Efficient derivation of embryonic stem cells by inhibition of glycogen synthase kinase-3

Mouse Embryonic Stem Cell Pluripotency Factors Regulate RNA Methylation

The pluripotency of embryonic stem cells (ESCs) is actively promoted by a diverse set of factors, including leukemia inhibitory factor (LIF), glycogen synthase kinase-3 (Gsk-3) and mitogen-activated protein kinase kinase (MEK) inhibitors, ascorbic acid, and α-ketoglutarate. Strikingly, several of these factors intersect with the post-transcriptional methylation of RNA (m 6 A), which has also been shown to play a role in ESC pluripotency. Therefore, we explored the possibility that these factors converge on this biochemical pathway to promote the retention of ESC pluripotency. Mouse ESCs were treated with various combinations of small molecules, and the relative levels of m 6 A RNA were measured, as well as the expression of genes marking naïve and primed ESCs. The most surprising result was the discovery that replacing glucose with high levels of fructose pushed ESCs to a more naïve state and reduced m 6 A RNA abundance. Our results suggest a correlation between molecules previously shown to promote the retention of ESC pluripotency and m 6 A RNA levels, strengthening a molecular connection between reduced m 6 A RNA and the pluripotent state, and provides a foundation for future mechanistic studies on the role of m 6 A and ESC pluripotency.

Wnt signaling and the regulation of pluripotency

The role of Wnt signaling in stem cells has been mired in seemingly contradictory findings. On one hand, Wnt has been heralded as a self-renewal factor. On the other hand, Wnt's association with differentiation and lineage commitment is indisputable. This apparent contradiction is particularly evident in pluripotent stem cells, where Wnt promotes self-renewal as well as differentiation. To resolve this discrepancy one must delve into fundamental principles of pluripotency and gain an appreciation for the concept of pluripotency states, which exist in a continuum with intermediate metastable states, some of which have been stabilized in vitro. Wnt signaling is a critical regulator of transitions between pluripotent states. Here, we will discuss Wnt's roles in maintaining pluripotency, promoting differentiation, as well as stimulating reprogramming of somatic cells to an induced pluripotent state.

Highlights on Advancing Frontiers in Tissue Engineering

The field of tissue engineering continues to advance, sometimes in exponential leaps forward, but also sometimes at a rate that does not fulfill the promise that the field imagined a few decades ago. This review is in part a catalog of success in an effort to inform the process of innovation. Tissue engineering has recruited new technologies and developed new methods for engineering tissue constructs that can be used to mitigate or model disease states for study. Key to this antecedent statement is that the scientific effort must be anchored in the needs of a disease state and be working toward a functional product in regenerative medicine. It is this focus on the wildly important ideas coupled with partnered research efforts within both academia and industry that have shown most translational potential. The field continues to thrive and among the most important recent developments are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies that warrant special attention. Developments in the aforementioned areas as well as future directions are highlighted in this article. Although several early efforts have not come to fruition, there are good examples of commercial profitability that merit continued investment in tissue engineering. Impact statement Tissue engineering led to the development of new methods for regenerative medicine and disease models. Among the most important recent developments in tissue engineering are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies. These technologies and an understanding of them will have impact on the success of tissue engineering and its translation to regenerative medicine. Continued investment in tissue engineering will yield products and therapeutics, with both commercial importance and simultaneous disease mitigation.

Hypertonic pressure affects the pluripotency and self-renewal of mouse embryonic stem cells

As an important mechanical cue in the extracellular microenvironment, osmotic stress directly affects the proliferation, migration, and differentiation of cells. In this paper, we focused on the influence of hypertonic pressure on the colony morphology, stemness, and self-renew of mouse embryonic stem cells (mESCs). Our results showed that culture media with hypertonic pressure are more conducive to the maintenance of 3D colony morphology and pluripotency of mESCs after withdrawing the glycogen synthase kinase 3β (GSK3β) inhibitor CHIR99021 and the mitogen-activated protein kinase (MEK) inhibitor PD0325901 (hereinafter referred to as 2i) for 48 h. Furthermore, we revealed the microscopic mechanisms of the this finding: hypertonic pressure resulted in the depolymerization of F-actin cytoskeleton and limits Yes-associated protein (hereinafter referred to as YAP) transmission into the nucleus which play a vital role in the regulation of cell proliferation, and resulting in cell-cycle arrest at last.

Distinct requirements for the maintenance and establishment of mouse embryonic stem cells

Mouse embryonic stem cells (ESCs) that maintain a sustainable pluripotent state are derived from the inner cell mass (ICM) of blastocysts, in which pluripotency is lost during differentiation in vivo. It is unclear when and how the ability to maintain pluripotency is acquired during the derivation of ESCs. We analyzed the required culture condition for the maintenance and establishment of ESCs in detail. Even at low concentration of the GSK3β inhibitor and LIF (LowGiL), the expression levels of pluripotency markers and the chimera-producing ability of the cells were comparable with those of ESCs cultured in the presence of both inhibitors and LIF (2iL). However, blastocysts underwent spontaneous differentiation, and ESCs were not established under LowGiL condition. Time-course analysis showed that 2iL condition for three days from the initiation of culture was sufficient for the acquisition of permanent pluripotency. Although X chromosome-linked pluripotent genes were significantly up-regulated during the culture of both male and female blastocysts in 2iL condition, no such up-regulation was observed in LowGiL condition. In conclusion, 2iL-dependent activation of these X-linked genes at the earliest phase of ESC derivation is one of the molecular bases for the acquisition of permanent pluripotency.

Efficient derivation of extended pluripotent stem cells from NOD-scid Il2rg-/- mice

Recently we have established a new culture condition enabling the derivation of extended pluripotent stem (EPS) cells, which, compared to conventional pluripotent stem cells, possess superior developmental potential and germline competence. However, it remains unclear whether this condition permits derivation of EPS cells from mouse strains that are refractory or non-permissive to pluripotent cell establishment. Here, we show that EPS cells can be robustly generated from non-permissive NOD-scid Il2rg^−/− mice through de novo derivation from blastocysts. Furthermore, these cells can also be efficiently generated by chemical reprogramming from embryonic NOD-scid Il2rg^−/− fibroblasts. NOD-scid Il2rg^−/− EPS cells can be expanded for more than 20 passages with genomic stability and can be genetically modified through gene targeting. Notably, these cells contribute to both embryonic and extraembryonic lineages in vivo. More importantly, they can produce chimeras and integrate into the E13.5 genital ridge. Our study demonstrates the feasibility of generating EPS cells from refractory mouse strains, which could potentially be a general strategy for deriving mouse pluripotent cells. The generation of NOD-scid Il2rg^−/− EPS cell lines permits sophisticated genetic modification in NOD-scid Il2rg^−/− mice, which may greatly advance the optimization of humanized mouse models for biomedical applications.

Glycogen synthase kinase-3 (GSK-3) activity regulates mRNA methylation in mouse embryonic stem cells

Glycogen synthase kinase-3 (GSK-3) activity regulates multiple signal transduction pathways and is also a key component of the network responsible for maintaining stem cell pluripotency. Genetic deletion of Gsk-3α and Gsk-3β or inhibition of GSK-3 activity via small molecules promotes stem cell pluripotency, yet the mechanism underlying the role for GSK-3 in this process remains ambiguous. Another cellular process that has been shown to affect stem cell pluripotency is mRNA methylation (m⁶A). Here, we describe an intersection between these components, the regulation of m⁶A by GSK-3. We find that protein levels for the RNA demethylase, FTO (fat mass and obesity-associated protein), are elevated in Gsk-3α;Gsk-3β-deficient mouse embryonic stem cells (ESCs). FTO is normally phosphorylated by GSK-3, and MS identified the sites on FTO that are phosphorylated in a GSK-3-dependent fashion. GSK-3 phosphorylation of FTO leads to polyubiquitination, but in Gsk-3 knockout ESCs, that process is impaired, resulting in elevated levels of FTO protein. As a consequence of altered FTO protein levels, mRNAs in Gsk-3 knockout ESCs have 50% less m⁶A than WT ESCs, and m⁶A-Seq analysis reveals the specific mRNAs that have reduced m⁶A modifications. Taken together, we provide the first evidence for how m⁶A demethylation is regulated in mammalian cells and identify a putative novel mechanism by which GSK-3 activity regulates stem cell pluripotency.

Capturing Human Naïve Pluripotency in the Embryo and in the Dish

Although human embryonic stem cells (hESCs) were first derived almost 20 years ago, it was only recently acknowledged that they share closer molecular and functional identity to postimplantation lineage-primed murine epiblast stem cells than to naïve preimplantation inner cell mass-derived mouse ESCs (mESCs). A myriad of transcriptional, epigenetic, biochemical, and metabolic attributes have now been described that distinguish naïve and primed pluripotent states in both rodents and humans. Conventional hESCs and human induced pluripotent stem cells (hiPSCs) appear to lack many of the defining hallmarks of naïve mESCs. These include important features of the naïve ground state murine epiblast, such as an open epigenetic architecture, reduced lineage-primed gene expression, and chimera and germline competence following injection into a recipient blastocyst-stage embryo. Several transgenic and chemical methods were recently reported that appear to revert conventional human PSCs to mESC-like ground states. However, it remains unclear if subtle deviations in global transcription, cell signaling dependencies, and extent of epigenetic/metabolic shifts in these various human naïve-reverted pluripotent states represent true functional differences or alternatively the existence of distinct human pluripotent states along a spectrum. In this study, we review the current understanding and developmental features of various human pluripotency-associated phenotypes and discuss potential biological mechanisms that may support stable maintenance of an authentic epiblast-like ground state of human pluripotency.

CFTR-β-catenin interaction regulates mouse embryonic stem cell differentiation and embryonic development

Cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-regulated anion channel capable of conducting both Cl^- and HCO₃^-, mutations of which cause cystic fibrosis (CF), a common autosomal recessive disease. Although CF patients are known to have varied degree of developmental problems, the biological role of CFTR in embryonic development remains elusive. Here, we show that CFTR is functionally expressed in mouse ESCs. CFTR^-/- mESCs exhibit dramatic defect in mesendoderm differentiation. In addition, CFTR physically interacts with β-catenin, defect of which leads to premature degradation of β-catenin and suppressed activation of β-catenin signaling. Furthermore, knockdown of CFTR retards the early development of Xenopus laevis with impaired mesoderm/endoderm differentiation and β-catenin signaling. Our study reveals a previously undefined role of CFTR in controlling ESC differentiation and early embryonic development via its interaction with β-catenin, and provides novel insights into the understanding of embryonic development.

Inhibition of JAK-STAT ERK/MAPK and Glycogen Synthase Kinase-3 Induces a Change in Gene Expression Profile of Bovine Induced Pluripotent Stem Cells

Pluripotent stem cells (PSCs) fall in two states, one highly undifferentiated, the naïve state, and the primed state, characterized by the inability to contribute to germinal lineage. Several reports have demonstrated that these states can be modified by changes to the cell culture conditions. With the advent of nuclear reprogramming, bovine induced pluripotent stem cells (biPSCs) have been generated. These cells represent examples of a transient-intermediate state of pluripotency with remarkable characteristics and biotechnological potential. Herein, we generated and characterized biPSC. Next, we evaluated different culture conditions for the ability to affect the expression of the set of core pluripotent transcription factors in biPSC. It was found that the use of 6-bromoindirubin-3-oxime and Sc1 inhibitors alone or in combination with 5-AzaC induced significantly higher levels of expression of endogenous REX1, OCT4, NANOG, and SOX2. Furthermore, LIF increased the levels of expression of OCT4 and REX1, compared with those cultured with LIF + bFGF. By contrast, bFGF decreased the levels of expression for both REX1 and OCT4. These results demonstrate that the biPSC gene expression profile is malleable by modification of the cell culture conditions well after nuclear reprogramming, and the culture conditions may determine their differentiation potential.

Pluripotent stem cells derived from mouse primordial germ cells by small molecule compounds

Primordial germ cells (PGCs) can give rise to pluripotent stem cells known as embryonic germ cells (EGCs) when cultured with basic fibroblast growth factor (bFGF), stem cell factor (SCF), and leukemia inhibitory factor. Somatic cells can give rise to induced pluripotent stem cells (iPSCs) by introduction of the reprogramming transcription factors Oct4, Sox2, and Klf4. The effects of Sox2 and Klf4 on somatic cell reprogramming can be reproduced using the small molecule compounds, transforming growth factor-β receptor (TGFβR) inhibitor and Kempaullone, respectively. Here we examined the effects of TGFβR inhibitor and Kempaullone on EGC derivation from PGCs. Treatment of PGCs with TGFβR inhibitor and/or Kempaullone generated pluripotent stem cells under standard embryonic stem cell (ESC) culture conditions without bFGF and SCF, which we termed induced EGCs (iEGCs). The derivation efficiency of iEGCs was dependent on the differentiation stage and sex. DNA methylation levels of imprinted genes in iEGCs were reduced, with the exception of the H19 gene. The promoters of genes involved in germline development were generally hypomethylated in PGCs, but three germline genes showed comparable DNA methylation levels among iEGs, ESCs, and iPSCs. These results show that PGCs can be reprogrammed into pluripotent state using small molecule compounds, and that DNA methylation of these germline genes is not maintained in iEGCs.

Wnt/ß-catenin signalling and the dynamics of fate decisions in early mouse embryos and embryonic stem (ES) cells

Wnt/ß-catenin signalling is a widespread cell signalling pathway with multiple roles during vertebrate development. In mouse embryonic stem (mES) cells, there is a dual role for ß-catenin: it promotes differentiation when activated as part of the Wnt/ß-catenin signalling pathway, and promotes stable pluripotency independently of signalling. Although mES cells resemble the preimplantation epiblast progenitors, the first requirement for Wnt/ß-catenin signalling during mouse development has been reported at implantation [1,2]. The relationship between ß-catenin and pluripotency and that of mES cells with epiblast progenitors suggests that ß-catenin might have a functional role during preimplantation development. Here we summarize the expression and function of Wnt/ß-catenin signalling elements during the early stages of mouse development and consider the reasons why the requirement in ES cells do not reflect the embryo.

Glycogen synthase kinase 3β inhibition enhanced proliferation, migration and functional re-endothelialization of endothelial progenitor cells in hypercholesterolemia microenvironment

Hypercholesterolemia impairs the quantity and function of endothelial progenitor cell. We hypothesized that glycogen synthase kinase 3β activity is involved in regulating biological function of endothelial progenitor cells in hypercholesterolemia microenvironment. For study, endothelial progenitor cells derived from apolipoprotein E-deficient mice fed with high-fat diet were used. Glycogen synthase kinase 3β activity was interfered with glycogen synthase kinase 3β inhibitor lithium chloride or transduced with replication defective adenovirus vector expressing catalytically inactive glycogen synthase kinase 3β (GSK3β-KM). Functions of endothelial progenitor cells, proliferation, migration, secretion and network formation of endothelial progenitor cells were assessed in vitro. The expression of phospho-glycogen synthase kinase 3β, β-catenin and cyclinD1 in endothelial progenitor cells was detected by Western blot. The in vivo function re-endothelialization and vasodilation were also analyzed by artery injury model transplanted with glycogen synthase kinase 3β-inhibited endothelial progenitor cells. We demonstrated that while the proliferation, migration, network formation as well as VEGF and NO secretion were impaired in apolipoprotein E-deficient endothelial progenitor cells, glycogen synthase kinase 3β inhibition significantly improved all these functions. Apolipoprotein E-deficient endothelial progenitor cells showed decreased phospho-glycogen synthase kinase 3β, β-catenin and cyclinD1 expression, whereas these signals were enhanced by glycogen synthase kinase 3β inhibition and accompanied with β-catenin nuclear translocation. Our in vivo model showed that glycogen synthase kinase 3β inhibition remarkably increased re-endothelial and vasodilation. Taken together, our data suggest that inhibition of glycogen synthase kinase 3β is associated with endothelial progenitor cell biological functions both in vitro and in vivo. It might be an important interference target in hypercholesterolemia microenvironment.

Efficient induction of pluripotency in primordial germ cells by dual inhibition of TGF-β and ERK signaling pathways

Primordial germ cells (PGCs) have the ability to be reprogrammed into a pluripotent state and are defined as embryonic germ cells (EGCs) in vitro. EGC formation is more efficient, has a shorter culture period than somatic cell reprogramming, and does not require exogenous genetic manipulation. Therefore, EGCs are a good model to analyze mechanisms by which committed cells acquire a pluripotent state. In the present study we have attempted to elucidate a more defined and robust protocol that promotes EGC generation through the suppression of transforming growth factor-β (TGF-β) and extracellular signal-regulated kinase (ERK) signaling pathways by SB431542 (SB) and PD0325901 (PD), respectively. Under this condition the efficiency of transformation of PGCs into EGCs was more than the inhibition of glycogen synthase kinase 3 and ERK signaling pathways. Pluripotency of the resultant-derived EGC lines were further confirmed by gene expression, immunofluorescent staining, directed differentiation ability, teratoma formation, and their contribution to chimeric mice and germ-line transmission. These results showed that PGCs from different embryonic stages (E8.5 and E12.5) could be reprogrammed, maintained, and expanded efficiently under feeder- and serum-free chemically defined conditions by dual inhibition of TGF-β and ERK signaling pathways, regardless of the animal's genetic background.

A membrane-associated β-catenin/Oct4 complex correlates with ground-state pluripotency in mouse embryonic stem cells

The maintenance of pluripotency in mouse embryonic stem cells (mESCs) relies on the activity of a transcriptional network that is fuelled by the activity of three transcription factors (Nanog, Oct4 and Sox2) and balanced by the repressive activity of Tcf3. Extracellular signals modulate the activity of the network and regulate the differentiation capacity of the cells. Wnt/β-catenin signaling has emerged as a significant potentiator of pluripotency: increases in the levels of β-catenin regulate the activity of Oct4 and Nanog, and enhance pluripotency. A recent report shows that β-catenin achieves some of these effects by modulating the activity of Tcf3, and that this effect does not require its transcriptional activation domain. Here, we show that during self-renewal there is negligible transcriptional activity of β-catenin and that this is due to its tight association with membranes, where we find it in a complex with Oct4 and E-cadherin. Differentiation triggers a burst of Wnt/β-catenin transcriptional activity that coincides with the disassembly of the complex. Our results establish that β-catenin, but not its transcriptional activity, is central to pluripotency acting through a β-catenin/Oct4 complex.

A new chemical approach to the efficient generation of mouse embryonic stem cells

Here, we present a highly efficient and reproducible method for the establishment of mouse embryonic stem cells (mESCs) from embryonic day 3.5 (E3.5) whole blastocysts. This protocol involves the use of small molecules SB431542 and PD0325901, which inhibit transforming growth factor-β (TGF-β) and extracellular signal-regulated kinases (ERK1/2), respectively. This protocol is universal in the derivation of mESC lines from NMRI, C57BL/6, BALB/c, DBA/2, and FVB/N strains, which have previously been considered refractory or non-permissive for ESC establishment. The efficiency of mESC lines generation is 100%, regardless of genetic background.

Efficient and user-friendly pluripotin-based derivation of mouse embryonic stem cells

Classic derivation of mouse embryonic stem (ES) cells from blastocysts is inefficient, strain-dependent, and requires expert skills. Over recent years, several major improvements have greatly increased the success rate for deriving mouse ES cell lines. The first improvement was the establishment of a user-friendly and reproducible medium-alternating protocol that allows isolation of ES cells from C57BL/6 transgenic mice with efficiencies of up to 75%. A recent report describes the use of this protocol in combination with leukemia inhibitory factor and pluripotin treatment, which made it possible to obtain ES cells from F1 strains with high efficiency. We report modifications of these protocols for user-friendly and reproducible derivation of mouse ES cells with efficiencies of up to 100%. Our protocol involves a long initial incubation of primary outgrowths from blastocysts with pluripotin, which results in the formation of large spherical outgrowths. These outgrowths are morphologically distinct from classical inner cell mass (ICM) outgrowths and can be easily picked and trypsinized. Pluripotin was omitted after the first trypsinization because we found that it blocks attachment of ES cells to the feeder layer and its removal facilitated formation of ES cell colonies. The newly established ES cells exhibited normal karyotypes and generated chimeras. In summary, our user-friendly modified protocol allows formation of large spherical ICM outgrowths in a robust and reliable manner. These outgrowths gave rise to ES cell lines with success rates of up to 100%.

Pleiotropy of glycogen synthase kinase-3 inhibition by CHIR99021 promotes self-renewal of embryonic stem cells from refractory mouse strains

Background

Inhibition of glycogen synthase kinase-3 (GSK-3) improves the efficiency of embryonic stem (ES) cell derivation from various strains of mice and rats, as well as dramatically promotes ES cell self-renewal potential. β-catenin has been reported to be involved in the maintenance of self-renewal of ES cells through TCF dependent and independent pathway. But the intrinsic difference between ES cell lines from different species and strains has not been characterized. Here, we dissect the mechanism of GSK-3 inhibition by CHIR99021 in mouse ES cells from refractory mouse strains.

Methodology/Principal Findings

We found that CHIR99021, a GSK-3 specific inhibitor, promotes self-renewal of ES cells from recalcitrant C57BL/6 (B6) and BALB/c mouse strains through stabilization of β-catenin and c-Myc protein levels. Stabilized β-catenin promoted ES self-renewal through two mechanisms. First, β-catenin translocated into the nucleus to maintain stem cell pluripotency in a lymphoid-enhancing factor/T-cell factor–independent manner. Second, β-catenin binds plasma membrane-localized E-cadherin, which ensures a compact, spherical morphology, a hallmark of ES cells. Further, elevated c-Myc protein levels did not contribute significantly to CH-mediated ES cell self-renewal. Instead, the role of c-Myc is dependent on its transformation activity and can be replaced by N-Myc but not L-Myc. β-catenin and c-Myc have similar effects on ES cells derived from both B6 and BALB/c mice.

Conclusions/Significance

Our data demonstrated that GSK-3 inhibition by CH promotes self-renewal of mouse ES cells with non-permissive genetic backgrounds by regulation of multiple signaling pathways. These findings would be useful to improve the availability of normally non-permissive mouse strains as research tools.

Insulin increases epiblast cell number of in vitro cultured mouse embryos via the PI3K/GSK3/p53 pathway

High-quality embryos give rise to embryonic stem cells (ESCs) at greater efficiencies than poor-quality embryos. However, most embryos available for human ESC derivation are of a reduced quality as a result of culture in relatively simple media up to 10 years earlier, before cryopreservation, or before compaction. In the present study, we used a mouse model to determine whether a culture with insulin from the 8-cell stage could increase the number of ESC progenitor epiblast cells in blastocysts, as well as endeavor to determine the molecular mechanism of the insulin's effect. Culture in media containing 1.7 ρM insulin increased epiblast cell number (determined by Oct4 and Nanog co-expression), and proportion in day 6 blastocysts. The inhibition of phosphoinositide 3 kinase (PI3K) (via LY294002), an early second messenger of the insulin receptor, blocked this effect. The inhibition of glycogen synthase kinase 3 (GSK3) or p53, 2 s messengers inactivated by insulin signaling (via CT99021 or pifithrin-α, respectively), increased epiblast cell numbers. When active, GSK3 and p53 block the transcription of Nanog, which is important for maintaining pluripotency. A simultaneous inhibition of GSK3 and p53 had no synergistic effects on epiblast cell number. The induced activation of GSK3 and p53, via the inhibition of proteins responsible for their inactivation (PKA via H-89 and SIRT-1 via nicotinamide, respectively), blocked the insulin's effect on the epiblast.From our findings, we conclude that insulin increases epiblast cell number via the activation of PI3K, which ultimately inactivates GSK3 and p53. Furthermore, we suggest that the inclusion of insulin in culture media could be used as a strategy for increasing the efficiency with which the ESC lines can be derived from cultured embryos.

In vitro tissue engineering of smooth muscle sheets with peristalsis using a murine induced pluripotent stem cell line

PURPOSE

Currently, therapeutic options for short gut syndrome are limited, ranging from total parenteral nutrition pending intestinal adaption to small bowel transplantation with its associated problems of rejection. The aim of this study was to differentiate murine induced pluripotent stem cells (iPSCs) into gut tissues, including contracting smooth muscle, as a precursor to using tissue engineering techniques to generate functioning intestinal tissue from the patient's own cells.

METHOD

Induced pluripotent stem cells were cultured for 6 days in low adherent 96-well plates (500-5000 cells per well) in a differentiation medium comprising Knockout Dulbecco's modified Eagle medium (Invitrogen, Carlsbad, Calif) supplemented with 10% fetal bovine serum, l-glutamine, nonessential amino acids, 2-mercaptoethanol, penicillin, and streptomycin. After 6 days, the embryoid body that had formed in each well was transferred into a 12-well plate, each well containing 8 embryoid bodies.

RESULTS

Outgrowth culture produced differentiated cell clusters, including cardiaclike cells, sheets of smooth muscle with peristalticlike activity, and mucosal cells. Cardiaclike cells exhibited spontaneous rhythmic regular contraction, but the sheets of smooth muscle contracted in a co-ordinated way, just as is seen in peristaltic bowel, as shown using video imaging.

CONCLUSION

Tissue engineering techniques using iPSCs have the potential to ultimately replace the need for small bowel transplantation and allow patients to "grow" their own small bowel.

It's a lipid's world: bioactive lipid metabolism and signaling in neural stem cell differentiation

Lipids are often considered membrane components whose function is to embed proteins into cell membranes. In the last two decades, studies on brain lipids have unequivocally demonstrated that many lipids have critical cell signaling functions; they are called "bioactive lipids". Pioneering work in Dr. Robert Ledeen's laboratory has shown that two bioactive brain sphingolipids, sphingomyelin and the ganglioside GM1 are major signaling lipids in the nuclear envelope. In addition to derivatives of the sphingolipid ceramide, the bioactive lipids discussed here belong to the classes of terpenoids and steroids, eicosanoids, and lysophospholipids. These lipids act mainly through two mechanisms: (1) direct interaction between the bioactive lipid and a specific protein binding partner such as a lipid receptor, protein kinase or phosphatase, ion exchanger, or other cell signaling protein; and (2) formation of lipid microdomains or rafts that regulate the activity of a group of raft-associated cell signaling proteins. In recent years, a third mechanism has emerged, which invokes lipid second messengers as a regulator for the energy and redox balance of differentiating neural stem cells (NSCs). Interestingly, developmental niches such as the stem cell niche for adult NSC differentiation may also be metabolic compartments that respond to a distinct combination of bioactive lipids. The biological function of these lipids as regulators of NSC differentiation will be reviewed and their application in stem cell therapy discussed.

Reprogramming of somatic cells

Reprogramming of adult somatic cells into pluripotent stem cells may provide an attractive source of stem cells for regenerative medicine. It has emerged as an invaluable method for generating patient-specific stem cells of any cell lineage without the use of embryonic stem cells. A revolutionary study in 2006 showed that it is possible to convert adult somatic cells directly into pluripotent stem cells by using a limited number of pluripotent transcription factors and is called as iPS cells. Currently, both genomic integrating viral and nonintegrating nonviral methods are used to generate iPS cells. However, the viral-based technology poses increased risk of safety, and more studies are now focused on nonviral-based technology to obtain autologous stem cells for clinical therapy. In this review, the pros and cons of the present iPS cell technology and the future direction for the successful translation of this technology into the clinic are discussed.

WNTing embryonic stem cells

Embryonic stem cells (ESCs) - undifferentiated cells originating from preimplantation stage embryos - have prolonged self-renewal capacity and are pluripotent. Activation of the canonical Wnt pathway is implicated in maintenance of and exit from the pluripotent state. Recent findings demonstrate that the essential mediator of canonical Wnt signaling, β-catenin, is dispensable for ESC maintenance; however, its activation inhibits differentiation through derepression of T cell factor 3 (Tcf3)-bound genes. Wnt agonists are useful in deriving ESCs from recalcitrant mouse strains and the rat and in nuclear reprogramming of somatic stem cells. We discuss recent advances in our understanding of the role of canonical Wnt signaling in the regulation of ESC self-renewal and how its manipulation can improve pluripotent ESC derivation and maintenance.

Functions of GSK-3 Signaling in Development of the Nervous System

Glycogen synthase kinase-3 (GSK-3) is central to multiple intracellular pathways including those activated by Wnt/β-catenin, Sonic Hedgehog, Notch, growth factor/RTK, and G protein-coupled receptor signals. All of these signals importantly contribute to neural development. Early attention on GSK-3 signaling in neural development centered on the regulation of neuronal polarity using in vitro paradigms. However, recent creation of appropriate genetic models has demonstrated the importance of GSK-3 to multiple aspects of neural development including neural progenitor self-renewal, neurogenesis, neuronal migration, neural differentiation, and synaptic development.

Regulation of embryonic stem cell self-renewal and pluripotency by leukaemia inhibitory factor

LIF (leukaemia inhibitory factor) is a key cytokine for maintaining self-renewal and pluripotency of mESCs (mouse embryonic stem cells). Upon binding to the LIF receptor, LIF activates three major intracellular signalling pathways: the JAK (Janus kinase)/STAT3 (signal transducer and activator of transcription 3), PI3K (phosphoinositide 3-kinase)/AKT and SHP2 [SH2 (Src homology 2) domain-containing tyrosine phosphatase 2]/MAPK (mitogen-activated protein kinase) pathways. These pathways converge to orchestrate the gene expression pattern specific to mESCs. Among the many signalling events downstream of the LIF receptor, activation and DNA binding of the transcription factor STAT3 plays a central role in transducing LIF's functions. The fundamental role of LIF for pluripotency was highlighted further by the discovery that LIF accelerates the conversion of epiblast-derived stem cells into a more fully pluripotent state. In the present review, we provide an overview of the three major LIF signalling pathways, the molecules that interact with STAT3 and the current interpretations of the roles of LIF in pluripotency.

Generation of Induced Pluripotent Stem (iPS) Cells by Nuclear Reprogramming

During embryonic development pluripotency is progressively lost irreversibly by cell division, differentiation, migration and organ formation. Terminally differentiated cells do not generate other kinds of cells. Pluripotent stem cells are a great source of varying cell types that are used for tissue regeneration or repair of damaged tissue. The pluripotent stem cells can be derived from inner cell mass of blastocyte but its application is limited due to ethical concerns. The recent discovery of iPS with defined reprogramming factors has initiated a flurry of works on stem cell in various laboratories. The pluripotent cells can be derived from various differentiated adult cells as well as from adult stem cells by nuclear reprogramming, somatic cell nuclear transfer etc. In this review article, different aspects of nuclear reprogramming are discussed.

Short-term serum-free culture reveals that inhibition of Gsk3β induces the tumor-like growth of mouse embryonic stem cells

Here, we present evidence that the tumor-like growth of mouse embryonic stem cells (mESCs) is suppressed by short-term serum-free culture, which is reversed by pharmacological inhibition of Gsk3β. Mouse ESCs maintained under standard conditions using fetal bovine serum (FBS) were cultured in a uniquely formulated chemically-defined serum-free (CDSF) medium, namely ESF7, for three passages before being subcutaneously transplanted into immunocompromised mice. Surprisingly, the mESCs failed to produce teratomas for up to six months, whereas mESCs maintained under standard conditions generated well-developed teratomas in five weeks. Mouse ESCs cultured under CDSF conditions maintained the expression of Oct3/4, Nanog, Sox2 and SSEA1, and differentiated into germ cells in vivo. In addition, when mESCs were cultured under CDSF conditions supplemented with FBS, or when the cells were cultured under CDSF conditions followed by standard culture conditions, they consistently developed into teratomas. Thus, these results validate that the pluripotency of mESCs was not compromised by CDSF conditions. Mouse ESCs cultured under CDSF conditions proliferated significantly more slowly than mESCs cultured under standard conditions, and were reminiscent of Eras-null mESCs. In fact, their slower proliferation was accompanied by the downregulation of Eras and c-Myc, which regulate the tumor-like growth of mESCs. Remarkably, when mESCs were cultured under CDSF conditions supplemented with a pharmacological inhibitor of Gsk3β, they efficiently proliferated and developed into teratomas without upregulation of Eras and c-Myc, whereas mESCs cultured under standard conditions expressed Eras and c-Myc. Although the role of Gsk3β in the self-renewal of ESCs has been established, it is suggested with these data that Gsk3β governs the tumor-like growth of mESCs by means of a mechanism different from the one to support the pluripotency of ESCs.

Differential requirement for the dual functions of β-catenin in embryonic stem cell self-renewal and germ layer formation

Canonical Wnt-signalling has been implicated in mouse and human embryonic stem cell (ESC) maintenance, however its requirement is controversial. β-catenin is the key component in this highly conserved Wnt pathway, acting as a transcriptional transactivator. Yet, β-catenin has additional roles at the plasma membrane regulating cell-cell adhesion, complicating the analyses of cells/tissues lacking β-catenin. We report here the generation of a β-catenin deficient mouse ESC (mESC) line and show that self-renewal is maintained in absence of β-catenin. Cell-adhesion is partially rescued by plakoglobin up-regulation, but fails to be maintained during differentiation. When differentiated as aggregates, wild-type mESCs form descendents of all three germ layers, while mesendodermal germ layer formation and neuronal differentiation are defective in β-catenin deficient mESCs. A Tcf/Lef-signalling defective β-catenin variant, which re-establishes cadherin-mediated cell-adhesion, rescues definitive endoderm and neuroepithelial formation, suggesting that β-catenin cell-adhesion function is more important than its signalling function for these processes.

Simple and efficient derivation of mouse embryonic stem cell lines using differentiation inhibitors or proliferation stimulators

The inhibition of endogenous differentiation-inducing signaling or the enhancement of growth capacity and viability of preimplantation embryos, via 2i (PD0325901 and CHIR99021), dramatically improves the establishment of mouse embryonic stem cells (mESCs). Using adrenocorticotropic hormone fragments 1-24 (ACTH 1-24), which enhances survival and/or proliferation of mESCs, also increases the derivation of mESCs from single blastomeres significantly. The CHIR99021 pathway and the proposed ACTH pathway are likely different. Therefore, this study aimed to assess the synergetic effects of 2i and ACTH 1-24 on derivation of mESCs. Results in the present study demonstrate that germline-transmitted mESCs could be efficiently derived from ICR and C57BL/6J at 0.5-4.5 days postcoitum denuded zygotes to blastocysts or isolated blastomeres of 2-8-cell embryos and cultured in 10 μL droplets with human foreskin fibroblast (Hs68) or STO (a mouse embryonic fibroblast line) feeders and in knockout serum replacement (KSR) ESC medium containing 2i or ACTH 1-24. The overall success rates for C57BL/6J and ICR were 56.2% when cultured in 2i+ACTH 1-24, 26.6% in 2i, 6.7% in ACTH 1-24, and 4.8% in KSR ESC medium. These results imply that CHIR99021 and ACTH 1-24 are synergistically enhancing the establishment of mESCs. The proposed protocol also demonstrates a highly efficient and reproducible method, has a simple layout, is easy to apply, and could be used as an alternative method for routinely establishing mESC lines.

Factors regulating pluripotency and differentiation in early mammalian embryos and embryo-derived stem cells

Mammalian development relies on the cellular proliferation and precisely orchestrated differentiation processes. In preimplantation embryos preservation of the pluripotent state and timely onset of differentiation are secured by specific mechanisms involving such factors as OCT₄, NANOG, SOX₂, or SALL₄. The pluripotency-sustaining cellular machinery is operational not only in the cells of preimplantation embryos but also in embryo-derived embryonic stem cells and epiblast stem cells. However, certain variations in the execution of pluripotency exist and result in the differences not only between embryonic cells and stem cells of the same mammalian species, but also between those of different mammalian species, such as mouse, rat, bank vole, or humans. In this review we describe the involvement of exogenous stimuli (e.g., LIF, WNT, BMP, FGF, and Activin) and function of intrinsic factors (e.g., OCT₄, NANOG, SOX₂, SALL₄) in the regulation of pluripotency in mammalian preimplantation embryos and pluripotent stem cells derived from them. We also focus at the existence of species-specific differences at the level of growth factor requirements, signaling pathways, and transcription factors. Thus, we discuss differences in mechanisms which understanding is one of the necessary steps allowing establishment of methods of efficient derivation, defined in vitro culture conditions, and possible future therapeutic applications of pluripotent stem cells.

Inhibition of GSK3beta enhances both adhesive and signalling activities of beta-catenin in mouse embryonic stem cells

BACKGROUND

GSK3beta (glycogen synthase kinase 3beta) regulates the expression level and activity of various target proteins, including beta-catenin. beta-Catenin is a co-activator of Wnt-dependent genes as well as a partner for transmembrane cadherins to mediate cell-to-cell adhesion. In some cases, inhibition of GSK3beta activity was shown to promote self-renewal of ESCs (embryonic stem cells), but immediate effects of GSK3beta inhibitors in these cells still remain elusive.

RESULTS

Here, we address the effects of GSK3beta inhibitors BIO (6-bromoindirubin-3'-oxime) and CHIR99021 on mESCs (mouse ESCs), focusing on modulation of beta-catenin activities. We found that, upon GSK3beta inhibition, the colonies of undifferentiated mESCs acquire a more compact morphology. This change is paralleled by two somewhat polar effects: (i) the accumulation of the beta-catenin, which is co-localized with E-cadherin at the plasma membrane, and the cytoplasmic, tyrosine unphosphorylated beta-catenin, which is able to bind the GST (glutathione transferase)-fused cytoplasmic domain of E-cadherin; and (ii) the accumulation of the tyrosine phosphorylated beta-catenin and its nuclear translocation that is accompanied by activation of the Tcf (T-cell factor)/beta-catenin-dependent transcription of Top-Flash reporter. The Tcf-mediated activation, however, does not affect most of the analysed Wnt-responsive genes involved in EMT (epithelial-mesenchymal transition) or cell-cycle progression, suggesting that the adhesive function of beta-catenin is dominant over transcription in undifferentiated mESCs. Treatment with BIO decreases proliferation rates of mESCs. This is not due to apoptosis, but rather to accumulation of cells in G1 phase of the cell cycle and is accompanied by down-regulation of the c-myc mRNA content.

CONCLUSION

Our results suggest that inhibition of GSK3beta activity in mESCs enhances both the beta-catenin/E-cadherin-mediated adhesion and the Tcf/beta-catenin-dependent transcription, but does not activate transcription in most of the examined genes involved in EMT and cell cycle progression.

The use of signalling pathway inhibitors and chromatin modifiers for enhancing pluripotency

Pluripotent embryonic stem cells have been isolated from a limited number of species. The new advances with inducing pluripotency in somatic cells have resulted in the generation of pluripotent stem cells while circumventing the need for embryos. In this review we describe the main signalling pathways involved in maintaining pluripotency and inducing differentiation. Inhibition of the signalling pathways involved in differentiation enhances the derivation and cultivation of pluripotent stem cells. Furthermore, we discuss the use of chromatin modifiers to maintain an open chromatin state which is characteristic of pluripotent stem cells, to facilitate the derivation of pluripotent cell lines.

Generation of human-induced pluripotent stem cells in the absence of exogenous Sox2

Induced pluripotent stem cell technology has attracted enormous interest for potential application in regenerative medicine. Here, we report that a specific glycogen synthase kinase 3 (GSK-3) inhibitor, CHIR99021, can induce the reprogramming of mouse embryonic fibroblasts transduced by only two factors, Oct4 and Klf4. When combined with Parnate (also named tranylcypromine), an inhibitor of lysine-specific demethylase 1, CHIR99021 can cause the reprogramming of human primary keratinocyte transduced with the two factors, Oct4 and Klf4. To our knowledge, this is the first time that human iPS cells have been generated from somatic cells without exogenous Sox2 expression. Our studies suggest that the GSK-3 inhibitor might have a general application to replace transcription factors in both mouse and human reprogramming.

Suppression of Erk signalling promotes ground state pluripotency in the mouse embryo

Embryonic stem (ES) cells can be derived and propagated from multiple strains of mouse and rat through application of small-molecule inhibitors of the fibroblast growth factor (FGF)/Erk pathway and of glycogen synthase kinase 3. These conditions shield pluripotent cells from differentiation-inducing stimuli. We investigate the effect of these inhibitors on the development of pluripotent epiblast in intact pre-implantation embryos. We find that blockade of Erk signalling from the 8-cell stage does not impede blastocyst formation but suppresses development of the hypoblast. The size of the inner cell mass (ICM) compartment is not reduced, however. Throughout the ICM, the epiblast-specific marker Nanog is expressed, and in XX embryos epigenetic silencing of the paternal X chromosome is erased. Epiblast identity and pluripotency were confirmed by contribution to chimaeras with germline transmission. These observations indicate that segregation of hypoblast from the bipotent ICM is dependent on FGF/Erk signalling and that in the absence of this signal, the entire ICM can acquire pluripotency. Furthermore, the epiblast does not require paracrine support from the hypoblast. Thus, naïve epiblast and ES cells are in a similar ground state, with an autonomous capacity for survival and replication, and high vulnerability to Erk signalling. We probed directly the relationship between naïve epiblast and ES cells. Dissociated ICM cells from freshly harvested late blastocysts gave rise to up to 12 ES cell clones per embryo when plated in the presence of inhibitors. We propose that ES cells are not a tissue culture creation, but are essentially identical to pre-implantation epiblast cells.

Pluripotin combined with leukemia inhibitory factor greatly promotes the derivation of embryonic stem cell lines from refractory strains

Most mouse embryonic stem (ES) cells are derived from a 129 or C57BL/6 background, whereas the derivation efficiency of ES cells is extremely low on certain refractory types of background for which ES cells are highly desired. Here we report an optimized, highly efficient protocol by combining pluripotin, a small molecule, and leukemia inhibitory factor (LIF) for the derivation of mouse ES cells. With this method, we successfully isolated ES cell lines from five strains of mice, with an efficiency of 57% for NOD-scid, 63% for SCID beige, 80% for CD-1, and 100% for two F1 strains from C57BL/6xCD-1. By tracking the Oct4-positive cells in the Oct4-green fluorescent protein embryos in the process of ES cell isolation, we found that pluripotin combined with LIF improved the efficiency of ES cell isolation by selectively maintaining the Oct4-positive cells in the outgrowth. To our knowledge, this is the first report of ES cells being efficiently derived from immunodeficient mice on refractory backgrounds (NOD-scid on a NOD background and SCID beige on a BALB/c background).

Transcriptional heterogeneity in mouse embryonic stem cells

The embryonic stem (ES) cell is a stem cell derived from early embryos that can indefinitely repeat self-renewing cell division cycles as an undifferentiated cell in vitro and give rise to all specialised cell types in the body. However, manipulating ES cell differentiation in vitro is a challenge due to, at least in part, heterogeneous gene induction. Recent experimental evidence has demonstrated that undifferentiated mouse ES cells maintained in culture exhibit heterogeneous expression of Dppa3, Nanog, Rex1, Pecam1 and Zscan4 as well as genes (Brachyury/T, Rhox6/9 and Twist2) normally expressed in specialised cell types. The Nanog-negative, Rex1-negative or T-positive ES cell subpopulation has a unique differentiation potential. Thus, studying the mechanism that generates ES cell subpopulations will improve manipulation of ES cell fate and help our understanding of the nature of embryonic development.

Subcellular localization of glycogen synthase kinase 3beta controls embryonic stem cell self-renewal

Phosphatidylinositol 3-kinase (PI3K), protein kinase B (AKT1), and c-myc have well-established roles in promoting the maintenance of murine embryonic stem cells (mESCs). In contrast, the activity of glycogen synthase kinase 3beta (GSK3beta), a negatively regulated target of AKT1 signaling, antagonizes self-renewal. Here, we show that PI3K/AKT1 signaling promotes self-renewal by suppressing GSK3beta activity and restricting its access to nuclear substrates such as c-myc. GSK3beta shuttles between the cytoplasm and nucleus in mESCs but accumulates in the cytoplasm in an inactive form due to AKT1-dependent nuclear export and inhibitory phosphorylation. When PI3K/AKT1 signaling declines following leukemia inhibitory factor withdrawal, active GSK3beta accumulates in the nucleus, where it targets c-myc through phosphorylation on threonine 58 (T58), promoting its degradation. Ectopic nuclear localization of active GSK3beta promotes differentiation, but this process is blocked by a mutant form of c-myc (T58A) that evades phosphorylation by GSK3beta. This novel mechanism explains how AKT1 promotes self-renewal by regulating the activity and localization of GSK3beta. This pathway converges on c-myc, a key regulator of mESC self-renewal.

Effects of Akt signaling on nuclear reprogramming

Reprogramming of the epigenetic state from differentiated to pluripotent cells can be attained by cell fusion of differentiated somatic cells with embryonic stem (ES) cells or transfer of the nucleus of a differentiated cell into an enucleated oocyte. Activation of Akt signaling is sufficient to maintain pluripotency of ES cells and promotes derivation of embryonic germ (EG) cells from primordial germ cells (PGCs). Here we analyzed the effects of Akt signaling on somatic cell nuclear reprogramming after cell fusion and nuclear transfer. We found that forced activation of Akt signaling stimulated reprogramming after cell fusion of ES cells with thymocytes or mouse embryonic fibroblasts. These hybrid cells showed ES cell characteristics, including in vitro and in vivo differentiation capacity. In contrast, Akt signaling significantly reduced the efficiency of reprogramming with nuclear transfer. Our results demonstrate that Akt signaling plays important roles on the nuclear reprogramming of somatic cells.

Culture of mouse embryonic stem cells

In this unit standard culture conditions for mouse embryonic stem cells (mESCs) on primary murine embryonic fibroblast (PMEF or MEF) monolayers, culture conditions without MEF for feeder-independent mESCs, and culture conditions in chemically defined media for both feeder-independent mESCs and feeder-dependent mESCs are described. For expansion of an mESC line, it is crucial that cells maintain their undifferentiated state and their self-renewal capacity, and that they remain karyotypically normal, all of which are necessary for successful chimerization of the germ line upon blastocyst injection. Derivation and culture conditions for the original mESCs have been described (notably Robertson, 1987; Smith, 1991; Nagy et al., 2003), however, as there are more and more mESC lines available, it becomes evident that culture conditions are cell-line specific to some extent, and there is a constant demand for culturing details for mESC lines derived from different mouse strains.

AKT signaling promotes derivation of embryonic germ cells from primordial germ cells

Primordial germ cells (PGCs) are embryonic germ cell precursors. Although the developmental potency of PGCs is restricted to the germ lineage, PGCs can acquire pluripotency, as verified by the in vitro establishment of embryonic germ (EG) cells and the in vivo production of testicular teratomas. PGC-specific inactivation of PTEN, which is a lipid phosphatase antagonizing phosphoinositide-3 kinase (PI3K), enhances both EG cell production and testicular teratoma formation. Here, we analyzed the effect of the serine/threonine kinase AKT, one of the major downstream effectors of PI3K, on the developmental potency of PGCs. We used transgenic mice that expressed an AKT-MER fusion protein, the kinase activity of which could be regulated by the ligand of modified estrogen receptor (MER), 4-hydroxytamoxifen. We found that hyperactivation of AKT signaling in PGCs at the proliferative phase dramatically augmented the efficiency of EG cell establishment. Furthermore, AKT signaling activation substituted to some extent for the effects of bFGF, an essential growth factor for EG cell establishment. By contrast, AKT activation had no effect on germ cells that were in mitotic arrest or that began meiosis at a later embryonic stage. In the transgenic PGCs, AKT activation induced phosphorylation of GSK3, which inhibits its kinase activity; enhanced the stability and nuclear localization of MDM2; and suppressed p53 phosphorylation, which is required for its activation. The p53 deficiency, but not GSK3 inhibition, recapitulated the effects of AKT hyperactivation on EG cell derivation, suggesting that p53 is one of the crucial downstream targets of the PI3K/AKT signal and that GSK3 is not.