Differences between human and mouse embryonic stem cells

Human embryonic stem cells: an in vitro model to study mechanisms controlling pluripotency in early mammalian development

The property of pluripotency confers the capacity for differentiation into a large number of cell types including extra-embryonic, somatic and germinal cells. During normal development, pluripotency is acquired by the cells of the early embryo, which shortly thereafter undergo differentiation, whereas embryonic stem cells (ESCs) uniquely maintain pluripotency while undergoing extensive in vitro proliferation. Studies using ESCs have begun to unravel the network of cytokines and transcription factors responsible for their maintenance of pluripotency. Surprisingly, mouse and human ESCs display significant differences in such mechanisms despite their similar embryonic origins. In this review, we compare the properties of pluripotent embryonic cells with those of ESCs to establish a general model for the mechanisms maintaining pluripotency. We first consider whether mouse and human ESCs represent comparable stages of early embryonic development. We then describe how human embryoid body (EB) differentiation could be used as a model of embryonic development. Finally, to concretely illustrate the discussion, we discuss our recent results concerning Nodal function in controlling cell fate at early stages of human EB development. With the new perspective of these findings, we suggest a previously unrecognized role of TGF-beta pathway signaling in maintaining pluripotency at early stages of mammalian embryonic development.

Molecular profiling of stem cells

Stem cells, with their profound implication in development and enormous potential in regenerative medicine, have been the subject of extensive molecular profiling studies in search of better markers and regulatory schema governing self-renewal versus differentiation. In this review article, we will discuss current advancement in high throughput technologies dedicated to the transcriptome, proteome and genome-wide localization analyses, and how they have been adopted in molecular profiling of stem cells with an emphasis on embryonic stem cell (ESC), hematopoietic stem cell (HSC) and neural stem cell (NSC).

Gene regulation networks related to neural differentiation of hESC

With the unique property of self-renewal and developmental pluripotency, human embryonic stem cells (hESC) provide an opportunity to study molecular aspects of developmental biology. Understanding gene regulation of hESC pluripotency is a critical step toward directing hESC differentiation for regenerative medicine. However, currently little is known about hESC gene regulation of hESC pluripotency. Applying network analysis to microarray gene expression profiling data, we compared gene expression profiles from pluripotent hESC to hESC-derived astrocytes and identified potential gene regulation networks. These gene regulation networks suggest that hECS has stringent control of cell cycle and apoptosis. Our data reveal several potential hESC differentiation biomarkers and suggest that IGF2 and A2M could play a role in hESC pluripotency by altering the availability of cytokines at the local environment of hECS. These findings underscore the importance of network analysis among differentially expressed genes, and should facilitate future study for understanding the gene regulation of hESC pluripotency.

Expansion of mouse embryonic stem cells on microcarriers

Embryonic stem (ES) cells have been shown to differentiate in vitro into a wide variety of cell types having significant potential for tissue regeneration. Therefore, the operational conditions for the ex vivo expansion and differentiation should be optimized for large-scale cultures. The expansion of mouse ES cells has been evaluated in static culture. However, in this system, culture parameters are difficult to monitor and scaling-up becomes time consuming. The use of stirred bioreactors facilitates the expansion of cells under controlled conditions but, for anchorage-dependent cells, a proper support is necessary. Cytodex-3, a microporous microcarrier made up of a dextran matrix with a collagen layer at the surface, was tested for its ability to support the expansion of the mouse S25 ES cell line in spinner flasks. The effect of inocula and microcarrier concentration on cell growth and metabolism were analyzed. Typically, after seeding, the cells exhibited a growth curve consisting of a short death or lag phase followed by an exponential phase leading to the maximum cell density of 2.5-3.9 x 10(6) cells/mL. Improved expansion was achieved using an inoculum of 5 x 10(4) cells/mL and a microcarrier concentration of 0.5 mg/mL. Medium replacement allowed the supply of the nutrients and the removal of waste products inhibiting cell growth, leading to the maintenance of the cultures in steady state for several days. These conditions favored the preservation of the S25 cells pluripotent state, as assessed by quantitative real-time PCR and immunostaining analysis.

Human stem cells, chromatin, and tissue engineering: Boosting relevancy in developmental toxicity testing

Risk assessment derives its confidence from toxicology research that is based on relevancy to human health. This article focuses on two highly topical areas of current scientific research, stem cells and chromatin biology, which present new avenues for preclinical and clinical applications, and the frontier role of tissue engineering and regeneration. Appreciating the utility and necessity of chromatin and human somatic stem cells as research tools and looking toward tissue engineering may close the uncertainty gaps between animal and human cross-species toxicology evaluations. The focus will be on developmental toxicology applications, but appropriate extrapolation to any other areas of toxicology can be made. We further provide background on basic biology of these three areas and examples of how early life exposure to known and potential environmental toxicants induce malformations, childhood and adult-onset diseases, through aberrant chromatin modification of critical gene expressions (acute lymphocyte leukemia, heavy-metal nickel and cadmium-associated defects, and reproductive tract malformations and carcinomas induced by the synthetic estrogen, diethylstilbestrol).

Hematopoietic Development from Human Embryonic Stem Cells

The most common human cell-based therapy applied today is hematopoietic stem cell (HSC) transplantation. HSCs can be defined by two essential properties: self-renewal and multilineage hematopoietic differentiation. These combined HSC properties allow them to differentiate into all blood cell types (multilineage) in a sustained manner for the lifetime of the animal, which requires their ability to make cellular copies of themselves (self-renewal). These features can be tested by transplantation from donor to recipient and provide a functional basis to define and identify HSCs. Currently, human bone marrow (BM), mobilized peripheral blood, and umbilical cord blood (CB) represent the major sources of transplantable HSCs, but their availability for use is limited by both quantity and compatibility. Although increasing evidence suggests that somatic HSCs can be expanded to meet current needs, their in vivo potential is concomitantly compromised after ex vivo culture. Pluripotent human embryonic stem cells (hESCs) may provide an alternative. hESCs possess indefinite proliferative capacity in vitro, and have been shown to differentiate into the hematopoietic cell fate, giving rise to erythroid, myeloid, and lymphoid lineages using a variety of differentiation procedures. In most cases, hESC-derived hematopoietic cells show similar clonogenic progenitor capacity and primitive phenotype to somatic sources of hematopoietic progenitors, but possess limited in vivo repopulating capacity when transplanted into immunodeficient mice. Although this suggests HSC function can be derived from hESCs, the efficiency and quality of these cells must be characterized using surrogate models for potential clinical applications.

Molecular mechanisms involved in self-renewal and pluripotency of embryonic stem cells

Embryonic stem cells (ES cells) are derived from inner cell mass (ICM). The self-renewal and pluripotency are the main specificities of ES cells, which are likely to reveal a deeper understanding of human cellular biology and which are considered to be promising sources for cell therapy to treat patients with degenerative diseases in clinical. Growth of ES cells as a pluripotent population requires a balance between survival, proliferation, and self-renewal signals. In fact, the precise mechanism that regulates stem cell self-renewal and pluripotency remains largely unknown. Recently, in vitro and in vivo studies have identified several genetic regulators that may play important roles in the self-renewal and pluripotency process of human and mouse ES cells, including extracellular signaling factors, transcription factors, cell-cycle regulators, microRNA, genes implicated in chromosomal stability, and DNA methylation. In this review, we will summarize the currently known molecular regulators for ES cells self-renewal, and we will propose some possibilities to explain the ways in which these distinct pathways might interact.

The genomic signature of breast cancer prevention

Early pregnancy imprints in the breast permanent genomic changes or a signature that reduces the susceptibility of this organ to cancer. The breast attains its maximum development during pregnancy and lactation. After menopause, the breast regresses in both nulliparous and parous women containing lobular structures designated Lob.1. The Lob 1 found in the breast of nulliparous women and of parous women with breast cancer never went through the process of differentiation, retaining a high concentration of epithelial cells that are targets for carcinogens and therefore susceptible to undergoing neoplastic transformation, these cell are called Stem cells 1, whereas Lob 1 structures found in the breast of early parous postmenopausal women free of mammary pathology, on the other hand, are composed of an epithelial cell population that is refractory to transformation called Stem cells 2. The degree of differentiation acquired through early pregnancy has changed the genomic signature that differentiates the Lob 1 from the early parous women from that of the nulliparous women by shifting the Stem cell 1 to a Stem cell 2, making this the postulated mechanism of protection conferred by early full-term pregnancy. The identification of a putative breast stem cell (Stem cell 1) has reached in the last decade a significant impulse and several markers also reported for other tissues have been found in the mammary epithelial cells of both rodents and humans. The data obtained thus far is supporting the concept that the lifetime protective effect of an early pregnancy against breast cancer is due to the complete differentiation of the mammary gland, which results in the replacement of the Stem cell 1 that is a component of the nulliparous breast epithelium with a new stem cell, called Stem cell 2, which is characterized by a specific genomic signature. The pattern of gene expression of the stem cell 2 could potentially be used as useful intermediate end points for evaluating the degree of mammary gland differentiation and for evaluating preventive agents such as human chorionic gonadotropin.

Meta-analysis of differentiating mouse embryonic stem cell gene expression kinetics reveals early change of a small gene set

Stem cell differentiation involves critical changes in gene expression. Identification of these should provide endpoints useful for optimizing stem cell propagation as well as potential clues about mechanisms governing stem cell maintenance. Here we describe the results of a new meta-analysis methodology applied to multiple gene expression datasets from three mouse embryonic stem cell (ESC) lines obtained at specific time points during the course of their differentiation into various lineages. We developed methods to identify genes with expression changes that correlated with the altered frequency of functionally defined, undifferentiated ESC in culture. In each dataset, we computed a novel statistical confidence measure for every gene which captured the certainty that a particular gene exhibited an expression pattern of interest within that dataset. This permitted a joint analysis of the datasets, despite the different experimental designs. Using a ranking scheme that favored genes exhibiting patterns of interest, we focused on the top 88 genes whose expression was consistently changed when ESC were induced to differentiate. Seven of these (103728_at, 8430410A17Rik, Klf2, Nr0b1, Sox2, Tcl1, and Zfp42) showed a rapid decrease in expression concurrent with a decrease in frequency of undifferentiated cells and remained predictive when evaluated in additional maintenance and differentiating protocols. Through a novel meta-analysis, this study identifies a small set of genes whose expression is useful for identifying changes in stem cell frequencies in cultures of mouse ESC. The methods and findings have broader applicability to understanding the regulation of self-renewal of other stem cell types.

Differential expression of glucose transporter isoforms during embryonic stem cell differentiation

In mouse blastocysts six facilitative glucose transporter isoforms (GLUT)1-4, 8 and 9 are expressed. We have used the mouse embryonic stem (ES) cell line D3 and spontaneously differentiating embryoid bodies (EB) to investigate GLUT expression and the influence of glucose during differentiation of early embryonic cells. Both ES cells and EBs (2d-20d) expressed GLUT1, 3, and 8, whereas the isoforms 2 and 4 were detectable exclusively in EBs. Differentiation-associated expression of GLUT was analyzed by double staining with stage-specific embryonic antigen (SSEA-1), cytokeratins (CK18, 19), nestin, and desmin. Similar to trophoblast cells in mouse blastocysts the outer cell layer of endoderm-like cells showed a high GLUT3 expression in early EBs. In 20-day-old EBs no GLUT3 protein and only minor GLUT3 mRNA amounts could be detected. A minimal glucose concentration of 5 mM applied during 2 and 8 days of EB culture resulted in up-regulated GLUT4, Oct-4 and SSEA-1 levels and a delay in EB differentiation. We conclude that GLUT expression depends on cellular differentiation and that the expression is modulated by glucose concentration. The developmental and glucose-dependent regulation of GLUT strongly suggests a functional role of glucose and glucose transporters in ES cell differentiation and embryonic development.

Transcriptional Profiling of Rhesus Monkey Embryonic Stem Cells1

Embryonic stem cells (ESCs) may be able to cure or alleviate the symptoms of various degenerative diseases. However, unresolved issues regarding survival, functionality, and tumor formation mean a prudent approach should be adopted towards advancing ESCs into human clinical trials. The rhesus monkey provides an ideal model organism for developing strategies to prevent immune rejection and test the feasibility, safety, and efficacy of ESC-based medical treatments. Transcriptional profiling of rhesus monkey ESCs provides a foundation for pre-clinical ESC research in this species. In the present study, we used microarray technology, immunocytochemistry, reverse transcription polymerase chain reaction (RT-PCR) and quantitative real-time PCR (qPCR) to characterize and transcriptionally profile rhesus monkey ESCs. We identified 367 stemness gene candidates that were highly (>85%) conserved across five different ESC lines. Rhesus monkey ESC lines maintained a pluripotent undifferentiated state over a wide range of POU5F1 (also known as OCT4) expression levels, and comparisons between rhesus monkey, mouse, and human stemness genes revealed five mammalian stemness genes: CCNB1, GDF3, LEFTB, POU5F1, and NANOG. These five mammalian genes are strongly expressed in rhesus monkey, mouse, and human ESCs, albeit only in the undifferentiated state, and represent the core key mammalian stemness factors.

Fibroblast growth factors as regulators of stem cell self-renewal and aging

Organ and tissue dysfunction which is readily observable during aging results from a loss of cellular homeostasis and reduced stem cell self-renewal. Over the past 10 years, studies have been aimed at delineating growth factors that will sustain and promote the self-renewal potential of stem cells and support the expansion of primitive stem cells in vitro and in vivo. Recently, strong evidence is emerging indicating that fibroblast growth factors (FGFs) play a crucial role in stem cell maintenance. FGFs belong to a family of polypeptide growth factors that are involved in multiple functions including cell proliferation, differentiation, survival and motility. In this review, we discuss the regulatory role of FGFs on hematopoietic stem cells (HSCs), neural stem cells (NSCs) and embryonic stem (ES) cells in maintaining stem cell self-renewal. These findings are useful and important to further our knowledge in stem cell biology and for therapeutic approaches.

Transcriptional and post-transcriptional regulation of retrotransposons IAP and MuERV-L affect pluripotency of mice ES cells

BACKGROUND

In the mouse, culture of embryonic stem (ES) cells may decrease their pluripotency and give rise to foetal abnormalities in recipient embryos. These abnormalities are frequently associated with both, chromosome abnormalities or epigenetic alteration of imprinting genes; however, little is known about the epigenetic stability of endogenous retrotransposable elements (REs). In our laboratory, we came across a R1 ES cell line, which at passage 27, lost the ability of germline transmission and started inducing the kinky tail phenotype in all chimeric animals produced with it.

METHODS

In order to investigate whether this phenotype was associated with chromosome alteration, inadvertent differentiation, or epigenetic modification, we characterized and compared this R1 ES cell line at passage 27 with an early passage and with a second ES cell line C57/CBAF1 generated in our laboratory. We assessed: i) karyotype; ii) expression of pluripotent and differentiation markers, iii) mRNA transcription by qRT-PCR of two REs, intracisternal-A particle (IAP) and murine endogenous-retrovirus-L (MuERV-L), and iv) methylation of IAP and MuERV-L.

RESULTS

The R1 ES cell at passage 27, presented normal morphology, karyotype, and expression of genetic markers characteristic of pluripotent; however, it was detected an altered mRNA transcription of sense and antisense RNA strands of both REs, concomitantly with an altered methylation pattern for the IAP element but not for MuERV-L. These results indicate that besides methylation, other post-transcriptional processes are involved in gene silencing of some REs; and that culture of ES cells may decrease their pluripotency by producing inadvertent alterations in the expression of REs without significantly affecting the morphology, chromosome structure, and expression of pluripotent or differentiation markers.

CONCLUSION

Inadvertent REs instability may have important consequences for the use of ES cells in transgenesis (chimera formation) or in cell therapy.

Epithelial–mesenchymal transition process in human embryonic stem cells cultured in feeder-free conditions

Feeder-free human embryonic stem cell (hESC) culture is associated with the presence of mesenchymal-like cells appearing at the periphery of the colonies. The aim of this study was to identify this early differentiation process. Long-term feeder-free hESC cultures using matrigel and conditioned medium from mouse and from human origin revealed that the appearance of mesenchymal-like cells was similar regardless of the conditioned medium used. Standard characterization confirmed the preservation of hESC properties, but the feeder-free cultures could not be maintained longer than 37 passages. The early differentiation process was characterized in the short term after switching hESCs cultured on feeders to feeder-free conditions. Transmission electron microscopy showed an epithelium-like structure inside the hESC colonies, whereas the peripheral cells revealed the acquisition of a rather mesenchymal-like phenotype. Immunochemistry analysis showed that cells at the periphery of the colonies had a negative E-cadherin expression and a positive Vimentin expression, suggesting an epithelial-mesenchymal transition (EMT). Nuclear staining of beta-catenin, positive N-cadherin and negative Connexin 43 expression were also found in the mesenchymal-like cell population. After RT-PCR analysis, Slug and Snail, both EMT-related transcription factors, were detected as up-regulated in the mesenchymal-like cell population. Taken together, our data suggest that culturing hESCs in feeder-free conditions enhances an early differentiation process identified as an EMT.

Cell therapy and the safety of embryonic stem cell-derived grafts

Recent developments in the identification, in vitro culture and differentiation of stem cells point to the unprecedented potential of these cells, or their derivatives, to cure degenerative disorders. Human embryonic stem cells (hESC) offer the particular advantage of prolonged proliferative capacity and great versatility in the lineages that can be formed in culture. Translating these advantages into clinical benefits faces many challenges, including efficient differentiation into the desired cell type(s), maintaining genetic stability during long-term culture and, finally, ensuring the absence of potentially tumorigenic hESC from the final product. It is this final safety issue that will form the focus of this review.

Expansion of Undifferentiated Murine Embryonic Stem Cells as Aggregates in Suspension Culture Bioreactors

Pluripotent embryonic stem cells (ESCs) have recently been considered as a primary material for regenerating tissues lost to injuries and degenerative diseases. For clinical implementation of this technology, a quality controlled, reproducible culture system is necessary for the expansion and differentiation of the cells. Used in many bioprocess applications, suspension bioreactors have gained considerable attention for the regulated large-scale expansion of cells. The current study presents a bioreactor process for the large-scale expansion of undifferentiated murine ESCs as aggregates. In this system, the level of ESC aggregation and differentiation was effectively controlled by adjusting shear forces and inoculation density, achieving a 31-fold expansion in 5 days. Pluripotency markers Oct-4, Nanog, SSEA-1, ALP, and rex-1 were assessed using flow cytometry analysis and gene expression profiles and showed that the undifferentiated nature of the cells within the ESC aggregates was maintained. Colony-forming efficiencies and embryoid body formation tests of the expanded cultures demonstrated that characteristic functional attributes of undifferentiated cells were not lost. Overcoming a major impediment in the area of ESC expansion, this study describes a successful process for the controlled and reproducible largescale expansion of ESCs using suspension culture bioreactors.

Comparison of Schwann cell and sciatic nerve transcriptomes indicates that mouse is a valid model for the human peripheral nervous system

High-throughput gene expression analyses of murine models of the peripheral nervous system (PNS), and its cellular components, have yielded enormous amounts of expression data of the PNS in various conditions. These data provided clues for future research directions to further decipher this complex organ in relation to acquired and inherited PNS diseases. Various studies addressing the validity of mouse models for human conditions in other tissues and cell types have indicated that in many cases the mouse model only poorly represents the human situation. To determine how well the mouse can serve as model to study the biological processes occurring in the PNS, we compared the gene expression profiles that we generated for mouse and human sciatic nerve and cultured Schwann cells derived thereof. A two-way analysis based on the differentially expressed genes between the sciatic nerve and the cultured Schwann cell, and which takes into account the differential expression between mouse and man, indicates that the human PNS is well represented by that of the mouse in terms of the "biological processes" ontology.

Long-term cryopreserved amniocytes retain proliferative capacity and differentiate to ectodermal and mesodermal derivatives in vitro

Putative stem cells have recently been isolated from several extra-embryonic tissues, including Wharton's Jelly and umbilical cord blood. Relevant studies have focused on primary cultures established from freshly isolated tissues. In this report, we examine the plasticity of 472 cells, a cryopreserved human amniocyte cell line originally isolated in 1974. Under conditions conducive for proliferation, the amniocytes displayed fibroblast-like morphologies and expressed Oct4 and Rex1, genes associated with pluripotency. Perhaps indicative of inherent plasticity, 472 cells simultaneously expressed ectodermal beta-III-tubulin and mesodermal fibronectin. When cultured under conditions that promote neural differentiation, the cells adopted neuronal morphologies and expressed neuronal genes, including Gap-43, NF-M, tau, and synaptophysin. Exposure to culture conditions that encourage osteogenic differentiation resulted in increased expression of alkaline phosphatase (ALP) and the deposition of mineralized matrix, established markers of bone cell differentiation. In sum, this population of human amniocytes appears to be multipotent, capable of in vitro differentiation to ectodermal and mesodermal cell types. Retention of this plasticity through decades of cryopreservation suggests that amniocytes might be candidates for future cell-based therapies.

Cross-species transcriptional profiles establish a functional portrait of embryonic stem cells

An understanding of the regulatory mechanisms responsible for pluripotency in embryonic stem cells (ESCs) is critical for realizing their potential in medicine and science. Significant similarities exist among ESCs harvested from different species, yet major differences have also been observed. Here, by cross-species analysis of a large set of functional categories and all transcription factors and growth factors, we reveal conserved and divergent functional landscapes underlining fundamental and species-specific mechanisms that regulate ESC development. Global transcriptional trends derived from all expressed genes, instead of differentially expressed genes alone, were examined, allowing for a higher discriminating power in the functional portrait. We demonstrate that cross-species correlation of transcriptional changes that occur upon ESC differentiation is a powerful predictor of ESC-important biological pathways and functional cores within a pathway. Hundreds of functional modules, as defined by Gene Ontology, were associated with conserved expression patterns but bear no overt relationship to ESC development, suggestive of new mechanisms critical to ESC pluripotency. Yet other functional modules were not conserved; instead, they were significantly up-regulated in ESCs of either species, suggestive of species-specific regulation. The comparisons of ESCs across species and between human ESCs and embryonal carcinoma stem cells suggest that while pluripotency as an essential function in multicellular organisms is conserved throughout evolution, mechanisms primed for differentiation are less conserved and contribute substantially to the differences among stem cells derived from different tissues or species. Our findings establish a basis for defining the "stemness" properties of ESCs from the perspective of functional conservation and variation. The data and analyses resulting from this study provide a framework for new hypotheses and research directions and a public resource for functional genomics of ESCs.

Challenges and prospects for the establishment of embryonic stem cell lines of domesticated ungulates

Embryonic stem (ES) cell lines provide an invaluable research tool for genetic engineering, developmental biology and disease models. These cells can be maintained indefinitely in culture and yet maintain competence to produce all the cells within a fetus. While mouse ES cell lines were first established over two decades ago and primate ES cells in the 1990 s, validated ES cell lines have yet to be established in ungulates. Why competent, pluripotent ES cells can be established from certain strains of mice and from primates, and not from cows, sheep, goats or pigs is an on-going topic of interest to animal reproduction scientists. The identification of appropriate stem cell markers, functional cytokine pathways, and key pluripotency-maintaining factors along with the release of more comprehensive bovine and porcine genomes, provide encouragement for establishment of ungulate ES cell lines in the near future.

A severe de novo methylation of episomal vectors by human ES cells

Episomal vectors can allow efficient genetic modification of cells and have the potential advantage of avoiding chromosomal position of integration effects. Here we explore the use of an Epstein-Barr virus-based episomal vector with human embryonic stem (ES) cells, and find high initial transfection rates, but a rapid loss of reporter gene expression. Similar to mouse ES cells, human ES cells express high levels of the de novo DNA methyltransferases, and we detected dramatic CpG methylation and minor non-CpG methylation on the episomes recovered from the human ES cells 7 days after the transfection, which was not present on the same episome recovered from 293 cells. Interestingly, the oriP region of the episomes was relatively excluded from this methylation. These findings define some of the limitations of using episomal vectors with human ES cells and offer a unique platform for analyzing epigenetic gene silencing in human ES cells.

Expression of leukemia inhibitory factor and its receptors is increased during differentiation of human embryonic stem cells

OBJECTIVE

To investigate gene expression profiles during the early spontaneous differentiation of human embryonic stem cells (hESCs), with particular emphasis on leukemia inhibitory factor (LIF)-induced pathways and the ultrastructural surface morphology of the undifferentiated and spontaneously differentiated hESCs.

DESIGN

Prospective experimental study.

SETTING

University laboratory.

PATIENT(S)

Four hESC cell lines.

INTERVENTION(S)

The effect of LIF on receptor expression level was studied in cultures.

MAIN OUTCOME MEASURE(S)

Gene expression in the hESC line HS237 was analyzed using microarrays. Real-time reverse-transcription polymerase chain reaction was used to validate the microarray results in four hESC lines (HS181, HS235, HS237, HS293). Immunohistochemistry was used to assay LIF, LIF receptor, and gp130 protein expression. Cell surface morphology was studied using scanning electron microscopy.

RESULT(S)

The expression of LIF, LIF receptor, and gp130 messenger RNA and protein was increased in spontaneously differentiated HS237 cells compared with undifferentiated cells, with high expression of an inhibitor of LIF-mediated signaling, suppressor of cytokine signaling-1, in undifferentiated hESCs. Genes, those expressed specifically and those shared in undifferentiated hESCs, differentiated cells, and in fibroblasts, were identified. Supplementation with LIF did not affect the LIF receptor expression.

CONCLUSION(S)

The expression of LIF and its receptors is low in undifferentiated hESCs but increases during differentiation. Added LIF does not prevent spontaneous differentiation. Suppressor of cytokine signaling-1 may prevent LIF signaling in hESCs.

Differences between human embryonic stem cell lines

The promise of human embryonic stem cell (hESC) lines for treating injuries and degenerative diseases, for understanding early human development, for disease modelling and for drug discovery, has brought much excitement to scientific communities as well as to the public. Although all of the lines derived worldwide share the expression of characteristic pluripotency markers, many differences are emerging between lines that may be more associated with the wide range of culture conditions in current use than the inherent genetic variation of the embryos from which embryonic stem cells were derived. Thus, the validity of many comparisons between lines published thus far is difficult to interpret. This article reviews the evidence for differences between lines, focusing on studies of pluripotency marker molecules, transcriptional profiling, genetic stability and epigenetic stability, for which there is most evidence. Recognition and assessment of environmentally induced differences will be important to facilitate the development of culture systems that maximize stability in culture and provide lines with maximal potential for safety and success in the range of possible applications.

Characterization and Gene Expression Profiling of Five New Human Embryonic Stem Cell Lines Derived in Taiwan

Many human embryonic stem cell (hESC) lines have been reported, but only a few of them have been fully characterized. In this report, five new hESC lines were derived from 32 discarded blastocysts in Taiwan, and these lines were continuously cultured on mitotically inactivated mouse embryonic fibroblast (MEF) feeder layer in the hESC medium for more than 44 passages and underwent freezing/thawing processes. All five hESC lines expressed characteristic undifferentiated hESC markers, such as SSEA-4, TRA-1-81, alkaline phosphatase, TERT, and the transcription factors POU5F1 (OCT4) and NANOG. hESC lines T1 and T3 possess normal female karyotypes, whereas lines T4 and T5 are normal male, but line T2 is male trisomy 12 (47XY,+12). hESC lines T1, T2, T3, and T5 were able to produce teratomas in severe combined immunodeficient (SCID) mice, and line T4 could only form embryoid bodies (EBs) in vitro. Global gene expression profiles of these five newly derived hESC lines were analyzed using the Affymetrix human genome U133 plus 2.0 GeneChip. The results showed that 4,145 transcripts, including 19% of unknown functions, were detected in all five hESC lines. Comparison of the 4,145 genes commonly expressed in the five hESC lines with those genes expressed in teratomas produced by the hESC line T1 and placenta revealed 40 genes exclusively expressed in all five hESC lines. These 40 genes include the previously reported stemness genes, such as POU5F1 (OCT4), NANOG, TDGF1 (CRIPTO), SALL4, LECT1, and BUB1 responsible for self-renewal and pluripotent differentiation. The global gene expression analysis also indicated that the transforming growth factor-beta (TGF-beta)/activin branch components inhibin BC, ACVR2A, ACVR1 (ALK2), TGFBR1 (ALK5), and SMAD2 were found to be highly expressed in undifferentiated states of these five hESC lines and decreased upon differentiation. In short, the hESC nature of these five hESC lines is supported by the undifferentiated state, extensive renewal capacity, and pluripotency, including the ability to form teratomas and/or EBs. These cell lines will be useful for human embryonic stem cell biology and drug development.

Adult human bone marrow stromal spheres express neuronal traits in vitro and in a rat model of Parkinson's disease

Adult human bone marrow stromal cells (hMSCs) grown in suspension culture gave rise to spheres of neural progenitor (NP) cells, capable of expressing both dopaminergic (DA) and GABAergic (GABA) traits. After transplantation into the Parkinsonian rat, human NPs and neurons were present at 2 weeks. Although no DA neurons appeared to survive transplantation, there were abundant GABA neurons present in the graft. By 4 weeks, however, all cells had died. Finding ways to prolong survival and promote the appropriate neurotransmitter phenotype is essential if hMSCs are to be clinically useful.

A Quest for Human and Mouse Embryonic Stem Cell-specific Proteins

Embryonic stem cells (ESCs) are of immense interest as they can proliferate indefinitely in vitro and give rise to any adult cell type, serving as a potentially unlimited source for tissue replacement in regenerative medicine. Extensive analyses of numerous human and mouse ESC lines have shown generic similarities and differences at both the transcriptional and functional level. However, comprehensive proteome analyses are missing or are restricted to mouse ESCs. Here we have used an extensive proteomic approach to search for ESC-specific proteins by analyzing the differential protein expression profiles of human and mouse ESCs and their differentiated derivatives. The data sets comprise 1,775 non-redundant proteins identified in human ESCs, 1,532 in differentiated human ESCs, 1,871 in mouse ESCs, and 1,552 in differentiated mouse ESCs with a false positive rate of <0.2%. Comparison of the data sets distinguished 191 proteins exclusively identified in both human and mouse ESCs but not in their differentiated derivatives. Besides well known ESC benchmarks, this subset included many uncharacterized proteins, some of which may be novel ESC-specific markers. To complement the mass spectrometric approach, differential expression of a selection of these proteins was confirmed by Western blotting, immunofluorescence confocal microscopy, and fluorescence-activated cell sorting. Additionally two other independently isolated and cultured human ESC lines as well as their differentiated derivatives were monitored for differential expression of selected proteins. Some of these proteins were identified exclusively in ESCs of all three human lines and may thus serve as generic ESC markers. Our wide scale proteomic approach enabled us to screen thousands of proteins rapidly and select putative ESC-associated proteins for further analysis. Validation by three independent conventional protein analysis techniques shows that our methodology is robust, provides an excellent tool to characterize ESCs at the protein level, and may disclose novel ESC-specific benchmarks.

Sox3 expression identifies neural progenitors in persistent neonatal and adult mouse forebrain germinative zones

Neural precursors persist throughout life in the rodent forebrain subventricular zone (SVZ) and hippocampal dentate gyrus. The regulation of persistent neural stem cells is poorly understood, in part because of the lack of neural progenitor markers. The Sox B1 subfamily of HMG-box transcription factors (Sox1-3) is expressed by precursors in the embryonic nervous system, where these factors maintain neural progenitors in an undifferentiated state while suppressing neuronal differentiation. Sox2 expression persists in germinative zones of the adult rodent brain, but Sox3 expression in the postnatal brain remains largely unexplored. Here we examine Sox3 expression in the neonatal and adult mouse brain to gain insight into its potential involvement in regulating persistent neural stem cells and neurogenesis. We also investigate Sox3 expression during expansion and neural differentiation of postnatal mouse SVZ neural stem cell and human embryonic stem cell (hESC) cultures. We find that Sox3 is expressed transiently by proliferating and differentiating neural progenitors in the SVZ-olfactory bulb pathway and dentate gyrus. Sox3 immunoreactivity also persists in specific postmitotic neuronal populations. In vitro, high Sox3 protein expression levels in undifferentiated, SVZ-derived neurospheres decline markedly with differentiation. Sox3 immunoreactivity in hESCs appears upon differentiation to neural progenitors and then decreases as cells differentiate further into neurons. These findings suggest that Sox3 labels specific stages of hESC-derived and murine neonatal and adult neural progenitors and are consistent with a role for Sox3 in neural stem cell maintenance. Persistent Sox3 expression in some mature neuronal populations suggests additional undefined roles for Sox3 in neuronal function.

Concise review: scientific and ethical roadblocks to human embryonic stem cell therapy

Despite the identified therapeutic potential of embryonic stem cells for treating human disease and injury, a number of roadblocks, scientific and ethical, stand in the way of progress toward this goal. We identify six areas of particular interest: tumorigenicity, animal product contamination, genetic compatibility, funding, cell type for transplantation, "embryo-friendly" derivation methods and discuss avenues for moving beyond the difficulties.

Isolation and characterization of novel rhesus monkey embryonic stem cell lines

ESCs are important as research subjects since the mechanisms underlying cellular differentiation, expansion, and self-renewal can be studied along with differentiated tissue development and regeneration in vitro. Furthermore, human ESCs hold promise for cell and tissue replacement approaches to treating human diseases. The rhesus monkey is a clinically relevant primate model that will likely be required to bring these clinical applications to fruition. Monkey ESCs share a number of properties with human ESCs, and their derivation and use are not affected by bioethical concerns. Here, we summarize our experience in the establishment of 18 ESC lines from rhesus monkey preimplantation embryos generated by the application of the assisted reproductive technologies. The newly derived monkey ESC lines were maintained in vitro without losing their chromosomal integrity, and they expressed markers previously reported present in human and monkey ESCs. We also describe initial efforts to compare the pluripotency of ESC lines by expression profiling, chimeric embryo formation, and in vitro-directed differentiation into endodermal, mesodermal, and ectodermal lineages.

Genome-wide transcriptional profiling of human embryonic stem cells differentiating to cardiomyocytes

Mammals are unable to regenerate their heart after major cardiomyocyte loss caused by myocardial infarction. Human embryonic stem cells (hESCs) can give rise to functional cardiomyocytes and therefore have exciting potential as a source of cells for replacement therapy. Understanding the molecular regulation of cardiomyocyte differentiation from stem cells is crucial for the stepwise enhancement and scaling of cardiomyocyte production that will be necessary for transplantation therapy. Our novel hESC differentiation protocol is now efficient enough for meaningful genome-wide transcriptional profiling by microarray technology of hESCs, differentiating toward cardiomyocytes. Here, we have identified and validated time-dependent gene expression patterns and shown a reflection of early embryonic events; induction of genes of the primary mesoderm and endodermal lineages is followed by those of cardiac progenitor cells and fetal cardiomyocytes in consecutive waves of known and novel genes. Collectively, these results permit enhancement of stepwise differentiation and facilitate isolation and expansion of cardiac progenitor cells. Furthermore, these genes may provide new clinically relevant clues for identifying causes of congenital heart defects.

Transcriptional profiling of mouse and human ES cells identifies SLAIN1, a novel stem cell gene

We analyzed the transcriptional profiles of differentiating mouse embryonic stem cells (mESCs) and show that embryoid bodies (EBs) sequentially expressed genes associated with the epiblast, primitive streak, mesoderm and endoderm of the developing embryo, validating ESCs as a model system for identifying cohorts of genes marking specific stages of embryogenesis. By comparing the transcriptional profiles of undifferentiated ESCs to those of their differentiated progeny, we identified 503 mESC and 983 hESC genes selectively expressed in undifferentiated ES cells. Over 75% of the mESC genes were expressed in hESC and vice versa, attesting to the underlying similarity of mESCs and hESCs. The expression of a cohort of 68 genes decreased greater than 2-fold during differentiation in both mESCs and hESCs. As well as containing many validated ESC genes such as Oct4 [Pou5f1], Nanog and Nodal, this cohort included an uncharacterised gene (FLJ30046), which we designated SLAIN1/Slain1. Slain1 was expressed at the stem cell and epiblast stages of ESC differentiation and in the epiblast, nervous system, tailbud and somites of the developing mouse embryo. SLAIN1 and its more widely expressed homologue SLAIN2 comprise a new family of structurally unique genes conserved throughout vertebrate evolution.

Gap junctions modulate apoptosis and colony growth of human embryonic stem cells maintained in a serum-free system

We investigated the gap junctional properties of human embryonic stem cells (hESC) cultivated in a serum-free system using sphingosine-1-phosphate and platelet-derived growth factor (S1P/PDGF). We compared this condition to hESC grown on Matrigel in mouse embryonic fibroblast conditioned medium (MEF-CM) or unconditioned medium (UM). We show that in all culture systems, hESC express connexins 43 and 45. hESC maintained in S1P/PDGF conditions and hESC grown in presence of MEF-CM are coupled through gap junctions while hESC maintained on Matrigel in UM do not exhibit gap junctional intercellular communication. In this latter condition, coupling was retrieved by addition of noggin, suggesting that BMP-like activity in UM inhibits gap junctional communication. Last, our data indicate that the closure of gap junctions by the decoupling agent alpha-glycyrrhetinic acid increases cell apoptosis and inhibits hESC colony growth. Altogether, these results suggest that gap junctions play an important role in hESC maintenance.

Human embryonic stem cells: the battle between self-renewal and differentiation

Human embryonic stem cells are pluripotent cells derived from the inner cell mass of blastocyst-stage embryos. These cells possess two unique properties: an indefinite self-renewal capacity and pluripotency, the ability to differentiate to cells from the three germ layers. The pathways governing self-renewal and pluripotency are currently under intensive research. Much effort is devoted to the establishment of feeder-free cultures by elucidation of the cytokines and growth factors required for cell propagation. These seem thus far, to be distinct from those required by mouse embryonic stem cells. In addition, transcriptional regulators unique to embryonic stem cells seem to govern the pluripotent state. These transcriptional regulators determine cell fate, and decide whether the cell will remain pluripotent or differentiate. Together, the understanding of the exogenous and endogenous factors determining cell fate will facilitate the use of these cells in cell-based therapies and will allow understanding of early developmental processes.

The role of PI3K/AKT, MAPK/ERK and NFkappabeta signalling in the maintenance of human embryonic stem cell pluripotency and viability highlighted by transcriptional profiling and functional analysis

Understanding the molecular mechanism by which pluripotency is maintained in human embryonic stem cells (hESC) is important for the development of improved methods to derive, culture and differentiate these into cells of potential therapeutic use. Large-scale transcriptional comparison of the hES-NCL1 line derived from a day 8 embryo with H1 line derived from a day 5 embryo (WiCell Inc.) showed that only 0.52% of the transcripts analysed varied significantly between the two cell lines. This is within the variability range that has been reported when hESC derived from days 5-6 embryos have been compared with each other. This implies that transcriptional differences between the cell lines are likely to reflect their genetic profile rather than the embryonic stage from which they were derived. Bioinformatic analysis of expression changes observed when these cells were induced to differentiate as embryoid bodies suggested that quite a few of the downregulated genes were components of signal transduction networks. Subsequent analysis using western blotting, flow cytometry and antibody arrays implicated components of the PI3K/AKT kinase, MAPK/ERK and NFkappabeta pathways and confirmed that these components are decreased upon differentiation. Disruption of these pathways in isolation using specific inhibitors resulted in loss of pluripotency and/or loss of viability suggesting the importance of such signalling pathways in embryonic stem cell maintenance.

Mechanisms of self-renewal in human embryonic stem cells

Embryonic stem cells (ESCs) are the pluripotent cell population derived from the inner cell mass of pre-implantation embryos and are characterised by prolonged self-renewal and the potential to differentiate into cells representing all three germ layers both in vitro and in vivo. Preservation of the undifferentiated status of the ESC population requires the maintenance of self-renewal whilst inhibiting differentiation and regulating senescence and apoptosis. In this review, we discuss the intrinsic and extrinsic factors associated with self-renewal process, together with possible signalling pathway interactions and mechanisms of regulation.

Cell surface 5T4 antigen is transiently upregulated during early human embryonic stem cell differentiation: effect of 5T4 phenotype on neural lineage formation

The 5T4 oncofoetal antigen is a cell surface glycoprotein that is transiently expressed during mouse ES cell differentiation and correlates with decreased pluripotency of such cells. We show that 5T4 antigen is transiently unregulated during HES4 and H1 human ES cell differentiation and its expression correlates with loss of the pluripotent markers OCT-4 and Tra-1-60 and upregulation of transcript markers associated with the three primary germ layers. To confirm that absence of cell surface 5T4 antigen represents a pluripotent hES cell phenotype, we performed mechanical transfer of either 5T4-ve or 5T4+ve HES4 colonies identified using live cell staining. 5T4-ve transfers maintained expression of OCT-4 in over 90% of resultant colonies, whereas 5T4+ve transfers exhibited significantly lower numbers of OCT-4-expressing colonies (92 +/- 1.4 vs. 2.9 +/- 2.0%). Interestingly, low cell density 5T4-ve colony transfers exhibited increased numbers of OCT-4-expressing colonies compared to large 5T4-ve transfers (92 +/- 1.4 vs. 63.2 +/- 1.9%). 5T4-ve and 5T4+ve HES4 and H1 ES cell lines expressed markers representative of neuroectoderm lineages, and we assessed the formation of neural lineages from these phenotypes in serum-containing medium and N2B27 medium. Expression of 5T4 was found to be inversely related to the yield of tyrosine-hydroxylase (TH+)-expressing neurons in N2B27 medium, with additional mesoderm and endoderm transcript markers detected. Homogeneous glial cell populations were derived from low cell density 5T4-ve colony transfers cultured in serum-containing medium, with TH+ neuronal formation inhibited in a cell-density-dependent manner. We conclude that the 5T4 antigen is a transient marker of hES cell differentiation and that 5T4 phenotype, colony seeding density and culture conditions significantly influence the maintenance of pluripotent hES cells and their differentiation to neural lineages.

Notch signaling is inactive but inducible in human embryonic stem cells

The NOTCH signaling pathway performs a wide range of critical functions in a number of different cell types during development and differentiation. The role of NOTCH signals in human embryonic stem cells (hESCs) has not been tested. We measured the activity of canonical NOTCH signaling in undifferentiated embryonic stem (ES) cells and tested the requirement for NOTCH activity in hESC self-renewal or differentiation by growing hESCs in the presence of gamma-secretase inhibitors. Our results suggest that NOTCH signaling is not required for the propagation of undifferentiated human ES cells but instead is required for the maintenance of the differentiating cell types that accumulate in human ES cell cultures. Our studies suggest that NOTCH signaling is not required in human embryonic differentiation until the formation of extraembryonic, germ layer, or tissue-specific stem cells and progenitors.

Proteomic analysis of neural differentiation of mouse embryonic stem cells

Mouse embryonic stem cells (mESCs) can differentiate into different types of cells, and serve as a good model system to study human embryonic stem cells (hESCs). We showed that mESCs differentiated into two types of neurons with different time courses. To determine the global protein expression changes after neural differentiation, we employed a proteomic strategy to analyze the differences between the proteomes of ES cells (E14) and neurons. Using 2-DE plus LC/MS/MS, we have generated proteome reference maps of E14 cells and derived dopaminergic neurons. Around 23 proteins with an increase or decrease in expression or phosphorylation after differentiation have been identified. We confirmed the downregulation of translationally controlled tumor protein (TCTP) and upregulation of alpha-tubulin by Western blotting. We also showed that TCTP was further downregulated in derived motor neurons than in dopaminergic neurons, and its expression level was independent of extracellular Ca(2+) concentration during neural differentiation. Potential roles of TCTP in modulating neural differentiation through binding to Ca(2+), tubulin and Na,K-ATPase, as well as the functional significance of regulation of other proteins such as actin-related protein 3 (Arp3) and Ran GTPase are discussed. This study demonstrates that proteomic tools are valuable in studying stem cell differentiation and elucidating the underlying molecular mechanisms.

Embryonic stem cells and cardiomyocyte differentiation: phenotypic and molecular analyses

Embryonic stem (ES) cell lines, derived from the inner cell mass (ICM) of blastocyst-stage embryos, are pluripotent and have a virtually unlimited capacity for self-renewal and differentiation into all cell types of an embryoproper. Both human and mouse ES cell lines are the subject of intensive investigation for potential applications in developmental biology and medicine. ES cells from both sources differentiate in vitro into cells of ecto-, endoand meso-dermal lineages, and robust cardiomyogenic differentiation is readily observed in spontaneously differentiating ES cells when cultured under appropriate conditions. Molecular, cellular and physiologic analyses demonstrate that ES cell-derived cardiomyocytes are functionally viable and that these cell derivatives exhibit characteristics typical of heart cells in early stages of cardiac development. Because terminal heart failure is characterized by a significant loss of cardiomyocytes, the use of human ES cell-derived progeny represents one possible source for cell transplantation therapies. With these issues in mind, this review will focus on the differentiation of pluripotent embryonic stem cells into cardiomyocytes as a developmental model, and the possible use of ES cell-derived cardiomyocytes as source of donor cells.

Overexpression of NANOG in human ES cells enables feeder-free growth while inducing primitive ectoderm features

Human embryonic stem cells (HESCs) are pluripotent cells derived from the ICM of blastocyst stage embryos. As the factors needed for their growth are largely undefined, they are propagated on feeder cells or with conditioned media from feeder cells. This is in contrast to mouse embryonic stem cells(MESCs) where addition of leukemia inhibitory factor (LIF) replaces the need for a feeder layer. Recently, the transcription factor Nanog was suggested to allow LIF and feeder-free growth of MESCs. Here, we show that NANOG overexpression in HESCs enables their propagation for multiple passages during which the cells remain pluripotent. NANOGoverexpressing cells form colonies efficiently even at a very low density, an ability lost upon excision of the transgene. Cells overexpressing NANOG downregulate expression of markers specific to the ICM and acquire expression of a marker specific to the primitive ectoderm (the consecutive pluripotent population in the embryo). Examination of global transcriptional changes upon NANOG overexpression by DNA microarray analysis reveals new markers suggested to discriminate between these populations. These results are significant in the understanding of self-renewal and pluripotency pathways in HESCs, and of their use for modeling early development in humans.

Fibroblast growth factor signaling in embryonic and cancer stem cells

Cancer stem cells are cancer cells that originate from the transformation of normal stem cells. The most important property of any stem cell is the ability to self-renew. Through this property, there are striking parallels between normal stem cells and cancer stem cells. Both cell types share various markers of "stemness". In particular, normal stem cells and cancer stem cells utilize similar molecular mechanisms to drive self-renewal, and similar signaling pathways may induce their differentiation. The fibroblast growth factor 2 (FGF-2) pathway is one of the most significant regulators of human embryonic stem cell (hESC) self-renewal and cancer cell tumorigenesis. Here we summarize recent data on the effects of FGF-2 and its receptors on hESCs and leukemic stem/progenitor cells. Also, we discuss the similarities of these findings with stem cell renewal and differentiation phenotypes.

Cytotrophoblast stem cell lines derived from human embryonic stem cells and their capacity to mimic invasive implantation events

BACKGROUND

An effective embryonic-maternal interaction is crucial for successful human pregnancy. Failure of this process is a major cause of infertility and can lead to placental dysfunction resulting in recurrent miscarriage, fetal retardation and pre-eclampsia. Research is severely constrained by ethical and practical considerations; therefore, we aimed to generate cytotrophoblast stem (CTBS) cell lines from human embryonic stem cells (HESCs).

METHOD

Beta-HCG was used as a marker of viable trophoblast cells. In defined culture, embryoid bodies were generated from HESCs and selected for trophoblast enrichment by rounds of cellular aggregation and disaggregation. Distinct CTBS cell lines were isolated and characterized. Spheroid cytotrophoblast bodies were generated and their interaction with luteal-phase endometrial stroma was analysed by real-time image analysis.

RESULTS

Three CTBS cell lines were derived, which were maintained in the absence of residual HESCs, fibroblast feeder cells or extracellular matrix. CTBS cells displayed typical cytotrophoblast and syncytiotrophoblast characteristics and exhibited further differentiation to invasive endovascular cell phenotype. One cell line was generated with constitutive expression of enhanced green fluorescent protein (eGFP). Spheroid trophoblast bodies mimicked closely the early invasive stages of implantation when incubated with human endometrial stromal preparations in vitro.

CONCLUSION

These human CTBS cell lines are a significant new model for investigating human placentation and may have considerable potential in cell therapy applications.

NTera2: a model system to study dopaminergic differentiation of human embryonic stem cells

NTera2, a human embryonal carcinoma (EC) stem cell line, shares many characteristics with human embryonic stem cells (hESCs). To determine whether NTera2 can serve as a useful surrogate for hESCs, we compared global gene expression between undifferentiated NTera2, multiple undifferentiated hESC cell lines, and their differentiated derivatives, and we showed that NTera2 cells share multiple markers with hESCs. Similar to hESCs, NTera2 cells differentiated into TH-positive cells that express dopaminergic markers including AADC, DAT, Nurr1, TrkB, TrkC, and GFRA1 when co-cultured with PA6 cells. Flow cytometry analysis showed that tyrosine hydroxylase (TH) and neural cell adhesion molecule (NCAM) expression increased, whereas SSEA4 expression decreased as cells differentiated. Medium conditioned by PA6 cells stimulated differentiation of NTera2 cells to generate TH-positive cells that expressed dopaminergic markers. Flow cytometry selected polysialylated (PSA-NCAM) cells responded to medium conditioned by PA6 cells by differentiating into TH-positive cells and expressed dopaminergic markers. Sorted cells differentiated for 4 weeks in PA6 cell conditioned media included functional neurons that responded to neurotransmitters and exhibited electronic excitability. Therefore, NTera2 cell dopaminergic neuronal differentiation and PSA-NCAM enrichment provides a useful system for the future study of hESCs.

Strategies for Developing Therapeutic Application of Human Embryonic Stem Cells

The ongoing debate on human embryonic stem cells (hESC) is fuelled by ethical concerns but also by the legitimate hope that hESC could one day be used for the cure of presently untreatable human diseases. Here we discuss current approaches to and constraints upon hESC differentiation and describe their potential application in clinical medicine.

TGFbeta inhibition of yolk-sac-like differentiation of human embryonic stem-cell-derived embryoid bodies illustrates differences between early mouse and human development

Transforming growth factor beta (TGFbeta) plays an important role in development and maintenance of murine yolk sac vascular development. Targeted deletions of Tgfb1 and other components of this signaling pathway, such as Acvrl1, Tgfbr1 and Tgfbr2, result in abnormal vascular development especially of the yolk sac, leading to embryonic lethality. There are significant differences between murine and primate development that limit interpretation of studies from mouse models. Thus, to examine the role of TGFbeta in early human vascular development we used the model of differentiating human embryonic stem cell-derived embryoid bodies to recapitulate early stages of embryonic development. TGFbeta was applied for different time frames after initiation of embryoid body cultures to assess its effect on differentiation. TGFbeta inhibited the expression of endodermal, endothelial and hematopoietic markers, which contrasts with findings in the mouse in which TGFbeta reduced the level of endodermal markers but increased endothelial marker expression. The inhibition observed was not due to changes in proliferation or apoptosis. This marked contrast between the two species may reflect the different origins of the yolk sac hemangiogenic lineages in mouse and human. TGFbeta effects on the hypoblast, from which these cell lineages are derived in human, would decrease subsequent differentiation of hematopoietic, endothelial and endodermal cells. By contrast, TGFbeta action on murine hypoblast, while affecting endoderm would not affect the hemangiogenic lineages that are epiblast-derived in the mouse. This study highlights important differences between early human and mouse embryonic development and suggests a role of TGFbeta in human hypoblast differentiation.

Activin/Nodal and FGF pathways cooperate to maintain pluripotency of human embryonic stem cells

Maintenance of pluripotency is crucial to the mammalian embryo's ability to generate the extra-embryonic and embryonic tissues that are needed for intrauterine survival and foetal development. The recent establishment of embryonic stem cells from human blastocysts (hESCs) provides an opportunity to identify the factors supporting pluripotency at early stages of human development. Using this in vitro model, we have recently shown that Nodal can block neuronal differentiation, suggesting that TGFbeta family members are involved in cell fate decisions of hESCs, including preservation of their pluripotency. Here, we report that Activin/Nodal signalling through Smad2/3 activation is necessary to maintain the pluripotent status of hESCs. Inhibition of Activin/Nodal signalling by follistatin and by overexpression of Lefty or Cerberus-Short, or by the Activin receptor inhibitor SB431542, precipitates hESC differentiation. Nevertheless, neither Nodal nor Activin is sufficient to sustain long-term hESC growth in a chemically defined medium without serum. Recent studies have shown that FGF2 can also maintain long-term expression of pluripotency markers, and we find that inhibition of the FGF signalling pathway by the tyrosine kinase inhibitor SU5402 causes hESC differentiation. However, this effect of FGF on hESC pluripotency depends on Activin/Nodal signalling, because it is blocked by SB431542. Finally, long-term maintenance of in-vitro pluripotency can be achieved with a combination of Activin or Nodal plus FGF2 in the absence of feeder-cell layers, conditioned medium or Serum Replacer. These findings suggest that the Activin/Nodal pathway maintains pluripotency through mechanism(s) in which FGF acts as a competence factor and therefore provide further evidence of distinct mechanisms for preservation of pluripotency in mouse and human ESCs.

Confinement and clearance of OCT4 in the porcine embryo at stereomicroscopically defined stages around gastrulation

In the areas of developmental biology and embryonic stem cell research, reliable molecular markers of pluripotency and early lineage commitment are sparse in large animal species. In this study, we present morphological and immunohistochemical findings on the porcine embryo in the period around gastrulation, days 8-17 postinsemination, introducing a stereomicroscopical staging system in this species. In embryos at the expanding hatched blastocyst stage, OCT4 is confined to the inner cell mass. Following detachment of the hypoblast, and formation of the embryonic disk, this marker of pluripotency was selectively observed in the epiblast. A prominent crescent-shaped thickening at the posterior region of the embryonic disk marked the first polarization within this structure reflecting incipient cell ingression. Following differentiation of the epiblast, clearance of OCT4 from the three germ layers was observed at defined stages, suggesting correlations to lineage specification. In the endoderm, clearance of OCT4 was apparent from early during its formation at the primitive streak stage. The endoderm harbored progenitors of the "fourth germ layer," the primordial germ cells (PGCs), the only cells maintaining expression of OCT4 at the end of gastrulation. In the ectodermal and mesodermal cell lineages, OCT4 became undetectable at the neural groove and somite stage, respectively. As in the mouse, PGCs showed onset of c-kit expression when located in extraembryonal compartments. They appeared to follow the endoderm during extraembryonal allocation and the mesoderm on return to the genital ridge.

Long-Term Proliferation of Human Embryonic Stem Cell-Derived Neuroepithelial Cells Using Defined Adherent Culture Conditions

Research on the cell fate determination of embryonic stem cells is of enormous interest given the therapeutic potential in regenerative cell therapy. Human embryonic stem cells (hESCs) have the ability to renew themselves and differentiate into all three germ layers. The main focus of this study was to examine factors affecting derivation and further proliferation of multipotent neuroepithelial (NEP) cells from hESCs. hESCs cultured in serum-deprived defined medium developed distinct tube structures and could be isolated either by dissociation or adherently. Dissociated cells survived to form colonies of cells characterized as NEP when conditioned medium from human hepatocellular carcinoma HepG2 cell line (MEDII) was added. However, cells isolated adherently developed an enriched population of NEP cells independent of MEDII medium. Further characterization suggested that they were NEP cells because they had a similar phenotype profile to in vivo NEP cells and expression SOX1, SOX2, and SOX3 genes. They were positive for Nestin, a neural intermediate filament protein, and Musashi-1, a neural RNA-binding protein, but few cells expressed further differentiation markers, such as PSNCAM, A2B5, MAPII, GFAP, or O4, or other lineage markers, such as muscle actin, alpha fetoprotein, or the pluripotent marker Oct4. Further differentiation of these putative NEP cells gave rise to a mixed population of progenitors that included A2B5-positive and PSNCAM-positive cells and postmitotic neurons and astrocytes. To proliferate and culture these derived NEP cells, ideal conditions were obtained using neurobasal medium supplemented with B27 and basic fibroblast growth factor in 5% oxygen. NEP cells were continuously propagated for longer than 6 months without losing their multipotent cell characteristics and maintained a stable chromosome number.

Are there morally acceptable alternatives to blastocyst derived ESC?

ESC derivation, use and SCNT have raised many moral and ethical issues. In this opinion piece I have focused on the argument that morally less ambiguous alternatives to ESC derived from the ICM of blastocysts exist. These possibilities range from using multiple adult stem cell populations each of which is uniquely suited for a particular disease target or identifying adult ESC-like populations, using transdifferentiated ESC-like cells or alternate methods of deriving ESC. I suggest that while it is important to support such efforts, current results do not provide sufficient compelling data to allow one to stop the use of ESC and perhaps adult cells will never be a reliable alternative. All options need to be fully explored and decisions need to be made with scientific rigor and respect for each individual's moral compass.