Differences between human and mouse embryonic stem cells

Upregulation of NF-kappaB upon differentiation of mouse embryonic stem cells

NF-kappaB is a transcriptional regulator involved in many biological processes including proliferation, survival, and differentiation. Recently, we reported that expression and activity of NF-kappaB is comparatively low in undifferentiated human embryonic stem (ES) cells, but increases during differentiation. Here, we found a lower expression of NF-kappaB p65 protein in mouse ES cells when compared with mouse embryonic fibroblast cells. Protein levels of NF-kappaB p65 and relB were clearly enhanced during retinoic acid-induced differentiation. Furthermore, increased DNA binding activity of NF-kappaB in response to TNF-alpha, an agonist of NF-kappaB signaling, was seen in differentiated but not undifferentiated mouse ES cells. Taken together with our previous data in human ES cells, it is likely that NF-kappaB expression and activity of the NF-kappaB signaling pathway is comparatively low in undifferentiated ES cells, but increases during differentiation of ES cells in general.

Expression profiling of nuclear receptors in human and mouse embryonic stem cells

Nuclear receptors (NRs) regulate gene expression in essential biological processes including differentiation and development. Here we report the systematic profiling of NRs in human and mouse embryonic stem cell (ESC) lines and during their early differentiation into embryoid bodies. Expression of the 48 human and mouse NRs was assessed by quantitative real-time PCR. In general, expression of NRs between the two human cell lines was highly concordant, whereas in contrast, expression of NRs between human and mouse ESCs differed significantly. In particular, a number of NRs that have been implicated previously as crucial regulators of mouse ESC biology, including ERRbeta, DAX-1, and LRH-1, exhibited diametric patterns of expression, suggesting they may have distinct species-specific functions. Taken together, these results highlight the complexity of the transcriptional hierarchy that exists between species and governs early development. These data should provide a unique resource for further exploration of the species-specific roles of NRs in ESC self-renewal and differentiation.

Generation of new human embryonic stem cell lines with diploid and triploid karyotypes

Human pluripotent embryonic stem cells (hESC) have great promise for research into human developmental biology and the development of cell therapies for the treatment of diseases. To meet the increased demand for characterized hESC lines, we present the derivation and characterization of five hESC lines on mouse embryonic fibroblast cells. Our stem cell lines are characterized by morphology, long-term expansion, and expression profiles of a number of specific markers, including TRA-1-60, TRA-1-81, alkaline phosphatase, connexin 43, OCT-4, NANOG, CXCR4, NODAL, LEFTY2, THY-1, TDGF1, PAX6, FOXD3, SOX2, EPHA2, FGF4, TAL1, AC133 and REX-1. The pluripotency of the cell line was confirmed by spontaneous differentiation under in vitro conditions. Whereas all of the cell lines expressed all the characteristics of undifferentiated pluripotent hESC, two of the cell lines carried a triploid karyotype.

Embryonic stem cell test remastered: comparison between the validated EST and the new molecular FACS-EST for assessing developmental toxicity in vitro

The embryonic stem cell test (EST) represents a reliable, scientifically validated in vitro system for the detection and classification of compounds according to their teratogenic potency. However, some serious issues were frequently raised against the widespread implementation and practicability of the EST in its original version. Most importantly, the evaluation of the morphological endpoint of beating cell agglomerates requires extensive experimental experience and is prone to misjudgment. Also, the testing period of 10 days is too long and costly to be attractive for industries interested in high-throughput screening of potential drug candidates. These drawbacks prompted us to work out a new molecular approach based on analysis of the expression of certain marker proteins specific for developing heart tissue. We have previously reported that quantitative flow cytometry of marker proteins (i.e., sarcomeric myosin heavy chain and alpha-actinin) can be performed at day 7 in embryonic stem cells from mice and combined with concurrent cell viability analysis. In the present study, extensive investigations were performed in order to explore the predictive power and validity of the newly established EST, subsequently referred to as molecular fluorescence activated cell sorting (FACS)-EST, by applying and comparing a set of 10 well-known embryotoxicants that encompasses the full range of chemical inherent embryotoxic potencies possible. While the molecular FACS-EST offered the same sensitivity compared to the validated EST protocol, the test duration could be significantly reduced. Due to significant improvements, this new molecular method holds promise as a sensitive, more rapid and reproducible screen highly suited to predict developmental toxicity in vivo from in vitro data.

Cell surface biomarkers of embryonic stem cells

Embryonic stem cells (ESCs) can give rise to any adult cell type and thus offer enormous potential for regenerative medicine and drug discovery. Molecular biomarkers serve as valuable tools to classify and isolate ESCs and to monitor their differentiation state by antibody-based techniques. A number of biomarkers, such as certain cell surface antigens, are used to assign pluripotent ESCs; however, accumulating evidence suggests that ESCs are heterogeneous in morphology, phenotype and function, and are thereby classified into subpopulations characterized by multiple sets of molecular biomarkers. Biomarker discovery is also important for ESC biology to elucidate the molecular mechanisms that regulate pluripotency and differentiation. This review summarizes studies of ESC biomarker discovery. "Genome-wide" expression profiling of ESC mRNAs and proteins and direct analyses of the cell surface subproteome have demonstrated that ESCs express a diverse range of biomarkers, cell surface antigens, and signaling molecules found in different cell lineages, as well as a number of key molecules that assure "stemness". Clearly, future quantitative proteomics approaches will enhance our knowledge of the stage- and lineage-specific expression of the proteome and its temporal changes upon differentiation, and provide a more detailed view of nascent and clonally amplified ESCs.

Paving the axonal highway: from stem cells to myelin repair

Multiple sclerosis (MS), a demyelinating disorder of the central nervous system (CNS), remains among the most prominent and devastating diseases in contemporary neurology. Despite remarkable advances in anti-inflammatory therapies, the inefficiency or failure of myelin-forming oligodendrocytes to remyelinate axons and preserve axonal integrity remains a major impediment for the repair of MS lesions. To this end, the enhancement of remyelination through endogenous and exogenous repair mechanisms and the prevention of axonal degeneration are critical objectives for myelin repair therapies. Thus, recent advances in uncovering myelinating cell sources and the intrinsic and extrinsic factors that govern neural progenitor differentiation and myelination may pave a way to novel strategies for myelin regeneration. The scope of this review is to discuss the potential sources of stem/progenitor cells for CNS remyelination and the molecular mechanisms underlying oligodendrocyte myelination.

Notch signaling activation in human embryonic stem cells is required for embryonic, but not trophoblastic, lineage commitment

The Notch signaling pathway plays important roles in cell-fate determination during embryonic development and adult life. In this study, we focus on the role of Notch signaling in governing cell-fate choices in human embryonic stem cells (hESCs). Using genetic and pharmacological approaches, we achieved both blockade and conditional activation of Notch signaling in several hESC lines. We report here that activation of Notch signaling is required for undifferentiated hESCs to form the progeny of all three embryonic germ layers, but not trophoblast cells. In addition, transient Notch signaling pathway activation enhanced generation of hematopoietic cells from committed hESCs. These new insights into the roles of Notch in hESC-fate determination may help to efficiently direct hESC differentiation into therapeutically relevant cell types.

Germline competent embryonic stem cells derived from rat blastocysts

Rats have important advantages over mice as an experimental system for physiological and pharmacological investigations. The lack of rat embryonic stem (ES) cells has restricted the availability of transgenic technologies to create genetic models in this species. Here, we show that rat ES cells can be efficiently derived, propagated, and genetically manipulated in the presence of small molecules that specifically inhibit GSK3, MEK, and FGF receptor tyrosine kinases. These rat ES cells express pluripotency markers and retain the capacity to differentiate into derivatives of all three germ layers. Most importantly, they can produce high rates of chimerism when reintroduced into early stage embryos and can transmit through the germline. Establishment of authentic rat ES cells will make possible sophisticated genetic manipulation to create models for the study of human diseases.

Hematopoiesis from Human Embryonic Stem Cells: Overcoming the Immune Barrier in Stem Cell Therapies

The multipotency and proliferative capacity of human embryonic stem cells (hESCs) make them a promising source of stem cells for transplant therapies and of vital importance given the shortage in organ donation. Recent studies suggest some immune privilege associated with hESC-derived tissues. However, the adaptability of the immune system makes it unlikely that fully differentiated tissues will permanently evade immune rejection. One promising solution is to induce a state of immune tolerance to a hESC line using tolerogenic hematopoietic cells derived from it. This could provide acceptance of other differentiated tissues from the same line. However, this approach will require efficient multilineage hematopoiesis from hESCs. This review proposes that more efficient differentiation of hESCs to the tolerogenic cell types required is most likely to occur through applying knowledge gained of the ontogeny of complex regulatory signals used by the embryo for definitive hematopoietic development in vivo. Stepwise formation of mesoderm, induction of definitive hematopoietic stem cells, and the application of factors key to their self-renewal may improve in vitro production both quantitatively and qualitatively.

Cultivation of Human Embryonic Stem Cells Without the Embryoid Body Step Enhances Osteogenesis In Vitro

Osteogenic cultures of embryonic stem cells (ESCs) are predominately derived from three-dimensional cell spheroids called embryoid bodies (EBs). An alternative method that has been attempted and merits further attention avoids EBs through the immediate separation of ESC colonies into single cells. However, this method has not been well characterized and the effect of omitting the EB step is unknown. Herein, we report that culturing human embryonic stem cells (hESCs) without the EB stage leads to a sevenfold greater number of osteogenic cells and to spontaneous bone nodule formation after 10-12 days. In contrast, when hESCs were differentiated as EBs for 5 days followed by plating of single cells, bone nodules formed after 4 weeks only in the presence of dexamethasone. Furthermore, regardless of the inclusion of EBs, bone matrix formed, including cement line matrix and mineralized collagen, which displayed apatitic mineral (PO4) with calcium-to-phosphorous ratios similar to those of hydroxyapatite and human bone. Together these results demonstrate that culturing hESCs without an EB step can be used to derive large quantities of functional osteogenic cells for bone tissue engineering.

Human mammary progenitor cell fate decisions are products of interactions with combinatorial microenvironments

In adult tissues, multi-potent progenitor cells are some of the most primitive members of the developmental hierarchies that maintain homeostasis. That progenitors and their more mature progeny share identical genomes, suggests that fate decisions are directed by interactions with extrinsic soluble factors, ECM, and other cells, as well as physical properties of the ECM. To understand regulation of fate decisions, therefore, would require a means of understanding carefully choreographed combinatorial interactions. Here we used microenvironment protein microarrays to functionally identify combinations of cell-extrinsic mammary gland proteins and ECM molecules that imposed specific cell fates on bipotent human mammary progenitor cells. Micropatterned cell culture surfaces were fabricated to distinguish between the instructive effects of cell-cell versus cell-ECM interactions, as well as constellations of signaling molecules; and these were used in conjunction with physiologically relevant 3 dimensional human breast cultures. Both immortalized and primary human breast progenitors were analyzed. We report on the functional ability of those proteins of the mammary gland that maintain quiescence, maintain the progenitor state, and guide progenitor differentiation towards myoepithelial and luminal lineages.

Large scale production of stem cells and their derivatives

Stem cells have been envisioned to become an unlimited cell source for regenerative medicine. Notably, the interest in stem cells lies beyond direct therapeutic applications. They might also provide a previously unavailable source of valuable human cell types for screening platforms, which might facilitate the development of more efficient and safer drugs. The heterogeneity of stem cell types as well as the numerous areas of application suggests that differential processes are mandatory for their in vitro culture. Many of the envisioned applications would require the production of a high number of stem cells and their derivatives in scalable, well-defined and potentially clinical compliant manner under current good manufacturing practice (cGMP). In this review we provide an overview on recent strategies to develop bioprocesses for the expansion, differentiation and enrichment of stem cells and their progenies, presenting examples for adult and embryonic stem cells alike.

Neural transplantation and stem cells

Recent results have raised important questions on our ability to amplify stem cell populations in sufficient numbers as to be useful for therapy. Several reports have indicated that human stem cell populations harvested from the adult have low or undetectable telomerase levels, age in culture, and may not be propagated indefinitely. Other groups have shown that stem cells age and as such, their properties will have changed depending on the age of the individual from which they are harvested, and the time for which they are propagated in culture. Other groups have shown that cells maintained in culture may undergo alterations as they are propagated, and that these alterations may alter the predicted behavior of stem cells. Yet others have shown that human cells differ from their counterparts in other species in significant ways and have identified important difficulties in assessing cells in a xeno environment. Clinical colleagues have identified issues of variability and difficulties in the long-term follow-up that is being requested. Researchers in the stem cell field focused on translational work need to develop a practical plan that takes into account such difficulties while developing manufacturing protocols, designing animal studies, or developing trial protocols. Such proactive planning will be critical in ensuring a successful transition from the bench to the clinic.

Laminin isoforms in human embryonic stem cells: synthesis, receptor usage and growth support

To reveal the functional intrinsic niche of human embryonic stem cells (hESC) we examined the production of basement membrane (BM) proteins and the presence of their receptors in feeder-free cell culture conditions. In addition, we investigated binding of hESCs to purified human BM proteins and identified the receptors mediating these contacts. Also, we tested whether purified human laminin (Lm) isoforms have a role in hESC self-renewal and growth in short-term cultures. The results show that hESCs synthesize Lm alpha(1) and Lm alpha(5) chains together with Lm beta(1) and gamma(1) chains suggesting the production of Lms-111 and -511 into the culture medium and deposits on cells. hESCs contain functionally important integrin (Int) subunits, Int beta(1), alpha(3), alpha(6), alpha(5), beta(5) and alpha(V), as well as the Lm alpha(5) receptor, Lutheran (Lu) glycoprotein and its truncated form, basal cell adhesion molecule (B-CAM). In cell adhesion experiments, Int beta(1) was crucial for adhesion to most of the purified human BM proteins. Lu/B-CAM mediated adhesion to Lm-511 together with Int alpha(3)beta(1), and was essential for the adhesion of hESCs to embryonic feeder cells. Adhesion to Lm-411 was mediated by Int alpha(6)beta(1). Lm-511 supported hESC growth in defined medium equally well as Matrigel. These results provide consequential information of the biological role of BM in hESCs, warranting further investigation of BM biology of human pluripotent stem cells.

Analysis of mammalian gene batteries reveals both stable ancestral cores and highly dynamic regulatory sequences

Analysis of the evolutionary dynamics of target gene batteries controlled by 16 different transcription factors reveals stable ancestral cores and highly dynamic regulatory sequences

Background

Changes in gene regulation are suspected to comprise one of the driving forces for evolution. To address the extent of cis-regulatory changes and how they impact on gene regulatory networks across eukaryotes, we systematically analyzed the evolutionary dynamics of target gene batteries controlled by 16 different transcription factors.

Results

We found that gene batteries show variable conservation within vertebrates, with slow and fast evolving modules. Hence, while a key gene battery associated with the cell cycle is conserved throughout metazoans, the POU5F1 (Oct4) and SOX2 batteries in embryonic stem cells show strong conservation within mammals, with the striking exception of rodents. Within the genes composing a given gene battery, we could identify a conserved core that likely reflects the ancestral function of the corresponding transcription factor. Interestingly, we show that the association between a transcription factor and its target genes is conserved even when we exclude conserved sequence similarities of their promoter regions from our analysis. This supports the idea that turnover, either of the transcription factor binding site or its direct neighboring sequence, is a pervasive feature of proximal regulatory sequences.

Conclusions

Our study reveals the dynamics of evolutionary changes within metazoan gene networks, including both the composition of gene batteries and the architecture of target gene promoters. This variation provides the playground required for evolutionary innovation around conserved ancestral core functions.

Differentiation of nonhuman primate embryonic stem cells along neural lineages

The differentiation of embryonic stem cells (ESCs) into neurons and glial cells represents a promising cell-based therapy for neurodegenerative diseases. Because the rhesus macaque is physiologically and phylogenetically similar to humans, it is a clinically relevant animal model for ESC research. In this study, the pluripotency and neural differentiation potential of a rhesus monkey ESC line (ORMES6) was investigated. ORMES6 was derived from an in vitro produced blastocyst, which is the same way human ESCs have been derived. ORMES6 stably expressed the embryonic transcription factors POU5F1 (Oct4), Sox2 and NANOG. Stage-specific embryonic antigen 4 (SSEA 4) and the glycoproteins TRA-1-60 and TRA-1-81 were also expressed. The embryoid bodies (EBs) formed from ORMES6 ESCs spontaneously gave rise to cells of three germ layers. After exposure to basic fibroblast growth factor (bFGF) for 14-16 days, columnar rosette cells formed in the EB outgrowths. Sox2, microtubule-associated protein (MAP2), beta-tublinIII and glial fibrillary acidic protein (GFAP) genes and Nestin, FoxD3, Pax6 and beta-tublinIII antigens were expressed in the rosette cells. Oct4 and NANOG expression were remarkably down-regulated in these cells. After removal of bFGF from the medium, the rosette cells differentiated along neural lineages. The differentiated cells expressed MAP2, beta-tublinIII, Neuro D and GFAP genes. Most differentiated cells expressed early neuron-specific antigen beta-tublinIII (73+/-4.7%) and some expressed intermediate neuron antigen MAP2 (18+/-7.2%). However, some differentiated cells expressed the glial cell antigens A2B5 (7.17%+/-1.2%), GFAP (4.93+/-1.9%), S100 (7+/-3.5%) and O4 (0.27+/-0.2%). The rosette cells were transplanted into the striatum of immune-deficient NIHIII mice. The cells persisted for approximately 2 weeks and expressed Ki67, NeuN, MAP2 and GFAP. These results demonstrate that the rhesus monkey ESC line ORMES6 retains the pluripotent characteristics of ESCs and can be efficiently induced to differentiate along neural lineages.

The growth factor environment defines distinct pluripotent ground states in novel blastocyst-derived stem cells

Pluripotent stem cell lines can be derived from blastocyst embryos, which yield embryonic stem cell lines (ES cells), as well as the postimplantation epiblast, which gives rise to epiblast stem cell lines (EpiSCs). Remarkably, ES cells and EpiSCs display profound differences in the combination of growth factors that maintain their pluripotent state. Molecular and functional differences between these two stem cell types demonstrate that the tissue of origin and/or the growth factor milieu may be important determinants of the stem cell identity. We explored how developmental stage of the tissue of origin and culture growth factor conditions affect the stem cell pluripotent state. Our findings indicate that novel stem cell lines, with unique functional and molecular properties, can be generated from murine blastocyst embryos. We demonstrate that the culture growth factor environment and cell-cell interaction play a critical role in defining several unique and stable stem cell ground states.

Robust generation of hemangioblastic progenitors from human embryonic stem cells

BACKGROUND

Human embryonic stem cells (hESCs) are a potentially inexhaustible source of cells for replacement therapy. However, successful preclinical and clinical progress requires efficient and controlled differentiation towards the specific differentiated cell fate.

METHODS

We previously developed a strategy to generate blast cells (BCs) from hESCs that were capable of differentiating into vascular structures as well as into all hematopoietic cell lineages. Although the BCs were shown to repair damaged vasculature in multiple animal models, the large-scale generation of cells under these conditions was challenging. Here we report a simpler and more efficient method for robust generation of hemangioblastic progenitors.

RESULTS

In addition to eliminating several expensive factors that are unnecessary, we demonstrate that bone morphogenetic protein (BMP)-4 and VEGF are necessary and sufficient to induce hemangioblastic commitment and development from hESCs during early stages of differentiation. BMP-4 and VEGF significantly upregulate T-brachyury, KDR, CD31 and Lmo2 gene expression, while dramatically downregulating Oct-4 expression. The addition of basic FGF during growth and expansion was found to further enhance BC development, consistently generating approximately 1 x 10(8) BCs from one six well plate of hESCs.

CONCLUSION

This new method represents a significantly improved system for generating hemangioblasts from hESCs, and although simplified, results in an eightfold increase in cell yield.

Expression profiling of human glial precursors

BACKGROUND

We have generated gene expression databases for human glial precursors, neuronal precursors, astrocyte precursors and neural stem cells and focused on comparing the profile of glial precursors with that of other populations.

RESULTS

A total of 14 samples were analyzed. Each population, previously distinguished from each other by immunocytochemical analysis of cell surface markers, expressed genes related to their key differentiation pathways. For the glial precursor cell population, we identified 458 genes that were uniquely expressed. Expression of a subset of these individual genes was validated by RT-PCR. We also report genes encoding cell surface markers that may be useful for identification and purification of human glial precursor populations.

CONCLUSION

We provide gene expression profile for human glial precursors. Our data suggest several signaling pathways that are important for proliferation and differentiation of human glial precursors. Such information may be utilized to further purify glial precursor populations, optimize media formulation, or study the effects of glial differentiation.

Rho-associated kinase inhibitor Y-27632 promotes survival of cynomolgus monkey embryonic stem cells

Non-human primates are suitable models for preclinical research aimed at cell-replacement therapies. Recently, it has been reported that Rho-associated kinase inhibitor Y-27632 markedly reduced dissociation-induced apoptosis of human embryonic stem (hES) cells, and is expected as a novel supplement for hES cell maintenance or differentiation inductions; however, the effects of the chemical are still to be determined in model animals. Here, we demonstrated the effect of Y-27632 on cynomolgus monkey ES (cyES) cells. Also, in cyES cells, Y-27632 treatment dramatically improved the efficiency of colony formation from single cells without affecting the pluripotent state and karyotype. Y-27632 supplementation was also effective for feeder-free culture and differentiation induction. Neural stem cells directly induced from cyES cells could give rise to neurons, astrocytes and dopamine producing cells. The present result not only suggests that the chemical was effective for improving the culture system of primate ES cells, but also the similarity between cyES and hES cells regarding the reactions to the chemical, which might be further evidence that cyES cells are superior models for hES cells.

Evolutionarily conserved transcriptional co-expression guiding embryonic stem cell differentiation

Background

Understanding the molecular mechanisms controlling pluripotency in embryonic stem cells (ESCs) is of central importance towards realizing their potentials in medicine and science. Cross-species examination of transcriptional co-expression allows elucidation of fundamental and species-specific mechanisms regulating ESC self-renewal or differentiation.

Methodology/Principal Findings

We examined transcriptional co-expression of ESCs from pathways to global networks under the framework of human-mouse comparisons. Using generalized singular value decomposition and comparative partition around medoids algorithms, evolutionarily conserved and divergent transcriptional co-expression regulating pluripotency were identified from ESC-critical pathways including ACTIVIN/NODAL, ATK/PTEN, BMP, CELL CYCLE, JAK/STAT, PI3K, TGFβ and WNT. A set of transcription factors, including FOX, GATA, MYB, NANOG, OCT, PAX, SOX and STAT, and the FGF response element were identified that represent key regulators underlying the transcriptional co-expression. By transcriptional intervention conducted in silico, dynamic behavior of pathways was examined, which demonstrate how much and in which specific ways each gene or gene combination effects the behavior transition of a pathway in response to ESC differentiation or pluripotency induction. The global co-expression networks of ESCs were dominated by highly connected hub genes such as IGF2, JARID2, LCK, MYCN, NASP, OCT4, ORC1L, PHC1 and RUVBL1, which are possibly critical in determining the fate of ESCs.

Conclusions/Significance

Through these studies, evolutionary conservation at genomic, transcriptomic, and network levels is shown to be an effective predictor of molecular factors and mechanisms controlling ESC development. Various hypotheses regarding mechanisms controlling ESC development were generated, which could be further validated by in vitro experiments. Our findings shed light on the systems-level understanding of how ESC differentiation or pluripotency arises from the connectivity or networks of genes, and provide a “road-map” for further experimental investigation.

Generation of pluripotent stem cells from adult human testis

Human primordial germ cells and mouse neonatal and adult germline stem cells are pluripotent and show similar properties to embryonic stem cells. Here we report the successful establishment of human adult germline stem cells derived from spermatogonial cells of adult human testis. Cellular and molecular characterization of these cells revealed many similarities to human embryonic stem cells, and the germline stem cells produced teratomas after transplantation into immunodeficient mice. The human adult germline stem cells differentiated into various types of somatic cells of all three germ layers when grown under conditions used to induce the differentiation of human embryonic stem cells. We conclude that the generation of human adult germline stem cells from testicular biopsies may provide simple and non-controversial access to individual cell-based therapy without the ethical and immunological problems associated with human embryonic stem cells.

Human mastoid periosteum-derived stem cells: promising candidates for skeletal tissue engineering

Currently, mesenchymal stem cells (MSCs) are considered as the most eligible cells for skeletal tissue engineering. However, factors such as difficult stimulation and control of differentiation in vivo hamper their clinical use. In contrast, periosteum or periosteum-derived cells (PCs) are routinely clinically applied for bone and cartilage repair. PCs have often been named MSCs but, although cells of osteochondrogenic lineages arise from MSCs, it is unclear whether periosteum really contains MSCs. Our aim was to investigate the MSC-like character of PCs derived from the periosteum of mastoid bone. Harvesting of periosteum from mastoid bone is easy, so mastoid represents a good source for the isolation of PCs. Therefore, we analysed the MSC-like growth behaviour and the expression of embryonic, ectodermal, endodermal and mesodermal markers by microarray and FACS technology, and the multilineage developmental capacity of human PCs. Regarding clinical relevance, experiments were performed in human serum-supplemented medium. We show that PCs do not express early embryonic stem cell markers such as Oct4 and Nanog, or the marker of haematopoietic stem cells CD34, but express some other MSC markers. Osteogenesis resulted in the formation of calcified matrix, increased alkaline phosphatase activity, and induction of the osteogenic marker gene osteocalcin. Staining of proteoglycans and deposition of type II collagen documented chondrogenic development. As shown for the first time, adipogenic stimulation of mastoid-derived PCs resulted in the formation of lipid droplets and expression of the adipogenic marker genes aP2 and APM1. These results suggest MSC-like PCs from mastoid as candidates for therapy of complex skeletal defects.

Highly efficient transient gene expression and gene targeting in primate embryonic stem cells with helper-dependent adenoviral vectors

Human embryonic stem (hES) cells are regarded as a potentially unlimited source of cellular materials for regenerative medicine. For biological studies and clinical applications using primate ES cells, the development of a general strategy to obtain efficient gene delivery and genetic manipulation, especially gene targeting via homologous recombination (HR), would be of paramount importance. However, unlike mouse ES (mES) cells, efficient strategies for transient gene delivery and HR in hES cells have not been established. Here, we report that helper-dependent adenoviral vectors (HDAdVs) were able to transfer genes in hES and cynomolgus monkey (Macaca fasicularis) ES (cES) cells efficiently. Without losing the undifferentiated state of the ES cells, transient gene transfer efficiency was approximately 100%. Using HDAdVs with homology arms, approximately one out of 10 chromosomal integrations of the vector was via HR, whereas the rate was only approximately 1% with other gene delivery methods. Furthermore, in combination with negative selection, approximately 45% of chromosomal integrations of the vector were targeted integrations, indicating that HDAdVs would be a powerful tool for genetic manipulation in hES cells and potentially in other types of human stem cells, such as induced pluripotent stem (iPS) cells.

Heterokaryon-based reprogramming of human B lymphocytes for pluripotency requires Oct4 but not Sox2

Differentiated cells can be reprogrammed through the formation of heterokaryons and hybrid cells when fused with embryonic stem (ES) cells. Here, we provide evidence that conversion of human B-lymphocytes towards a multipotent state is initiated much more rapidly than previously thought, occurring in transient heterokaryons before nuclear fusion and cell division. Interestingly, reprogramming of human lymphocytes by mouse ES cells elicits the expression of a human ES-specific gene profile, in which markers of human ES cells are expressed (hSSEA4, hFGF receptors and ligands), but markers that are specific to mouse ES cells are not (e.g., Bmp4 and LIF receptor). Using genetically engineered mouse ES cells, we demonstrate that successful reprogramming of human lymphocytes is independent of Sox2, a factor thought to be required for induced pluripotent stem (iPS) cells. In contrast, there is a distinct requirement for Oct4 in the establishment but not the maintenance of the reprogrammed state. Experimental heterokaryons, therefore, offer a powerful approach to trace the contribution of individual factors to the reprogramming of human somatic cells towards a multipotent state.

One of the most pressing objectives of medical research today is the development of approaches to restore the function of tissues damaged by accident or disease. An important goal for this work is the isolation of stem cell populations to replace missing or nonfunctioning cells. Because problems of immune rejection are likely to occur unless the recipient and donor stem cells are very closely matched, a desirable strategy is to convert differentiated cells (such as white blood cells) from patients into immature tailored stem cell populations. Here, we have experimentally fused human white blood cells and mouse embryonic stem cells and shown that this reprograms them to become stem-like. This kind of “differentiation reversal” is shown to be rapid and stable. It requires the stem cell–specific factor Oct4, but does not require Sox2. This approach allows the identification of factors that are required to reprogram human blood cells with the long-term perspective to eventually generate patient-specific stem cells.

Laminin-511 but not -332, -111, or -411 enables mouse embryonic stem cell self-renewal in vitro

We tested specific laminin (LN) isoforms for their ability to serve as substrata for maintaining mouse embryonic stem (ES) cells pluripotent in vitro in the absence of leukemia inhibitory factor or any other differentiation inhibitors or feeder cells. Recombinant human LN-511 alone was sufficient to enable self-renewal of mouse ES cells for up to 169 days (31 passages). Cells cultured on LN-511 maintained expression of pluripotency markers, such as Oct4, Sox2, Tert, UTF1, and Nanog, during the entire period, and cells cultured for 95 days (17 passages) were used to generate chimeric mice. LN-332 enabled ES cells proliferation but not pluripotency. In contrast, under the same conditions LN-111, Matrigel, and gelatin caused rapid differentiation, whereas LN-411 and poly-d-lysine did not support survival. ES cells formed a thin monolayer on LN-511 that differed strikingly from typical dense cluster ES cell morphology. However, expression of pluripotency markers was not affected by morphological changes. The effect was achieved at low ES cell density (<200 cell/mm(2)). The ability of LN-511 and LN-332 to support ES cell proliferation correlated with increased cell contact area with those adhesive substrata. ES cells interacted with LN-511 via beta1-integrins, mostly alpha6beta1 and alphaVbeta1. This is the first demonstration that certain extracellular matrix molecules can support ES cell self-renewal in the absence of differentiation inhibitors and at low cell density. The results suggest that recombinant laminin isoforms can provide a basis for defined surface coating systems for feeder-free maintenance of undifferentiated mammalian ES cells in vitro. Disclosure of potential conflicts of interest is found at the end of this article.

Feeder-free monolayer cultures of human embryonic stem cells express an epithelial plasma membrane protein profile

Human embryonic stem cells (hESCs) are often cocultured on mitotically inactive fibroblast feeder cells to maintain their undifferentiated state. Under these growth conditions, hESCs form multilayered colonies of morphologically heterogeneous cells surrounded by flattened mesenchymal cells. In contrast, hESCs grown in feeder cell-conditioned medium on Matrigel instead tend to grow as monolayers with uniform morphology. Using mass spectrometry and immunofluorescence microscopy, we showed that hESCs under these conditions primarily express proteins belonging to epithelium-related cell-cell adhesion complexes, including adherens junctions, tight junctions, desmosomes, and gap junctions. This indicates that monolayers of hESCs cultured under feeder-free conditions retain a homogeneous epithelial phenotype similar to that of the upper central cell layer of colonies maintained on feeder cells. Notably, feeder-free hESCs also coexpressed vimentin, which is usually associated with mesenchyme, suggesting that these cells may have undergone epithelium-to-mesenchyme transitions, indicating differentiation. However, if grown on a "soft" substrate (Hydrogel), intracellular vimentin levels were substantially reduced. Moreover, when hESCs were transferred back to feeder cells, expression of vimentin was again absent from the epithelial cell population. These results imply that on tissue culture substrates, vimentin expression is most likely a stress-induced response, unrelated to differentiation. Disclosure of potential conflicts of interest is found at the end of this article.

Whole-blastocyst culture followed by laser drilling technology enhances the efficiency of inner cell mass isolation and embryonic stem cell derivation from good- and poor-quality mouse embryos: new insights for derivation of human embryonic stem cell lines

The optimization of human embryonic stem (hES) cell line derivation methods is challenging because many worldwide laboratories have neither access to spare human embryos nor ethical approval for using supernumerary human embryos for hES cell derivation purposes. Additionally, studies performed directly on human embryos imply a waste of precious human biological material. In this study, we developed a new strategy based on the combination of whole-blastocyst culture followed by laser drilling destruction of the trophoectoderm for improving the efficiency of inner cell mass (ICM) isolation and ES cell derivation using murine embryos. Embryos were divided into good- and poor-quality embryos. We demonstrate that the efficiency of both ICM isolation and ES cell derivation using this strategy is significantly superior to whole-blastocyst culture or laser drilling technology itself. Regardless of the ICM isolation method, the ES cell establishment depends on a feeder cell growth surface. Importantly, this combined methodology can be successfully applied to poor-quality blastocysts that otherwise would not be suitable for laser drilling itself nor immunosurgery in an attempt to derive ES cell lines due to the inability to distinguish the ICM. The ES cell lines derived by this combined method were characterized and shown to maintain a typical morphology, undifferentiated phenotype, and in vitro and in vivo three germ layer differentiation potential. Finally, all ES cell lines established using either technology acquired an aneuploid karyotype after extended culture periods, suggesting that the method used for ES cell derivation does not seem to influence the karyotype of the ES cells after extended culture. This methodology may open up new avenues for further improvements for the derivation of hES cells, the majority of which are derived from frozen, poor-quality human embryos.

The pursuit of ES cell lines of domesticated ungulates

In contrast to differentiated cells, embryonic stem cells (ESC) maintain an undifferentiated state, have the ability to self-renew, and exhibit pluripotency, i.e., they can give rise to most if not all somatic cell types and to the germ cells, egg and sperm. These characteristics make ES cell lines important resources for the advancement of human regenerative medicine, and, if established for domesticated ungulates, would help make possible the improvement of farm animals through their contribution to genetic engineering technology. Combining other genetic engineering technologies, such as somatic cell nuclear transfer with ESC technology may result in synergistic gains in the ability to precisely make and study genetic alterations in mammals. Unfortunately, despite significant advances in our understanding of human and mouse ESC, the derivation of ES cell lines from ungulate species has been unsuccessful. This may result from a lack of understanding of species-specific mechanisms that promote or influence cell pluripotency. Thorough molecular characterizations, including the elucidation of stem cell "marker" signaling cascade hierarchy, species-appropriate pluripotency markers, and pluripotency-associated chromatin alterations in the genomes of ungulate species, should improve the chances of developing efficient, reproducible technologies for the establishment of ES cell lines of economically important species like the pig, cow, goat, sheep and horse.

Tyrosine kinase signalling in embryonic stem cells

Pluripotent ES (embryonic stem) cells can be expanded in culture and induced to differentiate into a wide range of cell types. Self-renewal of ES cells involves proliferation with concomitant suppression of differentiation. Some critical and conserved pathways regulating self-renewal in both human and mouse ES cells have been identified, but there is also evidence suggesting significant species differences. Cytoplasmic and receptor tyrosine kinases play important roles in proliferation, survival, self-renewal and differentiation in stem, progenitor and adult cells. The present review focuses on the role of tyrosine kinase signalling for maintenance of the undifferentiated state, proliferation, survival and early differentiation of ES cells.

Deconstructing human embryonic stem cell cultures: niche regulation of self-renewal and pluripotency

The factors and signaling pathways controlling pluripotent human cell properties, both embryonic and induced, have not been fully investigated. Failure to account for functional heterogeneity within human embryonic stem cell (hESC) cultures has led to inconclusive results in previous work examining extrinsic influences governing hESC fate (self renewal vs. differentiation vs. death). Here, we attempt to reconcile these inconsistencies with recent reports demonstrating that an autologously produced in vitro niche regulates hESCs. Moreover, we focus on the reciprocal paracrine signals within the in vitro hESC niche allowing for the maintenance and/or expansion of the hESC colony-initiating cell (CIC). Based on this, it is clear that separation of hESC-CICs, apart from their differentiated derivatives, will be essential in future studies involving their molecular regulation. Understanding how extrinsic factors control hESC self-renewal and differentiation will allow us to culture and differentiate these pluripotent cells with higher efficiency. This knowledge will be essential for clinical applications using human pluripotent cells in regenerative medicine.

Proteomics and human embryonic stem cells

The derivation of human embryonic stem cells (hESCs) brought cell therapy-based regenerative medicine significantly closer to clinical application. However, expansion of undifferentiated cells and their directed differentiation in vitro have proven difficult to control. This is mainly because of a lack of knowledge of the intracellular signaling events that direct these complex processes. Additionally, extracellular factors, either secreted by feeder cells that support self-renewal and maintain pluripotency or present in serum supplementing proprietary culture media, that influence hESC behavior are largely unknown. Xeno-free media that effectively support long-term hESC self-renewal and differentiation to specific types of specialized cells are only slowly becoming available. Microarray-based transcriptome analyses have produced valuable gene expression profiles of hESCs and indicated changes in transcription that occur during differentiation. However, proteins are the actual effectors of these events and changes in their levels do not always match changes in their corresponding mRNA. Furthermore, information on posttranslational modifications that influence the activity of pivotal proteins is still largely missing. Over the years, mass spectrometry has experienced major breakthroughs in high-throughput identification of proteins and posttranslational modifications in cells under different conditions. Mass spectrometry-based proteomic techniques are being applied with increasing frequency to analyze hESCs, as well as media conditioned by feeder cells, and have generated proteome profiles that not only support, but also complement, existing microarray data. In this review, the various proteomic studies on hESCs and feeder cells are discussed. In a meta-analysis, comparison of published data sets distinguished 32 intracellular proteins and 16 plasma membrane proteins that are present in multiple hESC lines but not in differentiated cells, which were therefore likely to include proteins important for hESCs. In addition, 13 and 24 proteins, respectively, were commonly found in different feeder cell lines of mouse and human origin, some of which may be extracellular signaling molecules that play a key role in the undifferentiated propagation of hESCs. These findings underscore the power of mass spectrometry-based techniques to identify novel proteins associated with hESCs by studying these cells in an unbiased, discovery-oriented manner on a proteome-wide scale.

Trophoblast differentiation defect in human embryonic stem cells lacking PIG-A and GPI-anchored cell-surface proteins

Pluripotent human embryonic stem (hES) cells can differentiate into various cell types derived from the three embryonic germ layers and extraembryonic tissues such as trophoblasts. The mechanisms governing lineage choices of hES cells are largely unknown. Here, we report that we established two independent hES cell clones lacking a group of cell surface molecules, glycosyl-phosphatidyl-inositol-anchored proteins (GPI-APs). The GPI-AP deficiency in these two hES clones is due to the deficiency in the gene expression of PIG-A (phosphatidyl-inositol-glycan class A), which is required for the first step of GPI synthesis. GPI-AP-deficient hES cells were capable of forming embryoid bodies and initiating cell differentiation into the three embryonic germ layers. However, GPI-AP-deficient hES cells failed to form trophoblasts after differentiation induction by embryoid body formation or by adding exogenous BMP4. The defect in trophoblast formation was due to the lack of GPI-anchored BMP coreceptors, resulting in the impairment of full BMP4 signaling activation in the GPI-AP-deficient hES cells. These data reveal that GPI-AP-enhanced full activation of BMP signaling is required for human trophoblast formation.

Bcl2, a transcriptional target of p38alpha, is critical for neuronal commitment of mouse embryonic stem cells

Mouse embryonic stem (ES) cells remain pluripotent in vitro when grown in the presence of leukemia inhibitory factor (LIF) cytokine. LIF starvation leads to cell commitment, and part of the ES-derived differentiated cells die by apoptosis together with caspase3-cleavage and p38alpha activation. Inhibition of p38 activity by chemical compounds (PD169316 and SB203580), along with LIF withdrawal, leads to different outcomes on cell apoptosis, giving the opportunity to study the influence of apoptosis on cell differentiation. By gene profiling studies on ES-derived differentiated cells treated or not with these inhibitors, we have characterized the common and specific set of genes modulated by each inhibitor. We have also identified key genes that might account for their different survival effects. In addition, we have demonstrated that some genes, similarly regulated by both inhibitors (upregulated as Bcl2, Id2, Cd24a or downregulated as Nodal), are bona fide p38alpha targets involved in neurogenesis and found a correlation with their expression profiles and the onset of neuronal differentiation triggered upon retinoic acid treatment. We also showed, in an embryoid body differentiation protocol, that overexpression of EGFP (enhanced green fluorescent protein)-BCL2 fusion protein and repression of p38alpha are essential to increase formation of TUJ1-positive neuronal cell networks along with an increase in Map2-expressing cells.

Conventional pluripotency markers are unspecific for bovine embryonic-derived cell-lines

Bovine embryonic stem cells are of potentially big value in transgenic research and studies of lineage commitment and development. Nevertheless, key aspects of the establishment of bovine embryonic stem cells such as the identification of specific pluripotency markers need to be clarified to achieve successful results. Bovine blastocysts were produced in vitro and cultured for 8 days up to the expanded or hatched stage. The trophectoderm, the inner cell mass and its embryonic stem cell-derived lines, all showed a common positive immunocytochemical staining for stage-specific embryonic antigen-4, tumour-rejection antigen gp96 and NANOG proteins. The antigenic profile obtained partially agrees with previous data from bovine and other species. Until a validated pluripotent bovine stem cell marker can be identified, it might be advisable to combine the use of epiblast and trophoblast-specific markers to rule out the presence of early committed trophectoderm cells in bovine embryonic stem cell cultures.

Neural stem cells in the mammalian brain

New fundamental results on stem cell biology have been obtained in the past 15 years. These results allow us to reinterpret the functioning of the cerebral tissue in health and disease. Proliferating stem cells have been found in the adult brain, which can be involved in postinjury repair and can replace dead cells under specific conditions. Numerous genomic mechanisms controlling stem cell proliferation and differentiation have been identified. The involvement of stem cells in the genesis of malignant tumors has been demonstrated. Neural stem cell tropism toward tumors has been shown. These findings suggest new lines of research on brain functioning and development. Stem cells can be used to develop radically new treatments of neurodegenerative and cancer diseases of the brain.

A highly homozygous and parthenogenetic human embryonic stem cell line derived from a one-pronuclear oocyte following in vitro fertilization procedure

Homozygous human embryonic stem cells (hESCs) are thought to be better cell sources for hESC banking because their human leukocyte antigen (HLA) haplotype would strongly increase the degree of matching for certain populations with relatively smaller cohorts of cell lines. Homozygous hESCs can be generated from parthenogenetic embryos, but only heterozygous hESCs have been established using the current strategy to artificially activate the oocyte without second polar body extrusion. Here we report the first successful derivation of a human homozygous ESC line (chHES-32) from a one-pronuclear oocyte following routine in vitro fertilization treatment. chHES-32 cells express common markers and genes with normal hESCs. They have been propagated in an undifferentiated state for more than a year (>P50) and have maintained a stable karyotype of 46, XX. When differentiated in vivo and in vitro, chHES-32 cells can form derivatives from all three embryonic germ layers. The almost undetectable expression of five paternally expressed imprinted genes and their HLA genotype identical to the oocyte donor indicated their parthenogenetic origin. Using genome-wide single-nucleotide polymorphism analysis and DNA fingerprinting, the homozygosity of chHES-32 cells was further confirmed. The results indicated that 'unwanted' one-pronuclear oocytes might be a potential source for human homozygous and parthenogenetic ESCs, and suggested an alternative strategy for obtaining homozygous hESC lines from parthenogenetic haploid oocytes.

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.