Regulation of single-cell genome organization into TADs and chromatin nanodomains

The genome folds into a hierarchy of three-dimensional structures within the nucleus. At the sub-megabase scale, chromosomes form topologically associating domains (TADs)1-4. However, how TADs fold in single cells is elusive. Here, we reveal TAD features inaccessible to cell population analysis by using super-resolution microscopy. TAD structures and physical insulation associated with their borders are variable between individual cells, yet chromatin intermingling is enriched within TADs compared to adjacent TADs in most cells. The spatial segregation of TADs is further exacerbated during cell differentiation. Favored interactions within TADs are regulated by cohesin and CTCF through distinct mechanisms: cohesin generates chromatin contacts and intermingling while CTCF prevents inter-TAD contacts. Furthermore, TADs are subdivided into discrete nanodomains, which persist in cells depleted of CTCF or cohesin, whereas disruption of nucleosome contacts alters their structural organization. Altogether, these results provide a physical basis for the folding of individual chromosomes at the nanoscale.

Genomic Repeats Categorize Genes with Distinct Functions for Orchestrated Regulation

Repetitive elements are abundantly distributed in mammalian genomes. Here, we reveal a striking association between repeat subtypes and gene function. SINE, L1, and low-complexity repeats demarcate distinct functional categories of genes and may dictate the time and level of gene expression by providing binding sites for different regulatory proteins. Importantly, imaging and sequencing analysis show that L1 repeats sequester a large set of genes with specialized functions in nucleolus- and lamina-associated inactive domains that are depleted of SINE repeats. In addition, L1 transcripts bind extensively to its DNA in embryonic stem cells (ESCs). Depletion of L1 RNA in ESCs leads to relocation of L1-enriched chromosomal segments from inactive domains to the nuclear interior and de-repression of L1-associated genes. These results demonstrate a role of L1 DNA and RNA in gene silencing and suggest a general theme of genomic repeats in orchestrating the function, regulation, and expression of their host genes.

Spatiotemporal Characterizations of Spontaneously Beating Cardiomyocytes with Adaptive Reference Digital Image Correlation

We developed an Adaptive Reference-Digital Image Correlation (AR-DIC) method that enables unbiased and accurate mechanics measurements of moving biological tissue samples. We applied the AR-DIC analysis to a spontaneously beating cardiomyocyte (CM) tissue, and could provide correct quantifications of tissue displacement and strain for the beating CMs utilizing physiologically-relevant, sarcomere displacement length-based contraction criteria. The data were further synthesized into novel spatiotemporal parameters of CM contraction to account for the CM beating homogeneity, synchronicity, and propagation as holistic measures of functional myocardial tissue development. Our AR-DIC analyses may thus provide advanced non-invasive characterization tools for assessing the development of spontaneously contracting CMs, suggesting an applicability in myocardial regenerative medicine.

High glucose concentrations mask cellular phenotypes in a stem cell model of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a neurodevelopmental disorder caused by deletions in the TSC1 or TSC2 genes that is associated with epilepsy in up to 90% of patients. Seizures are suggested to start in benign brain tumors, cortical tubers, or in the perituberal tissue making these tubers an interesting target for further research into mechanisms underlying epileptogenesis in TSC. Animal models of TSC insufficiently capture the neurodevelopmental biology of cortical tubers, and hence, human stem cell-based in vitro models of TSC are being increasingly explored in attempts to recapitulate tuber development and epileptogenesis in TSC. However, in vitro culture conditions for stem cell-derived neurons do not necessarily mimic physiological conditions. For example, very high glucose concentrations of up to 25 mM are common in culture media formulations. As TSC is potentially caused by a disruption of the mechanistic target of rapamycin (mTOR) pathway, a main integrator of metabolic information and intracellular signaling, we aimed to examine the impact of different glucose concentrations in the culture media on cellular phenotypes implicated in tuber characteristics. Here, we present preliminary data from a pilot study exploring cortical neuronal differentiation on human embryonic stem cells (hES) harboring a TSC2 knockout mutation (TSC2-/-) and an isogenic control line (TSC2+/+). We show that the commonly used high glucose media profoundly mask cellular phenotypes in TSC2-/- cultures during neuronal differentiation. These phenotypes only become apparent when differentiating TSC2+/+ and TSC2-/- cultures in more physiologically relevant conditions of 5 mM glucose suggesting that the careful consideration of culture conditions is vital to ensuring biological relevance and translatability of stem cell models for neurological disorders such as TSC. This article is part of the Special Issue "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures".

Instant Hepatic Differentiation of Human Embryonic Stem Cells Using Activin a and a Deleted Variant of HGF

Human embryonic stem (hES) cells have the ability to differentiate into a variety of different cell lineages and potentially provide a source of differentiated cells for many therapeutic uses. Here we investigated an efficient method of hepatic differentiation from hES cells. A human ES cell line, KhES-1, was used and maintained by a nonfeeder method. KhES-1 cells were cultured for 5 days in the presence of human activin A (50 ng/ml) and then treated with a deleted variant of hepatocyte growth factor (dHGF) at 0, 100, or 500 ng/ml for 7 days. The resultant cells were biologically analyzed. The expression of the endodermal genes SOX17 and FOXA2 increased in KhES-1 cells after activin A treatment. In contrast, Oct4, a self-renewal undifferentiated marker, decreased in a time-dependent manner in KhES-1 cells. Following a 7-day treatment of the resultant cells with dHGF, especially at 500 ng/ml, KhES-1 cells showed an expression of the hepatic makers albumin, AFP, and CK18. Transitional electron microscopy showed well-developed glycogen rosettes and a gap junction in KhES-1 cells treated with 500 ng/ml of dHGF. We developed an efficient method to differentiate KhES-1 cells into hepatocyte-like cells in vitro using 50 ng/ml of activin A and 500 ng/ml of dHGF.

Coupling between chromosome intermingling and gene regulation during cellular differentiation

In this article, we summarize current findings for the emergence of biophysical properties such as nuclear stiffness, chromatin compaction, chromosome positioning, and chromosome intermingling during stem cell differentiation, which eventually correlated with the changes of gene expression profiles during cellular differentiation. An overview is first provided to link stem cell differentiation with alterations in nuclear architecture, chromatin compaction, along with nuclear and chromatin dynamics. Further, we highlight the recent biophysical and molecular approaches, imaging methods and computational developments in characterizing transcription-related chromosome organization especially chromosome intermingling and nano-scale chromosomal contacts. Finally, the article ends with an outlook towards the emergence of a functional roadmap in setting up chromosome positioning and intermingling in a cell type specific manner during cellular differentiation.

Nucleolar Reorganization Upon Site-Specific Double-Strand Break Induction

DNA damage response (DDR) in ribosomal genes and mechanisms of DNA repair in embryonic stem cells (ESCs) are less explored nuclear events. DDR in ESCs should be unique due to their high proliferation rate, expression of pluripotency factors, and specific chromatin signature. Given short population doubling time and fast progress through G1 phase, ESCs require a sustained production of rRNA, which leads to the formation of large and prominent nucleoli. Although transcription of rRNA in the nucleolus is relatively well understood, little is known about DDR in this nuclear compartment. Here, we directed formation of double-strand breaks in rRNA genes with I- PpoI endonuclease, and we studied nucleolar morphology, DDR, and chromatin modifications. We observed a pronounced formation of I- PpoI-induced nucleolar caps, positive on BRCA1, NBS1, MDC1, γH2AX, and UBF1 proteins. We showed interaction of nucleolar protein TCOF1 with HDAC1 and TCOF1 with CARM1 after DNA injury. Moreover, H3R17me2a modification mediated by CARM1 was found in I- PpoI-induced nucleolar caps. Finally, we report that heterochromatin protein 1 is not involved in DNA repair of nucleolar caps.

ROCK inhibitor is not required for embryoid body formation from singularized human embryonic stem cells

We report a technology to form human embryoid bodies (hEBs) from singularized human embryonic stem cells (hESCs) without the use of the p160 rho-associated coiled-coil kinase inhibitor (ROCKi) or centrifugation (spin). hEB formation was tested under four conditions: +ROCKi/+spin, +ROCKi/-spin, -ROCKi/+spin, and -ROCKi/-spin. Cell suspensions of BG01V/hOG and H9 hESC lines were pipetted into non-adherent hydrogel substrates containing defined microwell arrays. hEBs of consistent size and spherical geometry can be formed in each of the four conditions, including the -ROCKi/-spin condition. The hEBs formed under the -ROCKi/-spin condition differentiated to develop the three embryonic germ layers and tissues derived from each of the germ layers. This simplified hEB production technique offers homogeneity in hEB size and shape to support synchronous differentiation, elimination of the ROCKi xeno-factor and rate-limiting centrifugation treatment, and low-cost scalability, which will directly support automated, large-scale production of hEBs and hESC-derived cells needed for clinical, research, or therapeutic applications.

[Effect of embryonic anlage allografts of the rat spinal cord on growth of regenerating fibers of the recipient nerve]

A comparative study of the effect of tissue and suspension allografts of an embryonic spinal cord on regeneration of nerve fibers of impaired (by application of a ligature) sciatic nerve in rats was conducted. It was demonstrated that unlike tissue grafts that reach a large volume 21 and 60 days after transplantation, suspension grafts do not inhibit the growth of axons of the recipient to the periphery. It was established that introduction of a suspension of dissociated cells of the spinal cord embryonic anlages (but not fragments of these anlages) into the impaired sciatic nerve in rats results in an increase in the amount of myelinated regenerating nerve fibers of the recipient 60 days after the operation.

Subcellular localization of ENS-1/ERNI in chick embryonic stem cells

The protein of retroviral origin ENS-1/ERNI plays a major role during neural plate development in chick embryos by controlling the activity of the epigenetic regulator HP1γ, but its function in the earlier developmental stages is still unknown. ENS-1/ERNI promoter activity is down-regulated upon differentiation but the resulting protein expression has never been examined. In this study, we present the results obtained with custom-made antibodies to gain further insights into ENS-1 protein expression in Chicken embryonic stem cells (CES) and during their differentiation. First, we show that ENS-1 controls the activity of HP1γ in CES and we examined the context of its interaction with HP1γ. By combining immunofluorescence and western blot analysis we show that ENS-1 is localized in the cytoplasm and in the nucleus, in agreement with its role on gene's promoter activity. During differentiation, ENS-1 decreases in the cytoplasm but not in the nucleus. More precisely, three distinct forms of the ENS-1 protein co-exist in the nucleus and are differently regulated during differentiation, revealing a new level of control of the protein ENS-1. In silico analysis of the Ens-1 gene copies and the sequence of their corresponding proteins indicate that this pattern is compatible with at least three potential regulation mechanisms, each accounting only partially. The results obtained with the anti-ENS-1 antibodies presented here reveal that the regulation of ENS-1 expression in CES is more complex than expected, providing new tracks to explore the integration of ENS-1 in CES cells regulatory networks.

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

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

Intracerebral neural stem cell transplantation improved the auditory of mice with presbycusis

Stem cell-based regenerative therapy is a potential cellular therapeutic strategy for patients with incurable brain diseases. Embryonic neural stem cells (NSCs) represent an attractive cell source in regenerative medicine strategies in the treatment of diseased brains. Here, we assess the capability of intracerebral embryonic NSCs transplantation for C57BL/6J mice with presbycusis in vivo. Morphology analyses revealed that the neuronal rate of apoptosis was lower in the aged group (10 months of age) but not in the young group (2 months of age) after NSCs transplantation, while the electrophysiological data suggest that the Auditory Brain Stem Response (ABR) threshold was significantly decreased in the aged group at 2 weeks and 3 weeks after transplantation. By contrast, there was no difference in the aged group at 4 weeks post-transplantation or in the young group at any time post-transplantation. Furthermore, immunofluorescence experiments showed that NSCs differentiated into neurons that engrafted and migrated to the brain, even to sites of lesions. Together, our results demonstrate that NSCs transplantation improve the auditory of C57BL/6J mice with presbycusis.

Unique kinetics of Oct3/4 microlocalization following dissociation of human embryonic stem cell colonies

To investigate the effects of the Rho-dependent protein kinase (ROCK) inhibitor Y-27632 on the kinetics of E-cadherin, F-actin, and Oct3/4 distributions in dissociated human embryonic stem (hES) cells and to analyze their interactions morphologically, Y-27632-treated [R(i) (+)] and untreated [R(i) (-)] cells were immunohistochemically stained for E-cadherin and Oct3/4 within 24h of dissociation and also for F-actin. Furthermore, the gene expression of E-cadherin, Oct3/4, and RhoA was confirmed by quantitative real-time RT-PCR. E-cadherin expression intensified linearly along the membranes of R(i) (+) cells or intercellular junctions in cell clusters. F-actin accumulated along the periphery of cells and expanded in a web-like manner along junctions in cell clusters, and Oct3/4 was restricted to the nucleus within few hours of dissociation. However, R(i) (-) cells exhibited deformation and blebbing and appeared to die over time. E-cadherin exhibited a punctate pattern along the periphery, after which it accumulated on one or both sides of the cytoplasm. Actin filaments were concentrated at the bleb bases. Oct3/4 was detected in the cytoplasm, not in the nucleus the recovery of integrated E-cadherin distribution. Quantitative real-time RT-PCR revealed RhoA upregulation and E-cadherin downregulation at 12h after dissociation. Oct3/4 gene expression was unaffected by ROCK inhibition. These results revealed that the cooperative nature of hES cells is maintained by the E-cadherin-actin cytoskeleton system along with the restricted distribution of Oct3/4 in the nucleus. RhoA activation followed by dissociation disorders this system and accelerates cell death, which is partially suppressed by ROCK inhibition.

Mannosidase 2, alpha 1 deficiency is associated with ricin resistance in embryonic stem (ES) cells

Host gene products required for mediating the action of toxins are potential targets for reversing or controlling their pathogenic impact following exposure. To identify such targets libraries of insertional gene-trap mutations generated with a PiggyBac transposon in Blm-deficient embryonic stem cells were exposed to the plant toxin, ricin. Resistant clones were isolated and genetically characterised and one was found to be a homozygous mutant of the mannosidase 2, alpha 1 (Man2α1) locus with a matching defect in the homologous allele. The causality of the molecular lesion was confirmed by removal of the transposon following expression of PB-transposase. Comparative glycomic and lectin binding analysis of the Man2α1 (-/-) ricin resistant cells revealed an increase in the levels of hybrid glycan structures and a reduction in terminal β-galactose moieties, potential target receptors for ricin. Furthermore, naïve ES cells treated with inhibitors of the N-linked glycosylation pathway at the mannosidase 2, alpha 1 step exhibited either full or partial resistance to ricin. Therefore, we conclusively identified mannosidase 2, alpha 1 deficiency to be associated with ricin resistance.

[Comparative characteristics of new human embryonic stem cell lines SC5, SC6, SC7, and SC3a]

Numerous human embryonic stem cell lines with different genetic background are widely used as cell models for fundamental, biomedical and pharmacological research. New hES cell lines SC5, SC6, SC7, and SC3a are derived from the blastocysts and maintained on mitotically inactivated human feeder cells. All derived hES cell lines passed through more than 120 cell population doublings, retained normal diploid karyotype and ability of in vitro differentiation in the derivates of three germ layers. These lines express the markers of undifferentiated hES cells: Oct-4, Nanog, SSEA-4, TRA-1-60, and alkaline phosphatase. Moreover, undifferentiated cells of SC5, SC6, and SC7 lines expressed germ line specific genes DPPA3/STELLA and DAZL and did not express somatic lineages specific genes. In contrast, undifferentiated cells of SC3a line did not express DPPA3/STELLA and DAZL but expressed extra embryonic endoderm cell markers GATA4 and AFP. Double staining of SC5 and SC3a colonies by antibodies against transcription factors Oct-4 and GATA4 has demonstrated that most SC3a cells in colonies were positive for both factors. Furthermore, the cells of SC5, SC6, SC7 lines but not of SC3a line formed teratomas containing the derivates of the three germ layers. These results indicate that, in contrast to the other cell lines, the cells in the SC3a colonies represent an early committed cell population. Moreover, expression of the multidrug resistance transporter gene ABCG2 was detected in undifferentiated cells and differentiating embryonic bodies during 10 days of all lines by immunofluorescent and RT-PCR analyses, whereas RT-PCR analysis has revealed up-regulation of the ABCB1 transporter gene expression in differentiating embryoid bodies of SC5, SC6, and SC7 cells only. Thus, these findings demonstrate different characteristics and differentiation potential of SC5, SC6, SC7, and SC3a hES cell lines which were derived in different conditions.

Large-scale expansion of mouse embryonic stem cells on microcarriers

A large-scale stirred culture system for the expansion of mouse embryonic stem cells (mESCs) in spinner flasks under serum-free conditions was established using macroporous microcarriers for cell attachment and growth. This type of microcarrier was chosen as it potentially offers more protection to cells against shear stress in the absence of serum compared to microporous ones. In addition, methods to characterize ESCs after large-scale expansion were established. The pluripotency of expanded mESCs was evaluated based on both flow cytometry and alkaline phosphatase staining. Envisaging the application of ESCs as a potential source of neural progenitors, the neural commitment potential of cells after expansion in the spinner flask was also determined by culturing cells in serum-free adherent monolayer conditions.

Osteogenic differentiation of embryonic stem cells in 2D and 3D culture

Osteoblasts are the cells that contribute to the formation and function of bone tissue. Knowledge of their biology is important to understanding of the normal processes of bone repair, the development of diseases affecting bone tissue, and to the investigation of approaches to improve bone repair and to treat or prevent bone diseases. Osteoblasts can be readily isolated from bone tissues and grown in culture, and under relatively simple culture conditions, they will recapitulate many aspects of their normal biology. These culture conditions can be also applied to adult stem cells, such as mesenchymal/bone marrow stromal stem cells. More recently, these studies have been extended to include embryonic stem cells. This chapter provides detailed step-by-step protocols to investigate the differentiation of embryonic stem cells into osteoblasts. Several 2D and 3D culture methods are presented and enable comparisons to be made on the efficiency and mechanisms of osteogenic differentiation. Emphasis is also placed on methods to analyse and confirm osteogenic differentiation.

Metabolic properties of chicken embryonic stem cells

Cellular energy metabolism correlates with cell fate, but the metabolic properties of chicken embryonic stem (chES) cells are poorly understood. Using a previously established chES cell model and electron microscopy (EM), we found that undifferentiated chES cells stored glycogen. Additionally, undifferentiated chES cells expressed lower levels of glucose transporter 1 (GLUT1) and phosphofructokinase (PFK) mRNAs but higher levels of hexokinase 1 (HK1) and glycogen synthase (GYS) mRNAs compared with control primary chicken embryonic fibroblast (CEF) cells, suggesting that chES cells direct glucose flux towards the glycogenic pathway. Moreover, we demonstrated that undifferentiated chES cells block gluconeogenic outflow and impede the accumulation of glucose-6-phosphate (G6P) from this pathway, as evidenced by the barely detectable levels of pyruvate carboxylase (PCX) and mitochondrial phosphoenolpyruvate carboxykinase (PCK2) mRNAs. Additionally, cell death occurred in undifferentiated chES cells as shown by Hoechst 33342 and propidium iodide (PI) double staining, but it could be rescued by exogenous G6P. However, we found that differentiated chES cells decreased the glycogen reserve through the use of PAS staining. Moreover, differentiated chES cells expressed higher levels of GLUT1, HK1 and PFK mRNAs, while the level of GYS mRNA remained similar in control CEF cells. These data indicate that undifferentiated chES cells continue to synthesize glycogen from glucose at the expense of G6P, while differentiated chES cells have a decreased glycogen reserve, which suggests that the amount of glycogen is indicative of the chES cell state.

Biocompatibility of synthetic poly(ester urethane)/polyhedral oligomeric silsesquioxane matrices with embryonic stem cell proliferation and differentiation

Incorporation of polyhedral oligomeric silsesquioxanes (POSS) into poly(ester urethanes) (PEU) as a building block results in a PEU/POSS hybrid polymer with increased mechanical strength and thermostability. An attractive feature of the new polymer is that it forms a porous matrix when cast in the form of a thin film, making it potentially useful in tissue engineering. In this study, we present detailed microscopic analysis of the PEU/POSS matrix and demonstrate its biocompatibility with cell culture. The PEU/POSS polymer forms a continuous porous matrix with open pores and interconnected grooves. From SEM image analysis, it is calculated that there are about 950 pores/mm(2) of the matrix area with pore diameter size in the range 1-15 µm. The area occupied by the pores represents approximately 7.6% of the matrix area. Using mouse embryonic stem cells (ESCs), we demonstrate that the PEU/POSS matrix provides excellent support for cell proliferation and differentiation. Under the cell culture condition optimized to maintain self-renewal, ESCs grown on a PEU/POSS matrix exhibit undifferentiated morphology, express pluripotency markers and have a similar growth rate to cells grown on gelatin. When induced for differentiation, ESCs underwent dramatic morphological change, characterized by the loss of clonogenecity and increased cell size, with well-expanded cytoskeleton networks. Differentiated cells are able to form a continuous monolayer that is closely embedded in the matrix. The excellent compatibility between the PEU/POSS matrix and ESC proliferation/differentiation demonstrates the potential of using PEU/POSS polymers in future ESC-based tissue engineering.

Engineering embryonic stem-cell aggregation allows an enhanced osteogenic differentiation in vitro

Pluripotent embryonic stem (ES) cells hold great promise for the field of tissue engineering, with numerous studies investigating differentiation into various cell types including cardiomyocytes, chondrocytes, and osteoblasts. Previous studies have detailed osteogenic differentiation via dissociated embryoid body (EB) culture in osteoinductive media comprising of ascorbic acid, beta-glycerophosphate, and dexamethasone. It is hoped that these osteogenic cultures will have clinical application in bone tissue repair and regeneration and pharmacological testing. However, differentiation remains highly inefficient and generates heterogeneous populations. We have previously reported an engineered three-dimensional culture system for controlled ES cell-ES cell interaction via the avidin-biotin binding complex. Here we investigate the effect of such engineering on ES cell differentiation. Engineered EBs exhibit enhanced osteogenic differentiation assessed by cadherin-11, Runx2, and osteopontin expression, alkaline phosphatase activity, and bone nodule formation. Results show that cultures produced from intact EBs aggregated for 3 days generated the greatest levels of osteogenic differentiation when cultured in osteoinductive media. However, when cultured in control media, only engineered samples appeared to exhibit bone nodule formation. In addition, polymerase chain reaction analysis revealed a decrease in endoderm and ectoderm expression within engineered samples. This suggests that engineered ES cell aggregation has increased mesoderm homogeneity, contributing to enhanced osteogenic differentiation.

Embryonic-like stem cell derived from adult bone marrow: immature morphology, cell surface markers, ultramicrostructure and differentiation into multinucleated fibers in vitro

Embryonic-like stem cell (ELSC), expressing part of surface markers of human embryonic stem cells, may be a better candidate for cell therapy of degenerative muscular disease than mesenchymal stem cell (MSC). We isolated ELSC and MSC from bone marrow, respectively, and compared their differences in the characteristics and the capacity of myogenic differentiation. Results showed that ELSC could be isolated successfully from 3 adult bone marrow samples by using serum-free medium with 10ng/ml basic fibroblast growth factor (bFGF). At the same cell density, MSC could also be isolated from the same samples by using DMEM/F12 medium containing 10% new cattle serum. However, ELSC appeared as small, morphologically slenderer, upregulated expression of SSEA-4 and ultramicroscopically more immature than MSC derived from the same samples. Immunofluorescent staining and RT-PCR analysis showed ELSC weakly expressed Oct-4, Nanog-3 and Sox-2. Moreover, ELSC and MSC could be induced into long, multinucleated fibers expressing myogenin and myosin heavy chain (MHC) in myogenic differentiation medium, but by day 10, proportion of multinucleated fibers positive for MHC was respectively 25.0%+/-6.9% and 13.8%+/-7.6% in ELSC and MSC culture. These data suggest that bone marrow derived ELSC represent an ideal candidate for cell therapy of degenerative muscular disease.

Neural differentiation of human embryonic stem cells at the ultrastructural level

Neurodegerative disorders affect millions of people worldwide. Neural cells derived from human embryonic stem cells (hESC) have the potential for cell therapies and/or compound screening for treating affected individuals. While both protein and gene expression indicative of a neural phenotype has been exhibited in these differentiated cells, ultrastuctural studies thus far have been lacking. The objective of this study was to correlate hESC to neural differentiation culture conditions with ultrastructural changes observed in the treated cells. We demonstrate here that in basic culture conditions without growth factors or serum we obtain neural morphology. The addition of brain-derived neurotrophic factor (BDNF) and serum to cultures resulted in more robust neural differentiation. In addition to providing cues such as cell survival or lineage specification, additional factors also altered the intracellular structures and cell morphologies. Even though the addition of BDNF and serum did not increase synaptic formation, altered cellular structures such as abundant polyribosomes and more developed endoplasmic reticulum indicate a potential increase in protein production.

[Chromosomal instability of in vitro cultured mouse embryonic stem cells and induced pluripotent stem cells]

A perspective of using embryonic stem (ES) and induced pluripotent stem (iPS) cells in clinical medicine makes karyological analysis of these cells an important issue. Using methods of classical and molecular cytogenetics chromosomal analysis, we have carried out karyological study of two mouse ES and two iPS cell lines derived de novo. We have found monosomy of X chromosome in all studied ES and iPS cell lines, thus making a modal number of chromosomes in these cell lines 39. A chromosomal instability (aneuploidy) was revealed in both studied iPS cell lines. Moreover, we have detected chromosomal rearrangements and chromosomal fragments in one of iPS cell line. Our findings underline the importance of careful cytogenetic evaluation of pluripotent cell lines, especially iPS cell lines, which should be carried out prior to any clinical use of these cells.

Differentiation of E14 mouse embryonic stem cells into thyrocytes in vitro

BACKGROUND

If methods of differentiating stem cells into thyrocytes can be perfected, they may provide a ready source of normal thyrocytes for basic research and clinical application. We developed a novel culture method capable of differentiating mouse embryonic stem (ES) cells into thyroid follicular cells.

METHODS

E14 mouse ES cells were allowed to differentiate into embryoid bodies and then stimulated with thyroid-stimulating hormone, insulin, and potassium iodide. The resulting differentiated cells were observed for expression of thyrocyte-specific mRNA transcripts with reverse transcriptase (RT)-polymerase chain reaction. To definitively identify thyrocytes, we simultaneously observed the thyrocyte-specific proteins, thyroid transcription factor-1 and PAX-8, with dual-color immunofluorescent labeling. The cells were further characterized by electron microscopy.

RESULTS

The ES cells were successfully differentiated into thyrocytes. Differentiated cells expressed PAX-8, thyroid-stimulating hormone receptor, sodium/iodide symporter, thyroperoxidase, and thyroglobulin mRNAs, and coexpressed thyroid transcription factor-1 and PAX-8 proteins. The extent of differentiation was further explored by electron microscopy, which showed that differentiated cells had ultrastructural features similar to adult human thyrocytes, whereas the cells from unstimulated cultures were mostly disintegrated and lacked developed organelle structures.

CONCLUSIONS

These data show that E14 mouse ES cells can be differentiated into thyrocytes by culturing with thyroid-stimulating hormone, insulin, and potassium iodide. The development of reliable methods to produce thyroid cells from ES cells is important to future research in thyroid biology and medical applications.

[Physiological and pathological consequences of a presence of germ line stem cells in adult tissues]

Various therapheutic strategies employing stem cells have been proposed as the alternative, effective methods for therapy of multitude diseases, difficult to treat using standard, well-established methods. Advancing regenerative medicine, which is becoming a novel branch of clinical medicine, has high hopes of stem cells which could be used in treatment of injuried organs such as myocardium after heart infarction, brain after stroke, spinal cord after mechanical injury as well as in treatment of diabetes and Parkinson disease. Application of embryonic stem cells, harvested from developing embryos, is highly controversial. Hence, the stem/primitive cells isolated from adult tissuses are considered to be an optimal source of cells for therapy. Recently our research team has isolated a population of very primitive stem cells from adult tissues (very small embryonic-like stem cells - VSELs) that show several embryonic-like features. These cells can become an alternative and more ethical source of the stem cells for therapy when compared to those isolated from the developing embryos.

Development of human nervous tissue upon differentiation of embryonic stem cells in three-dimensional culture

Researches on neural differentiation using embryonic stem cells (ESC) require analysis of neurogenesis in conditions mimicking physiological cellular interactions as closely as possible. In this study, we report an air-liquid interface-based culture of human ESC. This culture system allows three-dimensional cell expansion and neural differentiation in the absence of added growth factors. Over a 3-month period, a macroscopically visible, compact tissue developed. Histological coloration revealed a dense neural-like neural tissue including immature tubular structures. Electron microscopy, immunochemistry, and electrophysiological recordings demonstrated a dense network of neurons, astrocytes, and oligodendrocytes able to propagate signals. Within this tissue, tubular structures were niches of cells resembling germinal layers of human fetal brain. Indeed, the tissue contained abundant proliferating cells expressing markers of neural progenitors. Finally, the capacity to generate neural tissues on air-liquid interface differed for different ESC lines, confirming variations of their neurogenic potential. In conclusion, this study demonstrates in vitro engineering of a human neural-like tissue with an organization that bears resemblance to early developing brain. As opposed to previously described methods, this differentiation (a) allows three-dimensional organization, (b) yields dense interconnected neural tissue with structurally and functionally distinct areas, and (c) is spontaneously guided by endogenous developmental cues.

Adapting collagen/CNT matrix in directing hESC differentiation

The lineage selection in human embryonic stem cell (hESC) differentiation relies on both the growth factors and small molecules in the media and the physical characteristics of the micro-environment. In this work, we utilized various materials, including the collagen-carbon nanotube (collagen/CNT) composite material, as cell culture matrices to examine the impact of matrix properties on hESC differentiation. Our AFM analysis indicated that the collagen/CNT formed rigid fibril bundles, which polarized the growth and differentiation of hESCs, resulting in more than 90% of the cells to the ectodermal lineage in Day 3 in the media commonly used for spontaneous differentiation. We also observed the differentiated cells followed the coarse alignment of the collagen/CNT matrix. The research not only revealed the responsiveness of hESCs to matrix properties, but also provided a simple yet efficient way to direct the hESC differentiation, and imposed the potential of forming neural-cell based bio-devices for further applications.

Transfer of microRNAs by embryonic stem cell microvesicles

Microvesicles are plasma membrane-derived vesicles released into the extracellular environment by a variety of cell types. Originally characterized from platelets, microvesicles are a normal constituent of human plasma, where they play an important role in maintaining hematostasis. Microvesicles have been shown to transfer proteins and RNA from cell to cell and they are also believed to play a role in intercellular communication. We characterized the RNA and protein content of embryonic stem cell microvesicles and show that they can be engineered to carry exogenously expressed mRNA and protein such as green fluorescent protein (GFP). We demonstrate that these engineered microvesicles dock and fuse with other embryonic stem cells, transferring their GFP. Additionally, we show that embryonic stem cells microvesicles contain abundant microRNA and that they can transfer a subset of microRNAs to mouse embryonic fibroblasts in vitro. Since microRNAs are short (21–24 nt), naturally occurring RNAs that regulate protein translation, our findings open up the intriguing possibility that stem cells can alter the expression of genes in neighboring cells by transferring microRNAs contained in microvesicles. Embryonic stem cell microvesicles may be useful therapeutic tools for transferring mRNA, microRNAs, protein, and siRNA to cells and may be important mediators of signaling within stem cell niches.

Interaction of enteric bacterial pathogens with murine embryonic stem cells

Embryonic stem (ES) cells are susceptible to genetic manipulation and retain the potential to differentiate into diverse cell types, which are factors that make them potentially attractive cells for studying host-pathogen interactions. Murine ES cells were found to be susceptible to invasion by Salmonella enterica serovar Typhimurium and Shigella flexneri and to the formation of attaching and effacing lesions by enteropathogenic Escherichia coli. S. enterica serovar Typhimurium and S. flexneri cell entry was dependent on the Salmonella pathogenicity island 1 and Shigella mxi/spa type III secretion systems, respectively. Microscopy studies indicated that both S. enterica serovar Typhimurium and S. flexneri were located in intracellular niches in ES cells that were similar to the niches occupied in differentiated cells. ES cells were eventually killed following bacterial invasion, but no evidence of activation of classical caspase-associated apoptotic or innate immune pathways was found. To demonstrate the potential of mutant ES cells, we employed an ES cell line defective in cholesterol synthesis and found that the mutant cells were less susceptible to infection by Salmonella and Shigella than the parental ES cells. Thus, we highlighted the practical use of genetically modified ES cells for studying microbe-host interactions.

[Influence of clinorotation on embryoid bodies morphology]

The compensative effects of gravitation at the first stages of embryonic development stages have been investigated using slow clinorotation of embryoid bodies from mouse R1 stem cell lines. Semithin sections (1-2 microm) analysis and electron microscopy study of embryonic bodies cells allowed to reveal morphological features of cells at different maturation stages. Significant decrease in the number of embryonic stem cells undergoing apoptosis as well as noticeable reduction of "lacunas" relative areas were found in clinorotated embryonic bodies compared to control. We propose that large cyst absence may be caused by initial differentiation and morphogenesis stages delay associated with autophagy processes in embryonic bodies.

In vivo characterization of transplanted human embryonic stem cell-derived pancreatic endocrine islet cells

OBJECTIVES

Islet-like clusters (ILCs), differentiated from human embryonic stem cells (hESCs), were characterized both before and after transplantation under the kidney capsule of streptozotocin-induced diabetic immuno-incompetent mice.

MATERIALS AND METHODS

Multiple independent ILC preparations (n = 8) were characterized by immunohistochemistry, flow cytometry and cell insulin content, with six preparations transplanted into diabetic mice (n = 42), compared to controls, which were transplanted with either a human fibroblast cell line or undifferentiated hESCs (n = 28).

RESULTS

Prior to transplantation, ILCs were immunoreactive for the islet hormones insulin, C-peptide and glucagon, and for the ductal epithelial marker cytokeratin-19. ILCs also had cellular insulin contents similar to or higher than human foetal islets. Expression of islet and pancreas-specific cell markers was maintained for 70 days post-transplantation. The mean survival of recipients was increased by transplanted ILCs as compared to transplanted human fibroblast cells (P < 0.0001), or undifferentiated hESCs (P < 0.042). Graft function was confirmed by secretion of human C-peptide in response to an oral bolus of glucose.

CONCLUSIONS

hESC-derived ILC grafts continued to contain cells that were positive for islet endocrine hormones and were shown to be functional by their ability to secrete human C-peptide. Further enrichment and maturation of ILCs could lead to generation of a sufficient source of insulin-producing cells for transplantation into patients with type 1 diabetes.

Non-invasive multiphoton imaging of extracellular matrix structures

Multiphoton microscopy has become a powerful method for the artifact-free, nondestructive evaluation of deep-tissue cells and extracellular matrix (ECM) structures in their native environment. By interacting with highly non-centrosymmetric molecular assemblies such as fibrillar collagen, the non-linear process called second harmonic generation (SHG) has also proven to be an important diagnostic tool for the visualization of ECM compartments in situ with submicron resolution without the need for tissue processing. This review reports on applications of multiphoton-induced autofluorescence and SHG microscopy to identify collagen and elastic fiber orientation in native, tissue-engineered and processed, as well as healthy and diseased, tissues and organs. SHG signal profiling was used to quantify ECM damage in various cardiovascular and exocrine tissues, as well as cartilage. These novel imaging modalities open the general possibility of high-resolution in situ and more important in vivo imaging of ECM structures, cells and intracellular organelles in living intact tissues.

Human ESCs predisposition to karyotypic instability: Is a matter of culture adaptation or differential vulnerability among hESC lines due to inherent properties?

BACKGROUND

The use of human embryonic stem cells (hESCs) in research is increasing and hESCs hold the promise for many biological, clinical and toxicological studies. Human ESCs are expected to be chromosomally stable since karyotypic changes represent a pitfall for potential future applications. Recently, several studies have analysed the genomic stability of several hESC lines maintained after prolonged in vitro culture but controversial data has been reported. Here, we prompted to compare the chromosomal stability of three hESC lines maintained in the same laboratory using identical culture conditions and passaging methods.

RESULTS

Molecular cytogenetic analyses performed in three different hESC lines maintained in parallel in identical culture conditions revealed significant differences among them in regard to their chromosomal integrity. In feeders, the HS181, SHEF-1 and SHEF-3 hESC lines were chromosomally stable up to 185 passages using either mechanical or enzymatic dissection methods. Despite the three hESC lines were maintained under identical conditions, each hESC line behaved differently upon being transferred to a feeder-free culture system. The two younger hESC lines, HS181 (71 passages) and SHEF-3 (51 passages) became chromosomally unstable shortly after being cultured in feeder-free conditions. The HS181 line gained a chromosome 12 by passage 17 and a marker by passage 21, characterized as a gain of chromosome 20 by SKY. Importantly, the mosaicism for trisomy 12 gradually increased up to 89% by passage 30, suggesting that this karyotypic abnormality provides a selective advantage. Similarly, the SHEF-3 line also acquired a trisomy of chromosome 14 as early as passage 10. However, this karyotypic aberration did not confer selective advantage to the genetically abnormal cells within the bulk culture and the level of mosaicism for the trisomy 14 remained overtime between 15%-36%. Strikingly, however, a much older hESC line, SHEF-1, which was maintained for 185 passages in feeders did not undergo any numerical or structural chromosomal change after 30 passages in feeder-free culture and over 215 passages in total.

CONCLUSION

These results support the concept that feeder-free conditions may partially contribute to hESC chromosomal changes but also confirm the hypothesis that regardless of the culture conditions, culture duration or splitting methods, some hESC lines are inherently more prone than others to karyotypic instability.

Comparison of gene expression profiles in erythroid-like cells derived from mouse embryonic stem cells differentiated in simple and co-culture systems

The feeder layer and the presence of specific growth factors are thought to induce the differentiation of embryonic stem cells (ESCs) in culture. The aim of this study was to evaluate the effect of erythropoietin (EPO) on the differentiation of ESCs into erythroid colonies in simple and co-culture systems. Embryoid bodies were dissociated and replated in semisolid medium in simple culture or in a co-culture system with bone-marrow stromal cells (BMSCs), both in the presence or absence of EPO. Colony assays, benzidine staining, and ultrastructural studies were carried out until day 10 of culture. Expression of the epsilon globin, betaH1 globin, runt-related transcription factor 1 (RUNX1), betamajor globin, and erythropoietin receptor (EPOR) genes was evaluated using semi-quantitative RT-PCR. A comparison with the corresponding controls showed that colony size increased in both systems (P <or= 0.05). The number of benzidine-positive colonies in the co-culture system with EPO (86.6+/-17.86) was significantly different compared to the simple culture system with EPO (43.6+/-4.77; P <or= 0.05). The hemoglobin content of the differentiated cells was visualized in micrographs. Analysis of gene expression showed that all genes except betamajor globin were expressed in the simple culture system, whereas in the co-culture system all genes were expressed. These results confirmed that the presence of EPO in a BMSC co-culture system with ESCs improves the differentiation of ESCs to erythroid colonies. Moreover, evidence of primitive and definitive erythropoiesis was observed in this co-culture system.

[Fate of parental mitochondria in embryonic stem hybrid cells]

When hybrid cells are created, not only the nuclear genomes of parental cells unite but their cytoplasm as well. Mitochondrial DNA (mtDNA) is a convenient marker of cytoplasm allowing one to gain insight into the organization of hybrid cell cytoplasm. We analyzed the parental mtDNAs in hybrid cells resulting from fusion of Mus musculus embryonic stem (ES) cells with splenocytes and fetal fibroblasts of DD/c mice or with splenocytes of M. caroli. Identification of the parental mtDNAs in hybrid cells was based on polymorphism among the parental mtDNAs for certain restrictases. We found that intra- and inter-specific ES cell-splenocyte hybrid cells lost entirely or partially mtDNA derived from the somatic partner, whereas ES cell-fibroblast hybrids retained mtDNAs from both parents in similar ratios with a slight bias. The lost of the “somatic” mitochondria by ES-splenocyte hybrids implies non-random segregation of the parental mitochondria as supported by a computer simulation of genetic drift. In contrast, ES cell-fibroblast hybrids show bilateral random segregation of the parental mitochondria judging from analysis of mtDNA in single cells. Preferential segregation of “somatic” mitochondria does not depend on the differences in sequences of the parental mtDNAs but depends on replicative state of the parental cells.

BMPs regulate differentiation of a putative visceral endoderm layer within human embryonic stem-cell-derived embryoid bodies

Human embryonic stem cells (HESCs), pluripotent cells derived from the inner cell mass (ICM) of human blastocysts, represent a novel tool for the study of early human developmental events. When cultured in suspension with serum, HESCs form spherical structures resembling embryoid bodies (EBs). We show that differentiation of HESCs within EBs occurs radially, with central cells then undergoing apoptosis in association with EB cavitation. Cells within the outer layer of cavitating EBs display stage-specific immunoreactivity to pan-keratin, cytokeratin-8, GATA6, alpha-fetoprotein, and transthyretin specific antibodies, and hybridization to disabled-2, GATA4, and GATA6 specific riboprobes. Transmission electron microscopy of these cells reveals clathrin-coated micropinocytotic vesicles, microvilli, and many vacuoles, a phenotype consistent with mouse visceral endoderm (VE) rather than mouse definitive or parietal endoderm. When cultured in media supplemented with the BMP inhibitor noggin, or in the absence of serum, HESC derivatives do not develop the mouse VE-like phenotype. The addition of BMP-4 to noggin-treated HESCs cultured in serum or in serum-free conditions reconstituted development of the VE-like phenotype. These data demonstrate that human EBs undergo developmental events similar to those of mouse EBs and that in vitro BMP signalling induces derivatives of the human ICM to express a phenotype similar to mouse VE.

LIF-immobilized nonwoven polyester fabrics for cultivation of murine embryonic stem cells

Embryonic stem (ES) cells have a great interest for tissue engineering because of their pluripotent nature and proliferative capacity. The objective of this study is to constitute a synthetic microenvironment to support the in vitro propagation of murine ES cells in an undifferentiated state. That is why we used a three-dimensional matrix, nonwoven polyester fabric (NWPF), which was formed from poly(ethylene terephthalate) (PET) fibers. NWPF discs were partially hydrolyzed, and then the carboxyl groups were coupled with leukemia inhibitory factor (LIF) in the presence of water-soluble carbodiimide. The effectiveness of immobilization process was checked with ATR-FTIR spectroscopy, fluorimetry, and cell culture studies. ES cell colony morphology, alkaline phosphatase (AP) activity, stage-specific embryonic antigen-1 (SSEA-1) immunoreactivity, and SEM analysis following a 72 - 96-h culture period upon hydrolyzed and LIF-immobilized surfaces were assessed to determine the pluripotent status of ES cells. Results revealed that LIF was active in immobilized form; undifferentiated colonies had not only a significant AP and SSEA-1 immunoreactivity, but also a higher undifferentiated colony ratio on LIF-immobilized surfaces than that of hydrolyzed surfaces. The immobilized LIF protein might be a good model to provide a feeder-free system, but the physical properties of the scaffold is more convenient for differentiation studies.

Differentiation of human embryonic stem cells induces condensation of chromosome territories and formation of heterochromatin protein 1 foci

Human embryonic stem cells (hES) are unique in their pluripotency and capacity for self-renewal. Therefore, we have studied the differences in the level of chromatin condensation in pluripotent and all-trans retinoic acid-differentiated hES cells. Nuclear patterns of the Oct4 (6p21.33) gene, responsible for hES cell pluripotency, the C-myc (8q24.21) gene, which controls cell cycle progression, and HP1 protein (heterochromatin protein 1) were investigated in these cells. Unlike differentiated hES cells, pluripotent hES cell populations were characterized by a high level of decondensation for the territories of both chromosomes 6 (HSA6) and 8 (HSA8). The Oct4 genes were located on greatly extended chromatin loops in pluripotent hES cell nuclei, outside their respective chromosome territories. However, this phenomenon was not observed for the Oct4 gene in differentiated hES cells, for the C-myc gene in the cell types studied. The high level of chromatin decondensation in hES cells also influenced the nuclear distribution of all the variants of HP1 protein, particularly HP1 alpha, which did not form distinct foci, as usually observed in most other cell types. Our experiments showed that unlike C-myc, the Oct4 gene and HP1 proteins undergo a high level of decondensation in hES cells. Therefore, these structures seem to be primarily responsible for hES cell pluripotency due to their accessibility to regulatory molecules. Differentiated hES cells were characterized by a significantly different nuclear arrangement of the structures studied.

Chromosome stability differs in cloned mouse embryos and derivative ES cells

The mechanisms that have evolved to maintain genome stability during cell cycle progression are challenged when a somatic cell nucleus is placed in a meiotic environment such as the ooplasm. Chromosomal spindle aberrations ensue in the majority of reconstructed oocytes within 2 h of transplantation, but it is not known if they recover or persist with the onset of embryonic divisions. We analyzed the chromosomal spindles and the karyotype of cumulus cell-derived mouse clones through the initial and hence most critical mitoses. Cloned embryos start out with less aneuploidy than fertilized embryos but surpass them after ES cell derivation, as measured by frequencies of chromosome trisomies and structural rearrangements. Despite the limited proportion of cloned mouse embryos that reach late gestation, a phenotypic mutation lacking a karyotypic mark was found in a newborn mouse cloned in 2002 and has been inherited since by its offspring. These data concur with a prevalent epigenetic, rather than genetic, basis for cloned embryo failure, but they also warn against the temptation to think that all conditions of clones are epigenetic and recover during gametogenesis. The cloning procedure is defenseless (no matter how technically refined) towards pre-existing or induced subchromosomal mutations that are below the experimental detection limit of the cytogenetic assay.

A chip-based platform for the in vitro generation of tissues in three-dimensional organization

We describe a multi-purpose platform for the three-dimensional cultivation of tissues. The device is composed of polymer chips featuring a microstructured area of 1-2 cm(2). The chip is constructed either as a grid of micro-containers measuring 120-300 x 300 x 300 microm (h x l x w), or as an array of round recesses (300 microm diameter, 300 microm deep). The micro-containers may be separately equipped with addressable 3D-micro-electrodes, which allow for electrical stimulation of excitable cells and on-site measurements of electrochemically accessible parameters. The system is applicable for the cultivation of high cell densities of up to 8 x 10(6) cells and, because of the rectangular grid layout, allows the automated microscopical analysis of cultivated cells. More than 1000 micro-containers enable the parallel analysis of different parameters under superfusion/perfusion conditions. Using different polymer chips in combination with various types of bioreactors we demonstrated the principal suitability of the chip-based bioreactor for tissue culture applications. Primary and established cell lines have been successfully cultivated and analysed for functional properties. When cells were cultured in non-perfused chips, over time a considerable degree of apoptosis could be observed indicating the need for an active perfusion. The system presented here has also been applied for the differentiation analysis of pluripotent embryonic stem cells and may be suitable for the analysis of the stem cell niche.

Structural differentiation, proliferation, and association of human embryonic stem cell-derived cardiomyocytes in vitro and in their extracardiac tissues

The proliferation, structural differentiation, and capacity of association of human ES cell-derived cardiomyocytes were assessed in culture and in extracardiac graft tissues. Embryoid body (EB) outgrowths having cardiomyocytes, and their transplants in mice retroperitoneum or renal subcapsular region were analyzed mainly by immunochemistry. During the culture of EB outgrowths, colonies of cardiomyocytes grew in size exhibiting synchronized beatings. Subcellular structures of those cardiomyocytes involved in the contraction, hormone production, and intercellular integration differentiated with distinct immunoreactivity for constituent proteins/peptides. Judging from PCNA staining, proliferation potential was maintained in part for more than 70 days. In teratoma tissues on post-transplantation Day 7, cardiomyocytes maintained their integration with connexin 43 and cadherin at their junctions. They partly exhibited strong PCNA reactivity. On Day 28, large part of the cardiomyocytes lost their association, dispersing among non-cardiac cells without discernible cadherin reactivity. Proliferation potential was generally low irrespective of their tissue diversity. From these results, structural differentiation and active proliferation of human ES cell-derived cardiomyocytes occurred in vitro, maintaining their association. When developed in extracardiac tissues, however, the cardiomyocytes showed low proliferation potential and reduced cellular integration. This leads to the proposal that some procedure will be necessary to accelerate or maintain the proliferation of cardiomyocytes in vivo.

Controlling size, shape and homogeneity of embryoid bodies using poly(ethylene glycol) microwells

Directed differentiation of embryonic stem (ES) cells is useful for creating models of human disease and could potentially generate a wide array of functional cell types for therapeutic applications. Methods to differentiate ES cells often involve the formation of cell aggregates called embryoid bodies (EBs), which recapitulate early stages of embryonic development. EBs are typically made from suspension cultures, resulting in heterogeneous structures with a wide range of sizes and shapes, which may influence differentiation. Here, we use microfabricated cell-repellant poly(ethylene glycol) (PEG) wells as templates to initiate the formation of homogenous EBs. ES cell aggregates were formed with controlled sizes and shapes defined by the geometry of the microwells. EBs generated in this manner remained viable and maintained their size and shape within the microwells relative to their suspension counterparts. Intact EBs could be easily retrieved from the microwells with high viability (>95%). These results suggest that the microwell technique could be a useful approach for in vitro studies involving ES cells and, more specifically, for initiating the differentiation of EBs of greater uniformity based on controlled microenvironments.

Desmin immunolocalisation in autosomal dominant Emery-Dreifuss muscular dystrophy

Autosomal dominant Emery-Dreifuss muscular dystrophy (AD-EDMD) is one of a number of allelic disorders caused by mutations in the nuclear lamina proteins, lamins A and C. The disorder is characterised by the early onset of skeletal muscle weakness and joint contractures and later, by dilated cardiomyopathy and cardiac arrythmias. Although the pathophysiology is not understood, one theory suggests that disordered structural organisation at weakened nuclei in contractile cells may underlie the disease. Previous work shows that mice deficient in lamin A/C develop similar skeletal and cardiac muscle signs to patients with AD-EDMD and ultrastructural examination of muscle from these mice shows abnormal localisation of desmin. We hypothesised therefore that desmin localisation may be abnormal in muscle or cells from patients with AD-EDMD and/or in cells expressing mutant lamins. In order to evaluate this, desmin immunolocalisation was determined in skeletal muscle biopsy sections from patients with AD-EDMD and cell lines including MyoD-transfected fibroblast-derived myotubes from AD-EDMD patients and murine embryonic stem cell-derived cardiomyocytes stably transfected with mutant human lamin A. Ultrastructural examination of patient muscle was also performed. Desmin was expressed and localised normally in patient muscle and cell lines and ultrastructural examination was similar to controls. These results fail to provide any evidence that dominant mutations in lamin A/C lead to a disorganisation of the desmin associated cytoskeleton.

Long-Term Culturing of Undifferentiated Embryonic Stem Cells in Conditioned Media and Three-Dimensional Fibrous Matrices Without Extracellular Matrix Coating

ESCs have unlimited proliferation potential and capability to differentiate into all tissue types. They are ideal cell sources for tissue engineering and cell therapy, but their supplies are limited. Current in vitro ESC cultures are carried out in tissue flasks with the surface precoated with extracellular matrix (ECM) proteins. T-flask cultures also require frequent subculturing because their limited surface area cannot support long-term growth of ESCs. In this work, ECM coating and frequent subculturing required in two-dimensional (2D) cultures were circumvented by culturing murine ESCs in three-dimensional (3D) polyethylene terephthalate (PET) fibrous matrices. Also, media conditioned with STO fibroblast cells were used to replace leukemia inhibitory factor and to effectively maintain the pluripotency of murine ESCs in a long-term static culture. However, the lactic acid present in the conditioned medium could inhibit ESC growth and induce spontaneous differentiation when its concentration exceeded 1.5 g/l. In addition, the 3D static culture could be limited by oxygen, which was depleted in the long-term culture when cell density in the matrix was high. However, these problems can be alleviated in dynamic culture with improved oxygen transfer and continuous media perfusion. The matrix pore size also had profound effects on ESCs. The smaller-pore (30-60 mum) matrix gave a higher proliferation rate and Oct-4 and stage specific embryonic antigen-1 expressions. Overall, the 3D culturing method is superior to the 2D culture method and can provide an economical way to mass-produce undifferentiated ESCs in uncoated matrices and conditioned media.

Differentiation of human embryonic stem cells into corneal epithelial-like cells by in vitro replication of the corneal epithelial stem cell niche

Human embryonic stem cells (hESCs) are pluripotent cells capable of differentiating into any cell type of the body. It has long been known that the adult stem cell niche is vital for the maintenance of adult stem cells. The cornea at the front of the eye is covered by a stratified epithelium that is renewed by stem cells located at its periphery in a region known as the limbus. These so-called limbal stem cells are maintained by factors within the limbal microenvironment, including collagen IV in basement membrane and limbal fibroblasts in the stroma. Because this niche is very specific to the stem cells (rather than to the more differentiated cells) of the corneal epithelium, it was hypothesized that replication of these factors in vitro would result in hESC differentiation into corneal epithelial-like cells. Indeed, here we show that culturing of hESC on collagen IV using medium conditioned by the limbal fibroblasts results in the loss of pluripotency and differentiation into epithelial-like cells. Further differentiation results in the formation of terminally differentiated epithelial-like cells not only of the cornea but also of skin. Scanning electron microscopy shows that some differences exist between hESC-derived and adult limbal epithelial-like cells, necessitating further investigation using in vivo animal models of limbal stem cell deficiency. Such a model of hESC differentiation is useful for understanding the early events of epithelial lineage specification and to the eventual potential application of epithelium differentiated from hESC for clinical conditions of epithelial stem cell loss. Disclosure of potential conflicts of interest is found at the end of this article.

Molecular and pharmacological properties of human embryonic stem cell-derived cardiomyocytes

Human embryonic stem cells (hESCs) can be coaxed to differentiate into specific cell types, including cardiomyocyte-like cells. These cells express cardiac-specific markers and display functional similarities to their adult counterparts. Based on these properties, hESC-derived cardiomyocytes have the potential to be extremely useful in various in vitro applications and to provide the opportunity for cardiac cell replacement therapies. However, before this can become a reality, the molecular and functional characteristics of these cells need to be investigated in more detail. In the present study we differentiate hESCs into cardiomyocyte-like cells via embryoid bodies (EBs). The fraction of spontaneously beating clusters obtained from the EBs averaged approximately 30% of the total number of EBs used. These cell clusters were isolated, dissociated into single-cell suspensions, and frozen for long-term storage. The cryopreserved cells could be successfully thawed and subcultured. Using electron microscopy, we observed Z discs and tight junctions in the hESC-derived cardiomyocytes, and by immunohistochemical analysis we detected expression of cardiac-specific markers (cTnI and cMHC). Notably, using BrdU labeling we also could demonstrate that some of the hESC-derived cardiomyocytes retain a proliferative capacity. Furthermore, pharmacological stimulation of the cells resulted in responses indicative of functional adrenergic and muscarinic receptor coupling systems. Taken together, these results lend support to the notion that hESCs can be used as a source for the procurement of cardiomyocytes for in vitro and in vivo applications.

Tissue engineering of vascularized cardiac muscle from human embryonic stem cells

Transplantation of a tissue-engineered heart muscle represents a novel experimental therapeutic paradigm for myocardial diseases. However, this strategy has been hampered by the lack of sources for human cardiomyocytes and by the scarce vasculature in the ischemic area limiting the engraftment and survival of the transplanted muscle. Beyond the necessity of endothelial capillaries for the delivery of oxygen and nutrients to the grafted muscle tissue, interactions between endothelial and cardiomyocyte cells may also play a key role in promoting cell survival and proliferation. In the present study, we describe the formation of synchronously contracting engineered human cardiac tissue derived from human embryonic stem cells containing endothelial vessel networks. The 3D muscle consisted of cardiomyocytes, endothelial cells (ECs), and embryonic fibroblasts (EmFs). The formed vessels were further stabilized by the presence of mural cells originating from the EmFs. The presence of EmFs decreased EC death and increased EC proliferation. Moreover, the presence of endothelial capillaries augmented cardiomyocyte proliferation and did not hamper cardiomyocyte orientation and alignment. Immunostaining, ultrastructural analysis (using transmission electron microscopy), RT-PCR, pharmacological, and confocal laser calcium imaging studies demonstrated the presence of cardiac-specific molecular, ultrastructural, and functional properties of the generated tissue constructs with synchronous activity mediated by action potential propagation through gap junctions. In summary, this is the first report of the construction of 3D vascularized human cardiac tissue that may have unique applications for studies of cardiac development, function, and tissue replacement therapy.

Digital imaging of stem cells by electron microscopy

This chapter deals with basic techniques of scanning and transmission electron microscopy applicable to stem cell imaging. It is sometimes desirable to characterize the fine structure of embryonic and adult stem cells to supplement the images obtained by phase-contrast and confocal immunofluorescent microscopy to compare with the microstructure of cells and tissues reported in the literature. This would help confirm their true identity whilst defining their surface and internal morphology. The intention is to put a face on stem cells during their differentiation.

Morphological and molecular characterization of novel population of CXCR4+ SSEA-4+ Oct-4+ very small embryonic-like cells purified from human cord blood: preliminary report

Recently, we purified from adult murine bone marrow (BM) a population of CXCR4(+), Oct-4(+) SSEA-1(+), Sca-1(+) lin(-) CD45(-) very small embryonic-like (VSEL) stem cells and hypothesized that similar cells could be also present in human cord blood (CB). Here, we report that by employing a novel two-step isolation procedure -- removal of erythrocytes by hypotonic lysis combined with multiparameter sorting -- we could isolate from CB a population of human cells that are similar to murine BM-derived VSELs, described previously by us. These CB-isolated VSELs (CB-VSEL) are very small (3-5 micro m) and highly enriched in a population of CXCR4(+)AC133(+)CD34(+)lin(-) CD45(-) CB mononuclear cells, possess large nuclei containing unorganized euchromatin and express nuclear embryonic transcription factors Oct-4 and Nanog and surface embryonic antigen SSEA-4. Further studies are needed to see if human CB-isolated VSELs similar to their murine BM-derived counterparts are endowed with pluripotent stem cell properties.