Differences between human and mouse embryonic stem cells

Cellular response on Auger- and Beta-emitting nuclides: human embryonic stem cells (hESC) vs. keratinocytes

PURPOSE

We studied the response of human embryonic stem cells (hESC) to the β-emitter (131)I, which affects the entire cell and to the Auger electron emitter (125)I-deoxyuridine ((125)I-dU), primarily affecting the deoxyribonuleic acid (DNA). The effects were also studied in keratinocytes as a prototype for somatic cells.

METHODS

HESC (H1) and human keratinocytes (HaCaT, human) were exposed to (125)I-dU (5 × 10(-5) - 5 MBq/ml) and (131)I-iodide (5 × 10(-5) - 12.5 MBq/ml) and apoptosis was measured by DNA-fragmentation. Cell morphology was studied by light microscopy and electron microscopy. Transcriptional profiling was done on the Agilent oligonucleotide microarray platform.

RESULTS

Auger-process induced no apoptosis but a strong transcriptional response in hESC. In contrast, HaCaT cells showed a pronounced induction of apoptosis but only a moderate transcriptional response. Transcriptional response of hESC was similar after (125)I-dU and (131)I treatments, whereas HaCaT cells expressed a much more pronounced response to (125)I-dU than to (131)I. A striking radiation-induced down-regulation of pluripotency genes was observed in hESC whereas in keratinocytes the enriched gene annotations were related primarily to apoptosis, cell division and proliferation.

CONCLUSIONS

Human embryonic stem cells respond to ionizing radiation by (125)I-dU and (131)I in a different way compared to keratinocytes. Transcriptional response and gene expression appear to facilitate an escape from programmed cell death by striking a new path which probably leads to cell differentiation.

Stimulation of cultured h9 human embryonic stem cells with thyroid stimulating hormone does not lead to formation of thyroid-like cells

The sodium-iodine symporter (NIS) is expressed on the cell membrane of many thyroid cancer cells, and is responsible for the radioactive iodine accumulation. However, treatment of anaplastic thyroid cancer is ineffective due to the low expression of NIS on cell membranes of these tumor cells. Human embryonic stem cells (ESCs) provide a potential vehicle to study the mechanisms of NIS expression regulation during differentiation. Human ESCs were maintained on feeder-independent culture conditions. RT-qPCR and immunocytochemistry were used to study differentiation marker expression, ¹²⁵I uptake to study NIS function. We designed a two-step protocol for human ESC differentiation into thyroid-like cells, as was previously done for mouse embryonic stem cells. First, we obtained definitive endoderm from human ESCs. Second, we directed differentiation of definitive endoderm cells into thyroid-like cells using various factors, with thyroid stimulating hormone (TSH) as the main differentiating factor. Expression of pluripotency, endoderm and thyroid markers and ¹²⁵I uptake were monitored throughout the differentiation steps. These approaches did not result in efficient induction of thyroid-like cells. We conclude that differentiation of human ESCs into thyroid cells cannot be induced by TSH media supplementation alone and most likely involves complicated developmental patterns that are yet to be understood.

A molecular signature for purified definitive endoderm guides differentiation and isolation of endoderm from mouse and human embryonic stem cells

Embryonic definitive endoderm (DE) generates the epithelial compartment of vital organs such as liver, pancreas, and intestine. However, purification of DE in mammals has not been achieved, limiting the molecular "definition" of endoderm, and hindering our understanding of DE development and attempts to produce endoderm from sources such as embryonic stem (ES) cells. Here, we describe purification of mouse DE using fluorescence-activated cell sorting (FACS) and mice harboring a transgene encoding enhanced green fluorescent protein (eGFP) inserted into the Sox17 locus, which is expressed in the embryonic endoderm. Comparison of patterns of signaling pathway activation in native mouse DE and endoderm-like cells generated from ES cells produced novel culture modifications that generated Sox17-eGFP⁺ progeny whose gene expression resembled DE more closely than achieved with standard methods. These studies also produced new FACS methods for purifying DE from nontransgenic mice and mouse ES cell cultures. Parallel studies of a new human SOX17-eGFP ES cell line allowed analysis of endoderm differentiation in vitro, leading to culture modifications that enhanced expression of an endoderm-like signature. This work should accelerate our understanding of mechanisms regulating DE development in mice and humans, and guide further use of ES cells for tissue replacement.

What does it take to make a heart?

Ever increasing advances are being made in our quest to understand what it takes to direct pluripotent precursor cells to adopt a specific developmental fate. Eventually, the obvious goal is that targeted manipulation of these precursor cells will result in an efficient and reliable production of tissue-specific cells, which can be safely employed for therapeutic purposes. We have gained an incredible insight as to which molecular pathways are involved in governing neural, skeletal and cardiac muscle fate decisions. However, we still face the challenge of how to direct, for example, a cardiac fate in stem cells in the amounts needed to be employed for regenerative means. Equally importantly, we need to resolve critical questions such as: can the in vitro generated cardiomyocytes actually functionally replace damaged heart tissue? Here I will provide an overview of the molecules and signalling pathways that have first been demonstrated in embryological studies to function in cardiogenesis, and summarize how this knowledge is being applied to differentiate mouse and human embryonic stem cells into cardiomyocytes.

Contribution of intragenic DNA methylation in mouse gametic DNA methylomes to establish oocyte-specific heritable marks

Genome-wide dynamic changes in DNA methylation are indispensable for germline development and genomic imprinting in mammals. Here, we report single-base resolution DNA methylome and transcriptome maps of mouse germ cells, generated using whole-genome shotgun bisulfite sequencing and cDNA sequencing (mRNA-seq). Oocyte genomes showed a significant positive correlation between mRNA transcript levels and methylation of the transcribed region. Sperm genomes had nearly complete coverage of methylation, except in the CpG-rich regions, and showed a significant negative correlation between gene expression and promoter methylation. Thus, these methylome maps revealed that oocytes and sperms are widely different in the extent and distribution of DNA methylation. Furthermore, a comparison of oocyte and sperm methylomes identified more than 1,600 CpG islands differentially methylated in oocytes and sperm (germline differentially methylated regions, gDMRs), in addition to the known imprinting control regions (ICRs). About half of these differentially methylated DNA sequences appear to be at least partially resistant to the global DNA demethylation that occurs during preimplantation development. In the absence of Dnmt3L, neither methylation of most oocyte-methylated gDMRs nor intragenic methylation was observed. There was also genome-wide hypomethylation, and partial methylation at particular retrotransposons, while maintaining global gene expression, in oocytes. Along with the identification of the many Dnmt3L-dependent gDMRs at intragenic regions, the present results suggest that oocyte methylation can be divided into 2 types: Dnmt3L-dependent methylation, which is required for maternal methylation imprinting, and Dnmt3L-independent methylation, which might be essential for endogenous retroviral DNA silencing. The present data provide entirely new perspectives on the evaluation of epigenetic markers in germline cells.

In mammals, germ-cell–specific methylation patterns and genomic imprints are established throughout large-scale de novo DNA methylation in oogenesis and spermatogenesis. These steps are required for normal germline differentiation and embryonic development; however, current DNA methylation analyses only provide us a partial picture of germ cell methylome. To the best of our knowledge, this is the first study to generate comprehensive maps of DNA methylomes and transcriptomes at single base resolution for mouse germ cells. These methylome maps revealed genome-wide opposing DNA methylation patterns and differential correlation between methylation and gene expression levels in oocyte and sperm genomes. In addition, our results indicate the presence of 2 types of methylation patterns in the oocytes: (i) methylation across the transcribed regions, which might be required for the establishment of maternal methylation imprints and normal embryogenesis, and (ii) retroviral methylation, which might be essential for silencing of retrotransposons and normal oogenesis. We believe that an extension of this work would lead to a better understanding of the epigenetic reprogramming in germline cells and of the role for gene regulations.

Characterization and gene expression profiling of five human embryonic stem cell lines derived in Taiwan

Human embryonic stem cell (hESC) lines have been derived from the inner cell mass of blastocysts. Five hESC lines have been derived from 32 discarded blastocysts in Taiwan, and these lines have since been continuously cultured on mitotically inactivated mouse embryonic fibroblasts as feeder in the hESC medium for more than 44 passages and underwent freezing/thawing processes. All of five hESC lines expressed characteristic undifferentiated hESC markers such as SSEA-4, TRA-1-81, alkaline phosphatase, TERT, transcription factors POU5F1 (OCT4), and NANOG. The hESC lines T1 and T3 possess normal female karyotypes, whereas lines T4 and T5 are normal male, but line T2 is male trisomy 12 (47XY,+12). The hESC lines T1, T2, T3, and T5 were able to produce teratomas in SCID mice, and line T4 could only form embryoid bodies in vitro. Global gene expression profiles of single colonies of these five hESC lines were analyzed using Affymetrix human genome U133 plus 2.0 GeneChip. The results showed that 4,145 transcripts, including 19% of unknown functions, were detected in all five hESC lines. Comparison of the 4,145 genes commonly expressed in the five hESC lines with those genes expressed in teratoma produced by hESC line T1 and placenta revealed 40 genes exclusively expressed in all five hESC lines. These 40 genes include the previously reported stemness genes such as POU5F1 (OCT4), NANOG, TDGF1 (CRIPTO), SALL4, LECT1, and BUB1 responsible for self-renewal and pluripotent differentiation. The global gene expression analysis also indicated that the TGFβ/activin branch components inhibin BC, ACVR2A, ACVR1 (ALK2), TGFBR1 (ALK5), and SMAD2 were found to be highly expressed in undifferentiated states of these five hESC lines and decreased upon differentiation. The epigenetic states and expression of 32 known imprinted genes in these five hESC lines and/or differentiated derivatives were also investigated. In short, the hESC nature of these five hESC lines is supported by the undifferentiated state, extensive renewal capacity, and pluripotency, including the ability to form teratomas and/or embryoid bodies; and these cell lines will be useful for research on human embryonic stem cell biology and drug development/toxicity testing. The epigenetic states and expression of imprinted genes in hESC lines should be thoroughly studied after extended culture and upon differentiation in order to understand epigenetic stability in hESC lines before their clinical applications.

Reprogramming capacity of Nanog is functionally conserved in vertebrates and resides in a unique homeodomain

Pluripotency is a developmental ground state that can be recreated by direct reprogramming. Establishment of pluripotency is crucially dependent on the homeodomain-containing transcription factor Nanog. Compared with other pluripotency-associated genes, however, Nanog shows relatively low sequence conservation. Here, we investigated whether Nanog orthologs have the capacity to orchestrate establishment of pluripotency in Nanog(-/-) somatic cells. Mammalian, avian and teleost orthologs of Nanog enabled efficient reprogramming to full pluripotency, despite sharing as little as 13% sequence identity with mouse Nanog. Nanog orthologs supported self-renewal of pluripotent cells in the absence of leukemia inhibitory factor, and directly regulated mouse Nanog target genes. Related homeodomain transcription factors showed no reprogramming activity. Nanog is distinguished by the presence of two unique residues in the DNA recognition helix of its homeodomain, and mutations in these positions impaired reprogramming. On the basis of genome analysis and homeodomain identity, we propose that Nanog is a vertebrate innovation, which shared an ancestor with the Bsx gene family prior to the vertebrate radiation. However, cephalochordate Bsx did not have the capacity to replace mouse Nanog in reprogramming. Surprisingly, the Nanog homeodomain, a short sequence that contains the only recognizable conservation between Nanog orthologs, was sufficient to induce naive pluripotency in Nanog(-/-) somatic cells. This shows that control of the pluripotent state resides within a unique DNA-binding domain, which appeared at least 450 million years ago in a common ancestor of vertebrates. Our results support the hypothesis that naive pluripotency is a generic feature of vertebrate development.

Immunological applications of stem cells in type 1 diabetes

Current approaches aiming to cure type 1 diabetes (T1D) have made a negligible number of patients insulin-independent. In this review, we revisit the role of stem cell (SC)-based applications in curing T1D. The optimal therapeutic approach for T1D should ideally preserve the remaining β-cells, restore β-cell function, and protect the replaced insulin-producing cells from autoimmunity. SCs possess immunological and regenerative properties that could be harnessed to improve the treatment of T1D; indeed, SCs may reestablish peripheral tolerance toward β-cells through reshaping of the immune response and inhibition of autoreactive T-cell function. Furthermore, SC-derived insulin-producing cells are capable of engrafting and reversing hyperglycemia in mice. Bone marrow mesenchymal SCs display a hypoimmunogenic phenotype as well as a broad range of immunomodulatory capabilities, they have been shown to cure newly diabetic nonobese diabetic (NOD) mice, and they are currently undergoing evaluation in two clinical trials. Cord blood SCs have been shown to facilitate the generation of regulatory T cells, thereby reverting hyperglycemia in NOD mice. T1D patients treated with cord blood SCs also did not show any adverse reaction in the absence of major effects on glycometabolic control. Although hematopoietic SCs rarely revert hyperglycemia in NOD mice, they exhibit profound immunomodulatory properties in humans; newly hyperglycemic T1D patients have been successfully reverted to normoglycemia with autologous nonmyeloablative hematopoietic SC transplantation. Finally, embryonic SCs also offer exciting prospects because they are able to generate glucose-responsive insulin-producing cells. Easy enthusiasm should be mitigated mainly because of the potential oncogenicity of SCs.

Polycomb genes and cancer: time for clinical application?

Polycomb group genes (PcGs) are epigenetic effectors, essential for stem cell self-renewal and pluripotency. Two main Polycomb repressive complexes (PRC1, PRC2) mediate gene silencing through histone post-translational modifications. PcGs have been the focus of investigation in cancer research. Many cancer types show an over-expression of PcGs, predicting poor prognosis, metastasis and chemoresistance. Genetic polymorphisms of EZH2 (a PRC2 component) are significantly associated to lung cancer risk. Recently, 3-Deazaneplanocin A (DZNeP) was identified as an efficient inhibitor of PRC2 activity. DZNeP impairs cancer stem cell self-renewal and tumorigenicity. Despite the well-established role of PcGs in cancer stem cell biology, few studies dissected the clinical significance of these genes. In this paper, we explore PcGs as predictive and prognostic factors in oncology, with particular emphasis on what they can add to current biomarkers. We also propose a model for the rational development of DZNeP-based anticancer regimens and suggest the therapeutic applications of this drug.

p53, Stem Cells, and Reprogramming: Tumor Suppression beyond Guarding the Genome

p53 is well recognized as a potent tumor suppressor. In its classic role, p53 responds to genotoxic insults by inducing cell cycle exit or programmed cell death to limit the propagation of cells with corrupted genomes. p53 is also implicated in a variety of other cellular processes in which its involvement is less well understood including self-renewal, differentiation, and reprogramming. These activities represent an emerging area of intense interest for cancer biologists, as they provide potential mechanistic links between p53 loss and the stem cell-like cellular plasticity that has been suggested to contribute to tumor cell heterogeneity and to drive tumor progression. Despite accumulating evidence linking p53 loss to stem-like phenotypes in cancer, it is not yet understood how p53 contributes to acquisition of "stemness" at the molecular level. Whether and how stem-like cells confer survival advantages to propagate the tumor also remain to be resolved. Furthermore, although it seems reasonable that the combination of p53 deficiency and the stem-like state could contribute to the genesis of cancers that are refractory to treatment, direct linkages and mechanistic underpinnings remain under investigation. Here, we discuss recent findings supporting the connection between p53 loss and the emergence of tumor cells bearing functional and molecular similarities to stem cells. We address several potential molecular and cellular mechanisms that may contribute to this link, and we discuss implications of these findings for the way we think about cancer progression.

Identity, fate and potential of cells grown as neurospheres: species matters

It is commonly accepted that adult neurogenesis and gliogenesis follow the same principles through the mammalian class. However, it has been reported that neurogenesis might differ between species, even from the same order, like in rodents. Currently, it is not known if neural stem/progenitor cells (NSPCs) from various species differ in their cell identity and potential. NSPCs can be expanded ex vivo as neurospheres (NSph), a model widely used to study neurogenesis in vitro. Here we demonstrate that rat (r) and mouse (m) NSph display different cell identities, differentiation fate, electrophysiological function and tumorigenic potential. Adult rNSph consist mainly of oligodendroglial progenitors (OPCs), which after repeated passaging proliferate independent of mitogens, whereas adult mNSph show astroglial precursor-like characteristics and retain their mitogen dependency. Most of the cells in rNSph express OPC markers and spontaneously differentiate into oligodendrocytes after growth factor withdrawal. Electrophysiological analysis confirmed OPC characteristics. mNSph have different electrophysiological properties, they express astrocyte precursor markers and spontaneously differentiate primarily into astrocytes. Furthermore, rNSph have the potential to differentiate into oligodendrocytes and astrocytes, whereas mNSph are restricted to the astrocytic lineage. The phenotypic differences between rNSph and mNSph were not due to a distinct response to species specific derived growth factors and are probably not caused by autocrine mechanisms. Our findings suggest that NSph derived from adult rat and mouse brains display different cell identities. Thus, results urge for caution when data derived from NSph are extrapolated to other species or to the in vivo situation, especially when aimed towards the clinical use of human NSph.

Replication timing: a fingerprint for cell identity and pluripotency

Many types of epigenetic profiling have been used to classify stem cells, stages of cellular differentiation, and cancer subtypes. Existing methods focus on local chromatin features such as DNA methylation and histone modifications that require extensive analysis for genome-wide coverage. Replication timing has emerged as a highly stable cell type-specific epigenetic feature that is regulated at the megabase-level and is easily and comprehensively analyzed genome-wide. Here, we describe a cell classification method using 67 individual replication profiles from 34 mouse and human cell lines and stem cell-derived tissues, including new data for mesendoderm, definitive endoderm, mesoderm and smooth muscle. Using a Monte-Carlo approach for selecting features of replication profiles conserved in each cell type, we identify “replication timing fingerprints” unique to each cell type and apply a k nearest neighbor approach to predict known and unknown cell types. Our method correctly classifies 67/67 independent replication-timing profiles, including those derived from closely related intermediate stages. We also apply this method to derive fingerprints for pluripotency in human and mouse cells. Interestingly, the mouse pluripotency fingerprint overlaps almost completely with previously identified genomic segments that switch from early to late replication as pluripotency is lost. Thereafter, replication timing and transcription within these regions become difficult to reprogram back to pluripotency, suggesting these regions highlight an epigenetic barrier to reprogramming. In addition, the major histone cluster Hist1 consistently becomes later replicating in committed cell types, and several histone H1 genes in this cluster are downregulated during differentiation, suggesting a possible instrument for the chromatin compaction observed during differentiation. Finally, we demonstrate that unknown samples can be classified independently using site-specific PCR against fingerprint regions. In sum, replication fingerprints provide a comprehensive means for cell characterization and are a promising tool for identifying regions with cell type-specific organization.

While continued advances in stem cell and cancer biology have uncovered a growing list of clinical applications for stem cell technology, errors in indentifying cell lines have undermined a number of recent studies, highlighting a growing need for improvements in cell typing methods for both basic biological and clinical applications of stem cells. Induced pluripotent stem cells (iPSCs)—adult cells reprogrammed to a pluripotent state—show great promise for patient-specific stem cell treatments, but more efficient derivation of iPSCs depends on a more comprehensive understanding of pluripotency. Here, we describe a method to identify sets of regions that replicate at unique times in any given cell type (replication timing fingerprints) using pluripotent stem cells as an example, and show that genes in the pluripotency fingerprint belong to a class previously shown to be resistant to reprogramming in iPSCs, identifying potential new target genes for more efficient iPSC production. We propose that the order in which DNA is replicated (replication timing) provides a novel means for classifying cell types, and can reveal cell type specific features of genome organization.

Pluripotent stem cells for the study of CNS development

The mammalian central nervous system is a complex neuronal network consisting of a diverse array of cellular subtypes generated in a precise spatial and temporal pattern throughout development. Achieving a greater understanding of the molecular and genetic mechanisms that direct a relatively uniform population of neuroepithelial progenitors into diverse neuronal subtypes remains a significant challenge. The advent of pluripotent stem cell (PSC) technology allows researchers to generate diverse neural populations in vitro. Although the primary focus of PSC-derived neural cells has been their therapeutic potential, utilizing PSCs to study neurodevelopment is another frequently overlooked and equally important application. In this review, we explore the potential for utilizing PSCs to study neural development. We introduce the types of neurodevelopmental questions that PSCs can help to address, and we discuss the different strategies and technologies that researchers use to generate diverse subtypes of PSC-derived neurons. Additionally, we highlight the derivation of several thoroughly characterized neural subtypes; spinal motoneurons, midbrain dopaminergic neurons and cortical neurons. We hope that this review encourages researchers to develop innovative strategies for using PSCs for the study of mammalian, and specifically human, neurodevelopment.

Differential adhesion molecule expression during murine embryonic stem cell commitment to the hematopoietic and endothelial lineages

Mouse embryonic stem cells (ESC) make cell fate decisions based on intrinsic and extrinsic factors. The decision of ESC to differentiate to multiple lineages in vitro occurs during the formation of embryoid bodies (EB) and is influenced by cell-environment interactions. However, molecular mechanisms underlying cell-environmental modulation of ESC fate decisions are incompletely understood. Since adhesion molecules (AM) influence proliferation and differentiation in developing and adult tissues, we hypothesized that specific AM interactions influence ESC commitment toward hematopoietic and endothelial lineages. Expression of AM in the adherens, tight and gap junction pathways in ESC subpopulations were quantified. E-cadherin (E-cad), Claudin-4 (Cldn4), Connexin-43 (Cx43), Zona Occludens-1 (ZO-1) and Zona Occludens-2 (ZO-2) transcript levels were differentially expressed during early stages of hematopoietic/endothelial commitment. Stable ESC lines were generated with reduced expression of E-cad, Cldn4, Cx43, ZO-1 and ZO-2 using shRNA technology. Functional and phenotypic consequences of modulating AM expression were assessed using hematopoietic colony forming assays, endothelial sprouting assays and surface protein expression. A decrease in E-cad, Cldn4, Cx43 and ZO-1 expression was associated with less commitment to the hematopoietic lineage and increased endothelial differentiation as evidenced by functional and phenotypic analysis. A reduction in ZO-2 expression did not influence endothelial differentiation, but decreased hematopoietic commitment two-fold. These data indicate that a subset of AM influence ESC decisions to commit to endothelial and hematopoietic lineages. Furthermore, differentially expressed AM may provide novel markers to delineate early stages of ESC commitment to hematopoietic/endothelial lineages.

The changes of stemness biomarkers expression in human adipose-derived stem cells during long-term manipulation

One of the advantages of human adipose-derived stem cells (ASCs) in regenerative medicine is that they can be harvested in abundance. However, the stemness biomarkers, which marked the safety and efficacy of ASCs in accordance with the good manufacturing practice guidelines, is not yet well established. This study was designed to investigate the effect of long-term culture on the stemness properties of ASCs using quantitative real-time polymerase chain reaction and flow cytometry. Results showed the growth rate of ASCs was at its peak when they reached P10 (population doubling; PD = 26) but started to decrease when they were expanded to P15 (PD = 36) and P20 (PD = 46). The ASCs can be culture expanded with minimal alteration in the stemness genes and cluster of differentiation (CD) markers expression up to P10. Expression level of Sox2, Nestin, and Nanog3 was significantly decreased at later passage. CD31, CD45, CD117, and human leukocyte antigen DR, DQ, and DP were lowly expressed at P5 and P10 but their expressions increased significantly at P15 or P20. The differentiation ability of ASCs (adipogenesis, osteogenesis, and neurogenesis) also decreased in long-term culture. Our findings suggested that P10 (PD = 26) should be the "cutoff point" for clinical usage because ASCs at passage 15 onward showed significant changes in the stemness genes, CD markers expression, and differentiation capability.

FBF represses the Cip/Kip cell-cycle inhibitor CKI-2 to promote self-renewal of germline stem cells in C. elegans

Although the decision between stem cell self-renewal and differentiation has been linked to cell-cycle modifications, our understanding of cell-cycle regulation in stem cells is very limited. Here, we report that FBF/Pumilio, a conserved RNA-binding protein, promotes self-renewal of germline stem cells by repressing CKI-2(Cip/Kip), a Cyclin E/Cdk2 inhibitor. We have previously shown that repression of CYE-1 (Cyclin E) by another RNA-binding protein, GLD-1/Quaking, promotes germ cell differentiation. Together, these findings suggest that a post-transcriptional regulatory circuit involving FBF and GLD-1 controls the self-renewal versus differentiation decision in the germline by promoting high CYE-1/CDK-2 activity in stem cells, and inhibiting CYE-1/CDK-2 activity in differentiating cells.

Efficient differentiation of human embryonic and induced pluripotent stem cells into functional astrocytes

Human high-grade gliomas (hHGG) remain a therapeutic challenge in neuro-oncology despite current multimodality treatments. We recently demonstrated that murine embryonic stem cell (mESC)-derived astrocytes conditionally expressing proapoptotic genes can successfully be used to induce apoptosis and tumor shrinkage of hHGG tumor in vitro and in an in vivo mouse model. The first step in the translation of these results to the clinical settings, however, requires availability of human embryonic stem cells (hESC)- and/or induced pluripotent cell (hiPSC)-derived astrocytes engineered to express proapoptotic genes. The potential for directed differentiation of hESCs and hiPSCs to functional postmitotic astrocytes is not fully characterized. In this study, we show that once specified to neuro-epithelial lineage, hiPSC could be differentiated to astrocytes with a similar efficiency as hESC. However, our analyses of 2 hESC and 2 hiPSC cell lines showed some variability in differentiation potential into astrocytic lineages. Both the hESC- and hiPSC-derived astrocytes appeared to follow the functional properties of mESC-derived astrocytes, namely, migration and tropism for hHGG. This work provides evidence that hESC- and hiPSC-derived cells are able to generate functionally active astrocytes. These results demonstrate the feasibility of using iPSC-derived astrocytes, a new potential source for therapeutic use for brain tumors and other neurological diseases.

Generation of leukemia inhibitory factor and basic fibroblast growth factor-dependent induced pluripotent stem cells from canine adult somatic cells

For more than thirty years, the dog has been used as a model for human diseases. Despite efforts made to develop canine embryonic stem cells, success has been elusive. Here, we report the generation of canine induced pluripotent stem cells (ciPSCs) from canine adult fibroblasts, which we accomplished by introducing human OCT4, SOX2, c-MYC, and KLF4. The ciPSCs expressed critical pluripotency markers and showed evidence of silencing the viral vectors and normal karyotypes. Microsatellite analysis indicated that the ciPSCs showed the same profile as the donor fibroblasts but differed from cells taken from other dogs. Under culture conditions favoring differentiation, the ciPSCs could form cell derivatives from the ectoderm, mesoderm, and endoderm. Further, the ciPSCs required leukemia inhibitory factor and basic fibroblast growth factor to survive, proliferate, and maintain pluripotency. Our results demonstrate an efficient method for deriving canine pluripotent stem cells, providing a powerful platform for the development of new models for regenerative medicine, as well as for the study of the onset, progression, and treatment of human and canine genetic diseases.

Altered characteristics of cancer stem/initiating cells in a breast cancer cell line treated with persistent 5-FU chemotherapy

Drug resistance of cancer stem/initiating cells has been considered to be one of the main reasons for tumor relapse. However, knowledge concerning the changes in stem/ initiating cells during chemotherapy is limited. In the present study, the breast cancer cell line MDA-MB-468 was cultured with 5-fluorouracil and serially passaged. Six cell generations were collected. Semi-quantitative RT-PCR and flow cytometric techniques were used to evaluate the protein and mRNA expression of stem/initiating factors (CD44(+)/CD24(-), Oct 3/4, SOX2 and β-catenin), drug-resistance genes (BCRP and MRP1) and an anti-apoptosis gene (survivin). The clone formation rate was also examined in every generation of cells. The results showed that, under conditions of persistent chemotherapy, the factors representing the quantity of stem/initiating cells (β-catenin, Oct 3/4 and SOX2) followed a fluctuating trend of decrease-increase-further increase-decrease-increase-decrease, and factors representing the proportion of stem/initiating cells (proportion of CD44(+)/CD24(-) and the clone formation rate) demonstrated a fluctuating trend of increase-further increase-further increase-decrease. The drug-resistance genes (BCRP and MRP1) and the anti-apoptosis gene (survivin) demonstrated a wave of increase-further increase-further increase-decrease-increase (MRP1 decrease)-decrease. β-catenin, Oct 3/4 and SOX2 showed a positive correlation (r=1, p<0.01). Our study confirmed that the drug resistance of cancer cells is mainly due to tumor stem/initiating cells, and that under conditions of persistent chemotherapy, the quantity or function of breast cancer stem/initiating cells increases and decreases alternately.

Expression and interdependencies of pluripotency factors LIN28, OCT3/4, NANOG and SOX2 in human testicular germ cells and tumours of the testis

OCT3/4, NANOG, SOX2 and, most recently, LIN28 have been identified as key regulators of pluripotency in mammalian embryonic and induced stem cells, and are proven to be crucial for generation of the mouse germ-cell lineage. These factors are a hallmark of certain histological types of germ-cell tumours (GCTs). Here, we report novel information on the temporal and spatial expression pattern of LIN28 during normal human male germ-cell development as well as various types of GCTs. To investigate LIN28 expression, immunohistochemical analyses and quantitative proximity ligation assay-based TaqMan protein assays were applied on snap-frozen and formalin-fixed, paraffin-embedded samples as well as representative cell lines. LIN28 was found in primordial germ cells, gonocytes and pre-spermatogonia, in contrast to OCT3/4 and NANOG, which were found only in the first two stages. LIN28 was also found in all precursor lesions (carcinoma in situ and gonadoblastoma) of type II GCTs, as well as the invasive components seminoma and the non-seminomatous elements embryonal carcinoma and yolk sac tumour. Choriocarcinoma showed a heterogeneous pattern, while teratomas and spermatocytic seminomas (type III GCTs) were negative. This expression pattern suggests that LIN28 is associated with malignant behaviour of type II GCTs. Cell line experiments involving siRNA knockdown of LIN28, OCT3/4 and SOX2 showed that LIN28 plays a role in the maintenance of the undifferentiated state of both seminoma and embryonal carcinoma, closely linked to, and likely upstream of OCT3/4 and NANOG. In conclusion, LIN28 regulates the differentiation status of seminoma and embryonal carcinoma and is likely to play a related role in normal human germ-cell development.

The multiparametric effects of hydrodynamic environments on stem cell culture

Stem cells possess the unique capacity to differentiate into many clinically relevant somatic cell types, making them a promising cell source for tissue engineering applications and regenerative medicine therapies. However, in order for the therapeutic promise of stem cells to be fully realized, scalable approaches to efficiently direct differentiation must be developed. Traditionally, suspension culture systems are employed for the scale-up manufacturing of biologics via bioprocessing systems that heavily rely upon various types of bioreactors. However, in contrast to conventional bench-scale static cultures, large-scale suspension cultures impart complex hydrodynamic forces on cells and aggregates due to fluid mixing conditions. Stem cells are exquisitely sensitive to environmental perturbations, thus motivating the need for a more systematic understanding of the effects of hydrodynamic environments on stem cell expansion and differentiation. This article discusses the interdependent relationships between stem cell aggregation, metabolism, and phenotype in the context of hydrodynamic culture environments. Ultimately, an improved understanding of the multifactorial response of stem cells to mixed culture conditions will enable the design of bioreactors and bioprocessing systems for scalable directed differentiation approaches.

Functional ion channels in stem cells

Bioelectrical signals generated by ion channels play crucial roles in excitation genesis and impulse conduction in excitable cells as well as in cell proliferation, migration and apoptosis in proliferative cells. Recent studies have demonstrated that multiple ion channels are heterogeneously present in different stem cells; however, patterns and phenotypes of ion channels are species- and/or origin-dependent. This editorial review focuses on the recent findings related to the expression of functional ion channels and the roles of these channels in regulation of cell proliferation in stem cells. Additional effort is required in the future to clarify the ion channel expression in different types of stem cells; special attention should be paid to the relationship between ion channels and stem cell proliferation, migration and differentiation.

Paracrine and epigenetic control of trophectoderm differentiation from human embryonic stem cells: the role of bone morphogenic protein 4 and histone deacetylases

Our understanding of paracrine and epigenetic control of trophectoderm (TE) differentiation is limited by available models of preimplantation human development. Simple, defined media for selective TE differentiation of human embryonic stem cells (hESCs) were developed, enabling mechanistic studies of early placental development. Paracrine requirements of preimplantation human development were evaluated with hESCs by measuring lineage-specific transcription factor expression levels in single cells and morphological transformation in response to selected paracrine and epigenetic modulators. Bone morphogenic protein 4 (BMP4) addition to feeder-free pluripotent stem cells on matrigel frequently formed CDX2-positive TE. However, BMP4 or activin A inhibition alone also produced a mix of mesoderm and extraembryonic endoderm under these conditions. Further, BMP4 failed to form TE from adherent hESC maintained in standard feeder-dependent monolayers. Given that the efficiency and selectivity of BMP4-induced TE depended on medium components, we developed a basal medium containing insulin and heparin. In this medium, BMP4 induction of TE was dose dependent and with activin A inhibition by SB431542 (SB), approached 100% of cells. This paracrine stimulation of pluripotent cells transformed colony morphology from a cuboidal to squamous epithelium quantitatively on day 3, and produced significant multinucleated syncytiotrophoblasts by day 8. Addition of trichostatin A, a histone deacetylase (HDAC) inhibitor, reduced HDAC3, histone H3K9 methylation, and slowed differentiation in a dose-dependent manner. Modulators of BMP4- or HDAC-dependent signaling might adversely influence the timing and viability of early blastocyst developed in vitro. Since blastocyst development is synchronized to uterine receptivity, epigenetic regulators of TE differentiation might adversely affect implantation in vivo.

Delta40p53 controls the switch from pluripotency to differentiation by regulating IGF signaling in ESCs

Δ40p53 is a transactivation-deficient isoform of the tumor suppressor p53. We discovered that Δ40p53, in addition to being highly expressed in embryonic stem cells (ESCs), is the major p53 isoform during early stages of embryogenesis in the mouse. By altering the dose of Δ40p53 in ESCs, we identified a critical role for this isoform in maintaining the ESC state. Haploinsufficiency for Δ40p53 causes a loss of pluripotency in ESCs and acquisition of a somatic cell cycle, while increased dosage of Δ40p53 prolongs pluripotency and inhibits progression to a more differentiated state. Δ40p53 controls the switch from pluripotent ESCs to differentiated somatic cells by controlling the activity of full-length p53 at critical targets such as Nanog and the IGF-1 receptor (IGF-1R). The IGF axis plays a central role in the switch between pluripotency and differentiation in ESCs-and Δ40p53, by controlling the level of the IGF-1R, acts as a master regulator of this switch. We propose that this is the primary function of Δ40p53 in cells of the early embryo and stem cells, which are the only normal cells in which this isoform is expressed.

Pig epiblast stem cells depend on activin/nodal signaling for pluripotency and self-renewal

Activin/Nodal signaling is required for maintaining pluripotency and self-renewal of mouse epiblast stem cells and human embryonic stem cells (hESC). In this study, we investigated whether this signaling mechanism is also operative in cultured epiblasts derived from Days 10.5-12 pig embryos. Pig epiblast stem cell lines (pEpiSC) were established on mouse feeder layers and medium supplemented with basic fibroblast growth factor (bFGF). pEpiSC express the core pluripotency factors OCT4 (or POU5F1), NANOG, SOX2, and NODAL, but they do not express REX1 or alkaline phosphatase activity. Blocking leukemia inhibitory factor (LIF)/JAK/STAT3 pathway by adding the specific JAK I inhibitor 420099 and an anti-LIF antibody over 3 passages did not affect pluripotency of pEpiSC. In contrast, cells grown with the Alk-5 inhibitor SB431542, which blocks Activin/Nodal pathway, differentiated readily toward the neural lineage. pEpiSC are pluripotent, as established by their differentiation potential to ectoderm, mesoderm, and endoderm. These cells can be induced to differentiate toward trophectoderm and to germ cell precursors in response to bone morphogenetic protein 4 (BMP-4). In conclusion, our study demonstrates that pig epiblasts express the core pluripotency genes and that the capacity for maintaining self-renewal in pEpiSC depends on Activin/Nodal signaling. This study provides further evidence that maintenance of pluripotency via Activin/Nodal signal is conserved in mammals.

Transforming growth factor-beta superfamily in mouse embryonic stem cell self-renewal

Embryonic stem (ES) cells are pluripotent cells that maintain the capability of undifferentiated self-renewal in culture. As mouse ES cells have the capacity to give rise to all the tissues of the body, they are an excellent developmental biology model system and a model for regenerative therapies. The extracellular cues and the intracellular signaling cascades that regulate ES cell self-renewal and cell-fate choices are complex and actively studied. Many developmental signaling pathways regulate the ES cell phenotype, and their intracellular programs interact to modulate the gene networks controlling ES cell pluripotency. This review focuses on the current understanding and outstanding questions of the roles of the transforming growth factor-beta-related signaling pathways in regulating pluripotency and differentiation of mouse ES cells. The complex dichotomic roles of bone morphogenetic protein signaling in maintaining the undifferentiated state and also inducing specific cell fates will be reviewed. The emerging roles of Nodal signaling in ES cell self-renewal will also be discussed.

Markers of stemness in equine mesenchymal stem cells: a plea for uniformity

Mesenchymal stromal cells (MSC) are a very promising subpopulation of adult stem cells for cell-based regenerative therapies in veterinary medicine. Despite major progress in the knowledge on adult stem cells during recent years, a proper identification of MSC remains a challenge. In human medicine, the Mesenchymal and Tissue Stem Cell Committee of the International Society for Cellular Therapy (ISCT) recently proposed three criteria to define MSC. Firstly, cells must be plastic-adherent when maintained under standard culture conditions. Secondly, MSC must express CD73, CD90 and CD105, and lack expression of CD34, CD45, CD14 or CD11b, CD79α or CD19 and MHC class II antigens. Thirdly, MSC must be able to differentiate into osteoblasts, adipocytes and chondroblasts in vitro. Successful isolation and differentiation of equine MSC from different sources such as bone marrow, fat tissue, umbilical cord blood, Wharton's Jelly or peripheral blood has been widely reported. However, their unequivocal immunophenotyping is hampered by the lack of a single specific marker and the limited availability of monoclonal anti-horse antibodies, which are two major factors complicating successful research on equine MSC. Detection of gene expression on mRNA level is hereby a valuable alternative, although the need still exists to test several antibody clones in search for cross-reactivity. To date, commercial antibodies recognizing equine epitopes are only available for CD13, CD44 and MHC-II. Moreover, as the expression of certain adult stem cell markers may differ between species, it is mandatory to define a set of CD markers which can be uniformly applied for the identification of equine MSC.

Gene targeting and Calcium handling efficiencies in mouse embryonic stem cell lines

AIM

To compare gene targeting efficiencies, expression profiles, and Ca(2+) handling potentials in two widely used mouse embryonic stem cell lines.

METHODS

The two widely used mouse embryonic stem cell lines, R1 and HM-1, were cultured and maintained on Mitomycin C treated mouse embryonic fibroblast feeder cell layers, following standard culture procedures. Cells were incubated with primary and secondary antibodies before fluorescence activated cell sorting analysis to compare known pluripotency markers. Moreover, cells were harvested by trypsinization and transfected with a kinase-inactive murine Tyk2 targeting construct, following the BioRad and Amaxa transfection procedures. Subsequently, the cells were cultured and neomycin-resistant cells were picked after 13 d of selection. Surviving clones were screened twice by polymerase chain reaction (PCR) and finally confirmed by Southern blot analysis before comparison. Global gene expression profiles of more than 20 400 probes were also compared and significantly regulated genes were confirmed by real time PCR analysis. Calcium handling potentials of these cell lines were also compared using various agonists.

RESULTS

We found significant differences in transfection efficiencies of the two cell lines (91% ± 6.1% vs 75% ± 4.2%, P = 0.01). Differences in the targeting efficiencies were also significant whether the Amaxa or BioRad platforms were used for comparison. We did not observe significant differences in the levels of many known pluripotency markers. However, our genome-wide expression analysis using more than 20 400 spotted cDNA arrays identified 55 differentially regulated transcripts (P < 0.05) implicated in various important biological processes, including binding molecular functions (particularly Ca(2+) binding roles). Subsequently, we measured Ca(2+) signals in these cell lines in response to various calcium agonists, both in high and low Ca(2+) solutions, and found significant differences (P < 0.05) in the regulation of Ca(2+) homeostasis between the investigated cell lines. Then we further compared the detection and expression of various membrane and intracellular Ca(2+) receptors and similarly found significant (P < 0.05) variations in a number of calcium receptors between these cell lines.

CONCLUSION

Results of this study emphasize the importance of considering intrinsic cellular variations, during selection of cell lines for experiments and interpretations of experimental results.

De novo myocardial regeneration: advances and pitfalls

The capability of adult tissue-derived stem cells for cardiogenesis has been extensively studied in experimental animals and clinical studies for treatment of postischemic cardiomyopathy. The less-than-anticipated improvement in the heart function in most clinical studies with skeletal myoblasts and bone marrow cells has warranted a search for alternative sources of stem cells. Despite their multilineage differentiation potential, ethical issues, teratogenicity, and tissue rejection are main obstacles in developing clinically feasible methods for embryonic stem cell transplantation into patients. A decade-long research on embryonic stem cells has paved the way for discovery of alternative approaches for generating pluripotent stem cells. Genetic manipulation of somatic cells for pluripotency genes reprograms the cells to pluripotent status. Efforts are currently focused to make reprogramming protocols safer for clinical applications of the reprogrammed cells. We summarize the advancements and complicating features of stem cell therapy and discuss the decade-and-a-half-long efforts made by stem cell researchers for moving the field from bench to the bedside as an adjunct therapy or as an alternative to the contemporary therapeutic modalities for routine clinical application. The review also provides a special focus on the advancements made in the field of somatic cell reprogramming.

Regulation of stem cell pluripotency and differentiation by G protein coupled receptors

Stem cell-based therapeutics have the potential to effectively treat many terminal and debilitating human diseases, but the mechanisms by which their growth and differentiation are regulated are incompletely defined. Recent data from multiple systems suggest major roles for G protein coupled receptor (GPCR) pathways in regulating stem cell function in vivo and in vitro. The goal of this review is to illustrate common ground between the growing field of stem cell therapeutics and the long-established field of G protein coupled receptor signaling. Herein, we briefly introduce basic stem cell biology and discuss how several conserved pathways regulate pluripotency and differentiation in mouse and human stem cells. We further discuss general mechanisms by which GPCR signaling may impact these pluripotency and differentiation pathways, and summarize specific examples of receptors from each of the major GPCR subfamilies that have been shown to regulate stem cell function. Finally, we discuss possible therapeutic implications of GPCR regulation of stem cell function.

Derivation and characterization of novel nonhuman primate embryonic stem cell lines from in vitro-fertilized baboon preimplantation embryos

The development of nonhuman primate (NHP) embryonic stem cell (ESC) models holds great promise for cell-mediated treatment of debilitating diseases and to address numerous unanswered questions regarding the therapeutic efficacy of ESCs while supplanting ethical considerations involved with human studies. Here we report successful establishment and characterization of 3 novel baboon (Papio cynocephalus) ESC lines from the inner cell mass of intracytoplasmic sperm injection-derived blastocysts. Embryos were cultured in an improved baboon embryo in vitro culture protocol. The inner cell mass of blastocyst was laser-dissected and plated on mouse embryonic fibroblast feeder cell monolayer in the NHP ESC culture medium. Three cell lines with characteristic ESC morphology have been cultured through an extended period (>14 months), with 2 male cell lines (UT-1 and -2) and 1 female cell line (UT-3) displaying normal baboon karyotypes. Reverse transcription-polymerase chain reaction analysis confirmed that all 3 lines express primate ESC pluripotency markers, including OCT-4, NANOG, SOX-2, TERT, TDGF, LEFTYA, and REX-1. All 3 lines demonstrated positive immunocytochemical staining for OCT-4, stage-specific embryonic antigen-3, stage-specific embryonic antigen-4, TRA-1-60, and TRA-1-81. Baboon ESCs injected into NOD/SCID mice formed teratomas with all 3 germ layers. In addition, embryoid body-like spherical structures were derived and initial outgrowth was observed when embedded into extracellular matrix Matrigel. The ESC lines established in this NHP model have the potential to extend our knowledge in the fields of developmental biology, regenerative medicine, and future applications, including preclinical safety assessment of in vivo stem cell therapy.

Novel peptide ligands that bind specifically to mouse embryonic stem cells

The search for new ES cell markers is critical not only for identification, isolation and visualization of embryonic stem (ES) cells, but also for potential clinical treatment as a targeting agent. Here, by using phage display technology, 12-mer peptide ligands that bind specifically to mouse ES cells were isolated. After four rounds of negative-positive selection, nine sequences in 20 random samples from the chosen clones were selected. Enzyme-linked immunosorbent assay results suggested the Seq2 peptide (KHMHWHPPALNT) had high affinity and specificity to the mouse ES cells. The binding capability of the Seq2 phage could be matched with that of a chemically synthesized peptide with a sequence identical to that displayed by the phage, indicating that this ability was due to the peptide sequence itself. Immunofluorescence analysis confirmed that Seq2 phage selectively bound to the mouse ES cells but not to the differentiated mouse ES cells. Western blot analysis proved the Seq2 phage was bound to two mouse ES membrane proteins which were about 18/20KD, suggesting that the selected peptide targeted to a unique receptor expressed on the mouse ES cells with specificity. Peptides obtained from the study may provide a way to label, identify, and characterize ES cells.

Functional genomics of 5- to 8-cell stage human embryos by blastomere single-cell cDNA analysis

Blastomere fate and embryonic genome activation (EGA) during human embryonic development are unsolved areas of high scientific and clinical interest. Forty-nine blastomeres from 5- to 8-cell human embryos have been investigated following an efficient single-cell cDNA amplification protocol to provide a template for high-density microarray analysis. The previously described markers, characteristic of Inner Cell Mass (ICM) (n = 120), stemness (n = 190) and Trophectoderm (TE) (n = 45), were analyzed, and a housekeeping pattern of 46 genes was established. All the human blastomeres from the 5- to 8-cell stage embryo displayed a common gene expression pattern corresponding to ICM markers (e.g., DDX3, FOXD3, LEFTY1, MYC, NANOG, POU5F1), stemness (e.g., POU5F1, DNMT3B, GABRB3, SOX2, ZFP42, TERT), and TE markers (e.g., GATA6, EOMES, CDX2, LHCGR). The EGA profile was also investigated between the 5-6- and 8-cell stage embryos, and compared to the blastocyst stage. Known genes (n = 92) such as depleted maternal transcripts (e.g., CCNA1, CCNB1, DPPA2) and embryo-specific activation (e.g., POU5F1, CDH1, DPPA4), as well as novel genes, were confirmed. In summary, the global single-cell cDNA amplification microarray analysis of the 5- to 8-cell stage human embryos reveals that blastomere fate is not committed to ICM or TE. Finally, new EGA features in human embryogenesis are presented.

Propagation of undifferentiated human embryonic stem cells with nano-liposomal ceramide

Human embryonic stem (hES) cells, located on the periphery of the colonies, express the neuroectodermal markers nestin and Tuj1, suggesting a prematurely differentiated subgroup of cells. Here, we report that ceramide, a bioactive sphingolipid, selectively eliminates hES cells differentially expressing nestin and Tuj1. In contrast, undifferentiated cells are resistant to the apoptotic effects of ceramide. Ceramide-resistant hES cells express higher levels of the messenger RNA for ceramide-metabolizing enzymes that convert ceramide into pro-mitogenic metabolites. Based on these findings, we conducted long-term studies to determine whether liposomal ceramide can be used to maintain undifferentiated hES cells free of feeder cells. We continuously cultured hES cells on matrigel for 4 months with liposomal ceramide in a feeder cell-free system. Human ES cells treated with liposomal ceramide maintained their pluripotent state as determined by in vivo and in vitro differentiation studies and contained no chromosomal abnormalities. In conclusion, our findings suggest that exposure to ceramide provides a viable strategy to prevent premature hES cell differentiation and to maintain pluripotent stem cell populations in the absence of feeder cells.

Derivation and characterization of embryonic stem-like cells of Indian major carp Catla catla

Embryonic stem (ES)-like cells were derived from mid-blastula stage embryos of a freshwater fish, catla Catla catla, under feeder-free condition and designated as CCES cells. The conditioned media was optimized with 10% foetal bovine serum (FBS), fish embryo extract (FEE) having 100 µg ml(-1) protein concentration, 15 ng ml(-1) basic fibroblast growth factor (bFGF) and basic media containing Leibovitz-15, DMEM with 4·5 g l(-1) glucose and Ham's F12 (LDF) in 2:1:1 ratio using a primary culture of CCES cells. Cells attached to gelatin-coated plates after 24 h of seeding and ES-like colonies were obtained at day 5 onwards. A stable cell culture was obtained after passage 10 and further maintained up to passage 44. These cells were characterized by their typical morphology, high alkaline phosphatase activity, positive expression of cell-surface antigen SSEA-1, transcription factor Oct4, germ cell marker vasa and consistent karyotype up to extended periods. The undifferentiated state was confirmed by their ability to form embryoid bodies and their differentiation potential.

Nodal/Activin signaling predicts human pluripotent stem cell lines prone to differentiate toward the hematopoietic lineage

Lineage-specific differentiation potential varies among different human pluripotent stem cell (hPSC) lines, becoming therefore highly desirable to prospectively know which hPSC lines exhibit the highest differentiation potential for a certain lineage. We have compared the hematopoietic potential of 14 human embryonic stem cell (hESC)/induced pluripotent stem cell (iPSC) lines. The emergence of hemogenic progenitors, primitive and mature blood cells, and colony-forming unit (CFU) potential was analyzed at different time points. Significant differences in the propensity to differentiate toward blood were observed among hPSCs: some hPSCs exhibited good blood differentiation potential, whereas others barely displayed blood-differentiation capacity. Correlation studies revealed that the CFU potential robustly correlates with hemogenic progenitors and primitive but not mature blood cells. Developmental progression of mesoendodermal and hematopoietic transcription factors expression revealed no correlation with either hematopoietic initiation or maturation efficiency. Microarray studies showed distinct gene expression profile between hPSCs with good versus poor hematopoietic potential. Although neuroectoderm-associated genes were downregulated in hPSCs prone to hematopoietic differentiation many members of the Nodal/Activin signaling were upregulated, suggesting that this signaling predicts those hPSC lines with good blood-differentiation potential. The association between Nodal/Activin signaling and the hematopoietic differentiation potential was confirmed using loss- and gain-of-function functional assays. Our data reinforce the value of prospective comparative studies aimed at determining the lineage-specific differentiation potential among different hPSCs and indicate that Nodal/Activin signaling seems to predict those hPSC lines prone to hematopoietic specification.

Keeping an eye on retinoblastoma control of human embryonic stem cells

Human embryonic stem cells (hESCs) hold great promise in regenerative medicine. However, before the full potential of these cells is achieved, major basic biological questions need to be addressed. In particular, there are still gaps in our knowledge of the molecular mechanisms underlying the derivation of hESCs from blastocysts, the regulation of the undifferentiated, pluripotent state, and the control of differentiation into specific lineages. Furthermore, we still do not fully understand the tumorigenic potential of hESCs, limiting their use in regenerative medicine. The RB pathway is a key signaling module that controls cellular proliferation, cell survival, chromatin structure, and cellular differentiation in mammalian cells. Members of the RB pathway are important regulators of hESC biology and manipulation of the activity of this pathway may provide novel means to control the fate of hESCs. Here we review what is known about the expression and function of members of the RB pathway in hESCs and discuss areas of interest in this field.