Significant variations in differentiation properties between independent mouse ES cell lines cultured under defined conditions

Targeted Mutations in the Mouse via Embryonic Stem Cells

Genetic modification of mouse embryonic stem (ES) cells is a powerful technology that enabled the generation of a plethora of mutant mouse lines to study gene function and mammalian biology. Here we describe ES cell culture and transfection techniques used to manipulate the ES cell genome to obtain targeted ES cell clones. We include the standard gene targeting approach as well as the application of the CRISPR/Cas9 system that can improve the efficiency of homologous recombination in ES cells by introducing a double-strand DNA break at the target site.

Considerations and Implications in the Purification of Extracellular Vesicles - A Cautionary Tale

Extracellular vesicles (EVs) are nano-sized particles constitutively released from cells into all biological fluids. Interestingly, these vesicles contain genetic cargoes including proteins, RNA and bioactive lipids that can be functionally delivered and affect recipient cells. As a result, there is growing interest in studying EVs in pathological conditions, including central nervous system (CNS)-related diseases, as EVs may be used for diagnostic purposes or as therapeutic agents. However, one major bottleneck is the need for better EV purification strategies when considering complex biological sources such as serum/protein-rich media or plasma. In this study, we have performed a systematic comparison study between the current gold-standard method: ultracentrifugation, to an alternative: size-exclusion chromatography (LC), using induced pluripotent stem cell (iPSC) derived complex media as a model system. We demonstrate that LC allows for derivation of purer EVs from iPSCs, which was previously impossible with the original UC method. Importantly, our study further highlights the various drawbacks when using the conventional UC approach that lead to misinterpretation of EV data. Lastly, we describe novel data on our iPSC-EVs; how they could relate to stem cell biology and discuss their potential use as EV therapeutics for CNS diseases.

An improved Red/ET recombineering system and mouse ES cells culture conditions for the generation of targeted mutant mice

Targeted mutant mice generated on a C57BL/6 background are powerful tools for analysis of the biological functions of genes, and gene targeting technologies using mouse embryonic stem (ES) cells have been used to generate such mice. Recently, a bacterial artificial chromosome (BAC) recombineering system was established for the construction of targeting vectors. However, gene retrieval from BACs for the generation of gene targeting vectors using this system remains difficult. Even when construction of a gene targeting vector is successful, the efficiency of production of targeted mutant mice from ES cells derived from C57BL/6 mice are poor. Therefore, in this study, we first improved the strategy for the retrieval of genes from BACs and their transfer into a DT-A plasmid, for the generation of gene targeting vectors using the BAC recombineering system. Then, we attempted to generate targeted mutant mice from ES cell lines derived from C57BL/6 mice, by culturing in serum-free medium. In conclusion, we established an improved strategy for the efficient generation of targeted mutant mice on a C57BL/6 background, which are useful for the in vivo analysis of gene functions and regulation.

A Newly Defined and Xeno-Free Culture Medium Supports Every-Other-Day Medium Replacement in the Generation and Long-Term Cultivation of Human Pluripotent Stem Cells

Human pluripotent stem cells (hPSCs) present an unprecedented opportunity to advance human health by offering an alternative and renewable cell resource for cellular therapeutics and regenerative medicine. The present demand for high quality hPSCs for use in both research and clinical studies underscores the need to develop technologies that will simplify the cultivation process and control variability. Here we describe the development of a robust, defined and xeno-free hPSC medium that supports reliable propagation of hPSCs and generation of human induced pluripotent stem cells (hiPSCs) from multiple somatic cell types; long-term serial subculturing of hPSCs with every-other-day (EOD) medium replacement; and banking fully characterized hPSCs. The hPSCs cultured in this medium for over 40 passages are genetically stable, retain high expression levels of the pluripotency markers TRA-1-60, TRA-1-81, Oct-3/4 and SSEA-4, and readily differentiate into ectoderm, mesoderm and endoderm. Importantly, the medium plays an integral role in establishing a cGMP-compliant process for the manufacturing of hiPSCs that can be used for generation of clinically relevant cell types for cell replacement therapy applications.

Regeneration of Leydig cells in ectopically autografted adult mouse testes

Ectopic autografting of testis tissue is a promising approach for studying testicular development, male germline preservation and restoration of male fertility. In this study, we examined the fate of various testicular cells in adult mouse testes following ectopic autografting at 1, 2, 4 and 8 weeks post grafting. Histological examination showed no evidence of re-establishment of spermatogenesis in autografts, and progressive degeneration of seminiferous tubules was detected. Expression of germ cell-specific proteins such as POU5F1, DAZL, TNP1, TNP2, PRM1 and PRM2 revealed that, although proliferating and differentiating spermatogenic germ cells such as spermatogonia, spermatocytes and spermatids could survive in autografts until 4 weeks, only terminally differentiated germ cells such as sperm persisted in autografts until 8 weeks. The presence of Sertoli and peritubular myoid cells, as indicated by expression of WT1 and ACTA2 proteins, respectively, was evident in the autografts until 8 weeks. Interestingly, seminal vesicle weight and serum testosterone level were restored in autografted mice by 8 weeks post grafting. The expression of Leydig cell-specific proteins such as CYP11A1, HSD3B2 and LHCGR showed revival of Leydig cell (LC) populations in autografts over time since grafting. Elevated expression of PDGFRA, LIF, DHH and NEFH in autografts indicated de novo regeneration of LC populations. Autografted adult testis can be used as a model for investigating Leydig cell regeneration, steroidogenesis and regulation of the intrinsic factors involved in Leydig cell development. The success of this rodent model can have therapeutic applications for adult human males undergoing sterilizing cancer therapy.

DNA methylation is dispensable for suppression of the agouti viable yellow controlling element in murine embryonic stem cells

The agouti viable (A^vy) locus is considered a model to understand how retroelements function as controlling elements in mammals. Epigenetic factors, principally CpG methylation, are widely held to play a dominant regulatory role in controlling the locus' activity. The purpose of this study was to examine its behavior in ES cells and determine if this locus could be exploited for use in screen-based investigations. We have derived multiple A^vy ES cell lines from the C57BL/6 strain and generated a cell line carrying a GFP-reporter gene (A^vy/A^GFP). Use of the DNA demethylating drug 5-azacitidine on various ES cell lines does not induce either agouti or GFP expression. Methylation analysis reveals that although most lines display normal methylation at IAP elements in general, the A^vy IAP element is essentially unmethylated. In addition, we find that different repeat compartments are epigenetically unstable in a number of derived cell lines.

Embryonic stem cell-derived CD166+ precursors develop into fully functional sinoatrial-like cells

RATIONALE

A cell-based biological pacemaker is based on the differentiation of stem cells and the selection of a population displaying the molecular and functional properties of native sinoatrial node (SAN) cardiomyocytes. So far, such selection has been hampered by the lack of proper markers. CD166 is specifically but transiently expressed in the mouse heart tube and sinus venosus, the prospective SAN.

OBJECTIVE

We have explored the possibility of using CD166 expression for isolating SAN progenitors from differentiating embryonic stem cells.

METHODS AND RESULTS

We found that in embryonic day 10.5 mouse hearts, CD166 and HCN4, markers of the pacemaker tissue, are coexpressed. Sorting embryonic stem cells for CD166 expression at differentiation day 8 selects a population of pacemaker precursors. CD166+ cells express high levels of genes involved in SAN development (Tbx18, Tbx3, Isl-1, Shox2) and function (Cx30.2, HCN4, HCN1, CaV1.3) and low levels of ventricular genes (Cx43, Kv4.2, HCN2, Nkx2.5). In culture, CD166+ cells form an autorhythmic syncytium composed of cells morphologically similar to and with the electrophysiological properties of murine SAN myocytes. Isoproterenol increases (+57%) and acetylcholine decreases (-23%) the beating rate of CD166-selected cells, which express the β-adrenergic and muscarinic receptors. In cocultures, CD166-selected cells are able to pace neonatal ventricular myocytes at a rate faster than their own. Furthermore, CD166+ cells have lost pluripotency genes and do not form teratomas in vivo.

CONCLUSIONS

We demonstrated for the first time the isolation of a nonteratogenic population of cardiac precursors able to mature and form a fully functional SAN-like tissue.

Pluripotent stem cells and gene therapy

Human pluripotent stem cells represent an accessible cell source for novel cell-based clinical research and therapies. With the realization of induced pluripotent stem cells (iPSCs), it is possible to produce almost any desired cell type from any patient's cells. Current developments in gene modification methods have opened the possibility for creating genetically corrected human iPSCs for certain genetic diseases that could be used later in autologous transplantation. Promising preclinical studies have demonstrated correction of disease-causing mutations in a number of hematological, neuronal, and muscular disorders. This review aims to summarize these recent advances with a focus on iPSC generation techniques, as well as gene modification methods. We will then further discuss some of the main obstacles remaining to be overcome before successful application of human pluripotent stem cell-based therapy arrives in the clinic and what the future of stem cell research may look like.

Induced pluripotent stem cells: past, present, and future

The development of iPSCs reflected the merging of three major scientific streams and has in turn led to additional new branches of investigation. However, there is still debate about whether iPSCs are functionally equivalent to ESCs. This question should be answered only by science, not by politics or business.

Differences in chimera formation and germline transmission between E14 and C2J embryonic stem cells in mice

Summary The goal of this project was to determine whether the originating strain of mouse embryonic stem (ES) cells affects the maintenance of their pluripotency under uniform culture conditions. ES cells from two strains of mice, E14 and C2J, were tested. Both ES cell lines were cultured in KOSR + 2i medium and then injected into C57BL/6J blastocysts. Our results demonstrate that this medium could support both E14 and C2J ES cells to keep their pluripotency, though E14 ES cells were found to have a higher chimeric rate than C2J ES cells. However, analysis by backcrossing revealed that C2J and E14 ES cells have the same ability for germline transmission. Our results demonstrate that ES cells derived from E14 and C2J cells have the same capacity for germline transmission when injected into C57BL/6J blastocysts; however, due to the limitation of mixed genetic background between E14 cells and host C57BL/6J embryos, C2J ES cells are preferable to E14 ES cells for use in gene-targeting and should become the cell line of choice for the generation of genetically engineered mutant mouse lines.

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.

WNTing embryonic stem cells

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

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.

Efficient generation of germ line transmitting chimeras from C57BL/6N ES cells by aggregation with outbred host embryos

Genetically modified mouse strains derived from embryonic stem (ES) cells have become essential tools for functional genomics and biomedical research. Large scale mutagenesis projects are producing libraries of mutant C57BL/6 (B6) ES cells to enable the functional annotation of every gene of the mouse genome. To realize the utility of these resources, efficient and accessible methods of generating mutant mice from these ES cells are necessary. Here, we describe a combination of ICR morula aggregation and a chemically-defined culture medium with widely available and accessible components for the high efficiency generation of germline transmitting chimeras from C57BL/6N ES cells. Together these methods will ease the access of the broader biomedical research community to the publicly available B6 ES cell resources.

Human cystic fibrosis embryonic stem cell lines derived on placental mesenchymal stromal cells

This study describes the production of two new human embryonic stem cell (hESC) lines affected by cystic fibrosis. These cell lines are heterozygous compounds, each a carrier of the DF508 mutations associated either with E585X or with 3849+10 kb C-->T. The derivation process was performed on irradiated human placental mesenchymal stromal cells and designed to minimize contact with xeno-components. This new source of feeder cells is easy to obtain and devoid of ethical concerns. The cells have a great capacity to proliferate which reduces the need for continuous preparation of new feeder cell lines. In addition, three normal hESC lines were obtained in the same conditions. The five stem cell lines retained hESC-specific features, including an unlimited and undifferentiated proliferation capacity, marker expression and the maintenance of stable karyotype. They also demonstrated pluripotency in vitro, forming cell lineages of the three germ layers, as indicated by immunolocalization of beta-tubulin, alpha-fetoprotein and actin. These new genetic cell lines represent an important in-vitro tool to study the physiological processes underlying this genetic disease, drug screening, and tissue engineering.

Generation of primordial germ cells from pluripotent stem cells

Embryonic stem (ES) cells, derived from pre-implantation embryo, embryonic germ (EG) cells, derived from embryonic precursors of gametes, primordial germ cells (PGCs), can differentiate into any cell type in the body. Moreover, ES cells have the capacity to differentiate into PGCs in vitro. In the present study we have shown the differentiation capacity of six EG cell lines to form PGCs in vitro, in comparison to ES cells. Cell lines were differentiated via embryoid body (EB) formation using the co-expression of mouse vasa homolog (Mvh) and Oct-4 to identify newly formed PGCs in vitro. We found an increase of PGC numbers in almost all analysed cell lines in 5-day-old EBs, thus suggesting that EG and ES cells have similar efficiency to generate PGCs. The addition of retinoic acid confirmed that the cultures had attained a PGC-like identity and continued to proliferate. Furthermore we have shown that the expression pattern of Prmt5 and H3K27me3 in newly formed PGCs is similar to that observed in embryonic day E11.5 PGCs in vivo. By co-culturing EBs with Chinese hamster ovary (CHO) cells some of the PGCs entered into meiosis, as judged by Scp3 expression. The derivation of germ cells from pluripotent stem cells in vitro could provide an invaluable model system to study both the genetic and epigenetic programming of germ cell development in vivo.

Propensity of human embryonic stem cell lines during early stage of lineage specification controls their terminal differentiation into mature cell types

Human embryonic stem cells (hESCs) are able to stably maintain their characteristics for an unlimited period; nevertheless, substantial differences among cell lines in gene and protein expression not manifested during the undifferentiated state may appear when cells differentiate. It is widely accepted that developing an efficient protocol to control the differentiation of hESCs will enable us to produce adequate numbers of desired cell types with relative ease for diverse applications ranging from basic research to cell therapy and drug screening. Hence of late, there has been considerable interest in understanding whether and how hESC lines are equivalent or different to each other in their in vitro developmental tendencies. In this study, we compared the developmental competences of two hESC lines (HUES-9 and HUES-7) at molecular, cellular and functional levels, upon spontaneous differentiation without any added inducing agents. Both cell lines generated the three embryonic germ layers, extra-embryonic tissues and primordial germ cells during embryoid body (EB) formation. However HUES-9 showed a stronger propensity towards formation of neuroectodermal lineages, whereas HUES-7 differentiated preferentially into mesoderm and endoderm. Upon further differentiation, HUES-9 generated largely neural cells (neurons, oligodendrocytes, astrocytes and gangliosides) whereas HUES-7 formed mesendodermal derivatives, including cardiomyocytes, skeletal myocytes, endothelial cells, hepatocytes and pancreatic cells. Overall, our findings endorse the hypothesis that independently-derived hESCs biologically differ among themselves, thereby displaying varying differentiation propensity. These subtle differences not only highlight the importance of screening and deriving lines for lineage-specific differentiation but also indicate that individual lines may possess a repertoire of capabilities that is unique.

Liver-enriched transcription factors are critical for the expression of hepatocyte marker genes in mES-derived hepatocyte-lineage cells

Background

Induction of stem cell differentiation toward functional hepatocytes is hampered by lack of knowledge of the hepatocyte differentiation processes. The overall objective of this project is to characterize key stages in the hepatocyte differentiation process.

Results

We established a mouse embryonic stem (mES) cell culture system which exhibited changes in gene expression profiles similar to those observed in the development of endodermal and hepatocyte-lineage cells previously described in the normal mouse embryo. Transgenic mES cells were established that permitted isolation of enriched hepatocyte-lineage populations. This approach has isolated mES-derived hepatocyte-lineage cells that express several markers of mature hepatocytes including albumin, glucose-6-phosphatase, tyrosine aminotransferase, cytochrome P450-3a, phosphoenolpyruvate carboxykinase and tryptophan 2,3-dioxygenase. In addition, our results show that the up-regulation of the expression levels of hepatocyte nuclear factor-3α, -4α, -6, and CCAAT-enhancer binding protein-β might be critical for passage into late-stage differentiation towards functional hepatocytes. These data present important steps for definition of regulatory phenomena that direct specific cell fate determination.

Conclusion

The mES cell culture system generated in this study provides a model for studying transition between stages of the hepatocyte development and has significant potential value for studying the molecular basis of hepatocyte differentiation in vitro.

Leydig cell re-generation and expression of cell signaling molecules in the germ cell-free testis

Leydig cells in the rat testis can be specifically ablated with ethane dimethane sulfonate (EDS) and will subsequently re-generate. In this study, we have characterized Leydig cell re-generation and expression of selected cell-signaling molecules in a germ cell-free model of EDS action. This model offers the advantage that re-generation occurs on a stable background without confounding changes from the regressing and repopulating germ cell population. Adult rats were treated with busulfan to remove the germ cell population and Leydig cells were then ablated with EDS. Testicular testosterone levels declined markedly within 24 h of EDS treatment and started to recover after 8 days. After EDS treatment there were marked declines in levels of Leydig cell-specific mRNA transcripts coding for steroidogenic enzymes cytochrome P450 11a1 (Cyp11a1), cytochrome P450 17a1 (Cyp17a1), 3beta-hydroxysteroid dehydrogenase type 1 (Hsd3b1), 17beta-hydroxysteroid dehydrogenase type 3 (Hsd17b3) and the LH receptor. Levels of all transcripts recovered within 20 days of EDS treatment apart from Hsd17b3, which remained undetectable up to 20 days. Immunohistochemical localization of CYP11A1 during the phase of early Leydig cell re-generation showed that the Leydig cell precursors are spindle-shaped peritubular cells. Studies on factors which may be involved in Leydig cell re-generation showed there were significant but transient increases in platelet-derived growth factor A (Pdgfa), leukemia inhibitory factor (Lif), and neurofilament heavy polypeptide (Nefh) after EDS, while desert hedgehog (Dhh) levels declined sharply but recovered by 3 days. This study shows that the Leydig cell precursors are peritubular cells and that expression of Pdgfa and Lif is increased at the start of the re-generation process when precursor proliferation is likely to be taking place.

Effects of oxygen on mouse embryonic stem cell growth, phenotype retention, and cellular energetics

Most embryonic stem (ES) cell research is performed with a gas phase oxygen partial pressure (pO(2)) of 142 mmHg, whereas embryonic cells in early development are exposed to pO(2) values of 0-30 mmHg. To understand effects of these differences, we studied murine ES (mES) growth, maintenance of stem cell phenotype, and cell energetics over a pO(2) range of 0-285 mmHg, in the presence or absence of differentiation-suppressing leukemia inhibitory factor (LIF). With LIF, growth rate was sensitive to pO(2) but constant with time, and expression of self-renewal transcription factors decreased at extremes of pO(2). Subtle morphological changes suggested some early differentiation, but cells retained the ability to differentiate into derivatives of all three germ layers at low pO(2). Without LIF, growth rate decreased with time, and self-renewal transcription factor mRNA decreased further. Gross morphological changes occurred, and overt differentiation occurred at all pO(2). These findings suggested that hypoxia in the presence of LIF promoted limited early differentiation. ES cells survived oxygen starvation with negligible cell death by increasing anaerobic metabolism within 48 h of anoxic exposure. Decreasing pO(2) to 36 mmHg or lower decreased oxygen consumption rate and increased lactate production rate. The fraction of ATP generated aerobically was 60% at or above 142 mmHg and decreased to 0% under anoxia, but the total ATP production rate remained nearly constant at all pO(2). In conclusion, undifferentiated ES cells adapt their energy metabolism to proliferate at all pO(2) between 0 and 285 mmHg. Oxygen has minimal effects on undifferentiated cell growth and phenotype, but may exert more substantial effects under differentiating conditions.

Diverse hematopoietic potentials of five human embryonic stem cell lines

Despite a growing body of literature concerning the hematopoietic differentiation of human embryonic stem cells (hESCs), the full hematopoietic potential of the majority of existing hESC lines remains unknown. In this study, the hematopoietic response of five NIH-approved hESC lines (H1, hSF6, BG01, BG02, and BG03) was compared. Our data show that despite expressing similar hESC markers under self-renewing conditions and initiating mesodermal differentiation under spontaneous differentiation conditions, marked differences in subsequent hematopoietic differentiation potential among these lines existed. A high degree of hematopoietic differentiation was attained only by H1 and BG02, whereas this process appeared to be abortive in nature for hSF6, BG01, and BG03. This difference in hematopoietic differentiation predisposition was readily apparent during spontaneous differentiation, and further augmented under hematopoietic-inducing conditions. This predisposition appeared to be intrinsic to the specific hESC line and independent of passage number or gender karyotype. Interestingly, H1 and BG02 displayed remarkable similarities in their kinetics of hematopoietic marker expression, hematopoietic colony formation, erythroid differentiation, and globin expression, suggesting that a similar, predetermined differentiation sequence is followed. The identification of intrinsic and extrinsic factors governing the hematopoietic differentiation potential of hESCs will be of great importance for the putative clinical utility of hESC lines.

Novel vectors for homologous recombination strategies in mouse embryonic stem cells: an ES cell line expressing EGFP under control of the 5T4 promoter

The use of gene mutation/knock-out strategies in mouse embryonic stem (ES) cells has revolutionized the study of gene function in ES cells and embryonic development. However, the construction of vectors for homologous recombination strategies requires considerable expertise and time. We describe two novel vectors that can generate site specific knock-out or EGFP knock-in ES cells within 6 weeks from construct design to identification of positive ES cell clones. As proof-of-principle, we have utilized the knock-out targeting vector to modify the NEIL2 locus in ES cells. In addition, using the knock-in vector, we have inserted EGFP downstream of the 5T4 oncofetal antigen promoter in ES cells (5T4-GFP ES cells). Undifferentiated 5T4-GFP ES cells lack EGFP and maintain expression of the pluripotent markers OCT-4 and NANOG. Upon differentiation, EGFP expression is increased in 5T4-GFP ES cells and this correlates with 5T4 transcript expression of the unmodified allele, loss of Nanog and Oct-4 transcripts and upregulation of differentiation-associated transcripts. Furthermore, we demonstrate that fluorescent activated cell sorting of 5T4-GFP ES cells allows isolation of pluripotent or differentiated cells from a heterogeneous population. These vectors provide researchers with a rapid method of modifying specific ES cell genes to study cellular differentiation and embryonic development.

Global gene expression profiling reveals similarities and differences among mouse pluripotent stem cells of different origins and strains

Pluripotent stem cell lines with similar phenotypes can be derived from both blastocysts (embryonic stem cells, ESC) and primordial germ cells (embryonic germ cells, EGC). Here, we present a compendium DNA microarray analysis of multiple mouse ESCs and EGCs from different genetic backgrounds (strains 129 and C57BL/6) cultured under standard conditions and in differentiation-promoting conditions by the withdrawal of Leukemia Inhibitory Factor (LIF) or treatment with retinoic acid (RA). All pluripotent cell lines showed similar gene expression patterns, which separated them clearly from other tissue stem cells with lower developmental potency. Differences between pluripotent lines derived from different sources (ESC vs. EGC) were smaller than differences between lines derived from different mouse strains (129 vs. C57BL/6). Even in the differentiation-promoting conditions, these pluripotent cells showed the same general trends of gene expression changes regardless of their origin and genetic background. These data indicate that ESCs and EGCs are indistinguishable based on global gene expression patterns alone. On the other hand, a detailed comparison between a group of ESC lines and a group of EGC lines identified 20 signature genes whose average expression levels were consistently higher in ESC lines, and 84 signature genes whose average expression levels were consistently higher in EGC lines, irrespective of mouse strains. Similar analysis identified 250 signature genes whose average expression levels were consistently higher in a group of 129 cell lines, and 337 signature genes whose average expression levels were consistently higher in a group of C57BL/6 cell lines. Although none of the genes was exclusively expressed in either ESCs versus EGCs or 129 versus C57BL/6, in combination these signature genes provide a reliable separation and identification of each cell type. Differentiation-promoting conditions also revealed some minor differences between the cell lines. For example, in the presence of RA, EGCs showed a lower expression of muscle- and cardiac-related genes and a higher expression of gonad-related genes than ESCs. Taken together, the results provide a rich source of information about the similarities and differences between ESCs and EGCs as well as 129 lines and C57BL/6 lines. Such information will be crucial to our understanding of pluripotent stem cells. The results also underscore the importance of studying multiple cell lines from different strains when making comparisons based on gene expression analysis.

Caspase-dependent proteolytic cleavage of STAT3alpha in ES cells, in mammary glands undergoing forced involution and in breast cancer cell lines

Background

The STAT (Signal Transducers and Activators of Transcription) transcription factor family mediates cellular responses to a wide range of cytokines. Activated STATs (particularly STAT3) are found in a range of cancers. Further, STAT3 has anti-apoptotic functions in a range of tumour cell lines. After observing a proteolytic cleavage in STAT3α close to a potential apoptotic caspase protease cleavage site we investigated whether STAT3α might be a caspase substrate.

Methods

STAT3α status was investigated in vitro in several cell systems:- HM-1 murine embryonic stem (ES) cells following various interventions; IOUD2 murine ES cells following induction to differentiate along neural or adipocyte lineages; and in a number of breast cancer cell lines. STAT3α status was also analysed in vivo in wild type murine mammary glands undergoing controlled, forced involution.

Results

Immunoblotting for STAT3α in HM-1 ES cell extracts detected amino and carboxy terminal species of approximately 48 kDa and 43 kDa respectively – which could be diminished dose-dependently by cell treatment with the nitric oxide (NO) donor drug sodium nitroprusside (SNP). UV irradiation of HM-1 ES cells triggered the STAT3α cleavage (close to a potential caspase protease cleavage site). Interestingly, the pan-caspase inhibitor z-Val-Ala-DL-Asp-fluoromethylketone (z-VAD-FMK) and the JAK2 tyrosine kinase inhibitor AG490 both inhibited cleavage dose-dependently, and cleavage was significantly lower in a heterozygous JAK2 knockout ES cell clone. STAT3α cleavage also occurred in vivo in normal murine mammary glands undergoing forced involution, coinciding with a pulse of phosphorylation of residue Y705 on full-length STAT3α. Cleavage also occurred during IOUD2 ES cell differentiation (most strikingly along the neural lineage) and in several human breast cancer cell lines, correlating strongly with Y705 phosphorylation.

Conclusion

This study documents a proteolytic cleavage of STAT3α into 48 kDa amino and 43 kDa carboxyl terminal fragments in a range of cell types. STAT3α cleavage occurs close to a potential caspase site, and can be inhibited dose-dependently by SNP, AG490 and z-VAD-FMK. The cleavage seems to be caspase-dependent and requires the phosphorylation of STAT3α at the Y705 residue. This highly regulated STAT3α cleavage may play an important role in modulating STAT3 transcriptional activity.

Derivation and characterization of three new Spanish human embryonic stem cell lines (VAL -3 -4 -5) on human feeder and in serum-free conditions

A total of 184 human embryos, frozen for >5 years, were donated; informed consent was obtained according to Spanish law 45/2003. Survival rate was 40% and three out of 24 blastocysts (12.5%) developed into putative hESC lines, named VAL-3, VAL-4, and VAL-5. The derivation process was performed on microbiologically tested and irradiated human foreskin fibroblasts and designed to minimize contact with xeno-components in knockout DMEM supplemented with knockout serum replacement, and basic fibroblast growth factor. Fingerprinting and HLA typing of the cell lines allowed their identification and traceability. Karyotype was normal for VAL-3 (46XY), VAL-4 (46XX) and VAL-5 (46XX). All three hESC lines expressed specific markers for non-differentiation (Nanog, stage-specific embryonic antigen-4 [SSEA-4], tumour-related antigen [TRA]-1-60, and TRA-1-81) and were negative for SSEA-1. RT-PCR further demonstrated the expression of Oct-4, Sox2, Rex-1, Nanog, Cripto, Thy-1, and Lefty-A. Furthermore, they were found to be negative for classical differentiation markers such as neurofilament heavy chain (ectoderm), renin (mesoderm), and amylase (endoderm). All three cell lines displayed high levels of telomerase activity, and were shown to successfully overcome cryopreservation and thawing. Finally, these three new hESC lines have demonstrated the potential to differentiate in vitro and in vivo (teratoma formation) into cell types originating from all three germ layers.

Neuroprotective role of ERK1/2 and ERK5 in a dopaminergic cell line under basal conditions and in response to oxidative stress

Loss of motor function in Parkinson's disease is due in part to degeneration of dopamine (DA) neurons. Pharmacological evidence suggests that the mitogen-activated protein kinase signaling pathways involving extracellular signal-regulated kinases (ERKs) play important roles in neuroprotection of DA neurons. However, the relative roles of the several ERK isoforms in the viability of DA neurons have not yet been determined. In the present study, we investigated the contributions of ERK5, as well as ERK1/2, to MN9D cell survival under basal conditions and in response to 6-hydroxydopamine (6-OHDA). We observed that U0126, an inhibitor of ERK activation, decreased basal survival of these cells. To differentiate between ERK1/2 and ERK5, cells were transfected with a dominant negative form of either ERK5 or MEK1, the upstream activator of ERK1/2. Transfection of MN9D cells with either dominant negative construct mimicked U0126, reducing cell survival. Moreover, transfection of the cells in such a way as to increase ERK5 or ERK1/2 activity inhibited 6-OHDA-induced cell death, although this effect was significant only in the case of ERK1/2 activation. These studies suggest that activations of ERK5 and ERK1/2 both promote basal DA cell survival and that ERK1/2 also protects DA cells from oxidative stress. These are the first studies to demonstrate a role for ERK5 in DA neuronal survival and to investigate the relative roles of ERK1/2 and ERK5 in basal DA survival and neuroprotection from oxidative stress.

Cell surface 5T4 antigen is transiently upregulated during early human embryonic stem cell differentiation: effect of 5T4 phenotype on neural lineage formation

The 5T4 oncofoetal antigen is a cell surface glycoprotein that is transiently expressed during mouse ES cell differentiation and correlates with decreased pluripotency of such cells. We show that 5T4 antigen is transiently unregulated during HES4 and H1 human ES cell differentiation and its expression correlates with loss of the pluripotent markers OCT-4 and Tra-1-60 and upregulation of transcript markers associated with the three primary germ layers. To confirm that absence of cell surface 5T4 antigen represents a pluripotent hES cell phenotype, we performed mechanical transfer of either 5T4-ve or 5T4+ve HES4 colonies identified using live cell staining. 5T4-ve transfers maintained expression of OCT-4 in over 90% of resultant colonies, whereas 5T4+ve transfers exhibited significantly lower numbers of OCT-4-expressing colonies (92 +/- 1.4 vs. 2.9 +/- 2.0%). Interestingly, low cell density 5T4-ve colony transfers exhibited increased numbers of OCT-4-expressing colonies compared to large 5T4-ve transfers (92 +/- 1.4 vs. 63.2 +/- 1.9%). 5T4-ve and 5T4+ve HES4 and H1 ES cell lines expressed markers representative of neuroectoderm lineages, and we assessed the formation of neural lineages from these phenotypes in serum-containing medium and N2B27 medium. Expression of 5T4 was found to be inversely related to the yield of tyrosine-hydroxylase (TH+)-expressing neurons in N2B27 medium, with additional mesoderm and endoderm transcript markers detected. Homogeneous glial cell populations were derived from low cell density 5T4-ve colony transfers cultured in serum-containing medium, with TH+ neuronal formation inhibited in a cell-density-dependent manner. We conclude that the 5T4 antigen is a transient marker of hES cell differentiation and that 5T4 phenotype, colony seeding density and culture conditions significantly influence the maintenance of pluripotent hES cells and their differentiation to neural lineages.

In search of rat stem Leydig cells: identification, isolation, and lineage-specific development

Leydig cells (LCs) are thought to differentiate from spindle-shaped precursor cells that exhibit some aspects of differentiated function, including 3beta-hydroxysteroid dehydrogenase (3betaHSD) activity. The precursor cells ultimately derive from undifferentiated stem LCs (SLCs), which are postulated to be present in testes before the onset of precursor cell differentiation. We searched for cells in the neonatal rat testis with the abilities to: (i) proliferate and expand indefinitely in vitro (self renew); (ii) differentiate (i.e., 3betaHSD and ultimately synthesize testosterone); and (iii) when transplanted into host rat testes, colonize the interstitium and subsequently differentiate in vivo. At 1 week postpartum, spindle-shaped cells were seen in the testicular interstitium that differed from the precursor cells in that they were 3betaHSD-negative, luteinizing hormone (LH) receptor (LHR)-negative, and platelet-derived growth factor receptor alpha (PDGFR alpha)-positive. These cells were purified from the testes of 1-week-old rats. The cells contained proteins known to be involved in LC development, including GATA4, c-kit receptor, and leukemia inhibitory factor receptor. The putative SLCs expanded over the course of 6 months while remaining undifferentiated. When treated in media that contained thyroid hormone, insulin-like growth factor I, and LH, 40% of the putative SLCs came to express 3betaHSD and to synthesize testosterone. When transplanted into host rat testes from which LCs had been eliminated, the putative SLCs colonized the interstitium and subsequently expressed 3betaHSD, demonstrating their ability to differentiate in vivo. We conclude that these cells are likely to be the sought-after SLCs.

Human embryonic stem cell derivation: from the IVF perspective to therapeutic applications

Human embryonic stem cells (hESC) are capable of proliferating indefinitely in an undifferentiated state and are pluripotent, being able to differentiate into most cell types under the correct conditions. Since the establishment of the first hESC line in 1998, the hope has existed that these cells could constitute an unlimited cell source for replacement therapy in the treatment of various diseases and disabilities. However, there is opposition and concern within society towards hESC derivation. The purpose of this article is to introduce the medical and scientific issues surrounding hESC derivation for clinical use concerning the source for this research (human embryos donated from in vitro fertilization procedures), and the methodologies implicated in feeder-free, xeno-free derivation that will allow potential clinical applications.

Derivation of clinical-grade human embryonic stem cells

Embryonic stem cells proliferate in vitro while maintaining an undifferentiated state, and are capable of differentiating into most cell types under appropriate conditions. These properties imply great potential in the treatment of various diseases and disabilities. In fact, the first clinical trials with hESC for treating spinal cord injuries will begin next year. However, therapeutic application of human embryonic stem cell derivatives is compromised by the exposure of existing lines to animal and human components, with the subsequent risk of contamination with retroviruses and other pathogens, which can be transmitted to patients. The scientific community is striving to avoid the use of xenogeneic or allogeneic components in the process of derivation new hESC lines. This review summarizes attempts that have been made to avoid these contaminants and the breakthroughs achieved in the derivation of clinical-grade hESC that could be used for therapeutic purposes.

Derivation and characterization of new human embryonic stem cell lines: SNUhES1, SNUhES2, and SNUhES3

Here we report the derivation and characterization of new human embryonic stem cell (hESC) lines, SNUhES1, SNUhES2, and SNUhES3. These cells, established from the inner cell mass using an STO feeder layer, satisfy the criteria that characterize pluripotent hESCs: The cell lines express high levels of alkaline phosphatase, cell surface markers (such as SSEA-3, SSEA-4, TRA-1-60, and TRA-1-81), transcription factor Oct-4, and telomerase. When grafted into severe combined immunodeficient mice after prolonged proliferation, these cells maintained the developmental potentials to form derivatives of all three embryonic germ layers. The cell lines have normal karyotypes and distinct identities, revealed from DNA fingerprinting. Interestingly, analysis by electron microscopy clearly shows the morphological difference between undifferentiated and differentiated hESCs. Undifferentiated hESCs have a high ratio of nucleus to cytoplasm, prominent nucleoli, indistinct cell membranes, free ribosomes, and small mitochondria with a few crista, whereas differentiated cells retain irregular nuclear morphology, desmosomes, extensive cytoplasmic membranes, tonofilaments, and highly developed cellular organelles such as Golgi complex with secretory vesicles, endoplasmic reticulum studded with ribosomes, and large mitochondria. Existence of desmosomes and tonofilaments indicates that these cells differentiated into epithelial cells. When in vitro differentiation potentials of these cell lines into cardiomyocytes were examined, SNUhES3 was found to differentiate into cardiomyocytes most effectively.

Genetic basis of human testicular germ cell cancer: insights from the fruitfly and mouse

The prevalence of tumours of the germ line is increasing in the male population. This complex disease has a complex aetiology. We examine the contribution of genetic mutations to the development of germ line tumours in this review. In particular, we concentrate on fly and mouse experimental systems in order to demonstrate that mutations in some conserved genes cause pathologies typical of certain human germ cell tumours, whereas other mutations elicit phenotypes that are unique to the experimental model. Despite these experimental systems being imperfect, we show that they are useful models of human testicular germ cell tumourigenesis.

Insulin stimulates Ca2+ uptake via PKC, cAMP, and p38 MAPK in mouse embryonic stem cells

Embryonic stem (ES) cells are provided as a powerful tool for developmental biology and have been shown to respond to insulin. However, little is known about the effect of insulin on [Ca2+]i regulation in the ES cells, although many cellular functions are tightly regulated by [Ca2+]i. Therefore, we examined the effect of insulin on Ca2+ uptake and its related signal pathways in the mouse ES cells. Mouse ES cells expressed alkaline phosphatase (AP), transcription factor Oct-4, and stage-specific embryonic antigen-1 (SSEA-1). Insulin increased the Ca2+ uptake in a time- and dose-dependent manner and the effect was blocked by L-type Ca2+ channel blockers, nifedifine and methoxyverapamil. Genistein or herbimycin A (tyrosine kinase inhibitors), wortmannin (PI-3K inhibitor), and staurosporine or bisindolylmaleimide I (PKC inhibitors) completely prevented insulin-induced increase of Ca2+ uptake. Wortmannin blocked insulin-induced PKC activation, but SQ 22536 (adenylate cyclase inhibitor) did not. Insulin also rapidly increased formation of inositol phosphates (IPs). We examined the involvement of MAPKs in mediating the effect of insulin on Ca2+ uptake. SB 203580 (p38 MAPK inhibitor) but not PD 98059 (p44/42 MAPKs inhibitor) blocked insulin-induced increase of Ca2+ uptake. Insulin significantly increased the phosphorylation of p38 MAPK but not p44/42 MAPKs. In addition, genistein, PKI, and bisindolylmaleimide I blocked the phosphorylation of p38 MAPK by insulin, suggesting a causal relationship. In conclusion, insulin partially stimulated Ca2+ uptake via PKC, cAMP, and p38 MAPK signaling pathways in mouse ES cells.

Single inner cell masses yield embryonic stem cell lines differing in lifr expression and their developmental potential

The unique differentiation potential of inner cell mass derived embryonic stem cells together with their outstanding self-renewal capacity makes them a desirable source for somatic cell therapy of human diseases. Somatic cells are gained by in vitro differentiation of embryonic stem cells, however, the differentiation potential of embryonic stem cells varied even between isogenic cell lines. Variable differentiation potentials may either be a consequence of an inherent inhomogeneity of gene expression in the inner cell mass or may have technical reasons. To understand variations in the differentiation potential, we generated pairs of isogenic, monozygotic twin, and single inner cell mass derived clonal embryonic stem cell lines, and demonstrate that they differentially express the leukaemia inhibitory factor receptor gene. Variations of leukaemia inhibitory factor receptor protein levels are already evident in the inner cell mass and predispose the cardiomyogenic potential of embryonic stem cell lines in a Janus activated kinase dependent manner. Thus, a single inner cell mass may give rise to embryonic stem cell lines with different developmental potentials.