Directed induction of anterior and posterior primitive streak by Wnt from embryonic stem cells cultured in a chemically defined serum-free medium

Dependence of cell fate potential and cadherin switching on primitive streak coordinate during differentiation of human pluripotent stem cells

During gastrulation, the primitive streak (PS) forms and begins to differentiate into mesendodermal subtypes. This process involves an epithelial-mesenchymal transition (EMT), which is marked by cadherin switching, where E-Cadherin is downregulated, and N-Cadherin is upregulated. To understand the relationships between differentiation, EMT, and cadherin switching, we made measurements of these processes during differentiation of human pluripotent stem cells (hPSCs) to PS and subsequently to mesendoderm subtypes using established protocols, as well as variants in which signaling through key pathways including Activin, BMP, and Wnt were modulated. We found that perturbing signaling so that cells acquired identities ranging from anterior to posterior PS had little impact on the subsequent differentiation potential of cells but strongly impacted the degree of cadherin switching. The degree of E-Cadherin downregulation and N-Cadherin upregulation were uncorrelated and had different dependence on signaling. The exception to the broad potential of cells throughout the PS was the loss of definitive endoderm potential in cells with mid to posterior PS identities. Thus, cells induced to different PS coordinates had similar potential within the mesoderm but differed in cadherin switching. Consistently, E-Cadherin knockout did not alter cell fates outcomes during differentiation. Overall, cadherin switching and EMT are modulated independently of cell fate commitment in mesendodermal differentiation.

Complete suspension culture of human induced pluripotent stem cells supplemented with suppressors of spontaneous differentiation

Human induced pluripotent stem cells (hiPSCs) are promising resources for producing various types of tissues in regenerative medicine; however, the improvement in a scalable culture system that can precisely control the cellular status of hiPSCs is needed. Utilizing suspension culture without microcarriers or special materials allows for massive production, automation, cost-effectiveness, and safety assurance in industrialized regenerative medicine. Here, we found that hiPSCs cultured in suspension conditions with continuous agitation without microcarriers or extracellular matrix components were more prone to spontaneous differentiation than those cultured in conventional adherent conditions. Adding PKCβ and Wnt signaling pathway inhibitors in the suspension conditions suppressed the spontaneous differentiation of hiPSCs into ectoderm and mesendoderm, respectively. In these conditions, we successfully completed the culture processes of hiPSCs, including the generation of hiPSCs from peripheral blood mononuclear cells with the expansion of bulk population and single-cell sorted clones, long-term culture with robust self-renewal characteristics, single-cell cloning, direct cryopreservation from suspension culture and their successful recovery, and efficient mass production of a clinical-grade hiPSC line. Our results demonstrate that precise control of the cellular status in suspension culture conditions paves the way for their stable and automated clinical application.

Trisomy 12 compromises the mesendodermal differentiation propensity of human pluripotent stem cells

Trisomy 12 is one of the most frequent chromosomal abnormalities in cultured human pluripotent stem cells (hPSCs). Although potential oncogenic properties and augmented cell cycle caused by trisomy 12 have been reported, the consequences of trisomy 12 in terms of cell differentiation, which is the basis for regenerative medicine, drug development, and developmental biology studies, have not yet been investigated. Here, we report that trisomy 12 compromises the mesendodermal differentiation of hPSCs. We identified sublines of hPSCs carrying trisomy 12 after their prolonged culture. Transcriptome analysis revealed that these hPSC sublines carried abnormal gene expression patterns in specific signaling pathways in addition to cancer-related cell cycle pathways. These hPSC sublines showed a lower propensity for mesendodermal differentiation in embryoid bodies cultured in a serum-free medium. BMP4-induced exit from the self-renewal state was impaired in the trisomy 12 hPSC sublines, with less upregulation of key transcription factor gene expression. As a consequence, the differentiation efficiency of hematopoietic and hepatic lineages was also impaired in the trisomy 12 hPSC sublines. We reveal that trisomy 12 disrupts the genome-wide expression patterns that are required for proper mesendodermal differentiation.

Evaluation of the effect of boron derivatives on cardiac differentiation of mouse pluripotent stem cells

BACKGROUND

The heart is one of the first organs to form during embryonic development and has a very important place. So much that the formation of a functional heart is completed on the 55th day of human development and the 15th day of mouse development. Myocardial, endocardial and epicardial cells, which are derived from the mesoderm layer, are the cells that form the basis of the heart. Cardiac development, like other embryonic developments, is tightly controlled and regulated by various signaling pathways. The WNT signaling pathway is the most studied of these signaling pathways and the one with the clearest relationship with heart development. It is known that boron compounds and the Wnt/β-catenin pathway are highly correlated. Therefore, this study aimed to investigate the role of boron compounds in heart development as well as its effect on pluripotency of mouse embryonic stem cells for the first time in the literature.

METHODS

Toxicity of boron compounds was evaluated by using MTS analysis and obtained results were supported by morphological pictures, Trypan Blue staining and Annexin V staining. Additionally, the possible boron-related change in pluripotency of embryonic stem cells were analyzed with alkaline phosphatase activity and immunocytochemical staining of Oct4 protein as well as gene expression levels of pluripotency related OCT4, SOX2 and KLF4 genes. The alterations in the embryonic body formation capacity of mouse embryonic stem cells due to the application boron derivatives were also evaluated. Three linage differentiation was conducted to clarify the real impact of boron compounds on embryonic development. Lastly, cardiac differentiation of mESCs was investigated by using morphological pictures, cytosolic calcium measurement, gene expression and immunocytochemical analysis of cardiac differentiation related genes and in the presence of boron compounds.

RESULTS

Obtained results show that boron treatment maintains the pluripotency of embryonic stem cells at non-toxic concentrations. Additionally, endodermal, and mesodermal fate was found to be triggered after boron treatment. Also, initiation of cardiomyocyte differentiation by boron derivative treatments caused an increased gene expression levels of cardiac differentiation related TNNT2, Nkx2.5 and ISL-1 gene expression levels.

CONCLUSION

This study indicates that boron application, which is responsible for maintaining pluripotency of mESCs, can be used for increased cardiomyocyte differentiation of mESCs.

Lateral plate mesoderm cell-based organoid system for NK cell regeneration from human pluripotent stem cells

Human pluripotent stem cell (hPSC)-induced NK (iNK) cells are a source of off-the-shelf cell products for universal immune therapy. Conventional methods for iNK cell regeneration from hPSCs include embryoid body (EB) formation and feeder-based expansion steps, which are time-consuming and cause instability and high costs of manufacturing. Here, we develop an EB-free, organoid aggregate method for NK cell regeneration from hPSCs. In a short time-window of 27-day induction, millions of hPSC input can output over billions of iNK cells without the necessity of NK cell expansion feeders. The iNK cells highly express classical toxic granule proteins, apoptosis-inducing ligands, as well as abundant activating and inhibitory receptors. Functionally, the iNK cells eradicate human tumor cells via mechanisms of direct cytotoxicity, apoptosis, and antibody-dependent cellular cytotoxicity. This study provides a reliable scale-up method for regenerating human NK cells from hPSCs, which promotes the universal availability of NK cell products for immune therapy.

Environmentally relevant exposure to TBBPA and its analogues may not drastically affect human early cardiac development

Tetrabromobisphenol A (TBBPA) and its substitutes and derivatives have been widely used as halogenated flame retardants (HFRs), in the past few decades. As a consequence, these compounds are frequently detected in the environment, as well as human bodily fluids, especially umbilical cord blood and breast milk. This has raised awareness of their potential risks to fetuses and infants. In this study, we employed human embryonic stem cell differentiation models to assess the potential developmental toxicity of six TBBPA-like compounds, at human relevant nanomolar concentrations. To mimic early embryonic development, we utilized embryoid body-based 3D differentiation in presence of the six HFRs. Transcriptomics data showed that HFR exposure over 16 days of differentiation only interfered with the expression of a few genes, indicating those six HFRs may not have specific tissue/organ targets during embryonic development. Nevertheless, further analyses revealed that some cardiac-related genes were dysregulated. Since the heart is also the first organ to develop, we employed a cardiac differentiation model to analyze the six HFRs' potential developmental toxicity in more depth. Overall, HFRs of interest did not significantly disturb the canonical WNT pathway, which is an essential signal transduction pathway for cardiac development. In addition, the six HFRs showed only mild changes in gene expression levels for cardiomyocyte markers, such as NKX2.5, MYH7, and MYL4, as well as a significant down-regulation of some but not all the epicardial and smooth muscle cell markers selected. Taken together, our results show that the six studied HFRs, at human relevant concentrations, may impose negligible effects on embryogenesis and heart development. Nevertheless, higher exposure doses might affect the early stages of heart development.

Generation of pancreatic progenitors from human pluripotent stem cells by small molecules

Human pluripotent stem cell (hPSC)-derived pancreatic progenitors (PPs) provide promising cell therapies for type 1 diabetes. Current PP differentiation requires a high amount of Activin A during the definitive endoderm (DE) stage, making it economically difficult for commercial ventures. Here we identify a dose-dependent role for Wnt signaling in controlling DE differentiation without Activin A. While high-level Wnt activation induces mesodermal formation, low-level Wnt activation by a small-molecule inhibitor of glycogen synthase kinase 3 is sufficient for DE differentiation, yielding SOX17+FOXA2+ DE cells. BMP inhibition further enhances this DE differentiation, generating over 87% DE cells. These DE cells could be further differentiated into PPs and functional β cells. RNA-sequencing analysis of PP differentiation from hPSCs revealed expected transcriptome dynamics and new gene regulators during our small-molecule PP differentiation protocol. Overall, we established a robust growth-factor-free protocol for generating DE and PP cells, facilitating scalable production of pancreatic cells for regenerative applications.

Liver Organoids: Recent Developments, Limitations and Potential

Liver cell types derived from induced pluripotent stem cells (iPSCs) share the potential to investigate development, toxicity, as well as genetic and infectious disease in ways currently limited by the availability of primary tissue. With the added advantage of patient specificity, which can play a role in all of these areas. Many iPSC differentiation protocols focus on 3 dimensional (3D) or organotypic differentiation, as these offer the advantage of more closely mimicking in vivo systems including; the formation of tissue like architecture and interactions/crosstalk between different cell types. Ultimately such models have the potential to be used clinically and either with or more aptly, in place of animal models. Along with the development of organotypic and micro-tissue models, there will be a need to co-develop imaging technologies to enable their visualization. A variety of liver models termed "organoids" have been reported in the literature ranging from simple spheres or cysts of a single cell type, usually hepatocytes, to those containing multiple cell types combined during the differentiation process such as hepatic stellate cells, endothelial cells, and mesenchymal cells, often leading to an improved hepatic phenotype. These allow specific functions or readouts to be examined such as drug metabolism, protein secretion or an improved phenotype, but because of their relative simplicity they lack the flexibility and general applicability of ex vivo tissue culture. In the liver field these are more often constructed rather than developed together organotypically as seen in other organoid models such as brain, kidney, lung and intestine. Having access to organotypic liver like surrogates containing multiple cell types with in vivo like interactions/architecture, would provide vastly improved models for disease, toxicity and drug development, combining disciplines such as microfluidic chip technology with organoids and ultimately paving the way to new therapies.

Generation of craniofacial myogenic progenitor cells from human induced pluripotent stem cells for skeletal muscle tissue regeneration

Craniofacial skeletal muscle is composed of approximately 60 muscles, which have critical functions including food uptake, eye movements and facial expressions. Although craniofacial muscles have significantly different embryonic origin, most current skeletal muscle differentiation protocols using human induced pluripotent stem cells (iPSCs) are based on somite-derived limb and trunk muscle developmental pathways. Since the lack of a protocol for craniofacial muscles is a significant gap in the iPSC-derived muscle field, we have developed an optimized protocol to generate craniofacial myogenic precursor cells (cMPCs) from human iPSCs by mimicking key signaling pathways during craniofacial embryonic myogenesis. At each different stage, human iPSC-derived cMPCs mirror the transcription factor expression profiles seen in their counterparts during embryo development. After the bi-potential cranial pharyngeal mesoderm is established, cells are committed to cranial skeletal muscle lineages with inhibition of cardiac lineages and are purified by flow cytometry. Furthermore, identities of Ipsc-derived cMPCs are verified with human primary myoblasts from craniofacial muscles using RNA sequencing. These data suggest that our new method could provide not only in vitro research tools to study muscle specificity of muscular dystrophy but also abundant and reliable cellular resources for tissue engineering to support craniofacial reconstruction surgery.

Cyclooxygenases Inhibitors Efficiently Induce Cardiomyogenesis in Human Pluripotent Stem Cells

Application of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) is limited by the challenges in their efficient differentiation. Recently, the Wingless (Wnt) signaling pathway has emerged as the key regulator of cardiomyogenesis. In this study, we evaluated the effects of cyclooxygenase inhibitors on cardiac differentiation of hPSCs. Cardiac differentiation was performed by adherent monolayer based method using 4 hPSC lines (HES3, H9, IMR90, and ES4SKIN). The efficiency of cardiac differentiation was evaluated by flow cytometry and RT-qPCR. Generated hPSC-CMs were characterised using immunocytochemistry, electrophysiology, electron microscopy, and calcium transient measurements. Our data show that the COX inhibitors Sulindac and Diclofenac in combination with CHIR99021 (GSK-3 inhibitor) efficiently induce cardiac differentiation of hPSCs. In addition, inhibition of COX using siRNAs targeted towards COX-1 and/or COX-2 showed that inhibition of COX-2 alone or COX-1 and COX-2 in combination induce cardiomyogenesis in hPSCs within 12 days. Using IMR90-Wnt reporter line, we showed that inhibition of COX-2 led to downregulation of Wnt signalling activity in hPSCs. In conclusion, this study demonstrates that COX inhibition efficiently induced cardiogenesis via modulation of COX and Wnt pathway and the generated cardiomyocytes express cardiac-specific structural markers as well as exhibit typical calcium transients and action potentials. These cardiomyocytes also responded to cardiotoxicants and can be relevant as an in vitro cardiotoxicity screening model.

Trans-spliced long non-coding RNA: an emerging regulator of pluripotency

With dual capacities for unlimited self-renewal and pluripotent differentiation, pluripotent stem cells (PSCs) give rise to many cell types in our body and PSC culture systems provide an unparalleled opportunity to study early human development and disease. Accumulating evidence indicates that the molecular mechanisms underlying pluripotency maintenance in PSCs involve many factors. Among these regulators, recent studies have shown that long non-coding RNAs (lncRNAs) can affect the pluripotency circuitry by cooperating with master pluripotency-associated factors. Additionally, trans-spliced RNAs, which are generated by combining two or more pre-mRNA transcripts to produce a chimeric RNA, have been identified as regulators of various biological processes, including human pluripotency. In this review, we summarize and discuss current knowledge about the roles of lncRNAs, including trans-spliced lncRNAs, in controlling pluripotency.

Differentiation of hepatocyte-like cells from human pluripotent stem cells using small molecules

A variety of approaches have been developed for the derivation of hepatocyte-like cells from pluripotent stem cells. Currently, most of these strategies employ step-wise differentiation approaches with recombinant growth-factors or small-molecule analogs to recapitulate developmental signaling pathways. Here, we tested the efficacy of a small-molecule based differentiation protocol for the generation of hepatocyte-like cells from human pluripotent stem cells. Quantitative gene-expression, immunohistochemical, and western blot analyses for SOX17, FOXA2, CXCR4, HNF4A, AFP, indicated the stage-specific differentiation into definitive endoderm, hepatoblast and hepatocyte-like derivatives. Furthermore, hepatocyte-like cells displayed morphological and functional features characteristic of primary hepatocytes, as indicated by the production of ALB (albumin) and α-1-antitrypsin (A1AT), as well as glycogen storage capacity by periodic acid-Schiff staining. Together, these data support that the small-molecule based hepatic differentiation protocol is a simple, reproducible, and inexpensive method to efficiently drive the differentiation of human pluripotent stem cells towards a hepatocyte-like phenotype, for downstream pharmacogenomic and regenerative medicine applications.

Developing a Cost-Effective and Scalable Production of Human Hepatic Competent Endoderm from Size-Controlled Pluripotent Stem Cell Aggregates

Dynamic suspension culture of human pluripotent stem cells (hPSCs) in stirred bioreactors provides a valuable scalable culture platform for integrated differentiation toward different lineages for potential research and therapeutic applications. However, current protocols for scalable and integrated differentiation of hPSCs limited due to high cost of growth factors and technical challenges. Here, hPSCs aggregates primed with 6 and 12 μM of CHIR99021 (CHIR), a Wnt agonist, in combination with different concentrations of high cost Activin A (10, 25, 50, 100 ng/mL). We sought to determine the appropriate treatment duration for efficient and cost-effective differentiation protocol for foregut definitive endoderm production in a dynamic suspension culture. Afterward, we evaluated the impact of the initial hPSC aggregate sizes (small: 86 ± 18 μm; medium: 142 ± 32 μm; large: 214 ± 34 μm) as critical bioprocess parameter on differentiation efficacy at the beginning of induction. The results indicated that 1-day priming of hPSCs as 3D aggregates (hPSpheres) with 6 μM CHIR followed by treatment with a low concentration of Activin (10 ng/mL) for 2 days resulted in efficient differentiation to definitive endoderm. This finding confirmed by the presence of ≥70% SOX17/FOXA2-double positive cells that highly expressed the anterior endodermal marker HEX. These endodermal cells differentiated efficiently into mature functional hepatocytes [60% albumin (ALB)-positive cells]. The results showed that the initial size of hPSC aggregates significantly impacted on the efficacy of differentiation. The medium sized-hPSpheres resulted in higher productivity and differentiation efficiency for scalable hepatocytes production, whereas small aggregates resulted in significant cell-loss after CHIR treatment and large aggregates had less efficacious endodermal differentiation. Differentiated cells exhibited multiple characteristics of primary hepatocytes as evidenced by expressions of liver-specific markers, indocyanine green and low-density lipoprotein uptake, and glycogen storage. Thus, this platform could be employed for scalable production of hPSC-derived hepatocytes for clinical and drug discovery applications.

Short-term retinoic acid treatment sustains pluripotency and suppresses differentiation of human induced pluripotent stem cells

Human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) derived from blastocyst and human induced pluripotent stem cells (hiPSCs) generated from somatic cells by ectopic expression of defined transcriptional factors, have both the ability to self-renew and to differentiate into all cell types. Here we explored the two antagonistic effects of retinoic acid (RA) on hiPSCs. Although RA has been widely described as a pharmacological agent with a critical role in initiating differentiation of pluripotent stem cells, we demonstrate that short-term RA exposure not only antagonizes cell differentiation and sustains pluripotency of hiPSCs, but it also boosts and improves their properties and characteristics. To shed light on the mechanistic insights involved in the resistance to differentiation of hiPSCs cultured in RA conditions, as well as their improved pluripotency state, we focused our attention on the Wnt pathway. Our findings show that RA inhibits the Wnt canonical pathway and positively modulates the Akt/mTOR signaling, explaining why such perturbations, under our experimental conditions, do not lead to hiPSCs differentiation. Altogether, these data uncover a novel role for RA in favouring the maintenance of ground-state pluripotency, supporting its bivalent role, dose- and time-dependent, for hiPSCs differentiation and self-renewal processes.

Effects of Activin in Embryoid Bodies Expressing Fibroblast Growth Factor 5

Nodal/activin signaling is indispensable for embryonic development. We examined what activin does to the embryoid bodies (EBs) produced from mouse embryonic stem cells (mESCs) expressing an epiblast marker. The EBs were produced by culturing mESCs by the hanging drop method for 24 hours. The resulting EBs were transferred onto gelatin-coated dishes and allowed to further differentiate. The 24-hour EBs showed a stronger expression of fibroblast growth factor (FGF)5 and Brachyury (specific to the epiblast) in comparison with mESCs. Treating the transferred EBs with activin A maintained transcript levels of FGF5 and Oct4, while inhibiting definitive endoderm differentiation. The activin A treatment reversed the endoderm differentiation induced by retinoic acid (RA), while the inhibition of nodal/activin signaling promoted RA-induced endoderm differentiation. Inhibition of nodal/activin signaling in EBs, including epiblast-like cells, promotes differentiation into the endoderm, facilitating the transition from the pluripotent state to specification of the endoderm.

Making muscle: skeletal myogenesis in vivo and in vitro

Skeletal muscle is the largest tissue in the body and loss of its function or its regenerative properties results in debilitating musculoskeletal disorders. Understanding the mechanisms that drive skeletal muscle formation will not only help to unravel the molecular basis of skeletal muscle diseases, but also provide a roadmap for recapitulating skeletal myogenesis in vitro from pluripotent stem cells (PSCs). PSCs have become an important tool for probing developmental questions, while differentiated cell types allow the development of novel therapeutic strategies. In this Review, we provide a comprehensive overview of skeletal myogenesis from the earliest premyogenic progenitor stage to terminally differentiated myofibers, and discuss how this knowledge has been applied to differentiate PSCs into muscle fibers and their progenitors in vitro.

Dynamics of embryonic stem cell differentiation inferred from single-cell transcriptomics show a series of transitions through discrete cell states

The complexity of gene regulatory networks that lead multipotent cells to acquire different cell fates makes a quantitative understanding of differentiation challenging. Using a statistical framework to analyze single-cell transcriptomics data, we infer the gene expression dynamics of early mouse embryonic stem (mES) cell differentiation, uncovering discrete transitions across nine cell states. We validate the predicted transitions across discrete states using flow cytometry. Moreover, using live-cell microscopy, we show that individual cells undergo abrupt transitions from a naïve to primed pluripotent state. Using the inferred discrete cell states to build a probabilistic model for the underlying gene regulatory network, we further predict and experimentally verify that these states have unique response to perturbations, thus defining them functionally. Our study provides a framework to infer the dynamics of differentiation from single cell transcriptomics data and to build predictive models of the gene regulatory networks that drive the sequence of cell fate decisions during development.

DOI:http://dx.doi.org/10.7554/eLife.20487.001

Long-term self-renewing human epicardial cells generated from pluripotent stem cells under defined xeno-free conditions

The epicardium contributes both multi-lineage descendants and paracrine factors to the heart during cardiogenesis and cardiac repair, underscoring its potential for cardiac regenerative medicine. Yet little is known about the cellular and molecular mechanisms that regulate human epicardial development and regeneration. Here, we show that the temporal modulation of canonical Wnt signaling is sufficient for epicardial induction from 6 different human pluripotent stem cell (hPSC) lines, including a WT1-2A-eGFP knock-in reporter line, under chemically-defined, xeno-free conditions. We also show that treatment with transforming growth factor beta (TGF-β)-signalling inhibitors permitted long-term expansion of the hPSC-derived epicardial cells, resulting in a more than 25 population doublings of WT1+ cells in homogenous monolayers. The hPSC-derived epicardial cells were similar to primary epicardial cells both in vitro and in vivo, as determined by morphological and functional assays, including RNA-seq. Our findings have implications for the understanding of self-renewal mechanisms of the epicardium and for epicardial regeneration using cellular or small-molecule therapies.

Generation of human muscle fibers and satellite-like cells from human pluripotent stem cells in vitro

Progress toward finding a cure for muscle diseases has been slow because of the absence of relevant cellular models and the lack of a reliable source of muscle progenitors for biomedical investigation. Here we report an optimized serum-free differentiation protocol to efficiently produce striated, millimeter-long muscle fibers together with satellite-like cells from human pluripotent stem cells (hPSCs) in vitro. By mimicking key signaling events leading to muscle formation in the embryo, in particular the dual modulation of Wnt and bone morphogenetic protein (BMP) pathway signaling, this directed differentiation protocol avoids the requirement for genetic modifications or cell sorting. Robust myogenesis can be achieved in vitro within 1 month by personnel experienced in hPSC culture. The differentiating culture can be subcultured to produce large amounts of myogenic progenitors amenable to numerous downstream applications. Beyond the study of myogenesis, this differentiation method offers an attractive platform for the development of relevant in vitro models of muscle dystrophies and drug screening strategies, as well as providing a source of cells for tissue engineering and cell therapy approaches.

WNT/β-catenin signaling mediates human neural crest induction via a pre-neural border intermediate

Neural crest (NC) cells arise early in vertebrate development, migrate extensively and contribute to a diverse array of ectodermal and mesenchymal derivatives. Previous models of NC formation suggested derivation from neuralized ectoderm, via meso-ectodermal, or neural-non-neural ectoderm interactions. Recent studies using bird and amphibian embryos suggest an earlier origin of NC, independent of neural and mesodermal tissues. Here, we set out to generate a model in which to decipher signaling and tissue interactions involved in human NC induction. Our novel human embryonic stem cell (ESC)-based model yields high proportions of multipotent NC cells (expressing SOX10, PAX7 and TFAP2A) in 5 days. We demonstrate a crucial role for WNT/β-catenin signaling in launching NC development, while blocking placodal and surface ectoderm fates. We provide evidence of the delicate temporal effects of BMP and FGF signaling, and find that NC development is separable from neural and/or mesodermal contributions. We further substantiate the notion of a neural-independent origin of NC through PAX6 expression and knockdown studies. Finally, we identify a novel pre-neural border state characterized by early WNT/β-catenin signaling targets that displays distinct responses to BMP and FGF signaling from the traditional neural border genes. In summary, our work provides a fast and efficient protocol for human NC differentiation under signaling constraints similar to those identified in vivo in model organisms, and strengthens a framework for neural crest ontogeny that is separable from neural and mesodermal fates.

Stem Cells in Skeletal Tissue Engineering: Technologies and Models

This review surveys the use of pluripotent and multipotent stem cells in skeletal tissue engineering. Specific emphasis is focused on evaluating the function and activities of these cells in the context of development in vivo, and how technologies and methods of stem cell-based tissue engineering for stem cells must draw inspiration from developmental biology. Information on the embryonic origin and in vivo differentiation of skeletal tissues is first reviewed, to shed light on the persistence and activities of adult stem cells that remain in skeletal tissues after embryogenesis. Next, the development and differentiation of pluripotent stem cells is discussed, and some of their advantages and disadvantages in the context of tissue engineering are presented. The final section highlights current use of multipotent adult mesenchymal stem cells, reviewing their origin, differentiation capacity, and potential applications to tissue engineering.

Wnt/β-Catenin and MEK-ERK Signaling are Required for Fibroblast-Derived Extracellular Matrix-Mediated Endoderm Differentiation of Embryonic Stem Cells

Human embryonic stem cells (hESCs) have the potential to differentiate into all cells of the three germ layers, thus making them an attractive source of cells for use in regenerative medicine. The greatest challenge lies in regulating the differentiation of hESCs into specific cell lineages by both intrinsic and extrinsic factors. In this study we determined the effect of a fibroblast-derived extracellular matrix (fd-ECM) on hESCs differentiation. We demonstrate that growth of hESCs on fd-ECM results in hESCs losing their stemness and proliferation potential. As the stem cells differentiate they attain gene expression profiles similar to the primitive streak of the in vivo embryo. The activation of both the MEK-ERK and Wnt/β-catenin signaling pathways is required for the fd-ECM-mediated differentiation of hESCs towards the endoderm and involves integrins α1, α2, α3 and β1. This study illustrates the importance of the cellular microenvironment in directing stem cell fate and that the nature and composition of the extracellular matrix is a crucial determining factor.

Late stage definitive endodermal differentiation can be defined by Daf1 expression

Background

Definitive endoderm (DE) gives rise to the respiratory apparatus and digestive tract. Sox17 and Cxcr4 are useful markers of the DE. Previously, we identified a novel DE marker, Decay accelerating factor 1(Daf1/CD55), by identifying DE specific genes from the expression profile of DE derived from mouse embryonic stem cells (ESCs) by microarray analysis, and in situ hybridization of early embryos. Daf1 is expressed in a subpopulation of E-cadherin + Cxcr4+ DE cells. The characteristics of the Daf1-expressing cells during DE differentiation has not been examined.

Results

In this report, we utilized the ESC differentiation system to examine the characteristics of Daf1-expressing DE cells. We found that Daf1 expression could discriminate late DE from early DE. Early DE cells are Daf1-negative (DE-) and late DE cells are Daf1-positive (DE+). We also found that Daf1+ late DE cells show low proliferative and low cell matrix adhesive characteristics. Furthermore, the purified SOX17^low early DE cells gave rise to Daf1+ Sox17^high late DE cells.

Conclusion

Daf1-expressing late definitive endoderm proliferates slowly and show low adhesive capacity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-016-0120-2) contains supplementary material, which is available to authorized users.

Human pluripotent stem cells: Prospects and challenges as a source of cardiomyocytes for in vitro modeling and cell-based cardiac repair

Human pluripotent stem cells (PSCs) represent an attractive source of cardiomyocytes with potential applications including disease modeling, drug discovery and safety screening, and novel cell-based cardiac therapies. Insights from embryology have contributed to the development of efficient, reliable methods capable of generating large quantities of human PSC-cardiomyocytes with cardiac purities ranging up to 90%. However, for human PSCs to meet their full potential, the field must identify methods to generate cardiomyocyte populations that are uniform in subtype (e.g. homogeneous ventricular cardiomyocytes) and have more mature structural and functional properties. For in vivo applications, cardiomyocyte production must be highly scalable and clinical grade, and we will need to overcome challenges including graft cell death, immune rejection, arrhythmogenesis, and tumorigenic potential. Here we discuss the types of human PSCs, commonly used methods to guide their differentiation into cardiomyocytes, the phenotype of the resultant cardiomyocytes, and the remaining obstacles to their successful translation.

Dickkopf Wnt signaling pathway inhibitor 1 regulates the differentiation of mouse embryonic stem cells in vitro and in vivo

Embryonic stem cells (ESCs) are pluripotent stem cells derived from early stage embryos. It remains unclear whether inhibiting the Wnt/β‑catenin signaling pathway using dickkopf Wnt signaling pathway inhibitor 1 (DKK1) impacts on the differentiation potential of mouse ESCs in vitro and in vivo. In the present study, immunohistochemical staining was used to measure the expression of markers of the three germ layers in ESCs and teratomas derived from ESCs. The expression of markers for the Wnt/β‑catenin signaling pathway were detected by reverse transcription‑polymerase chain reaction (RT‑qPCR). Immunohistochemistry and western blotting indicated that the expression levels of octamer‑binding transcription factor 4 in the DKK1‑treated ESC group were significantly greater compared with the control ESCs. Reduced expression levels of NeuroD and bone morphogenetic protein 4 were observed in the DKK1‑treated ESCs and teratomas derived from DKK1‑treated ESCs compared with the control group. Increased expression levels of SOX17 were observed in the DKK1‑treated ESCs compared with the control group. RT‑qPCR indicated that β‑catenin expression was significantly reduced in DKK1‑treated ESCs and teratomas derived from DKK1‑treated ESCs compared with the control groups. Western blotting indicated no alterations in the expression of GSK‑3β, however, the levels of phosphorylated‑GSK‑3β were significantly greater in the DKK1 treatment groups, while cyclin D1 and c‑Myc expression levels were significantly reduced in the DKK1 treatment groups compared with the control groups. These results suggest that inhibiting Wnt signaling in ESCs using DKK1 may promote mouse ESCs to differentiate into endoderm in vitro and in vivo, and suppress the tumorigenicity of ESCs.

Small-molecule-driven hepatocyte differentiation of human pluripotent stem cells

The differentiation of pluripotent stem cells to hepatocytes is well established, yet current methods suffer from several drawbacks. These include a lack of definition and reproducibility, which in part stems from continued reliance on recombinant growth factors. This has remained a stumbling block for the translation of the technology into industry and the clinic for reasons associated with cost and quality. We have devised a growth-factor-free protocol that relies on small molecules to differentiate human pluripotent stem cells toward a hepatic phenotype. The procedure can efficiently direct both human embryonic stem cells and induced pluripotent stem cells to hepatocyte-like cells. The final population of cells demonstrates marker expression at the transcriptional and protein levels, as well as key hepatic functions such as serum protein production, glycogen storage, and cytochrome P450 activity.

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Development of small-molecule-driven hepatocyte differentiation procedure for hPSCs

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Small-molecule-derived hepatocytes demonstrate key hepatic functions

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Significantly reduces the cost of hepatocyte differentiation

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Procedure is applicable to multiple human pluripotent stem cell lines

The generation of definitive endoderm from human embryonic stem cells is initially independent from activin A but requires canonical Wnt-signaling

The activation of the TGF-beta pathway by activin A directs ES cells into the definitive endoderm germ layer. However, there is evidence that activin A/TGF-beta is not solely responsible for differentiation into definitive endoderm. GSK3beta inhibition has recently been shown to generate definitive endoderm-like cells from human ES cells via activation of the canonical Wnt-pathway. The GSK3beta inhibitor CHIR-99021 has been reported to generate mesoderm from human iPS cells. Thus, the specific role of the GSK3beta inhibitor CHIR-99021 was analyzed during the differentiation of human ES cells and compared against a classic endoderm differentiation protocol. At high concentrations of CHIR-99021, the cells were directed towards mesodermal cell fates, while low concentrations permitted mesodermal and endodermal differentiation. Finally, the analyses revealed that GSK3beta inhibition rapidly directed human ES cells into a primitive streak-like cell type independently from the TGF-beta pathway with mesoderm and endoderm differentiation potential. Addition of low activin A concentrations effectively differentiated these primitive streak-like cells into definitive endoderm. Thus, the in vitro differentiation of human ES cells into definitive endoderm is initially independent from the activin A/TGF-beta pathway but requires high canonical Wnt-signaling activity.

Protein kinases and associated pathways in pluripotent state and lineage differentiation

Protein kinases (PKs) mediate the reversible conversion of substrate proteins to phosphorylated forms, a key process in controlling intracellular signaling transduction cascades. Pluripotency is, among others, characterized by specifically expressed PKs forming a highly interconnected regulatory network that culminates in a finely-balanced molecular switch. Current high-throughput phosphoproteomic approaches have shed light on the specific regulatory PKs and their function in controlling pluripotent states. Pluripotent cell-derived endothelial and hematopoietic developments represent an example of the importance of pluripotency in cancer therapeutics and organ regeneration. This review attempts to provide the hitherto known kinome profile and the individual characterization of PK-related pathways that regulate pluripotency. Elucidating the underlying intrinsic and extrinsic signals may improve our understanding of the different pluripotent states, the maintenance or induction of pluripotency, and the ability to tailor lineage differentiation, with a particular focus on endothelial cell differentiation for anti-cancer treatment, cell-based tissue engineering, and regenerative medicine strategies.

Molecular basis of embryonic stem cell self-renewal: from signaling pathways to pluripotency network

Embryonic stem cells (ESCs) can be maintained in culture indefinitely while retaining the capacity to generate any type of cell in the body, and therefore not only hold great promise for tissue repair and regeneration, but also provide a powerful tool for modeling human disease and understanding biological development. In order to fulfill the full potential of ESCs, it is critical to understand how ESC fate, whether to self-renew or to differentiate into specialized cells, is regulated. On the molecular level, ESC fate is controlled by the intracellular transcriptional regulatory networks that respond to various extrinsic signaling stimuli. In this review, we discuss and compare important signaling pathways in the self-renewal and differentiation of mouse, rat, and human ESCs with an emphasis on how these pathways integrate into ESC-specific transcription circuitries. This will be beneficial for understanding the common and conserved mechanisms that govern self-renewal, and for developing novel culture conditions that support ESC derivation and maintenance.

Efficient differentiation of human pluripotent stem cells to endothelial progenitors via small-molecule activation of WNT signaling

Human pluripotent stem cell (hPSC)-derived endothelial cells and their progenitors may provide the means for vascularization of tissue-engineered constructs and can serve as models to study vascular development and disease. Here, we report a method to efficiently produce endothelial cells from hPSCs via GSK3 inhibition and culture in defined media to direct hPSC differentiation to CD34⁺CD31⁺ endothelial progenitors. Exogenous vascular endothelial growth factor (VEGF) treatment was dispensable, and endothelial progenitor differentiation was β-catenin dependent. Furthermore, by clonal analysis, we showed that CD34⁺CD31⁺CD117⁺TIE-2⁺ endothelial progenitors were multipotent, capable of differentiating into calponin-expressing smooth muscle cells and CD31⁺CD144⁺vWF⁺I-CAM1⁺ endothelial cells. These endothelial cells were capable of 20 population doublings, formed tube-like structures, imported acetylated low-density lipoprotein, and maintained a dynamic barrier function. This study provides a rapid and efficient method for production of hPSC-derived endothelial progenitors and endothelial cells and identifies WNT/β-catenin signaling as a primary regulator for generating vascular cells from hPSCs.

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WNT pathway activation directs hPSC differentiation to endothelial progenitors

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hPSC-derived endothelial progenitors can differentiate to endothelial cells

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Purified hPSC-derived endothelial cells are capable of 20 population doublings

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WNT pathway activation permits defined production of endothelial cells from hPSCs

Endoderm complexity in the mouse gastrula is revealed through the expression of spink3

Endoderm formation in the mammalian embryo occurs first in the blastocyst, when the primitive endoderm and pluripotent cells resolve into separate lineages, and again during gastrulation, when the definitive endoderm progenitor population emerges from the primitive streak. The formation of the definitive endoderm can be modeled using pluripotent cell differentiation in culture. The differentiation of early primitive ectoderm-like (EPL) cells, a pluripotent cell population formed from embryonic stem (ES) cells, was used to identify and characterize definitive endoderm formation. Expression of serine peptidase inhibitor, Kazal type 3 (Spink3) was detected in EPL cell–derived endoderm, and in a band of endoderm immediately distal to the embryonic–extra-embryonic boundary in pregastrula and gastrulating embryos. Later expression marked a region of endoderm separating the yolk sac from the developing gut. In the embryo, Spink3 expression marked a region of endoderm comprising the distal visceral endoderm, as determined by an endocytosis assay, and the proximal region of the definitive endoderm. This region was distinct from the more distal definitive endoderm population, marked by thyrotropin-releasing hormone (Trh). Endoderm expressing either Spink3 or Trh could be formed during EPL cell differentiation, and the prevalence of these populations could be influenced by culture medium and growth factor addition. Moreover, further differentiation suggested that the potential of these populations differed. These approaches have revealed an unexpected complexity in the definitive endoderm lineage, a complexity that will need to be accommodated in differentiation protocols to ensure the formation of the appropriate definitive endoderm progenitor in the future.

Totipotency: what it is and what it is not

There is surprising confusion surrounding the concept of biological totipotency, both within the scientific community and in society at large. Increasingly, ethical objections to scientific research have both practical and political implications. Ethical controversy surrounding an area of research can have a chilling effect on investors and industry, which in turn slows the development of novel medical therapies. In this context, clarifying precisely what is meant by "totipotency" and how it is experimentally determined will both avoid unnecessary controversy and potentially reduce inappropriate barriers to research. Here, the concept of totipotency is discussed, and the confusions surrounding this term in the scientific and nonscientific literature are considered. A new term, "plenipotent," is proposed to resolve this confusion. The requirement for specific, oocyte-derived cytoplasm as a component of totipotency is outlined. Finally, the implications of twinning for our understanding of totipotency are discussed.

Rapid and efficient differentiation of human pluripotent stem cells into intermediate mesoderm that forms tubules expressing kidney proximal tubular markers

Human pluripotent stem cells (hPSCs) can generate a diversity of cell types, but few methods have been developed to derive cells of the kidney lineage. Here, we report a highly efficient system for differentiating human embryonic stem cells and induced pluripotent stem cells (referred to collectively as hPSCs) into cells expressing markers of the intermediate mesoderm (IM) that subsequently form tubule-like structures. Treatment of hPSCs with the glycogen synthase kinase-3β inhibitor CHIR99021 induced BRACHYURY(+)MIXL1(+) mesendoderm differentiation with nearly 100% efficiency. In the absence of additional exogenous factors, CHIR99021-induced mesendodermal cells preferentially differentiated into cells expressing markers of lateral plate mesoderm with minimal IM differentiation. However, the sequential treatment of hPSCs with CHIR99021 followed by fibroblast growth factor-2 and retinoic acid generated PAX2(+)LHX1(+) cells with 70%-80% efficiency after 3 days of differentiation. Upon growth factor withdrawal, these PAX2(+)LHX1(+) cells gave rise to apically ciliated tubular structures that coexpressed the proximal tubule markers Lotus tetragonolobus lectin, N-cadherin, and kidney-specific protein and partially integrated into embryonic kidney explant cultures. With the addition of FGF9 and activin, PAX2(+)LHX1(+) cells specifically differentiated into cells expressing SIX2, SALL1, and WT1, markers of cap mesenchyme nephron progenitor cells. Our findings demonstrate the effective role of fibroblast growth factor signaling in inducing IM differentiation in hPSCs and establish the most rapid and efficient system whereby hPSCs can be differentiated into cells with features characteristic of kidney lineage cells.

Microfluidic perfusion culture of human induced pluripotent stem cells under fully defined culture conditions

Human induced pluripotent stem cells (hiPSCs) are a promising cell source for drug screening. For this application, self-renewal or differentiation of the cells is required, and undefined factors in the culture conditions are not desirable. Microfluidic perfusion culture allows the production of small volume cultures with precisely controlled microenvironments, and is applicable to high-throughput cellular environment screening. Here, we developed a microfluidic perfusion culture system for hiPSCs that uses a microchamber array chip under defined extracellular matrix (ECM) and culture medium conditions. By screening various ECMs we determined that fibronectin and laminin are appropriate for microfluidic devices made out of the most popular material, polydimethylsiloxane (PDMS). We found that the growth rate of hiPSCs under pressure-driven perfusion culture conditions was higher than under static culture conditions in the microchamber array. We applied our new system to self-renewal and differentiation cultures of hiPSCs, and immunocytochemical analysis showed that the state of the hiPSCs was successfully controlled. The effects of three antitumor drugs on hiPSCs were comparable between microchamber array and 96-well plates. We believe that our system will be a platform technology for future large-scale screening of fully defined conditions for differentiation cultures on integrated microfluidic devices.

Stem cell-based tissue engineering approaches for musculoskeletal regeneration

The field of regenerative medicine and tissue engineering is an ever evolving field that holds promise in treating numerous musculoskeletal diseases and injuries. An important impetus in the development of the field was the discovery and implementation of stem cells. The utilization of mesenchymal stem cells, and later embryonic and induced pluripotent stem cells, opens new arenas for tissue engineering and presents the potential of developing stem cell-based therapies for disease treatment. Multipotent and pluripotent stem cells can produce various lineage tissues, and allow for derivation of a tissue that may be comprised of multiple cell types. As the field grows, the combination of biomaterial scaffolds and bioreactors provides methods to create an environment for stem cells that better represent their microenvironment for new tissue formation. As technologies for the fabrication of biomaterial scaffolds advance, the ability of scaffolds to modulate stem cell behavior advances as well. The composition of scaffolds could be of natural or synthetic materials and could be tailored to enhance cell self-renewal and/or direct cell fates. In addition to biomaterial scaffolds, studies of tissue development and cellular microenvironments have determined other factors, such as growth factors and oxygen tension, that are crucial to the regulation of stem cell activity. The overarching goal of stem cell-based tissue engineering research is to precisely control differentiation of stem cells in culture. In this article, we review current developments in tissue engineering, focusing on several stem cell sources, induction factors including growth factors, oxygen tension, biomaterials, and mechanical stimulation, and the internal and external regulatory mechanisms that govern proliferation and differentiation.

Activation of GSK3β by Sirt2 is required for early lineage commitment of mouse embryonic stem cell

Sirt2, a member of the NAD(+)-dependent protein deacetylase family, is increasingly recognized as a critical regulator of the cell cycle, cellular necrosis and cytoskeleton organization. However, its role in embryonic stem cells (ESCs) remains unclear. Here we demonstrate that Sirt2 is up-regulated during RA (retinoic acid)-induced and embryoid body (EB) differentiation of mouse ESCs. Using lentivirus-mediated shRNA methods, we found that knockdown of Sirt2 compromises the differentiation of mouse ESCs into ectoderm while promoting mesoderm and endoderm differentiation. Knockdown of Sirt2 expression also leads to the activation of GSK3β through decreased phosphorylation of the serine at position 9 (Ser9) but not tyrosine at position 216 (Tyr216). Moreover, the constitutive activation of GSK3β during EB differentiation mimics the effect of Sirt2 knockdown, while down-regulation of GSK3β rescues the effect of Sirt2 knockdown on differentiation. In contrast to the effect on lineage differentiation, Sirt2 knockdown and GSK3β up-regulation do not change the self-renewal state of mouse ESCs. Overall, our report reveals a new function for Sirt2 in regulating the proper lineage commitment of mouse ESCs.

WNT3A promotes hematopoietic or mesenchymal differentiation from hESCs depending on the time of exposure

We investigated the role of canonical WNT signaling in mesoderm and hematopoietic development from human embryonic stem cells (hESCs) using a recombinant human protein-based differentiation medium (APEL). In contrast to prior studies using less defined culture conditions, we found that WNT3A alone was a poor inducer of mesoderm. However, WNT3A synergized with BMP4 to accelerate mesoderm formation, increase embryoid body size, and increase the number of hematopoietic blast colonies. Interestingly, inclusion of WNT3A or a GSK3 inhibitor in methylcellulose colony-forming assays at 4 days of differentiation abrogated blast colony formation but supported the generation of mesospheres that expressed genes associated with mesenchymal lineages. Mesospheres differentiated into cells with characteristics of bone, fat, and smooth muscle. These studies identify distinct effects for WNT3A, supporting the formation of hematopoietic or mesenchymal lineages from human embryonic stem cells, depending upon differentiation stage at the time of exposure.

Efficient derivation of lateral plate and paraxial mesoderm subtypes from human embryonic stem cells through GSKi-mediated differentiation

The vertebrae mesoderm is a source of cells that forms a variety of tissues, including the heart, vasculature, and blood. Consequently, the derivation of various mesoderm-specific cell types from human embryonic stem cells (hESCs) has attracted the interest of many investigators owing to their therapeutic potential in clinical applications. However, the need for efficient and reliable methods of differentiation into mesoderm lineage cell types remains a significant challenge. Here, we demonstrated that inhibition of glycogen synthase kinase-3 (GSK-3) is an essential first step toward efficient generation of the mesoderm. Under chemically defined conditions without additional growth factors/cytokines, short-term GSK inhibitor (GSKi) treatment effectively drives differentiation of hESCs into the primitive streak (PS), which can potentially commit toward the mesoderm when further supplemented with bone morphogenetic protein 4. Further analysis confirmed that the PS-like cells derived from GSKi treatment are bipotential, being able to specify toward the endoderm as well. Our findings suggest that the bipotential, PS/mesendoderm-like cell population exists only at the initial stages of GSK-3 inhibition, whereas long-term inhibition results in an endodermal fate. Lastly, we demonstrated that our differentiation approach could efficiently generate lateral plate (CD34(+)KDR(+)) and paraxial (CD34(-)PDGFRα(+)) mesoderm subsets that can be further differentiated along the endothelial and smooth muscle lineages, respectively. In conclusion, our study presents a unique approach for generating early mesoderm progenitors in a chemically directed fashion through the use of small-molecule GSK-3 inhibitor, which may be useful for future applications in regenerative medicine.

Engraftment potential of spheroid-forming hepatic endoderm derived from human embryonic stem cells

Transplantation and drug discovery programs for liver diseases are hampered by the shortage of donor tissue. While recent studies have shown that hepatic cells can be derived from human embryonic stem cells (hESCs), few cases have shown selective enrichment of hESC-derived hepatocytes and their integration into host liver tissues. Here we demonstrate that the dissociation and reaggregation procedure after an endodermal differentiation of hESC produces spheroids mainly consisted of cells showing hepatic phenotypes in vitro and in vivo. A combined treatment with Wnt3a and bone morphogenic protein 4 efficiently differentiated hESCs into definitive endoderm in an adherent culture. Dissociation followed by reaggregation of these cells in a nonadherent condition lead to the isolation of spheroid-forming cells that preferentially expressed early hepatic markers from the adherent cell population. Further differentiation of these spheroid cells in the presence of the hepatocyte growth factor, oncostatin M, and dexamethasone produced a highly enriched population of cells exhibiting characteristics of early hepatocytes, including glycogen storage, indocyanine green uptake, and synthesis of urea and albumin. Furthermore, we show that grafted spheroid cells express hepatic features and attenuate the serum aspartate aminotransferase level in a model of acute liver injury. These data suggest that hepatic progenitor cells can be enriched by the spheroid formation of differentiating hESCs and that these cells have engraftment potential to replace damaged liver tissues.

Geminin promotes an epithelial-to-mesenchymal transition in an embryonic stem cell model of gastrulation

Geminin is a nuclear protein that performs the related functions of modulating cell cycle progression by binding Cdt1, and controlling differentiation by binding transcription factors. Since embryonic stem cells (ESC) and the epiblast share a similar gene expression profile and an attenuated cell cycle, ESC form an accessible and tractable model system to study lineage choice at gastrulation. We derived several ESC lines in which Geminin can be inducibly expressed, and employed short hairpin RNAs targeting Geminin. As in the embryo, a lack of Geminin protein resulted in DNA damage and cell death. In monolayer culture, in defined medium, Geminin supported neural differentiation; however, in three-dimensional culture, overexpression of Geminin promoted mesendodermal differentiation and epithelial-to-mesenchymal transition. In vitro, ESC overexpressing Geminin rapidly recolonized a wound, downregulated E-cadherin expression, and activated Wnt signaling. We suggest that Geminin may promote differentiation via binding Groucho/TLE proteins and upregulating canonical Wnt signaling.

Protein kinase C regulates human pluripotent stem cell self-renewal

Background

The self-renewal of human pluripotent stem (hPS) cells including embryonic stem and induced pluripotent stem cells have been reported to be supported by various signal pathways. Among them, fibroblast growth factor-2 (FGF-2) appears indispensable to maintain self-renewal of hPS cells. However, downstream signaling of FGF-2 has not yet been clearly understood in hPS cells.

Methodology/Principal Findings

In this study, we screened a kinase inhibitor library using a high-throughput alkaline phosphatase (ALP) activity-based assay in a minimal growth factor-defined medium to understand FGF-2-related molecular mechanisms regulating self-renewal of hPS cells. We found that in the presence of FGF-2, an inhibitor of protein kinase C (PKC), GF109203X (GFX), increased ALP activity. GFX inhibited FGF-2-induced phosphorylation of glycogen synthase kinase-3β (GSK-3β), suggesting that FGF-2 induced PKC and then PKC inhibited the activity of GSK-3β. Addition of activin A increased phosphorylation of GSK-3β and extracellular signal-regulated kinase-1/2 (ERK-1/2) synergistically with FGF-2 whereas activin A alone did not. GFX negated differentiation of hPS cells induced by the PKC activator, phorbol 12-myristate 13-acetate whereas Gö6976, a selective inhibitor of PKCα, β, and γ isoforms could not counteract the effect of PMA. Intriguingly, functional gene analysis by RNA interference revealed that the phosphorylation of GSK-3β was reduced by siRNA of PKCδ, PKCε, and ζ, the phosphorylation of ERK-1/2 was reduced by siRNA of PKCε and ζ, and the phosphorylation of AKT was reduced by PKCε in hPS cells.

Conclusions/Significance

Our study suggested complicated cross-talk in hPS cells that FGF-2 induced the phosphorylation of phosphatidylinositol-3 kinase (PI3K)/AKT, mitogen-activated protein kinase/ERK-1/2 kinase (MEK), PKC/ERK-1/2 kinase, and PKC/GSK-3β. Addition of GFX with a MEK inhibitor, U0126, in the presence of FGF-2 and activin A provided a long-term stable undifferentiated state of hPS cells even though hPS cells were dissociated into single cells for passage. This study untangles the cross-talk between molecular mechanisms regulating self-renewal and differentiation of hPS cells.

Potential for Respiratory Epithelium Regeneration from Induced Pluripotent Stem Cells

Objectives:

In cases of laryngeal inflammatory lesions and tracheal invasion of a malignant tumor, autologous tissue implantation techniques using skin or cartilage are often applied. However, these techniques are both invasive and unstable. The purpose of this study was to evaluate the potential use of induced pluripotent stem (iPS) cells in the regeneration of respiratory epithelium.

Methods:

We seeded iPS cells on low-attachment plates in serum-free media to generate embryoid bodies (EBs). After a 3-day culture, the EBs were transferred to a gelatin-coated dish supplemented with activin A alone or with basic fibroblast growth factor (induction groups). As a control, EBs were cultured without these growth factors (control group). Cultured tissues from all groups were histologically examined for 2 weeks.

Results:

In the induction groups, the presence of respiratory epithelium-like tissue was observed with hematoxylin and eosin staining after 14 days of culture.

Conclusions:

This study demonstrated the potential use of iPS cells in regeneration of the respiratory epithelium.

Time to reconsider stem cell induction strategies

Recent developments in stem cell research suggest that it may be time to reconsider the current focus of stem cell induction strategies. During the previous five years, approximately, the induction of pluripotency in somatic cells, i.e., the generation of so-called ‘induced pluripotent stem cells’ (iPSCs), has become the focus of ongoing research in many stem cell laboratories, because this technology promises to overcome limitations (both technical and ethical) seen in the production and use of embryonic stem cells (ESCs). A rapidly increasing number of publications suggest, however, that it is now possible to choose instead other, alternative ways of generating stem and progenitor cells bypassing pluripotency. These new strategies may offer important advantages with respect to ethics, as well as to safety considerations. The present communication discusses why these strategies may provide possibilities for an escape from the dilemma presented by pluripotent stem cells (self-organization potential, cloning by tetraploid complementation, patenting problems and tumor formation risk).

NO-β-catenin crosstalk modulates primitive streak formation prior to embryonic stem cell osteogenic differentiation

Nitric oxide (NO) has been shown to play a crucial role in bone formation in vivo. We sought to determine the temporal effect of NO on murine embryonic stem cells (ESCs) under culture conditions that promote osteogenesis. Expression profiles of NO pathway members and osteoblast-specific markers were analyzed using appropriate assays. We found that NO was supportive of osteogenesis specifically during an early phase of in vitro development (days 3-5). Furthermore, ESCs stably overexpressing the inducible NO synthase showed accelerated and enhanced osteogenesis in vitro and in bone explant cultures. To determine the role of NO in early lineage commitment, a stage in ESC differentiation equivalent to primitive streak formation in vivo, ESCs were transfected with a T-brachyury-GFP reporter. Expression levels of T-brachyury and one of its upstream regulators, β-catenin, the major effector in the canonical Wnt pathway, were responsive to NO levels in differentiating primitive streak-like cells. Our results indicate that NO may be involved in early differentiation through regulation of β-catenin and T-brachyury, controlling the specification of primitive-streak-like cells, which may continue through differentiation to later become osteoblasts.

Robust cardiomyocyte differentiation from human pluripotent stem cells via temporal modulation of canonical Wnt signaling

Human pluripotent stem cells (hPSCs) offer the potential to generate large numbers of functional cardiomyocytes from clonal and patient-specific cell sources. Here we show that temporal modulation of Wnt signaling is both essential and sufficient for efficient cardiac induction in hPSCs under defined, growth factor-free conditions. shRNA knockdown of β-catenin during the initial stage of hPSC differentiation fully blocked cardiomyocyte specification, whereas glycogen synthase kinase 3 inhibition at this point enhanced cardiomyocyte generation. Furthermore, sequential treatment of hPSCs with glycogen synthase kinase 3 inhibitors followed by inducible expression of β-catenin shRNA or chemical inhibitors of Wnt signaling produced a high yield of virtually (up to 98%) pure functional human cardiomyocytes from multiple hPSC lines. The robust ability to generate functional cardiomyocytes under defined, growth factor-free conditions solely by genetic or chemically mediated manipulation of a single developmental pathway should facilitate scalable production of cardiac cells suitable for research and regenerative applications.

Wnt/β-catenin signaling promotes differentiation, not self-renewal, of human embryonic stem cells and is repressed by Oct4

Signal transduction pathways play diverse, context-dependent roles in vertebrate development. In studies of human embryonic stem cells (hESCs), conflicting reports claim Wnt/β-catenin signaling promotes either self-renewal or differentiation. We use a sensitive reporter to establish that Wnt/β-catenin signaling is not active during hESC self-renewal. Inhibiting this pathway over multiple passages has no detrimental effect on hESC maintenance, whereas activating signaling results in loss of self-renewal and induction of mesoderm lineage genes. Following exposure to pathway agonists, hESCs exhibit a delay in activation of β-catenin signaling, which led us to postulate that Wnt/β-catenin signaling is actively repressed during self-renewal. In support of this hypothesis, we demonstrate that OCT4 represses β-catenin signaling during self-renewal and that targeted knockdown of OCT4 activates β-catenin signaling in hESCs. Using a fluorescent reporter of β-catenin signaling in live hESCs, we observe that the reporter is activated in a very heterogeneous manner in response to stimulation with Wnt ligand. Sorting cells on the basis of their fluorescence reveals that hESCs with elevated β-catenin signaling express higher levels of differentiation markers. Together these data support a dominant role for Wnt/β-catenin signaling in the differentiation rather than self-renewal of hESCs.

Wnt/β-catenin signaling promotes differentiation, not self-renewal, of human embryonic stem cells and is repressed by Oct4

Signal transduction pathways play diverse, context-dependent roles in vertebrate development. In studies of human embryonic stem cells (hESCs), conflicting reports claim Wnt/β-catenin signaling promotes either self-renewal or differentiation. We use a sensitive reporter to establish that Wnt/β-catenin signaling is not active during hESC self-renewal. Inhibiting this pathway over multiple passages has no detrimental effect on hESC maintenance, whereas activating signaling results in loss of self-renewal and induction of mesoderm lineage genes. Following exposure to pathway agonists, hESCs exhibit a delay in activation of β-catenin signaling, which led us to postulate that Wnt/β-catenin signaling is actively repressed during self-renewal. In support of this hypothesis, we demonstrate that OCT4 represses β-catenin signaling during self-renewal and that targeted knockdown of OCT4 activates β-catenin signaling in hESCs. Using a fluorescent reporter of β-catenin signaling in live hESCs, we observe that the reporter is activated in a very heterogeneous manner in response to stimulation with Wnt ligand. Sorting cells on the basis of their fluorescence reveals that hESCs with elevated β-catenin signaling express higher levels of differentiation markers. Together these data support a dominant role for Wnt/β-catenin signaling in the differentiation rather than self-renewal of hESCs.

Human pluripotent stem cells for modeling toxicity

The development of xenobiotics, driven by the demand for therapeutic, domestic and industrial uses continues to grow. However, along with this increasing demand is the risk of xenobiotic-induced toxicity. Currently, safety screening of xenobiotics uses a plethora of animal and in vitro model systems which have over the decades proven useful during compound development and for application in mechanistic studies of xenobiotic-induced toxicity. However, these assessments have proven to be animal-intensive and costly. More importantly, the prevalence of xenobiotic-induced toxicity is still significantly high, causing patient morbidity and mortality, and a costly impediment during drug development. This suggests that the current models for drug safety screening are not reliable in toxicity prediction, and the results not easily translatable to the clinic due to insensitive assays that do not recapitulate fully the complex phenotype of a functional cell type in vivo. Recent advances in the field of stem cell research have potentially allowed for a readily available source of metabolically competent cells for toxicity studies, derived using human pluripotent stem cells harnessed from embryos or reprogrammed from mature somatic cells. Pluripotent stem cell-derived cell types also allow for potential disease modeling in vitro for the purposes of drug toxicology and safety pharmacology, making this model possibly more predictive of drug toxicity compared with existing models. This article will review the advances and challenges of using human pluripotent stem cells for modeling metabolism and toxicity, and offer some perspectives as to where its future may lie.