Pluripotent differentiation in vitro of murine ES-D3 embryonic stem cells

Fut9 Deficiency Causes Abnormal Neural Development in the Mouse Cerebral Cortex and Retina

α1,3-Fucosyltransferase 9 (Fut9) is responsible for the synthesis of Lewis X [Le^X, Galβ1-4(Fucα1-3)GlcNAc] carbohydrate epitope, a marker for pluripotent or multipotent tissue-specific stem cells. Although Fut9-deficient mice show anxiety-related behaviors, structural and cellular abnormalities in the brain remain to be investigated. In this study, using in situ hybridization and immunohistochemical techniques in combination, we clarified the spatiotemporal expression of Fut9, together with Le^X, in the brain and retina. We found that Fut9-expressing cells are positive for Ctip2, a marker of neurons residing in layer V/VI, and TLE4, a marker of corticothalamic projection neurons (CThPNs) in layer VI, of the cortex. A birthdating analysis using 5-ethynyl-2'-deoxyuridine at embryonic day (E)11.5, 5-bromo-2'-deoxyuridine at E12.5, and in utero electroporation of a GFP expression plasmid at E14.5 revealed a reduction in the percentage of neurons produced at E11.5 in layer VI/subplate of the cortex and in the ganglion cell layer of the retina in P0 Fut9^-/- mice. Furthermore, this reduction in layer VI/subplate neurons persisted into adulthood, leading to a reduction in the number of Ctip2^strong/Satb2^- excitatory neurons in layer V/VI of the adult Fut9^-/- cortex. These results suggest that Fut9 plays significant roles in the differentiation, migration, and maturation of neural precursor cells in the cortex and retina.

Changes in the phosphorylation of nucleotide metabolism‑associated proteins by leukemia inhibitory factor in mouse embryonic stem cells

Leukemia inhibitory factor (LIF) is a stem cell growth factor that maintains self‑renewal of mouse embryonic stem cells (mESCs). LIF is a cytokine in the interleukin‑6 family and signals via the common receptor subunit gp130 and ligand‑specific LIF receptor. LIF causes heterodimerization of the LIF receptor and gp130, activating the Janus kinase/STAT and MAPK pathways, resulting in changes in protein phosphorylation. The present study profiled LIF‑mediated protein phosphorylation changes in mESCs via proteomic analysis. mESCs treated in the presence or absence of LIF were analyzed via two‑dimensional differential in‑gel electrophoresis and protein and phosphoprotein staining. Protein identification was performed by matrix‑assisted laser desorption/ionization‑time of flight mass spectrophotometry. Increased phosphorylation of 16 proteins and decreased phosphorylation of 34 proteins in response to LIF treatment was detected. Gene Ontology terms enriched in these proteins included 'organonitrogen compound metabolic process', 'regulation of mRNA splicing via spliceosome' and 'nucleotide metabolic process'. The present results revealed that LIF modulated phosphorylation levels of nucleotide metabolism‑associated proteins, thus providing insight into the mechanism underlying LIF action in mESCs.

Tumorigenesis of nuclear transfer-derived embryonic stem cells is reduced through differentiation and enrichment following transplantation in the infarcted rat heart

The aim of the present study was to evaluate the tumorigenic potential of nuclear transfer-derived (nt) mouse embryonic stem cells (mESCs) transplanted into infarcted rat hearts. The nt‑mESCs were cultured using a bioreactor system to develop embryoid bodies, which were induced with 1% ascorbic acid to differentiate into cardiomyocytes. The nt‑mESC‑derived cardiomyocytes (nt‑mESCs‑CMs) were enriched using Percoll density gradient separation to generate nt‑mESCs‑percoll‑enriched (PE)‑CMs. Ischemia was induced by ligating the left anterior descending coronary artery in female Sprague‑Dawley rats. Immunosuppressed rats (daily intraperitoneal injections of cyclosporine A and methylprednisolone) were randomly assigned to receive an injection containing 5x106 mESCs, nt‑mESCs, nt‑mESC‑CMs or nt‑mESC‑PE‑CMs. Analysis performed 8 weeks following transplantation revealed teratoma formation in 80, 86.67 and 33.33% of the rats administered with the mESCs, nt‑mESCs and nt‑mESC‑CMs, respectively, indicating no significant difference between the mESCs and nt‑mESCs; but significance (P<0.05) between the nt‑mESC‑CMs and nt‑mESCs. The mean tumor volumes were 82.72±6.52, 83.17±3.58 and 50.40±5.98 mm3, respectively (P>0.05 mESCs, vs. nt‑mESCs; P<0.05 nt‑mESC‑CMs, vs. nt‑mESCs). By contrast, no teratoma formation was detected in the rats, which received nt‑mESC‑PE‑CMs. Octamer‑binding transcription factor‑4, a specific marker of undifferentiated mESCs, was detected using polymerase chain reaction in the rats, which received nt‑mESCs and nt‑mESC‑CMs, but not in rats administered with nt‑mESC‑PE‑CMs. In conclusion, nt‑mESCs exhibited the same pluripotency as mESCs, and teratoma formation following nt‑mESC transplantation was reduced by cell differentiation and enrichment.

The Lewis X-related α1,3-fucosyltransferase, Fut10, is required for the maintenance of stem cell populations

Lewis X (Le(X), Galβ1-4(Fucα1-3)GlcNAc) is a carbohydrate epitope that is present at the nonreducing terminus of sugar chains of glycoproteins and glycolipids, and is abundantly expressed in several stem cell populations. Le(X) antigen can be used in conjunction with fluorescence-activated cell sorting to isolate neurosphere-forming neural stem cells (NSCs) from embryonic mouse brains. However, its function in the maintenance and differentiation of stem cells remains largely unknown. In this study, we examined mice deficient for fucosyltransferase 9 (Fut9), which is thought to synthesize most, if not all, of the Le(X) moieties in the brain. We found that the number of NSCs was increased in the brain of Fut9(-/-) embryos, suggesting that Fut9-synthesized Le(X) is dispensable for the maintenance of NSCs. Another α1,3-fucosyltransferase gene, fucosyltransferase 10 (Fut10), is expressed in the ventricular zone of the embryonic brain. Overexpression of Fut10 enhanced the self-renewal of NSCs. Conversely, suppression of Fut10 expression induced the differentiation of NSCs and embryonic stem cells. In addition, knockdown of Fut10 expression in the cortical ventricular zone of the embryonic brain by in utero electroporation of Fut10-miRNAs impaired the radial migration of neural precursor cells. Our data suggest that Fut10 is involved in a unique α1,3-fucosyltransferase activity with stringent substrate specificity, and that this activity is required to maintain stem cells in an undifferentiated state.

Mouse embryonic stem cells are deficient in type I interferon expression in response to viral infections and double-stranded RNA

Embryonic stem cells (ESCs) are considered to be a promising cell source for regenerative medicine because of their unlimited capacity for self-renewal and differentiation. However, little is known about the innate immunity in ESCs and ESC-derived cells. We investigated the responses of mouse (m)ESCs to three types of live viruses as follows: La Crosse virus, West Nile virus, and Sendai virus. Our results demonstrated mESCs were susceptible to viral infection, but they were unable to express type I interferons (IFNα and IFNβ, IFNα/β), which differ from fibroblasts (10T1/2 cells) that robustly express IFNα/β upon viral infections. The failure of mESCs to express IFNα/β was further demonstrated by treatment with polyIC, a synthetic viral dsRNA analog that strongly induced IFNα/β in 10T1/2 cells. Although polyIC transiently inhibited the transcription of pluripotency markers, the stem cell morphology was not significantly affected. However, polyIC can induce dsRNA-activated protein kinase in mESCs, and this activation resulted in a strong inhibition of cell proliferation. We conclude that the cytosolic receptor dsRNA-activated protein kinase is functional, but the mechanisms that mediate type I IFN expression are deficient in mESCs. This conclusion is further supported by the findings that the major viral RNA receptors are either expressed at very low levels (TLR3 and MDA5) or may not be active (retinoic acid-inducible gene I) in mESCs.

Transient inhibition of cell proliferation does not compromise self-renewal of mouse embryonic stem cells

Embryonic stem cells (ESCs) have unlimited capacity for self-renewal and can differentiate into various cell types when induced. They also have an unusual cell cycle control mechanism driven by constitutively active cyclin dependent kinases (Cdks). In mouse ESCs (mESCs). It is proposed that the rapid cell proliferation could be a necessary part of mechanisms that maintain mESC self-renewal and pluripotency, but this hypothesis is not in line with the finding in human ESCs (hESCs) that the length of the cell cycle is similar to differentiated cells. Therefore, whether rapid cell proliferation is essential for the maintenance of mESC state remains unclear. We provide insight into this uncertainty through chemical intervention of mESC cell cycle. We report here that inhibition of Cdks with olomoucine II can dramatically slow down cell proliferation of mESCs with concurrent down-regulation of cyclin A, B and E, and the activation of the Rb pathway. However, mESCs display can recover upon the removal of olomoucine II and are able to resume normal cell proliferation without losing self-renewal and pluripotency, as demonstrated by the expression of ESC markers, colony formation, embryoid body formation, and induced differentiation. We provide a mechanistic explanation for these observations by demonstrating that Oct4 and Nanog, two major transcription factors that play critical roles in the maintenance of ESC properties, are up-regulated via de novo protein synthesis when the cells are exposed to olomoucine II. Together, our data suggest that short-term inhibition of cell proliferation does not compromise the basic properties of mESCs.

Embryotoxicity assessment of developmental neurotoxicants using a neuronal endpoint in the embryonic stem cell test

The embryonic stem cell test (EST) is a validated in vitro embryotoxicity test; however, as the inhibition of cardiac differentiation alone is used as a differentiation endpoint in the EST, it may not be a useful test to screen embryotoxic chemicals that affect the differentiation of noncardiac tissues. Previously, methylmercury (MeHg), cadmium and arsenic compounds, which are heavy metals that induce developmental neurotoxicity in vivo, were misclassified as nonembryotoxic with the EST. The aim of this study was to improve the EST to correctly screen such developmental neurotoxicants. We developed a neuronal endpoint (Tuj-1 ID₅₀) using flow cytometry analysis of Tuj-1-positive cells to screen developmental neurotoxicants (MeHg, valproic acid, sodium arsenate and sodium arsenite) correctly using an adherent monoculture differentiation method. Using Tuj-1 ID₅₀ in the EST instead of cardiac ID₅₀, all of the tested chemicals were classified as embryotoxic, while the negative controls were correctly classified as nonembryotoxic. To support the validity of Tuj-1 ID₅₀) , we compared the results from two experimenters who independently tested MeHg using our modified EST. An additional neuronal endpoint (MAP2 ID₅₀), obtained by analyzing the relative quantity of MAP2 mRNA, was used to classify the same chemicals. There were no significant differences in the three endpoint values of the two experimenters or in the classification results, except for isoniazid. In conclusion, our results indicate that Tuj-1 ID₅₀ can be used as a surrogate endpoint of the traditional EST to screen developmental neurotoxicants correctly and it can also be applied to other chemicals.

The embryonic stem cell test combined with toxicogenomics as an alternative testing model for the assessment of developmental toxicity

One of the most studied in vitro alternative testing methods for identification of developmental toxicity is the embryonic stem cell test (EST). Although the EST has been formally validated, the applicability domain as well as the predictability of the model needs further study to allow successful implementation of the EST as an alternative testing method in regulatory toxicity testing. Genomics technologies have already provided a proof of principle of their value in identification of toxicants such as carcinogenic compounds. Also within the EST, gene expression profiling has shown its value in the identification of developmental toxicity and in the evaluation of factors critical for risk assessment, such as dose and time responses. It is expected that the implementation of genomics into the EST will provide a more detailed end point evaluation as compared to the classical morphological scoring of differentiation cultures. Therefore, genomics may contribute to improvement of the EST, both in terms of definition of its applicability domain as well as its predictive capacity. In the present review, we present the progress that has been made with regard to the prediction of developmental toxicity using the EST combined with transcriptomics. Furthermore, we discuss the developments of additional aspects required for further optimization of the EST, including kinetics, the use of human embryonic stem cells (ESC) and computational toxicology. Finally, the current and future use of the EST model for prediction of developmental toxicity in testing strategies and in regulatory toxicity evaluations is discussed.

Fibronectin-mediated upregulation of α5β1 integrin and cell adhesion during differentiation of mouse embryonic stem cells

Embryonic stem (ES) cells have a broad potential application in regenerative medicine and can be differentiated into cells of all three germ layers. Adhesion of ES cells to extracellular matrix (ECM) proteins is essential for the differentiation pathway; Cell-ECM adhesion is mediated by integrins that have the ability to activate many intracellular signaling pathways. Therefore, we hypothesize that the expression and function of integrin receptors is a critical step in ES differentiation. Using functional cell adhesion assays, our study demonstrates that α5β1 is a major functional integrin receptor expressed on the cell surface of undifferentiated mouse ES-D3 cells, which showed significantly higher binding to fibronectin as compared to collagens. This adhesion was specific mediated by integrin α5β1 as evident from the inhibition with a disintegrin selective for this particular integrin. Differentiation of ES-D3 cells on fibronectin or on a collagen type1/fibronectin matrix, caused further selective up-regulation of the α5β1 integrin. Differentiation of the cells, as evaluated by immunofluorescence, FACS analysis and quantitative RT-PCR, was accompanied by the upregulation of mesenchymal (Flk1, isolectin B4, α-SMA, vimentin) and endodermal markers (FoxA2, SOX 17, cytokeratin) in parallel to increased expression of α5β1 integrin. Taken together, the data indicate that fibronectin-mediated, upregulation of α5β1 integrin and adhesion of ES-D3 cells to specific ECM molecules are linked to early stages of mouse embryonic stem cells commitment to meso-endodermal differentiation.

Tumourigenesis in the infarcted rat heart is eliminated through differentiation and enrichment of the transplanted embryonic stem cells

AIMS

The therapeutic potential of embryonic stem cells (ESCs) in ischaemic heart disease has been widely explored. However, tumourigenesis upon implantation interferes with the clinical application of ESC transplantation. This study aims to evaluate the influence of differentiation and enrichment of transplanted ESCs on tumourigenesis in infarcted rat hearts.

METHODS AND RESULTS

Mouse ESCs (mESCs) were cultured using a bioreactor system to develop embryoid bodies, which were then induced with 1% ascorbic acid to differentiate into cardiomyocytes. The mESCs-derived cardiomyocytes (mESCs-CMs) were enriched by Percoll density gradient separation. The specific markers (OCT-4, Sox2, and Nanog) of undifferentiated ESCs were detected by PCR both in mESCs and in mESCs-CMs, but not in the mESC-derived Percoll-enriched cardiomyocytes (mESC-PE-CMs). Immunosuppressed rats with infarcted hearts were randomly injected with the mESCs, mESC-CMs, or mESC-PE-CMs. Eight weeks after cell transplantation, histological and immunohistochemical analysis showed that the transplantation of both mESCs and mESC-CMs caused the formation of teratomas. The incidence of teratoma was markedly lower (P < 0.05) in the mESC-CMs group than in the mESCs group. The average tumour volume was significantly lower (P < 0.05) in the mESC-CMs group than in the mESCs group. Tumour formation was absent in the mESC-PE-CMs group.

CONCLUSION

Enrichment of the mESC-differentiated cardiomyocytes inhibited the development of teratoma after cell transplantation in the infarcted rat hearts. These findings offer a new strategy for eliminating teratoma formation in ESCs transplantation and could be a step forward in the development of human ESCs transplantation therapy in ischaemic heart disease.

Nuclear magnetic resonance detects phosphoinositide 3-kinase/Akt-independent traits common to pluripotent murine embryonic stem cells and their malignant counterparts

Pluripotent embryonic stem (ES) cells, a potential source of somatic precursors for cell therapies, cause tumors after transplantation. Studies of mammalian carcinogenesis using nuclear magnetic resonance (NMR) spectroscopy have revealed changes in the choline region, particularly increased phosphocholine (PCho) content. High PCho levels in murine ES (mES) cells have recently been attributed to cell pluripotency. The phosphoinositide 3-kinase (PI3K)/Akt pathway has been implicated in tumor-like properties of mES cells. This study aimed to examine a potential link between the metabolic profile associated with choline metabolism of pluripotent mES cells and PI3K/Akt signaling. We used mES (ES-D3) and murine embryonal carcinoma cells (EC-F9) and compared the metabolic profiles of 1) pluripotent mES (ESD0), 2) differentiated mES (ESD14), and 3) pluripotent F9 cells. Involvement of the PI3K/Akt pathway was assessed using LY294002, a selective PI3K inhibitor. Metabolic profiles were characterized in the extracted polar fraction by (1)H NMR spectroscopy. Similarities were found between the levels of choline phospholipid metabolites (PCho/total choline and PCho/glycerophosphocholine [GPCho]) in ESD0 and F9 cell spectra and a greater-than five-fold decrease of the PCho/GPCho ratio associated with mES cell differentiation. LY294002 caused no significant change in relative PCho levels but led to a greater-than two-fold increase in PCho/GPCho ratios. These results suggest that the PCho/GPCho ratio is a metabolic trait shared by pluripotent and malignant cells and that PI3K does not underlie its development. It is likely that the signature identified here in a mouse model may be relevant for safe therapeutic applications of human ES cells.

BMP4 induction of trophoblast from mouse embryonic stem cells in defined culture conditions on laminin

Because mouse embryonic stem cells (mESCs) do not contribute to the formation of extraembryonic placenta when they are injected into blastocysts, it is believed that mESCs do not differentiate into trophoblast whereas human embryonic stem cells (hESCs) can express trophoblast markers when exposed to bone morphogenetic protein 4 (BMP4) in vitro. To test whether mESCs have the potential to differentiate into trophoblast, we assessed the effect of BMP4 on mESCs in a defined monolayer culture condition. The expression of trophoblast-specific transcription factors such as Cdx2, Dlx3, Esx1, Gata3, Hand1, Mash2, and Plx1 was specifically upregulated in the BMP4-treated differentiated cells, and these cells expressed trophoblast markers. These results suggest that BMP4 treatment in defined culture conditions enabled mESCs to differentiate into trophoblast. This differentiation was inhibited by serum or leukemia inhibitory factor, which are generally used for mESC culture. In addition, we studied the mechanism underlying BMP4-directed mESC differentiation into trophoblast. Our results showed that BMP4 activates the Smad pathway in mESCs inducing Cdx2 expression, which plays a crucial role in trophoblast differentiation, through the binding of Smad protein to the Cdx2 genomic enhancer sequence. Our findings imply that there is a common molecular mechanism underlying hESC and mESC differentiation into trophoblast.

Recombinant mouse SPARC promotes parietal endoderm differentiation and cardiomyogenesis in embryoid bodies

In the absence of leukemia inhibitory factor, murine embryonic stem cells cultured in vitro spontaneously aggregate to from three-dimensional embryoid bodies that differentiate to produce hematopoietic, endothelial, muscle, and neuronal cell lineages in a manner recapitulating the events of early embryogenesis. Cardiomyogenesis in embryoid bodies was recently demonstrated to be promoted by PYS-2-derived native SPARC (secreted protein, acidic and rich in cysteine), whose expression is upregulated in parietal endoderm at the onset of the epithelial to mesenchymal transition. Here, we confirm the stimulatory effects of mouse SPARC on cardiomyogenesis using a recombinant baculovirus-produced protein (rmSPARC). Embryoid bodies cultured in the presence of glycosylated rmSPARC, or an unglycosylated peptide spanning the C-terminal EF-hand domain, developed greater numbers of beating cardiomyocytes than did time-matched controls, with enhanced expression of cardiac marker genes including Nkx2.5, Troponin, BMP-2, and MHCα. Histochemical analysis revealed an expansion of the peripheral endoderm, with thicker layers of extracellular matrix (ECM) material observed atop underlying cells. Embryoid bodies treated with SPARC also displayed increased adherence to polystyrene culture dishes, with enhanced expression of ECM mRNAs including collagen IVα3, collagen IVα5, and laminin α1. These results indicate that, in addition to the promotion of cardiomyogenesis, SPARC may also help regulate the molecular composition and organization of ECM secreted by the mesenchymal parietal endoderm.

Requirement of leukemia inhibitory factor for establishing and maintaining embryonic stem cells in mice

OBJECTIVE

To evaluate the necessity of leukemia inhibitory factor (LIF) in establishing and self-renewing embryonic stem cells (ESCs).

DESIGN

Prospective animal model study.

SETTING

Gamete and Stem Cell Biotechnology Laboratory, Seoul National University, Korea.

ANIMAL(S)

F1 hybrid B6D2F1 mice.

INTERVENTION(S)

Inner cell mass (ICM) cells of blastocysts were cultured or commercially available ESCs were maintained in LIF-free or LIF-containing medium on mouse embryonic fibroblast (MEF) feeder.

MAIN OUTCOME MEASURE(S)

Cell morphology, LIF concentration, and mRNA expression.

RESULT(S)

The MEFs themselves secreted 146.5-175.3 pg/mL LIF in LIF-free medium. The ICM cells formed ESC-like colonies on MEF feeder, and E14 and R1 ESCs were successfully maintained in LIF-free medium. Expression of the genes either mediating LIF function or regulating stemness was not altered significantly, and change in the growth of ESCs was not prominent in LIF-free medium. Neither mRNA expression of differentiation-related genes nor differentiation into embryoid body was changed in the ESCs.

CONCLUSION(S)

Addition of LIF to culture medium is not necessary for establishing ICM-derived ESC-like colonies in the presence of fibroblast monolayer, and established ESCs can be maintained in an LIF-free medium.

Integrins regulate mouse embryonic stem cell self-renewal

Extracellular matrix (ECM) components regulate stem-cell behavior, although the exact effects elicited in embryonic stem (ES) cells are poorly understood. We previously developed a simple, defined, serum-free culture medium that contains leukemia inhibitory factor (LIF) for propagating pluripotent mouse embryonic stem (mES) cells in the absence of feeder cells. In this study, we determined the effects of ECM components as culture substrata on mES cell self-renewal in this culture medium, comparing conventional culture conditions that contain serum and LIF with gelatin as a culture substratum. mES cells remained undifferentiated when cultured on type I and type IV collagen or poly-D-lysine. However, they differentiated when cultured on laminin or fibronectin as indicated by altered morphologies, the activity of alkaline phosphatase decreased, Fgf5 expression increased, and Nanog and stage-specific embryonic antigen 1 expression decreased. Under these conditions, the activity of signal transducer and activator of transcription (STAT)3 and Akt/protein kinase B (PKB), which maintain cell self-renewal, decreased. In contrast, the extracellular signal-regulated kinase (ERK)1/2 activity, which negatively controls cell self-renewal, increased. In the defined conditions, mES cells did not express collagen-binding integrin subunits, but they expressed laminin- and fibronectin-binding integrin subunits. The expression of some collagen-binding integrin subunits was downregulated in an LIF concentration-dependent manner. Blocking the interactions between ECM and integrins inhibited this differentiation. Conversely, the stimulation of ECM-integrin interactions by overexpressing collagen-binding integrin subunits induced differentiation of mES cells cultured on type I collagen. The results of the study indicated that inactivation of the integrin signaling is crucial in promoting mouse embryonic stem cell self-renewal. Disclosure of potential conflicts of interest is found at the end of this article.

In vitro comparison of the biological effects of three transfection methods for magnetically labeling mouse embryonic stem cells with ferumoxides

In vivo MRI of stem cells (SCs) is an emerging application to evaluate the role of cell therapy in restoring the injured myocardium. The high spatial and temporal resolution combined with iron-oxide-based intracellular labeling techniques will provide a sensitive, noninvasive, dual imaging modality for both cells and myocardium. In order to facilitate this novel imaging approach, much effort has been directed towards developing efficient transfection methods. While techniques utilizing poly-L-lysine (PLL), protamine sulfate (PS), and electroporation (ELP) have been proposed, the fundamental biological effects of these methods on mouse embryonic SCs (mESC) have not been investigated systematically. In this study a longitudinal in vitro evaluation of cellular viability, apoptosis, proliferation, and cardiac differentiation of magnetically labeled mESC was conducted. No significant difference was seen in these biological parameters among the three transfection methods. However, cardiac differentiation was most attenuated by ELP, and iron uptake was most effective by PS.

Functional redundancy of GSK-3alpha and GSK-3beta in Wnt/beta-catenin signaling shown by using an allelic series of embryonic stem cell lines

In mammalian cells, glycogen synthase kinase-3 (GSK-3) exists as two homologs, GSK-3alpha and GSK-3beta, encoded by independent genes, which share similar kinase domains but differ substantially in their termini. Here, we describe the generation of an allelic series of mouse embryonic stem cell (ESC) lines with 0-4 functional GSK-3 alleles and examine GSK-3-isoform function in Wnt/beta-catenin signaling. No compensatory upregulation in GSK-3 protein levels or activity was detected in cells lacking either GSK-3alpha or GSK-3beta, and Wnt/beta-catenin signaling was normal. Only in cells lacking three or all four of the alleles was a gene-dosage effect on beta-catenin/TCF-mediated transcription observed. Indeed, GSK-3alpha/beta double-knockout ESCs displayed hyperactivated Wnt/beta-catenin signaling and were severely compromised in their ability to differentiate, but could be rescued to normality by re-expression of functional GSK-3. The rheostatic regulation of GSK-3 highlights the importance of considering the contributions of both homologs when studying GSK-3 functions in mammalian systems.

Controlling size, shape and homogeneity of embryoid bodies using poly(ethylene glycol) microwells

Directed differentiation of embryonic stem (ES) cells is useful for creating models of human disease and could potentially generate a wide array of functional cell types for therapeutic applications. Methods to differentiate ES cells often involve the formation of cell aggregates called embryoid bodies (EBs), which recapitulate early stages of embryonic development. EBs are typically made from suspension cultures, resulting in heterogeneous structures with a wide range of sizes and shapes, which may influence differentiation. Here, we use microfabricated cell-repellant poly(ethylene glycol) (PEG) wells as templates to initiate the formation of homogenous EBs. ES cell aggregates were formed with controlled sizes and shapes defined by the geometry of the microwells. EBs generated in this manner remained viable and maintained their size and shape within the microwells relative to their suspension counterparts. Intact EBs could be easily retrieved from the microwells with high viability (>95%). These results suggest that the microwell technique could be a useful approach for in vitro studies involving ES cells and, more specifically, for initiating the differentiation of EBs of greater uniformity based on controlled microenvironments.

Acidic fibroblast growth factor promotes hepatic differentiation of monkey embryonic stem cells

Embryonic stem (ES) cells can replicate indefinitely and differentiate into all cell types, including hepatocytes. Research using primate ES cells is considered to be important for studies of potential cell therapies. Recently, we established cynomolgus monkey ES cells designated as CMK6. The CMK6 cell line is a useful tool for investigating the mechanism of differentiation in primate ES cells and developing cell therapies, because of its biological similarity to human ES cells. To examine whether cynomolgus monkey ES cells differentiate into hepatocytes, CMK6 cells were cultured with or without acidic fibroblast growth factor (aFGF). Evaluation of the hepatic differentiation was performed by analysis of the mRNA expression in early hepatic marker genes using the reverse transcriptase-polymerase chain reaction (RT-PCR). The protein expression of albumin (ALB) was also studied by immunocytochemistry. RT-PCR analyses revealed mRNA expressions of alpha-fetoprotein, transthyretin, and ALB in the presence of aFGF at 3 wk of differentiation, whereas no mRNA expression of these genes was detected in cells without aFGF. The protein expression of ALB in the presence of aFGF at 3 wk of differentiation was also confirmed by immunocytochemistry. However, tyrosine aminotransferase, which is a mature hepatic marker, was not detected in the presence or absence of aFGF at any stage of differentiation. These results suggested that aFGF successfully promoted in vitro differentiation of cynomolgus monkey ES cells to an early hepatic lineage.

Enhanced chondrogenic differentiation of murine embryonic stem cells in hydrogels with glucosamine

Differentiation of embryonic stem (ES) cells generally occurs after formation of three-dimensional cell aggregates, known as embryoid bodies (EBs). We have previously reported that hydrogels provide EBs a supportive environment for in vitro chondrogenic differentiation and three dimensional tissue formation [Hwang NS, et al. The Effects of three dimensional culture and growth factors on the chondrogenic differentiation of murine ES cells. Stem Cells 2006;24:284-91]. In this study, we report chondrogenic differentiation of murine ES cells encapsulated in photopolymerizing poly(ethylene-glycol)-based (PEG) hydrogels in the presence of glucosamine (GlcN), an amino monosaccharide found in chitin, glycoproteins and glycosaminoglycans such as hyaluronic acid, chondroitin sulfate and heparin sulfate. We examined the growth and differentiation of encapsulated EBs in standard chondrogenic differentiation medium containing 0-, 2-, and 10-mm GlcN. Morphometric analysis and examination of gene and protein expression indicated that treatment of hydrogel cultures with 2-mm GlcN for 21 days significantly increased EB size, levels of aggrecan mRNA, and tissue-specific extracellular matrix accumulation. GlcN can induce multiple aspects of cell behavior and optimal GlcN concentrations can be beneficial for directing the differentiation and tissue formation of ES cells.

Creation of Engineered Cardiac Tissue In Vitro From Mouse Embryonic Stem Cells

Background— Embryonic stem (ES) cells can terminally differentiate into all types of somatic cells and are considered a promising source of seed cells for tissue engineering. However, despite recent progress in in vitro differentiation and in vivo transplantation methodologies of ES cells, to date, no one has succeeded in using ES cells in tissue engineering for generation of somatic tissues in vitro for potential transplantation therapy.

Methods and Results— ES-D3 cells were cultured in a slow-turning lateral vessel for mass production of embryoid bodies. The embryoid bodies were then induced to differentiate into cardiomyocytes in a medium supplemented with 1% ascorbic acid. The ES cell–derived cardiomyocytes were then enriched by Percoll gradient centrifugation. The enriched cardiomyocytes were mixed with liquid type I collagen supplemented with Matrigel to construct engineered cardiac tissue (ECT). After in vitro stretching for 7 days, the ECT can beat synchronously and respond to physical and pharmaceutical stimulation. Histological, immunohistochemical, and transmission electron microscopic studies further indicate that the ECTs both structurally and functionally resemble neonatal native cardiac muscle. Markers related to undifferentiated ES cell contamination were not found in reverse transcriptase–polymerase chain reaction analysis of the Percoll-enriched cardiomyocytes. No teratoma formation was observed in the ECTs implanted subcutaneously in nude mice for 4 weeks.

Conclusions— ES cells can be used as a source of seed cells for cardiac tissue engineering. Additional work remains to demonstrate engraftment of the engineered heart tissue in the case of cardiac defects and its functional integrity within the host’s remaining healthy cardiac tissue.

Transcriptional profiling of reporter genes used for molecular imaging of embryonic stem cell transplantation

Stem cell therapy offers exciting promise for treatment of ischemic heart disease. Recent advances in molecular imaging techniques now allow investigators to monitor cell fate noninvasively and repetitively. Here we examine the effects of a triple-fusion reporter gene on embryonic stem (ES) cell transcriptional profiles. Murine ES cells were stably transfected with a self-inactivating lentiviral vector carrying a triple-fusion (TF) construct consisting of fluorescence, bioluminescence, and positron emission tomography (PET) reporter genes. Fluorescence-activated cell sorting (FACS) analysis allowed isolation of stably transfected populations. Microarray studies comparing gene expression in nontransduced control ES cells vs. stably transduced ES cells expressing triple fusion (ES-TF) revealed some increases in transcriptional variability. Annotation analysis showed that ES-TF cells downregulated cell cycling, cell death, and protein and nucleic acid metabolism genes while upregulating homeostatic and anti-apoptosis genes. Despite these transcriptional changes, expression of the TF reporter gene had no significant effects on ES cell viability, proliferation, and differentiation capability. Importantly, transplantation studies in murine myocardium demonstrated the feasibility of tracking ES-TF cells in living subjects using bioluminescence and PET imaging. Taken together, this is the first study to analyze in detail the effects of reporter genes on molecular imaging of ES cells.

Effects of Three-Dimensional Culture and Growth Factors on the Chondrogenic Differentiation of Murine Embryonic Stem Cells

Embryonic stem (ES) cells have the ability to self-replicate and differentiate into cells from all three germ layers, holding great promise for tissue regeneration applications. However, controlling the differentiation of ES cells and obtaining homogenous cell populations still remains a challenge. We hypothesize that a supportive three-dimensional (3D) environment provides ES cell-derived cells an environment that more closely mimics chondrogenesis in vivo. In the present study, the chondrogenic differentiation capability of ES cell-derived embryoid bodies (EBs) encapsulated in poly(ethylene glycol)-based (PEG) hydrogels was examined and compared with the chondrogenic potential of EBs in conventional monolayer culture. PEG hydrogel-encapsulated EBs and EBs in monolayer were cultured in vitro for up to 17 days in chondrogenic differentiation medium in the presence of transforming growth factor (TGF)-beta1 or bone morphogenic protein-2. Gene expression and protein analyses indicated that EB-PEG hydrogel culture upregulated cartilage-relevant markers compared with a monolayer environment and induction of chondrocytic phenotype was stimulated with TGF-beta1. Histology of EBs in PEG hydrogel culture with TGF-beta1 demonstrated basophilic extracellular matrix deposition characteristic of neocartilage. These findings suggest that EB-PEG hydrogel culture, with an appropriate growth factor, may provide a suitable environment for chondrogenic differentiation of intact ES cell-derived EBs.

Leukemia inhibitory factor as an anti-apoptotic mitogen for pluripotent mouse embryonic stem cells in a serum-free medium without feeder cells

We have developed a serum-free medium, designated ESF7, in which leukemia inhibitory factor (LIF) clearly stimulated murine embryonic stem (ES) cell proliferation accompanied by increased expression of nanog and Rex-1 and decreased FGF-5 expression. These effects were dependent on the concentration of LIF. The ES cells maintained in ESF7 medium for more than 2 yr retained an undifferentiated phenotype, as manifested by the expression of the transcription factor Oct-3/4, the stem cell marker SSEA-1, and alkaline phosphatase. Withdrawal of LIF from ESF7 medium resulted in ES cell apoptosis. Addition of serum to ESF7 medium promoted ES cell differentiation. Addition of BMP4 promoted ES cell differentiation into simple epithelial-like cells. In contrast, FGF-2 promoted ES cell differentiation into neuronal and glial-like cells. Under serum-free culture conditions, LIF was sufficient to stimulate cell proliferation, it inhibited cell differentiation, and it maintained self-renewal of ES cells. Because this simple serum-free adherent monoculture system supports the long-term propagation of pluripotent ES cells in vitro, it will allow the elucidation of ES cell responses to growth factors under defined conditions.

Development of Novel Markers for the Characterization of Chicken Primordial Germ Cells

This study was undertaken to develop novel markers for chicken primordial germ cells (PGCs), which are of potentially enormous value in transgenic research. Gonadal cells collected from 5.5-day-old chicken embryos were cultured in a Dulbecco's minimal essential medium and the PGC colonies formed during the primary culture period were subcultured three times. Characterization of the PGCs with the candidate marker reagents was performed on the mixed cell population 2 hours after seeding, after the primary culture period (day 10), and after the third passage (day 40). Mouse embryonic stem (ES) cells were used as controls. The cytochemical reagents investigated included periodic acid-Schiff (PAS) stain, antibodies to stage-specific embryonic antigens (SSEA-1, SSEA-3, and SSEA-4), antibody to epithelial membrane antigen (EMA)-1, antibodies to integrins alpha6 and beta1, several lectins (Solanum tuberosum agglutinin [STA], Dolichos biflorus agglutinin [DBA], concanavalin A agglutinin [ConA], and wheat germ agglutinin [WGA]), and double staining with antibodies to SSEA-1, SSEA-3, SSEA-4, integrin alpha6, or integrin beta1 and then with the lectin STA. Densitometric quantification was used to identify PGC-specific markers. The results showed that chicken PGCs were stained selectively by PAS and by antibodies to SSEA-1, SSEA-3, SSEA-4, EMA-1, integrin alpha6, and integrin beta1. The control mouse ES cells reacted with PAS, anti-SSEA-1, and anti-EMA-1 antibodies, as well as with antibodies to integrins alpha6 and beta1, but not with antibodies to SSEA-3 and SSEA-4. Chicken PGCs reacted with the lectins STA and DBA, but mouse ES cells reacted with STA and WGA. The results of double staining of PGC colonies subcultured three times showed that the intensity of staining was not altered by concomitant use of the marker reagents. This study demonstrated that, in addition to PAS and antibodies to SSEA-1 and EMA-1, new specific markers of chicken PGCs are recognized by the lectins STA and DBA and by antibodies to SSEA-3 and SSEA-4 and integrins alpha6 and beta1. Double staining using these newly developed markers might be the method of choice for rapid characterization of chicken PGCs.