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

Utility of Lymphoblastoid Cell Lines for Induced Pluripotent Stem Cell Generation

A large number of EBV immortalized LCLs have been generated and maintained in genetic/epidemiological studies as a perpetual source of DNA and as a surrogate in vitro cell model. Recent successes in reprograming LCLs into iPSCs have paved the way for generating more relevant in vitro disease models using this existing bioresource. However, the overall reprogramming efficiency and success rate remain poor and very little is known about the mechanistic changes that take place at the transcriptome and cellular functional level during LCL-to-iPSC reprogramming. Here, we report a new optimized LCL-to-iPSC reprogramming protocol using episomal plasmids encoding pluripotency transcription factors and mouse p53DD (p53 carboxy-terminal dominant-negative fragment) and commercially available reprogramming media. We achieved a consistently high reprogramming efficiency and 100% success rate using this optimized protocol. Further, we investigated the transcriptional changes in mRNA and miRNA levels, using FC-abs ≥ 2.0 and FDR ≤ 0.05 cutoffs; 5,228 mRNAs and 77 miRNAs were differentially expressed during LCL-to-iPSC reprogramming. The functional enrichment analysis of the upregulated genes and activation of human pluripotency pathways in the reprogrammed iPSCs showed that the generated iPSCs possess transcriptional and functional profiles very similar to those of human ESCs.

Concise Review: Advances in Generating Hepatocytes from Pluripotent Stem Cells for Translational Medicine

The liver is one of the major organs in the human body. Severe or prolonged exposure of the liver to different factors may cause life-threatening disease, which necessitates donor organ transplantation. While orthotopic liver transplantation can be used to effectively treat liver failure, it is an invasive procedure, which is severely limited by organ donation. Therefore, alternative sources of liver support have been proposed and studied. This includes the use of pluripotent stem cell-derived hepatocytes as a renewable source of cells for therapy. In addition to cell-based therapies, in vitro engineered liver tissue provides powerful models for human drug discovery and disease modeling. This review focuses on the generation of hepatocyte-like cells from pluripotent stem cells and their application in translational medicine. Stem Cells 2016;34:1421-1426.

Capturing Identity and Fate Ex Vivo: Stem Cells from the Mouse Blastocyst

During mouse preimplantation development, three molecularly, morphologically, and spatially distinct lineages are formed, the embryonic epiblast, the extraembryonic primitive endoderm, and the trophectoderm. Stem cell lines representing each of these lineages have now been derived and can be indefinitely maintained and expanded in culture, providing an unlimited source of material to study the interplay of tissue-specific transcription factors and signaling pathways involved in these fundamental cell fate decisions. Here we outline our current understanding of the derivation, maintenance, and properties of these in vitro stem cell models representing the preimplantation embryonic lineages.

Stem Cell Surface Marker Expression Defines Late Stages of Reprogramming to Pluripotency in Human Fibroblasts

Our current understanding of the induction of pluripotency by defined factors indicates that this process occurs in discrete stages characterized by specific alterations in the cellular transcriptome and epigenome. However, the final phase of the reprogramming process is incompletely understood. We sought to generate tools to characterize the transition to a fully reprogramed state. We used combinations of stem cell surface markers to isolate colonies emerging after transfection of human fibroblasts with reprogramming factors and then analyzed their expression of genes associated with pluripotency and early germ lineage specification. We found that expression of a subset of these genes, including the cell-cell adhesion molecule CDH3, characterized a late stage in the reprogramming process. Combined live-cell staining with the antibody GCTM-2 and anti-CDH3 during reprogramming identified colonies of cells that showed gene expression patterns very similar to those of embryonic stem cell or established induced pluripotent stem cell lines, and gave rise to stable induced pluripotent stem cell lines at high frequency. Our findings will facilitate studies of the final stages of reprogramming of human cells to pluripotency and will provide a simple means for prospective identification of fully reprogrammed cells.

SIGNIFICANCE

Reprogramming of differentiated cells back to an embryonic pluripotent state has wide ranging applications in understanding and treating human disease. However, how cells traverse the barriers on the journey to pluripotency still is not fully understood. This report describes tools to study the late stages of cellular reprogramming. The findings enable a more precise approach to dissecting the final phases of conversion to pluripotency, a process that is particularly poorly defined. The results of this study also provide a simple new method for the selection of fully reprogrammed cells, which could enhance the efficiency of derivation of cell lines for research and therapy.

Capturing the ephemeral human pluripotent state

During human development, pluripotency is present only in early stages of development. This ephemeral cell potential can be captured in vitro by obtaining pluripotent stem cells (PSC) with self-renewal properties, the human embryonic stem cells (hESC). However, diverse studies suggest the existence of a plethora of human PSC (hPSC) that can be derived from both embryonic and somatic sources, depending on defined culture conditions, their spatial origin, and the genetic engineering used for reprogramming. This review will focus on hPSC, covering the conventional primed hESC, naïve-like hPSC that resemble the ground-state of development, region-selective PSC, and human induced PSC (hiPSC). We will analyze differences and similarities in their differentiation potential as well as in the molecular circuitry of pluripotency. Finally, we describe the need for human feeder cells to derive and maintain hPSC, because they could emulate the interaction of in vivo pluripotent cells with extraembryonic structures that support development. Developmental Dynamics 245:762-773, 2016. © 2016 Wiley Periodicals, Inc.

RISC-mediated control of selected chromatin regulators stabilizes ground state pluripotency of mouse embryonic stem cells

BACKGROUND

Embryonic stem cells are intrinsically unstable and differentiate spontaneously if they are not shielded from external stimuli. Although the nature of such instability is still controversial, growing evidence suggests that protein translation control may play a crucial role.

RESULTS

We performed an integrated analysis of RNA and proteins at the transition between naïve embryonic stem cells and cells primed to differentiate. During this transition, mRNAs coding for chromatin regulators are specifically released from translational inhibition mediated by RNA-induced silencing complex (RISC). This suggests that, prior to differentiation, the propensity of embryonic stem cells to change their epigenetic status is hampered by RNA interference. The expression of these chromatin regulators is reinstated following acute inactivation of RISC and it correlates with loss of stemness markers and activation of early cell differentiation markers in treated embryonic stem cells.

CONCLUSIONS

We propose that RISC-mediated inhibition of specific sets of chromatin regulators is a primary mechanism for preserving embryonic stem cell pluripotency while inhibiting the onset of embryonic developmental programs.

TGF-β and the TGF-β Family: Context-Dependent Roles in Cell and Tissue Physiology

The transforming growth factor-β (TGF-β) is the prototype of the TGF-β family of growth and differentiation factors, which is encoded by 33 genes in mammals and comprises homo- and heterodimers. This review introduces the reader to the TGF-β family with its complexity of names and biological activities. It also introduces TGF-β as the best-studied factor among the TGF-β family proteins, with its diversity of roles in the control of cell proliferation and differentiation, wound healing and immune system, and its key roles in pathology, for example, skeletal diseases, fibrosis, and cancer.

A Multi-Lineage Screen Reveals mTORC1 Inhibition Enhances Human Pluripotent Stem Cell Mesendoderm and Blood Progenitor Production

Human pluripotent stem cells (hPSCs) exist in heterogeneous micro-environments with multiple subpopulations, convoluting fate-regulation analysis. We patterned hPSCs into engineered micro-environments and screened responses to 400 small-molecule kinase inhibitors, measuring yield and purity outputs of undifferentiated, neuroectoderm, mesendoderm, and extra-embryonic populations. Enrichment analysis revealed mammalian target of rapamycin (mTOR) inhibition as a strong inducer of mesendoderm. Dose responses of mTOR inhibitors such as rapamycin synergized with Bone Morphogenetic protein 4 (BMP4) and activin A to enhance the yield and purity of BRACHYURY-expressing cells. Mechanistically, small interfering RNA knockdown of RAPTOR, a component of mTOR complex 1, phenocopied the mesendoderm-enhancing effects of rapamycin. Functional analysis during mesoderm and endoderm differentiation revealed that mTOR inhibition increased the output of hemogenic endothelial cells 3-fold, with a concomitant enhancement of blood colony-forming cells. These data demonstrate the power of our multi-lineage screening approach and identify mTOR signaling as a node in hPSC differentiation to mesendoderm and its derivatives.

Cellular and molecular aspects of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy that affects nearly 50,000 patients each year. The overall 5-year survival rate for this malignancy remains the lowest of any cancer at around 7% due to limited diagnostic methods, disease aggressiveness and a lack of targeted therapeutic interventions. This review highlights the successes achieved over the past several decades as well as the significant cellular and molecular hurdles that remain in combatting this deadly disease at a translational level.

What Kind of Signaling Maintains Pluripotency and Viability in Human-Induced Pluripotent Stem Cells Cultured on Laminin-511 with Serum-Free Medium?

Xeno-free medium contains no animal-derived components, but is composed of minimal growth factors and is serum free; the medium may be supplemented with insulin, transferrin, and selenium (ITS medium). Serum-free and xeno-free culture of human-induced pluripotent stem cells (hiPSCs) uses a variety of components based on ITS medium and Dulbecco's modified Eagle's medium/Ham's nutrient mixture F12 (DMEM/F12) that contain high levels of iron salt and glucose. Culture of hiPSCs also requires scaffolding materials, such as extracellular matrix, collagen, fibronectin, laminin, proteoglycan, and vitronectin. The scaffolding component laminin-511, which is composed of α5, β1, and γ1 chains, binds to α3β1, α6β1, and α6β4 integrins on the cell membrane to induce activation of the PI3K/AKT- and Ras/MAPK-dependent signaling pathways. In hiPSCs, the interaction of laminin-511/α6β1 integrin with the cell–cell adhesion molecule E-cadherin confers protection against apoptosis through the Ras homolog gene family member A (RhoA)/Rho kinase (ROCK) signaling pathway (the major pathways for cell death) and the proto-oncogene tyrosine-protein kinase Fyn (Fyn)-RhoA-ROCK signaling pathway. The expression levels of α6β1 integrin and E-cadherin on cell membranes are controlled through the activation of insulin receptor/insulin, FGF receptor/FGF2, or activin-like kinase 5 (ALK5)-dependent TGF-β signaling. A combination of growth factors, medium constituents, cell membrane-located E-cadherin, and α6β1 integrin-induced signaling is required for pluripotent cell proliferation and for optimal cell survival on a laminin-511 scaffold. In this review, we discuss and explore the influence of growth factors on the cadherin and integrin signaling pathways in serum-free and xeno-free cultures of hiPSCs during the preparation of products for regenerative medicinal therapies. In addition, we suggest the optimum serum-free medium components for use with laminin-511, a new scaffold for hiPSC culture.

Primary Cilium-Autophagy-Nrf2 (PAN) Axis Activation Commits Human Embryonic Stem Cells to a Neuroectoderm Fate

Under defined differentiation conditions, human embryonic stem cells (hESCs) can be directed toward a mesendoderm (ME) or neuroectoderm (NE) fate, the first decision during hESC differentiation. Coupled with lineage-specific G1 lengthening, a divergent ciliation pattern emerged within the first 24 hr of induced lineage specification, and these changes heralded a neuroectoderm decision before any neural precursor markers were expressed. By day 2, increased ciliation in NE precursors induced autophagy that resulted in the inactivation of Nrf2 and thereby relieved transcriptional activation of OCT4 and NANOG. Nrf2 binds directly to upstream regions of these pluripotency genes to promote their expression and repress NE derivation. Nrf2 suppression was sufficient to rescue poorly neurogenic iPSC lines. Only after these events had been initiated did neural precursor markers get expressed at day 4. Thus, we have identified a primary cilium-autophagy-Nrf2 (PAN) control axis coupled to cell-cycle progression that directs hESCs toward NE.

Dissecting microRNA-mediated regulation of stemness, reprogramming, and pluripotency

Increasing evidence indicates that microRNAs (miRNAs), endogenous short non-coding RNAs 19–24 nucleotides in length, play key regulatory roles in various biological events at the post-transcriptional level. Embryonic stem cells (ESCs) represent a valuable tool for disease modeling, drug discovery, developmental studies, and potential cell-based therapies in regenerative medicine due to their unlimited self-renewal and pluripotency. Therefore, remarkable progress has been made in recent decades toward understanding the expression and functions of specific miRNAs in the establishment and maintenance of pluripotency. Here, we summarize the recent knowledge regarding the regulatory roles of miRNAs in self-renewal of pluripotent ESCs and during cellular reprogramming, as well as the potential role of miRNAs in two distinct pluripotent states (naïve and primed).

Neural Conversion and Patterning of Human Pluripotent Stem Cells: A Developmental Perspective

Since the reprogramming of adult human terminally differentiated somatic cells into induced pluripotent stem cells (hiPSCs) became a reality in 2007, only eight years have passed. Yet over this relatively short period, myriad experiments have revolutionized previous stem cell dogmata. The tremendous promise of hiPSC technology for regenerative medicine has fuelled rising expectations from both the public and scientific communities alike. In order to effectively harness hiPSCs to uncover fundamental mechanisms of disease, it is imperative to first understand the developmental neurobiology underpinning their lineage restriction choices in order to predictably manipulate cell fate to desired derivatives. Significant progress in developmental biology provides an invaluable resource for rationalising directed differentiation of hiPSCs to cellular derivatives of the nervous system. In this paper we begin by reviewing core developmental concepts underlying neural induction in order to provide context for how such insights have guided reductionist in vitro models of neural conversion from hiPSCs. We then discuss early factors relevant in neural patterning, again drawing upon crucial knowledge gained from developmental neurobiological studies. We conclude by discussing open questions relating to these concepts and how their resolution might serve to strengthen the promise of pluripotent stem cells in regenerative medicine.

Endothelin-1 supports clonal derivation and expansion of cardiovascular progenitors derived from human embryonic stem cells

Coronary arteriogenesis is a central step in cardiogenesis, requiring coordinated generation and integration of endothelial cell and vascular smooth muscle cells. At present, it is unclear whether the cell fate programme of cardiac progenitors to generate complex muscular or vascular structures is entirely cell autonomous. Here we demonstrate the intrinsic ability of vascular progenitors to develop and self-organize into cardiac tissues by clonally isolating and expanding second heart field cardiovascular progenitors using WNT3A and endothelin-1 (EDN1) human recombinant proteins. Progenitor clones undergo long-term expansion and differentiate primarily into endothelial and smooth muscle cell lineages in vitro, and contribute extensively to coronary-like vessels in vivo, forming a functional human–mouse chimeric circulatory system. Our study identifies EDN1 as a key factor towards the generation and clonal derivation of ISL1⁺ vascular intermediates, and demonstrates the intrinsic cell-autonomous nature of these progenitors to differentiate and self-organize into functional vasculatures in vivo.

Understanding coronary vessels development provides basis for regenerative strategies. Here, Soh et al. identify endothelin-1 as a key molecule driving long-term expansion of ISL1⁺ bipotent vascular progenitors derived from human embryonic stem cells, and show that these cells can regenerate coronary vessels in mice.

Snapshots of Pluripotency

Pluripotency is a unique developmental state that lays the foundation upon which the entire embryo is built. Pluripotent cells possess the unique capacity to generate, in an exquisitely defined sequence, all the distinct cell types comprising the fetal and adult organism. The discovery of pluripotent stem cells and now the ability to generate them from differentiated cells has had a profound impact on a vast array of scientific disciplines. In addition to their clinical potential as a source of therapeutic cell types, pluripotent stem cells provide scalable access to otherwise experimentally inaccessible development- and disease-associated biology. Here I provide my perspective on the continuum of pluripotency in the early mammalian embryo. I also discuss how novel genomic technologies are now enabling the capture of molecular “snapshots” of the several distinct pluripotent states that stem cells undergo during this pivotal developmental period.

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Pluripotency is a developmental continuum

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Snapshots of pluripotency can be captured in derivative stem cell lines

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Two dominant attractor states of pluripotency can be maintained in vitro

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Synergistic studies of both states have provided a new understanding of development

Metaboloepigenetic Regulation of Pluripotent Stem Cells

The differentiation of pluripotent stem cells is associated with extensive changes in metabolism, as well as widespread remodeling of the epigenetic landscape. Epigenetic regulation is essential for the modulation of differentiation, being responsible for cell type specific gene expression patterns through the modification of DNA and histones, thereby establishing cell identity. Each cell type has its own idiosyncratic pattern regarding the use of specific metabolic pathways. Rather than simply being perceived as a means of generating ATP and building blocks for cell growth and division, cellular metabolism can directly influence cellular regulation and the epigenome. Consequently, the significance of nutrients and metabolites as regulators of differentiation is central to understanding how cells interact with their immediate environment. This review serves to integrate studies on pluripotent stem cell metabolism, and the regulation of DNA methylation and acetylation and identifies areas in which current knowledge is limited.

Generating Diverse Spinal Motor Neuron Subtypes from Human Pluripotent Stem Cells

Resolving the mechanisms underlying human neuronal diversification remains a major challenge in developmental and applied neurobiology. Motor neurons (MNs) represent a diverse pool of neuronal subtypes exhibiting differential vulnerability in different human neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA). The ability to predictably manipulate MN subtype lineage restriction from human pluripotent stem cells (PSCs) will form the essential basis to establishing accurate, clinically relevant in vitro disease models. I first overview motor neuron developmental biology to provide some context for reviewing recent studies interrogating pathways that influence the generation of MN diversity. I conclude that motor neurogenesis from PSCs provides a powerful reductionist model system to gain insight into the developmental logic of MN subtype diversification and serves more broadly as a leading exemplar of potential strategies to resolve the molecular basis of neuronal subclass differentiation within the nervous system. These studies will in turn permit greater mechanistic understanding of differential MN subtype vulnerability using in vitro human disease models.

Pluripotent Stem Cells: Current Understanding and Future Directions

Pluripotent stem cells have the ability to undergo self-renewal and to give rise to all cells of the tissues of the body. However, this definition has been recently complicated by the existence of distinct cellular states that display these features. Here, we provide a detailed overview of the family of pluripotent cell lines derived from early mouse and human embryos and compare them with induced pluripotent stem cells. Shared and distinct features of these cells are reported as additional hallmark of pluripotency, offering a comprehensive scenario of pluripotent stem cells.

Production of human pluripotent stem cell therapeutics under defined xeno-free conditions: progress and challenges

Recent advances on human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) have brought us closer to the realization of their clinical potential. Nonetheless, tissue engineering and regenerative medicine applications will require the generation of hPSC products well beyond the laboratory scale. This also mandates the production of hPSC therapeutics in fully-defined, xeno-free systems and in a reproducible manner. Toward this goal, we summarize current developments in defined media free of animal-derived components for hPSC culture. Bioinspired and synthetic extracellular matrices for the attachment, growth and differentiation of hPSCs are also reviewed. Given that most progress in xeno-free medium and substrate development has been demonstrated in two-dimensional rather than three dimensional culture systems, translation from the former to the latter poses unique difficulties. These challenges are discussed in the context of cultivation platforms of hPSCs as aggregates, on microcarriers or after encapsulation in biocompatible scaffolds.

Cell-based therapies of liver diseases: age-related challenges

The scope of this review is to revise recent advances of the cell-based therapies of liver diseases with an emphasis on cell donor's and patient's age. Regenerative medicine with cell-based technologies as its integral part is focused on the structural and functional restoration of tissues impaired by sickness or aging. Unlike drug-based medicine directed primarily at alleviation of symptoms, regenerative medicine offers a more holistic approach to disease and senescence management aimed to achieve restoration of homeostasis. Hepatocyte transplantation and organ engineering are very probable forthcoming options of liver disease treatment in people of different ages and vigorous research and technological innovations in this area are in progress. Accordingly, availability of sufficient amounts of functional human hepatocytes is crucial. Direct isolation of autologous hepatocytes from liver biopsy is problematic due to related discomfort and difficulties with further expansion of cells, particularly those derived from aging people. Allogeneic primary human hepatocytes meeting quality standards are also in short supply. Alternatively, autologous hepatocytes can be produced by reprogramming of differentiated cells through the stage of induced pluripotent stem cells. In addition, fibroblasts and mesenchymal stromal cells can be directly induced to undergo advanced stage hepatogenic differentiation. Reprogramming of cells derived from elderly people is accompanied by the reversal of age-associated changes at the cellular level manifesting itself by telomere elongation and the U-turn of DNA methylation. Cell reprogramming can provide high quality rejuvenated hepatocytes for cell therapy and liver tissue engineering. Further technological advancements and establishment of national and global registries of induced pluripotent stem cell lines homozygous for HLA haplotypes can allow industry-style production of livers for immunosuppression-free transplantation.

FGF, Insulin, and SMAD Signaling Cooperate for Avian Primordial Germ Cell Self-Renewal

Precise self-renewal of the germ cell lineage is fundamental to fertility and reproductive success. The early precursors for the germ lineage, primordial germ cells (PGCs), survive and proliferate in several embryonic locations during their migration to the embryonic gonad. By elucidating the active signaling pathways in migratory PGCs in vivo, we were able to create culture conditions that recapitulate this embryonic germ cell environment. In defined medium conditions without feeder cells, the growth factors FGF2, insulin, and Activin A, signaling through their cognate-signaling pathways, were sufficient for self-renewal of germline-competent PGCs. Forced expression of constitutively active MEK1, AKT, and SMAD3 proteins could replace their respective upstream growth factors. Unexpectedly, we found that BMP4 could replace Activin A in non-clonal growth conditions. These defined medium conditions identify the key molecular pathways required for PGC self-renewal and will facilitate efforts in biobanking of chicken genetic resources and genome editing.

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Avian primordial germ cell self-renewal is dependent on FGF2, insulin, and Activin A molecules

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BMP4 can replace Activin A in non-clonal growth conditions

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Defined culture medium conditions will facilitate studies of germ cell self-renewal in other vertebrate species

Variations in Glycogen Synthesis in Human Pluripotent Stem Cells with Altered Pluripotent States

Human pluripotent stem cells (hPSCs) represent very promising resources for cell-based regenerative medicine. It is essential to determine the biological implications of some fundamental physiological processes (such as glycogen metabolism) in these stem cells. In this report, we employ electron, immunofluorescence microscopy, and biochemical methods to study glycogen synthesis in hPSCs. Our results indicate that there is a high level of glycogen synthesis (0.28 to 0.62 μg/μg proteins) in undifferentiated human embryonic stem cells (hESCs) compared with the glycogen levels (0 to 0.25 μg/μg proteins) reported in human cancer cell lines. Moreover, we found that glycogen synthesis was regulated by bone morphogenetic protein 4 (BMP-4) and the glycogen synthase kinase 3 (GSK-3) pathway. Our observation of glycogen bodies and sustained expression of the pluripotent factor Oct-4 mediated by the potent GSK-3 inhibitor CHIR-99021 reveals an altered pluripotent state in hPSC culture. We further confirmed glycogen variations under different naïve pluripotent cell growth conditions based on the addition of the GSK-3 inhibitor BIO. Our data suggest that primed hPSCs treated with naïve growth conditions acquire altered pluripotent states, similar to those naïve-like hPSCs, with increased glycogen synthesis. Furthermore, we found that suppression of phosphorylated glycogen synthase was an underlying mechanism responsible for altered glycogen synthesis. Thus, our novel findings regarding the dynamic changes in glycogen metabolism provide new markers to assess the energetic and various pluripotent states in hPSCs. The components of glycogen metabolic pathways offer new assays to delineate previously unrecognized properties of hPSCs under different growth conditions.

Pluripotent Stem Cells from Domesticated Mammals

This review deals with the latest advances in the study of embryonic stem cells (ESC) and induced pluripotent stem cells (iPSC) from domesticated species, with a focus on pigs, cattle, sheep, goats, horses, cats, and dogs. Whereas the derivation of fully pluripotent ESC from these species has proved slow, reprogramming of somatic cells to iPSC has been more straightforward. However, most of these iPSC depend on the continued expression of the introduced transgenes, a major drawback to their utility. The persistent failure in generating ESC and the dependency of iPSC on ectopic genes probably stem from an inability to maintain the stability of the endogenous gene networks necessary to maintain pluripotency. Based on work in humans and rodents, achievement of full pluripotency will likely require fine adjustments in the growth factors and signaling inhibitors provided to the cells. Finally, we discuss the future utility of these cells for biomedical and agricultural purposes.

Canonical and noncanonical Wnt signaling in neural stem/progenitor cells

The first mammalian Wnt to be discovered, Wnt-1, was found to be essential for the development of a large part of the mouse brain over 25 years ago. We have since learned that Wnt family secreted glycolipoproteins, of which there are nineteen, which activate a diverse network of signals that are particularly important during embryonic development and tissue regeneration. Wnt signals in the developing and adult brain can drive neural stem cell self-renewal, expansion, asymmetric cell division, maturation and differentiation. The molecular events taking place after a Wnt binds to its cell-surface receptors are complex and, at times, controversial. A deeper understanding of these events is anticipated to lead to improvements in the treatment of neurodegenerative diseases and stem cell-based replacement therapies. Here, we review the roles played by Wnts in neural stem cells in the developing mouse brain, at neurogenic sites of the adult mouse and in neural stem cell culture models.

Replication Stress and Telomere Dysfunction Are Present in Cultured Human Embryonic Stem Cells

Replication stress causes DNA damage at fragile sites in the genome. DNA damage at telomeres can initiate breakage-fusion-bridge cycles and chromosome instability, which can result in replicative senescence or tumor formation. Little is known about the extent of replication stress or telomere dysfunction in human embryonic stem cells (hESCs). hESCs are grown in culture with the expectation of being used therapeutically in humans, making it important to minimize the levels of replication stress and telomere dysfunction. Here, the hESC line UCSF4 was cultured in a defined medium with growth factor Activin A, exogenous nucleosides, or DNA polymerase inhibitor aphidicolin. We used quantitative fluorescence in situ hybridization to analyze individual telomeres for dysfunction and observed that it can be increased by aphidicolin or Activin A. In contrast, adding exogenous nucleosides relieved dysfunction, suggesting that telomere dysfunction results from replication stress. Whether these findings can be applied to other hESC lines remains to be determined. However, because the loss of telomeres can lead to chromosome instability and cancer, we conclude that hESCs grown in culture for future therapeutic purposes should be routinely checked for replication stress and telomere dysfunction.

An in vitro gastrulation model recapitulates the morphogenetic impact of pharmacological inhibitors of developmental signaling pathways

Certain chemical agents act as teratogens, causing birth defects and fetal deaths when pregnant women are exposed to them. The establishment of in vitro models that recapitulate crucial embryonic events is therefore vital to facilitate screening of potential teratogens. Previously, we created a three-dimensional culture method for mouse P19C5 embryonal carcinoma stem cells that, when cultured as embryoid bodies, display elongation morphogenesis resembling gastrulation, which is the critical event resulting in the germ layers and major body axes. Determination of how well this in vitro morphogenesis represents in vivo gastrulation is essential to assess its applicability as well as to identify limitations of the model for detecting teratogenic agents. Here, we investigated the morphological and molecular characteristics of P19C5 morphogenesis using pharmacological agents that are known to cause abnormal patterning in the embryo in vivo by inhibiting major developmental signaling--e.g., involving Wnt, Nodal, Bone morphogenic protein (Bmp), Fibroblast growth factor (Fgf), Retinoic acid, Notch, and Hedgehog pathways. Inhibitors of Wnt, Nodal, Bmp, Fgf, and Retinoic acid signaling caused distinct changes in P19C5 morphogenesis that were quantifiable using morphometric parameters. These five inhibitors, plus the Notch inhibitor, also altered temporal expression profiles of developmental regulator genes in a manner consistent with the in vivo roles of the corresponding signaling pathways. In contrast, the Hedgehog inhibitor did not have any impact on the process, suggesting an absence of active Hedgehog signaling in these embryoid bodies. These results indicate that the P19C5 in vitro gastrulation model is a promising tool to screen for teratogenic agents that interfere with many of the key developmental signals.

MSX2 mediates entry of human pluripotent stem cells into mesendoderm by simultaneously suppressing SOX2 and activating NODAL signaling

How BMP signaling integrates into and destabilizes the pluripotency circuitry of human pluripotent stem cells (hPSCs) to initiate differentiation into individual germ layers is a long-standing puzzle. Here we report muscle segment homeobox 2 (MSX2), a homeobox transcription factor of msh family, as a direct target gene of BMP signaling and a master mediator of hPSCs' differentiation to mesendoderm. Enforced expression of MSX2 suffices to abolish pluripotency and induce directed mesendoderm differentiation of hPSCs, while MSX2 depletion impairs mesendoderm induction. MSX2 is a direct target gene of the BMP pathway in hPSCs, and can be synergistically activated by Wnt signals via LEF1 during mesendoderm induction. Furthermore, MSX2 destabilizes the pluripotency circuitry through direct binding to the SOX2 promoter and repression of SOX2 transcription, while MSX2 controls mesendoderm lineage commitment by simultaneous suppression of SOX2 and induction of NODAL expression through direct binding and activation of the Nodal promoter. Interestingly, SOX2 can promote the degradation of MSX2 protein, suggesting a mutual antagonism between the two lineage-specifying factors in the control of stem cell fate. Together, our findings reveal crucial new mechanisms of destabilizing pluripotency and directing lineage commitment in hPSCs.

MSX2 mediates entry of human pluripotent stem cells into mesendoderm by simultaneously suppressing SOX2 and activating NODAL signaling

How BMP signaling integrates into and destabilizes the pluripotency circuitry of human pluripotent stem cells (hPSCs) to initiate differentiation into individual germ layers is a long-standing puzzle. Here we report muscle segment homeobox 2 (MSX2), a homeobox transcription factor of msh family, as a direct target gene of BMP signaling and a master mediator of hPSCs' differentiation to mesendoderm. Enforced expression of MSX2 suffices to abolish pluripotency and induce directed mesendoderm differentiation of hPSCs, while MSX2 depletion impairs mesendoderm induction. MSX2 is a direct target gene of the BMP pathway in hPSCs, and can be synergistically activated by Wnt signals via LEF1 during mesendoderm induction. Furthermore, MSX2 destabilizes the pluripotency circuitry through direct binding to the SOX2 promoter and repression of SOX2 transcription, while MSX2 controls mesendoderm lineage commitment by simultaneous suppression of SOX2 and induction of NODAL expression through direct binding and activation of the Nodal promoter. Interestingly, SOX2 can promote the degradation of MSX2 protein, suggesting a mutual antagonism between the two lineage-specifying factors in the control of stem cell fate. Together, our findings reveal crucial new mechanisms of destabilizing pluripotency and directing lineage commitment in hPSCs.

ProNodal acts via FGFR3 to govern duration of Shh expression in the prechordal mesoderm

The secreted glycoprotein sonic hedgehog (Shh) is expressed in the prechordal mesoderm, where it plays a crucial role in induction and patterning of the ventral forebrain. Currently little is known about how Shh is regulated in prechordal tissue. Here we show that in the embryonic chick, Shh is expressed transiently in prechordal mesoderm, and is governed by unprocessed Nodal. Exposure of prechordal mesoderm microcultures to Nodal-conditioned medium, the Nodal inhibitor CerS, or to an ALK4/5/7 inhibitor reveals that Nodal is required to maintain both Shh and Gsc expression, but whereas Gsc is largely maintained through canonical signalling, Nodal signals through a non-canonical route to maintain Shh. Further, Shh expression can be maintained by a recombinant Nodal cleavage mutant, proNodal, but not by purified mature Nodal. A number of lines of evidence suggest that proNodal acts via FGFR3. ProNodal and FGFR3 co-immunoprecipitate and proNodal increases FGFR3 tyrosine phosphorylation. In microcultures, soluble FGFR3 abolishes Shh without affecting Gsc expression. Further, prechordal mesoderm cells in which Fgfr3 expression is reduced by Fgfr3 siRNA fail to bind to proNodal. Finally, targeted electroporation of Fgfr3 siRNA to prechordal mesoderm in vivo results in premature Shh downregulation without affecting Gsc. We report an inverse correlation between proNodal-FGFR3 signalling and pSmad1/5/8, and show that proNodal-FGFR3 signalling antagonises BMP-mediated pSmad1/5/8 signalling, which is poised to downregulate Shh. Our studies suggest that proNodal/FGFR3 signalling governs Shh duration by repressing canonical BMP signalling, and that local BMPs rapidly silence Shh once endogenous Nodal-FGFR3 signalling is downregulated.

Highlighted article: In the chick prechordal mesoderm, the Nodal precursor proNodal acts via a non-canonical route to inhibit BMP signalling and thus maintain Shh expression

LIF signaling in stem cells and development

Leukemia inhibitory factor (LIF) is a member of the interleukin-6 (IL-6) cytokine family. All members of this family activate signal transducer and activator of transcription 3 (STAT3), a transcription factor that influences stem and progenitor cell identity, proliferation and cytoprotection. The role of LIF in development was first identified when LIF was demonstrated to support the propagation of mouse embryonic stem cells. Subsequent studies of mice deficient for components of the LIF pathway have revealed important roles for LIF signaling during development and homeostasis. Here and in the accompanying poster, we provide a broad overview of JAK-STAT signaling during development, with a specific focus on LIF-mediated JAK-STAT3 activation.

Enhanced Reprogramming Efficiency and Kinetics of Induced Pluripotent Stem Cells Derived from Human Duchenne Muscular Dystrophy

The generation of disease-specific induced pluripotent stem cells (iPSCs) holds a great promise for understanding disease mechanisms and for drug screening. Recently, patient-derived iPSCs, containing identical genetic anomalies of the patient, have offered a breakthrough approach to studying Duchenne muscular dystrophy (DMD), a fatal disease caused by the mutation in the dystrophin gene. However, development of scalable and high fidelity DMD-iPSCs is hampered by low reprogramming efficiency, the addition of expensive growth factors and slow kinetics of disease-specific fibroblasts. Here, we show an efficient generation of DMD-iPSCs on bFGF secreting human foreskin fibroblast feeders (I-HFF) by employing single polycistronic lentiviral vector for delivering of transcription factors to DMD patient-specific fibroblast cells. Using this method, DMD-iPSCs generated on I-HFF feeders displayed pluripotent characteristics and disease genotype with improved reprogramming efficiency and kinetics over to mouse feeders. Moreover, we were able to maintain disease-specific iPSCs without additional supplementation of bFGF on I-HFF feeders. Our findings offer improvements in the generation of DMD-iPSCs and will facilitate in understanding of pathological mechanisms and screening of safer drugs for clinical intervention. Key Words: Duchenne Muscular Dystrophy, Reprogramming, Induced pluripotent Stem Cells, Immortalized Human Feeder, Basic Fibroblast Growth Factor, Stem Cell Cassette

Choice of Feeders Is Important When First Establishing iPSCs Derived From Primarily Cultured Human Deciduous Tooth Dental Pulp Cells

Feeder cells are generally required to maintain embryonic stem cells (ESCs)/induced pluripotent stem cells (iPSCs). Mouse embryonic fibroblasts (MEFs) isolated from fetuses and STO mouse stromal cell line are the most widely used feeder cells. The aim of this study was to determine which cells are suitable for establishing iPSCs from human deciduous tooth dental pulp cells (HDDPCs). Primary cultures of HDDPCs were cotransfected with three plasmids containing human OCT3/4, SOX2/KLF4, or LMYC/LIN28 and pmaxGFP by using a novel electroporation method, and then cultured in an ESC qualified medium for 15 days. Emerging colonies were reseeded onto mitomycin C-treated MEFs or STO cells. The colonies were serially passaged for up to 26 passages. During this period, colony morphology was assessed to determine whether cells exhibited ESC-like morphology and alkaline phosphatase activity to evaluate the state of cellular reprogramming. HDDPCs maintained on MEFs were successfully reprogrammed into iPSCs, whereas those maintained on STO cells were not. Once established, the iPSCs were maintained on STO cells without loss of pluripotency. Our results indicate that MEFs are better feeder cells than STO cells for establishing iPSCs. Feeder choice is a key factor enabling efficient generation of iPSCs.

Defining the three cell lineages of the human blastocyst by single-cell RNA-seq

Here, we provide fundamental insights into early human development by single-cell RNA-sequencing of human and mouse preimplantation embryos. We elucidate conserved transcriptional programs along with those that are human specific. Importantly, we validate our RNA-sequencing findings at the protein level, which further reveals differences in human and mouse embryo gene expression. For example, we identify several genes exclusively expressed in the human pluripotent epiblast, including the transcription factor KLF17. Key components of the TGF-β signalling pathway, including NODAL, GDF3, TGFBR1/ALK5, LEFTY1, SMAD2, SMAD4 and TDGF1, are also enriched in the human epiblast. Intriguingly, inhibition of TGF-β signalling abrogates NANOG expression in human epiblast cells, consistent with a requirement for this pathway in pluripotency. Although the key trophectoderm factors Id2, Elf5 and Eomes are exclusively localized to this lineage in the mouse, the human orthologues are either absent or expressed in alternative lineages. Importantly, we also identify genes with conserved expression dynamics, including Foxa2/FOXA2, which we show is restricted to the primitive endoderm in both human and mouse embryos. Comparison of the human epiblast to existing embryonic stem cells (hESCs) reveals conservation of pluripotency but also additional pathways more enriched in hESCs. Our analysis highlights significant differences in human preimplantation development compared with mouse and provides a molecular blueprint to understand human embryogenesis and its relationship to stem cells.

Summary: Single-cell RNA-sequencing of human and mouse embryos reveals conserved and human-specific transcriptional programmes as well as a functional requirement for TGFβ signalling in human embryos.

Optimization of Buffalo (Bubalus bubalis) Embryonic Stem Cell Culture System

OBJECTIVE

In order to retain an undifferentiated pluripotent state, embryonic stem (ES) cells have to be cultured on feeder cell layers. However, use of feeder layers limits stem cell research, since experimental data may result from a combined ES cell and feeder cell response to various stimuli.

MATERIALS AND METHODS

In this experimental study, a buffalo ES cell line was established from in vitro derived blastocysts and characterized by the Alkaline phosphatase (AP) and immunoflourescence staining of various pluripotency markers. We examined the effect of various factors like fibroblast growth factor 2 (FGF-2), leukemia inhibitory factor (LIF) and Y-27632 to support the growth and maintenance of bubaline ES cells on gelatin coated dishes, in order to establish feeder free culture systems. We also analyzed the effect of feeder-conditioned media on stem cell growth in gelatin based cultures both in the presence as well as in the absence of the growth factors.

RESULTS

The results showed that Y-27632, in the presence of FGF-2 and LIF, resulted in higher colony growth and increased expression of Nanog gene. Feeder-Conditioned Medium resulted in a significant increase in growth of buffalo ES cells on gelatin coated plates, however, feeder layer based cultures produced better results than gelatin based cultures. Feeder layers from buffalo fetal fibroblast cells can support buffalo ES cells for more than two years.

CONCLUSION

We developed a feeder free culture system that can maintain buffalo ES cells in the short term, as well as feeder layer based culture that can support the long term maintenance of buffalo ES cells.

Reinforcement of STAT3 activity reprogrammes human embryonic stem cells to naive-like pluripotency

Leukemia inhibitory factor (LIF)/STAT3 signalling is a hallmark of naive pluripotency in rodent pluripotent stem cells (PSCs), whereas fibroblast growth factor (FGF)-2 and activin/nodal signalling is required to sustain self-renewal of human PSCs in a condition referred to as the primed state. It is unknown why LIF/STAT3 signalling alone fails to sustain pluripotency in human PSCs. Here we show that the forced expression of the hormone-dependent STAT3-ER (ER, ligand-binding domain of the human oestrogen receptor) in combination with 2i/LIF and tamoxifen allows human PSCs to escape from the primed state and enter a state characterized by the activation of STAT3 target genes and long-term self-renewal in FGF2- and feeder-free conditions. These cells acquire growth properties, a gene expression profile and an epigenetic landscape closer to those described in mouse naive PSCs. Together, these results show that temporarily increasing STAT3 activity is sufficient to reprogramme human PSCs to naive-like pluripotent cells.

LIF/STAT3 signalling characterizes naive pluripotency in mouse embryonic stem cells (ESCs), but whether this pathway can sustain a similar state in human cells is not completely understood. Here the authors show that LIF stimulation and enhancement of STAT3 activity allow human ESCs to escape from FGF2 dependency and facilitates their entry into a naive-like state of pluripotency.

IER3 Promotes Expansion of Adipose Progenitor Cells in Response to Changes in Distinct Microenvironmental Effectors

Adipose tissue expansion is well-orchestrated to fulfill the energy demand. It results from adipocyte hypertrophy and hyperplasia due to adipose progenitor cell (APC) expansion and differentiation. Chronic low grade inflammation and hypoxia take place in obese adipose tissue microenvironment. Both of these events were shown to impact the APC pool by promoting increased self-renewal along with a decrease in the APC differentiation potential. However, no common target has been identified so far. Here we show that the immediate early response 3 gene (IER3) is preferentially expressed in APCs and is essential for APC proliferation and self-renewal. Experiments based on RNA interference revealed that impairing IER3 expression altered cell proliferation through ERK1/2 phosphorylation and clonogenicity. IER3 expression was induced by Activin A, which plays a crucial role in adipocyte differentiation as well as by a decrease in oxygen tension through HIF1-induced transcriptional activation. Interestingly, high levels of IER3 were detected in native APCs (CD34+/CD31- cells) isolated from obese patients and conditioned media from obese adipose tissue-macrophages stimulated its expression. Overall, these results indicate that IER3 is a key player in expanding the pool of APC while highlighting the role of distinct effectors found in an obese microenvironment in this process.

Synergistic effects of FGF-2 and Activin A on early neural differentiation of human pluripotent stem cells

Neural differentiation is an important target of human embryonic stem cells, which provide a source for cell-based therapy, developmental biology, and pharmaceutical research. Previous studies revealed that inhibition of the bone morphogenetic protein is required for neural induction from human embryonic stem cells. On the contrary, the functions of fibroblast growth factors and Activin/Nodal signaling are controversial. Fibroblast growth factor-2 and Activin/Nodal pathways exert divergent influences on human embryonic stem cell concerning the maintenance of both pluripotency and cellular differentiation. We hypothesized that the combination of fibroblast growth factor-2 and Activin A at various concentrations synergistically exerts diverse effects on cell differentiation. To determine the effects of fibroblast growth factor-2 and Activin A on cellular differentiation into neural lineages, we examined the expression of neural differentiation markers in human embryonic stem cells treated with fibroblast growth factor-2 and/or Activin A at various concentrations in a growth factor-defined serum-free medium in short-term culture. In this study, we provide evidence that fibroblast growth factor-2 and Activin A synergistically regulated the initiation of human embryonic stem cell differentiation into neural cell lineages even though human embryonic stem cells autonomously differentiate into neural cell lineages.

Pluripotent and Metabolic Features of Two Types of Porcine iPSCs Derived from Defined Mouse and Human ES Cell Culture Conditions

The domestic pig is an excellent animal model for stem cell research and clinical medicine. There is still no suitable culture condition to generate authentic porcine embryonic stem cells (pESCs) and high quality porcine induced pluripotent stem cells (piPSCs). In this study, we found that culture conditions affected pluripotent and metabolic features of piPSCs. Using defined human embryonic stem cell (hESC) and mouse ESC (mESC) culture conditions, we generated two types of piPSCs, one of which was morphologically similar to hESCs (here called hpiPSCs), the other resembled mESCs (here called mpiPSCs). Transcriptome analysis and signaling pathway inhibition results suggested that mpiPSCs shared more of mESC signaling pathways, such as the BMP pathway and JAK/STAT pathway and hpiPSCs shared more hESC signaling pathways, such as the FGF pathway. Importantly, the mpiPSCs performed embryonic chimera incorporation more efficiently than the hpiPSCs did. In addition, the mpiPSCs showed mitochondrial features of naive ESCs and lipid droplets accumulation. These evidences may facilitate understanding of the gene regulation network and metabolism in piPSCs and promote derivation of bona fide pESCs for translational medicine.

Rotary suspension culture enhances mesendoderm differentiation of embryonic stem cells through modulation of Wnt/β-catenin pathway

Recently, physical factors in the local cellular microenvironment have been confirmed with strong influences on regulating stem cell fate. Despite the recent identification of the rotary cell culture system (RCCS) as a bioreactor for culturing stem cells, the underlying biological role provided by RCCS in the lineage differentiation of embryonic stem cells (ESCs) remains largely undefined. Here, we explored the embryoid body (EB) formation and subsequent differentiation of mouse ESCs in RCCS. We demonstrated that EBs formed in RCCS were more homogeneous and bigger in size compared with those in the static condition. Further, we determined that mesendoderm differentiation was prominently enhanced, while neuroectodermal differentiation was significantly suppressed in RCCS. Surprisingly, we found that Wnt/β-catenin signaling was greatly enhanced mainly due to the increased expression of Wnt3 during ESC differentiation in RCCS. Inhibition of Wnt/β-catenin signaling by DKK1 decreased the expression of Brachyury and attenuated mesendoderm differentiation in RCCS. Intriguingly, Wnt3a markedly increased Brachyury expression under static condition rather than in RCCS. Taken together, our findings uncover a new role of rotary suspension culture in initializing the early differentiation of ESCs.

Response to Nodal morphogen gradient is determined by the kinetics of target gene induction

Morphogen gradients expose cells to different signal concentrations and induce target genes with different ranges of expression. To determine how the Nodal morphogen gradient induces distinct gene expression patterns during zebrafish embryogenesis, we measured the activation dynamics of the signal transducer Smad2 and the expression kinetics of long- and short-range target genes. We found that threshold models based on ligand concentration are insufficient to predict the response of target genes. Instead, morphogen interpretation is shaped by the kinetics of target gene induction: the higher the rate of transcription and the earlier the onset of induction, the greater the spatial range of expression. Thus, the timing and magnitude of target gene expression can be used to modulate the range of expression and diversify the response to morphogen gradients.

DOI:http://dx.doi.org/10.7554/eLife.05042.001

How a cell can tell where it is in a developing embryo has fascinated scientists for decades. The pioneering computer scientist and mathematical biologist Alan Turing was the first person to coin the term ‘morphogen’ to describe a protein that provides information about locations in the body. A morphogen is released from a group of cells (called the ‘source’) and as it moves away its activity (called the ‘signal’) declines gradually. Cells sense this signal gradient and use it to detect their position with respect to the source. Nodal is an important morphogen and is required to establish the correct identity of cells in the embryo; for example, it helps determine which cells should become a brain or heart or gut cell and so on.

The zebrafish is a widely used model to study animal development, in part because its embryos are transparent; this allows cells and proteins to be easily observed under a microscope. When Nodal acts on cells, another protein called Smad2 becomes activated, moves into the cell's nucleus, and then binds to specific genes. This triggers the expression of these genes, which are first copied into mRNA molecules via a process known as transcription and are then translated into proteins. The protein products of these targeted genes control cell identity and movement.

Several models have been proposed to explain how different concentrations of Nodal switch on the expression of different target genes; that is to say, to explain how a cell interprets the Nodal gradient. Dubrulle et al. have now measured factors that underlie how this gradient is interpreted. Individual cells in zebrafish embryos were tracked under a microscope, and Smad2 activation and gene expression were assessed. Dubrulle et al. found that, in contradiction to previous models, the amount of Nodal present on its own was insufficient to predict the target gene response. Instead, their analysis suggests that the size of each target gene's response depends on its rate of transcription and how quickly it is first expressed in response to Nodal.

These findings of Dubrulle et al. suggest that timing and transcription rate are important in determining the appropriate response to Nodal. Further work will be now needed to find out whether similar mechanisms regulate other processes that rely on the activity of morphogens.

DOI:http://dx.doi.org/10.7554/eLife.05042.002

Heightened potency of human pluripotent stem cell lines created by transient BMP4 exposure

Human pluripotent stem cells (PSCs) show epiblast-type pluripotency that is maintained with ACTIVIN/FGF2 signaling. Here, we report the acquisition of a unique stem cell phenotype by both human ES cells (hESCs) and induced pluripotent stem cells (iPSCs) in response to transient (24-36 h) exposure to bone morphogenetic protein 4 (BMP4) plus inhibitors of ACTIVIN signaling (A83-01) and FGF2 (PD173074), followed by trypsin dissociation and recovery of colonies capable of growing on a gelatin substratum in standard medium for human PSCs at low but not high FGF2 concentrations. The self-renewing cell lines stain weakly for CDX2 and strongly for NANOG, can be propagated clonally on either Matrigel or gelatin, and are morphologically distinct from human PSC progenitors on either substratum but still meet standard in vitro criteria for pluripotency. They form well-differentiated teratomas in immune-compromised mice that secrete human chorionic gonadotropin (hCG) into the host mouse and include small areas of trophoblast-like cells. The cells have a distinct transcriptome profile from the human PSCs from which they were derived (including higher expression of NANOG, LEFTY1, and LEFTY2). In nonconditioned medium lacking FGF2, the colonies spontaneously differentiated along multiple lineages, including trophoblast. They responded to PD173074 in the absence of both FGF2 and BMP4 by conversion to trophoblast, and especially syncytiotrophoblast, whereas an A83-01/PD173074 combination favored increased expression of HLA-G, a marker of extravillous trophoblast. Together, these data suggest that the cell lines exhibit totipotent potential and that BMP4 can prime human PSCs to a self-renewing alternative state permissive for trophoblast development. The results may have implications for regulation of lineage decisions in the early embryo.

A stable chimeric fibroblast growth factor (FGF) can successfully replace basic FGF in human pluripotent stem cell culture

Fibroblast growth factors (FGFs) are essential for maintaining self-renewal in human embryonic stem cells and induced pluripotent stem cells. Recombinant basic FGF (bFGF or FGF2) is conventionally used to culture pluripotent stem cells; however, because of the instability of bFGF, repeated addition of fresh bFGF into the culture medium is required in order to maintain its concentration. In this study, we demonstrate that a heat-stable chimeric variant of FGF, termed FGFC, can be successfully used for maintaining human pluripotent stem cells. FGFC is a chimeric protein composed of human FGF1 and FGF2 domains that exhibits higher thermal stability and protease resistance than do both FGF1 and FGF2. Both human embryonic stem cells and induced pluripotent stem cells were maintained in ordinary culture medium containing FGFC instead of FGF2. Comparison of cells grown in FGFC with those grown in conventional FGF2 media showed no significant differences in terms of the expression of pluripotency markers, global gene expression, karyotype, or differentiation potential in the three germ lineages. We therefore propose that FGFC may be an effective alternative to FGF2, for maintenance of human pluripotent stem cells.

Activin/nodal signaling and NANOG orchestrate human embryonic stem cell fate decisions by controlling the H3K4me3 chromatin mark

Stem cells can self-renew and differentiate into multiple cell types. These characteristics are maintained by the combination of specific signaling pathways and transcription factors that cooperate to establish a unique epigenetic state. Despite the broad interest of these mechanisms, the precise molecular controls by which extracellular signals organize epigenetic marks to confer multipotency remain to be uncovered. Here, we use human embryonic stem cells (hESCs) to show that the Activin-SMAD2/3 signaling pathway cooperates with the core pluripotency factor NANOG to recruit the DPY30-COMPASS histone modifiers onto key developmental genes. Functional studies demonstrate the importance of these interactions for correct histone 3 Lys4 trimethylation and also self-renewal and differentiation. Finally, genetic studies in mice show that Dpy30 is also necessary to maintain pluripotency in the pregastrulation embryo, thereby confirming the existence of similar regulations in vivo during early embryonic development. Our results reveal the mechanisms by which extracellular factors coordinate chromatin status and cell fate decisions in hESCs.