituents of the eggs. However it is not likely that target protein is produced as kinetically expected because various factors affect target gene expression. Although there have been various attempts to minimize the silencing of transgenes, a generalized study that uses multiple cis-acting elements in chicken has not been made. The aim of the present study was to analyze whether various cis-acting elements can help to sustain transgene expression in chicken fibroblasts.

Results

We investigated the optimal transcriptional regulatory elements for enhancing stable transgene expression in chicken cells. We generated eight constructs that encode enhanced green fluorescent protein (eGFP) driven by either CMV or CAG promoters (including the control), containing three types of key regulatory elements: a chicken lysozyme matrix attachment region (cMAR), 5'-DNase I-hypersensitive sites 4 (cHS4), and the woodchuck hepatitis virus posttranscriptional regulatory element (WPRE). Then we transformed immortalized chicken embryonic fibroblasts with these constructs by electroporation, and after cells were expanded under G418 selection, analyzed mRNA levels and mean fluorescence intensity (MFI) by quantitative real-time PCR and flow cytometry, respectively. We found that the copy number of each construct significantly decreased as the size of the construct increased (R² = 0.701). A significant model effect was found in the expression level among various constructs in both mRNA and protein (P < 0.0001). Transcription with the CAG promoter was 1.6-fold higher than the CMV promoter (P = 0.027) and the level of eGFP expression activity in cMAR- or cHS4-flanked constructs increased by two- to three-fold compared to the control CMV or CAG promoter constructs. In addition, flow cytometry analysis showed that constructs having cis-acting elements decreased the level of gene silencing as well as the coefficient of variance of eGFP-expressing cells (P < 0.0001).

Conclusions

Our current data show that an optimal combination of cis-acting elements and promoters/enhancers for sustaining gene expression in chicken cells is suggested. These results provide important information for avian transgenesis and gene function studies in poultry.

Analysis of the cellular localization of herpes simplex virus 1 immediate-early protein ICP22

Nuclear proteins often form punctiform structures, but the precise mechanism for this process is unknown. As a preliminary study, we investigated the aggregation of an HSV-1 immediate-early protein, infected-cell protein 22 (ICP22), in the nucleus by observing the localization of ICP22-EGFP fusion protein. Results showed that, in high-level expression conditions, ICP22-EGFP gradually concentrates in the nucleus, persists throughout the cell cycle without disaggregation even in the cell division phase, and is finally distributed to daughter cells. We subsequently constructed a mammalian cell expression system, which had tetracycline-dependent transcriptional regulators. Consequently, the location of ICP22-EGFP in the nucleus changed with distinct induction conditions. This suggests that the cellular location of ICP22 is also influenced by promoter regulation, in addition to its own structure. Our findings provide new clues for the investigation of transcriptional regulation of viral genes. In addition, the non-protease reporter system we constructed could be utilized to evaluate the role of internal ribosome entry sites (IRES) on transcriptional regulation.

Detection of calcium transients in embryonic stem cells and their differentiated progeny

A central issue in stem cell biology is the determination of function and activity of differentiated stem cells, features that define the true phenotype of mature cell types. Commonly, physiological mechanisms are used to determine the functionality of mature cell types, including those of the nervous system. Calcium imaging provides an indirect method of determining the physiological activities of a mature cell. Camgaroos are variants of yellow fluorescent protein that act as intracellular calcium sensors in transfected cells. We expressed one version of the camgaroos, Camgaroo-2, in mouse embryonic stem (ES) cells under the control of the CAG promoter system. Under the control of this promoter, Camgaroo-2 fluorescence was ubiquitously expressed in all cell types derived from the ES cells that were tested. In response to pharmacological stimulation, the fluorescence levels in transfected cells correlated with cellular depolarization and hyperpolarization. These changes were observed in both undifferentiated ES cells as well as ES cells that had been neurally induced, including putative neurons that were differentiated from transfected ES cells. The results presented here indicate that Camgaroo-2 may be used like traditional fluorescent proteins to track cells as well as to study the functionality of stem cells and their progeny.

Chemical genetics identifies c-Src as an activator of primitive ectoderm formation in murine embryonic stem cells

Multiple Src family kinases (SFKs) are present in murine embryonic stem (mES) cells. Whereas complete inhibition of SFK activity blocks mES cell differentiation, sole inhibition of the SFK member c-Yes induces differentiation. Thus, individual SFKs may have opposing roles in the regulation of mES cell fate. To test this possibility, we generated SFK mutants with engineered resistance to a nonselective SFK inhibitor. The presence of an inhibitor-resistant c-Src mutant, but not analogous mutants of Hck, Lck, c-Yes, or Fyn, reversed the differentiation block associated with inhibitor treatment, resulting in the formation of cells with properties of primitive ectoderm. These results show that distinct SFK signaling pathways regulate mES cell fate and demonstrate that the formation of primitive ectoderm is regulated by the activity of c-Src.

Establishment and characterization of novel porcine embryonic stem cell lines expressing hrGFP

The purpose of this study was to establish transgenic porcine embryonic stem (pES) cell lines that can stably express report gene. Established pES cell line at passage 44 was transfected with pAAV-hrGFP Control Plasmid by electroporation-mediated, viral vector-mediated, and liposome-mediated strategies. Although there were several pES colonies expressing green fluorescent protein (GFP) obtained from the retrovirus-mediated and liposome-mediated transfection methods, no stable GFP-expressing pES cell line was then derived. A total of 28 GFP-expressing pES cell colonies were obtained following electroporation with two DC pulses of 150 V/cm for 10 msec and three GFP-expressing pES (pES/GFP(+)) cell lines were established. These pES/GFP(+) cell lines stably expressed exogenous GFP and continuously proliferated in vitro for more than 90 passages in 20 months. They maintained normal karyotype of 36 + XX and typical characteristics of pluripotent stem cells, including expression of pluripotent markers Oct-4, AP, SSEA-4, TRA-1-60, and TRA-1-81, formation of embryoid bodies under suspension culture. They were able to differentiate in vitro into neural and cardiomyocytic lineage, respectively, under suitable induction. To our knowledge, there has been no report of establishing GFP-expressing pES cell lines. These novel pES/GFP(+) cell lines established in this study might serve as a nonrodent model and would benefit to the studies involving ES cell transplantation, cell replacement therapy, and tissue regeneration due to their traceable capacity.

Development of a prokaryotic-like polycistronic baculovirus expression vector by the linkage of two internal ribosome entry sites

Recombinant baculoviruses are suitable for the high-level production of large multi-protein complexes. A tri-cistronic expression vector was constructed by the inclusion of two internal ribosome entry sites (IRESs). In this novel polycistronic vector, one single polyhedrin promoter controlled the transcription of a tri-cistronic transcript. Also, the first cistron was translated through a cap-dependent mechanism, while the second and third cistrons were translated by the IRESs derived from the 5' UTR of Rhopalosiphum padi virus (RhPV) and Perina nuda virus (PnV), respectively. The ratio of tri-cistronic gene expression levels produced by the three translational initiation modules is about 2:1:1 (cap:PnV IRES:RhPV IRES). This study indicates that polycistronic genes can be co-expressed at the translational level as in prokaryotic expression system by baculovirus biotechnology.

Development and application of a dual-purpose nanoparticle platform for delivery and imaging of siRNA in tumors

The vision of using a single therapeutic agent with sufficient generality to allow application to a wide variety of diseases, yet specific enough to permit intervention at single molecular stages of the pathology, is rapidly becoming a reality through the emergence of RNA interference. RNA interference can be used to inhibit the expression of virtually any gene and, at the same time, has single-nucleotide specificity. Major challenges in applying RNA interference in vivo are adequate delivery of the siRNA molecule to the tissue of interest and methods of monitoring this delivery in a noninvasive manner. With this in mind, we have developed an approach not only to deliver siRNA to tumors, but also to track the success of the delivery by noninvasive imaging. To accomplish this, we designed a dual-function probe, MN-NIRF-siRNA, which consists of magnetic nanoparticles (MN) for magnetic resonance imaging (MRI), labeled with Cy5.5 dye for near-infrared in vivo optical imaging (NIRF), conjugated to myristoylated polyarginine peptides (MPAPs) for translocation of the complex into the cytosol, and carrying siRNA targeting tumor-specific genes. Administration of MN-NIRF-siRNA to tumor-bearing mice allowed us to monitor the delivery of the agent to tumors by MRI and NIRF imaging and resulted in efficient silencing of the target genes. This approach can significantly advance the therapeutic potential of RNA interference by providing a way not only to effectively shuttle siRNA to target sites but also to noninvasively assess the bioavailability of the siRNA molecule.

An efficient transfection method for mouse embryonic stem cells

Embryonic stem (ES) cells are considered to have potentials for tissue regeneration and treatment of diverse human diseases. ES cells are capable of indefinite renewal and proliferation, which can be induced to differentiate into tissues of all three germ lines. Despite these exciting potential, it remains unclear as to how the renewal and differentiation programs are operated and regulated at the genetic level. Genetic manipulation such as delivery of exogenous gene expression or knockdown with small interfering RNA (siRNA) is commonly used in most of cancer or transformed cells but relatively rare in ES cells. In this study, we compare the transfection efficacies of several liposome-based transfection methods by introduction of a plasmid encoding enhanced green fluorescent protein (EGFP) into mouse ES (mES) cells. Our results show that transfection by Effectene achieves the efficiency of >98% in CCE and >80% in D3 cells. The optimal ratio of DNA:Effectene for EGFP transfection is between 1:4 and 1:8. Transient-expressed EGFP or endogenous protein kinase A (PKA) were significantly knocked down by Effectene transfection of specific siRNA. High EGFP level expression and accumulation in mES cells induces minor cytotoxicity but can be reduced by introducing siRNA of EGFP. Further, this transfection method did not significantly affect mES properties of proliferation or differentiation. Our results provide an optimal protocol to achieve an efficient transfection for mES cells.

Promoter-dependent EGFP expression during embryonic stem cell propagation and differentiation

Genetic modification is an important tool in embryonic stem (ES) cell research and requires efficient promoter systems. Here, we have compared the transcriptional activities of three ubiquitous promoters, elongation factor-1alpha (EF1alpha), phosphoglycerate kinase-1 (PGK), and cytomegalovirus (CMV), during propagation and differentiation of mouse (m) ES cells by using stable mES cell lines expressing enhanced green fluorescent protein (EGFP) under each of these promoters. In undifferentiated ES cells, the EGFP expression driven by the EF1alpha was most stable, followed by the PGK, whereas the down-regulation of EGFP expression driven by the CMV promoter was most significant during propagation up to passage 35. A similar pattern for the activities of these promoters was observed in embryoid bodies (EBs) during 14 days of differentiation, with brighter EGFP signals driven by the EF1alpha promoter versus the other two. Moreover, the EF1alpha and PGK promoters, but not CMV, were effective in almost all mES cell-differentiated neuronal cells, cardiomyocytes, and visceral endoderm cells, with the fluorescent signal intensity higher for EF1alpha and even for PGK. The CMV promoter yielded a weak fluorescent signal in about 60-80% of these differentiated cells, while a few differentiated cells with the CMV promoter showed bright EGFP expression like that with the EF1alpha promoter. These results extend previous observations for the activities of these promoters in mES cells and provide new information for choosing appropriate promoters to facilitate genetic modification of mES cells.

Improvement of reporter activity by IRES-mediated polycistronic reporter system

Many in vitro and in vivo applications for transgenesis require co-expression of heterologous genes. The use of internal ribosome entry sites (IRESs) in dicistronic expression vectors enables the expression of two genes controlled by one promoter in target cells or whole organisms. Here we describe the expansion of IRES exploitation to generate multicistronic vectors capable of expressing multiple reporter genes, especially to improve the fluorescence yield of autofluorescent reporter gene products such as green fluorescent protein (GFP). We found that the increase in fluorescence output of GFP is proportional to the number of IRES-GFP repeats in the multicistronic vector. At least four genes can be expressed from a multicistonic vector by using tandem IRES elements, with no significant alteration of the expression level of the cap-dependent translated gene. Moreover, gene expression under the control of multiple IRES element has no effect on the posttranscriptional regulation through 3′-untranslated regions (3′UTR). Thus, endogenous gene expression and regulation, especially those controlled by weak promoters, can be analyzed with our IRES-dependent polycistronic reporter gene expression system.

The CMV early enhancer/chicken beta actin (CAG) promoter can be used to drive transgene expression during the differentiation of murine embryonic stem cells into vascular progenitors

Background

Mouse embryonic stem cells cultured in vitro have the ability to differentiate into cells of the three germ layers as well as germ cells. The differentiation mimics early developmental events, including vasculogenesis and early angiogenesis and several differentiation systems are being used to identify factors that are important during the formation of the vascular system. Embryonic stem cells are difficult to transfect, while downregulation of promoter activity upon selection of stable transfectants has been reported, rendering the study of proteins by overexpression difficult.

Results

CCE mouse embryonic stem cells were differentiated on collagen type IV for 4–5 days, Flk1⁺ mesodermal cells were sorted and replated either on collagen type IV in the presence of VEGFA to give rise to endothelial cells and smooth muscle cells or in collagen type I gels for the formation of vascular tubes. The activity of the CMV and β-actin promoters was downregulated during selection of stable transfectants and during differentiation to the Flk1 stage, while the CMV immediate enhancer/β-actin promoter in the pCAGIPuro-GFP vector led to 100% of stably transfected undifferentiated and differentiated cells expressing GFP. To further test this system we expressed syndecan-2 and -4 in these cells and demonstrated high levels of transgene expression in both undifferentiated cells and cells differentiated to the Flk1 stage.

Conclusion

Vectors containing the CAG promoter offer a valuable tool for the long term expression of transgenes during stem cell differentiation towards mesoderm, while the CMV and β-actin promoters lead to very poor transgene expression during this process.

Efficiency of the elongation factor-1alpha promoter in mammalian embryonic stem cells using lentiviral gene delivery systems

The establishment of new technology for genetic modification in human embryonic stem (ES) cell lines has raised great hopes for achieving new ground in basic and clinical research. Recently, lentiviral vector technology has been shown to be highly effective and therefore could emerge as a popular tool for human ES cell genetic modification. The objectives of this study were to evaluate the efficiency of promoters in lentiviral gene delivery systems in mammalian ES cells, including mouse, monkey, and human, and to construct efficient and optimized conditions for lentivirus-mediated transfection systems. Mammalian ES cells were transfected with self-inactivating (SIN) human immunodeficiency virus type-1 (HIV-1)-based lentiviral vectors containing the human polypeptide chain elongation factor-1alpha (EF-1alpha) promoter or cytomegalovirus (CMV) promoter and analyzed by fluorescence-activated cell sorting (FACS) analysis for the expression of the enhanced green fluorescent protein (eGFP) reporter gene. The efficiency of the EF-1alpha promoter was higher than that of the CMV promoter in all ES cells tested. The EF-1alpha promoter efficiently drove gene expression (14.74%) compared with CMV promoter (3.69%) in human ES cells. We generated a stable eGFP+ human ES cell line (CHA3-EGFP human ES cells) that continuously expressed high levels of EGFP ( approximately 95%) from the EF-1alpha promoter and was maintained for up to 60 weeks with undifferentiated proliferation. The established CHA3-EGFP human ES cell lines were characterized as being negative for nondifferentiation markers and teratoma formation. These results imply that genetic modification by lentiviral vectors with specific promoters in ES cells constitute a powerful tool for guided differentiation as well as gene therapy.

Analysis of HSV-I ICP22 effects on HCMV major immediate-early promoter structure

The human cytomegalovirus (HCMV) major immediate-early (MIE) promoter has strong transcriptional promoting capability. Its cis-acting regulatory elements form a special structure in this region that is repeated multiple times; the biological significance of these elements and their different compositions in the transcriptional promoting process remain unclear. Our results demonstrate that the HSV-I MIE protein ICP22 can generate strong repression of many viral and cellular promoters and enhancers. We further studied the transcriptional effects of ICP22 on structural elements and mutations in various HCMV MIE promoters by using a CAT assay. In spite of different transcriptional effects of all the elements in the presence of ICP22, the transcriptional efficiencies exhibited by mutations generated by different compositions and an entire HCMV promoter, are not the simple sum of the functions of these elements. Furthermore, the transcriptional activities of specific sequences were not affected by the presence of ICP22. Therefore, it is assumed that the HCMV MIE promoter co-regulates expression of downstream genes by using viral and cellular specific factors via a specific pathway.

Repression of kit expression by Plzf in germ cells

Male mice lacking expression of Plzf, a DNA sequence-specific transcriptional repressor, show progressive germ cell depletion due to exhaustion of the spermatogonial stem cell population. This is likely due to the deregulated expression of genes controlling the switch between spermatogonial self-renewal and differentiation. Here we show that Plzf directly represses the transcription of kit, a hallmark of spermatogonial differentiation. Plzf represses both endogenous kit expression and expression of a reporter gene under the control of the kit promoter region. A discrete sequence of the kit promoter, required for Plzf-mediated kit transcriptional repression, is bound by Plzf both in vivo and in vitro. A 3-bp mutation in this Plzf binding site abolishes the responsiveness of the kit promoter to Plzf repression. A significant increase in kit expression is also found in the undifferentiated spermatogonia isolated from Plzf(-/-) mice. Thus, we suggest that one mechanism by which Plzf maintains the pool of spermatogonial stem cells is through a direct repression of kit expression.

Flow cytometric detection of tandem repeat mutations induced by various chemical classes

To facilitate detection of genotoxicity from environmental mutagen exposure, we generated an in vitro enhanced green fluorescence protein (EGFP) reactivation assay that quickly and effectively detects frameshift mutations in tandem repeat sequences (TRS). Two murine cell lines, C3H10T1/2 and mismatch repair deficient MC2a, were stably transfected with EGFP reporter plasmids in which the EGFP constructs contain TRS that put the EGFP sequence out of frame. These included several 2, 3, 4, 5 and 6 bp repeat sequences, a control non-repetitive sequence and a human gene sequence containing a 4 bp repeat motif. Transfected cultures were exposed to five model mutagens and carcinogens: hydrogen peroxide (H(2)O(2)), 12-O-tetradecanoyl-phorbol-13-acetate (TPA), benzo-a-pyrene-diol-epoxide (BPDE), ethyl nitrosourea (ENU), 9-aminoacridine (9AA) and two controls: acetone and ethanol. Frameshift mutations resulted in green fluorescent revertants, as determined by flow cytometry, and were confirmed, for 9AA treatments, by sequencing. All five treatments with model agents induced statistically significant sequence- and exposure-dependent responses in MC2a cells and a negative response with the two negative control treatments, acetone and ethanol. Similar responses were seen in a smaller panel of treatments and plasmids in C3H10T1/2 cells. The mutation frequencies were higher in cells transfected with the plasmids containing TRS than those harbouring the control construct lacking repeats. The highest mutation frequencies were observed with H(2)O(2) and 9AA treatments, yielding up to a 50-fold difference between vehicle and highest concentration treatment. ENU, BPDE, and to a lesser extent TPA treatments, also showed a statistically significant exposure response. Results from these experiments reveal that the assay responds robustly to various classes of mutagenic substances, as well as to rodent carcinogens that are inactive in conventional mutation assays, and that responses are not linked to cytotoxicity. This assay is a promising approach for detecting chemically induced frameshifts within certain DNA sequences of interest, but further characterization and validation are required prior to general use in genotoxicity screening.

Transfection of CCE Mouse Embryonic Stem Cells with EGFP and BDNF Genes by the Electroporation Method

Embryonic stem (ES) cells are pluripotent cells that can differentiate into a wide variety of cell types. This has made them an attractive source of donor cells for developmental studies and cell therapy. Blocking the differentiation of ES cells in culture and using them in clinical applications requires genetic manipulation of the cells. The aim of the present study was to transfect CCE ES cells with EGFP and BDNF genes, in which pcDNA3-hBDNF-v5 and pIRES2-EGFP plasmids were used, respectively. Transformation of DH5alpha competent bacteria by the plasmids was done. Then the plasmids were purified and transfected into ES cells using the electroporation method. The expression of the EGFP gene was confirmed using invert fluorescent microscopy; accordingly, RT-PCR was used for the BDNF gene. The latter was evaluated by extracting the total RNA from the transfected cells. cDNA was obtained by using reverse transcriptase and was amplified by specific primers. The products of the PCR were separated and visualized by agarose gel electrophoresis. Both techniques revealed a successful transfection of CCE ES cells by both plasmids. The obtained data indicated that electroporation is an efficient method for transfection of CCE ES cells.

Gene delivery to embryonic stem cells

Since the establishment of embryonic stem (ES) cells and the identification of tissue-specific stem cells, researchers have made great strides in the analysis of the natural biology of such stem cells for the development of therapeutic applications. Specifically, ES cells are capable of differentiating into all of the cell types that constitute the whole body. Thus, ES cell research promises new type of treatments and possible cures for a variety of debilitating diseases and injuries. The potential medical benefits obtained from stem cell technology are compelling and stem cell research sees a bright future. Control of the growth and differentiation of stem cells is a critical tool in the fields of regenerative medicine, tissue engineering, drug discovery, and toxicity testing. Toward such a goal, we present here an overview of gene delivery in ES cells, covering the following topics: significance of gene delivery in ES cells, stable versus transient gene delivery, cytotoxicity, suspension versus adherent cells, expertise, time, cost, viral vectors for gene transduction (lentiviruses, adenoviruses, and adeno-associated viruses, chemical methods for gene delivery, and mechanical or physical gene delivery methods (electroporation, nucleofection, microinjection, and nuclear transfer).

Efficient transfection of embryonic and adult stem cells

The ability of embryonic stem cells and adult stem cells to differentiate into specific cell types holds immense potential for therapeutic use in cell and gene therapy. Realization of this potential depends on efficient and optimized protocols for genetic manipulation of stem cells. In the study reported here, we demonstrate the use of nucleofection as a method to introduce plasmid DNA into embryonic and adult stem cells with significantly greater efficiency than electroporation or lipid-based transfection methods have. Using enhanced green fluorescent protein (eGFP) as a reporter gene, mouse embryonic stem cells were transfected both transiently and stably at a rate nearly 10-fold higher than conventional methods. The transfected cells retained their stem cell properties, including continued expression of the stem cell markers SSEA1, Oct4, and Rex1; formation of embryoid bodies; differentiation into cardiomyocytes in the presence of appropriate inducers; and, when injected into developing blastocysts, contribution to chimeras. Higher levels of transfection were also obtained with human embryonic carcinoma and human embryonic stem cells. Particularly hard-to-transfect adult stem cells, including bone marrow and multipotent adult progenitor cells, were also transfected efficiently by the method of nucleofection. Based on our results, we conclude that nucleofection is superior to currently available methods for introducing plasmid DNA into a variety of embryonic and adult stem cells. The high levels of transfection achieved by nucleofection will enable its use as a rapid screening tool to evaluate the effect of ectopically expressed transcription factors on tissue-specific differentiation of stem cells.

Stem cells may reshape the prospect of Parkinson's disease therapy

The concept of cell replacement to compensate for cell loss and restore functionality has entered several disease entities including neurodegenerative disorders. Recent clinical studies have shown that transplantation of fetal dopaminergic (DA) cells into the brain of Parkinson's disease (PD) patients can reduce disease-associated motor deficits. However, the use of fetal tissue is associated with practical and ethical problems including low efficiency, variability in the clinical outcome and controversy regarding the use of fetuses as donor. An alternative cell resource could be embryonic stem (ES) cells, which can be cultivated in unlimited amounts and which have the potential to differentiate into mature DA cells. Several differentiation protocols have been developed, and some progress has been made in understanding the mechanisms underlying DA specification in ES cell development, but the "holy grail" in this paradigm, which is the production of sufficient amounts of the "right" therapeutic DA cell, has not yet been accomplished. To achieve this goal, several criteria on the transplanted DA cells need to be fulfilled, mainly addressing cell survival, accurate integration in the brain circuitry, normal function, no tumor formation, and no immunogenicity. Here, we summarize the current state of ES cell-derived DA neurogenesis and discuss the aspects involved in generating an optimal cell source for cell replacement in PD.

Human Embryonal Carcinoma Stem Cells Expressing Green Fluorescent Protein Form Functioning Neurons In Vitro: A Research Tool for Co-culture Studies

Neural differentiation is controlled by complex molecular mechanisms that determine cell fate and diversity within the nervous system. Interactions between developing tissues play an important role in regulating this process. In vitro co-culture experiments offer a method to study cell differentiation and function under controlled conditions, with the additional benefit of investigating how interactions between populations of cells influence cell growth and behavior. However, it can often be difficult to distinguish between populations of co-cultured cells. Here we report the development of a human embryonal carcinoma (EC) stem cell line (named TERA2.cl.SP12-GFP) that expresses the genetic marker, green fluorescent protein (GFP). Here, we demonstrate that TERA2.cl.SP12-GFP stem cells stably express GFP and that this remains detectable during retinoic acid-induced differentiation. Regulated expression of neural markers during cell development correlated with the formation of morphologically identifiable neurons. Populations of post-mitotic GFP-positive neurons were readily purified and electrophysiological characterization confirmed that such neurons were functionally active. Thus, cultured TERA2.cl.SP12-GFP cells can be readily distinguished from alternative cell types in vitro and provide an amenable system for live cell imaging to study the development and function of human neurons in isolation, and in co-culture with other tissue types.

Electroporation of cynomolgus monkey embryonic stem cells

Efficient genetic modification of primate embryonic stem (ES) cells is essential for the application for both basic and preclinical research. The transfection efficiency of primate ES cells is reportedly lower than that of mouse ES cells. Cynomolgus monkey ES cells provide a powerful model for understanding human development and disease. We evaluated electroporation as a method to introduce foreign genes into cynomolgus monkey ES cells. Our examination has allowed us to establish a protocol producing about 100 stably transfected clones from 10(7) cynomolgus monkey ES cells. Differences in efficiency, however, were observed for other ES cell lines. We compared the transcriptional activities of the PGK-1, CMV, and SV40 promoters in cynomolgus monkey ES cells generating efficient G418 selection. Although the PGK-1 and SV40 promoters efficiently drove neo gene expression, the CMV promoter was significantly less transcriptionally active in cynomolgus monkey ES cells. Using this electroporation method, we established fluorescent cynomolgus monkey ES cell lines. These cells may be useful tools for tracing grafted cells in transplantation studies using a variety of functional cells derived from cynomolgus monkey ES cells.

The 5T4 oncofoetal antigen is an early differentiation marker of mouse ES cells and its absence is a useful means to assess pluripotency

5T4 oncotrophoblast antigen is a transmembrane glycoprotein expressed by trophoblast and many carcinomas but not most normal adult tissues. Results from overexpression of human and mouse 5T4 cDNA in cell lines are consistent with it having an influence on adhesion, shape and motility. We show that murine embryonic stem cell lines are 5T4 negative but that there is rapid up regulation of protein and transcripts upon differentiation, including derivatives of each primary germ layer, as evidenced by cell surface FACS, western and RT-PCR analyses. The kinetics of differentiation and 5T4 expression are closely correlated, with early events linking 5T4 expression to changes in motility and morphology. Comparison of 5T4 expression with other ES cell transcript (Oct 3/4; Rex-1) and antigen markers (Forsmann, SSEA-1) establishes 5T4 as a useful marker for the non-destructive detection of early differentiation of ES cells. For example, `undifferentiated' ES phenotype defined as SSEA-1 positive and 5T4 negative is seven times more efficient at chimera formation than SSEA-1-positive/5T4-positive cells. Thus, 5T4 glycoprotein expression is associated with early differentiative events of ES cells involving altered motility, and it has useful practical consequences for assessing ES potency and studying similar processes in development and metastasis.

Stable Expression of hrGFP by Mouse Embryonic Stem Cells: Promoter Activity in the Undifferentiated State and During Dopaminergic Neural Differentiation

Three promoters, cellular polypeptide chain elongation factor 1 alpha (EF1), cytomegalovirus (CMV), and Rous sarcoma virus (RSV) were examined for stable transgene expression in mouse embryonic stem (ES) cells and their progeny during dopaminergic neural differentiation. In undifferentiated ES cells the EF1 promoter was highly effective, while CMV had moderate activity. After 3 months in culture, expression of humanized renilla green fluorescent protein (hrGFP) was unchanged for the EF1 promoter and decreased for CMV. At the nestin-positive stage of differentiation, hrGFP and nestin were colocalized in about 20% of cells for EF1, in contrast to 80% of cells for the CMV promoter. In tyrosine hydroxylase (TH)-positive neurons neither the EF1 nor CMV promoter were effective. The RSV promoter was inactive in undifferentiated, nestin-positive, and TH-positive cells. Thus, EF1 and CMV are effective promoters for transgene expression in undifferentiated ES cells and nestin-positive neural precursors.

Engineered Zinc Finger Proteins for Controlling Stem Cell Fate

Stem cells are functionally defined as progenitor cells that can self-renew and differentiate. Critical transitions in these cells are controlled via signaling pathways and subsequent transcriptional regulation. Technologies capable of modulating the levels of gene expression, especially those of transcription factors, represent powerful tools for research and could potentially be used in therapeutic applications. In this study, we evaluated the ability of synthetic zinc finger protein transcription factors (ZFP-TFs) to cause the differentiation of embryonic stem (ES) cells. We constructed ZFP-TFs that target the mouse Oct-4 gene (which is a major regulator of ES cell pluripotency and self-renewal). These designed transcription factors were able to regulate the transcription of Oct-4, affecting the expression of downstream genes and thus regulating ES cell differentiation.