Induction and monitoring of definitive and visceral endoderm differentiation of mouse ES cells

Role of SLC6A6 in promoting the survival and multidrug resistance of colorectal cancer

The treatment of colorectal cancer (CRC) might be improved by the identification of a signalling pathway that could be targeted with novel therapeutics. The results of this study indicate that the taurine transporter SLC6A6 is highly expressed in CRC cells compared with normal colonocytes. SLC6A6 knockdown (KD) attenuated cell survival and was accompanied by enhanced drug sensitivity to 5-fluorouracil (5-FU), doxycycline (DOX) and SN-38. Both the population frequency of the side population (SP) cells and their cancer stem cell (CSC)-like properties (such as tumour initiation, differentiation and chemoresistance) were abrogated by SLC6A6-KD. Conversely, SLC6A6 overexpression increased cell survival and the proportion of SP cells, enhancing multidrug resistance (MDR). Additionally, SLC6A6-siRNA treatment enhanced the cytotoxic effects of all 3 drugs, whereas the efficacy of ABCG2-siRNA treatment was limited to its 2 substrate drugs, DOX and SN-38. This study indicates that SLC6A6 plays an important role in the maintenance of CSC characteristics, thus promoting cell survival signalling and chemoresistance. Therefore, SLC6A6 inhibition may be a promising therapeutic strategy for refractory CRC.

Klf4 and Klf5 differentially inhibit mesoderm and endoderm differentiation in embryonic stem cells

Krüppel-like factors (Klf) 4 and 5 are two closely related members of the Klf family, known to play key roles in cell cycle regulation, somatic cell reprogramming and pluripotency. Here we focus on the functional divergence between Klf4 and Klf5 in the inhibition of mouse embryonic stem (ES) cell differentiation. Using microarrays and chromatin immunoprecipitation coupled to ultra-high-throughput DNA sequencing, we show that Klf4 negatively regulates the expression of endodermal markers in the undifferentiated ES cells, including transcription factors involved in the commitment of pluripotent stem cells to endoderm differentiation. Knockdown of Klf4 enhances differentiation towards visceral and definitive endoderm. In contrast, Klf5 negatively regulates the expression of mesodermal markers, some of which control commitment to the mesoderm lineage, and knockdown of Klf5 specifically enhances differentiation towards mesoderm. We conclude that Klf4 and Klf5 differentially inhibit mesoderm and endoderm differentiation in murine ES cells.

Systems level approach reveals the correlation of endoderm differentiation of mouse embryonic stem cells with specific microstructural cues of fibrin gels

Stem cells receive numerous cues from their associated substrate that help to govern their behaviour. However, identification of influential substrate characteristics poses difficulties because of their complex nature. In this study, we developed an integrated experimental and systems level modelling approach to investigate and identify specific substrate features influencing differentiation of mouse embryonic stem cells (mESCs) on a model fibrous substrate, fibrin. We synthesized a range of fibrin gels by varying fibrinogen and thrombin concentrations, which led to a range of substrate stiffness and microstructure. mESCs were cultured on each of these gels, and characterization of the differentiated cells revealed a strong influence of substrate modulation on gene expression patterning. To identify specific substrate features influencing differentiation, the substrate microstructure was quantified by image analysis and correlated with stem cell gene expression patterns using a statistical model. Significant correlations were observed between differentiation and microstructure features, specifically fibre alignment. Furthermore, this relationship occurred in a lineage-specific manner towards endoderm. This systems level approach allows for identification of specific substrate features from a complex material which are influential to cellular behaviour. Such analysis may be effective in guiding the design of scaffolds with specific properties for tissue engineering applications.

Sox17-mediated maintenance of fetal intra-aortic hematopoietic cell clusters

During mouse development, definitive hematopoiesis is first detected around embryonic day 10.5 (E10.5) in the aorta-gonad-mesonephros (AGM) region, which exhibits intra-aortic cell clusters. These clusters are known to contain hematopoietic stem cells (HSCs). On the other hand, it is not clear how the cells in such clusters maintain their HSC phenotype and how they are triggered to differentiate. Here we found that an endodermal transcription factor marker, Sox17, and other F-group (SoxF) proteins, Sox7 and Sox18, were expressed in E10.5 intra-aortic cell clusters. Forced expression of any of these SoxF proteins, particularly Sox17, in E10.5 AGM CD45(low) c-Kit(high) cells, which are the major component of intra-aortic clusters, led to consistent formation of cell clusters in vitro during several passages of cocultures with stromal cells. Cluster-forming cells with constitutive Sox17 expression retained long-term bone marrow reconstitution activity in vivo. Notably, shutdown of exogenously introduced Sox17 gene expression resulted in immediate hematopoietic differentiation. These results indicate that SoxF proteins, especially Sox17, contribute to the maintenance of cell clusters containing HSCs in the midgestation AGM region. Furthermore, SoxF proteins play a pivotal role in controlling the HSC fate decision between indefinite self-renewal and differentiation during fetal hematopoiesis.

miR-335 promotes mesendodermal lineage segregation and shapes a transcription factor gradient in the endoderm

Transcription factors (TFs) pattern developing tissues and determine cell fates; however, how spatio-temporal TF gradients are generated is ill defined. Here we show that miR-335 fine-tunes TF gradients in the endoderm and promotes mesendodermal lineage segregation. Initially, we identified miR-335 as a regulated intronic miRNA in differentiating embryonic stem cells (ESCs). miR-335 is encoded in the mesoderm-specific transcript (Mest) and targets the 3'-UTRs of the endoderm-determining TFs Foxa2 and Sox17. Mest and miR-335 are co-expressed and highly accumulate in the mesoderm, but are transiently expressed in endoderm progenitors. Overexpression of miR-335 does not affect initial mesendoderm induction, but blocks Foxa2- and Sox17-mediated endoderm differentiation in ESCs and ESC-derived embryos. Conversely, inhibition of miR-335 activity leads to increased Foxa2 and Sox17 protein accumulation and endoderm formation. Mathematical modeling predicts that transient miR-335 expression in endoderm progenitors shapes a TF gradient in the endoderm, which we confirm by functional studies in vivo. Taken together, our results suggest that miR-335 targets endoderm TFs for spatio-temporal gradient formation in the endoderm and to stabilize lineage decisions during mesendoderm formation.

Concise review: pluripotent stem cell-based regenerative applications for failing β-cell function

Diabetes engenders the loss of pancreatic β-cell mass and/or function, resulting in insulin deficiency relative to the metabolic needs of the body. Diabetic care has traditionally relied on pharmacotherapy, exemplified by insulin replacement to target peripheral actions of the hormone. With growing understanding of the pathogenesis of diabetic disease, alternative approaches aiming at repair and restoration of failing β-cell function are increasingly considered as complements to current diabetes therapy regimens. To this end, emphasis is placed on transplantation of exogenous pancreas/islets or artificial islets, enhanced proliferation and maturation of endogenous β cells, prevention of β-cell loss, or fortified renewal of β-like-cell populations from stem cell pools and non-β-cell sources. In light of emerging clinical experiences with human embryonic stem cells and approval of the first in-human trial with induced pluripotent stem cells, in this study we highlight advances in β-cell regeneration strategies with a focus on pluripotent stem cell platforms in the context of translational applications.

Generation of β cells from human pluripotent stem cells: are we there yet?

In 1998, the landmark paper describing the isolation and culture of human embryonic stem cells (ESCs) was published. Since that time, the main goal of many diabetes researchers has been to derive β cells from ESCs as a renewable cell-based therapy for the treatment of patients with diabetes. In working toward this goal, numerous protocols that attempt to recapitulate normal pancreatic development have been published that result in the formation of pancreatic cell types from human pluripotent cells. This review examines stem cell differentiation methods and places them within the context of pancreatic development. We additionally compare strategies that are currently being used to generate pancreatic cell types and contrast them with approaches that have been used to generate functional cell types in different lineages. In doing this, we aim to identify how new approaches might be used to improve yield and functionality of in vitro-derived pancreatic β cells as an eventual cell-based therapy for type 1 diabetes.

Next-generation regenerative medicine: organogenesis from stem cells in 3D culture

The behavior of stem cells, when they work collectively, can be much more sophisticated than one might expect from their individual programming. This Perspective covers recent discoveries about the dynamic patterning and structural self-formation of complex organ buds in 3D stem cell culture, including the generation of various neuroectodermal and endodermal tissues. For some tissues, epithelial-mesenchymal interactions can also be manipulated in coculture to guide organogenesis. This new area of stem cell research-the spatiotemporal control of dynamic cellular interactions-will open a new avenue for next-generation regenerative medicine.

Differentiation of nonhuman primate embryonic stem cells into hepatocyte-like cells

OBJECTIVE

To investigate whether cells derived from rhesus monkey embryonic stem cells (ESC) had hepatocyte characteristics after the differentiation.

METHODS

Rhesus monkey ESC were induced towards hepatocyte-like cells via a four-step differentiation process: the formation of embryoid bodies (EB), EB in activin A and insulin-transferrin-selenium medium for 4 days, in fibroblast growth factor (FGF)-4 and bone morphogenetic protein-2 (BMP2) medium for 8 days, in hepatocyte culture medium containing hepatocyte growth factor for 3 days and then with oncostatin M and dexamethasone for another 5 days. Expression of albumin (ALB), glucose-6-phosphatase, α-fetoprotein (AFP) and α-1 antitrypsin (α1-AT) at the mRNA level in differentiated cells were detected by reverse transcription-polymerase chain reaction. The expression of hepatocyte markers AFP, ALB, hepatocyte nuclear factor 4 (HNF4), cytokeratin 8 (CK8), CK19 and cell proliferation marker, Ki67, in the differentiated cells were determined by immunocytochemistry. The ultrastructure of the differentiated cells was examined by electron microscopy. Indocyanine green (ICG) uptake was also explored.

RESULTS

After induction, some differentiated cells were binucleate, which is typical of hepatocytes. Hepatocyte-specific genes ALB, glucose-6-phosphatase, AFP and α1-AT were expressed in the differentiated cells. The differentiated cells expressed hepatocyte markers AFP, ALB, HNF4, CK8 and CK19 at the protein level. The cells also expressed cell proliferation marker Ki67. Under electron microscopy, the ultrastructures of hepatocyte-like cells, such as mitochondrion and catalase-containing peroxisomes, were observed in the differentiated cells. ICG uptake test was positive in differentiated cells.

CONCLUSIONS

With cytokine induction, rhesus monkey ESC differentiated into cells displaying morphological features, gene expression patterns and metabolic activities characteristic of hepatocytes.

Expansive generation of functional airway epithelium from human embryonic stem cells

Production of human embryonic stem cell (hESC)-derived lung progenitors has broad applicability for drug screening and cell therapy; however, this is complicated by limitations in demarcating phenotypic changes with functional validation of airway cell types. In this paper, we reveal the potential of hESCs to produce multipotent lung progenitors using a combined growth factor and physical culture approach, guided by the use of novel markers LIFRα and NRP1. Lung specification of hESCs was achieved by priming differentiation via matrix-specific support, followed by air-liquid interface to allow generation of lung progenitors capable of in vitro maturation into airway epithelial cell types, resulting in functional characteristics such as secretion of pulmonary surfactant, ciliation, polarization, and acquisition of innate immune activity. This approach provided a robust expansion of lung progenitors, allowing in vivo assessment, which demonstrated that only fully differentiated hESC-derived airway cells were retained in the distal airway, where they aided in physiological recovery in immunocompromised mice receiving airway injury. Our study provides a basis for translational applications of hESCs for lung diseases.

Induced pluripotent stem cell modeling of multisystemic, hereditary transthyretin amyloidosis

Familial transthyretin amyloidosis (ATTR) is an autosomal-dominant protein-folding disorder caused by over 100 distinct mutations in the transthyretin (TTR) gene. In ATTR, protein secreted from the liver aggregates and forms fibrils in target organs, chiefly the heart and peripheral nervous system, highlighting the need for a model capable of recapitulating the multisystem complexity of this clinically variable disease. Here, we describe the directed differentiation of ATTR patient-specific iPSCs into hepatocytes that produce mutant TTR, and the cardiomyocytes and neurons normally targeted in the disease. We demonstrate that iPSC-derived neuronal and cardiac cells display oxidative stress and an increased level of cell death when exposed to mutant TTR produced by the patient-matched iPSC-derived hepatocytes, recapitulating essential aspects of the disease in vitro. Furthermore, small molecule stabilizers of TTR show efficacy in this model, validating this iPSC-based, patient-specific in vitro system as a platform for testing therapeutic strategies.

Human iPS cell-derived alveolar epithelium repopulates lung extracellular matrix

The use of induced pluripotent stem cells (iPSCs) has been postulated to be the most effective strategy for developing patient-specific respiratory epithelial cells, which may be valuable for lung-related cell therapy and lung tissue engineering. We generated a relatively homogeneous population of alveolar epithelial type II (AETII) and type I (AETI) cells from human iPSCs that had phenotypic properties similar to those of mature human AETII and AETI cells. We used these cells to explore whether lung tissue can be regenerated in vitro. Consistent with an AETII phenotype, we found that up to 97% of cells were positive for surfactant protein C, 95% for mucin-1, 93% for surfactant protein B, and 89% for the epithelial marker CD54. Additionally, exposing induced AETII to a Wnt/β-catenin inhibitor (IWR-1) changed the iPSC-AETII-like phenotype to a predominantly AETI-like phenotype. We found that of induced AET1 cells, more than 90% were positive for type I markers, T1α, and caveolin-1. Acellular lung matrices were prepared from whole rat or human adult lungs treated with decellularization reagents, followed by seeding these matrices with alveolar cells derived from human iPSCs. Under appropriate culture conditions, these progenitor cells adhered to and proliferated within the 3D lung tissue scaffold and displayed markers of differentiated pulmonary epithelium.

Efficient definitive endoderm induction from mouse embryonic stem cell adherent cultures: a rapid screening model for differentiation studies

Definitive endoderm (DE) differentiation from mouse embryonic stem cell (mESC) monolayer cultures has been limited by poor cell survival or low efficiency. Recently, a combination of TGFβ and Wnt activation with BMP inhibition improved DE induction in embryoid bodies cultured in suspension. Based on these observations we developed a protocol to efficiently induce DE cells in monolayer cultures of mESCs. We obtained a good cell yield with 54.92% DE induction as shown by Foxa2, Sox17, Cxcr4 and E-Cadherin expression. These DE-cells could be further differentiated into posterior foregut and pancreatic phenotypes using a culture protocol initially developed for human embryonic stem cell (hESC) differentiation. In addition, this mESC-derived DE gave rise to hepatocyte-like cells after exposure to BMP and FGF ligands. Our data therefore indicate a substantial improvement of monolayer DE induction from mESCs and support the concept that differentiation conditions for mESC-derived DE are similar to those for hESCs. As mESCs are easier to maintain and manipulate in culture compared to hESCs, and considering the shorter duration of embryonic development in the mouse, this method of efficient DE induction on monolayer will promote the development of new differentiation protocols to obtain DE-derivatives, like pancreatic beta-cells, for future use in cell replacement therapies.

Location of transient ectodermal progenitor potential in mouse development

Ectoderm is one of the three classic germ layers in the early mouse embryo, with the capacity to develop into both the central nervous system and epidermis. Because it is a transient phase of development with few molecular markers, the early ectoderm is the least understood germ layer in mouse embryonic development. In this work, we studied the differentiation potential of isolated ectoderm tissue in response to BMP signaling at various developmental stages (E6.5, E7.0 and E7.5), and identified a transient region in the anterior-proximal side of the embryo at E7.0 that possesses the ability to become neural or epidermal ectoderm in response to the absence or presence of BMP4, respectively. Furthermore, we demonstrated that inhibition of Nodal signaling could direct the pluripotent E6.5 epiblast cells towards ectoderm lineages during differentiation in explants in vitro. Our work not only improves our understanding of ectodermal layer development in early embryos, but also provides a framework for regenerative differentiation towards ectodermal tissues.

Culture of mouse amniotic fluid-derived cells on irradiated STO feeders results in the generation of primitive endoderm cell lines capable of self-renewal in vitro

The cells present in amniotic fluid (AF) are currently used for prenatal diagnosis of fetal anomalies but are also a potential source of cells for cell therapy. To better characterize putative progenitor cell populations present in AF, we used culture conditions that support self-renewal to determine if these promoted the generation of stable cell lines from AF-derived cells (AFC). Cells isolated from E11.5 mouse were cultured on irradiated STO fibroblast feeder layers in human embryonic germ cell derivation conditions. The cultures grew multicellular epithelial colonies that could be repropagated from single cells. Reverse transcription semiquantitative polymerase chain reaction of established cell lines revealed that they belonged to the extraembryonic endoderm (ExEn) expressing high levels of Gata6, Gata4, Sox17, Foxa2 and Sox7 mRNA. Hierarchical clustering based on the whole transcriptome expression profile of the AFC lines (AFCL) shows significant correlation between transcription profiles of AFCL and blastocyst-derived XEN, an ExEn cell line. In vitro differentiation of AFCL results in the generation of cells expressing albumin and α-fetoprotein (AFP), while intramuscular injection of AFCL into immunodeficient mice produced AFP-positive tumors with primitive endodermal appearance. Hence, E11.5 mouse AF contains cells that efficiently produce XEN lines. These AF-derived XEN lines do not spontaneously differentiate into embryonic-type cells but are phenotypically stable and have the capacity for extensive expansion. The lack of requirement for reprogramming factors to turn AF-derived progenitor cells into stable cell lines capable of massive expansion together with the known ability of ExEn to contribute to embryonic tissue suggests that this cell type may be a candidate for banking for cell therapies.

The PR/SET domain zinc finger protein Prdm4 regulates gene expression in embryonic stem cells but plays a nonessential role in the developing mouse embryo

Prdm4 is a highly conserved member of the Prdm family of PR/SET domain zinc finger proteins. Many well-studied Prdm family members play critical roles in development and display striking loss-of-function phenotypes. Prdm4 functional contributions have yet to be characterized. Here, we describe its widespread expression in the early embryo and adult tissues. We demonstrate that DNA binding is exclusively mediated by the Prdm4 zinc finger domain, and we characterize its tripartite consensus sequence via SELEX (systematic evolution of ligands by exponential enrichment) and ChIP-seq (chromatin immunoprecipitation-sequencing) experiments. In embryonic stem cells (ESCs), Prdm4 regulates key pluripotency and differentiation pathways. Two independent strategies, namely, targeted deletion of the zinc finger domain and generation of a EUCOMM LacZ reporter allele, resulted in functional null alleles. However, homozygous mutant embryos develop normally and adults are healthy and fertile. Collectively, these results strongly suggest that Prdm4 functions redundantly with other transcriptional partners to cooperatively regulate gene expression in the embryo and adult animal.

Wnt/β-catenin signalling regulates Sox17 expression and is essential for organizer and endoderm formation in the mouse

Several signalling cascades are implicated in the formation and patterning of the three principal germ layers, but their precise temporal-spatial mode of action in progenitor populations remains undefined. We have used conditional gene deletion of mouse β-catenin in Sox17-positive embryonic and extra-embryonic endoderm as well as vascular endothelial progenitors to address the function of canonical Wnt signalling in cell lineage formation and patterning. Conditional mutants fail to form anterior brain structures and exhibit posterior body axis truncations, whereas initial blood vessel formation appears normal. Tetraploid rescue experiments reveal that lack of β-catenin in the anterior visceral endoderm results in defects in head organizer formation. Sox17 lineage tracing in the definitive endoderm (DE) shows a cell-autonomous requirement for β-catenin in midgut and hindgut formation. Surprisingly, wild-type posterior visceral endoderm (PVE) in midgut- and hindgut-deficient tetraploid chimera rescues the posterior body axis truncation, indicating that the PVE is important for tail organizer formation. Upon loss of β-catenin in the visceral endoderm and DE lineages, but not in the vascular endothelial lineage, Sox17 expression is not maintained, suggesting downstream regulation by canonical Wnt signalling. Strikingly, Tcf4/β-catenin transactivation complexes accumulated on Sox17 cis-regulatory elements specifically upon endoderm induction in an embryonic stem cell differentiation system. Together, these results indicate that the Wnt/β-catenin signalling pathway regulates Sox17 expression for visceral endoderm pattering and DE formation and provide the first functional evidence that the PVE is necessary for gastrula organizer gene induction and posterior axis development.

Foxa2-venus fusion reporter mouse line allows live-cell analysis of endoderm-derived organ formation

The Foxa2-winged helix/forkhead box transcription factor (TF) is absolutely required for endoderm formation and organogenesis. Foxa2 plays essential roles during lung, liver, pancreas, and gastrointestinal tract development and regulates cell-type specific programs in the adult organism. To specifically address Foxa2 function during organ development and homeostasis, we generated a Foxa2-Venus fusion (FVF) reporter protein by gene targeting in embryonic stem (ES) cells. The FVF knock-in reporter is expressed under endogenous Foxa2 control and the fluorescent protein fusion does not interfere with TF function, as homozygous mice are viable and fertile. Moreover, the FVF protein localizes to the nucleus, associates with chromatin during mitosis, and reflects the endogenous Foxa2 protein distribution pattern in several tissues in heterozygous animals. Importantly, live-cell imaging on single-cell level of the FVF and Sox17-Cherry fusion double knock-in reporter ES cell line reveals the dynamics of endoderm TF accumulation during ES cell differentiation. The FVF reporter also allowed us to identify the endoderm progenitors during gastrulation and to visualize the different branching morphogenesis modes of the lung and pancreas epithelium in ex vivo embryo and organ cultures. In summary, the generation of the FVF reporter line adds an important new tool to visualize and analyse endoderm-derived organ development and homeostasis on the cellular and molecular level.

Adaptation of a commonly used, chemically defined medium for human embryonic stem cells to stable isotope labeling with amino acids in cell culture

Metabolic labeling with stable isotopes is a prominent technique for comparative quantitative proteomics, and stable isotope labeling with amino acids in cell culture (SILAC) is the most commonly used approach. SILAC is, however, traditionally limited to simple tissue culture regimens and only rarely employed in the context of complex culturing conditions as those required for human embryonic stem cells (hESCs). Classic hESC culture is based on the use of mouse embryonic fibroblasts (MEFs) as a feeder layer, and as a result, possible xenogeneic contamination, contribution of unlabeled amino acids by the feeders, interlaboratory variability of MEF preparation, and the overall complexity of the culture system are all of concern in conjunction with SILAC. We demonstrate a feeder-free SILAC culture system based on a customized version of a commonly used, chemically defined hESC medium developed by Ludwig et al. and commercially available as mTeSR1 [mTeSR1 is a trade mark of WiCell (Madison, WI) licensed to STEMCELL Technologies (Vancouver, Canada)]. This medium, together with adjustments to the culturing protocol, facilitates reproducible labeling that is easily scalable to the protein amounts required by proteomic work flows. It greatly enhances the usability of quantitative proteomics as a tool for the study of mechanisms underlying hESCs differentiation and self-renewal. Associated data have been deposited to the ProteomeXchange with the identifier PXD000151.

Hepatic stellate cells promote the differentiation of embryonic stem cell-derived definitive endodermal cells into hepatic progenitor cells

AIM

Hepatic non-parenchymal cells are well known to be capable of providing an important microenvironment and growth factors for hepatic regeneration, but their capacity for directing embryonic stem cells (ESC) toward hepatocytes remains to be assessed. Thus, this study aims to investigate the role of hepatic stellate cells (HSC), the major type of hepatic non-parenchymal cells, in the differentiation of ESC as well as exploring the potentiality of ESC in regeneration medicine for cell-based therapy.

METHODS

A two-step differentiation procedure that utilized the capability of HSC to regulate proliferation and differentiation of hepatocytes was used to develop an approach for directing the differentiation of ESC towards hepatic progenitor cells. Mouse ESC were cultivated in a serum-free medium containing Activin A and fibroblast growth factor to generate definitive endodermal cells characterized by the CXCR4 cell-surface marker. After 6-8 days in culture, approximately 60% of the differentiated cells expressed CXCR4, and more than 90% of the CXCR4 positive cells could be recovered by cell sorting. The purified CXCR4 positive cells were co-cultured with mouse HSC as feeder cells in basal medium without additional hepatocyte growth factors. Differentiation was complete after 10-12 days of co-culture, and hepatic progenitor cell markers such as α-fetoprotein (afp) and albumin (alb) were detected in the terminally differentiated ESC.

CONCLUSION

These results show that HSC provide an appropriate microenvironment and pivotal growth factors for generation of hepatic progenitor cells from ESC-derived definitive endodermal cells, and suggest that this approach possibly allows for hepatic differentiation of ESC imitating the process of hepatic regeneration.

Hepatic differentiation of mouse iPS cells and analysis of liver engraftment potential of multistage iPS progeny

Hepatocyte transplantation is considered a promising therapy for patients with liver diseases. Induced pluripotent stem cells (iPSCs) are an unlimited source for the generation of functional hepatocytes. While several protocols that direct the differentiation of iPSCs into hepatocyte-like cells have already been reported, the liver engraftment potential of iPSC progeny obtained at each step of hepatic differentiation has not yet been thoroughly investigated. In this study, we present an efficient strategy to differentiate mouse iPSCs into hepatocyte-like cells and evaluate their liver engraftment potential at different time points of the protocol (5, 10, 15, and 20 days of differentiation). iPSCs were differentiated in the presence of cytokines, growth factors, and small molecules to finally generate hepatocyte-like cells. These iPSC-derived hepatocyte-like cells exhibited hepatocyte-associated functions, such as albumin secretion and urea synthesis. When we transplanted iPSC progeny into the spleen, we found that 15- and 20-day iPSC progeny engrafted into the livers and further acquired hepatocyte morphology. In contrast, 5- and 10-day iPSC progeny were also able to engraft but did not generate hepatocyte-like cells in vivo. Our data may aid in improving current protocols geared towards the use of iPSCs as a new source of liver-targeted cell therapies.

Secreted cerberus1 as a marker for quantification of definitive endoderm differentiation of the pluripotent stem cells

To date, CXCR4 and E-cadherin double-positive cells detected by flow cytometry have been used to identify the differentiation of embryonic stem (ES) cells or induced pluripotent stem (iPS) cells into definitive endoderm (DE) lineages. Quantification of DE differentiation from ES/iPS cells by using flow cytometry is a multi-step procedure including dissociation of the cells, antibody reaction, and flow cytometry analysis. To establish a quick assay method for quantification of ES/iPS cell differentiation into the DE without dissociating the cells, we examined whether secreted Cerberus1 (Cer1) protein could be used as a marker. Cer1 is a secreted protein expressed first in the anterior visceral endoderm and then in the DE. The amount of Cer1 secreted correlated with the proportion of CXCR4+/E-Cadherin+ cells that differentiated from mouse ES cells. In addition, we found that human iPS cell-derived DE also expressed the secreted CER1 and that the expression level correlated with the proportion of SOX17+/FOXA2+ cells present. Taken together, these results show that Cer1 (or CER1) serves as a good marker for quantification of DE differentiation of mouse and human ES/iPS cells.

Basics and applications of stem cells in the pancreas

Enormous efforts have been made to establish pancreatic stem/progenitor cells as a source for regenerative medicine for the treatment of diabetes mellitus. In recent years, it has been recognized that the self-renewal of beta cells is the dominant process involved in postnatal beta-cell regeneration and expansion. Nevertheless, several in-vitro studies have suggested that ductal or as yet unidentified cells are candidates for pancreatic stem/progenitor cells that can differentiate into multilineage cells, including insulin(+) cells. The question remains as to whether beta cells are generated postnatally from stem/progenitor cells other than pre-existing beta cells. Furthermore, mutated pancreatic stem cells are considered to be prospective candidates for cancer stem cells or tumor-initiating cells. This review highlights recent progress in pancreatic stem/progenitor cell research.

Derivation of extraembryonic endoderm stem (XEN) cells from mouse embryos and embryonic stem cells

At the time of implantation in the maternal uterus, the mouse blastocyst possesses an inner cell mass comprising two lineages: epiblast (Epi) and primitive endoderm (PrE). Representative stem cells derived from these two cell lineages can be expanded and maintained indefinitely in vitro as either embryonic stem (ES) or XEN cells, respectively. Here we describe protocols that can be used to establish XEN cell lines. These include the establishment of XEN cells from blastocyst-stage embryos in either standard embryonic or trophoblast stem (TS) cell culture conditions. We also describe protocols for establishing XEN cells directly from ES cells by either retinoic acid and activin-based conversion or by overexpression of the GATA transcription factor Gata6. XEN cells are a useful model of PrE cells, with which they share gene expression, differentiation potential and lineage restriction. The robust protocols for deriving XEN cells described here can be completed within 2-3 weeks.

The histone demethylase Jmjd3 sequentially associates with the transcription factors Tbx3 and Eomes to drive endoderm differentiation

Stem cell differentiation depends on transcriptional activation driven by lineage-specific regulators as well as changes in chromatin organization. However, the coordination of these events is poorly understood. Here, we show that T-box proteins team up with chromatin modifying enzymes to drive the expression of the key lineage regulator, Eomes during endodermal differentiation of embryonic stem (ES) cells. The Eomes locus is maintained in a transcriptionally poised configuration in ES cells. During early differentiation steps, the ES cell factor Tbx3 associates with the histone demethylase Jmjd3 at the enhancer element of the Eomes locus to allow enhancer-promoter interactions. This spatial reorganization of the chromatin primes the cells to respond to Activin signalling, which promotes the binding of Jmjd3 and Eomes to its own bivalent promoter region to further stimulate Eomes expression in a positive feedback loop. In addition, Eomes activates a transcriptional network of core regulators of endodermal differentiation. Our results demonstrate that Jmjd3 sequentially associates with two T-box factors, Tbx3 and Eomes to drive stem cell differentiation towards the definitive endoderm lineage.

Generating β-cells in vitro: progress towards a Holy Grail

PURPOSE OF REVIEW

Diabetes is a debilitating disease characterized by a chronic inability to normalize blood glucose levels. Transplanting cadaveric pancreata or isolated pancreatic islets can restore glucose homeostasis, but organ demand outstrips supply. Consequently, there is significant interest in alternative tissue sources. This review summarizes state-of-the-art efforts to generate scalable, functional β-cells to treat diabetes.

RECENT FINDINGS

Applying knowledge gleaned from developmental biology, human pluripotent stem cells can be treated stepwise with combinations of small molecules, developmentally relevant growth factors, and morphogens to generate pancreatic progenitor cells (PPCs) in vitro. Transplanted PPCs can then further mature in vivo into functional islet-like tissues containing all of the endocrine hormone cells present in adult islets and can reverse hyperglycemia in a diabetic animal model. Recent publications demonstrate that skin, liver, and other cell lineages may also be reprogrammed to functional β-like cells.

SUMMARY

Although generation of fully functional β-cells in vitro has not yet been achieved, possible intermediate approaches to treat diabetes include using PPCs or reprogramming adult cells to β-like cells. A cell therapy with either approach will require isolation from the host immune response. Ongoing efforts are addressing this need through the use of immune-isolation devices to avoid immunosuppressive drugs.

Functional evaluation of ES cell-derived endodermal populations reveals differences between Nodal and Activin A-guided differentiation

Embryonic stem (ES) cells hold great promise with respect to their potential to be differentiated into desired cell types. Of interest are organs derived from the definitive endoderm, such as the pancreas and liver, and animal studies have revealed an essential role for Nodal in development of the definitive endoderm. Activin A is a related TGFβ member that acts through many of the same downstream signaling effectors as Nodal and is thought to mimic Nodal activity. Detailed characterization of ES cell-derived endodermal cell types by gene expression analysis in vitro and functional analysis in vivo reveal that, despite their similarity in gene expression, Nodal and Activin-derived endodermal cells exhibit a distinct difference in functional competence following transplantation into the developing mouse embryo. Pdx1-expressing cells arising from the respective endoderm populations exhibit extended differences in their competence to mature into insulin/c-peptide-expressing cells in vivo. Our findings underscore the importance of functional cell-type evaluation during stepwise differentiation of stem cells.

Modulation of the Wnt/beta-catenin pathway in human oligodendroglioma cells by Sox17 regulates proliferation and differentiation

Oligodendrogliomas originate from oligodendrocyte progenitor cells (OPCs), whose development is regulated by the Sonic hedgehog and Wnt/beta-catenin pathways. We investigated the contribution of these pathways in the proliferation and differentiation of human oligodendroglioma cells (HOG). Inhibition of Hedgehog signaling with cyclopamine decreased cell survival and increased phosphorylated beta-catenin without altering myelin protein levels. Conversely, treatment of HOG with the Wnt antagonist secreted frizzled related protein (SFRP1), led to increased myelin protein levels and reduced cell proliferation, suggesting cell cycle arrest and differentiation. Unlike normal primary human OPCs, beta-catenin in HOG cells is not associated with endogenous Sox17 protein despite high levels of both proteins. Retroviral overexpression of recombinant Sox17 increased HOG cell cycle exit and apoptosis, and raised myelin protein levels and the percentage of O4(+) cells, indicating increased differentiation. Recombinant Sox17 also increased beta-catenin-TCF4-Sox17 complex formation and decreased total cellular levels of beta-catenin. These changes were associated with increased SFRP1, and reduced expression of Wnt-1 and Frizzled-1, -3 and -7 RNA, indicating that Sox17 induced a Hedgehog target, and regulated Wnt signaling at multiple levels. Our studies indicate that Wnt signaling regulates HOG cell cycle arrest and differentiation, and that recombinant Sox17 mediates modulation of the Wnt pathway through changes in beta-catenin, SFRP1 and Wnt/Frizzled expression. Our results thus identify Sox17 as a potential molecular target to include in HOG therapeutic strategies.

Endodermal stem cell populations derived from pluripotent stem cells

The generation of functional endodermal lineages, such as hepatocytes and pancreatic endocrine cells, from pluripotent stem cells (PSCs) remains a challenge. One strategy to enhance the purity, yield and maturity of endodermal derivatives is to expand endoderm committed stem or progenitor cell populations derived from PSCs before final differentiation. Recent studies have shown that this is in fact a viable option both for expanding pure populations of endodermal cells as well as for generating more mature derivative tissues, as highlighted in the case of pancreatic beta cells.

TGF-β/Smad2/3 signaling directly regulates several miRNAs in mouse ES cells and early embryos

The Transforming Growth Factor-β (TGF-β) signaling pathway is one of the major pathways essential for normal embryonic development and tissue homeostasis, with anti-tumor but also pro-metastatic properties in cancer. This pathway directly regulates several target genes that mediate its downstream functions, however very few microRNAs (miRNAs) have been identified as targets. miRNAs are modulators of gene expression with essential roles in development and a clear association with diseases including cancer. Little is known about the transcriptional regulation of the primary transcripts (pri-miRNA, pri-miR) from which several mature miRNAs are often derived. Here we present the identification of miRNAs regulated by TGF-β signaling in mouse embryonic stem (ES) cells and early embryos. We used an inducible ES cell system to maintain high levels of the TGF-β activated/phosphorylated Smad2/3 effectors, which are the transcription factors of the pathway, and a specific inhibitor that blocks their activation. By performing short RNA deep-sequencing after 12 hours Smad2/3 activation and after 16 hours inhibition, we generated a database of responsive miRNAs. Promoter/enhancer analysis of a subset of these miRNAs revealed that the transcription of pri-miR-181c/d and the pri-miR-341∼3072 cluster were found to depend on activated Smad2/3. Several of these miRNAs are expressed in early mouse embryos, when the pathway is known to play an essential role. Treatment of embryos with TGF-β inhibitor caused a reduction of their levels confirming that they are targets of this pathway in vivo. Furthermore, we showed that pri-miR-341∼3072 transcription also depends on FoxH1, a known Smad2/3 transcription partner during early development. Together, our data show that miRNAs are regulated directly by the TGF-β/Smad2/3 pathway in ES cells and early embryos. As somatic abnormalities in functions known to be regulated by the TGF-β/Smad2/3 pathway underlie tumor suppression and metastasis, this research also provides a resource for miRNAs involved in cancer.

Directed pancreatic acinar differentiation of mouse embryonic stem cells via embryonic signalling molecules and exocrine transcription factors

Pluripotent embryonic stem cells (ESC) are a promising cellular system for generating an unlimited source of tissue for the treatment of chronic diseases and valuable in vitro differentiation models for drug testing. Our aim was to direct differentiation of mouse ESC into pancreatic acinar cells, which play key roles in pancreatitis and pancreatic cancer. To that end, ESC were first differentiated as embryoid bodies and sequentially incubated with activin A, inhibitors of Sonic hedgehog (Shh) and bone morphogenetic protein (BMP) pathways, fibroblast growth factors (FGF) and retinoic acid (RA) in order to achieve a stepwise increase in the expression of mRNA transcripts encoding for endodermal and pancreatic progenitor markers. Subsequent plating in Matrigel® and concomitant modulation of FGF, glucocorticoid, and folllistatin signalling pathways involved in exocrine differentiation resulted in a significant increase of mRNAs encoding secretory enzymes and in the number of cells co-expressing their protein products. Also, pancreatic endocrine marker expression was down-regulated and accompanied by a significant reduction in the number of hormone-expressing cells with a limited presence of hepatic marker expressing-cells. These findings suggest a selective activation of the acinar differentiation program. The newly differentiated cells were able to release α-amylase and this feature was greatly improved by lentiviral-mediated expression of Rbpjl and Ptf1a, two transcription factors involved in the maximal production of digestive enzymes. This study provides a novel method to produce functional pancreatic exocrine cells from ESC.

Cell transplantation therapy for diabetes mellitus: endocrine pancreas and adipocyte

Experimental transplantation of endocrine tissues has led to significant advances in our understanding of endocrinology and metabolism. Endocrine cell transplantation therapy is expected to be applied to the treatment of metabolic endocriopathies. Restoration of functional pancreatic beta-cell mass or of functional adipose mass are reasonable treatment approaches for patients with diabetes or lipodystrophy, respectively. Human induced pluripotent stem (iPS) cell research is having a great impact on life sciences. Doctors Takahashi and Yamanaka discovered that the forced expression of a set of genes can convert mouse and human somatic cells into a pluripotent state [1, 2]. These iPS cells can differentiate into a variety of cell types. Therefore, iPS cells from patients may be a potential cell source for autologous cell replacement therapy. This review briefly summarizes the current knowledge about transplantation therapy for diabetes mellitus, the development of the endocrine pancreas and adipocytes, and endocrine-metabolic disease-specific iPS 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.

A preliminary study for constructing a bioartificial liver device with induced pluripotent stem cell-derived hepatocytes

Background

Bioartificial liver systems, designed to support patients with liver failure, are composed of bioreactors and functional hepatocytes. Immunological rejection of the embedded hepatocytes by the host immune system is a serious concern that crucially degrades the performance of the device. Induced pluripotent stem (iPS) cells are considered a desirable source for bioartificial liver systems, because patient-derived iPS cells are free from immunological rejection. The purpose of this paper was to test the feasibility of a bioartificial liver system with iPS cell-derived hepatocyte-like cells.

Methods

Mouse iPS cells were differentiated into hepatocyte-like cells by a multi-step differentiation protocol via embryoid bodies and definitive endoderm. Differentiation of iPS cells was evaluated by morphology, PCR assay, and functional assays. iPS cell-derived hepatocyte-like cells were cultured in a bioreactor module with a pore size of 0.2 μm for 7 days. The amount of albumin secreted into the circulating medium was analyzed by ELISA. Additionally, after a 7-day culture in a bioreactor module, cells were observed by a scanning electron microscope.

Results

At the final stage of the differentiation program, iPS cells changed their morphology to a polygonal shape with two nucleoli and enriched cytoplasmic granules. Transmission electron microscope analysis revealed their polygonal shape, glycogen deposition in the cytoplasm, microvilli on their surfaces, and a duct-like arrangement. PCR analysis showed increased expression of albumin mRNA over the course of the differentiation program. Albumin and urea production was also observed. iPS-Heps culture in bioreactor modules showed the accumulation of albumin in the medium for up to 7 days. Scanning electron microscopy revealed the attachment of cell clusters to the hollow fibers of the module. These results indicated that iPS cells were differentiated into hepatocyte-like cells after culture for 7 days in a bioreactor module with a pore size of 0.2 μm.

Conclusion

We consider the combination of a bioreactor module with a 0.2-μm pore membrane and embedded hepatocytes differentiated from iPS cells to be a promising option for bioartificial liver systems. This paper provides the basic concept and preliminary data for an iPS cell-oriented bioartificial liver system.

PACS code: 87. Biological and medical physics, 87.85.-d Biomedical engineering, 87.85.Lf Tissue engineering, 87.85.Tu Modeling biomedical systems.

Spatiotemporal clustering of the epigenome reveals rules of dynamic gene regulation

Spatial organization of different epigenomic marks was used to infer functions of the epigenome. It remains unclear what can be learned from the temporal changes of the epigenome. Here, we developed a probabilistic model to cluster genomic sequences based on the similarity of temporal changes of multiple epigenomic marks during a cellular differentiation process. We differentiated mouse embryonic stem (ES) cells into mesendoderm cells. At three time points during this differentiation process, we used high-throughput sequencing to measure seven histone modifications and variants—H3K4me1/2/3, H3K27ac, H3K27me3, H3K36me3, and H2A.Z; two DNA modifications—5-mC and 5-hmC; and transcribed mRNAs and noncoding RNAs (ncRNAs). Genomic sequences were clustered based on the spatiotemporal epigenomic information. These clusters not only clearly distinguished gene bodies, promoters, and enhancers, but also were predictive of bidirectional promoters, miRNA promoters, and piRNAs. This suggests specific epigenomic patterns exist on piRNA genes much earlier than germ cell development. Temporal changes of H3K4me2, unmethylated CpG, and H2A.Z were predictive of 5-hmC changes, suggesting unmethylated CpG and H3K4me2 as potential upstream signals guiding TETs to specific sequences. Several rules on combinatorial epigenomic changes and their effects on mRNA expression and ncRNA expression were derived, including a simple rule governing the relationship between 5-hmC and gene expression levels. A Sox17 enhancer containing a FOXA2 binding site and a Foxa2 enhancer containing a SOX17 binding site were identified, suggesting a positive feedback loop between the two mesendoderm transcription factors. These data illustrate the power of using epigenome dynamics to investigate regulatory functions.

Understanding pancreas development for β-cell repair and replacement therapies

The lack or dysfunction of insulin-producing β-cells is the cause of all forms of diabetes. In vitro generation of β-cells from pluripotent stem cells for cell-replacement therapy or triggering endogenous mechanisms of β-cell repair have great potential in the field of regenerative medicine. Both approaches rely on a thorough understanding of β-cell development and homeostasis. Here, we briefly summarize the current knowledge of β-cell differentiation during pancreas development in the mouse. Furthermore, we describe how this knowledge is translated to instruct differentiation of both mouse and human pluripotent stem cells towards the β-cell lineage. Finally, we shortly summarize the current efforts to identify stem or progenitor cells in the adult pancreatic organ and to harness the endogenous regenerative potential. Understanding development and regeneration of β-cells already led to identification of molecular targets for therapy and informed on pathomechanisms of diabetes. In the future this knowledge might [corrected] lead to β-cell repair and replacement therapies.

MicroRNA signatures of iPSCs and endoderm-derived tissues

MicroRNAs (miRNAs), small non-coding RNAs that fine-tune gene expression, play multiple roles in the cell, including cell fate specification. We have analyzed the differential expression of miRNAs during fibroblast reprogramming into induced pluripotent stem cells (iPSCs) and endoderm induction from iPSCs upon treatment with high concentrations of Activin-A. The reprogrammed iPSCs assumed an embryonic stem cell (ESC)-like miRNA signature, marked by the induction of pluripotency clusters miR-290-295 and miR-302/367 and conversely the downregulation of the let-7 family. On the other hand, endoderm induction in iPSCs resulted in the upregulation of 13 miRNAs. Given that the liver and the pancreas are common derivatives of the endoderm, analysis of the expression of these 13 upregulated miRNAs in hepatocytes and pancreatic islets revealed a tendency for these miRNAs to be expressed more in pancreatic islets than in hepatocytes. These observations provide insights into how differentiation may be guided more efficiently towards the endoderm and further into the liver or pancreas. Moreover, we also report novel miRNAs enriched for each of the cell types analyzed.

Highly efficient generation of definitive endoderm lineage from human induced pluripotent stem cells

BACKGROUND

Although hepatocytes can be an option for liver transplantation, the shortage of donor organs continues to worsen. Since the development of induced pluripotent stem (iPS) cell technology, it is eagerly anticipated to produce functional elements from pluripotent stem cells. These functional cells differentiated from iPS cells could be used for transplantation, drug screening, and in vitro toxicology.

METHODS

Human iPS cells are maintained on Mitomycin C-treated mouse embryonic fibroblast layers in DMEM-Ham F12-based medium supplemented with Knockout Serum Replacement, nonessential amino acids, 2-mercaptoethanol, and Glutamax. Differentiation of human iPS cells into a definitive endodermal lineage was induced with PRMI 1640 medium supplemented with B27 and 100 ng/mL human activin A. Two B27 supplements were examined with and without insulin. Furthermore, the PI3 kinase inhibitor LY294002 was used to examine the effect of inhibiting insulin signaling.

RESULTS AND DISCUSSION

We established efficient induction of definitive endodermal differentiation from iPS cells. Quantitative analysis revealed efficient (93.03 ± 2.74%) differentiation of human iPS cells into definitive endoderm cells using B27 minus insulin. This protocol may contribute as a fundamental technique to promote human iPS studies to develop cellular sources for transplantation.

TGF-β family signaling in stem cells

BACKGROUND

The diversity of cell types and tissue types that originate throughout development derives from the differentiation potential of embryonic stem cells and somatic stem cells. While the former are pluripotent, and thus can give rise to a full differentiation spectrum, the latter have limited differentiation potential but drive tissue remodeling. Additionally cancer tissues also have a small population of self-renewing cells with stem cell properties. These cancer stem cells may arise through dedifferentiation from non-stem cells in cancer tissues, illustrating their plasticity, and may greatly contribute to the resistance of cancers to chemotherapies.

SCOPE OF REVIEW

The capacity of the different types of stem cells for self-renewal, the establishment and maintenance of their differentiation potential, and the selection of differentiation programs are greatly defined by the interplay of signaling molecules provided by both the stem cells themselves, and their microenvironment, the niche. Here we discuss common and divergent roles of TGF-β family signaling in the regulation of embryonic, reprogrammed pluripotent, somatic, and cancer stem cells.

MAJOR CONCLUSIONS

Increasing evidence highlights the similarities between responses of normal and cancer stem cells to signaling molecules, provided or activated by their microenvironment. While TGF-β family signaling regulates stemness of normal and cancer stem cells, its effects are diverse and depend on the cell types and physiological state of the cells.

GENERAL SIGNIFICANCE

Further mechanistic studies will provide a better understanding of the roles of TGF-β family signaling in the regulation of stem cells. These basic studies may lead to the development of a new therapeutic or prognostic strategies for the treatment of cancers. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

Comparative epigenomic annotation of regulatory DNA

Despite the explosive growth of genomic data, functional annotation of regulatory sequences remains difficult. Here, we introduce "comparative epigenomics"-interspecies comparison of DNA and histone modifications-as an approach for annotation of the regulatory genome. We measured in human, mouse, and pig pluripotent stem cells the genomic distributions of cytosine methylation, H2A.Z, H3K4me1/2/3, H3K9me3, H3K27me3, H3K27ac, H3K36me3, transcribed RNAs, and P300, TAF1, OCT4, and NANOG binding. We observed that epigenomic conservation was strong in both rapidly evolving and slowly evolving DNA sequences, but not in neutrally evolving sequences. In contrast, evolutionary changes of the epigenome and the transcriptome exhibited a linear correlation. We suggest that the conserved colocalization of different epigenomic marks can be used to discover regulatory sequences. Indeed, seven pairs of epigenomic marks identified exhibited regulatory functions during differentiation of embryonic stem cells into mesendoderm cells. Thus, comparative epigenomics reveals regulatory features of the genome that cannot be discerned from sequence comparisons alone.

Eomesodermin induces Mesp1 expression and cardiac differentiation from embryonic stem cells in the absence of Activin

The transcription factor Eomesodermin (Eomes) is involved in early embryonic patterning, but the range of cell fates that it controls as well as its mechanisms of action remain unclear. Here we show that transient expression of Eomes promotes cardiovascular fate during embryonic stem cell differentiation. Eomes also rapidly induces the expression of Mesp1, a key regulator of cardiovascular differentiation, and directly binds to regulatory sequences of Mesp1. Eomes effects are strikingly modulated by Activin signalling: high levels of Activin inhibit the promotion of cardiac mesoderm by Eomes, while they enhance Eomes-dependent endodermal specification. These results place Eomes upstream of the Mesp1-dependent programme of cardiogenesis, and at the intersection of mesodermal and endodermal specification, depending on the levels of Activin/Nodal signalling.

Efficient differentiation of mouse embryonic stem cells into insulin-producing cells

Embryonic stem (ES) cells are a potential source of a variety of differentiated cells for cell therapy, drug discovery, and toxicology screening. Here, we present an efficacy strategy for the differentiation of mouse ES cells into insulin-producing cells (IPCs) by a two-step differentiation protocol comprising of (i) the formation of definitive endoderm in monolayer culture by activin A, and (ii) this monolayer endoderm being induced to differentiate into IPCs by nicotinamide, insulin, and laminin. Differentiated cells can be obtained within approximately 7 days. The differentiation IPCs combined application of RT-PCR, ELISA, and immunofluorescence to characterize phenotypic and functional properties. In our study, we demonstrated that IPCs produced pancreatic transcription factors, endocrine progenitor marker, definitive endoderm, pancreatic β-cell markers, and Langerhans α and δ cells. The IPCs released insulin in a manner that was dose dependent upon the amount of glucose added. These techniques may be able to be applied to human ES cells, which would have very important ramifications for treating human disease.

Generation of beta cells from human pluripotent stem cells: Potential for regenerative medicine

The loss of beta cells in Type I diabetes ultimately leads to insulin dependence and major complications that are difficult to manage by insulin injections. Given the complications associated with long-term administration of insulin, cell-replacement therapy is now under consideration as an alternative treatment that may someday provide a cure for this disease. Over the past 10 years, islet transplantation trials have demonstrated that it is possible to replenish beta cell function in Type I diabetes patients and, at least temporarily, eliminate their dependency on insulin. While not yet optimal, the success of these trials has provided proof-of-principle that cell replacement therapy is a viable option for treating diabetes. Limited access to donor islets has launched a search for alternative source of beta cells for cell therapy purposes and focused the efforts of many investigators on the challenge of deriving such cells from human embryonic (hESCs) and induced pluripotent stem cells (hiPSCs). Over the past five years, significant advances have been made in understanding the signaling pathways that control lineage development from human pluripotent stem cells (hPSCs) and as a consequence, it is now possible to routinely generate insulin producing cells from both hESCs and hiPSCs. While these achievements are impressive, significant challenges do still exist, as the majority of insulin producing cells generated under these conditions are polyhormonal and non functional, likely reflecting the emergence of the polyhormonal population that is known to arise in the early embryo during the phase of pancreatic development known as the 'first transition'. Functional beta cells, which arise during the second phase or transition of pancreatic development have been generated from hESCs, however they are detected only following transplantation of progenitor stage cells into immunocompromised mice. With this success, our challenge now is to define the pathways that control the development and maturation of this second transition population from hPSCs, and establish conditions for the generation of functional beta cells in vitro.

Donor-dependent variations in hepatic differentiation from human-induced pluripotent stem cells

Hepatocytes generated from human induced pluripotent stem cells (hiPSCs) are unprecedented resources for pharmaceuticals and cell therapy. However, the in vitro directed differentiation of human pluripotent stem cells into mature hepatocytes remains challenging. Little attention has so far been paid to variations among hiPSC lines in terms of their hepatic differentiation. In the current study, we developed an improved hepatic differentiation protocol and compared 28 hiPSC lines originated from various somatic cells and derived using retroviruses, Sendai viruses, or episomal plasmids. This comparison indicated that the origins, but not the derivation methods, may be a major determinant of variation in hepatic differentiation. The hiPSC clones derived from peripheral blood cells consistently showed good differentiation efficiency, whereas many hiPSC clones from adult dermal fibroblasts showed poor differentiation. However, when we compared hiPSCs from peripheral blood and dermal fibroblasts from the same individuals, we found that variations in hepatic differentiation were largely attributable to donor differences, rather than to the types of the original cells. These data underscore the importance of donor differences when comparing the differentiation propensities of hiPSC clones.

Patterning and shaping the endoderm in vivo and in culture

The definitive endoderm (DE) was first defined as the innermost germ layer found in all metazoan embryos. During development, it gives rise to a vast array of specialized epithelial cell types lining the respiratory and digestive systems, and contributes to associated organs such as thyroid, thymus, lungs, liver, and pancreas. In the adult, the DE provides a protective barrier against the environment and assumes many essential functions including digestion, nutrient absorption, and glucose homeostasis. Since general endoderm formation and patterning have been reviewed recently in a comprehensive manner [1], we will only provide a brief summary of how extracellular signals and downstream transcription factors control endoderm patterning. We will then focus on emerging work addressing the chromatin remodeling events occurring during endoderm organ specification and discuss how these molecular tools can be used to engineer endodermal organs in vitro.

Phf14, a novel regulator of mesenchyme growth via platelet-derived growth factor (PDGF) receptor-α

The regulation of mesenchymal cell growth by signaling molecules plays an important role in maintaining tissue functions. Aberrant mesenchymal cell proliferation caused by disruption of this regulatory process leads to pathogenetic events such as fibrosis. In the current study we have identified a novel nuclear factor, Phf14, which controls the proliferation of mesenchymal cells by regulating PDGFRα expression. Phf14-null mice died just after birth due to respiratory failure. Histological analyses of the lungs of these mice showed interstitial hyperplasia with an increased number of PDGFRα(+) mesenchymal cells. PDGFRα expression was elevated in Phf14-null mesenchymal fibroblasts, resulting in increased proliferation. We demonstrated that Phf14 acts as a transcription factor that directly represses PDGFRα expression. Based on these results, we used an antibody against PDGFRα to successfully treat mouse lung fibrosis. This study shows that Phf14 acts as a negative regulator of PDGFRα expression in mesenchymal cells undergoing normal and abnormal proliferation, and is a potential target for new treatments of lung fibrosis.

Endogenous production of fibronectin is required for self-renewal of cultured mouse embryonic stem cells

Pluripotent cells are attached to the extracellular matrix (ECM) as they make cell fate decisions within the stem cell niche. Here we show that the ubiquitous ECM protein fibronectin is required for self-renewal decisions by cultured mouse embryonic stem (mES) cells. Undifferentiated mES cells produce fibronectin and assemble a fibrillar matrix. Increasing the level of substrate fibronectin increased cell spreading and integrin receptor signaling through focal adhesion kinase, while concomitantly inducing the loss of Nanog and Oct4 self-renewal markers. Conversely, reducing fibronectin production by mES cells growing on a feeder-free gelatin substrate caused loss of cell adhesion, decreased integrin signaling, and decreased expression of self-renewal markers. These effects were reversed by providing the cells with exogenous fibronectin, thereby restoring adhesion to the gelatin substrate. Interestingly, mES cells do not adhere directly to the gelatin substrate, but rather adhere indirectly through gelatin-bound fibronectin, which facilitates self-renewal via its effects on cell adhesion. These results provide new insights into the mechanism of regulation of self-renewal by growth on a gelatin-coated surface. The effects of increasing or decreasing fibronectin levels show that self-renewal depends on an intermediate level of cell-fibronectin interactions. By providing cell adhesive signals that can act with other self-renewal factors to maintain mES cell pluripotency, fibronectin is therefore a necessary component of the self-renewal signaling pathway in culture.

Protein kinase C mediated extraembryonic endoderm differentiation of human embryonic stem cells

Unlike mouse embryonic stem cells (ESCs), which are closely related to the inner cell mass, human ESCs appear to be more closely related to the later primitive ectoderm. For example, human ESCs and primitive ectoderm share a common epithelial morphology, growth factor requirements, and the potential to differentiate to all three embryonic germ layers. However, it has previously been shown that human ESCs can also differentiate to cells expressing markers of trophoblast, an extraembryonic lineage formed before the formation of primitive ectoderm. Here, we show that phorbol ester 12-O-tetradecanoylphorbol 13-acetate causes human ESCs to undergo an epithelial mesenchymal transition and to differentiate into cells expressing markers of parietal endoderm, another extraembryonic lineage. We further confirmed that this differentiation is through the activation of protein kinase C (PKC) pathway and demonstrated that a particular PKC subtype, PKC-δ, is most responsible for this transition.