Spatial and temporal expression pattern of germ layer markers during human embryonic stem cell differentiation in embryoid bodies

The Analysis of Embryoid Body Formation and Its Role in Retinal Organoid Development

Within the last decade, a wide variety of protocols have emerged for the generation of retinal organoids. A subset of studies have compared protocols based on stem cell source, the physical features of the microenvironment, and both internal and external signals, all features that influence embryoid body and retinal organoid formation. Most of these comparisons have focused on the effect of signaling pathways on retinal organoid development. In this study, our aim is to understand whether starting cell conditions, specifically those involved in embryoid body formation, affect the development of retinal organoids in terms of differentiation capacity and reproducibility. To investigate this, we used the popular 3D floating culture method to generate retinal organoids from stem cells. This method starts with either small clumps of stem cells generated from larger clones (clumps protocol, CP) or with an aggregation of single cells (single cells protocol, SCP). Using histological analysis and gene-expression comparison, we found a retention of the pluripotency capacity on embryoid bodies generated through the SCP compared to the CP. Nonetheless, these early developmental differences seem not to impact the final retinal organoid formation, suggesting a potential compensatory mechanism during the neurosphere stage. This study not only facilitates an in-depth exploration of embryoid body development but also provides valuable insights for the selection of the most suitable protocol in order to study retinal development and to model inherited retinal disorders in vitro.

Human embryoids: A new strategy of recreating the first steps of embryonic development in vitro

Molecular mechanisms surrounding early human embryonic events such as blastocyst formation, implantation, and the specification of the body axes are some of the most attractive research questions of developmental biology today. A knowledge on the detailed signaling landscape underlying these critical events in the human could impact the way we treat early pregnancy disorders and infertility, and considerably advance our abilities to make precise human tissues in a lab. However, owing to ethical, technical, and policy restrictions, research on early human embryo development historically stalled behind animal models. The rapid progress in 3D culture of human embryonic stem cells over the past years created an opportunity to overcome this critical challenge. We review recently developed strategies of making 3D models of the human embryo built from embryonic stem cells, which we refer to as embryoids. We focus on models aimed at reconstituting the 3D epithelial characteristics of the early human embryo, namely the intra/extraembryonic signaling crosstalk, tissue polarity, and embryonic cavities. We identify distinct classes of embryoids based on whether they explicitly include extraembryonic tissues and we argue for the merit of compromising on certain aspects of embryo mimicry in balancing the experimental feasibility with ethical considerations. Human embryoids open gates toward a new field of synthetic human embryology, allowing to study the long inaccessible stages of early human development at unprecedented detail.

Defined Microenvironments Trigger In Vitro Gastrulation in Human Pluripotent Stem Cells

Gastrulation is a stage in embryo development where three germ layers arise to dictate the human body plan. In vitro models of gastrulation have been demonstrated by treating pluripotent stem cells with soluble morphogens to trigger differentiation. However, in vivo gastrulation is a multistage process coordinated through feedback between soluble gradients and biophysical forces, with the multipotent epiblast transforming to the primitive streak followed by germ layer segregation. Here, the authors show how constraining pluripotent stem cells to hydrogel islands triggers morphogenesis that mirrors the stages preceding in vivo gastrulation, without the need for exogenous supplements. Within hours of initial seeding, cells display a contractile phenotype at the boundary, which leads to enhanced proliferation, yes-associated protein (YAP) translocation, epithelial to mesenchymal transition, and emergence of SRY-box transcription factor 17 (SOX17)+ T/BRACHYURY+ cells. Molecular profiling and pathway analysis reveals a role for mechanotransduction-coupled wingless-type (WNT) signaling in orchestrating differentiation, which bears similarities to processes observed in whole organism models of development. After two days, the colonies form multilayered aggregates, which can be removed for further growth and differentiation. This approach demonstrates how materials alone can initiate gastrulation, thereby providing in vitro models of development and a tool to support organoid bioengineering efforts.

Effects of Sodium Arsenite on the Myocardial Differentiation in Mouse Embryonic Bodies

Arsenic in inorganic form is a known human carcinogen; even low levels of arsenic can interfere with the endocrine system. In mammalian development, arsenic exposure can cause a malformation of fetuses and be lethal. This study examined the effects of sodium arsenite (SA) as the inorganic form of arsenic in embryonic bodies (EBs) with three germ layers in the developmental stage. This condition is closer to the physiological condition than a 2D cell culture. The SA treatment inhibited EBs from differentiating into cardiomyocytes. A treatment with 1 μM SA delayed the initiation of beating, presenting successful cardiomyocyte differentiation. In particular, mitochondria function analysis showed that SA downregulated the transcription level of the Complex IV gene. SA increased the fission form of mitochondrion identified by the mitochondria number and length. In addition, a treatment with D-penicillamine, an arsenic chelator, restored the beat of EBs against SA, but not mitochondrial dysfunction. These findings suggest that SA is a toxicant that induces mitochondrial damage and interferes with myocardial differentiation and embryogenesis. This study suggests that more awareness of SA exposure during pregnancy is required because even minuscule amounts have irreversible adverse effects on embryogenesis through mitochondria dysfunction.

Genes Involved in DNA Repair and Mitophagy Protect Embryoid Bodies from the Toxic Effect of Methylmercury Chloride under Physioxia Conditions

The formation of embryoid bodies (EBs) from human pluripotent stem cells resembles the early stages of human embryo development, mimicking the organization of three germ layers. In our study, EBs were tested for their vulnerability to chronic exposure to low doses of MeHgCl (1 nM) under atmospheric (21%O₂) and physioxia (5%O₂) conditions. Significant differences were observed in the relative expression of genes associated with DNA repair and mitophagy between the tested oxygen conditions in nontreated EBs. When compared to physioxia conditions, the significant differences recorded in EBs cultured at 21% O₂ included: (1) lower expression of genes associated with DNA repair (ATM, OGG1, PARP1, POLG1) and mitophagy (PARK2); (2) higher level of mtDNA copy number; and (3) higher expression of the neuroectodermal gene (NES). Chronic exposure to a low dose of MeHgCl (1 nM) disrupted the development of EBs under both oxygen conditions. However, only EBs exposed to MeHgCl at 21% O₂ revealed downregulation of mtDNA copy number, increased oxidative DNA damage and DNA fragmentation, as well as disturbances in SOX17 (endoderm) and TBXT (mesoderm) genes expression. Our data revealed that physioxia conditions protected EBs genome integrity and their further differentiation.

Dual specificity phosphatase 7 drives the formation of cardiac mesoderm in mouse embryonic stem cells

Dual specificity phosphatase 7 (DUSP7) is a protein belonging to a broad group of phosphatases that can dephosphorylate phosphoserine/phosphothreonine as well as phosphotyrosine residues within the same substrate. DUSP7 has been linked to the negative regulation of mitogen activated protein kinases (MAPK), and in particular to the regulation of extracellular signal-regulated kinases 1 and 2 (ERK1/2). MAPKs play an important role in embryonic development, where their duration, magnitude, and spatiotemporal activity must be strictly controlled by other proteins, among others by DUSPs. In this study, we focused on the effect of DUSP7 depletion on the in vitro differentiation of mouse embryonic stem (ES) cells. We showed that even though DUSP7 knock-out ES cells do retain some of their basic characteristics, when it comes to differentiation, they preferentially differentiate towards neural cells, while the formation of early cardiac mesoderm is repressed. Therefore, our data indicate that DUSP7 is necessary for the correct formation of neuroectoderm and cardiac mesoderm during the in vitro differentiation of ES cells.

Single-cell quantification of a broad RNA spectrum reveals unique noncoding patterns associated with cell types and states

The ability to interrogate total RNA content of single cells would enable better mapping of the transcriptional logic behind emerging cell types and states. However, current single-cell RNA-sequencing (RNA-seq) methods are unable to simultaneously monitor all forms of RNA transcripts at the single-cell level, and thus deliver only a partial snapshot of the cellular RNAome. Here we describe Smart-seq-total, a method capable of assaying a broad spectrum of coding and noncoding RNA from a single cell. Smart-seq-total does not require splitting the RNA content of a cell and allows the incorporation of unique molecular identifiers into short and long RNA molecules for absolute quantification. It outperforms current poly(A)-independent total RNA-seq protocols by capturing transcripts of a broad size range, thus enabling simultaneous analysis of protein-coding, long-noncoding, microRNA, and other noncoding RNA transcripts from single cells. We used Smart-seq-total to analyze the total RNAome of human primary fibroblasts, HEK293T, and MCF7 cells, as well as that of induced murine embryonic stem cells differentiated into embryoid bodies. By analyzing the coexpression patterns of both noncoding RNA and mRNA from the same cell, we were able to discover new roles of noncoding RNA throughout essential processes, such as cell cycle and lineage commitment during embryonic development. Moreover, we show that independent classes of short-noncoding RNA can be used to determine cell-type identity.

Stem Cell-Based Embryo Models: En Route to a Programmable Future

Early-stage human embryogenesis, such as implantation, gastrulation, and neurulation, are critical for successful pregnancy. For decades, our knowledge about these stages has been limited by the inaccessibility to such embryo specimens in vivo and the difficulty in rebuilding them in vitro. Although human embryos could be cultured in vitro beyond implantation, it remains challenging for the cultured embryos to recapitulate the continuous, coordinated morphogenesis and cytodifferentiation as seen in vivo. Stem cell-based embryo models, mainly derived from human pluripotent stem cells, are organized structures mimicking essential developmental processes in the early-stage human embryos. Despite their invaluable potentials, most embryo models are based on the self-organization of human pluripotent stem cells, which are limited in controllability, reproducibility, and developmental fidelity. Recently, the integration of bioengineered tools and stem cell biology has fueled a technological transformation towards programmable, highly complex, high-fidelity stem cell-based embryo models. Given its scientific and clinical significance, we present an overview of recent paradigm-shifting advances as well as historical perspectives regarding the past, present, and future of synthetic human embryology. Following the developmental roadmap of human embryogenesis, we critically review existing stem cell-based models for implantation, gastrulation, and neurulation, respectively. We highlight the limitations encountered by autonomous self-organization strategy and discuss the concept and application of guided cell organization as a game-changer for innovating next-generation embryo models. Future endeavors in synthetic human embryology should rationally leverage both the self-organizing power and programmable microenvironmental guidance to secure faithful reconstructions of the hierarchical orders of human embryogenesis in vitro.

Low complexity domains, condensates, and stem cell pluripotency

Biological reactions require self-assembly of factors in the complex cellular milieu. Recent evidence indicates that intrinsically disordered, low-complexity sequence domains (LCDs) found in regulatory factors mediate diverse cellular processes from gene expression to DNA repair to signal transduction, by enriching specific biomolecules in membraneless compartments or hubs that may undergo liquid-liquid phase separation (LLPS). In this review, we discuss how embryonic stem cells take advantage of LCD-driven interactions to promote cell-specific transcription, DNA damage response, and DNA repair. We propose that LCD-mediated interactions play key roles in stem cell maintenance and safeguarding genome integrity.

Cell Mechanics in Embryoid Bodies

Embryoid bodies (EBs) resemble self-organizing aggregates of pluripotent stem cells that recapitulate some aspects of early embryogenesis. Within few days, the cells undergo a transition from rather homogeneous epithelial-like pluripotent stem cell colonies into a three-dimensional organization of various cell types with multifaceted cell-cell interactions and lumen formation-a process associated with repetitive epithelial-mesenchymal transitions. In the last few years, culture methods have further evolved to better control EB size, growth, cellular composition, and organization-e.g., by the addition of morphogens or different extracellular matrix molecules. There is a growing perception that the mechanical properties, cell mechanics, and cell signaling during EB development are also influenced by physical cues to better guide lineage specification; substrate elasticity and topography are relevant, as well as shear stress and mechanical strain. Epithelial structures outside and inside EBs support the integrity of the cell aggregates and counteract mechanical stress. Furthermore, hydrogels can be used to better control the organization and lineage-specific differentiation of EBs. In this review, we summarize how EB formation is accompanied by a variety of biomechanical parameters that need to be considered for the directed and reproducible self-organization of early cell fate decisions.

"Reprogram Enablement" as an Assay for Identifying Early Oncogenic Pathways by Their Ability to Allow Neoplastic Cells to Reacquire an Epiblast State

One approach to understanding how tissue-specific cancers emerge is to determine the requirements for “reprograming” such neoplastic cells back to their developmentally normal primordial pre-malignant epiblast-like pluripotent state and then scrutinizing their spontaneous reconversion to a neoplasm, perhaps rendering salient the earliest pivotal oncogenic pathway(s) (before other aberrations accumulate in the adult tumor). For the prototypical malignancy anaplastic thyroid carcinoma (ATC), we found that tonic RAS reduction was obligatory for reprogramming cancer cells to a normal epiblast-emulating cells, confirmed by changes in their transcriptomic and epigenetic profiles, loss of neoplastic behavior, and ability to derive normal somatic cells from their “epiblast organoids.” Without such suppression, ATCs re-emerged from the clones. Hence, for ATC, RAS inhibition was its “reprogram enablement” (RE) factor. Each cancer likely has its own RE factor; identifying it may illuminate pre-malignant risk markers, better classifications, therapeutic targets, and tissue-specification of a previously pluripotent, now neoplastic, cell.

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The factors for reprogramming a cancer cell to an epiblast-like cell can be assayed

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“Reprogram enablement” can yield insights into the earliest pivotal oncogenic steps

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For anaplastic thyroid carcinoma, RAS inhibition was obligatory for reprograming

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Each tissue-specific cancer will have its own reprogramming enablement requirement

Fluorescence-based actin turnover dynamics of stem cells as a profiling method for stem cell functional evolution, heterogeneity and phenotypic lineage parsing

Stem cells are widely explored in regenerative medicine as a source to produce diverse cell types. Despite the wide usage of stem cells like mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPSCs), there is a lack of robust methods to rapidly discern the phenotypic and functional heterogeneity of stem cells. The organization of actin cytoskeleton has been previously used to discern divergent stem cell differentiation pathways. In this paper, we highlight the versatility of a cell profiling method for actin turnover dynamics. Actin filaments in live stem cells are labeled using SiR-actin, a cell permeable fluorogenic probe, to determine the endogenous actin turnover. Live MSC imaging after days of induction successfully demonstrated lineage specific change in actin turnover. Next, we highlighted the differences in the cellular heterogeneity of actin dynamics during adipogenic or osteogenic MSC differentiation. Next, we applied the method to differentiating iPSCs in culture, and detected a progressive slowdown in actin turnover during differentiation upon stimulation with neural or cardiac media. Finally, as a proof of concept, the actin dynamic profiling was used to isolate MSCs via flow cytometry prior to sorting into three distinct sub-populations with low, intermediate or high actin dynamics. A greater fraction of MSCs with more rapid actin dynamics demonstrated increased inclination for adipogenesis, whereas, slower actin dynamics correlated with increased osteogenesis. Together, these results show that actin turnover can serve as a versatile biomarker to not only track cellular phenotypic heterogeneity but also harvest live cells with potential for differential phenotypic fates.

Establishment of an in Vitro Human Blood-Brain Barrier Model Derived from Induced Pluripotent Stem Cells and Comparison to a Porcine Cell-Based System

The blood-brain barrier (BBB) is responsible for the homeostasis between the cerebral vasculature and the brain and it has a key role in regulating the influx and efflux of substances, in healthy and diseased states. Stem cell technology offers the opportunity to use human brain-specific cells to establish in vitro BBB models. Here, we describe the establishment of a human BBB model in a two-dimensional monolayer culture, derived from human induced pluripotent stem cells (hiPSCs). This model was characterized by a transendothelial electrical resistance (TEER) higher than 2000 Ω∙cm² and associated with negligible paracellular transport. The hiPSC-derived BBB model maintained the functionality of major endothelial transporter proteins and receptors. Some proprietary molecules from our central nervous system (CNS) programs were evaluated revealing comparable permeability in the human model and in the model from primary porcine brain endothelial cells (PBECs).

The effect of folic acid deficiency on Mest/Peg1 in neural tube defects

OBJECTIVE

Neural tube defects (NTDs) are one of the most common and serious birth defects in human beings caused by genetic and environmental factors. Folate insufficiency is involved in the occurrence of NTDs and folic acid supplementation can prevent NTDs occurrence, however, the underlying mechanism remains poorly understood.

METHODS

We established cell and animal models of folic acid deficiency to detect the methylation modification and expression levels of genes by MassARRAY and real-time PCR, respectively. Results and conclusion: In the present study, we found firstly that in human folic acid-insufficient NTDs, the methylation level of imprinted gene Mest/Peg1 was decreased. By using a folic acid-deficient cell model, we demonstrated that Mest/Peg1 methylation was descended. Meanwhile, the mRNA level of Mest/Peg1 was up-regulated via hypomethylation modification under low folic acid conditions. Consistent with the results in cell models, Mest/Peg1 expression was elevated through hypomethylation regulation in folate-deficient animal models. Furthermore, the up-regulation of Mest/Peg1 inhibited the expression of Lrp6 gene, a crucial component of Wnt pathway. Similar results with Lrp6 down-regulation of fetal brain were verified in animal models under folic acid-deficient condition. Taken together, our findings indicated folic acid increased the expression of Mest/Peg1 via hypomethylation modification, and then inhibited Lrp6 expression, which may ultimately impact on the development of nervous system through the inactivation of Wnt pathway.

Effects of Natural Progesterone and Synthetic Progestin on Germ Layer Gene Expression in a Human Embryoid Body Model

Natural progesterone and synthetic progestin are widely used for the treatment of threatened abortion or in in vitro fertilization (IVF) cycles. This in vitro study aimed to assess whether the treatment with natural progesterone or synthetic progestin influences the germ layer gene expression on the early human embryonic development using human embryonic stem cells (hESCs)-derived embryoid bodies (hEBs) as a surrogate of early stage human embryonic development. Human EBs derived from hESCs were cultured for nine days, and were treated with natural progesterone (P4) or synthetic progestin, medroxyprogesterone acetate (MPA) at 10-7 M for five days. To reverse the effects of treatment, mifepristone (RU486) as progesterone antagonist was added to the hEBs for four days starting one day after the initiation of treatment. Mouse blastocysts (mBLs) were cultured in vitro for 24 h, and P4 or MPA at 10-7 M was treated for an additional 24 h. The treated embryos were further transferred onto in vitro cultured endometrial cells to evaluate chorionic gonadotropin (CG) expression. To analyze the effects of P4 or MPA, the expression of differentiation genes representing the three germ layers was investigated, GATA-binding factor 4 (GATA4), α-fetoprotein (AFP), hepatocyte nuclear factor (HNF)-3β, hepatocyte nuclear factor (HNF)-4α (endoderm), Brachyury, cardiac actin (cACT) (mesoderm), and Nestin (ectoderm), using quantitative reverse transcription PCR (qRT-PCR) and immunostaining. Significantly lower expressions of HNF-3β, HNF-4α, Brachyury, and Nestin were observed in MPA-treated hEBs (all p < 0.05), which was negated by RU486 treatment. This inhibitory effect of MPA was also observed in mouse embryos. Conclusively, the effects of natural progesterone and synthetic progestin may differ in the germ layer gene expression in the hEB model, which suggests that caution is necessary in the use of progestogen.

Effect of inoculum density on human-induced pluripotent stem cell expansion in 3D bioreactors

Objective

For optimized expansion of human‐induced pluripotent stem cells (hiPSCs) with regards to clinical applications, we investigated the influence of the inoculum density on the expansion procedure in 3D hollow‐fibre bioreactors.

Materials and Methods

Analytical‐scale bioreactors with a cell compartment volume of 3 mL or a large‐scale bioreactor with a cell compartment volume of 17 mL were used and inoculated with either 10 × 10⁶ or 50 × 10⁶ hiPSCs. Cells were cultured in bioreactors over 15 days; daily measurements of biochemical parameters were performed. At the end of the experiment, the CellTiter‐Blue^® Assay was used for culture activity evaluation and cell quantification. Also, cell compartment sections were removed for gene expression and immunohistochemistry analysis.

Results

The results revealed significantly higher values for cell metabolism, cell activity and cell yields when using the higher inoculation number, but also a more distinct differentiation. As large inoculation numbers require cost and time‐extensive pre‐expansion, low inoculation numbers may be used preferably for long‐term expansion of hiPSCs. Expansion of hiPSCs in the large‐scale bioreactor led to a successful production of 5.4 × 10⁹ hiPSCs, thereby achieving sufficient cell amounts for clinical applications.

Conclusions

In conclusion, the results show a significant effect of the inoculum density on cell expansion, differentiation and production of hiPSCs, emphasizing the importance of the inoculum density for downstream applications of hiPSCs. Furthermore, the bioreactor technology was successfully applied for controlled and scalable production of hiPSCs for clinical use.

A Novel Method for Isolation of Pluripotent Stem Cells from Human Umbilical Cord Blood

Very small embryonic-like cells (VSELs) are a population of very rare pluripotent stem cells isolated in adult murine bone marrow and many other tissues and organs, including umbilical cord blood (UCB). VSEL existence is still not universally accepted by the scientific community, so for this purpose, we sought to investigate whether presumptive VSELs (pVSELs) could be isolated from human UCB with an improved protocol based on the isolation of enriched progenitor cells by depletion of nonprogenitor cells with magnetic separation. Progenitor cells, likely including VSELs, cultured with retinoic acid were able to form dense colonies and cystic embryoid bodies and to differentiate toward the ecto-meso-endoderm lineages as shown by the positivity to specific markers. VSEL differentiative potential toward mesodermal lineage was further demonstrated in vitro upon exposure to an established inductive protocol, which induced the acquisition of renal progenitor cell phenotype. VSEL-derived renal progenitors showed regenerative potential in a cisplatin model of acute kidney injury by restoring renal function and tubular structure through induction of proliferation of endogenous renal cells. The data presented here foster the great debate that surrounds VSELs and, more in general, the existence of cells endowed with pluripotent features in adult tissues. In fact, the possibility to find and isolate subpopulations of cells that fully fit all the criteria utilized to define pluripotency remains, nowadays, almost unproven. Thus, efforts to better characterize the phenotype of these intriguing cells are crucial to understand their possible applications for regenerative and precision medicine purposes.

The Forkhead box transcription factor FOXM1 is required for the maintenance of cell proliferation and protection against oxidative stress in human embryonic stem cells

Human embryonic stem cells (hESCs) exhibit unique cell cycle structure, self-renewal and pluripotency. The Forkhead box transcription factor M1 (FOXM1) is critically required for the maintenance of pluripotency in mouse embryonic stem cells and mouse embryonal carcinoma cells, but its role in hESCs remains unclear. Here, we show that FOXM1 expression was enriched in undifferentiated hESCs and was regulated in a cell cycle-dependent manner with peak levels detected at the G2/M phase. Expression of FOXM1 did not correlate with OCT4 and NANOG during in vitro differentiation of hESCs. Importantly, knockdown of FOXM1 expression led to aberrant cell cycle distribution with impairment in mitotic progression but showed no profound effect on the undifferentiated state. Interestingly, FOXM1 depletion sensitized hESCs to oxidative stress. Moreover, genome-wide analysis of FOXM1 targets by ChIP-seq identified genes important for M phase including CCNB1 and CDK1, which were subsequently confirmed by ChIP and RNA interference analyses. Further peak set comparison against a differentiating hESC line and a cancer cell line revealed a substantial difference in the genomic binding profile of FOXM1 in hESCs. Taken together, our findings provide the first evidence to support FOXM1 as an important regulator of cell cycle progression and defense against oxidative stress in hESCs.

Both BMP4 and serum have significant roles in differentiation of embryonic stem cells to primitive and definitive endoderm

Differentiation of embryonic stem (ES) cells is a heterogeneous process which is influenced by different parameters, including growth and differentiation factors. The aim of the present study was to investigate the effect of bone morphogenetic protein-4 (BMP4) signaling on differentiation of mouse ES cells to endodermal lineages. For this purpose, differentiation of the ES cells was induced by embryoid body (EB) formation through hanging drop method. During the suspension stage, EBs were treated with BMP4 in a medium containing either fetal bovine serum (FBS) or knockout serum replacement (KoSR). After plating, EBs showed differentiation to a heterogeneous population of specialized cell types. Two weeks after plating, all the experimental groups expressed three germ layer markers and some primitive and definitive endoderm-specific genes. Quantitative real-time PCR analysis showed higher expression levels of Sox17, Pdx1, Cdx2 and Villin mRNAs in the KoSR plus BMP4 condition and higher Gata4 and Afp expression levels in the FBS plus BMP4 condition. Formation of visceral endoderm and derivatives of definitive endoderm was detected in the BMP4 treated EBs. In conclusion, we demonstrated that both BMP4 signaling and serum composition have significant roles in differentiation of mouse ES cells towards endodermal lineages.

Assessment of the Potential of CDK2 Inhibitor NU6140 to Influence the Expression of Pluripotency Markers NANOG, OCT4, and SOX2 in 2102Ep and H9 Cells

As cyclin-dependent kinases (CDKs) regulate cell cycle progression and RNA transcription, CDKs are attractive targets for creating cancer cell treatments. In this study we investigated the effects of the small molecular agent NU6140 (inhibits CDK2 and cyclin A interaction) on human embryonic stem (hES) cells and embryonal carcinoma-derived (hEC) cells via the expression of transcription factors responsible for pluripotency. A multiparameter flow cytometric method was used to follow changes in the expression of NANOG, OCT4, and SOX2 together in single cells. Both hES and hEC cells responded to NU6140 treatment by induced apoptosis and a decreased expression of NANOG, OCT4, and SOX2 in surviving cells. A higher sensitivity to NU6140 application in hES than hEC cells was detected. NU6140 treatment arrested hES and hEC cells in the G2 phase and inhibited entry into the M phase as evidenced by no significant increase in histone 3 phosphorylation. When embryoid bodies (EBs) formed from NU6104 treated hES cells were compared to EBs from untreated hES cells differences in ectodermal, endodermal, and mesodermal lineages were found. The results of this study highlight the importance of CDK2 activity in maintaining pluripotency of hES and hEC cells and in differentiation of hES cells.

In vitro spatially organizing the differentiation in individual multicellular stem cell aggregates

With significant potential as a robust source to produce specific somatic cells for regenerative medicine, stem cells have attracted increasing attention from both academia and government. In vivo, stem cell differentiation is a process under complicated regulations to precisely build tissue with unique spatial structures. Since multicellular spheroidal aggregates of stem cells, commonly called as embryoid bodies (EBs), are considered to be capable of recapitulating the events in early stage of embryonic development, a variety of methods have been developed to form EBs in vitro for studying differentiation of embryonic stem cells. The regulation of stem cell differentiation is crucial in directing stem cells to build tissue with the correct spatial architecture for specific functions. However, stem cells within the three-dimensional multicellular aggregates undergo differentiation in a less unpredictable and spatially controlled manner in vitro than in vivo. Recently, various microengineering technologies have been developed to manipulate stem cells in vitro in a spatially controlled manner. Herein, we take the spotlight on these technologies and researches that bring us the new potential for manipulation of stem cells for specific purposes.

Generation of organized germ layers from a single mouse embryonic stem cell

Mammalian inner cell mass cells undergo lineage-specific differentiation into germ layers of endoderm, mesoderm and ectoderm during gastrulation. It has been a long-standing challenge in developmental biology to replicate these organized germ layer patterns in culture. Here we present a method of generating organized germ layers from a single mouse embryonic stem cell cultured in a soft fibrin matrix. Spatial organization of germ layers is regulated by cortical tension of the colony, matrix dimensionality and softness, and cell–cell adhesion. Remarkably, anchorage of the embryoid colony from the 3D matrix to collagen-1-coated 2D substrates of ~1 kPa results in self-organization of all three germ layers: ectoderm on the outside layer, mesoderm in the middle and endoderm at the centre of the colony, reminiscent of generalized gastrulating chordate embryos. These results suggest that mechanical forces via cell–matrix and cell–cell interactions are crucial in spatial organization of germ layers during mammalian gastrulation. This new in vitro method could be used to gain insights on the mechanisms responsible for the regulation of germ layer formation.

The three germ layers are formed from the inner cell mass of the mammalian embryo during gastrulation. Here, the authors present a method by which a single mouse embryonic stem cell, derived from inner cell mass, differentiates into the three germ layers in a self-organized manner when cultured in soft fibrin gel.

Slow turning lateral vessel bioreactor improves embryoid body formation and cardiogenic differentiation of mouse embryonic stem cells

Embryonic stem cells (ESCs) have the ability to form aggregates, which are called embryoid bodies (EBs). EBs mimic early embryonic development and are commonly produced for cardiomyogenesis. Here, we describe a method of EB formation in hydrodynamic conditions using a slow-turning lateral vessel (STLV) bioreactor and the subsequent differentiation of EBs into cardiomyocytes. EBs formed in the STLV were compared with conventional techniques, such as hanging drop (HD) or static suspension cell culture (SSC), for homogeneity of EB size, shape, proliferation, apoptosis, and in vitro cardiac differentiation. After 3 days of culture, a four-fold improvement in the yield of EB formation/mL, a six-fold enhancement in total yield of EB/mL, and a nearly 10-fold reduction of cells that failed to incorporate into EBs were achieved in STLV versus SSC. During cardiac differentiation, a 1.5- to 4.2-fold increase in the area of cardiac troponin T (cTnT) per single EB in STLV versus SSC and HD was achieved. These results demonstrate that the STLV method improves the quality and quantity of ES cells to form EBs and enhances the efficiency of cardiac differentiation. We have demonstrated that the mechanical method of cell differentiation creates different microenvironments for the cells and thus influences their lineage commitments, even when genetic origin and the culture medium are the same. Ascorbic acid (ASC) improved further cardiac commitment in differentiation assays. Hence, this culture system is suitable for the production of large numbers of cells for clinical cell replacement therapies and industrial drug testing applications.

Short periods of cyclic mechanical strain enhance triple-supplement directed osteogenesis and bone nodule formation by human embryonic stem cells in vitro

Human embryonic stem cells (hESCs) are uniquely endowed with a capacity for both self-renewal and multilineage differentiation. The aim of this investigation was to determine if short periods of cyclic mechanical strain enhanced dexamethasone, ascorbic acid, and β-glycerophosphate (triple-supplement)-induced osteogenesis and bone nodule formation by hESCs. Colonies were cultured for 21 days and divided into control (no stretch) and three treatment groups; these were subjected to in-plane deformation of 2% for 5 s (0.2 Hertz) every 60 s for 1 h on alternate days in BioFlex plates linked to a Flexercell strain unit over the following periods (day 7-13), (day 15-21), and (day 7-21). Numerous bone nodules were formed, which stained positively for osteocalcin and type I collagen; in addition, MTS assays for cell number as well as total collagen assays showed a significant increase in the day 7-13 group compared to controls and other treatment groups. Alizarin Red staining further showed that cyclic mechanical stretching significantly increased the nodule size and mineral density between days 7-13 compared to control cultures and the other two experimental groups. We then performed a real-time polymerase chain reaction (PCR) microarray on the day 7-13 treatment group to identify mechanoresponsive osteogenic genes. Upregulated genes included the transcription factors RUNX2 and SOX9, bone morphogenetic proteins BMP1, BMP4, BMP5, and BMP6, transforming growth factor-β family members TGFB1, TGFB2, and TGFB3, and three genes involved in mineralization-ALPL, BGLAP, and VDR. In conclusion, this investigation has demonstrated that four 1-h episodes of cyclic mechanical strain acted synergistically with triple supplement to enhance osteogenesis and bone nodule formation by cultured hESCs. This suggests the development of methods to engineer three-dimensional constructs of mineralized bone in vitro, could offer an alternative approach to osseous regeneration by producing a biomaterial capable of providing stable surfaces for osteoblasts to synthesize new bone, while at the same time able to be resorbed by an osteoclastic activity-in other words, one that can recapitulate the remodeling dynamics of a naturally occurring bone matrix.

Ethical considerations on methods used in abortions

There is a fundamental inconsistency in Western society's treatment of non-human animals on the one hand, and of human foetuses on the other. While most Western countries allow the butchering of animals and their use in experimentation, this must occur under carefully controlled conditions that are intended to minimize their pain and suffering as much as possible. At the same time, most Western countries permit various abortion methods without similar concerns for the developing fetus. The only criteria for deciding which abortion method is used centre in the stage of the pregnancy, the size of the fetus, the health of the pregnant woman and the physician's preference. This is out of step with the underlying ethos of animal cruelty legislation, cannot be justified ethically and should be rectified by adjusting abortion methods to the capacity of the fetus to experience nociception and/or pain.

Confined 3D microenvironment regulates early differentiation in human pluripotent stem cells

The therapeutic potential of human pluripotent stem (hPS) cells is threatened, among various problems, by the difficulty to homogenously direct cell differentiation into specific lineages. The transition from hPSC into committed differentiated cells is accompanied by secretome activity, remodeling of extracellular matrix and self-organization into germ layers. In this work, we aimed to investigate how different three-dimensional microenvironments regulate the early differentiation of the three germ layers in human embryonic stem (hES) cells derived embryoid bodies. In particular, a permeable, biocompatible, hydrogel microwell array was specifically designed for recreating a confined niche in which EB secreted molecules accumulate in accordance with hydrogel diffusional cut-off. Fluorescence recovery after photobleaching technique was performed to accurately evaluate hydrogel permeability, mesh size and diffusional cutoff for soluble molecules. Three different culture conditions of EB culture were analyzed: suspension, confinement in microwells of width/depth ratio 1:1 and 1:2. Results show that EBs cultured in microwells are viable and have comparable average size after 8 days culture. Whole genome microarrays show that significative differential gene expression was observed between suspension and confined EBs culture. In particular, EBs culture in microwells promotes the expression of genes involved in pattern specification processes, brain development, ectoderm and endoderm differentiation. On the contrary, suspension EBs express instead genes involved in mesoderm specification and heart development. These results suggest that local accumulation of EBs secreted molecules drives differentiation patterns, as confirmed by immunofluorescence of germ layer markers, in hydrogel confined EB culture from both hES cells and human induced pluripotent stem (hiPS) cells. Our findings highlight an additional potential role of biomaterial in controlling hPSC differentiation through secreted factor niche specification.

Teratoma formation of human embryonic stem cells in three-dimensional perfusion culture bioreactors

Teratoma formation in mice is today the most stringent test for pluripotency that is available for human pluripotent cells, as chimera formation and tetraploid complementation cannot be performed with human cells. The teratoma assay could also be applied for assessing the safety of human pluripotent cell-derived cell populations intended for therapeutic applications. In our study we examined the spontaneous differentiation behaviour of human embryonic stem cells (hESCs) in a perfused 3D multi-compartment bioreactor system and compared it with differentiation of hESCs and human induced pluripotent cells (hiPSCs) cultured in vitro as embryoid bodies and in vivo in an experimental mouse model of teratoma formation. Results from biochemical, histological/immunohistological and ultrastuctural analyses revealed that hESCs cultured in bioreactors formed tissue-like structures containing derivatives of all three germ layers. Comparison with embryoid bodies and the teratomas revealed a high degree of similarity of the tissues formed in the bioreactor to these in the teratomas at the histological as well as transcriptional level, as detected by comparative whole-genome RNA expression profiling. The 3D culture system represents a novel in vitro model that permits stable long-term cultivation, spontaneous multi-lineage differentiation and tissue formation of pluripotent cells that is comparable to in vivo differentiation. Such a model is of interest, e.g. for the development of novel cell differentiation strategies. In addition, the 3D in vitro model could be used for teratoma studies and pluripotency assays in a fully defined, controlled environment, alternatively to in vivo mouse models.

Analysis of embryoid bodies derived from human induced pluripotent stem cells as a means to assess pluripotency

Human induced pluripotent stem cells (hiPSCs) have core properties of unlimited self-renewal and differentiation potential and have emerged as exciting cell sources for applications in regenerative medicine, drug discovery, understanding of development, and disease etiology. Key among numerous criteria to assess pluripotency includes the in vivo teratoma assay that has been widely proposed as a standard functional assay to demonstrate the pluripotency of hiPSCs. Yet, the lack of reliability across methodologies, lack of definitive clinical significance, and associated expenses bring into question use of the teratoma assay as the “gold standard” for determining pluripotency. We propose use of the in vitro embryoid body (EB) assay as an important alternative to the teratoma assay. This paper summarizes the methodologies for creating EBs from hiPSCs and the subsequent analyses to assess pluripotency and proposes its use as a cost-effective, controlled, and reproducible approach that can easily be adopted to determine pluripotency of generated hiPSCs.

The effect of human and mouse fibroblast feeder cells on cardiac differentiation of human pluripotent stem cells

Mouse embryonic fibroblasts (MEFs) and human foreskin fibroblasts (hFFs) are commonly used as feeder cells to maintain the pluripotent state of stem cells. The aim of the present study was to evaluate the effect of MEF and hFF feeders on the cardiac differentiation. Two human embryonic and two induced pluripotent stem cell lines were cultured on MEF and hFF before cardiac differentiation. The expression of Brachyury T was higher in cell lines cultured on MEF, than if cultured on hFF, suggesting enhanced mesoderm formation. However, significant positive influence of MEF feeders on cardiac differentiation was only seen with one cell line. Further, the ability of hFF to maintain pluripotency of stem cells originally cultured on MEF was quite poor. In conclusion, the cells behaved differently whether cultured on hFF or MEF feeders. However, the influence of the feeder cells on differentiation was less than the difference observed between the cell lines.

Engineered microenvironments for self-renewal and musculoskeletal differentiation of stem cells

Stem cells hold great promise for therapies aimed at regenerating damaged tissue, drug screening and studying in vitro models of human disease. However, many challenges remain before these applications can become a reality. One such challenge is developing chemically defined and scalable culture conditions for derivation and expansion of clinically viable human pluripotent stem cells, as well as controlling their differentiation with high specificity. Interaction of stem cells with their extracellular microenvironment plays an important role in determining their differentiation commitment and functions. Regenerative medicine approaches integrating cell-matrix and cell-cell interactions, and soluble factors could lead to development of robust microenvironments to control various cellular responses. Indeed, several of these recent developments have provided significant insight into the design of microenvironments that can elicit the targeted cellular response. In this article, we will focus on some of these developments with an emphasis on matrix-mediated expansion of human pluripotent stem cells while maintaining their pluripotency. We will also discuss the role of matrix-based cues and cell-cell interactions in the form of soluble signals in directing stem cell differentiation into musculoskeletal lineages.

Self-organization phenomena in embryonic stem cell-derived embryoid bodies: axis formation and breaking of symmetry during cardiomyogenesis

Aggregation of embryonic stem cells gives rise to embryoid bodies (EBs) which undergo developmental processes reminiscent of early eutherian embryonic development. Development of the three germ layers suggests that gastrulation takes place. In vivo, gastrulation is a highly ordered process but in EBs only few data support the hypothesis that self-organization of differentiating cells leads to morphology, reminiscent of the early gastrula. Here we demonstrate that a timely implantation-like process is a prerequisite for the breaking of the radial symmetry of suspended EBs. Attached to a surface, EBs develop a bilateral symmetry and presumptive mesodermal cells emerge between the center of the EBs and a horseshoe-shaped ridge of cells. The development of an epithelial sheet of cells on one side of the EBs allows us to define an 'anterior' and a 'posterior' end of the EBs. In the mesodermal area, first cardiomyocytes (CMCs) develop mainly next to this epithelial sheet of cells. Development of twice as many CMCs at the 'left' side of the EBs breaks the bilateral symmetry and suggests that cardiomyogenesis reflects a local or temporal asymmetry in EBs. The asymmetric appearance of CMCs but not the development of mesoderm can be disturbed by ectopic expression of the muscle-specific protein Desmin. Later, the bilateral morphology becomes blurred by an apparently chaotic differentiation of many cell types. The absence of comparable structures in aggregates of cardiovascular progenitor cells isolated from the heart demonstrates that the self-organization of cells during a gastrulation-like process is a unique feature of embryonic stem cells.

Histochemistry and cell biology: the annual review 2010

This review summarizes recent advances in histochemistry and cell biology which complement and extend our knowledge regarding various aspects of protein functions, cell and tissue biology, employing appropriate in vivo model systems in conjunction with established and novel approaches. In this context several non-expected results and discoveries were obtained which paved the way of research into new directions. Once the reader embarks on reading this review, it quickly becomes quite obvious that the studies contribute not only to a better understanding of fundamental biological processes but also provide use-oriented aspects that can be derived therefrom.