Efficient gene transfer into murine embryonic stem cells by nucleofection

Genetic manipulation of embryonic stem (ES) cells is performed by non-viral as well as viral transfection methods. We tested the recently developed nucleofection method delivering plasmid DNA directly into the nucleus for the introduction of a plasmid encoding enhanced green fluorescent protein (EGFP) into murine ES cells. Cell viability decreased from 77% before to 40% 24 h after nucleofection. Transfection effciencies in viable stem cells were between 85% and 96% with high levels of EGFP expression [mean fluorescence intensity (MFI): 630 +/- 90] 24 h after nucleofection. After a two week culture in geneticin (G418) selection medium, nearly 50% of the stem cells were EGFP positive and continued transgene expression (MFIs: 120-240) for a two further weeks. We conclude that nucleofection is an efficient nonviral gene transfer method for the introduction of genes into murine ES cells.     

Derivation of hematopoietic stem cells from murine embryonic stem cells

A stem cell is defined as a cell with the capacity to both self-renew and generate multiple differentiated progeny. Embryonic stem cells (ESC) are derived from the blastocyst of the early embryo and are pluripotent in differentiative ability. Their vast differentiative potential has made them the focus of much research centered on deducing how to coax them to generate clinically useful cell types. The successful derivation of hematopoietic stem cells (HSC) from mouse ESC has recently been accomplished and can be visualized in this video protocol. HSC, arguably the most clinically exploited cell population, are used to treat a myriad of hematopoietic malignancies and disorders. However, many patients that might benefit from HSC therapy lack access to suitable donors. ESC could provide an alternative source of HSC for these patients. The following protocol establishes a baseline from which ESC-HSC can be studied and inform efforts to isolate HSC from human ESC. In this protocol, ESC are differentiated as embryoid bodies (EBs) for 6 days in commercially available serum pre-screened for optimal hematopoietic differentiation. EBs are then dissociated and infected with retroviral HoxB4. Infected EB-derived cells are plated on OP9 stroma, a bone marrow stromal cell line derived from the calvaria of M-CSF-/- mice, and co-cultured in the presence of hematopoiesis promoting cytokines for ten days. During this co-culture, the infected cells expand greatly, resulting in the generation a heterogeneous pool of 100 s of millions of cells. These cells can then be used to rescue and reconstitute lethally irradiated mice.     

Genetic manipulation of murine embryonic stem cells with enhanced green fluorescence protein and sulfatase-modifying factor I genes

Background aimsMucopolysaccharidosis type IIIA (MPS IIIA) is a lysosomal storage disorder (LSD) in which an absence of sulfamidase results in incomplete degradation and subsequent accumulation of its substrate, heparan sulfate. Most neurodegenerative LSD remain untreatable. However, therapy options, such as gene, enzyme end cell therapy, are under investigation. Previously, we have constructed an embryonic stem (ES) cell line (NS21) that over-expresses human sulphamidase as a potential treatment for murine MPS IIIA.MethodsIn the present study the sulfatase-modifying factor I (SUMF1) and enhanced green fluorescence protein (eGFP) genes were co-introduced under a cytomegalovirus (CMV) promoter into NS21 cells, to enhance further sulfamidase activity and provide a marker for in vivo cell tracking, respectively. eGFP was also introduced under the control of the human elongation factor-1α (hEF-1α) promoter to compare the stability of transgene expression.ResultsDuring differentiation of ES cells into glial precursors, SUMF1 was down-regulated and was hardly detectable by day 18 of differentiation. Likewise, eGFP expression was heterogeneous and highly unstable. Use of a human EF-1α promoter resulted in more homogeneous eGFP expression, with ～ 50% of cells eGFP positive following differentiation into glial precursors. Compared with NS21 cells, the outgrowth of eGFP-expressing cells was not as confluent when differentiated into glial precursors.ConclusionsOur data suggest that SUMF1 enhances sulfamidase activity in ES cells, hEF-1α is a stronger promoter than CMV for ES cells and over-expression of eGFP may affect cell growth and contribute to unstable gene expression.     

Cloned murine fetuses produced by nuclear transfer using metaphase-arrested embryonic stem cells

We examined whether metaphase nuclei could be used as nuclear donors in nuclear transfer in mice. The reconstructed embryos were developed to fetuses in both the metaphase-nuclear transfer and the G1-nuclear transfer. We also performed enucleation of oocytes following nuclear injection (injection-enucleation method) using microinjection method with a piezo-driven micromanipulator in order to produce the cloned murine fetuses. We found that this method could shorten time for manipulation in comparison with the conventional method performing nuclear injection following enucleation of oocytes (enucleation-injection method). We produced successfully cloned fetuses by the injection-enucleation method. Furthermore, there was no difference of developmental efficiency in reconstructed embryos from between B6D2F1 and ddY strain as oocyte donor.     

Quantitative analysis of retroviral and lentiviral gene transfer to murine embryonic stem cells

The effectiveness of retrovirus or lentivirus transduction of embryonic stem (ES) cells is often limited because transgene expression is silenced or variegated. We wondered if other steps of transduction, in addition to gene expression, were restricted in ES cells. We quantitatively compared (1) the amount of virus binding, (2) the number of integrated transgenes, and (3) the resulting level of gene expression. We found that three- to fourfold fewer retroviruses and lentiviruses bound to R1 mES cells than to NIH 3T3 cells, suggesting that both types of viruses bind less efficiently to mES cells. Retroviruses and lentiviruses differed in the efficiency with which they completed post-binding steps of transduction. In R1 mES cells, we detected 3-fold fewer integrated retrovirus transgenes and 11-fold lower expression levels than in NIH 3T3 cells, which suggests that the primary limitation to retrovirus transduction may be low levels of transgene expression. In contrast, we detected 10-fold fewer integrated lentivirus transgenes and 8-fold lower expression levels in R1 mES cells than in NIH 3T3 cells, which suggests that lentivirus transduction may be limited by inefficient intracellular post-binding steps of transduction. The implications of our findings for developing improved viral vectors for transducing mES cells are discussed.     

Compactin enhances osteogenesis in murine embryonic stem cells

Embryonic stem (ES) cells have the capacity to differentiate into various cell types in vitro. In this study, we show that retinoic acid is important for the commitment of ES cells into osteoblasts. Culturing retinoic acid treated ES cells in the presence of the osteogenic supplements ascorbic acid and beta-glycerophosphate resulted in the expression of several osteoblast marker genes, osteocalcin, alkaline phosphatase, and osteopontin. However, there was only a slight amount of mineralized matrix secretion. Addition of bone morphogenic protein-2 or compactin, a drug of the statin family of HMG-CoA reductase inhibitors, resulted in a greatly enhanced formation of bone nodules. Compactin did not modify the expression of osteogenic markers, but at the late stage of differentiation promoted an increase in BMP-2 expression. These results establish ES-cell derived osteogenesis as an effective model system to study the molecular mechanisms by which the statin compactin promotes osteoblastic differentiation and bone nodule formation.     

Reconstituted skin from murine embryonic stem cells

Embryonic stem (ES) cell lines can be expanded indefinitely in culture while maintaining their potential to differentiate into any cell type. During embryonic development, the skin forms as a result of reciprocal interactions between mesoderm and ectoderm. Here, we report the in vitro differentiation and enrichment of keratinocytes from murine ES cells seeded on extracellular matrix (ECM) in the presence of Bone Morphogenic Protein-4 (BMP-4) or ascorbate. The enriched preparation of keratinocytes was able to form an epidermal equivalent composed of a stratified epithelium when cultured at the air-liquid interface on a collagen-coated acellular substratum. Interestingly, an underlying cellular compartment that belongs to the fibroblast lineage was systematically formed between the reconstituted epidermis and the inert membrane. The resulting tissue displayed morphological patterns similar to normal embryonic skin, as evidenced by light and transmission electron microscopy. Immunohistochemical studies revealed expression patterns of cytokeratins, basement membrane (BM) proteins and late differentiation markers of epidermis, as well as fibroblast markers, similar to native skin. The results demonstrate the capacity of ES cells to reconstitute in vitro a fully differentiated skin. This ES-derived bioengineered skin provides a powerful tool for studying the molecular mechanisms controlling epidermal and dermal commitments.     

L-alpha-glycerylphosphorylcholine inhibits the transfer function of phosphatidylinositol transfer protein alpha

Phosphatidylinositol transfer protein alpha (PITP-alpha) is a bifunctional phospholipid transfer protein that is highly selective for phosphatidylinositol (PtdIns) and phosphatidylcholine (PtdCho). Polar lipid metabolites, including L-alpha-glycerylphosphorylcholine (GroPCho), increasingly have been linked to changes in cellular function and to disease. In this study, polar lipid metabolites of PtdIns and PtdCho were tested for their ability to influence PITP-alpha activity. GroPCho inhibited the ability of PITP-alpha to transfer PtdIns or PtdCho between liposomes. The IC(50) of both processes was dependent on membrane composition. D-myo-inositol 1-phosphate and glycerylphosphorylinositol modestly enhanced PITP-alpha-mediated phospholipid transfer. Choline, phosphorylcholine (PCho), CDP-choline, glyceryl-3-phosphate, myo-inositol and D-myo-inositol 1,4,5-trisphosphate had little effect. Membrane surface charge was a strong determinant of the GroPCho inhibition with the inhibition being greatest for highly anionic membranes. GroPCho was shown to enhance the binding of PITP-alpha to anionic vesicles. In membranes of low surface charge, phosphatidylethanolamine (PtdEtn) was a determinant enabling the GroPCho inhibition. Anionic charge and PtdEtn content appeared to increase the strength of PITP-alpha-membrane interactions. The GroPCho-enhanced PITP-alpha-membrane binding was sufficient to cause inhibition, but not sufficient to account for the extent of inhibition observed. Processes associated with strengthened PITP-alpha-membrane binding in the presence of GroPCho appeared to impair the phospholipid insertion/extraction process.     

DNA repair in murine embryonic stem cells and differentiated cells

Embryonic stem (ES) cells are rapidly proliferating, self-renewing cells that have the capacity to differentiate into all three germ layers to form the embryo proper. Since these cells are critical for embryo formation, they must have robust prophylactic mechanisms to ensure that their genomic integrity is preserved. Indeed, several studies have suggested that ES cells are hypersensitive to DNA damaging agents and readily undergo apoptosis to eliminate damaged cells from the population. Other evidence suggests that DNA damage can cause premature differentiation in these cells. Several laboratories have also begun to investigate the role of DNA repair in the maintenance of ES cell genomic integrity. It does appear that ES cells differ in their capacity to repair damaged DNA compared to differentiated cells. This minireview focuses on repair mechanisms ES cells may use to help preserve genomic integrity and compares available data regarding these mechanisms with those utilized by differentiated cells.     

Neural differentiation of murine embryonic stem cells ES

Pluripotent murine embryonic stem (ES) cells can differentiate into all cell types both in vivo and in vitro. Based on their capability to proliferate and differentiate, these ES cells appear as a very promising tool for cell therapy. The understanding of the molecular mechanisms underlying the neural differentiation of the ES cells is a pre-requisite for selecting adequately the cells and conditions which will be able to correctly repair damaged brain and restore altered cognitive functions. Different methods allow obtaining neural cells from ES cells. Most of the techniques differentiate ES cells by treating embryoid bodies in order to keep an embryonic organization. More recent techniques, based on conditioned media, induce a direct differentiation of ES cells into neural cells, without going through the step of embryonic bodies. Beyond the fact that these techniques allow obtaining large numbers of neural precursors and more differentiated neural cells, these approaches also provide valuable information on the process of differentiation of ES cells into neural cells. Indeed, sequential studies of this process of differentiation have revealed that globally ES cells differentiating into neural cells in vitro recapitulate the molecular events governing the in vivo differentiation of neural cells. Altogether these data suggest that murine ES cells remain a highly valuable tool to obtain large amounts of precursor and differentiated neural cells as well as to get a better understanding of the mechanisms of neural differentiation, prior to a potential move towards the use of human ES cells in therapy.     

Hepatic differentiation of murine embryonic stem cells.

Murine embryonic stem (ES) cells can replicate indefinitely in culture and can give rise to all tissues, including the germline, when reimplanted into a murine blastocyst. ES cells can also be differentiated in vitro into a wide range of cell types. We have utilized a liver-specific marker to demonstrate that murine ES cells can differentiate into hepatocytes in vitro. We have used ES cells carrying a gene trap vector insertion (I.114) into an ankyrin repeat-containing gene (Gtar) that we have previously shown provides an exclusive beta-galactosidase marker for the early differentiation of hepatocytes in vivo. beta-Galactosidase-positive cells were differentiated from I.114 ES cells in vitro. The identity of these cells was confirmed by the expression of the proteins alpha-fetoprotein, albumin, and transferrin and by the fact that they have an ultrastructural appearance consistent with that of embryonic hepatocytes. We propose that this model system of hepatic differentiation in vitro could be used to define factors that are involved in specification of the hepatocyte lineage. In addition, human ES cells have recently been derived and it has been proposed that they may provide a source of differentiated cell types for cell replacement therapies in the treatment of a variety of diseases.     

AFM对小鼠胚胎干细胞的形态学研究

目的：对已建系BALB/c小鼠胚胎干细胞膜表面进行纳米级超微结构的初步形态学研究,从而为从分子水平研究胚胎干细胞的增殖与分化调控机理奠定基础。方法：利用原子力显微镜（AFM）,在空气中对小鼠胚胎干细胞膜表面扫描成像。结果：AFM图像表现BALB/c小鼠胚胎干细胞呈圆盘状,直径约10-15μm,高约2-4μm,胚胎干细胞膜表面比较复杂,随着扫描范围的减小,切向分辨率逐渐增大,可达到纳米分辨,细胞表面有许多紧密堆积的椭球状颗粒。颗粒尺寸（x-y方向）为40-80nm。结果：利用AFM可以得到胚胎干细胞表面高分辨的,可重复的图像。     

Signaling pathways regulating proliferation of murine embryonic stem cells

Murine embryonic stem cells (mESC) are capable of unlimiting proliferation with maintenance of pluripotency during long-term cultivation. Signaling pathways regulating the cell cycle of mESC are of the great interest for further investigation. This review concerns to the cell cycle regulation of mESC through different signaling pathways (LIF-STAT3, PI3K-Akt, Wnt-beta-catenin) and to the mechanisms of unlimited proliferation of mESC and their inability to undergo long-term block of proliferation in response to DNA-damaging and stress factors. The functioning of negative cell cycle regulators (cyclin-kinase inhibitors and Rb) and positive cell cycle regulators (cyclin-kinase complexes and E2F factors) are also topics of this review. It is considered that, permanent mitogenic stimuli are needed to prevent induction of apoptosis. Therefore, the agents which cause prolonged halt of proliferation without ongoing onset of differentiation or induction of apoptosis are currently unknown. The main focus is given to the role of the Wnt signaling pathway in sustaining the pluripotent state of mESC. The cell cycle regulation by downstream targets of LIF-STAT3, PI3-kinase and Wnt-beta-catenin pathways is discussed in light of cooperative action of these pathways for maintenance of undifferentiated state of mESC.     

Improved lentiviral gene transfer into human embryonic stem cells grown in co-culture with murine feeder and stroma cells

Genetic modification of human embryonic stem cells (hESCs) using biophysical DNA transfection methods are hampered by the very low single cell survival rate and cloning efficiency of hESCs. Lentiviral gene transfer strategies are widely used to genetically modify hESCs but limited transduction efficiencies in the presence of feeder or stroma cells present problems, particularly if vesicular stomatitis virus glycoprotein (VSV-G) pseudotyped viral particles are applied. Here, we investigated whether the recently described semen derived enhancer of virus infection (SEVI) and alternative viral envelope proteins derived from either Gibbon ape leukaemia virus (GALV) or feline leukaemia virus (RD114) are applicable for transducing hESCs during co-culture with feeder or stroma cells. Our first set of experiments demonstrates that SEVI has no toxic effect on murine or hESCs and that exposure to SEVI does not interfere with the pluripotency-associated phenotype. Focusing on hESCs, we were able to further demonstrate that SEVI increases the transduction efficiencies of GALV and RD114 pseudotyped lentiviral vectors. More importantly, aiming at targeted differentiation of hESCs into functional somatic cell types, GALV pseudotyped lentiviral particles could efficiently and exclusively transduce hESCs grown in co-culture with OP9-GFP stroma cells (which were often used to induce differentiation into haematopoietic derivatives).     

In vitro differentiation of murine embryonic stem cells into keratinocyte-like cells

Embryonic stem (ES) cells are omnipotent; they can differentiate into every cell type of the body. The development of culture conditions that allow their differentiation has made it conceivable to produce large numbers of cells with lineage-specific characteristics in vitro. Here, we describe a method by which murine ES cells can be differentiated into cells with characteristics of epidermal keratinocytes. Keratinocyte-like cells were isolated from embryoid bodies and grown in culture. Potential applications of this method are the in vitro differentiation of cells of interest from ES cells of mice with lethal phenotypes during embryonic development and the production of genetically modified epidermal keratinocytes that could be used as temporary wound dressing or as carriers of genes of interest in gene therapeutic treatments.     

DAZL regulates Tet1 translation in murine embryonic stem cells

Embryonic stem cell (ESC) cultures display a heterogeneous gene expression profile, ranging from a pristine naïve pluripotent state to a primed epiblast state. Addition of inhibitors of GSK3β and MEK (so‐called 2i conditions) pushes ESC cultures toward a more homogeneous naïve pluripotent state, but the molecular underpinnings of this naïve transition are not completely understood. Here, we demonstrate that DAZL, an RNA‐binding protein known to play a key role in germ‐cell development, marks a subpopulation of ESCs that is actively transitioning toward naïve pluripotency. Moreover, DAZL plays an essential role in the active reprogramming of cytosine methylation. We demonstrate that DAZL associates with mRNA of Tet1, a catalyst of 5‐hydroxylation of methyl‐cytosine, and enhances Tet1 mRNA translation. Overexpression of DAZL in heterogeneous ESC cultures results in elevated TET1 protein levels as well as increased global hydroxymethylation. Conversely, null mutation of Dazl severely stunts 2i‐mediated TET1 induction and hydroxymethylation. Our results provide insight into the regulation of the acquisition of naïve pluripotency and demonstrate that DAZL enhances TET1‐mediated cytosine hydroxymethylation in ESCs that are actively reprogramming to a pluripotent ground state.     

In vitro generation of germ cells from murine embryonic stem cells

The demonstration of germ cell and haploid gamete development from embryonic stem cells (ESCs) in vitro has engendered a unique set of possibilities for the study of germ cell development and the associated epigenetic phenomenon. The process of embryoid body (EB) differentiation, like teratoma formation, signifies a spontaneous differentiation of ESCs into cells of all three germ layers, and it is from these differentiating aggregates of cells that putative primordial germ cells (PGCs) and more mature gametes can be identified and isolated. The differentiation system presented here requires the differentiation of murine ESCs into EBs and the subsequent isolation of PGCs as well as haploid male gametes from EBs at various stages of differentiation. It serves as a platform for studying the poorly understood process of germ cell allocation, imprint erasure and gamete formation, with 4-6 weeks being required to isolate PGCs as well as haploid cells.