In vitro chamber specification during embryonic stem cell cardiogenesis. Expression of the ventricular myosin light chain-2 gene is independent of heart tube formation

Embryoid bodies as a model system for exploring early human embryonic development

This review article aims to summarize the existing concepts related to embryoid bodies (EBs) and explore their potential as a model system for studying various aspects of human embryonic development. The review involves the collection and analysis of information about the characteristics of EBs and the properties of stem cells that give rise to them. The results show that EBs derived from pluripotent stem cells are a promising model that closely replicates processes occurring in human embryos after implantation. The review also provides a comparative analysis of the advantages and limitations of models based on induced pluripotent stem cells (iPSCs) and embryonic stem cells (ESCs), with particular attention given to summarizing the results of limited studies on RNA sequencing in individual cells from human and mouse EBs. In conclusion, we would like to emphasize that embryoid bodies are an effective model system for studying early human embryogenesis. This opens up new possibilities for reproductive genetics and medicine.

Regulatory Light Chains in Cardiac Development and Disease

The role of regulatory light chains (RLCs) in cardiac muscle function has been elucidated progressively over the past decade. The RLCs are among the earliest expressed markers during cardiogenesis and persist through adulthood. Failing hearts have shown reduced RLC phosphorylation levels and that restoring baseline levels of RLC phosphorylation is necessary for generating optimal force of muscle contraction. The signalling mechanisms triggering changes in RLC phosphorylation levels during disease progression remain elusive. Uncovering this information may provide insights for better management of heart failure patients. Given the cardiac chamber-specific expression of RLC isoforms, ventricular RLCs have facilitated the identification of mature ventricular cardiomyocytes, opening up possibilities of regenerative medicine. This review consolidates the standing of RLCs in cardiac development and disease and highlights knowledge gaps and potential therapeutic advancements in targeting RLCs.

Inhibitory effect of progesterone during early embryonic development: Suppression of myocardial differentiation and calcium-related transcriptome by progesterone in mESCs: Progesterone disturb cardiac differentiation of mESCs through lower cytosolic Ca(2.)

Progesterone (PG) and its derivates are used in prevention of spontaneous miscarriage. However, some studies have reported that exposure to PG and its derivates during pregnancy can cause malformations and affect both blood pressure and the cardiovascular system. The effect of PG on cardiomyogenesis of mouse embryonic stem cells (mESCs) is not well known. Expression of Pgr mRNA showed an opposite pattern of beating-ratio during differentiation. PG treatment resulted in reduction of the beating ratio to 60.45±1.54% from 92.17±2.98% in normal differentiation, reduced transcripts of heart morphogenesis and Ca(2+) binding-related genes in the next generation sequencing data and significantly decreased expression levels of Ca(2+)/contraction-related genes including Ryr2, Calm2, Trpv2, and Mylk3, the intracellular Ca(2+) level, and the beating frequency. These results suggest that PG exerts inhibitory effects on differentiation of mESCs into functional cardiomyocytes.

Heme Oxygenase-1/Carbon Monoxide System and Embryonic Stem Cell Differentiation and Maturation into Cardiomyocytes

AIMS

The differentiation of embryonic stem (ES) cells into energetically efficient cardiomyocytes contributes to functional cardiac repair and is envisioned to ameliorate progressive degenerative cardiac diseases. Advanced cell maturation strategies are therefore needed to create abundant mature cardiomyocytes. In this study, we tested whether the redox-sensitive heme oxygenase-1/carbon monoxide (HO-1/CO) system, operating through mitochondrial biogenesis, acts as a mechanism for ES cell differentiation and cardiomyocyte maturation.

RESULTS

Manipulation of HO-1/CO to enhance mitochondrial biogenesis demonstrates a direct pathway to ES cell differentiation and maturation into beating cardiomyocytes that express adult structural markers. Targeted HO-1/CO interventions up- and downregulate specific cardiogenic transcription factors, transcription factor Gata4, homeobox protein Nkx-2.5, heart- and neural crest derivatives-expressed protein 1, and MEF2C. HO-1/CO overexpression increases cardiac gene expression for myosin regulatory light chain 2, atrial isoform, MLC2v, ANP, MHC-β, and sarcomere α-actinin and the major mitochondrial fusion regulators, mitofusin 2 and MICOS complex subunit Mic60. This promotes structural mitochondrial network expansion and maturation, thereby supporting energy provision for beating embryoid bodies. These effects are prevented by silencing HO-1 and by mitochondrial reactive oxygen species scavenging, while disruption of mitochondrial biogenesis and mitochondrial DNA depletion by loss of mitochondrial transcription factor A compromise infrastructure. This leads to failure of cardiomyocyte differentiation and maturation and contractile dysfunction.

INNOVATION

The capacity to augment cardiomyogenesis via a defined mitochondrial pathway has unique therapeutic potential for targeting ES cell maturation in cardiac disease.

CONCLUSION

Our findings establish the HO-1/CO system and redox regulation of mitochondrial biogenesis as essential factors in ES cell differentiation as well as in the subsequent maturation of these cells into functional cardiac cells.

Expression of podocalyxin separates the hematopoietic and vascular potentials of mouse embryonic stem cell-derived mesoderm

In the mouse embryo and differentiating embryonic stem cells, the hematopoietic, endothelial, and cardiomyocyte lineages are derived from Flk1+ mesodermal progenitors. Here, we report that surface expression of Podocalyxin (Podxl), a member of the CD34 family of sialomucins, can be used to subdivide the Flk1+ cells in differentiating embryoid bodies at day 4.75 into populations that develop into distinct mesodermal lineages. Definitive hematopoietic potential was restricted to the Flk1+Podxl+ population, while the Flk1-negative Podxl+ population displayed only primitive erythroid potential. The Flk1+Podxl-negative population contained endothelial cells and cardiomyocyte potential. Podxl expression distinguishes Flk1+ mesoderm populations in mouse embryos at days 7.5, 8.5, and 9.5 and is a marker of progenitor stage primitive erythroblasts. These findings identify Podxl as a useful tool for separating distinct mesodermal lineages.

Ultrastructural characteristics of three undifferentiated mouse embryonic stem cell lines and their differentiated three-dimensional derivatives: a comparative study

The fine structures of mouse embryonic stem cells (mESCs) grown as colonies and differentiated in three-dimensional (3D) culture as embryoid bodies (EBs) were analyzed by transmission electron microscopy. Undifferentiated mESCs expressed markers that proved their pluripotency. Differentiated EBs expressed different differentiation marker proteins from the three germ layers. The ultrastructure of mESCs revealed the presence of microvilli on the cell surfaces, large and deep infolded nuclei, low cytoplasm-to-nuclear ratios, frequent lipid droplets, nonprominent Golgi apparatus, and smooth endoplasmic reticulum. In addition, we found prominent juvenile mitochondria and free ribosomes-rich cytoplasm in mESCs. Ultrastructure of the differentiated mESCs as EBs showed different cell arrangements, which indicate the different stages of EB development and differentiation. The morphologies of BALB/c and 129 W9.5 EBs were very similar at day 4, whereas C57BL/6 EBs were distinct from the others at day 4. This finding suggested that differentiation of EBs from different cell lines occurs in the same pattern but not at the same rate. Conversely, the ultrastructure results of BALB/c and 129 W9.5 ESCs revealed differentiating features, such as the dilated profile of a rough endoplasmic reticulum. In addition, we found low expression levels of undifferentiated markers on the outer cells of BALB/c and 129 W9.5 mESC colonies, which suggests a faster differentiation potential.

Early cardiac development: a view from stem cells to embryos

From the 1920s, early cardiac development has been studied in chick and, later, in mouse embryos in order to understand the first cell fate decisions that drive specification and determination of the endocardium, myocardium, and epicardium. More recently, mouse and human embryonic stem cells (ESCs) have demonstrated faithful recapitulation of early cardiogenesis and have contributed significantly to this research over the past few decades. Derived almost 15 years ago, human ESCs have provided a unique developmental model for understanding the genetic and epigenetic regulation of early human cardiogenesis. Here, we review the biological concepts underlying cell fate decisions during early cardiogenesis in model organisms and ESCs. We draw upon both pioneering and recent studies and highlight the continued role for in vitro stem cells in cardiac developmental biology.

In vitro cellular models for cardiac development and pharmacotoxicology

Permanent cultures of cardiac cells described so far have limited value for studying cell biology and pharmacology of the developing heart because of the loss of proliferative capacity and cardiac-specific properties of cardiomyocytes during long-term cultivation. Pluripotent embryonic carcinoma (EC) and embryonic stem (ES) cells cultivated as permanent lines offer a new approach for studying cardiogenic differentiation in vitro. We describe cardiogenesis in vitro by differentiating EC and ES cells by way of embryo-like aggregates (embryoid bodies) into spontaneously beating cardiomyocytes. During cardiomyocyte differentiation three distinct developmental stages were defined by expression of specific action potentials and ionic currents measured by the whole-cell patch-clamp technique. Whereas early differentiated cardiomyocytes are characterized by action potentials and ionic currents typical for early pacemaker cells, terminally differentiated cardiomyocytes show action potentials and ionic currents inherent to ventricular-, atrial- or sinus nodal-like cells. These functional characteristics are in accordance with the expression of alpha- and beta-cardiac myosin heavy chain at early differentiation stages and the additional expression of ventricular-specific MLC-2V and atrial-specific ANF genes at terminal stages demonstrated by reverse transcription polymerase chain reaction (RT-PCR) analysis. Pharmacological studies performed by measuring chronotropic responses and by analysing the Ca(2+) channel activity correspond to data obtained with cardiac cells from living organisms. For testing the influence of exogenous compounds on cardiac differentiation the teratogenic compound retinoic acid (RA) was applied during distinct stages of embryoid body development. A temporally controlled influence of RA on cardiac differentiation and expression of cardiac-specific genes was found. We conclude that ES cell-derived cardiomyocytes provide an excellent cellular model to study early cardiac development and to perform pharmacological and embryotoxicological investigations.

Multiphoton flow cytometry to assess intrinsic and extrinsic fluorescence in cellular aggregates: applications to stem cells

Detection and tracking of stem cell state are difficult due to insufficient means for rapidly screening cell state in a noninvasive manner. This challenge is compounded when stem cells are cultured in aggregates or three-dimensional (3D) constructs because living cells in this form are difficult to analyze without disrupting cellular contacts. Multiphoton laser scanning microscopy is uniquely suited to analyze 3D structures due to the broad tunability of excitation sources, deep sectioning capacity, and minimal phototoxicity but is throughput limited. A novel multiphoton fluorescence excitation flow cytometry (MPFC) instrument could be used to accurately probe cells in the interior of multicell aggregates or tissue constructs in an enhanced-throughput manner and measure corresponding fluorescent properties. By exciting endogenous fluorophores as intrinsic biomarkers or exciting extrinsic reporter molecules, the properties of cells in aggregates can be understood while the viable cellular aggregates are maintained. Here we introduce a first generation MPFC system and show appropriate speed and accuracy of image capture and measured fluorescence intensity, including intrinsic fluorescence intensity. Thus, this novel instrument enables rapid characterization of stem cells and corresponding aggregates in a noninvasive manner and could dramatically transform how stem cells are studied in the laboratory and utilized in the clinic.

Enhanced proliferation of monolayer cultures of embryonic stem (ES) cell-derived cardiomyocytes following acute loss of retinoblastoma

Background

Cardiomyocyte (CM) cell cycle analysis has been impeded because of a reliance on primary neonatal cultures of poorly proliferating cells or chronic transgenic animal models with innate compensatory mechanisms.

Methodology/Principal Findings

We describe an in vitro model consisting of monolayer cultures of highly proliferative embryonic stem (ES) cell-derived CM. Following induction with ascorbate and selection with puromycin, early CM cultures are >98% pure, and at least 85% of the cells actively proliferate. During the proliferative stage, cells express high levels of E2F3a, B-Myb and phosphorylated forms of retinoblastoma (Rb), but with continued cultivation, cells stop dividing and mature functionally. This developmental transition is characterized by a switch from slow skeletal to cardiac TnI, an increase in binucleation, cardiac calsequestrin and hypophosphorylated Rb, a decrease in E2F3, B-Myb and atrial natriuretic factor, and the establishment of a more negative resting membrane potential. Although previous publications suggested that Rb was not necessary for cell cycle control in heart, we find following acute knockdown of Rb that this factor actively regulates progression through the G1 checkpoint and that its loss promotes proliferation at the expense of CM maturation.

Conclusions/Significance

We have established a unique model system for studying cardiac cell cycle progression, and show in contrast to previous reports that Rb actively regulates both cell cycle progression through the G1 checkpoint and maturation of heart cells. We conclude that this in vitro model will facilitate the analysis of cell cycle control mechanisms of CMs.

Essential role of Smad4 in maintaining cardiomyocyte proliferation during murine embryonic heart development

Transforming growth factor-beta/bone morphogenetic protein (TGF-beta/BMP) signaling pathway is essential for embryonic and postnatal heart development and remodeling. The intracellular factor Smad4 plays a pivotal role in mediating TGF-beta/BMP signal transduction in the nucleus. To examine the function of Smad4 in embryonic cardiac development during mid-gestation, we specifically deleted the Smad4 gene in embryonic cardiomyocytes using the Cre-LoxP system. Deletion of Smad4 as early as E9.5, led to embryonic lethality between E12.5 and E15.5, and embryos exhibited severe morphological defects in the heart, including a thin compact layer, disorganized trabeculae, and ventricular septum defects (VSD). Smad4 deletion also led to a dramatic decrease in cardiomyocyte proliferation accompanied by downregulation of contractile protein-encoding genes such as alpha-myosin heavy chain, beta-myosin heavy chain, ventricular myosin light chain 2, and alpha-cardiac actin. In addition, deletion of Smad4 resulted in perturbation of TGF-beta/BMP ligand expression and signaling, and defects in expression of several cardiac transcription factor genes such as Nkx2.5, GATA4, and MEF2c. These results provide direct genetic evidences that Smad4 is essential for regulating cardiomyocyte proliferation and differentiation during murine cardiogenesis, and provides new insights into potential causes of congenital heart disease.

The alpha catalytic subunit of protein kinase CK2 is required for mouse embryonic development

Protein kinase CK2 (formerly casein kinase II) is a highly conserved and ubiquitous serine/threonine kinase that is composed of two catalytic subunits (CK2alpha and/or CK2alpha') and two CK2beta regulatory subunits. CK2 has many substrates in cells, and key roles in yeast cell physiology have been uncovered by introducing subunit mutations. Gene-targeting experiments have demonstrated that in mice, the CK2beta gene is required for early embryonic development, while the CK2alpha' subunit appears to be essential only for normal spermatogenesis. We have used homologous recombination to disrupt the CK2alpha gene in the mouse germ line. Embryos lacking CK2alpha have a marked reduction in CK2 activity in spite of the presence of the CK2alpha' subunit. CK2alpha(-/-) embryos die in mid-gestation, with abnormalities including open neural tubes and reductions in the branchial arches. Defects in the formation of the heart lead to hydrops fetalis and are likely the cause of embryonic lethality. Thus, CK2alpha appears to play an essential and uncompensated role in mammalian development.

Icariin promotes expression of PGC-1alpha, PPARalpha, and NRF-1 during cardiomyocyte differentiation of murine embryonic stem cells in vitro

AIM

To investigate the effect of icariin on the expression of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1alpha), peroxisome proliferator-activated receptor alpha (PPARalpha), and nuclear respiratory factor 1 (NRF-1) on cardiomyocyte differentiation of murine embryonic stem (ES) cells in vitro.

METHODS

The cardiomyocytes derived from murine ES cells were verified by immunocytochemistry using confocal laser scanning microscopy. Cardiac-specific sarcomeric proteins (ie alpha-actinin, troponin T) were evaluated when embryoid bodies (EB) were treated with icariin or retinoid acid. The expression of PGC-1alpha, PPARalpha, and NRF-1 were analyzed using both semiquantitative RT-PCR and Western blotting in cardiomyocyte differentiation. The phosphorylation of the p38 mitogen-activated protein kinase (MAPK) was studied in the differentiation process, and its specific inhibitor SB203580 was employed to confirm the function of the p38 MAPK on icariin-induced cardiac differentiation.

RESULTS

The application of icariin significantly induced the cardiomyocyte differentiation of EB as indicated by the promoted expression of alpha-actinin and troponin T. The expression of PGC-1alpha, PPARalpha, and NRF-1 increased coincidently in early differentiation and the increase was dose-dependently upregulated by icariin treatment. The phosphorylation of the p38 MAPK peaked on d 6 and decreased after d 8, and the activation was further enhanced and prolonged when the EB were subjected to icariin, which was concurrent with the elevation of PGC-1alpha, PPARalpha, and NRF-1. Moreover, the inhibition of the p38 MAPK pathway by SB203580 efficiently abolished icariin-stimulated cardiomyocyte differentiation and resulted in the capture of the upregulation of PGC-1alpha, PPARalpha, and NRF-1.

CONCLUSION

Taken together, icariin promoted the expression of PGC-1alpha, PPARalpha, and NRF-1 during cardiomyocyte differentiation of murine ES cells in vitro and the effect was partly responsible for the activation of the p38 MAPK.

Effect of bone morphogenetic protein-4 on cardiac differentiation from mouse embryonic stem cells in serum-free and low-serum media

In spite of previous reports, the precise role of bone morphogenetic proteins (BMPs) on cardiomyocyte differentiation, especially in the absence or presence of minimum amount of serum in culture medium is still unclear. So, the aim of the present study was to investigate the effect of BMP-4 on mouse embryonic stem cells (ESCs)-derived cardiomyocyte differentiation in serum-free and low-serum media. The mouse ESCs differentiation to cardiomyocytes was induced by embryoid bodies' (EBs') development through hanging drop, suspension and plating stages. Different models of differentiation were designed according to addition of fetal bovine serum (FBS) or knockout serum replacement (KoSR) to the medium of three stages. 10 ng/ml BMP-4 was added throughout the suspension period. Up to 30 days after plating, contraction and beating frequency were monitored and evaluated daily. The growth characteristics of cardiomyocytes were assessed by cardioactive drugs, immunocytochemistry, transmission electron microscopy (TEM) and reverse transcription-polymerase chain reaction (RT-PCR). In the complete absence of serum, neither control nor BMP-4 treated groups resulted in cardiac differentiation. Addition of FBS to hanging drop stage resulted in the appearance of beating cardiac clusters in some BMP-4 treated EBs. In the best designed differentiation model in which only hanging drop and the first 24 h of plating stage was carried out at the presence of FBS, the BMP-4 treatment resulted in cardiac differentiation in EBs characterized by positive immunostaining for the applied antibodies, chronotropic response to the cardioactive drugs and cardiac-specific genes expression at different developmental stages. These cardiomyocytes showed immature myofibrils and numerous intercellular junctions. In conclusion, BMP-4 is unable to induce cardiomyocyte differentiation from mouse ESCs in serum-free models, and at least small amount of FBS in hanging drop stage is necessary. Furthermore, serum factors are not strictly necessary after the initial activation, but they do favor a better differentiation of cardiomyocytes.

In vitro differentiation of embryonic stem cells into hepatocytes induced by fibroblast growth factors and bone morphological protein-4

The feasibility of transforming embryonic endoderm into different cell types is tightly controlled by mesodermal and septum transversumal signalings during early embryonic development. Here, an induction protocol tracing embryonic liver development was designed, in which, three growth factors, acid fibroblast growth factor, basic fibroblast growth factor and bone morphological protein-4 that secreted from pre-cardiac mesoderm and septum transversum mesenchyme, respectively, were employed to investigate their specific potency of modulating the mature hepatocyte proportion during the differentiation process. Results showed that hepatic differentiation took place spontaneously at a low level, however, supplements of the three growth factors gave rise to a significant up-regulation of mature hepatocytes. Bone morphological protein-4 highlighted the differentiation ratio to 40-55%, showing the most effective promotion, and also exhibited a synergistic effect with the other two fibroblast factors, whereas no similar phenomenon was observed between the other two factors, which was reported for the first time. Our study not only provides a high-performance system of embryonic stem cells differentiating into hepatocytes, which would supply a sufficient hepatic population for related studies, but also make it clear of the inductive effects of three important growth factors, which could support for further investigation on the mechanisms of mesodermal and septumal derived signalings that regulate hepatic differentiation.

Fetal bovine serum enables cardiac differentiation of human embryonic stem cells

During development, cardiac commitment within the mesoderm requires endoderm-secreted factors. Differentiation of embryonic stem cells into the three germ layers in vitro recapitulates developmental processes and can be influenced by supplements added to culture medium. Hence, we investigated the effect of fetal bovine serum (FBS) and KnockOut serum replacement (SR) on germ layers specification and cardiac differentiation of H1 human embryonic stem cells (hESC) within embryoid bodies (EB). At the time of EB formation, FBS triggered an increased apoptosis. As assessed by quantitative PCR on 4-, 10-, and 20-day-old EB, FBS promoted a faster down-regulation of pluripotency marker Oct4 and an increased expression of endodermal (Sox17, alpha-fetoprotein, AFP) and mesodermal genes (Brachyury, CSX). While neuronal and hematopoietic differentiation occurred in both supplements, spontaneously beating cardiomyocytes were only observed in FBS. Action potential (AP) morphology of hESC-derived cardiomyocytes indicated that ventricular cells were present only after 2 months of culture. However, quantification of myosin light chain 2 ventricular (mlc2v)-positive areas revealed that mlc2v-expressing cardiomyocytes could be detected already after 2 weeks of differentiation, but not in all beating clusters. In conclusion, FBS enabled cardiac differentiation of hESC, likely in an endodermal-dependent pathway. Among cardiac cells, ventricular cardiomyocytes differentiated over time, but not as the predominant cardiac cell subtype.

Transplantation of undifferentiated murine embryonic stem cells in the heart: teratoma formation and immune response

Embryonic stem (ES) cells are promising for cardiac repair, but directing their differentiation toward cardiomyocytes remains challenging. We investigated whether the heart guides ES cells toward cardiomyocytes in vivo and whether allogeneic ES cells were immunologically tolerated. Undifferentiated mouse ES cells consistently formed cardiac teratomas in nude or immunocompetent syngeneic mice. Cardiac teratomas contained no more cardiomyocytes than hind-limb teratomas, suggesting lack of guided differentiation. ES cells also formed teratomas in infarcted hearts, indicating injury-related signals did not direct cardiac differentiation. Allogeneic ES cells also caused cardiac teratomas, but these were immunologically rejected after several weeks, in association with increased inflammation and up-regulation of class I and II histocompatibility antigens. Fusion between ES cells and cardiomyocytes occurred in vivo, but was rare. Infarct autofluorescence was identified as an artifact that might be mistaken for enhanced GFP expression and true regeneration. Hence, undifferentiated ES cells were not guided toward a cardiomyocyte fate in either normal or infarcted hearts, and there was no evidence for allogeneic immune tolerance of ES cell derivatives. Successful cardiac repair strategies involving ES cells will need to control cardiac differentiation, avoid introducing undifferentiated cells, and will likely require immune modulation to avoid rejection.

Effect of bone morphogenetic protein-4 (BMP-4) on cardiomyocyte differentiation from mouse embryonic stem cell

The present study was designed to evaluate the effect of BMP-4 on mouse embryonic stem cells (ESCs)-derived cardiomyocyte. Cardiac differentiation of the mouse ESCs was initiated by embryoid bodies (EBs) formation in hanging drops, transfer of EBs to the suspension culture and then plating onto gelatin-coated tissue culture plates. BMP-4 was added to culture medium throughout the suspension period. Cultures were observed daily with an inverted microscope for the appearance of contracting clusters. At the early, intermediate and terminal stages of differentiation, the choronotropic responses of cardiomyocytes to cardioactive drugs were assessed, and the cardiomyocytes immunostained for cardiac troponin I, desmin, alpha-actinin and nebulin. The contracting clusters were isolated for ultrastructural evaluation, at day 14 after plating. Moreover, total RNA extracted from contracting EBs of early and terminal stages of differentiation were examined for oct-4, alpha- and beta-myosin heavy chain, myosin light chain-2V and atrial natriuretic factor expression. The BMP-4 treatment resulted in a decrease in the percent of beating EBs and the percent of developing cardiomyocytes per EBs. As a whole, the chronotropic responses of beating cardiac clusters to cardioactive drugs in control group were better than BMP-4 treated group. The cardiomyocytes of both groups were positive immunostained for applied antibodies except for nebulin. Moreover, in the BMP-4 treated group, the ultrastructural characteristics and cardiac-specific genes expression were all retarded in the terminal stage of cardiomyocytes development. In conclusion, BMP-4 had an inhibitory effect on cardiomyocyte differentiation from the mouse ESCs in terms of ultrastructural characteristics, genes expression and functional properties.

Electrical stimulation modulates fate determination of differentiating embryonic stem cells

A clear understanding of cell fate regulation during differentiation is key in successfully using stem cells for therapeutic applications. Here, we report that mild electrical stimulation strongly influences embryonic stem cells to assume a neuronal fate. Although the resulting neuronal cells showed no sign of specific terminal differentiation in culture, they showed potential to differentiate into various types of neurons in vivo, and, in adult mice, contributed to the injured spinal cord as neuronal cells. Induction of calcium ion influx is significant in this differentiation system. This phenomenon opens up possibilities for understanding novel mechanisms underlying cellular differentiation and early development, and, perhaps more importantly, suggests possibilities for treatments in medical contexts.

Effects of oxytocin on cardiomyocyte differentiation from mouse embryonic stem cells

This study sought to investigate the presence of oxytocin receptors and the possible biological role of oxytocin as an effective factor in the differentiation of embryonic stem cells (ESCs) into cardiomyocytes. Mouse ESCs were cultivated in hanging drops to form embryoid bodies (EBs). The EBs were then treated with and without oxytocin (experimental and control groups). Up to 30 days after plating, contraction and beating frequency were monitored and evaluated daily. The growth characteristics of the ESC-derived cardiomyocytes were assessed by cardioactive drugs, immunocytochemistry, transmission electron microscopy (TEM) and reverse transcription-polymerase chain reaction (RT-PCR). In the experimental group, the percentage of the EBs with spontaneous contraction was significantly increased from 17th day onward. The spontaneous beating frequency of each EB in both groups was also changed with cardioactive drugs such as Bay K, carbachol, isopernaline and phenylephrine. However, in the experimental group, changes with isopernaline were more pronounced at the early and intermediate stages of cardiomyocyte development. The beating cells of both groups, stained positive with anti alpha-actinin, desmin, cardiac troponin I and connexin antibodies, and revealed similar ultrastructural features. Oxytocin receptors were detected on the ESCs and derived-differentiated cells. In addition, cardiac-specific genes such as cardiac alpha- and beta-myosin heavy chain, myosin light chain-2v, and atrial natriuretic factor were also detected in the ESC-derived differentiated cells of both groups. In the experimental group, all the specific genes, with the exception of alpha-myosin heavy chain, were more pronounced at the early stage of cardiomyocyte development. In conclusion, oxytocin has receptors on undifferentiated ESCs and derived differentiated cells, and in spite of better improvement of the EBs with spontaneous contraction, it can only promote the early maturation of ESC-derived cardiomyocytes in terms of chronotropic responses and expression of cardiac-specific genes, and have no effect on ultrastructural characteristics of cardiomyocytes in any stage of development.

Comparative proteomic analysis of mouse embryonic stem cells and neonatal-derived cardiomyocytes

Pluripotent embryonic stem cells (ESCs) spontaneously differentiate via embryo-like aggregates into cardiomyocytes. A thorough understanding of the molecular conditions in ESCs is necessary before other potential applications of these cells such as cell therapy can be materialized. We applied two dimensional electrophoresis to analyze and compare the proteome profiling of spontaneous mouse ESC-derived cardiomyocytes (ESC-DCs), undifferentiated mouse ESCs, and neonatal-derived cardiomyocytes (N-DCs). Ninety-five percent of the proteins detected on the ESC-DCs and N-DCs could be precisely paired with one other, whereas only twenty percent of the ESC proteins could be reliably matched with those on the ESC-DCs and N-DCSs, suggesting a striking similarity between them. Having identified sixty proteins in the said three cell types, we sought to provide possible explanations for their differential expression patterns and discuss their relevance to cell biology. This study provides a new insight into the gene expression pattern of differentiated cardiomyocytes and is further evidence for a close relation between ESC-DCs and N-DCSs.

Strategies for Developing Therapeutic Application of Human Embryonic Stem Cells

The ongoing debate on human embryonic stem cells (hESC) is fuelled by ethical concerns but also by the legitimate hope that hESC could one day be used for the cure of presently untreatable human diseases. Here we discuss current approaches to and constraints upon hESC differentiation and describe their potential application in clinical medicine.

Ciliated cells differentiated from mouse embryonic stem cells

In the present study, we demonstrated that the mouse embryonic stem cells were differentiated into ciliated epithelial cells, with characteristics of normal ciliated cells. These cells expressed ciliary marker proteins, such as beta-tubulin IV and hepatocyte nuclear factor-3/forkhead homolog 4 (HFH-4), and processed microtubules were arranged in the 9 + 2 structure, which is the same specific alignment observed in normal ciliary microtubules. The cilia of these cells were beating at a frequency of 17-20 Hz. The differentiated embryoid bodies (EBs) containing these ciliated cells expressed respiratory marker genes such as thyroid transcription factor-1 and surfactant protein-C. For the induction of ciliated cells, culture of EBs in serum-free medium during the initial 2 days of the attachment was indispensable. When EBs were treated with bone morphogenetic proteins, the expression of HFH-4 was decreased, and the ciliated cells were scarcely differentiated. Previous methods for inducing ciliated cells in vitro from embryonic or adult tissues involved an air-liquid interface. The system used in this study more closely mimics the normal development of ciliated cells; thus, an added advantage of the system is as a tool for studying the differentiation mechanism of normal ciliated epithelial cells.

Embryonic and adult stem cell-derived cardiomyocytes: lessons from in vitro models

For years, research has focused on how to treat heart failure by sustaining the overloaded remaining cardiomyocytes. Recently, the concept of cell replacement therapy as a treatment of heart diseases has opened a new area of investigation. In vitro-generated cardiomyocytes could be injected into the heart to rescue the function of a damaged myocardium. Embryonic and/or adult stem cells could provide cardiac cells for this purpose. Knowledge of fundamental cardiac differentiation mechanisms unraveled by studies on animal models has been improved using in vitro models of cardiogenesis such as mouse embryonal carcinoma cells, mouse embryonic stem cells and, recently, human embryonic stem cells. On the other hand, studies suggesting the existence of cardiac stem cells and the potential of adult stem cells from bone marrow or skeletal muscle to differentiate toward unexpected phenotypes raise hope and questions about their potential use for cardiac cell therapy. In this review, we compare the specificities of embryonic vs adult stem cell populations regarding their cardiac differentiation potential, and we give an overview of what in vitro models have taught us about cardiogenesis.

Complex cardiac Nkx2-5 gene expression activated by noggin-sensitive enhancers followed by chamber-specific modules

We previously reported that an Nkx2-5-GFP bacterial artificial chromosome in transgenic mice recapitulated the endogenous gene activity in the heart. Here, we identified three additional previously uncharacterized distal enhancer modules of Nkx2-5: UH6, which directed transgene expression in the right ventricle, interventricular septum, and atrial ventricular canal; UH5, which directed expression in both atria; and UH4, which directed transgene expression in tongue muscle. Nkx2-5 enhancers drive cardiogenic gene activity from the earliest progenitors to the late-stage embryonic heart, reside within its 27 kb of 5' flanking sequences, organized in a tandem array. Nkx2-5 enhancers involved with stomach-, tongue-, and chamber-restricted expression displayed lacZ transgene activity and chromatin histone acetylation patterns consistent with tissue-specific expression. An examination of Nkx2-5 gene activity in murine embryonic stem cells converted to beating embryoid bodies showed that only the proximal active region 2 and GATA-Smad enhancers were chromatin-remodeled. Chromatin remodeling of active region 2 and GATA-Smad enhancers were blunted by noggin coexpression, which indicated dependence on bone morphogenetic protein signaling for their chromatin activation during activation of Nkx2-5 expression.

Reduced genomic cytosine methylation and defective cellular differentiation in embryonic stem cells lacking CpG binding protein

Cytosine methylation at CpG dinucleotides is a critical epigenetic modification of mammalian genomes. CpG binding protein (CGBP) exhibits a unique DNA-binding specificity for unmethylated CpG motifs and is essential for early murine development. Embryonic stem cell lines deficient for CGBP were generated to further examine CGBP function. CGBP(-)(/)(-) cells are viable but show an increased rate of apoptosis and are unable to achieve in vitro differentiation following removal of leukemia inhibitory factor from the growth media. Instead, CGBP(-)(/)(-) embryonic stem cells remain undifferentiated as revealed by persistent expression of the pluripotent markers Oct4 and alkaline phosphatase. CGBP(-)(/)(-) cells exhibit a 60 to 80% decrease in global cytosine methylation, including hypo-methylation of repetitive elements, single-copy genes, and imprinted genes. Total DNA methyltransferase activity is reduced by 30 to 60% in CGBP(-)(/)(-) cells, and expression of the maintenance DNA methyltransferase 1 protein is similarly reduced. However, de novo DNA methyltransferase activity is normal. Nearly all aspects of the pleiotropic CGBP(-)(/)(-) phenotype are rescued by introduction of a CGBP expression vector. Hence, CGBP is essential for normal epigenetic modification of the genome by cytosine methylation and for cellular differentiation, consistent with the requirement for CGBP during early mammalian development.

Embryonic stem cells: prospects for developmental biology and cell therapy

Stem cells represent natural units of embryonic development and tissue regeneration. Embryonic stem (ES) cells, in particular, possess a nearly unlimited self-renewal capacity and developmental potential to differentiate into virtually any cell type of an organism. Mouse ES cells, which are established as permanent cell lines from early embryos, can be regarded as a versatile biological system that has led to major advances in cell and developmental biology. Human ES cell lines, which have recently been derived, may additionally serve as an unlimited source of cells for regenerative medicine. Before therapeutic applications can be realized, important problems must be resolved. Ethical issues surround the derivation of human ES cells from in vitro fertilized blastocysts. Current techniques for directed differentiation into somatic cell populations remain inefficient and yield heterogeneous cell populations. Transplanted ES cell progeny may not function normally in organs, might retain tumorigenic potential, and could be rejected immunologically. The number of human ES cell lines available for research may also be insufficient to adequately determine their therapeutic potential. Recent molecular and cellular advances with mouse ES cells, however, portend the successful use of these cells in therapeutics. This review therefore focuses both on mouse and human ES cells with respect to in vitro propagation and differentiation as well as their use in basic cell and developmental biology and toxicology and presents prospects for human ES cells in tissue regeneration and transplantation.

Inducible effects of icariin, icaritin, and desmethylicaritin on directional differentiation of embryonic stem cells into cardiomyocytes in vitro

AIM

To investigate the possible inducible effects of icariin, icaritin, and desmethylicaritin on the directional differentiation of embryonic stem (ES) cells into cardiomyocytes in vitro.

METHODS

ES cells were cultivated as embryoid bodies (EBs) in hanging drops with icariin, icaritin, or desmethylicaritin. ES cells treated with retinoic acid and with solvent were used as positive and negative controls, respectively. The cardiomyocytes derived from the ES cells were verified using immunocytochemistry. The expression of cardiac developmental-dependent genes was detected using the reverse transcription-polymerase chain reaction (RT-PCR) method. Cell cycle distribution and apoptosis were analyzed using flow cytometry to determine the partly inducible effect mechanisms involved.

RESULTS

The total percentage of beating EBs treated with 10(-7) mol/L icariin, icaritin, or desmethylicaritin was 87% (P<0.01), 59% (P<0.01), and 49%, respectively. All the beating cardiomyocytes derived from the ES cells expressed cardiac-specific proteins for a-actinin and troponin T. Among them, 10(-7) mol/L icariin treatment resulted in a significantly advanced and increased mRNA level of a-cardiac major histocompatibility complex (MHC) and myosin light chain 2v (MLC-2v) in EBs in the early cardiac developmental stage. Before shifting to the cardiomyocyte phenotype, icariin could evoke the accumulation of ES cells in G0/G1 and accelerate apoptosis of the cell population (P<0.05).

CONCLUSION

Icariin facilitated the directional differentiation of ES cells into cardiomyocytes at a concentration of 10(-7) mol/L. The promoting effect of icariin on cardiac differentiation was related to increasing and accelerating gene expression of a-cardiac MHC and MLC-2v, as well as regulating the cell cycles and inducing apoptosis.

Natriuretic peptides in ectopic myocardial tissues originating from mouse embryonic stem cells

In a previous report we described the survival and contractile function of mouse embryonic stem cell-derived cardiomyocytes in the host retroperitoneum. To further understand the nature of embryonic stem cell-derived cardiomyocytes, the study assessed the synthesis of natriuretic peptides in ectopic myocardial tissues of embryonic stem cell origin. Cardiomyocytes formed in embryoid body outgrowths were transplanted into the retroperitoneum of adult nude mice, and the myocardial tissues that developed were characterized by RT-PCR and immunohistochemistry concerning atrial and brain natriuretic peptides (ANP, BNP). In the outgrowths of embryoid bodies in vitro, gene expression of ANP and BNP was detected by RT-PCR and granules positive for the peptides were identified in a few cardiomyocytes by light and electron microscopic immunocytochemistry. Seven days after transplantation the transplants exhibited multidifferentiated teratoma tissues. Developing chamber myocardial tissues positive for cardiac troponin I, cadherin, and connexin 43 were evident in the transplants, which contained ANP-positive cardiomyocytes. Transplants with beating bundles were observed 30 days after transplantation, in which gene expression of both natriuretic peptides was detected. Myocardial tissues with abundant ANP-immunoreactivity, as well as with BNP-immunoreactivity to a lesser extent, were evident in the transplants. Also, myocardial tissues without immunoreactivity for natriuretic peptides were observed. Immunoelectron microscopy showed discernible secretory granules containing ANP and/or BNP in the cardiomyocytes. These results showed that part of the cardiomyocytes in embryonic stem cell-derived ectopic myocardial tissues are capable of producing natriuretic peptides, which suggests that they may be used as an endocrine source for cardiac hormones.

Scalable production of embryonic stem cell-derived cardiomyocytes

Cardiomyocyte transplantation could offer a new approach to replace scarred, nonfunctional myocardium in a diseased heart. Clinical application of this approach would require the ability to generate large numbers of donor cells. The purpose of this study was to develop a scalable, robust, and reproducible process to derive purified cardiomyocytes from genetically engineered embryonic stem (ES) cells. ES cells transfected with a fusion gene consisting of the alpha-cardiac myosin heavy chain (MHC) promoter driving the aminoglycoside phosphotransferase (neomycin resistance) gene were used for cardiomyocyte enrichment. The transfected cells were aggregated into embyroid bodies (EBs), inoculated into stirred suspension cultures, and differentiated for 9 days before selection of cardiomyocytes by the addition of G418 with or without retinoic acid (RA). Throughout the culture period, EB and viable cell numbers were measured. In addition, flow cytometric analysis was performed to monitor sarcomeric myosin (a marker for cardiomyocytes) and Oct-4 (a marker for undifferentiated ES cells) expression. Enrichment of cardiomyocytes was achieved in cultures treated with either G418 and retinoic acid (RA) or with G418 alone. Eighteen days after differentiation, G418-selected flasks treated with RA contained approximately twice as many cells as the nontreated flasks, as well as undetectable levels of Oct-4 expression, suggesting that RA may promote cardiac differentiation and/or survival. Immunohistological and electron microscopic analysis showed that the harvested cardiomyocytes displayed many features characteristic of native cardiomyocytes. Our results demonstrate the feasibility of large-scale production of viable, ES cell-derived cardiomyocytes for tissue engineering and/or implantation, an approach that should be transferable to other ES cell derived lineages, as well as to adult stem cells with in vitro cardiomyogenic activity.

Development of electrical activity in cardiac myocyte aggregates derived from mouse embryonic stem cells

Embryonic stem cells differentiate into cardiac myocytes, repeating in vitro the structural and molecular changes associated with cardiac development. Currently, it is not clear whether the electrophysiological properties of the multicellular cardiac structure follow cardiac maturation as well. In long-term recordings of extracellular field potentials with microelectrode arrays consisting of 60 substrate-integrated electrodes, we examined the electrophysiological properties during the ongoing differentiation process. The beating frequency of the growing preparations increased from 1 to 5 Hz concomitant to a decrease of the action potential duration and action potential rise time. A developmental increase of the conduction velocity could be attributed to an increased expression of connexin43 gap junction channels. Whereas isoprenalin elicited a positive chronotropic response from the first day of spontaneous beating onward, a concentration-dependent negative chronotropic effect of carbachol only developed after approximately 4 days. The in vitro development of the three-dimensional cardiac preparation thus closely follows the development described for the mouse embryonic heart, making it an ideal model to monitor the differentiation of electrical activity in embryonic cardiomyocytes.

Protein kinase C signaling transduces endorphin-primed cardiogenesis in GTR1 embryonic stem cells

The prodynorphin gene and its product, dynorphin B, have been found to promote cardiogenesis in embryonic cells by inducing the expression of GATA-4 and Nkx-2.5, two transcription factor-encoding genes essential for cardiogenesis. The molecular mechanism(s) underlying endorphin-induced cardiogenesis remain unknown. In the present study, we found that GTR1 embryonic stem (ES) cells expressed cell surface kappa opioid receptors, as well as protein kinase C (PKC)-alpha, -beta1, -beta2, -delta, -epsilon, and -zeta. Cardiac differentiation was associated with a marked increase in the Bmax value for a selective opioid receptor ligand and complex subcellular redistribution of selected PKC isozymes. PKC-alpha, -beta1, -beta2, -delta, and -epsilon all increased in the nucleus of ES-derived cardiac myocytes, compared with nuclei from undifferentiated cells. In both groups of cells, PKC-delta and -epsilon were mainly expressed at the nuclear level. The nuclear increase of PKC-alpha, -beta1, and -beta2 was due to a translocation from the cytosolic compartment. In contrast, the increase of both PKC-delta and PKC-epsilon in the nucleus of ES-derived cardiomyocytes occurred independently of enzyme translocation, suggesting changes in isozyme turnover and/or gene expression during cardiogenesis. No change in PKC-zeta expression was observed during cardiac differentiation. Opioid receptor antagonists prevented the nuclear increase of PKC-alpha, PKC-beta1, and PKC-beta2 and reduced cardiomyocyte yield but failed to affect the nuclear increase in PKC-delta and -epsilon. PKC inhibitors prevented the expression of cardiogenic genes and dynorphin B in ES cells and abolished their development into beating cardiomyocytes.

Chamber-specific differentiation of Nkx2.5-positive cardiac precursor cells from murine embryonic stem cells

Embryonic stem (ES) cells are a useful system to study cardiac differentiation in vitro. It has been difficult, however, to track the fates of chamber-specific cardiac lineages, since differentiation is induced within the embryoid body. We have established an in vitro culture system to track Nkx2.5(+) cell lineages during mouse ES cell differentiation by using green fluorescent protein (GFP) as a reporter. Nkx2.5/GFP(+) cardiomyocytes purified from embryoid bodies express sarcomeric tropomyosin and myosin heavy chain and heterogeneously express cardiac troponin I (cTnI), myosin light chain 2v (MLC2v) and atrial natriuretic peptide (ANP). After 4-week culture, GFP(+) cells exhibited electrophysiological characteristics specific to sinoatrial (SA) node, atrial, or ventricular type. Furthermore, we found that administration of 10(-7) M retinoic acid (RA) to embryoid bodies increased the percentage of MLC2v(-)ANP(+) cells; this also increased the expression of atrial-specific genes in the Nkx2.5/GFP(+) fraction, in a time- and dose-dependent fashion. These results suggest that Nkx2.5(+) lineage cells possess the potential to differentiate into various cardiomyocyte cell types and that RA can modify the differentiation potential of Nkx2.5(+) cardiomyocytes at an early stage.

Embryonic stem cells: new possible therapy for degenerative diseases that affect elderly people

The capacity of embryonic stem (ES) cells for virtually unlimited self renewal and differentiation has opened up the prospect of widespread applications in biomedical research and regenerative medicine. The use of these cells would overcome the problems of donor tissue shortage and implant rejection, if the cells are made immunocompatible with the recipient. Since the derivation in 1998 of human ES cell lines from preimplantation embryos, considerable research is centered on their biology, on how differentiation can be encouraged toward particular cell lineages, and also on the means to enrich and purify derivative cell types. In addition, ES cells may be used as an in vitro system not only to study cell differentiation but also to evaluate the effects of new drugs and the identification of genes as potential therapeutic targets. This review will summarize what is known about animal and human ES cells with particular emphasis on their application in four animal models of human diseases. Present studies of mouse ES cell transplantation reveal encouraging results but also technical barriers that have to be overcome before clinical trials can be considered.

Cardiovascular potential of embryonic stem cells

Initial events involved in the process of heart formation consist of myocardial differentiation as well as development of endothelial and endocardial tissues. As only limited means are allocated to the studying of cardiovascular system development, embryonic stem cells (ESCs) isolated from the inner cell mass (ICM) of developing mice or human blastocysts offer the first step toward the understanding of these complex and intriguing events. ESCs are able to differentiate into a wide range of cell types, including various vascular cells and cardiomyocytes, and their self-renewal capability renders them a unique, homogeneous, and unlimited preliminary population of cells for the investigation of early developmental events of cardiovascular system and lineage commitment. This review summarizes the accumulated knowledge of the cellular and molecular mechanisms involved in the development of the cardiovascular system.

Generation of confluent cardiomyocyte monolayers derived from embryonic stem cells in suspension: a cell source for new therapies and screening strategies

BACKGROUND

Cellular cardiomyoplasty is evolving as a new strategy to treat cardiac diseases. A prerequisite is a reliable source of pure cardiomyocytes, which could also help in the exploitation of recent advances in genomics and drug screening. Our goal was to establish a robust lab-scale process for the generation of embryonic stem (ES)-cell-derived cardiomyocytes in suspension.

METHODS

A 71 ES cell clone carrying a construct consisting of the alpha-cardiac myosin heavy chain (alphaMHC) promoter driving the neomycin resistance gene was used for antibiotic-driven cardiomyocyte enrichment. Rotating suspension culture was established to initiate embryoid body (EB) formation. To track growth and differentiation kinetics, cell count and flow cytometry for SSEA-I, E-cadherin (stem-cell marker)and sarcomeric myosin (cardiomyocytes marker) was performed. Oct4 expression was measured via real time (RT)-PCR.

RESULTS

Cultures comprising 2.5-8 x 10(6) differentiating FS cells/mL were obtained after 9 days in rotating suspension. Upon G418 addition,vigorous contracting spheres, termed cardiac bodies (CB), developed. These cultures consisted of about 2.1 x 10(5) enriched cardiomyocytes/mL after 6- 10 days of selection. Suspensions comprising 90- 95%viable single cells were generated using an improved dissociation method. Seeding of cardiomyocytes with 7 x 10(4) cell/cm(2) resulted in a homogeneous monolayer of synchronously contracting cells. Myocyte specific immunohistochemistry indicated purity of > 99%.

DISCUSSION

We have established a reliable lab-scale protocol to generate cultures of highly enriched cardiomyocytes in suspension. This will facilitate development of larger-scale processes for stem-cell based cardiomyocyte supply. An improved method is provided to derive vital suspensions of cardiomyocytes, which could be utilized for transplantation as well as for drug screening purposes.

Ventricular septal defect and cardiomyopathy in mice lacking the transcription factor CHF1/Hey2

Ventricular septal defects are common in human infants, but the genetic programs that control ventricular septation are poorly understood. Here we report that mice with a targeted disruption of the cardiovascular basic helix-loop-helix factor (CHF)1Hey2 gene show isolated ventricular septal defects. These defects result primarily in failure to thrive. Mice often succumbed within the first 3 wk after birth and showed pulmonary and liver congestion. The penetrance of this phenotype varied, depending on genetic background, suggesting the presence of modifier genes. Expression patterns of other cardiac-specific genes were not affected. Of the few animals on a mixed genetic background that survived to adulthood, most developed a cardiomyopathy but did not have ventricular septal defects. Our results indicate that CHF1 plays an important role in regulation of ventricular septation in mammalian heart development and is important for normal myocardial contractility. These mice provide a useful model for the study of the ontogeny and natural history of ventricular septal defects and cardiomyopathy.

Characterization and enrichment of cardiomyocytes derived from human embryonic stem cells

Cell replacement therapy is a promising approach for the treatment of cardiac diseases, but is challenged by a limited supply of appropriate cells. We have investigated whether functional cardiomyocytes can be efficiently generated from human embryonic stem (hES) cells. Cardiomyocyte differentiation was evaluated using 3 parent (H1, H7, and H9) hES cell lines and 2 clonal (H9.1 and H9.2) hES cell lines. All cell lines examined differentiated into cardiomyocytes, even after long-term culture (50 passages or approximately 260 population doublings). Upon differentiation, beating cells were observed after one week in differentiation conditions, increased in numbers with time, and could retain contractility for over 70 days. The beating cells expressed markers characteristic of cardiomyocytes, such as cardiac alpha-myosin heavy chain, cardiac troponin I and T, atrial natriuretic factor, and cardiac transcription factors GATA-4, Nkx2.5, and MEF-2. In addition, cardiomyocyte differentiation could be enhanced by treatment of cells with 5-aza-2'-deoxycytidine but not DMSO or retinoic acid. Furthermore, the differentiated cultures could be dissociated and enriched by Percoll density centrifugation to give a population containing 70% cardiomyocytes. The enriched population was proliferative and showed appropriate expression of cardiomyocyte markers. The extended replicative capacity of hES cells and the ability to differentiate and enrich for functional human cardiomyocytes warrant further development of these cells for clinical application in heart diseases.

In vitro differentiation of mouse embryonic stem cells after activation by retinoic acid

Embryonic stem (ES) cells are pluripotent cells isolated from the inner cell mass of blastocysts. ES cells are able to differentiate into the three primitive layers (endoderm, mesoderm, and ectoderm) of the organism, including the germline. In recent reports mouse ES cells have been successfully applied in the treatment of spinal cord injury, hereditary myelin disorder of the central nervous system, and diabetes mellitus. In this study, we investigated the induction of mouse ES cell differentiation, using culture of embryoid bodies (EBs) into the diverse tissues. EBs were formed by culturing ES cells (129/SV strain) in DMEM supplemented with 10% FBS, in the absence of feeder cells and leukemia inhibitory factor (LF). EBs were induced to differentiate by treatment with retinoic acid (RA). In control medium (non-RA medium) beating muscles, blood vessels, hemocytes, and cartilages were frequently observed in EBs. Moreover, when EBs were cultured in medium including RA (5 x 10(-8) M, and 5 x 10(-9) M), differentiation of the optic vesicle, lens, retina, and neural groove was observed. In this study we demonstrated that an efficient system for inducing the differentiation of ES cells using EBs.

Derivation of type II alveolar epithelial cells from murine embryonic stem cells

Embryonic stem (ES) cell pluripotency is being investigated increasingly to obtain specific cell lineages for tissue engineering. However, the possibility that ES cells can give rise to lung tissue has not been tested. We hypothesized that lung epithelial cells (type II pneumocytes) can be derived in vitro from murine ES cells. After withdrawal of leukemia inhibitory factor (LIF) and formation of embryoid bodies in maintenance medium for 10, 20, and 30 days, differentiating ES cells were kept in the same medium or transferred to serum-free small airway growth medium (SAGM) for a further 3 or 14 days of culture. The presence of type II pneumocytes in the resulting mixed cultures was demonstrated by reverse transcriptase-polymerase chain reaction (RT-PCR) of surfactant protein C (SPC) mRNA, immunostaining of SPC, and electron microscopy of osmiophilic lamellar bodies only at 30 days sampling time. SAGM appeared to be more favorable for type II cell formation than ES medium. No SPC transcripts were found in differentiating cells grown under the same conditions without formation of embryoid bodies. These findings could form the basis for the enrichment of ES cell-derived cultures with type II pneumocytes, and provide an in vitro system for investigating mechanisms of lung repair and regeneration.

Embryonic stem cells

The capacity of embryonic stem cells for virtually unlimited self-renewal and differentiation capacity has opened up the prospect of widespread applications in biomedical research and regenerative medicine. For the latter, the cells provide hope that it will be possible to overcome the problems of donor tissue shortage and also, by making the cells immunocompatible with the recipient, implant rejection. Four years after the first derivation of human pluripotent cell lines from pre-implantation embryos, a great deal has been learnt about their biology and how differentiation can be encouraged towards particular cell lineages. However, considerable research is needed, not least into means to enrich and purify derivative cell lineages, before clinical trials can be considered.

Overexpression of Polycomb-group gene rae28 in cardiomyocytes does not complement abnormal cardiac morphogenesis in mice lacking rae28 but causes dilated cardiomyopathy

The Polycomb-group genes (PcG) are widely conserved from Drosophila to mammals and are required for maintaining positional information during development. The rae28 gene (rae28) is a member of the mouse PcG. Mice deficient in rae28 (rae28(-/-)) demonstrated that rae28 has a role not only in anteroposterior patterning but also in cardiac morphogenesis. In this study we generated transgenic mice with ubiquitous or cardiomyocyte-specific exogenous rae28 expression. Genetic complementation experiments with these transgenic mice showed that ubiquitous expression of rae28 could reverse the cardiac anomalies in rae28(-/-), whereas cardiomyocyte-specific expression of rae28 could not, suggesting that rae28 is involved in cardiac morphogenesis through a noncardiomyocyte pathway. Interestingly, however, cardiomyocyte-specific overexpression of rae28 caused dilated cardiomyopathy, which was associated with cardiomyocyte apoptosis, abnormal myofibrils, and severe heart failure. Cardiac expression of rae28 was predominant in the early embryonic stage, whereas that of the other PcG members was relatively constitutive. Because rae28 forms multimeric complexes with other PcG proteins in the nucleus, it is presumed that constitutive cardiomyocyte-specific rae28 overexpression impaired authentic PcG functions in the heart. rae28-induced dilated cardiomyopathy may thus provide a clue for clarifying the direct role of PcG in the maintenance of cardiomyocytes.