Differences between human and mouse embryonic stem cells

Evaluation of in vitro cytotoxicity and paracellular permeability of intact monolayers with mouse embryonic stem cells

Mouse embryonic stem (mES) cells were induced to form intact monolayers in cell culture inserts, using combinations of extracellular matrix (ECM) components and growth factors (GFs). Progressive formation of intact monolayers was monitored using transepithelial electrical resistance (TEER) and passage of paracellular permeability (PP) markers. The mES cells were initially inoculated on inactivated mouse embryonic fibroblasts (MEFs) plus leukemia inhibitory factor (LIF). At 75% confluence, cells were passaged in the absence of MEF and LIF to stimulate formation of rounded multicellular aggregates (MA). After 4 days, cultures containing MA were transferred to culture inserts coated with ECM components only, and grown in the presence of selected individual GFs. An additional 10-14 days revealed confluent monolayers with TEER values of 500-700 ohms cm2 (Omega cm2). Monolayers grown on inserts coated with ECM components, such as fibronectin or collagen-IV, in the presence of epidermal growth factor or keratinocyte growth factor in the medium, yielded the highest TEER measurements when compared to cultures grown without GFs or ECM. Acute cytotoxicity (AC) studies with confluent monolayers of mES cells in 96-well plates indicated that there is a high correlation (R2=0.91) between cell viability and TEER for 24-h exposure time. Also, decrease in TEER is inversely proportional with increase in PP of markers. In comparison to standardized Registry of Cytotoxicity (RC) data and TEER measurements, MTT IC50 values for mES cells are lower. Thus, at equivalent concentrations for the same chemicals, cell viability decreases before the integrity of the monolayer is compromised. This system represents a novel approach for the manipulation of mES cells toward specific intact monolayers, as an in vitro model for biological monolayer formation, and most importantly, for applications to cytotoxicity testing.

Contrasting effects of basic fibroblast growth factor and epidermal growth factor on mouse neonatal olfactory mucosa cells

Basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) affect proliferation and survival of many cell types, but their role in the maintenance of olfactory mucosa cells remains unclear. In the neonatal mouse olfactory mucosa, cell proliferation mainly occurs in the neuroepithelium and, to a lesser extent, in the lamina propria. To establish whether bFGF and EGF affect proliferation and/or survival of these cells, we isolated olfactory mucosa cells from the neonatal mouse and cultured them as free-floating spheres under bFGF or EGF stimulation. Our data demonstrate that bFGF is a mitogen for the rapidly dividing cells (olfactory neuronal precursors and olfactory ensheathing cells), and also a survival factor for both slowly and rapidly dividing cells of the olfactory mucosa. In contrast, EGF appears to be primarily a survival factor for both the olfactory stem and precursor cells.

Expression analysis of pluripotency factors in the undifferentiated porcine inner cell mass and epiblast during in vitro culture

Limited understanding of the importance of known pluripotency factors in pig embryonic stem cells (ESC) impedes the establishment and validation of porcine ESC lines. This study evaluated the expression of known mouse ESC and human ESC (hESC) pluripotency markers in in vivo inner cell mass (ICM) and in vitro-cultured undifferentiated porcine epiblast cells isolated from 8-day porcine blastocysts, primary cultures of epiblast-derived neuroprogenitor cells, and endoderm cells. The expression profile of common pluripotency markers (POU domain 5 transcript factor 1, SRY-box containing gene 2, and Nanog homeobox), species-specific markers, ESC-associated factors, and differentiation markers was evaluated. The mRNA of uncultured ICMs, cultured epiblast cells, epiblast-derived neuroprogenitor cells, and endoderm cells was amplified prior to expression analysis of candidate genes by real-time RT-PCR. ESC factors whose expression correlated best with the undifferentiated epiblast state were identified by comparative mRNA expression analysis between porcine epiblast-derived somatic cell lines, fetal fibroblasts, and adult tissues. Across tissue types Nanog homeobox exhibited ubiquitous expression, whereas POU domain 5 transcript factor 1, teratocarcinoma-derived growth factor 1, and RNA exonuclease homolog 1 transcript expression was restricted primarily to undifferentiated epiblasts. Our results suggested that expression of pluripotency markers in undifferentiated pig epiblast cells more closely resembled that observed in hESC. Expression alterations of ESC-associated factors in epiblast cells were also observed during in vitro culture. Our data demonstrate the potential use of some pluripotency factors as markers of porcine epiblast stem cells and indicate that the in vitro environment may influence the cultured epiblast's developmental state.

Linkage of pluripotent stem cell-associated transcripts to regulatory gene networks

Knowledge of the transcriptional circuitry responsible for pluripotentiality and self-renewal in embryonic stem cells is tantamount to understanding early mammalian development and a prerequisite to determining their therapeutic potential. Various techniques have employed genomics to identify transcripts that were abundant in stem cells, in an attempt to define the molecular basis of 'stemness'. In this study, we have extended traditional genomic analyses to identify cis-elements that might be implicated in the control of embryonic stem cell-restricted gene promoters. The strategy relied on the generation of a problem-specific list from serial analysis of gene expression profiles and subsequent promoter analyses to identify frameworks of multiple cis-elements conserved in space and orientation among genes from the problem-specific list. Subsequent experimental data suggest that 2 novel transcription factors, B-Myb and Maz, predicted from these models, are implicated either in the maintenance of the undifferentiated stem cell state or in early steps of differentiation.

LongSAGE profiling of nine human embryonic stem cell lines

To facilitate discovery of novel human embryonic stem cell (ESC) transcripts, we generated 2.5 million LongSAGE tags from 9 human ESC lines. Analysis of this data revealed that ESCs express proportionately more RNA binding proteins compared with terminally differentiated cells, and identified novel ESC transcripts, at least one of which may represent a marker of the pluripotent state.

Neural differentiation of human ES cells

Human embryonic stem cells (hESCs) may be converted into highly enriched cultures of neural precursors under defined culture conditions. The neural precursors can proliferate in culture for prolonged periods of time, and can differentiate in vitro into mature neurons, astrocytes, and oligodendrocytes. The neurons are functional and have normal electrophysiological properties. After transplantation to the developing rodent brain, the neural precursors migrate extensively into the host brain parenchyma, respond to host brain signals, and differentiate in a region-specific manner to progeny of the three neural lineages. The establishment of neuroectodermal precursors from hESCs allows the study of human neurogenesis in vitro and is an aid in drug discovery. In addition, the neural precursors may potentially serve as a platform for the development of specific functional neural cells for transplantation and gene therapy of neurological disorders. In this unit, we introduce methods for the derivation, propagation and characterization of hESC-derived neural precursors.

Secreted factors from olfactory mucosa cells expanded as free-floating spheres increase neurogenesis in olfactory bulb neurosphere cultures

Background

The olfactory epithelium is a neurogenic tissue comprising a population of olfactory receptor neurons that are renewed throughout adulthood by a population of stem and progenitor cells. Because of their relative accessibility compared to intra-cranially located neural stem/progenitor cells, olfactory epithelium stem and progenitor cells make attractive candidates for autologous cell-based therapy. However, olfactory stem and progenitor cells expand very slowly when grown as free-floating spheres (olfactory-spheres) under growth factor stimulation in a neurosphere assay.

Results

In order to address whether olfactory mucosa cells extrinsically regulate proliferation and/or differentiation of immature neural cells, we cultured neural progenitor cells derived from mouse neonatal olfactory bulb or subventricular zone (SVZ) in the presence of medium conditioned by olfactory mucosa-derived spheres (olfactory-spheres). Our data demonstrated that olfactory mucosa cells produced soluble factors that affect bulbar neural progenitor cell differentiation but not their proliferation when compared to control media. In addition, olfactory mucosa derived soluble factors increased neurogenesis, especially favouring the generation of non-GABAergic neurons. Olfactory mucosa conditioned medium also contained several factors with neurotrophic/neuroprotective properties. Olfactory-sphere conditioned medium did not affect proliferation or differentiation of SVZ-derived neural progenitors.

Conclusion

These data suggest that the olfactory mucosa does not contain factors that are inhibitory to neural stem/progenitor cell proliferation but does contain factors that steer differentiation toward neuronal phenotypes. Moreover, they suggest that the poor expansion of olfactory-spheres may be in part due to intrinsic properties of the olfactory epithelial stem/progenitor cell population.

Derive and conquer: sourcing and differentiating stem cells for therapeutic applications

Although great progress has been made in the isolation and culture of stem cells, the future of stem-cell-based therapies and their productive use in drug discovery and regenerative medicine depends on two key factors: finding reliable sources of multipotent and pluripotent cells and the ability to control their differentiation to generate desired derivatives. It is essential for clinical applications to establish reliable sources of pathogen-free human embryonic stem cells (ESCs) and develop suitable differentiation techniques. Here, we address some of the problems associated with the sourcing of human ESCs and discuss the current status of stem-cell differentiation technology.

Human embryonic stem cells: mechanisms to escape replicative senescence?

Human embryonic stem cells (hESCs) are unique in that they can proliferate indefinitely in culture in an undifferentiated state as well as differentiate into any somatic cells. Undifferentiated hESCs do not appear to undergo senescence and remain nontransformed over multiple passages. Culture hESCs maintain telomere length and exhibit high telomerase activity after prolonged in vitro culture. The ability of hESCs to bypass senescence is lost as hESCs differentiate into fully differentiated somatic cells. This loss of immortality upon differentiation may be due to a variety aging related factors such as reduction in telomere length, alteration of telomerase activity, changes in cell cycle regulation and decrease in DNA repair ability. Absence of such aging factors as well as the lack of genomic, mitochondrial and epigenetic changes, may contribute to the lack of senescence in hESCs. In this review, we will summarize recent advances in determining changes in these aspects in prolonged hESC cultures. We will in particular discuss the potential roles of several cellular pathways including the telomerase, p53, and Rb pathways in escaping senescence in hESCs. We will also discuss the genomic and epigenetic changes in long-term hESC culture and their potential roles in bypassing senescence, as well as alternative sources of pluripotent stem cells.

Expression of cell-surface antigens and embryonic stem cell pluripotency genes in equine blastocysts

Embryonic stem-like (ES-like) cells have now been derived from the inner cell mass (ICM) of horse embryos at the blastocyst stage. Because they have been shown to express cell-surface antigens found in both human and mouse ES cells, the present study investigated gene expression patterns in day-7 horse blastocysts from which the horse ES-like cells had been derived originally. The genes studied included Oct-4, stage-specific embryonic antigen-1 (SSEA-1), SSEA-3, SSEA-4, tumor rejection antigen-1-60 (TRA-1-60), TRA-1-81, and alkaline phosphatase activity, and whereas all three of the SSEA antigens were expressed in both the ICM and the trophoblast on day 7, Oct-4, TRA-1-60, TRA-1-81, and alkaline phosphatase activity were localized mostly in the ICM. Upon in vitro differentiation of the horse ES-like cells, their expression of the stem cell markers was abolished. Therefore, the species-specific expression pattern of stem cell markers in horse ES-like cells reflects gene expression in the blastocysts from which they are derived.

Embryonic stem cell biology

ES cell research represents an exploding field of exploration. Initially predicted to provide rapid cures for numerous human diseases, the clinical usefulness of ES cell-derived cells remains untested in humans. However, ES cells have rapidly expanded our knowledge of human development and the molecular details of differentiation. Our ability to generate relatively pure populations of specifically differentiated cells for transplantation has markedly improved. It is hoped that soon researchers will overcome the biologic impediments to successful treatment of human disease with ES cell-derived cells.

A large-scale proteomic analysis of human embryonic stem cells

Background

Much of our current knowledge of the molecular expression profile of human embryonic stem cells (hESCs) is based on transcriptional approaches. These analyses are only partly predictive of protein expression however, and do not shed light on post-translational regulation, leaving a large gap in our knowledge of the biology of pluripotent stem cells.

Results

Here we describe the use of two large-scale western blot assays to identify over 600 proteins expressed in undifferentiated hESCs, and highlight over 40 examples of multiple gel mobility variants, which are suspected protein isoforms and/or post-translational modifications. Twenty-two phosphorylation events in cell signaling molecules, as well as potential new markers of undifferentiated hESCs were also identified. We confirmed the expression of a subset of the identified proteins by immunofluorescence and correlated the expression of transcript and protein for key molecules in active signaling pathways in hESCs. These analyses also indicated that hESCs exhibit several features of polarized epithelia, including expression of tight junction proteins.

Conclusion

Our approach complements proteomic and transcriptional analysis to provide unique information on human pluripotent stem cells, and is a framework for the continued analyses of self-renewal.

Recombinant HoxB4 fusion proteins enhance hematopoietic differentiation of human embryonic stem cells

Enforced expression of the HoxB4 gene promotes expansion of hematopoietic stem cells (HSCs) and enhances hematopoietic development of both murine and human embryonic stem (ES) cells. HoxB4- expanded HSCs have also been shown to retain their normal potential for differentiation and longterm self-renewal in vivo without the development of leukemia, suggesting that manipulation of HoxB4 expression might represent an effective way to expand functional HSCs for use in transplantation medicine. However, the genetic modification of cells poses clinical concerns, including a potentially increased risk of tumor genicity. Constitutive high-level ectopic viral expression of HoxB4 can also produce perturbations in the lineage differentiation of HSCs, an indication that uncontrolled HoxB4 manipulation may not be a satisfactory therapeutic strategy. Here we demonstrate that recombinant HoxB4 protein fused with a triple protein transduction domain (tPTD) promotes hematopoietic development of hES cells. The tPTD-HoxB4 protein enhanced the development of erythroid, myeloid, and multipotential progenitors in both early- and late-stage embryoid bodies (EBs). This effect varied considerably between different hES cell lines. Addition of the tPTD-HoxB4 protein did not alter the globin gene expression pattern; progeny derived from hES cells expressed high levels of embryonic (epsilon) and fetal (gamma) globin genes with or without tPTD-HoxB4 treatment. CD34+ cells derived from hES cells engrafted in bone marrow when transplanted into fetal CD1 mice, although supplementation of the differentiation medium with tPTD-HoxB4 protein did not result in increased repopulating capacity. This suggests that other gene(s), together with HoxB4, are required for generating more competitive HSCs. In summary, our study demonstrates that the tPTD-HoxB4 protein can be used with other recombinant proteins to efficiently generate transplantable HSCs from human ES cells.

Enhancement of NF-kappaB expression and activity upon differentiation of human embryonic stem cell line SNUhES3

NF-kappaB is involved in many biological processes including proliferation, survival, and differentiation. Because human embryonic stem (ES) cells have the potential to differentiate to various lineages, understanding mechanisms involved in stemness and lineage differentiation is an important issue. We investigated expression of NF-kappaB in the human ES cell lines SNUhES3 and MizhES4 and found that expression of NF-kappaB mRNA and protein in these two cell lines was significantly lower compared to those of other adult cell lines. However, when SNUhES3 cells were induced to differentiate by retinoic acid, expression levels of NF-kappaB significantly increased compared to undifferentiated SNUhES3 cells. As the components of tumor necrosis factor-alpha (TNF-alpha) signaling are expressed comparably in undifferentiated and differentiated SNUhES3 cells, we examined the responsiveness of SNUhES3 cells to treatment with TNF-alpha, an agonist of NF-kappaB signaling. Nuclear localization of NF-kappaB in response to TNF-alpha was evident in differentiated, but not undifferentiated, SNUhES3 cells. In agreement with this observation, induction of interleukin-8 (IL-8) in response to TNF-alpha was seen only in differentiated SNUhES3 cells. On the basis of an IkappaB kinase (IKK) inhibitor study, expression of IL-8 induced by TNF-alpha was dependent on NF-kappaB activity. Taken together, our results suggest that expression and activity of NF-kappaB is comparatively low in undifferentiated human ES cells, but increases during differentiation of the ES cells.

Epigenetic stability of embryonic stem cells and developmental potential

Recent studies highlight the tremendous potential of human embryonic stem (ES) cells and their derivatives as therapeutic tools for degenerative diseases. However, derivation and culture of ES cells can induce epigenetic alterations, which can have long lasting effects on gene expression and phenotype. Research on human and mouse stem cells indicates that developmental, cancer-related genes, and genes regulated by genomic imprinting are particularly susceptible to changes in DNA methylation. Together with the occurrence of genetic alterations, epigenetic instability needs to be monitored when considering human stem cells for therapeutic and technological purposes. Here, we discuss the maintenance of epigenetic information in cultured stem cells and embryos and how this influences their developmental potential.

Primate embryonic stem cells proceed to early gametogenesis in vitro

Embryonic stem cells (ESCs) of nonhuman primates are important for research into human gametogenesis because of similarities between the embryos and fetuses of nonhuman primates and those of humans. Recently, the formation of germ cells from mouse ESCs in vitro has been reported. In this study, we established cynomolgus monkey ES cell lines (cyESCs) and attempted to induce their differentiation into germ cells to obtain further information on the development of primate germ cells by observing the markers specific to germ cells. Three cyESCs were newly established and confirmed to be pluripotent. When the cells are induced to differentiate, the transcripts of Vasa and some meiotic markers were expressed. VASA protein accumulated in differentiated cell clumps and VASA-positive cells gathered in clumps as the number of differentiation days increased. In the later stages, VASA-positive clumps coexpressed OCT-4, suggesting that these cells might correspond to early gonocytes at the postmigration stage. Furthermore, meiosis-specific gene expression was also observed. These results demonstrate that cyESCs can differentiate to developing germ cells such as primordial germ cells (PGCs) or more developed gonocytes in our differentiation systems, and may be a suitable model for studying the mechanisms of primate germ cell development.

Gene Ontology analysis in multiple gene clusters under multiple hypothesis testing framework

OBJECTIVE

Gene Ontology (GO) has become a routine resource for functional analysis of gene lists. Although a number of tools have been provided to identify enriched GO terms in one or two gene lists, two technical challenges remain. First, how to handle multiple hypothesis testing in the analysis given that the tests are heavily correlated; second, how to identify GO terms that are enriched in a gene cluster, as compared to multiple other gene clusters. We provide a statistical procedure to rigorously treat these problems and offer a software tool for applying GO to the analysis of gene clusters.

METHODS

We previously introduced a statistical procedure that handles hypothesis testing in a two-group comparison scenario. In this paper we extend the two-group comparison procedure into a general procedure that enables the analysis of any number of gene lists/clusters. This new procedure enables identification of GO terms enriched in any gene cluster, while it controls for multiple hypothesis testing. This procedure is implemented into a user-friendly analysis tool: GoSurfer. The current version of GoSurfer takes one or several gene lists as input, and it identifies the GO terms that are enriched in any of the input gene lists. GoSurfer estimates a conservative false discovery rate (FDR) for every GO term. The FDR estimation procedure in GoSurfer has two advantages: it does not rely on independence assumption, and it does not assume all the hypotheses are null hypothesis (complete null). Thus GoSurfer's FDR estimates are mildly conservative rather than overly conservative.

RESULTS

We implemented the new procedure for GO analysis in multiple gene clusters into the GoSurfer software. We provide three examples on using GoSurfer to analyze time course gene expression data sets on the differentiation of embryonic stem cells. In the example of analysis of multiple gene clusters, we first used a typical clustering algorithm and identified five gene clusters, representing up-regulation, down-regulation and other patterns in the differentiation time course. Taking all the five gene clusters as input data, GoSurfer reports "cell adhesion" and "muscle contraction" as significant GO terms for the up-regulated cluster, "amino acids metabolism" as a significant GO term for the down-regulated gene cluster, and GoSurfer reports a number of GO terms related to RNA processing and RNA transport as significant terms to a cluster that is up-regulated in both early and late time points. This may suggest that genes for RNA processing and genes for RNA transport are coregulated in the differentiation process of embryonic stem cells.

CONCLUSION

The GoSurfer software is provided to analyze multiple gene clusters and identify GO terms that are enriched in any gene cluster. Gosurfer is available at: www.gosurfer.org.

Differentiation and enrichment of hepatocyte-like cells from human embryonic stem cells in vitro and in vivo

Human embryonic stem cells (hESC) may provide a cell source for functional hepatocytes. The aim of this study is to establish a viable human hepatocyte-like cell line from hESC that can be used for cell-based therapies. The differentiated hESC were enriched by transducing with a lentivirus vector containing the green fluorescent protein (GFP) gene driven by the alpha1-antitrypsin promoter; the GFP gene is expressed in committed hepatocyte progenitors and hepatocytes. GFP+ hESC were purified by laser microdissection and pressure catapulting. In addition, differentiated hESC that were transduced with a lentivirus triple-fusion vector were transplanted into NOD-SCID mice, and the luciferase-induced bioluminescence in the livers was evaluated by a charge-coupled device camera. GFP+ hESC expressed a large series of liver-specific genes, and expression levels of these genes were significantly improved by purifying GFP+ hESC; our results demonstrated that purified differentiated hESC express nearly physiological levels of liver-specific genes and have liver-specific functions that are comparable to those of primary human hepatocytes. The differentiated hESC survived and engrafted in mouse livers, and human liver-specific mRNA and protein species were detected in the transplanted mouse liver and serum at 3 weeks after transplantation. This is the first time that human albumin generated by hESC-derived hepatocytes was detected in the serum of an animal model. This also represents the first successful transplantation of differentiated hESC in an animal liver and the first bioluminescence imaging of hESC in the liver. This study is an initial step in establishing a viable hepatocyte-like cell line from hESC. Disclosure of potential conflicts of interest is found at the end of this article.

A UTF1-based selection system for stable homogeneously pluripotent human embryonic stem cell cultures

Undifferentiated transcription factor 1 (UTF1) was identified first in mouse embryonic stem cells and is also expressed in human embryonic and adult stem cells. UTF1 transcription ceases at the onset of differentiation, which clearly distinguishes it from less sensitive pluripotency markers, such as Oct4 or Nanog. We present here two transgenic hESC lines, named ZUN. Each line harbors one copy of the UTF1 promoter/enhancer driving a resistance gene and yielded highly homogeneous cultures under selection pressure, with a larger proportion of Oct4 and Sox2 positive cells. While ZUN cultures, like parental HUES8 cultures, retained the capacity to differentiate into tissues of all three germ layers using a SICD mouse teratoma model, they surprisingly exhibited an increased refractoriness to various differentiation cues in vitro. Together with its small size of only 2.4 kb for the entire cassette, these features render our selection system a powerful novel tool for many stem cell applications and human somatic cell reprogramming strategies.

Epigenetic dedifferentiation of somatic cells into pluripotency: cellular alchemy in the age of regenerative medicine?

Ever since the derivation of the first human embryonic stem cell line, hopes have persisted for the treatment of a wide range of cellular degenerative diseases. However, significant immuno-incompatibility between donor cells and recipient patients remains an unsolved challenge. Currently, three main strategies are investigated in humans to create autologous pluripotent stem cells: somatic cell nuclear transfer, cell fusion and cell extract incubation. All methods exploit the fact that a somatic genome is amenable to epigenetic dedifferentiation into a more plastic state, presumably through direct exposure to and manipulation by heterologous transcriptional factors. Epigenetic reprogramming includes profound modifications of chromatin structure, but the responsible mechanisms that work in toti- and pluripotent cells remain largely unknown. This review presents a brief introduction to stem cell terminology and epigenetics, followed by a critical examination of the predominant methodologies involved. Finally, the search for specific reprogramming factors is discussed, and obstacles for the clinical implementation of reprogrammed cells are addressed.

Stage-dependent Olig2 expression in motor neurons and oligodendrocytes differentiated from embryonic stem cells

Although embryonic stem (ES) cells are capable of forming any cell type in the body, the mechanisms that control cell type-specific differentiation are largely unknown. In the present study, we examined the process of differentiation to motor neurons and oligodendrocytes from mouse (Olig2GFP) ES cells. Mouse ES cells undergo a sequential process of differentiation over a 3-week period to generate motor neurons and oligodendrocytes. At day 7 of differentiation, Olig2-expressing cells are biased to a neuronal lineage. However, further differentiation (day 32) resulted in the majority of Olig2-expressing cells exhibiting an oligodendrocyte phenotype as well as a reduced ability to make motor neurons. Exposure of human ES cells to Sonic hedgehog (Shh) likewise resulted in enhanced motor neuron differentiation. Our results establish the requirements for directing ES cells to become motor neurons and oligodendrocytes and show that ES cell-derived Olig2 + cells can give rise to both motor neurons and oligodendrocytes, depending on the time at which differentiation is initiated.

Osteogenic differentiation of murine embryonic stem cells is mediated by fibroblast growth factor receptors

The mechanisms involved in the control of embryonic stem (ES) cell differentiation are yet to be fully elucidated. However, it has become clear that the family of fibroblast growth factors (FGFs) are centrally involved. In this study we examined the role of the FGF receptors (FGFRs 1-4) during osteogenesis in murine ES cells. Single cells were obtained after the formation of embryoid bodies, cultured on gelatin-coated plates, and coaxed to differentiate along the osteogenic lineage. Upregulation of genes was analyzed at both the transcript and protein levels using gene array, relative-quantitative PCR (RQ-PCR), and Western blotting. Deposition of a mineralized matrix was evaluated with Alizarin Red staining. An FGFR1-specific antibody was generated and used to block FGFR1 activity in mES cells during osteogenic differentiation. Upon induction of osteogenic differentiation in mES cells, all four FGFRs were clearly upregulated at both the transcript and protein levels with a number of genes known to be involved in osteogenic differentiation including bone morphogenetic proteins (BMPs), collagen I, and Runx2. Cells were also capable of depositing a mineralized matrix, confirming the commitment of these cells to the osteogenic lineage. When FGFR1 activity was blocked, a reduction in cell proliferation and a coincident upregulation of Runx2 with enhanced mineralization of cultures was observed. These results indicate that FGFRs play critical roles in cell recruitment and differentiation during the process of osteogenesis in mES cells. In particular, the data indicate that FGFR1 plays a pivotal role in osteoblast lineage determination.

Isolation, characterization, and differentiation of stem cells derived from the rat amniotic membrane

Stem-cell-based therapies may offer treatments for a variety of intractable diseases. A fundamental goal in stem-cell biology concerns the characterization of diverse populations that exhibit different potentials, growth capabilities, and therapeutic utilities. We report the characterization of a stem-cell population isolated from tissue explants of rat amniotic membrane. Similar to mesenchymal stem cells, these amnion-derived stem cells (ADSCs) express the surface markers CD29 and CD90, but were negative for the lymphohematopoietic markers CD45 and CD11b. ADSCs exist in culture in a multidifferentiated state, expressing neuroectodermal (neurofilament-M), mesodermal (fibronectin), and endodermal (alpha-1-antitrypsin) genes. To assess plasticity, ADSCs were subjected to a number of culture conditions intended to encourage differentiation into neuroectodermal, mesodermal, and endodermal cell types. ADSCs cultured in a defined neural induction media assumed neuronal morphologies and up-regulated neural-specific genes. Under different conditions, ADSCs were capable of differentiating into presumptive bone and fat cells, indicated by the deposition of mineralized matrix and accumulated lipid droplets, respectively. Moreover, ADSCs cultured in media that promotes liver cell differentiation up-regulated liver-specific genes (albumin) and internalized low-density lipoprotein (LDL), consistent with a hepatocyte phenotype. To determine whether this observed plasticity reflects the presence of true stem cells within the population, we have derived individual clones from single cells. Clonal lines recapitulate the expression pattern of parental ADSC cultures and are multipotent. ADSCs have been cultured for 20 passages without losing their plasticity, suggesting long-term self-renewal. In sum, our data suggest that ADSCs and derived clonal lines are capable of long-term self-renewal and multidifferentiation, fulfilling all the criteria of a stem-cell population.

The human fetal cochlea can be a source for auditory progenitors/stem cells isolation

The development of new stem cell-based technologies is creating new hopes in regenerative medicine. Hearing-impaired individuals should benefit greatly from the development of a cell-based regenerative strategy to treat deafness. An important achievement would be to develop a human-based system that could bring the advances made in animal models closer to clinical application. In this work, we have explored the suitability of the developing fetal cochlea to be used as a source for the extraction of auditory progenitor/stem cells. We have established cultures that express critical markers such as NESTIN, SOX2, GATA3 and PAX2. These cultures can be expanded in vitro for several months and differentiating markers such as ATOH1/HATH1 and POU4F3/BRN3C can be induced by manipulating the culture conditions using specific growth factors such as bFGF, EGF and retinoic acid.

Characterization of human embryonic stem cell lines by the International Stem Cell Initiative

The International Stem Cell Initiative characterized 59 human embryonic stem cell lines from 17 laboratories worldwide. Despite diverse genotypes and different techniques used for derivation and maintenance, all lines exhibited similar expression patterns for several markers of human embryonic stem cells. They expressed the glycolipid antigens SSEA3 and SSEA4, the keratan sulfate antigens TRA-1-60, TRA-1-81, GCTM2 and GCT343, and the protein antigens CD9, Thy1 (also known as CD90), tissue-nonspecific alkaline phosphatase and class 1 HLA, as well as the strongly developmentally regulated genes NANOG, POU5F1 (formerly known as OCT4), TDGF1, DNMT3B, GABRB3 and GDF3. Nevertheless, the lines were not identical: differences in expression of several lineage markers were evident, and several imprinted genes showed generally similar allele-specific expression patterns, but some gene-dependent variation was observed. Also, some female lines expressed readily detectable levels of XIST whereas others did not. No significant contamination of the lines with mycoplasma, bacteria or cytopathic viruses was detected.

Human embryonic stem cell transplantation to repair the infarcted myocardium

OBJECTIVE

To test the hypothesis that human embryonic stem cells (hESCs) can be guided to form new myocardium by transplantation into the normal or infarcted heart, and to assess the influence of hESC-derived cardiomyocytes (hESCMs) on cardiac function in a rat model of myocardial infarction (MI).

METHODS

Undifferentiated hESCs (0.5-1x10(6)), human embryoid bodies (hEBs) (4-8 days; 0.5-1x10(6)), 0.1 mm pieces of embryonic stem-derived beating myocardial tissue, and phosphate-buffered saline (control) were injected into the normal or infarcted myocardium of athymic nude rats (n = 58) by direct injection into the muscle or into preimplanted three-dimensional alginate scaffold. By 2-4 weeks after transplantation, heart sections were examined to detect the human cells and differentiation with fluorescent in situ hybridisation, using DNA probes specific for human sex chromosomes and HLA-DR or HLA-ABC immunostaining.

RESULTS

Microscopic examination showed transplanted human cells in the normal, and to a lesser extent in the infarcted myocardium (7/7 vs 2/6; p<0.05). The transplanted hESCs and hEBs rarely created new vessels and did not form new myocardium. Transplantation of hESCM tissue into normal heart produced islands of disorganised myofibres, fibrosis and, in a single case, a teratoma. However, transplantation of hESCMs into the infarcted myocardium did prevent post-MI dysfunction and scar thinning.

CONCLUSIONS

Undifferentiated hESCs and hEBs are not directed to form new myocardium after transplantation into normal or infarcted heart and may create teratoma. Nevertheless, this study shows that hESC-derived cardiomyocyte transplantation can attenuate post-MI scar thinning and left ventricular dysfunction.

Screening of target-specific stress-responsive genes for the development of cell-based biosensors using a DNA microarray

In this study, we describe a straightforward strategy to develop whole cell-based biosensors using fusions of the bacterial bioluminescence genes and the promoters from chemically responsive genes within Escherichia coli, in which chemical target-responsive genes were screened by using the information of gene expression data obtained from DNA microarray analysis. Paraquat was used as a model chemical to trigger gene expression changes of E. coli and to show the DNA microarray-assisted development of whole cell-based biosensors. Gene expression data from the DNA microarray were obtained by time course analysis (10, 30, and 60 min) after exposure to paraquat. After clustering gene expression data obtained by time course analysis, a group of highly expressed genes over the all time courses could be classified. Within this group, three genes expressed highly for overall time points were selected and promoters of these genes were used as fusion partners with reporter genes, lux CDABE, to construct whole cell-based biosensors. The constructed biosensors recognized the presence of model inducer, paraquat, and structural analogue chemicals of paraquat with a high specificity, and the results were reconfirmed by using DNA microarray experiments for those structural analogues. This strategy to develop whole cell-based biosensors assisted by DNA microarray information should be useful in general for constructing chemical-specific or stress-specific biosensors with a high-throughput manner.

Epigenetic signatures of stem-cell identity

Pluripotent stem cells, similar to more restricted stem cells, are able to both self-renew and generate differentiated progeny. Although this dual functionality has been much studied, the search for molecular signatures of 'stemness' and pluripotency is only now beginning to gather momentum. While the focus of much of this work has been on the transcriptional features of embryonic stem cells, recent studies have indicated the importance of unique epigenetic profiles that keep key developmental genes 'poised' in a repressed but activatable state. Determining how these epigenetic features relate to the transcriptional signatures of ES cells, and whether they are also important in other types of stem cell, is a key challenge for the future.

Bioprocessing of embryonic stem cells for drug discovery

Embryonic stem cells provide a potential resource for research and drug screening. To make such a resource feasible, it is necessary to generate cells of sufficient quality and quantity. The challenge is to expand cell numbers while maintaining the fidelity of phenotype and to control and direct differentiation to produce the cell type of interest in a format that is suitable for drug screening. At present, large-scale culturing of human ES cell lines is problematic and provides substantial challenges. This article provides an overview of current bioprocessing techniques that could be used to generate cells for drug discovery applications. This will generate further technical expertise that can be applied in the production of cells for potential therapeutic applications.

Fetal bovine serum enables cardiac differentiation of human embryonic stem cells

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

Embryonic Stem Cells

Stem cells are unique cell populations with the ability to choose between self-renewal and differentiation. Embryonic stem (ES) cells have the ability to form any fully differentiated cell of the body. To date, only three species of mammals have yielded long-term cultures of self-renewing ES cells- mice, monkeys, and humans. These cells have some special requirements to maintain their undifferentiated state in culture, e.g., presence of feeder cells, serum, or cytokines. Many scientific studies have tried to manipulate the growth and differentiation conditions with varied success. Studies of development in model systems, such as mice help our efforts to manipulate human stem cells in vitro. Data are now emerging that ES cells can be directed toward lineage-specific differentiation programs. On the basis of this property, it is likely that human ES cells will provide a useful differentiation culture system to study the mechanisms of human development. Recent advances in culturing ES cells and success in exploiting their pluripotency brings great hope for using human ES cell-based reparative therapy in future.

Human embryonic stem cells: Long term stability, absence of senescence and a potential cell source for neural replacement

Unlike normal somatic cells, human embryonic stem cells (hESCs) can proliferate indefinitely in culture in an undifferentiated state where they do not appear to undergo senescence and yet remain nontransformed. Cells maintain their pluripotency both in vivo and in vitro, exhibit high telomerase activity, and maintain telomere length after prolonged in vitro culture. Thus, hESCs may provide an unlimited cell source for replacement in a number of aging-related neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease as well as other neurological disorders including spinal cord injuries. The ability of hESCs to bypass senescence is lost as hESCs differentiate into fully differentiated somatic cells. Evidence has been accumulated that differences in telomere length, telomerase activity, cell cycle signaling, DNA repair ability, as well as the lack of genomic, mitochondrial and epigenetic changes, may contribute to the lack of senescence in hESC. In this manuscript, we will review recent advances in characterizing hESCs and monitoring changes in these aspects in prolonged cultures. We will focus on the potential roles of several cellular pathways including the telomerase, p53 and the Rb pathways in escaping senescence in hESCs. We will also discuss the genomic and epigenetic changes in long-term hESC culture and their potential roles in bypassing senescence.

A meta-analysis of human embryonic stem cells transcriptome integrated into a web-based expression atlas

Microarray technology provides a unique opportunity to examine gene expression patterns in human embryonic stem cells (hESCs). We performed a meta-analysis of 38 original studies reporting on the transcriptome of hESCs. We determined that 1,076 genes were found to be overexpressed in hESCs by at least three studies when compared to differentiated cell types, thus composing a "consensus hESC gene list." Only one gene was reported by all studies: the homeodomain transcription factor POU5F1/OCT3/4. The list comprised other genes critical for pluripotency such as the transcription factors NANOG and SOX2, and the growth factors TDGF1/CRIPTO and Galanin. We show that CD24 and SEMA6A, two cell surface protein-coding genes from the top of the consensus hESC gene list, display a strong and specific membrane protein expression on hESCs. Moreover, CD24 labeling permits the purification by flow cytometry of hESCs cocultured on human fibroblasts. The consensus hESC gene list also included the FZD7 WNT receptor, the G protein-coupled receptor GPR19, and the HELLS helicase, which could play an important role in hESCs biology. Conversely, we identified 783 genes downregulated in hESCs and reported in at least three studies. This "consensus differentiation gene list" included the IL6ST/GP130 LIF receptor. We created an online hESC expression atlas, http://amazonia.montp.inserm.fr, to provide an easy access to this public transcriptome dataset. Expression histograms comparing hESCs to a broad collection of fetal and adult tissues can be retrieved with this web tool for more than 15,000 genes.

High-throughput identification of genes promoting neuron formation and lineage choice in mouse embryonic stem cells

The potential of embryonic stem cells to differentiate to all cell types makes them an attractive model for development and a potential source of cells for transplantation therapies. Candidate approaches have identified individual genes and proteins that promote the differentiation of embryonic stem cells to desired fates. Here, we describe a rapid large-scale screening strategy for the identification of genes that influence the pluripotency and differentiation of embryonic stem cells to specific fates, and we use this approach to identify genes that induce neuron formation. The power of the strategy is validated by the fact that, of the 15 genes that resulted in the largest increase in neuron number, 8 have previously been implicated in neuronal differentiation or survival, whereas 7 represent novel genes or known genes not previously implicated in neuronal development. This is a simple, fast, and generally applicable strategy for the identification of genes promoting the formation of any specific cell type from embryonic stem cells. Disclosure of potential conflicts of interest is found at the end of this article.

Embryonic stem cell bank: a work proposal

Human embryonic stem cells (hESCs) have an unlimited capacity to proliferate by a self-renewal process and can be differentiated in the three germ layers, opening doors to new clinical therapies to replace missing or damaged cells. The number of research groups and projects using human stem cells has increased largely in the last 5 yr. The creation of stem cell banks is another important step to support the advance of research in this field. Banks must be operated within the strict regulatory famework of good manufacturing practices and good laboratory practices that assure the highest quality standards and must implement a quality system that complies with international quality systems standards. It may also be appropriate to aim at an accreditation in order to assure correct laboratory practices at all times. Stem cell banks should receive the lines previously derived by other groups and hESCs should be provided for groups that justify their use in a research project previously approved by an ethical committee. The assays generally accepted as typical of hESCs together with the microbiological analysis should be performed in order to assure a consistent, reliable, and safe line for the researchers. In this article, the Andalusian Stem Cell Bank proposes a model of a stem cell banking process in order to create a flow diagram of hESC lines and, following the international initiatives in stem cells research, to achieve the full characterization of cells and a standardization of protocols that would simplify the hESCs culture.

Transcriptional analysis of early lineage commitment in human embryonic stem cells

Background

The mechanisms responsible for the maintenance of pluripotency in human embryonic stem cells, and those that drive their commitment into particular differentiation lineages, are poorly understood. In fact, even our knowledge of the phenotype of hESC is limited, because the immunological and molecular criteria presently used to define this phenotype describe the properties of a heterogeneous population of cells.

Results

We used a novel approach combining immunological and transcriptional analysis (immunotranscriptional profiling) to compare gene expression in hESC populations at very early stages of differentiation. Immunotranscriptional profiling enabled us to identify novel markers of stem cells and their differentiated progeny, as well as novel potential regulators of hESC commitment and differentiation. The data show clearly that genes associated with the pluripotent state are downregulated in a coordinated fashion, and that they are co-expressed with lineage specific transcription factors in a continuum during the early stages of stem cell differentiation.

Conclusion

These findings, that show that maintenance of pluripotency and lineage commitment are dynamic, interactive processes in hESC cultures, have important practical implications for propagation and directed differentiation of these cells, and for the interpretation of mechanistic studies of hESC renewal and commitment. Since embryonic stem cells at defined stages of commitment can be isolated in large numbers by immunological means, they provide a powerful model for studying molecular genetics of stem cell commitment in the embryo.

Neurogenic neuroepithelial and radial glial cells generated from six human embryonic stem cell lines in serum-free suspension and adherent cultures

The great potential of human embryonic stem (hES) cells offers the opportunity both for studying basic developmental processes in vitro as well as for drug screening, modeling diseases, or future cell therapy. Defining protocols for the generation of human neural progenies represents a most important prerequisite. Here, we have used six hES cell lines to evaluate defined conditions for neural differentiation in suspension and adherent culture systems. Our protocol does not require fetal serum, feeder cells, or retinoic acid at any step, to induce neural fate decisions in hES cells. We monitored neurogenesis in differentiating cultures using morphological (including on-line follow up), immunocytochemical, and RT-PCR assays. For each hES cell line, in suspension or adherent culture, the same longitudinal progression of neural differentiation occurs. We showed the dynamic transitions from hES cells to neuroepithelial (NE) cells, to radial glial (RG) cells, and to neurons. Thus, 7 days after neural induction the majority of cells were NE, expressing nestin, Sox1, and Pax6. During neural proliferation and differentiation, NE cells transformed in RG cells, which acquired vimentin, BLBP, GLAST, and GFAP, proliferated and formed radial scaffolds. gamma-Aminobutyric acid (GABA)-positive and glutamate positive neurons, few oligodendrocyte progenitors and astrocytes were formed in our conditions and timing. Our system successfully generates human RG cells and could be an effective source for neuronal replacement, since RG cells predominantly generate neurons and provide them with support and guidance.

Comparative transcript profiles of cell cycle-related genes in mouse primordial germ cells, embryonic stem cells and embryonic germ cells

We used cDNA array to compare the relative transcript levels of 96 cell cycle-related genes in mouse primordial germ cells (PGCs), embryonic germ (EG) cells and embryonic stem (ES) cells. Among 38 genes of the G1 phase analysed, Ccnd3 (CyclinD3), Cdkn1c (p57(kip2)), Rb1, and Tceb1l (Skip1-like) were expressed at significantly higher levels in PGCs than in EG and ES cells; Ccnd1 (CyclinD1) was more abundant in EG cells than in PGCs. Except for higher mRNA levels of Ccng (CyclinG1) in EG and ES cells in comparison to PGCs, no difference among 20 genes of the S and 12 genes of G2/M phases was found. Less than half of the 26 genes regarded as DNA damage checkpoint/Trp53/Atm pathway genes showed significant transcript levels in all three cell populations. Among these, the transcript levels of Ube1x and Atm were significantly higher in PGCs than in EG and ES cells while that of Ube3a was higher in these latter. In addition, relatively high mRNA levels of Timp3 characterizes EG cells while transcripts of this gene were very low in PGCs and barely detectable in ES cells. With the exception of Tceb1l, differential transcript levels found in the cDNA array assay were confirmed by real time RT-PCR. Using this method, we also analysed the transcripts of two genes not present in the cDNA array: c-myc, known to be critical for the control of cell cycle in many cell types, and Eras, specifically expressed in ES cells and involved in the control of ES cell proliferation and their tumorigenic properties. While c-myc transcripts were present at similar levels in all three cell types examined, Eras was expressed at high levels in ES cells (10-fold) and even more so in EG cells (almost 40-fold) in comparison to PGCs. Taken together, these results indicate that despite similarities between PGCs and ES or EG cells, their cell cycles are differently regulated. In particular, it appears that PGCs, like most mitotic cells, possess a more regulatable control of G1 phase than EG and ES cells. Moreover, our data provide useful clues for further studies aimed at identifying cell cycle genes critical for PGC growth and their transformation in tumorigenic cells.

Differentiation of osteoblasts from mouse embryonic stem cells without generation of embryoid body

Osteoblasts are cells specialized in extracellular matrix production and mineralization. In collaboration with osteoclasts which are bone-resorbing cells, osteoblasts regulate bone homeostasis. The study of osteoblast differentiation from the earliest states of the differentiation can be performed using embryonic stem cells. Embryonic stem cells are pluripotent cells which have the capacity to give rise to all kinds of cells of the body. The main protocol to differentiate embryonic stem cells into osteoblast uses the generation of embryoid body which is a three-dimensional structure mimicking the developing embryo. Recently, it has been shown that human embryonic stem cells have the capacity to differentiate spontaneously into osteoblasts. In this manuscript, we showed that mouse embryonic stem cells have the capacity to differentiate spontaneously into osteoblasts, which can be visualized by the appearance of mineralization nodules and osteogenic markers.

In vitro characterization of a human neural progenitor cell coexpressing SSEA4 and CD133

The stage-specific embryonic antigen 4 (SSEA4) is commonly used as a cell surface marker to identify the pluripotent human embryonic stem (ES) cells. Immunohistochemistry on human embryonic central nervous system revealed that SSEA4 is detectable in the early neuroepithelium, and its expression decreases as development proceeds. Flow cytometry analysis of forebrain-derived cells demonstrated that the SSEA4-expressing cells are enriched in the neural stem/progenitor cell fraction (CD133(+)), but are rarely codetected with the neural stem cell (NSC) marker CD15. Using a sphere-forming assay, we showed that both subfractions CD133(+)/SSEA4(+) and CD133(+)/CD15(+) isolated from the embryonic forebrain are enriched in neurosphere-initiating cells. In addition CD133, SSEA4, and CD15 expression is sustained in the expanded neurosphere cells and also mark subfractions of neurosphere-initiating cells. Therefore, we propose that SSEA4 associated with CD133 can be used for both the positive selection and the enrichment of neural stem/progenitor cells from human embryonic forebrain.

Is Xenotransplantation of Embryonic Stem Cells a Realistic Option?

To test the purported immune privilege of embryonic stem cells (ESC) in the challenging setting of xenotransplantation, 14 immunocompetent baboons were subjected to a coronary artery occlusion-reperfusion sequence and, two weeks later, randomized to receive in-scar injections of culture medium or cardiac-committed mouse ESC engineered to express fluorescent reporter genes driven by cardiac-specific promoters. Two months after transplantation, left ventricular function, as assessed by echocardiography, deteriorated to a similar extent in control and treated baboons. This correlated with failure to identify the grafted cells by X-gal histology and immunofluorescence. Rejection did not seem to be mediated by xenoantibodies, but rather by T lymphocytes and natural killer cells as suggested by positive immunostaining for CD3 and CD56 early after transplantation. There was no increase in circulating levels of regulatory T cells. These data raise a cautionary note about the immune privilege of ESC and suggest that from a mere immunologic standpoint, ESC xenotransplantation is likely to be an unrealistic challenge.

Enhanced yield of neuroepithelial precursors and midbrain-like dopaminergic neurons from human embryonic stem cells using the bone morphogenic protein antagonist noggin

It is currently not known whether dopamine (DA) neurons derived from human embryonic stem cells (hESCs) can survive in vivo and alleviate symptoms in models of Parkinson disease (PD). Here, we report the use of Noggin (a bone morphogenic protein antagonist) to induce neuroectodermal cell development and increase the yield of DA neurons from hESCs. A combination of stromal-derived inducing activity and Noggin markedly enhanced the generation of neuroepithelial progenitors that could give rise to DA neurons. In addition, Noggin diminished the occurrence of a fibroblast-like Nestin-positive precursor population that differentiated into myocytes. After transplantation of differentiated hESCs to a rodent model of PD, some grafts contained human midbrain-like DA neurons. This protocol demonstrates hESC derivation and survival of human DA neurons appropriate for cell therapy in PD.

Hemangioblasts representing a functional endothelio-hematopoietic entity in ontogeny, postnatal life, and CML neovasculogenesis

The life-long interdependencies/interactions between hemato- and endotheliopoiesis suggest that they form a supplementary functional entity. This view is compatible with the concept of stem cell plasticity as a reversible continuum and is substantiated by the common hematopoietic-endothelial stem cell, i.e., hemangioblasts, with bidirectional, reversible gene transcription and persistence in postnatal life. Indeed, embryonal stem cells/hemangioblasts appear to form a reservior in the adult with the possibility of dedifferentiation of more differentiated progenitor cells back to hemangioblasts. The recent detection of BCR/ABL fusion proteins in endothelial cells during vascular neoangiogenesis in CML suggests that endothelial cells are part of the neoplastic clone, and extends the concept of a functional entity to include CML angiogenesis. Thus, hemangioblasts rather than committed hematopoietic stem cells appear to be target cells for the first oncogenic hit in CML, which could occur as early as during the first steps of embryonal stem cell differentiation towards hemato-endotheliopoiesis and/or in hemangioblasts persisting in adults. The relation of the other leukemias to hemangioblasts is not known.

Embryonic stem cells remain highly pluripotent following long term expansion as aggregates in suspension bioreactors

Increasing attention has been drawn towards pluripotent embryonic stem cells (ESCs) and their potential use as the primary material in various tissue engineering applications. Successful clinical implementation of this technology would require a quality controlled reproducible culture system for the expansion of the cells to be used in the generation of functional tissues. Recently, we showed that suspension bioreactors could be used in the regulated large-scale expansion of highly pluripotent murine ESCs. The current study illustrates that these bioreactor protocols can be adapted for long term culture and that murine ESC cultures remain highly undifferentiated, when serially passaged in suspension bioreactors for extended periods. Flow cytometry analysis and gene expression profiles of several pluripotency markers, in addition to colony and embryoid body (EB) formation tests were conducted at the start and end of the experiment and all showed that the ESC cultures remained highly undifferentiated over extended culture time in suspension. In vivo teratoma formation and in vitro differentiation into neural, cardiomyocyte, osteoblast and chondrocyte lineages, performed at the end of the long term culture, further supported the presence of functional and undifferentiated ESCs in the expanded population. Overall, this system enables the controlled expansion of highly pluripotent murine ESC populations.

Molecular basis of pregnancy-induced breast cancer protection

We have postulated that the lifetime protective effect of an early pregnancy against breast cancer is due to the complete differentiation of the mammary gland characterized by a specific genomic signature imprinted by the physiological process of pregnancy. In the present work, we show evidence that the breast tissue of postmenopausal parous women has had a shifting of stem cell 1 to stem cell 2 with a genomic signature different from similar structures derived from postmenopausal nulliparous women that have stem cell 1. Those genes that are significantly different are grouped in major categories on the basis of their putative functional significance. Among them are those gene transcripts related to immune surveillance, DNA repair, transcription, chromatin structure/activators/co-activators, growth factor and signal transduction pathway, transport and cell trafficking, cell proliferation, differentiation, cell adhesion, protein synthesis and cell metabolism. From these data, it was concluded that during pregnancy there are significant genomic changes that reflect profound alterations in the basic physiology of the mammary gland that explain the protective effect against carcinogenesis. The implication of this knowledge is that when the genomic signature of protection or refractoriness to carcinogenesis is acquired by the shifting of stem cell 1 to stem cell 2, the hormonal milieu induced by pregnancy or pregnancy-like conditions is no longer required. This is a novel concept that challenges the current knowledge that a chemopreventive agent needs to be given for a long period to suppress a metabolic pathway or abrogate the function of an organ.