Initiation of mammalian liver development from endoderm by fibroblast growth factors

Differentiation of human embryonic stem cells along a hepatic lineage

The limited availability of hepatic tissue suitable for the treatment of liver disease and drug discovery research advances the generation of hepatic-like cells from alternative sources as a valuable approach. In this investigation we exploited a unique hepatic differentiation approach to generate hepatocyte-like cells from human embryonic stem cells (hESCs). hESCs were cultured for 10-20 days on collagen substrate in highly defined and serum free hepatocyte media. The resulting cell populations exhibited hepatic cell-like morphology and were characterized with a variety of biological endpoint analyses. Real-time PCR analysis demonstrated that mRNA expression of the 'stemness' marker genes NANOG and alkaline phosphatase in the differentiated cells was significantly reduced, findings that were functionally validated using alkaline phosphatase activity detection measures. Immunofluorescence studies revealed attenuated levels of the 'stemness' markers OCT4, SOX2, SSEA-3, TRA-1-60, and TRA-1-81 in the hepatic-like cell population. The hepatic character of the cells was evaluated additionally by real-time PCR analyses that demonstrated increased mRNA expression of the hepatic transcription factors FOXA1, C/EBPα, and HNF1α, the nuclear receptors CAR, RXRα, PPARα, and HNF4α, the liver-generated plasma proteins α-fetoprotein, transthyretin, transferrin, and albumin, the protease inhibitor α-1-antitrypsin, metabolic enzymes HMGCS2, PEPCK, and biotransformation enzymes CYP3A7, CYP3A4, CYP3A5, and CYP2E1. Indocyanine green uptake albumin secretion and glycogen storage capacity further confirmed acquisition of hepatic function. These studies define an expeditious methodology that facilitates the differentiation of hESCs along a hepatic lineage and provide a framework for their subsequent use in pharmacological and toxicological research applications requiring a renewable supply of human hepatocytes.

Patterning and plasticity in development of the respiratory lineage

The mammalian respiratory lineage, consisting of the trachea and lung, originates from the ventral foregut in an early embryo. Reciprocal signaling interactions between the foregut epithelium and its associated mesenchyme guide development of the respiratory endoderm, from a naive sheet of cells to multiple cell types that line a functional organ. This review synthesizes current understanding of the early events in respiratory system development, focusing on three main topics: (1) specification of the respiratory system as a distinct organ of the endoderm, (2) patterning and differentiation of the nascent respiratory epithelium along its proximal-distal axis, and (3) plasticity of the respiratory cells during the process of development. This review also highlights areas in need of further study, including determining how early endoderm cells rapidly switch their responses to the same signaling cues during development, and how the general proximal-distal pattern of the lung is converted to fine-scale organization of multiple cell types along this axis.

Hepatocyte differentiation of human fibroblasts from cirrhotic liver in vitro and in vivo

BACKGROUND

Mesenchymal stem cells (MSCs) and fibroblasts have intimate relationships, and the phenotypic homology between fibroblasts and MSCs has been recently described. The aim of this study was to investigate the hepatic differentiating potential of human fibroblasts in cirrhotic liver.

METHODS

The phenotypes of fibroblasts in cirrhotic liver were labeled by biological methods. After that, the differentiation potential of these fibroblasts in vitro was characterized in terms of liver-specific gene and protein expression. Finally, an animal model of hepatocyte regeneration in severe combined immunodeficient (SCID) mice was created by retrorsine injection and partial hepatectomy, and the expression of human hepatocyte proteins in SCID mouse livers was checked by immunohistochemical analysis after fibroblast administration.

RESULTS

Surface immunophenotyping revealed that a minority of fibroblasts expressed markers of MSCs and hepatic epithelial cytokeratins as well as alpha-smooth muscle actin, but homogeneously expressed vimentin, desmin, prolyl 4-hydroxylase and fibronectin. These fibroblasts presented the characteristics of hepatocytes in vitro and differentiated directly into functional hepatocytes in the liver of hepatectomized SCID mice.

CONCLUSIONS

This study demonstrated that fibroblasts in cirrhotic liver have the potential to differentiate into hepatocyte-like cells in vitro and in vivo. Our findings infer that hepatic differentiation of fibroblasts may serve as a new target for reversion of liver fibrosis and a cell source for tissue engineering.

Model systems and experimental conditions that lead to effective repopulation of the liver by transplanted cells

In recent years, there has been substantial progress in transplanting cells into the liver with the ultimate goal of restoring liver mass and function in both inherited and acquired liver diseases. The basis for considering that this might be feasible is that the liver is a highly regenerative organ. After massive liver injury or surgical removal of two-thirds or more of the liver tissue, the organ can restore its mass with completely normal morphologic structure and function. It has also been found under highly selective conditions that transplanted hepatocytes can fully repopulate the liver and cure a metabolic disorder or deficiency state. Fetal liver cells can also substantially repopulate the normal liver, and it is hoped in the future that effective repopulation will be achievable with cultured cells or cell lines, pluripotent stem cells from other somatic tissues, embryonic stem cells, or induced pluripotent stem cells, which can now be generated in vitro by a variety of methods. The purpose of this review is to present the major systems that have been used for liver repopulation, the variables involved in obtaining successful repopulation and what has been achieved in these various systems to date with different cell types.

Stem cell-derived islet cells for transplantation

PURPOSE OF REVIEW

The promise of islet transplantation for type 1 diabetes has been hampered by the lack of a renewable source of insulin-producing cells. However, steadfast advances in the field have set the stage for stem cell-based approaches to take over in the near future. This review focuses on the most intriguing findings reported in recent years, which include not only progress in adult and embryonic stem cell differentiation, but also the direct reprogramming of nonendocrine tissues into insulin-producing beta cells.

RECENT FINDINGS

In spite of their potential for tumorigenesis, human embryonic stem (hES) cells are poised to be in clinical trials within the next decade. This situation is mainly due to the preclinical success of a differentiation method that recapitulates beta cell development. In contrast, adult stem cells still need one such gold standard of differentiation, and progress is somewhat impeded by the lack of consensus on the best source. A concerted effort is necessary to bring their potential to clinical fruition. In the meantime, reported success in reprogramming might offer a 'third way' towards the rescue of pancreatic endocrine function.

SUMMARY

Here we discuss the important strategic decisions that need to be made in order to maximize the therapeutic chances of each of the presented approaches.

Influence and timing of arrival of murine neural crest on pancreatic beta cell development and maturation

Interactions between cells from the ectoderm and mesoderm influence development of the endodermally-derived pancreas. While much is known about how mesoderm regulates pancreatic development, relatively little is understood about how and when the ectodermally-derived neural crest regulates pancreatic development and specifically, beta cell maturation. A previous study demonstrated that signals from the neural crest regulate beta cell proliferation and ultimately, beta cell mass. Here, we expand on that work to describe timing of neural crest arrival at the developing pancreatic bud and extend our knowledge of the non-cell autonomous role for neural crest derivatives in the process of beta cell maturation. We demonstrated that murine neural crest entered the pancreatic mesenchyme between the 26 and 27 somite stages (approximately 10.0 dpc) and became intermingled with pancreatic progenitors as the epithelium branched into the surrounding mesenchyme. Using a neural crest-specific deletion of the Forkhead transcription factor Foxd3, we ablated neural crest cells that migrate to the pancreatic primordium. Consistent with previous data, in the absence of Foxd3, and therefore the absence of neural crest cells, proliferation of insulin-expressing cells and insulin-positive area are increased. Analysis of endocrine cell gene expression in the absence of neural crest demonstrated that, although the number of insulin-expressing cells was increased, beta cell maturation was significantly impaired. Decreased MafA and Pdx1 expression illustrated the defect in beta cell maturation; we discovered that without neural crest, there was a reduction in the percentage of insulin-positive cells that co-expressed Glut2 and Pdx1 compared to controls. In addition, transmission electron microscopy analyses revealed decreased numbers of characteristic insulin granules and the presence of abnormal granules in insulin-expressing cells from mutant embryos. Together, these data demonstrate that the neural crest is a critical regulator of beta cell development on two levels: by negatively regulating beta cell proliferation and by promoting beta cell maturation.

Liver stem/progenitor cells: their characteristics and regulatory mechanisms

Liver stem cells give rise to both hepatocytes and bile duct epithelial cells also known as cholangiocytes. During liver development hepatoblasts emerge from the foregut endoderm and give rise to both cell types. Colony-forming cells are present in the liver primordium and clonally expanded cells differentiate into either hepatocytes or cholangiocytes depending on culture conditions, showing stem cell characteristics. The growth and differentiation of hepatoblasts are regulated by various extrinsic signals. For example, periportal mesenchymal cells provide a cue for bipotential hepatoblasts to become cholangiocytes, and mesothelial cells covering the parenchyma support the expansion of foetal hepatocytes by producing growth factors. The adult liver has an extraordinary capacity to regenerate, and after 70% hepatectomy the liver recovers its original mass by replication of the remaining hepatocytes without the activation of liver stem cells. However, in certain types of liver injury models, liver stem/progenitor-like cells, known as oval cells in rodents, proliferate around the portal vein, while the roles of such cells in liver regeneration remain a matter of debate. Clonogenic and bipotential cells are also present in the normal adult liver. In this minireview we describe recent studies on liver stem/progenitor cells by focusing on extracellular signals.

The "self-similarity logic" applied to the development of the vascular system

From a structural standpoint, living systems exhibit a hierarchical pattern of organization in which structures are nested within one another. From a temporal point of view, this type of organization is the outcome of a 'history' resulting from a set of developmental steps. Recently, it has been suggested that some auto similarity prevails at each nested level or time step and a principle of "self-similarity logic" has been proposed to convey the concept of a multi-level organization in which very similar rules (logic) apply at each level. In this study, the hypothesis is put forward that such a principle is particularly apparent in many morphological and developmental aspects of the vascular system. In fact, not only the morphology of the vascular system exhibits a high degree of geometrical self-similarity, but its remodelling processes also seem to be characterized by the application of almost the same rules, from the macroscopic to the endothelial cell to the sub-cellular levels, potentially allowing a unitary description of features such as sprouting and intussusceptive angiogenesis, and phenotypic differences of endothelial cells. The influence of the "self-similarity logic" shaping the vascular system on the organogenesis has been also discussed.

Retinoic acid stimulates myocardial expansion by induction of hepatic erythropoietin which activates epicardial Igf2

Epicardial signaling and Rxra are required for expansion of the ventricular myocardial compact zone. Here, we examine Raldh2(-/-) and Rxra(-/-) mouse embryos to investigate the role of retinoic acid (RA) signaling in this developmental process. The heart phenotypes of Raldh2 and Rxra mutants are very similar and are characterized by a prominent defect in ventricular compact zone growth. Although RA activity is completely lost in Raldh2(-/-) epicardium and the adjacent myocardium, RA activity is not lost in Rxra(-/-) hearts, suggesting that RA signaling in the epicardium/myocardium is not required for myocardial compact zone formation. We explored the possibility that RA-mediated target gene transcription in non-cardiac tissues is required for this process. We found that hepatic expression of erythropoietin (EPO), a secreted factor implicated in myocardial expansion, is dependent on both Raldh2 and Rxra. Chromatin immunoprecipitation studies support Epo as a direct target of RA signaling in embryonic liver. Treatment of an epicardial cell line with EPO, but not RA, upregulates Igf2. Furthermore, both Raldh2(-/-) and Rxra(-/-) hearts exhibit downregulation of Igf2 mRNA in the epicardium. EPO treatment of cultured Raldh2(-/-) hearts restores epicardial Igf2 expression and rescues ventricular cardiomyocyte proliferation. We propose a new model for the mechanism of RA-mediated myocardial expansion in which RA directly induces hepatic Epo resulting in activation of epicardial Igf2 that stimulates compact zone growth. This RA-EPO-IGF2 signaling axis coordinates liver hematopoiesis with heart development.

Directed differentiation of murine-induced pluripotent stem cells to functional hepatocyte-like cells

BACKGROUND & AIMS

Induced pluripotent stem (iPS) cells exert phenotypic and functional characteristics of embryonic stem cells even though the gene expression pattern is not completely identical. Therefore, it is important to develop procedures which are specifically oriented to induce iPS cell differentiation.

METHODS

In this study, we describe the differentiation of mouse iPS cells to hepatocyte-like cells, following a directed differentiation procedure that mimics embryonic and fetal liver development. The sequential differentiation was monitored by real-time PCR, immunostaining, and functional assays.

RESULTS

By sequential stimulation with cytokines known to play a role in liver development, iPS cells were specified to primitive streak/mesendoderm/definitive endoderm. They were then differentiated into two types of cells: those with hepatoblast features and those with hepatocyte characteristics. Differentiated hepatocyte-like cells showed functional properties of hepatocytes, such as albumin secretion, glycogen storage, urea production, and inducible cytochrome activity. Aside from hepatocyte-like cells, mesodermal cells displaying some characteristics of liver sinusoidal endothelium and stellate cells were also detected.

CONCLUSIONS

These data demonstrate that a protocol, modeled on embryonic liver development, can induce hepatic differentiation of mouse iPS cells, generating a population of cells with mature hepatic phenotype.

Beta-catenin signaling in hepatic development and progenitors: which way does the WNT blow?

The Wnt/β-catenin pathway is an evolutionarily conserved signaling cascade that plays key roles in development and adult tissue homeostasis and is aberrantly activated in many tumors. Over a decade of work in mouse, chick, xenopus, and zebrafish models has uncovered multiple functions of this pathway in hepatic pathophysiology. Specifically, beta-catenin, the central component of the canonical Wnt pathway, is implicated in the regulation of liver regeneration, development, and carcinogenesis. Wnt-independent activation of beta-catenin by receptor tyrosine kinases has also been observed in the liver. In liver development across various species, through regulation of cell proliferation, differentiation, and maturation, beta-catenin directs foregut endoderm specification, hepatic specification of the foregut, and hepatic morphogenesis. Its role has also been defined in adult hepatic progenitors or oval cells especially in their expansion and differentiation. Thus, beta-catenin undergoes tight temporal regulation to exhibit pleiotropic effects during hepatic development and in hepatic progenitor biology.

Enhanced expression of fibroblast growth factor 2 in bone marrow cells and its potential role in the differentiation of hepatic epithelial stem-like cells into the hepatocyte lineage

The transplantation of bone marrow cells (BMCs) has been applied in liver regenerative cell therapy. However, details of the interaction between the transplanted BMCs and hepatic stem cells have not been elucidated. The aim of the present study was to investigate the interaction of BMCs with hepatic stem-like cells (HSLCs) and to determine the BMC factor that steers HSLC differentiation into the hepatocyte lineage. Both BMCs and HSLCs were obtained from an adult Sprague-Dawley rat, and a co-culture system was established. Cell proliferation was analyzed by a proliferation assay, and the differentiation of HSLCs into the hepatocyte lineage was evaluated by the detection of cellular mRNA for liver-specific proteins. DNA microarray analysis was applied to BMCs co-cultured with HSLCs to determine the genes upregulated by their interaction. The proliferation of HSLCs co-cultured with BMCs was significantly higher than that of HSLCs cultured alone, and the expression of mRNAs for both albumin and tryptophan-2,3-dioxygenase was detectable in the co-cultured HSLCs. DNA microarray analysis showed the upregulated expression of fibroblast growth factor 2 (FGF2) mRNA in BMCs co-cultured with HSLCs, and the expression of mRNAs for both albumin and tyrosine aminotransferase became detectable in HSLCs cultured with FGF2. Thus, BMCs stimulate both the proliferation of HSLCs and their differentiation into the hepatocyte lineage. FGF2 is one of the factors that is produced by the interacting BMCs and that stimulates this differentiation.

Dynamic expression of Groucho-related genes Grg1 and Grg3 in foregut endoderm and antagonism of differentiation

While much is known about Groucho corepressors in Drosophila development, less is known about Grg homologs in mammalian embryogenesis. The transcription factors FoxA1 and FoxA2 are redundantly necessary for liver-inductive competence of the endoderm, and recently we found that FoxA factors bind Grg3, recruit the corepressor to FoxA target genes, and cause transcriptional repression, when Grg3 is ectopically expressed in adult liver cell lines that express little or no endogenous Grg. Unexpectedly, we now find that Grg1 and Grg3 mRNAs are co-expressed with FoxA factors in the foregut endoderm, prior to liver differentiation, though only Grg3 protein is expressed there. Grg3 mRNA and protein are extinguished at the onset of liver differentiation. Lentiviral delivery of Grg3 to explants of foregut endoderm suppresses liver gene induction. We suggest that Grg expression in the endoderm helps suppress the liver program and find that endodermal competence involves a balance between activators and corepressors.

Using growth factor arrays and micropatterned co-cultures to induce hepatic differentiation of embryonic stem cells

The success in driving embryonic stem cells towards hepatic lineage has been confounded by the complexity and cost of differentiation protocols that employ large quantities of expensive growth factors (GFs). Instead of supplementing culture media with soluble GFs, we investigated cultivation and differentiation of mouse embryonic stem cells (mESCs) on printed arrays of GFs. Hepatocyte growth factor (HGF), basic fibroblast growth factor (bFGF) and bone morphogenetic protein (BMP4) were mixed in solution with fibronectin and collagen (I) and then printed onto silane-modified glass slides to form 500 μm diameter protein spots. mESCs were cultured on top of GF spots for up to 12 days and analyzed by RT-PCR and immunostaining at different time points. The stem cells residing on HGF-containing combinations of GFs exhibited requisite features of hepatic differentiation including pronounced loss in pluripotency (Oct4), transient (up and down) expression of endoderm (Sox17) and upregulation of early hepatic markers--albumin and alpha-fetoprotein. The hepatic differentiation was enhanced further by adding hepatic stellate cells to surfaces that already contained mESCs on GF spots. A combination of co-culture with non-parenchymal liver cells and the optimal GF stimulation was found to induce endoderm and hepatic phenotype earlier and to a much greater extent than the GF arrays or micropatterned co-cultures used individually. While this paper investigated hepatic differentiation of mouse ESCs, our findings and stem cell culture approaches are likely to be relevant for human ESC cultivation. Overall, the platform combining printed GF arrays and heterotypic co-cultures will be broadly applicable for identifying the composition of the microenvironment niche for ESC differentiation into various tissue types.

Differentiation of mouse embryonic stem cells into endoderm without embryoid body formation

Pluripotent embryonic stem cells hold a great promise as an unlimited source of tissue for treatment of chronic diseases such as Type 1 diabetes. Herein, we describe a protocol using all-trans-retinoic acid, basic fibroblast growth factor and dibutyryl cAMP (DBcAMP) in the absence of embryoid body formation, for differentiation of murine embryonic stem cells into definitive endoderm that may serve as pancreatic precursors. The produced cells were analyzed by quantitative PCR, immunohistochemistry and static insulin release assay for markers of trilaminar embryo, and pancreas. Differentiated cells displayed increased Sox17 and Foxa2 expression consistent with definitive endoderm production. There was minimal production of Sox7, an extraembryonic endoderm marker, and Oct4, a marker of pluripotency. There was minimal mesoderm or neuroectoderm formation based on expression levels of the markers brachyury and Sox1, respectively. Various assays revealed that the cell clusters generated by this protocol express markers of the pancreatic lineage including insulin I, insulin II, C-peptide, PDX-1, carboxypeptidase E, pan-cytokeratin, amylase, glucagon, PAX6, Ngn3 and Nkx6.1. This protocol using all-trans-retinoic acid, DBcAMP, in the absence of embryoid bodies, generated cells that have features of definitive endoderm that may serve as pancreatic endocrine precursors.

Differentiation of embryonic stem cells into hepatocytes that coexpress coagulation factors VIII and IX

AIM

To establish an efficient culture system to support embryonic stem (ES) cell differentiation into hepatocytes that coexpress F-VIII and F-IX.

METHODS

Mouse E14 ES cells were cultured in differentiation medium containing sodium butyrate (SB), basic fibroblast growth factor (bFGF), and/or bone morphogenetic protein 4 (BMP4) to induce the differentiation of endoderm cells and hepatic progenitor cells. Hepatocyte growth factor, oncostatin M, and dexamethasone were then used to induce the maturation of ES cell-derived hepatocytes. The mRNA expression levels of endoderm-specific genes and hepatocyte-specific genes, including the levels of F-VIII and F-IX, were detected by RT-PCR and real-time PCR during various stages of differentiation. Protein expression was examined by immunofluorescence and Western blot. At the final stage of differentiation, flow cytometry was performed to determine the percentage of cells coexpressing F-VIII and F-IX, and ELISA was used to detect the levels of F-VIII and F-IX protein secreted into the culture medium.

RESULTS

The expression of endoderm-specific and hepatocyte-specific markers was upregulated to highest level in response to the combination of SB, bFGF, and BMP4. Treatment with the three inducers during hepatic progenitor differentiation significantly enhanced the mRNA and protein levels of F-VIII and F-IX in ES cell-derived hepatocytes. More importantly, F-VIII and F-IX were coexpressed with high efficiency at the final stage of differentiation, and they were also secreted into the culture medium.

CONCLUSION

We have established a novel in vitro differentiation protocol for ES-derived hepatocytes that coexpress F-VIII and F-IX that may provide a foundation for stem cell replacement therapy for hemophilia.

Histology atlas of the developing mouse hepatobiliary system with emphasis on embryonic days 9.5-18.5

Animal model phenotyping, in utero exposure toxicity studies, and investigation into causes of embryonic, fetal, or perinatal deaths have required pathologists to recognize and diagnose developmental disorders in spontaneous and engineered mouse models of disease. In mammals, the liver is the main site of hematopoiesis during fetal development, has endocrine and exocrine functions important for maintaining homeostasis in fetal and adult life; and performs other functions including waste detoxification, production and removal of glucose, glycogen storage, triglyceride and fatty acid processing, and serum protein production. Due to its role in many critical functions, alterations in the size, morphology, or function(s) of the liver often lead to embryonic lethality. Many publications and websites describe individual aspects of hepatobiliary development at defined stages. However, no single resource provides a detailed histological evaluation of H&E-stained sections of the developing murine liver and biliary systems using high-magnification and high-resolution color images. The work herein provides a histology atlas of hepatobiliary development between embryonic days 9.5-18.5. Although the focus of this work is normal hepatobiliary development, common defects in liver development are also described as a reference for pathologists who may be asked to phenotype mice with congenital, inherited, or treatment-related hepatobiliary defects. Authors' note: All digital images can be viewed online at https://niehsimagesepl-inc.com with the username "ToxPathLiver" and the password "embryolivers."

FGF receptors 1 and 2 control chemically induced injury and compound detoxification in regenerating livers of mice

BACKGROUND & AIMS

Fibroblast growth factor receptor 4 (FGFR4) controls bile acid metabolism and protects the liver from fibrosis, but the roles of FGFR1 and FGFR2 in the adult liver are largely unknown. We investigated the functions and mechanisms of action of these receptors in liver homeostasis, regeneration, and fibrosis.

METHODS

We generated mice with hepatocytes that lack FGFR1 and FGFR2 and subjected them to acute and chronic carbon tetrachloride-induced liver injury and partial hepatectomy; mice were also injected with FGF7. We performed histology, histomorphometry, real-time reverse transcription polymerase chain reaction, and immunoblot analyses.

RESULTS

In hepatocytes, loss of FGFR1 and FGFR2 eliminated responsiveness to FGF7 and related FGF family members but did not affect toxin-induced liver injury and fibrosis. However, mortality after partial hepatectomy increased because of severe hepatocyte necrosis. These effects appeared to be mediated by a failure of hepatocytes to induce the expression of the transcriptional regulators Dbp and Tef upon liver surgery; this affected expression of their target genes, which encode detoxifying cytochrome P450 enzymes. We found that Dbp and Tef expression was directly controlled by FGFR signaling in hepatocytes. As a consequence of the reduced expression of genes that control detoxification, the liver tissue that remained after partial hepatectomy failed to efficiently metabolize endogenous compounds and the drugs applied for anesthesia/analgesia.

CONCLUSIONS

We identified a new, cytoprotective effect of FGFR1 and FGFR2 in the regenerating liver and suggest the use of recombinant FGF7 to increase survival of patients after surgical resection of large amounts of liver tissue.

Effects of fibroblast growth factors on the differentiation of the pulmonary progenitors from murine embryonic stem cells

The fibroblast growth factors (FGFs) play an important role in the development of embryonic lung. In this study, we investigated the effects of mainly FGF 1, 2, and 10 at concentrations selected on the basis of data obtained from previous in vitro culture on the derivation of the pulmonary progenitors from murine embryonic stem cells cultured on gelatin or Matrigel-coated plates. For cells cultured on a gelatin-coated plate, high concentrations of FGF1 were found to enhance the expression of mRNAs for SPC and CC10, markers of distal airway epithelium, while high levels of FGF2 decreased the expression of RNAs for not only SPC, CC10 but also for the additional markers SPD and aquaporin 5. FGF10 at all tested concentrations was found to have no effect on the differentiation of pneumocytes when ESCs were grown on gelatin-coated plates. However, when differentiation was performed on Matrigel-coated plates, the addition of 60 ng/ml FGF10 enhanced the expression of pneumocyte markers, suggesting a synergic effect of FGF10 and extracellular matrix. In conclusion, growth factors were proven to be effective in the differentiation of pulmonary progenitors from mESCs. The need of signals from extracellular matrix proteins depends on the growth factors supplemented.

Factors from human embryonic stem cell-derived fibroblast-like cells promote topology-dependent hepatic differentiation in primate embryonic and induced pluripotent stem cells

The future clinical use of embryonic stem cell (ESC)-based hepatocyte replacement therapy depends on the development of an efficient procedure for differentiation of hepatocytes from ESCs. Here we report that a high density of human ESC-derived fibroblast-like cells (hESdFs) supported the efficient generation of hepatocyte-like cells with functional and mature hepatic phenotypes from primate ESCs and human induced pluripotent stem cells. Molecular and immunocytochemistry analyses revealed that hESdFs caused a rapid loss of pluripotency and induced a sequential endoderm-to-hepatocyte differentiation in the central area of ESC colonies. Knockdown experiments demonstrated that pluripotent stem cells were directed toward endodermal and hepatic lineages by FGF2 and activin A secreted from hESdFs. Furthermore, we found that the central region of ESC colonies was essential for the hepatic endoderm-specific differentiation, because its removal caused a complete disruption of endodermal differentiation. In conclusion, we describe a novel in vitro differentiation model and show that hESdF-secreted factors act in concert with regional features of ESC colonies to induce robust hepatic endoderm differentiation in primate pluripotent stem cells.

Human embryonic and rat adult stem cells with primitive endoderm-like phenotype can be fated to definitive endoderm, and finally hepatocyte-like cells

Stem cell-derived hepatocytes may be an alternative cell source to treat liver diseases or to be used for pharmacological purposes. We developed a protocol that mimics mammalian liver development, to differentiate cells with pluripotent characteristics to hepatocyte-like cells. The protocol supports the stepwise differentiation of human embryonic stem cells (ESC) to cells with characteristics of primitive streak (PS)/mesendoderm (ME)/definitive endoderm (DE), hepatoblasts, and finally cells with phenotypic and functional characteristics of hepatocytes. Remarkably, the same protocol can also differentiate rat multipotent adult progenitor cells (rMAPCs) to hepatocyte-like cells, even though rMAPC are isolated clonally from cultured rat bone marrow (BM) and have characteristics of primitive endoderm cells. A fraction of rMAPCs can be fated to cells expressing genes consistent with a PS/ME/DE phenotype, preceding the acquisition of phenotypic and functional characteristics of hepatocytes. Although the hepatocyte-like progeny derived from both cell types is mixed, between 10-20% of cells are developmentally consistent with late fetal hepatocytes that have attained synthetic, storage and detoxifying functions near those of adult hepatocytes. This differentiation protocol will be useful for generating hepatocyte-like cells from rodent and human stem cells, and to gain insight into the early stages of liver development.

Generating hepatic cell lineages from pluripotent stem cells for drug toxicity screening

Hepatotoxicity is an enormous and increasing problem for the pharmaceutical industry. Early detection of problems during the drug discovery pathway is advantageous to minimize costs and improve patient safety. However, current cellular models are sub-optimal. This review addresses the potential use of pluripotent stem cells in the generation of hepatic cell lineages. It begins by highlighting the scale of the problem faced by the pharmaceutical industry, the precise nature of drug-induced liver injury and where in the drug discovery pathway the need for additional cell models arises. Current research is discussed, mainly for generating hepatocyte-like cells rather than other liver cell-types. In addition, an effort is made to identify where some of the major barriers remain in translating what is currently hypothesis-driven laboratory research into meaningful platform technologies for the pharmaceutical industry.

The FoxA factors in organogenesis and differentiation

The genetic analysis of the Foxa genes in both total and conditional mutant mice has clearly established that organogenesis of multiple systems is controlled by this subfamily of winged helix transcription factors. These discoveries followed the establishment of the conceptional framework of the mechanism of action of the FoxA proteins as 'pioneer factors' that can engage chromatin before other transcription factors. Recent molecular and genomic studies have also shown that FoxA proteins can facilitate binding of several nuclear receptors to their respective targets in a context-dependent manner, greatly increasing the range and importance of FoxA factors in biology.

Tbx5 and Bmp signaling are essential for proepicardium specification in zebrafish

RATIONALE

The proepicardial organ (PE) contributes to the cellular diversity of the developing heart by giving rise to the epicardium as well as vascular smooth muscle cells and fibroblasts. Despite the importance of these cells in cardiac development, function and regeneration, the signals required for the specification of the PE remain largely unexplored.

OBJECTIVE

We aim to identify the signaling molecules and transcription factors that regulate PE specification.

METHODS AND RESULTS

Here, we present the first genetic evidence that bone morphogenetic protein (Bmp) signaling in conjunction with the T-box transcription factor Tbx5a is essential for PE specification in zebrafish. Specifically, Bmp4 from the cardiac region, but not the liver bud, acting through the type I BMP receptor Acvr1l, is required for PE specification. By overexpressing a dominant-negative form of a Bmp receptor at various embryonic stages, we determined when Bmp signaling was required for PE specification. We also found that overexpression of bmp2b right before PE specification led to the ectopic expression of PE specific markers including tbx18. Furthermore, using loss-of-function approaches, we discovered a previously unappreciated PE specification role for Tbx5a at early somite stages; this role occurs earlier than, and appears to be independent from, the requirement for Bmp signaling in this process.

CONCLUSION

Altogether, these data lead us to propose that Tbx5a confers anterior lateral plate mesodermal cells the competence to respond to Bmp signals and initiate PE development.

Pluripotent plasticity of stem cells and liver repopulation

Different types of stem cells have a role in liver regeneration or fibrous repair during and after several liver diseases. Otherwise, the origin of hepatic and/or extra-hepatic stem cells in reactive liver repopulation is under controversy. The ability of the human body to self-repair and replace the cells and tissues of some organs is often evident. It has been estimated that complete renewal of liver tissue takes place in about a year. Replacement of lost liver tissues is accomplished by proliferation of mature hepatocytes, hepatic oval stem cells differentiation, and sinusoidal cells as support. Hepatic oval cells display a distinct phenotype and have been shown to be a bipotential progenitor of two types of epithelial cells found in the liver, hepatocytes, and bile ductular cells. In gastroenterology and hepatology, the first attempts to translate stem cell basic research into novel therapeutic strategies have been made for the treatment of several disorders, such as inflammatory bowel diseases, diabetes mellitus, celiachy, and acute or chronic hepatopaties. In the future, pluripotent plasticity of stem cells will open a variety of clinical application strategies for the treatment of tissue injuries, degenerated organs. The promise of liver stem cells lie in their potential to provide a continuous and readily available source of liver cells that can be used for gene therapy, cell transplant, bio-artificial liver-assisted devices, drug toxicology testing, and use as an in vitro model to understand the developmental biology of the liver.

Differentiation of mouse embryonic stem cells into hepatocytes induced by a combination of cytokines and sodium butyrate

There is increasing evidence to suggest that embryonic stem cells (ESCs) are capable of differentiating into hepatocytes in vitro. In this study, we used a combination of cytokines and sodium butyrate in a novel three-step procedure to efficiently direct the differentiation of mouse ESCs into hepatocytes. Mouse ESCs were first differentiated into definitive endoderm cells by 3 days of treatment with Activin A. The definitive endoderm cells were then differentiated into hepatocytes by the addition of acidic fibroblast growth factor (aFGF) and sodium butyrate to the culture medium for 5 days. After 10 days of further in vitro maturation, the morphological and phenotypic markers of hepatocytes were characterized using immunohistochemistry, immunoblotting, and reverse transcription-polymerase chain reaction (RT-PCR). Furthermore, the cells were tested for functions associated with mature hepatocytes, including glycogen storage and indocyanine green uptake and release, and the ratio of hepatic differentiation was determined by counting the percentage of albumin-positive cells. In the presence of medium containing cytokines and sodium butyrate, numerous epithelial cells resembling hepatocytes were observed, and approximately 74% of the cells expressed the hepatic marker, albumin, after 18 days in culture. RT-PCR analysis and immunohistochemistry showed that these cells expressed adult liver cell markers, and had the abilities of glycogen storage and indocyanine green uptake and release. We have developed an efficient method for directing the differentiation of mouse ESCs into cells that exhibit the characteristics of mature hepatocytes. This technique will be useful for research into the molecular mechanisms underlying liver development, and could provide a source of hepatocytes for transplantation therapy and drug screening.

The mitochondrial import gene tomm22 is specifically required for hepatocyte survival and provides a liver regeneration model

Understanding liver development should lead to greater insights into liver diseases and improve therapeutic strategies. In a forward genetic screen for genes regulating liver development in zebrafish, we identified a mutant--oliver--that exhibits liver-specific defects. In oliver mutants, the liver is specified, bile ducts form and hepatocytes differentiate. However, the hepatocytes die shortly after their differentiation, and thus the resulting mutant liver consists mainly of biliary tissue. We identified a mutation in the gene encoding translocase of the outer mitochondrial membrane 22 (Tomm22) as responsible for this phenotype. Mutations in tomm genes have been associated with mitochondrial dysfunction, but most studies on the effect of defective mitochondrial protein translocation have been carried out in cultured cells or unicellular organisms. Therefore, the tomm22 mutant represents an important vertebrate genetic model to study mitochondrial biology and hepatic mitochondrial diseases. We further found that the temporary knockdown of Tomm22 levels by morpholino antisense oligonucleotides causes a specific hepatocyte degeneration phenotype that is reversible: new hepatocytes repopulate the liver as Tomm22 recovers to wild-type levels. The specificity and reversibility of hepatocyte ablation after temporary knockdown of Tomm22 provides an additional model to study liver regeneration, under conditions where most hepatocytes have died. We used this regeneration model to analyze the signaling commonalities between hepatocyte development and regeneration.

The role of mesodermal signals during liver organogenesis in zebrafish

Three germ cell layers, the ectoderm, mesoderm and endoderm, are established during the gastrulation stage. All cell types in different organs and tissues are derived from these 3 germ cell layers at later stages. For example, skin epithelial cells and neuronal cells are derived from the ectoderm, while endothelial cells and muscle cells from the mesoderm and lung, and intestine epithelial cells from the endoderm. While in a normal situation different germ cells are destined to specific cell fates in different organs and tissues, each type of germ cells or its derivatives also produce extracellular signaling molecules to direct and facilitate the specification and differentiation of other germ cells during organogenesis. Liver is derived from the endoderm, but completion of liver organogenesis is regulated at different levels. While the pan-endoderm factors (e.g. FoxA and Gata families) and liver specific factors (e.g. Prox1 and Hhex) are essential intrinsic factors for endoderm cells to be differentiated into hepatoblasts, the role of signals produced by neighboring mesoderm cells for liver organogenesis is equally important. This review summarizes recent progress in studying the role of Bone morphogenetic proteins (Bmp), Fibroblast growth factors (Fgf), retinoic acid (RA) and Wingless and Int (Wnt), the 4 types of signaling molecules produced by the mesoderm cells, in liver organogenesis in zebrafish.

Generation of functional hepatocytes from human embryonic stem cells under chemically defined conditions that recapitulate liver development

Generation of hepatocytes from human embryonic stem cells (hESCs) could represent an advantageous source of cells for cell therapy approaches as an alternative to orthotopic liver transplantation. However, the generation of differentiated hepatocytes from hESCs remains a major challenge, especially using a method compatible with clinical applications. We report a novel approach to differentiate hESCs into functional hepatic cells using fully defined culture conditions, which recapitulate essential stages of liver development. hESCs were first differentiated into a homogenous population of endoderm cells using a combination of activin, fibroblast growth factor 2, and bone morphogenetic protein 4 together with phosphoinositide 3-kinase inhibition. The endoderm cells were then induced to differentiate further into hepatic progenitors using fibroblast growth factor 10, retinoic acid, and an inhibitor of activin/nodal receptor. After further maturation, these cells expressed markers of mature hepatocytes, including asialoglycoprotein receptor, tyrosine aminotransferase, alpha1-antitrypsin, Cyp7A1, and hepatic transcription factors such as hepatocyte nuclear factors 4alpha and 6. Furthermore, the cells generated under these conditions exhibited hepatic functions in vitro, including glycogen storage, cytochrome activity, and low-density lipoprotein uptake. After transduction with a green fluorescent protein-expressing lentivector and transplantation into immunodeficient uPA transgenic mice, differentiated cells engrafted into the liver, grew, and expressed human albumin and alpha1-antitrypsin as well as green fluorescent protein for at least 8 weeks. In addition, we showed that hepatic cells could be generated from human-induced pluripotent cells derived from reprogrammed fibroblasts, demonstrating the efficacy of this approach with pluripotent stem cells of diverse origins.

CONCLUSION

We have developed a robust and efficient method to differentiate pluripotent stem cells into hepatic cells, which exhibit characteristics of human hepatocytes. Our approach should facilitate the development of clinical grade hepatocytes for transplantation and for research on drug discovery.

Embryonic and adult stem cell systems in mammals: ontology and regulation

Stem cells are defined as having the ability to self-renew and to generate differentiated cells. During embryogenesis, cells are initially proliferative and pluripotent and then they gradually become restricted to different cell fates. In the adult, tissue stem cells are normally quiescent, but become proliferative upon injury. Knowledge from developmental biology and insights into the properties of stem cells are keys to further understanding and successful manipulation. Here, we first focus on ES cells, then on embryonic development, and then on tissue stem cells of endodermally derived tissues, particularly the liver and pancreas.

Characterization and functional analyses of hepatic mesothelial cells in mouse liver development

BACKGROUND & AIMS

At the onset of liver development, cardiac mesoderm, septum transversum mesenchyme, and endothelial cells are involved in the specification and/or proliferation of hepatoblasts. After this initial stage, however, it is unclear which cells support the proliferation and differentiation of hepatocytes. Here we characterized the nature of mouse hepatic mesothelial cells (MCs) and investigated their role in organogenesis.

METHODS

Using anti-podocalyxin-like protein 1 (PCLP1) and anti-mesothelin antibodies, we characterized MCs during liver development by immunohistochemistry, flow cytometry, and gene expression analysis. The possible role of MCs in hepatogenesis was investigated by in vitro culture and analysis of Wilms' tumor 1 homologue (WT1) knockout mice.

RESULTS

PCLP1 was highly expressed in immature MCs, covering the surface of lobes. PCLP1 expression in MCs was down-regulated along with development, whereas mesothelin expression was up-regulated, indicating that these molecules distinguished developmental stages of MCs. The proliferation potential of MCs was high in the fetus and declined after birth. Fetal MCs expressed various growth factors and strongly enhanced the expansion of fetal hepatocytes in vitro, whereas differentiated MCs exhibited less growth factor expression, and differentiated MCs failed to enhance hepatocyte proliferation in vitro. In WT1-deficient embryos, hepatocyte proliferation was impaired due to defective MCs.

CONCLUSIONS

The mesothelium is not only an inert protective sheet covering the parenchyma but also changes its characteristics dynamically during development and plays an active role in organogenesis by promoting expansion of parenchymal cells.

Organogenesis and development of the liver

Embryonic development of the liver has been studied intensely, yielding insights that impact diverse areas of developmental and cell biology. Understanding the fundamental mechanisms that control hepatogenesis has also laid the basis for the rational differentiation of stem cells into cells that display many hepatic functions. Here, we review the basic molecular mechanisms that control the formation of the liver as an organ.

Minireview: beta-cell replacement therapy for diabetes in the 21st century: manipulation of cell fate by directed differentiation

Pancreatic beta-cell failure underlies type 1 diabetes; it also contributes in an essential way to type 2 diabetes. beta-Cell replacement is an important component of any cure for diabetes. The current options of islet and pancreas transplantation are not satisfactory as definitive forms of therapy. Here, we review strategies for induced de novo pancreatic beta-cell formation, which depend on the targeted differentiation of cells into pancreatic beta-cells. With this objective in mind, one can manipulate the fate of three different types of cells: 1) from terminally differentiated cells, e.g. exocrine pancreatic cells, into beta-cells; 2) from multipotent adult stem cells, e.g. hepatic oval cells, into pancreatic islets; and 3) from pluripotent stem cells, e.g. embryonic stem cells and induced pluripotent stem cells, into beta-cells. We will examine the pros and cons of each strategy as well as the hurdles that must be overcome before these approaches to generate new beta-cells will be ready for clinical application.

Effects of sodium butyrate on the differentiation of pancreatic and hepatic progenitor cells from mouse embryonic stem cells

Recently significant progress has been made in differentiating embryonic stem (ES) cells toward pancreatic cells. However, little is known about the generation and identification of pancreatic progenitor cells from ES cells. Here we explored the influence of sodium butyrate on pancreatic progenitor differentiation, and investigated the different effects of sodium butyrate on pancreatic and hepatic progenitor formation. Our results indicated that different concentration and exposure time of sodium butyrate led to different differentiating trends of ES cells. A relatively lower concentration of sodium butyrate with shorter exposure time induced more pancreatic progenitor cell formation. When stimulated by a higher concentration and longer exposure time of sodium butyrate, ES cells differentiated toward hepatic progenitor cells rather than pancreatic progenitor cells. These progenitor cells could further mature into pancreatic and hepatic cells with the supplement of exogenous inducing factors. The resulting pancreatic cells expressed specific markers such as insulin and C-peptide, and were capable of insulin secretion in response to glucose stimulation. The differentiated hepatocytes were characterized by the expression of a number of liver-associated genes and proteins, and had the capability of glycogen storage. Thus, the current study demonstrated that sodium butyrate played different roles in inducing ES cells toward pancreatic or hepatic progenitor cells. These progenitor cells could be further induced into mature pancreatic cells and hepatocytes. This finding may facilitate the understanding of pancreatic and hepatic cell differentiation from ES cells, and provide a potential source of transplantable cells for cell-replacement therapies.

FGF2 specifies hESC-derived definitive endoderm into foregut/midgut cell lineages in a concentration-dependent manner

Fibroblast growth factor (FGF) signaling controls axis formation during endoderm development. Studies in lower vertebrates have demonstrated that FGF2 primarily patterns the ventral foregut endoderm into liver and lung, whereas FGF4 exhibits broad anterior-posterior and left-right patterning activities. Furthermore, an inductive role of FGF2 during dorsal pancreas formation has been shown. However, whether FGF2 plays a similar role during human endoderm development remains unknown. Here, we show that FGF2 specifies hESC-derived definitive endoderm (DE) into different foregut lineages in a dosage-dependent manner. Specifically, increasing concentrations of FGF2 inhibits hepatocyte differentiation, whereas intermediate concentration of FGF2 promotes differentiation toward a pancreatic cell fate. At high FGF2 levels specification of midgut endoderm into small intestinal progenitors is increased at the expense of PDX1(+) pancreatic progenitors. High FGF2 concentrations also promote differentiation toward an anterior foregut pulmonary cell fate. Finally, by dissecting the FGF receptor intracellular pathway that regulates pancreas specification, we demonstrate for the first time to the best of our knowledge that induction of PDX1(+) pancreatic progenitors relies on FGF2-mediated activation of the MAPK signaling pathway. Altogether, these observations suggest a broader gut endodermal patterning activity of FGF2 that corresponds to what has previously been advocated for FGF4, implying a functional switch from FGF4 to FGF2 during evolution. Thus, our results provide new knowledge of how cell fate specification of human DE is controlled-facts that will be of great value for future regenerative cell therapies.

Isolation, characterization, and differentiation of thy1.1-sorted pancreatic adult progenitor cell populations

We have isolated a novel progenitor cell population from adult rat pancreatic ducts, termed pancreatic-derived progenitor cells (PDPCs). Here, we report the in vitro culture, selection, and characterization of Thy1.1-positive and Thy1.1-negative PDPC subpopulations. These cells exhibit bipotentiality for differentiation into both pancreatic and hepatic cell types. Significantly, they express Pdx-1. Using a serum-free FGF-4-containing differentiation protocol, we have observed a time course of both morphological and gene expression changes indicative of hepatic lineage differentiation for the Thy1.1-positive subpopulation. These cells express albumin and store glycogen, typical features of mature hepatocytes. The Thy1.1-positive subpopulation could also readily be induced to differentiate into a pancreatic lineage with characteristic morphological changes resulting in three-dimensional islet-like structures and the transcriptional expression of insulin and glucagon in addition to Pdx-1. No morphological evidence of islet-like clusters was observed using the Thy1.1-negative population. However, Thy1.1-negative cells grown in pancreatic differentiation medium did show insulin gene transcription. Glucagon was not expressed in the undifferentiated Thy1.1-negative cells, nor was it induced in vitro after differentiation. The detection of Pdx-1 transcriptional expression in both populations indicates their potential as a novel source of non-beta-cell-derived insulin.

Liver development, regeneration, and carcinogenesis

The identification of putative liver stem cells has brought closer the previously separate fields of liver development, regeneration, and carcinogenesis. Significant overlaps in the regulation of these processes are now being described. For example, studies in embryonic liver development have already provided the basis for directed differentiation of human embryonic stem cells and induced pluripotent stem cells into hepatocyte-like cells. As a result, the understanding of the cell biology of proliferation and differentiation in the liver has been improved. This knowledge can be used to improve the function of hepatocyte-like cells for drug testing, bioartificial livers, and transplantation. In parallel, the mechanisms regulating cancer cell biology are now clearer, providing fertile soil for novel therapeutic approaches. Recognition of the relationships between development, regeneration, and carcinogenesis, and the increasing evidence for the role of stem cells in all of these areas, has sparked fresh enthusiasm in understanding the underlying molecular mechanisms and has led to new targeted therapies for liver cirrhosis and primary liver cancers.

The Fox genes in the liver: from organogenesis to functional integration

Formation and function of the liver are highly controlled, essential processes. Multiple signaling pathways and transcriptional regulatory networks cooperate in this complex system. The evolutionarily conserved FOX, for Forkhead bOX, class of transcriptional regulators is critical to many aspects of liver development and function. The FOX proteins are small, mostly monomeric DNA binding factors containing the so-called winged helix DNA binding motif that distinguishes them from other classes of transcription factors. We discuss the biochemical and genetic roles of Foxa, Foxl1, Foxm1, and Foxo, as these have been shown to regulate many processes throughout the life of the organ, controlling both formation and function of the liver.

The homeobox gene Hex regulates hepatocyte differentiation from embryonic stem cell-derived endoderm

We investigated the role of the hematopoietically expressed homeobox (Hex) in the differentiation and development of hepatocytes within embryonic stem cell (ESC)-derived embryoid bodies (EBs). Analyses of hepatic endoderm derived from Hex(-/-) EBs revealed a dramatic reduction in the levels of albumin (Alb) and alpha-fetoprotein (Afp) expression. In contrast, stage-specific forced expression of Hex in EBs from wild-type ESCs led to the up-regulation of Alb and Afp expression and secretion of Alb and transferrin. These inductive effects were restricted to c-kit(+) endoderm-enriched EB-derived populations, suggesting that Hex functions at the level of hepatic specification of endoderm in this model. Microarray analysis revealed that Hex regulated the expression of a broad spectrum of hepatocyte-related genes, including fibrinogens, apolipoproteins, and cytochromes. When added to the endoderm-induced EBs, bone morphogenetic protein 4 acted synergistically with Hex in the induction of expression of Alb, Afp, carbamoyl phosphate synthetase, transcription factor 1, and CCAAT/enhancer binding protein alpha. These findings indicate that Hex plays a pivotal role during induction of liver development from endoderm in this in vitro model and suggest that this strategy may provide important insight into the generation of functional hepatocytes from ESCs.

Converting human pluripotent stem cells into beta-cells: recent advances and future challenges

PURPOSE OF REVIEW

The transplantation of insulin-producing beta-cells derived from human embryonic stem cells and induced pluripotent stem cells (collectively termed pluripotent stem cells or PSCs) holds great promise for therapy of diabetes mellitus. The purpose of this review is to summarize recent advances in this area, emphasizing the importance of studies of endocrine pancreas development in efforts to direct PSC differentiation into endocrine cells, as well as to outline the major challenges remaining before transplantation of PSC-derived beta-cells can become a reality.

RECENT FINDINGS

Although several protocols to generate glucose-responsive pancreatic beta-cells in vitro have been described, the most successful approaches are those that most closely mimic embryonic development of the endocrine pancreas. Until recently, cells generated by these methods have exhibited immature pancreatic endocrine phenotypes. However, protocols that generate more functional beta-like cells have now been described. In addition, small molecules are being used to improve protocols to direct differentiation of PSCs into endoderm and pancreatic lineages.

SUMMARY

Advances over the last decade suggest that generating functional beta-cells from human PSCs is achievable. However, there are aspects of beta-cell development that are not well understood and are hampering generation of PSC-derived beta-cells. In particular, the signaling pathways that instruct endocrine progenitor cells to differentiate into mature and functional beta-cells are poorly understood. Other significant obstacles remain, including the need for safe and cost-effective differentiation methods for large-scale generation of transplantation quality beta-cells, methods to prevent immune rejection of grafted tissues, and amelioration of the risks of tumorigenesis.

Dividing the tubular gut: generation of organ boundaries at the pylorus

The discrete organs that comprise the gastrointestinal tract (esophagus, stomach, small intestine, and large intestine) arise embryonically by regional differentiation of a single tube that is initially morphologically similar along its length. Regional organ differentiation programs, for example, for stomach or intestine, involve signaling cross-talk between epithelium and mesenchyme and result in the formation of precise boundaries between organs, across which dramatic differences in both morphology and gene expression are seen. The pylorus is a unique area of the gut tube because it not only marks an important organ boundary in the tubular gut (the stomach/intestinal boundary) but is also the hub for the development of multiple accessory organs (liver, pancreas, gall bladder, and spleen). This chapter examines: (a) our current understanding of the molecular and morphogenic processes that underlie the generation of the dramatic epithelial tissue boundary that compartmentalizes stomach and intestine; (b) the tissue interactions that promote development of the accessory organs in this area; and (c) the molecular interactions that specify patterning of the pyloric sphincter. Though the focus here is primarily on the mouse as a model organism, the molecular underpinnings of organ patterning near the pylorus are shared by chick and frog. Thus, further study of these conserved developmental programs could potentially shed light on the mechanisms underlying human pyloric malformations such as infantile hypertrophic pyloric stenosis.

Hepatic stem cells and liver development

The liver consists of many cell types with specialized functions. Hepatocytes are one of the main players in the organ and therefore are the most vulnerable cells to damage. Since they are not everlasting cells, they need to be replenished throughout life. Although the capacity of hepatocytes to contribute to their own maintenance has long been recognized, recent studies have indicated the presence of both intrahepatic and extrahepatic stem/progenitor cell populations that serve to maintain the normal organ and to regenerate damaged parenchyma in response to a variety of insults.The intrahepatic compartment most likely derives primarily from the biliary tree, particularly the most proximal branches, i.e. the canals of Hering and smallest ductules. The extrahepatic compartment is at least in part derived from diverse populations of cells from the bone marrow. Embryonic stem cells (ES's) are considered as a part of the extrahepatic compartment. Due to their pluripotent capabilities, ES cell-derived cells form a potential future source of hepatocytes, to replace or restore hepatic tissues that have been damaged by disease or injury. Progressing knowledge about stem cells in the liver would allow a better understanding of the mechanisms of hepatic homeostasis and regeneration. Although a human stem cell-derived cell type equivalent to primary hepatocytes does not yet exist, the promising results obtained with extrahepatic stem cells would open the way to cell-based therapy for liver diseases.

Isolation and culture of embryonic pancreas and liver

Culturing embryonic tissue in an in vitro setting offers the unique ability to manipulate the external medium and therefore to investigate the pathways involved in regulating normal organogenesis as well as providing models for developmental disorders. Here we describe a system for the in vitro culture of the dorsal pancreatic buds and liver buds from mouse embryos. The tissues are dissected from day 9.0 or 11.5 mouse embryos. The tissues are placed on fibronectin-coated coverslips in serum-containing medium and allowed to attach. Over the next few days, the buds grow as flattened structures which are thin enough to allow the use of wholemount immunostaining methods.

Markers and signaling factors for stem cell differentiation to hepatocytes: lessons from developmental studies

Liver transplantation is the preferred option to treat a number of hepatic diseases in adults and children, but the number of patients on the waiting list is exceeding the number of available livers for transplantation. Hepatocytes differentiated in vitro from stem cells are a promising and renewable source of tissue for transplantation. The principles guiding programmed differentiation of stem cells to hepatocytes are largely based on knowledge gained from studies on embryonic development of the liver. How key findings in developmental biology are translated into cell culture protocols driving stepwise differentiation of hepatocytes is illustrated in this chapter.

Comparative analysis of endoderm formation efficiency between mouse ES cells and iPS cells

Definitive endoderm (DE) derived from stem cells holds potential to differentiate into hepatocytes. Stem cell therapy using those cells has potential for a treatment of liver disease. To date, various ways of inducing hepatocytes from embryonic stem (ES) cells have been reported by researchers. However, it has not been proved enough that induced pluripotent stem (iPS) cells behave in the same manner as ES cells in endoderm differentiation. The purpose of this study was to establish an efficient method to induce DE from iPS cells, through comparatively analyzing the efficacy of endoderm formation from mouse ES cells. Furthermore, the efficiency of a serum-free medium in the differentiation into DE was investigated. Mouse ES cells and iPS cells were floated in culture medium for 2 or 5 days and embryoid bodies (EB) were formed. Subsequently, DE was induced with 100 ng/ml activin A and 100 ng/ml basic fibroblast growth factor (bFGF). RT-PCR and real-time PCR analyses were carried out at each step to determine the gene expression of EB markers. The difference in cellular proliferation between serum-containing and serum-free media was examined by an MTS assay in EB and DE induction. iPS cells showed the paralleled mRNA expression to ES cells in each step of differentiation into EB, but the levels of expression of Sox17 and Foxa2 were relatively higher in ES cell-derived DE, whereas Cxcr4 expression was higher in iPS cell-derived DE. The utilization of serum-free medium for iPS cells showed significantly favorable cellular proliferation during EB formation and subsequent DE induction. Forming EB for 5 days and subsequently DE induction with activin A and bFGF with serum-free medium was an appropriate protocol in iPS cells. This may represent an important step for generating hepatocytes from iPS cells for the development of cell therapy.

Highly efficient generation of human hepatocyte-like cells from induced pluripotent stem cells

There exists a worldwide shortage of donor livers available for orthotropic liver transplantation and hepatocyte transplantation therapies. In addition to their therapeutic potential, primary human hepatocytes facilitate the study of molecular and genetic aspects of human hepatic disease and development and provide a platform for drug toxicity screens and identification of novel pharmaceuticals with potential to treat a wide array of metabolic diseases. The demand for human hepatocytes, therefore, heavily outweighs their availability. As an alternative to using donor livers as a source of primary hepatocytes, we explored the possibility of generating patient-specific human hepatocytes from induced pluripotent stem (iPS) cells.

CONCLUSION

We demonstrate that mouse iPS cells retain full potential for fetal liver development and describe a procedure that facilitates the efficient generation of highly differentiated human hepatocyte-like cells from iPS cells that display key liver functions and can integrate into the hepatic parenchyma in vivo.

Recent advances in stem cell research for the treatment of diabetes

The success achieved over the last decade with islet transplantation has intensified interest in treating diabetes, not only by cell transplantation, but also by stem cells. The formation of insulin-producing cells from pancreatic duct, acinar, and liver cells is an active area of investigation. Protocols for the in vitro differentiation of embryonic stem (ES) cells based on normal developmental processes, have generated insulin-producing cells, though at low efficiency and without full responsiveness to extracellular levels of glucose. Induced pluripotent stem cells, which have been generated from somatic cells by introducing Oct3/4, Sox2, Klf4, and c-Myc, and which are similar to ES cells in morphology, gene expression, epigenetic status and differentiation, can also differentiate into insulin-producing cells. Overexpression of embryonic transcription factors in stem cells could efficiently induce their differentiation into insulin-expressing cells. The purpose of this review is to demonstrate recent progress in the research for new sources of β-cells, and to discuss strategies for the treatment of diabetes.

Lanford medium induces high quality hepatic lineage cell differentiation directly from mouse embryonic stem cell-derived mesendoderm

To establish an effective induction method for hepatic differentiation using serum-free media, the effects of activin in serum-containing and serum-free conditions on embryoid body (EB) induction into mesendoderm were investigated by Western blot analysis and real-time reverse transcription-polymerase chain reaction (RT-PCR) as a first step. The expression of P-smad2 and mesendodermal markers was markedly enhanced by 100ng/ml activin under serum-free conditions but were inhibited or masked under serum-containing conditions. Next, serum-free Lanford medium was used to attempt the direct induction of activin-treated EBs expressing mesendodermal markers into hepatic lineage cells and this induction was compared to that induced using Iscove's Modified Dulbecco's medium containing 20% fetal bovine serum. Once immersed in the Lanford medium, EBs began to show typical hepatic features by day 17, including Alb, AFP, TTR, and AAT expression detected by RT-PCR, and ALB, AFP, and CK18 expression detected by immunostaining. On day 22, these cells were of high quality characterized by the expression of metabolizing enzymes, including Ugt1a1, Slcola4, cyp3a11, cyp2b10, and cyp7a1 detected by real-time PCR, a 50-fold greater cyp3A11 response than control to 100muM dexamethasone stimulation, specific cellular uptake of indocyanine green, and glycogen storage in the cytoplasm. These results indicate that this simple two-step induction method under serum-free conditions induces hepatic lineage cells with high quality directly from mouse embryonic stem (ES) cell-derived mesendoderm.