Human embryonic germ cell derivatives express a broad range of developmentally distinct markers and proliferate extensively in vitro

Upscaling biological complexity to boost neuronal and oligodendroglia maturation and improve in vitro developmental neurotoxicity (DNT) evaluation

Human induced pluripotent stem cell (iPSC)-derived neuronal and glial cell models are suitable to assess the effects of environmental chemicals on the developing brain. Such test systems can recapitulate several key neurodevelopmental features, such as neural stem cell formation and differentiation towards different neuronal subtypes and astrocytes, neurite outgrowth, synapse formation and neuronal network formation and function, which are crucial for brain development. While monolayer, two-dimensional (2D) cultures of human iPSC-neuronal or glial derivatives are generally suited for high-throughput testing, they also show some limitations. In particular, differentiation towards myelinating oligodendrocytes can only be achieved after extended periods in differentiation. In recent years, the implementation of three-dimensional (3D) neuronal and glial models obtained from human iPSCs has been shown to compensate for such limitations, enabling robust differentiation towards both neuronal and glial cell populations, myelination and formation of more mature neuronal network activity. Here we compared the differentiation capacity of human iPSC-derived neural stem cells cultured either as 2D monolayer or as 3D neurospheres, and assessed chlorpyrifos (CPF) effects. Data indicate that 3D neurospheres differentiate towards neurons and oligodendroglia more rapidly than 2D cultures; however, the 2D model is more suitable to assess neuronal functionality by analysis of spontaneous electrical activity using multielectrode array. Moreover, 2D and 3D test systems are diversely susceptible to CPF treatment. In conclusion, the selection of the most suitable in vitro test system (either 2D or 3D) should take into account the context of use and intended research goals ('fit for purpose' principle).

Defining Human Pluripotency

Human pluripotent stem cells harbor the capacity to differentiate into cells from the three embryonic germ layers, and this ability grants them a central role in modeling human disorders and in the field of regenerative medicine. Here, we review pluripotency in human cells with respect to four different aspects: (1) embryonic development, (2) transcriptomes of pluripotent cell stages, (3) genes and pathways that reprogram somatic cells into pluripotent stem cells, and finally (4) the recent identification of the human pluripotent stem cell essentialome. These four aspects of pluripotency collectively culminate in a broader understanding of what makes a cell pluripotent.

TGFβ Family Signaling Pathways in Pluripotent and Teratocarcinoma Stem Cells' Fate Decisions: Balancing Between Self-Renewal, Differentiation, and Cancer

The transforming growth factor-β (TGFβ) family factors induce pleiotropic effects and are involved in the regulation of most normal and pathological cellular processes. The activity of different branches of the TGFβ family signaling pathways and their interplay with other signaling pathways govern the fine regulation of the self-renewal, differentiation onset and specialization of pluripotent stem cells in various cell derivatives. TGFβ family signaling pathways play a pivotal role in balancing basic cellular processes in pluripotent stem cells and their derivatives, although disturbances in their genome integrity induce the rearrangements of signaling pathways and lead to functional impairments and malignant transformation into cancer stem cells. Therefore, the identification of critical nodes and targets in the regulatory cascades of TGFβ family factors and other signaling pathways, and analysis of the rearrangements of the signal regulatory network during stem cell state transitions and interconversions, are key issues for understanding the fundamental mechanisms of both stem cell biology and cancer initiation and progression, as well as for clinical applications. This review summarizes recent advances in our understanding of TGFβ family functions in naїve and primed pluripotent stem cells and discusses how these pathways are involved in perturbations in the signaling network of malignant teratocarcinoma stem cells with impaired differentiation potential.

Dynamics of male canine germ cell development

Primordial germ cells (PGCs) are precursors of gametes that can generate new individuals throughout life in both males and females. Additionally, PGCs have been shown to differentiate into embryonic germ cells (EGCs) after in vitro culture. Most studies investigating germinative cells have been performed in rodents and humans but not dogs (Canis lupus familiaris). Here, we elucidated the dynamics of the expression of pluripotent (POU5F1 and NANOG), germline (DDX4, DAZL and DPPA3), and epigenetic (5mC, 5hmC, H3K27me3 and H3K9me2) markers that are important for the development of male canine germ cells during the early (22-30 days post-fertilization (dpf)), middle (35-40 dpf) and late (45-50 dpf) gestational periods. We performed sex genotype characterization, immunofluorescence, immunohistochemistry, and quantitative reverse transcriptase polymerase chain reaction (RT-qPCR) analyses. Furthermore, in a preliminary study, we evaluated the capacity of canine embryo PGCs (30 dpf) to differentiate into EGCs. To confirm the canine EGCs phenotype, we performed alkaline phosphatase detection, immunohistochemistry, electron and transmission scanning microscopy and RT-qPCR analyses. The PGCs were positive for POU5F1 and H3K27me3 during all assessed developmental periods, including all periods between the gonadal tissue stage and foetal testes development. The number of NANOG, DDX4, DAZL, DPPA3 and 5mC-positive cells increased along with the developing cords from 35-50 dpf. Moreover, our results demonstrate the feasibility of inducing canine PGCs into putative EGCs that present pluripotent markers, such as POU5F1 and the NANOG gene, and exhibit reduced expression of germinative genes and increased expression of H3K27me3. This study provides new insight into male germ cell development mechanisms in dogs.

Heterogeneity of Stem Cells: A Brief Overview

Stem cells possess the extraordinary capacity of self-renewal and differentiation to various cell types, thus to form original tissues and organs. Stem cell heterogeneity including genetic and nongenetic mechanisms refers to biological differences amongst normal and stem cells originated within the same tissue. Cell differentiation hierarchy and stochasticity in gene expression and signaling pathways may result in phenotypic differences of stem cells. The maintenance of stemness and activation of differentiation potential are fundamentally orchestrated by microenvironmental stem cell niche-related cellular and humoral signals.

In vitro germ cell differentiation from embryonic stem cells of mice: induction control by BMP4 signalling

The present study aims to confirm and analyse germ cell-related patterns and specific gene expressions at a very early stage of cell commitment. Following the XY cytogenetic confirmation of the CCE mouse embryonic stem cells (mESCs) line, cells were cultured to form embryoid bodies (EBs). Expression pattern assessment of the mouse vasa homologue (Mvh), Stra8, α6 and β1 integrin genes in ESC and 1–3-day-old EB showed that all genes except α6 integrin were expressed in the ESC. The mean calibration of Mvh, Stra8 and α6 integrin expression significantly increased upon EB formation compared with the ESCs. During mouse embryogenesis, the signalling of bone morphogenetic protein (BMP) is essential for germ-line formation. To investigate its role in germ-line induction in vitro, mESCs were cultured as 1-day-old EB aggregates with BMP4 for 4 days in STO co-culture systems, in the presence and absence of 5 ng/ml BMP4. At the end of the culture period, colony assay (number and diameter) was performed and the viability percentage and proliferation rate was determined. There were no significant statistical differences in the abovementioned criteria between these two groups. Moreover, the expression of Mvh, α6 and β1 integrins, Stra8 and Piwil2 genes was evaluated in co-culture groups. The molecular results of co-culture groups showed higher–but insignificant–Piwil2 and significant α6 integrin expressions in BMP4 treated co-culture systems. These results confirmed that the EB system and the presence of BMP4 in a STO co-culture system improve the differentiation of ESCs to germ cell.

Teratoma: from spontaneous tumors to the pluripotency/malignancy assay

A teratoma is a benign tumor containing a mixture of differentiated tissues and organotypic derivatives of the three germ layers, while a teratocarcinoma also contains embryonal carcinoma cells (EC cells). Experimental teratomas and teratocarcinomas have been derived from early mammalian embryos transplanted into the adult animal (ectopic sites). In the rat, the pluripotency of the transplanted epiblast was demonstrated and a quantifiable restriction of developmental potential persisted after subsequent transplantation of chemically defined cultivated postimplantation embryos. The rat is nonpermissive for teratocarcinoma development and rat pluripotent cell lines have been established only recently. Transplantation of mouse embryos, epiblast, or embryonic stem cells (mESCs) gave rise to teratocarcinomas. The pluripotency of reprogrammed human cells has been tested by a 'gold standard' trilaminar teratoma assay in immunocompromised mice in vivo. Human pluripotent stem cells proposed for use in regenerative medicine such as human embryonic stem cell (hESC), human nuclear-transfer/therapeutic cloning embryonic stem cell (NT-ESC), or human induced pluripotent stem cell (hiPSC) lines, once differentiated in vitro to the desired cell type, should be again tested in a long-term animal teratoma assay to exclude their malignancy. Such an approach led to a recently implemented human therapy with retinal pigmented epithelium. For greater biosafety, the teratoma assay should be standardized and complemented by assessments of mutations/epimutations, RNA/protein expression, and possible immunogenicity of autologous pluripotent cells. Furthermore, the standardized teratoma assay should be directed more to the assessment of EC/malignant cell features than of differentiated tissues, especially after a unique case of human therapy with neural stem cells was found to lead to malignancy. For further resources related to this article, please visit the WIREs website.

Exogenous p53 upregulated modulator of apoptosis (PUMA) decreases growth of lung cancer A549 cells

PURPOSE

To investigate the influence of exogenous p53 upregulated modulator of apoptosis (PUMA) expression on cell proliferation and apoptosis in human non-small cell lung cancer A549 cells and transplanted tumor cell growth in nude mice.

MATERIALS AND METHODS

A549 cells were divided into the following groups: control, non- carrier (NC), PUMA (transfected with pCEP4- (HA) 2-PUMA plasmid), DDP (10 μg/mL cisplatin treatment) and PUMA+DDP (transfected with pCEP4-(HA)2-PUMA plasmid and 10 μg/mL cisplatin treatment). The MTT method was used to detect the cell survival rate. Cell apoptosis rates were measured by flow cytometry, and PUMA, Bax and Bcl-2 protein expression levels were measured by Western blotting.

RESULTS

Compared to the control group, the PUMA, DDP and PUMA+DDP groups all had significantly decreased A549 cell proliferation (p<0.01), with the largest reduction in the PUMA+DDP group. Conversely, the apoptosis rates of the three groups were significantly increased (P<0.01), and the PUMA and DDP treatments were synergistic. Moreover, Bax protein levels significantly increased (p<0.01), while Bcl-2 protein levels significantly decreased (p<0.01). Finally, both the volume and the weights of transplanted tumors were significantly reduced (p<0.01), and the inhibition ratio of the PUMA+DDP group was significantly higher than in the single DDP or PUMA groups.

CONCLUSIONS

Exogenous PUMA effectively inhibited lung cancer A549 cell proliferation and transplanted tumor growth by increasing Bax protein levels and reducing Bcl-2 protein levels.

Comparison of the depolarization response of human mesenchymal stem cells from different donors

Bioelectric signaling is currently being explored as a novel regulator of cell processes in non-excitable cells. In particular, stem cells have demonstrated increasing evidence of electrophysiology-mediated regulation of stemness acquisition, proliferation, differentiation, and migration. However, in light of many reports of primary stem cell heterogeneity, it is important to characterize the variability of stem cell response to biophysical manipulations in order to assess the utility of bioelectric modulation as a universal strategy for stem cell control. In this work, human mesenchymal stem cells (hMSCs) from five donors were evaluated for their response to membrane potential (V_mem) depolarization. We compared the inter-donor variability of their osteogenic and adipogenic differentiation potential, as well as their ability to maintain a differentiated phenotype after induction. We identified the markers that responded most consistently across donors and found that calcium deposition and gene expression of bone sialoprotein, lipoprotein lipase, and fatty acid binding protein 4 are the preferred markers for assessing differentiation response to V_mem depolarization. We also note that since there exists variability even among some of these markers, these assays should be performed on any newly acquired hMSC population if their bioelectric properties are to be studied further.

Neurogenin 3 Expressing Cells in the Human Exocrine Pancreas Have the Capacity for Endocrine Cell Fate

Neurogenin 3 (NGN3) is necessary and sufficient for endocrine differentiation during pancreatic development and is expressed by a population of progenitor cells that give rise exclusively to hormone-secreting cells within islets. NGN3 protein can be detected in the adult rodent pancreas only following certain types of injury, when it is transiently expressed by exocrine cells undergoing reprogramming to an endocrine cell fate. Here, NGN3 protein can be detected in 2% of acinar and duct cells in living biopsies of histologically normal adult human pancreata and 10% in cadaveric biopsies of organ donor pancreata. The percentage and total number of NGN3+ cells increase during culture without evidence of proliferation or selective cell death. Isolation of highly purified and viable NGN3+ cell populations can be achieved based on coexpression of the cell surface glycoprotein CD133. Transcriptome and targeted expression analyses of isolated CD133+ / NGN3+ cells indicate that they are distinct from surrounding exocrine tissue with respect to expression phenotype and Notch signaling activity, but retain high level mRNA expression of genes indicative of acinar and duct cell function. NGN3+ cells have an mRNA expression profile that resembles that of mouse early endocrine progenitor cells. During in vitro differentiation, NGN3+ cells express genes in a pattern characteristic of endocrine development and result in cells that resemble beta cells on the basis of coexpression of insulin C-peptide, chromogranin A and pancreatic and duodenal homeobox 1. NGN3 expression in the adult human exocrine pancreas marks a dedifferentiating cell population with the capacity to take on an endocrine cell fate. These cells represent a potential source for the treatment of diabetes either through ex vivo manipulation, or in vivo by targeting mechanisms controlling their population size and endocrine cell fate commitment.

Pituitary Cell Turnover: From Adult Stem Cell Recruitment through Differentiation to Death

The recent demonstration using genetic tracing that in the adult pituitary stem cells are normally recruited from the niche in the marginal zone and differentiate into secretory cells in the adenopituitary has elegantly confirmed the proposal made when the pituitary stem cell niche was first discovered 5 years ago. Some of the early controversies have also been resolved. However, many questions remain, such as which are the markers that make a pituitary stem cell truly unique and the exact mechanisms that trigger recruitment from the niche. Little is known about the processes of commitment and differentiation once a stem cell has left the niche. Moreover, the acceptance that pituitary cells are renewed by stem cells implies the existence of regulated mechanisms of cell death in differentiated cells which must themselves be explained. The demonstration of an apoptotic pathway mediated by RET/caspase 3/Pit-1/Arf/p53 in normal somatotrophs is therefore an important step towards understanding how pituitary cell number is regulated. Further work will elucidate how the rates of the three processes of cell renewal, differentiation and apoptosis are balanced in tissue homeostasis after birth, but altered in pituitary hyperplasia in response to physiological stimuli such as puberty and lactation. Thus, we can aim to understand the mechanisms underlying human disease due to insufficient (hypopituitarism) or excess (pituitary tumor) cell numbers.

Comparison of human induced pluripotent stem-cell derived cardiomyocytes with human mesenchymal stem cells following acute myocardial infarction

INTRODUCTION

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have recently been shown to express key cardiac proteins and improve in vivo cardiac function when administered following myocardial infarction. However, the efficacy of hiPSC-derived cell therapies, in direct comparison to current, well-established stem cell-based therapies, is yet to be elucidated. The goal of the current study was to compare the therapeutic efficacy of human mesenchymal stem cells (hMSCs) with hiPSC-CMs in mitigating myocardial infarction (MI).

METHODS

Male athymic nude hyrats were subjected to permanent ligation of the left-anterior-descending (LAD) coronary artery to induce acute MI. Four experimental groups were studied: 1) control (non-MI), 2) MI, 3) hMSCs (MI+MSC), and 4) hiPSC-CMs (MI+hiPSC-derived cardiomyocytes). The hiPSC-CMs and hMSCs were labeled with superparamagnetic iron oxide (SPIO) in vitro to track the transplanted cells in the ischemic heart by high-field cardiac MRI. These cells were injected into the ischemic heart 30-min after LAD ligation. Four-weeks after MI, cardiac MRI was performed to track the transplanted cells in the infarct heart. Additionally, echocardiography (M-mode) was performed to evaluate the cardiac function. Immunohistological and western blot studies were performed to assess the cell tracking, engraftment and cardiac fibrosis in the infarct heart tissues.

RESULTS

Echocardiography data showed a significantly improved cardiac function in the hiPSC-CMs and hMSCs groups, when compared to MI. Immunohistological studies showed expression of connexin-43, α-actinin and myosin heavy chain in engrafted hiPSC-CMs. Cardiac fibrosis was significantly decreased in hiPSC-CMs group when compared to hMSCs or MI groups. Overall, this study demonstrated improved cardiac function with decreased fibrosis with both hiPSC-CMs and hMSCs groups when compared with MI group.

The role of purinergic receptors in stem cell differentiation

A major challenge modern society has to face is the increasing need for tissue regeneration due to degenerative diseases or tumors, but also accidents or warlike conflicts. There is great hope that stem cell-based therapies might improve current treatments of cardiovascular diseases, osteochondral defects or nerve injury due to the unique properties of stem cells such as their self-renewal and differentiation potential. Since embryonic stem cells raise severe ethical concerns and are prone to teratoma formation, adult stem cells are still in the focus of research. Emphasis is placed on cellular signaling within these cells and in between them for a better understanding of the complex processes regulating stem cell fate. One of the oldest signaling systems is based on nucleotides as ligands for purinergic receptors playing an important role in a huge variety of cellular processes such as proliferation, migration and differentiation. Besides their natural ligands, several artificial agonists and antagonists have been identified for P1 and P2 receptors and are already used as drugs. This review outlines purinergic receptor expression and signaling in stem cells metabolism. We will briefly describe current findings in embryonic and induced pluripotent stem cells as well as in cancer-, hematopoietic-, and neural crest-derived stem cells. The major focus will be placed on recent findings of purinergic signaling in mesenchymal stem cells addressed in in vitro and in vivo studies, since stem cell fate might be manipulated by this system guiding differentiation towards the desired lineage in the future.

Hematopoietic stem cells: an overview

Considerable efforts have been made in recent years in understanding the mechanisms that govern hematopoietic stem cell (HSC) origin, development, differentiation, self-renewal, aging, trafficking, plasticity and transdifferentiation. Hematopoiesis occurs in sequential waves in distinct anatomical locations during development and these shifts in location are accompanied by changes in the functional status of the stem cells and reflect the changing needs of the developing organism. HSCs make a choice of either self-renewal or committing to differentiation. The balance between self-renewal and differentiation is considered to be critical to the maintenance of stem cell numbers. It is still under debate if HSC can rejuvenate infinitely or if they do not possess ''true" self-renewal and undergo replicative senescence such as any other somatic cell. Gene therapy applications that target HSCs offer a great potential for the treatment of hematologic and immunologic diseases. However, the clinical success has been limited by many factors. This review is intended to summarize the recent advances made in the human HSC field, and will review the hematopoietic stem cell from definition through development to clinical applications.

Development of a pluripotent stem cell derived neuronal model to identify chemically induced pathway perturbations in relation to neurotoxicity: effects of CREB pathway inhibition

According to the advocated paradigm shift in toxicology, acquisition of knowledge on the mechanisms underlying the toxicity of chemicals, such as perturbations of biological pathways, is of primary interest. Pluripotent stem cells (PSCs), such as human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), offer a unique opportunity to derive physiologically relevant human cell types to measure molecular and cellular effects of such pathway modulations. Here we compared the neuronal differentiation propensity of hESCs and hiPSCs with the aim to develop novel hiPSC-based tools for measuring pathway perturbation in relation to molecular and cellular effects in vitro. Among other fundamental pathways, also, the cAMP responsive element binding protein (CREB) pathway was activated in our neuronal models and gave us the opportunity to study time-dependent effects elicited by chemical perturbations of the CREB pathway in relation to cellular effects. We show that the inhibition of the CREB pathway, using 2-naphthol-AS-E-phosphate (KG-501), induced an inhibition of neurite outgrowth and synaptogenesis, as well as a decrease of MAP2(+) neuronal cells. These data indicate that a CREB pathway inhibition can be related to molecular and cellular effects that may be relevant for neurotoxicity testing, and, thus, qualify the use of our hiPSC-derived neuronal model for studying chemical-induced neurotoxicity resulting from pathway perturbations.

The neonatal marmoset monkey ovary is very primitive exhibiting many oogonia

Oogonia are characterized by diploidy and mitotic proliferation. Human and mouse oogonia express several factors such as OCT4, which are characteristic of pluripotent cells. In human, almost all oogonia enter meiosis between weeks 9 and 22 of prenatal development or undergo mitotic arrest and subsequent elimination from the ovary. As a consequence, neonatal human ovaries generally lack oogonia. The same was found in neonatal ovaries of the rhesus monkey, a representative of the old world monkeys (Catarrhini). By contrast, proliferating oogonia were found in adult prosimians (now called Strepsirrhini), which is a group of ‘lower’ primates. The common marmoset monkey (Callithrix jacchus) belongs to the new world monkeys (Platyrrhini) and is increasingly used in reproductive biology and stem cell research. However, ovarian development in the marmoset monkey has not been widely investigated. Herein, we show that the neonatal marmoset ovary has an extremely immature histological appearance compared with the human ovary. It contains numerous oogonia expressing the pluripotency factors OCT4A, SALL4, and LIN28A (LIN28). The pluripotency factor-positive germ cells also express the proliferation marker MKI67 (Ki-67), which has previously been shown in the human ovary to be restricted to premeiotic germ cells. Together, the data demonstrate the primitiveness of the neonatal marmoset ovary compared with human. This study may introduce the marmoset monkey as a non-human primate model to experimentally study the aspects of primate primitive gonad development, follicle assembly, and germ cell biology in vivo.

Stem Cells on Biomaterials for Synthetic Grafts to Promote Vascular Healing

This review is divided into two interconnected parts, namely a biological and a chemical one. The focus of the first part is on the biological background for constructing tissue-engineered vascular grafts to promote vascular healing. Various cell types, such as embryonic, mesenchymal and induced pluripotent stem cells, progenitor cells and endothelial- and smooth muscle cells will be discussed with respect to their specific markers. The in vitro and in vivo models and their potential to treat vascular diseases are also introduced. The chemical part focuses on strategies using either artificial or natural polymers for scaffold fabrication, including decellularized cardiovascular tissue. An overview will be given on scaffold fabrication including conventional methods and nanotechnologies. Special attention is given to 3D network formation via different chemical and physical cross-linking methods. In particular, electron beam treatment is introduced as a method to combine 3D network formation and surface modification. The review includes recently published scientific data and patents which have been registered within the last decade.

Time-dependent processes in stem cell-based tissue engineering of articular cartilage

Articular cartilage (AC), situated in diarthrodial joints at the end of the long bones, is composed of a single cell type (chondrocytes) embedded in dense extracellular matrix comprised of collagens and proteoglycans. AC is avascular and alymphatic and is not innervated. At first glance, such a seemingly simple tissue appears to be an easy target for the rapidly developing field of tissue engineering. However, cartilage engineering has proven to be very challenging. We focus on time-dependent processes associated with the development of native cartilage starting from stem cells, and the modalities for utilizing these processes for tissue engineering of articular cartilage.

Tracing the conversion process from primordial germ cells to pluripotent stem cells in mice

To understand mechanisms underlying acquisition of pluripotency, it is critical to identify cells that can be converted to pluripotent stem cells. For this purpose, we focused on unipotent primordial germ cells (PGCs), which can be reprogrammed into pluripotent embryonic germ (EG) cells under defined conditions. Treatment of PGCs with combinations of signaling inhibitors, including inhibitors of MAP2K (MEK), GSK3B (GSK-3beta), and TGFB (TGFbeta) type 1 receptors, induced cells to enter a pluripotent state at a high frequency (12.1%) by Day 10 of culture. When we employed fluorescence-activated cell sorting to monitor conversion of candidate cells to a pluripotent state, we observed a cell cycle shift to S phase, indicating enrichment of pluripotent cells, during the early phase of EG formation. Transcriptome analysis revealed that PGCs retained expression of some pluripotent stem cell-associated genes, such as Pou5f1 and Sox2, during EG cell formation. On the other hand, PGCs lost their germ lineage characteristics and acquired expression of pluripotent stem cell markers, such as Klf4 and Eras. The overall gene expression profiles revealed by this system provide novel insight into how pluripotency is acquired in germ-committed cells.

Current Applications of Human Pluripotent Stem Cells: Possibilities and Challenges

Stem cells are self-renewable cells with the differentiation capacity to develop into somatic cells with biological functions. This ability to sustain a renewable source of multi- and/or pluripotential differentiation has brought new hope to the field of regenerative medicine in terms of cell therapy and tissue engineering. Moreover, stem cells are invaluable tools as in vitro models for studying diverse fields, from basic scientific questions such as developmental processes and lineage commitment, to practical application including drug screening and testing. The stem cells with widest differentiation potential are pluripotent stem cells (PSCs), which are rare cells with the ability to generate somatic cells from all three germ layers. PSCs are considered the most optimal choice for therapeutic potential of stem cells, bringing new impetus to the field of regenerative medicine. In this article, we discuss the therapeutic potential of human PSCs (hPSCs) including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), reviewing the current preclinical and clinical data using these stem cells. We describe the classification of different sources of hPSCs, ongoing research, and currently encountered clinical obstacles of these novel and versatile human stem cells.

An Engraftable Human Embryonic Stem Cell Neuronal Lineage-Specific Derivative Retains Embryonic Chromatin Plasticity for Scale-Up CNS Regeneration

BACKGROUND

Pluripotent human embryonic stem cells (hESCs) proffer cures for a wide range of neurological disorders by supplying the diversity of human neuronal cell types in the developing CNS for repair. However, realizing the therapeutic potential of hESC derivatives has been hindered by generating neuronal cells from pluripotent cells through uncontrollable and inefficient multi-lineage differentiation. Previously, we used a defined platform to identify retinoic acid as sufficient to induce the specification of neuroectoderm direct from the pluripotent state of hESCs and trigger uniform neuronal lineage-specific progression to human neuronal progenitors (hESC-I hNuPs) and neurons (hESC-I hNus) in the developing CNS with high efficiency.

METHODS

Having achieved uniformly conversion of pluripotent hESCs to a neuronal lineage, in this study, the expression and intracellular distribution patterns of a set of chromatin modifiers in hESC-I hNuPs were examined and compared to the two prototypical neuroepithelial-like human neural stem cells (hNSCs) either derived from hESCs or isolated directly from the human fetal neuroectoderm in vivo.

RESULTS

These hESC-I hNuPs expressed high levels of active chromatin modifiers, including acetylated histone H3 and H4, HDAC1, Brg-1, and hSNF2H, retaining an embryonic acetylated globally active chromatin state. Consistent with this observation, several repressive chromatin remodeling factors regulating histone H3K9 methylation, including SIRT1, SUV39H1, and Brm, were inactive in hESC-I hNuPs. These Nurr1-positive hESC-I hNuPs, which did not express the canonical hNSC markers, yielded neurons efficiently and exclusively, as they did not differentiate into glial cells. Following engraftment in the brain, hESC-I hNuPs yielded well-dispersed and well-integrated human neurons at a high prevalence.

CONCLUSIONS

These observations suggest that, unlike the prototypical neuroepithelial-like nestin-positive hNSCs, these in vitro neuroectoderm-derived Nurr1-positive hESC-I hNuPs are a more neuronal lineage-specific and plastic human stem cell derivative, providing an engraftable human embryonic neuronal progenitor in high purity and large supply with adequate neurogenic potential for scale-up CNS regeneration as stem cell therapy to be translated to patients in clinical trials.

No evidence for the presence of oogonia in the human ovary after their final clearance during the first two years of life

BACKGROUND

Conflicting results of studies on mouse and human have either verified or refuted the presence of oogonia/primordial germ cells in the post-natal ovary. The aim of this study was to trace whether oogonia recognized by immunohistochemical methods in the first trimester human ovary were present also in peri- and post-natal ovaries.

METHODS

For this study, 82 human ovaries were collected: 25 from embryos from 5 to 10 weeks post conception (wpc), 2 at 18 wpc, 32 from 32 wpc to 2 years and 23 from 2 to 32 years. Of these, 80 ovaries were fixed and paraffin-embedded and 2 (8 year-old) ovaries were processed for plastic sections. Serial sections were prepared for immunohistochemical detection of markers for oogonia: tyrosine kinase receptor for stem cell factor (SCF)(C-KIT), stage-specific embryonic antigen-4 (SSEA4), homeobox gene transcription factor (NANOG), octamer binding transcription factor 4 (OCT4) and melanoma antigen-4 (Mage-A4), while noting that C-KIT also stains diplotene oocytes.

RESULTS

Almost all oogonia exclusively stained for SSEA4, NANOG, OCT4 and C-KIT, whereas MAGE-A4 only stained a small fraction. At birth only a few oogonia were stained. These disappeared before 2 years, leaving only diplotene oocytes stained for C-KIT. From 18 wpc to 2 years, the medulla contained conglomerates of healthy and degenerating oogonia and small follicles, waste baskets (WBs) and oogonia enclosed in growing follicles (FWB). Medulla of older ovaries contained groups of primordial, healthy follicles.

CONCLUSIONS

We found no evidence for the presence of oogonia in the human ovary after their final clearing during the first 2 years. We suggest that perinatal medullary WB and FWB give rise to the groups of small, healthy follicles in the medulla.

Review article: current status of myocardial regeneration: new cell sources and new strategies

Clinical trials of stem cell therapy in cardiology are based upon a reasonably solid foundation in animal laboratory research. The most widely used cell source in clinical trials has been the patient's own reconstituted bone marrow cell (BMC) aspirate. Cell sources in human bone marrow include hematopoietic stem cells, mesenchymal progenitor cells, and other cell types with many desirable characteristics. In vitro, they can be induced to become typical sarcomeres with centrally positioned nuclei and abundant mitochondria and to express atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and contractile proteins including myosin heavy chain, myosin light chain, and alpha actin. Intracoronary BMC infusion significantly decreases infarct size, increases myocardial perfusion, and improves regional and global cardiac function. Meta-analyses of clinical trials of intracoronary autologous BMC infusion following acute myocardial infarction (MI) report that the mean absolute increase in ejection fraction (EF) is approximately 3% to 4%. This modest improvement in function appears to persist for 1 year. Some trials have shown that clinical events are reduced at 12 months, but others have reported no long-term clinical benefit, and the only 5-year follow-up suggests persistent benefit with decreased mortality, but also little evidence of significant myocardial regeneration in humans. These results have led to efforts to identify better cell sources and to create more conducive myocardial environment for cell proliferation. Among the cell types are skeletal myoblasts, cardiac stem cells, and induced pluripotent stem cells. Environmental modifiers are designed to increase cell survival, persistence, and proliferation.

Imprinting status of Galpha(s), NESP55, and XLalphas in cell cultures derived from human embryonic germ cells: GNAS imprinting in human embryonic germ cells

GNAS is a complex gene that through use of alternative first exons encodes signaling proteins Galpha(s) and XLalphas plus neurosecretory protein NESP55. Tissue-specific expression of these proteins is regulated through reciprocal genomic imprinting in fully differentiated and developed tissue. Mutations in GNAS account for several human disorders, including McCune-Albright syndrome and Albright hereditary osteodystrophy, and further knowledge of GNAS imprinting may provide insights into variable phenotypes of these disorders. We therefore analyzed expression of Galpha(s), NESP55, and XLalphas prior to tissue differentiation in cell cultures derived from human primordia germ cells. We found that the expression of Galpha(s) was biallelic (maternal allele: 52.6%+/- 2.5%; paternal allele: 47.2%+/- 2.5%; p= 0.07), whereas NESP55 was expressed preferentially from the maternal allele (maternal allele: 81.9%+/- 10%; paternal allele: 18.1%+/- 10%; p= 0.002) and XLalphas was preferentially expressed from the paternal allele (maternal allele: 2.7%+/- 0.3%; paternal allele: 97.3%+/- 0.3%; p= 0.007). These results demonstrate that imprinting of NESP55 occurs very early in development, although complete imprinting appears to take place later than 5-11 weeks postfertilization, and that imprinting of XLalphas occurs very early postfertilization. By contrast, imprinting of Galpha(s) most likely occurs after 11 weeks postfertilization and after tissue differentiation.

Engineering musculoskeletal tissues with human embryonic germ cell derivatives

The cells derived from differentiating embryoid bodies of human embryonic germ (hEG) cells express a broad spectrum of gene markers and have been induced toward ecto- and endodermal lineages. We describe here in vitro and in vivo differentiation of hEG-derived cells (LVEC line) toward mesenchymal tissues. The LVEC cells express many surface marker proteins characteristic of mesenchymal stem cells and differentiated into cartilage, bone, and fat. Homogenous hyaline cartilage was generated from cells after 63 population doublings. In vivo results demonstrate cell survival, differentiation, and tissue formation. The high proliferative capacity of hEG-derived cells and their ability to differentiate and form three-dimensional mesenchymal tissues without teratoma formation underscores their significant potential for regenerative medicine. The adopted coculture system also provides new insights into how a microenvironment comprised of extracellular and cellular components may be harnessed to generate hierarchically complex tissues from pluripotent cells.

Stem cells: The therapeutic role in the treatment of diabetes mellitus

The unlimited proliferative ability and plasticity to generate other cell types ensures that stem cells represent a dynamic system apposite for the identification of new molecular targets and the production and development of novel drugs. These cell lines derived from embryos could be used as a model for the study of basic and applied aspects in medical therapeutics, environmental mutagenesis and disease management. As a consequence, these can be tested for safety or to predict or anticipate potential toxicity in humans. Human ES cell lines may, therefore, prove clinically relevant to the development of safer and more effective drugs for patients presenting with diabetes mellitus.

ES, iPS, MSC, and AFS cells. Stem cells exploitation for Pediatric Surgery: current research and perspective

Despite the advancements that have been made in treating infants with congenital malformations, these still represent a major cause of disease and death during the first years of life and childhood. Regeneration of natural tissue from living cells to restore damaged tissues and organs is the main purpose of regenerative medicine. This relatively new field has emerged by the combination of tissue engineering and stem cell transplantation as a possible strategy for the replacement of damaged organs or tissues. This review would like to offer an insight on the latest evolution of stem cells with a glance at their possible application for regenerative medicine, particularly in the Paediatric Surgery field.

A robust approach to identifying tissue-specific gene expression regulatory variants using personalized human induced pluripotent stem cells

Normal variation in gene expression due to regulatory polymorphisms is often masked by biological and experimental noise. In addition, some regulatory polymorphisms may become apparent only in specific tissues. We derived human induced pluripotent stem (iPS) cells from adult skin primary fibroblasts and attempted to detect tissue-specific cis-regulatory variants using in vitro cell differentiation. We used padlock probes and high-throughput sequencing for digital RNA allelotyping and measured allele-specific gene expression in primary fibroblasts, lymphoblastoid cells, iPS cells, and their differentiated derivatives. We show that allele-specific expression is both cell type and genotype-dependent, but the majority of detectable allele-specific expression loci remains consistent despite large changes in the cell type or the experimental condition following iPS reprogramming, except on the X-chromosome. We show that our approach to mapping cis-regulatory variants reduces in vitro experimental noise and reveals additional tissue-specific variants using skin-derived human iPS cells.

Most complex traits likely result from a combination of genetic polymorphisms. The normal variation in gene expression is thought to be an important contributor. In order to examine a wide range of personalized tissue types from a given individual, we developed a robust method for detecting regulatory variants genome-wide in human induced pluripotent stem (iPS) cells. By having a platform capable of mapping regulatory variants despite large biological and experimental noise, and by being able to use in vitro differentiation to derive multiple human tissue types, our approach should enable the identification of large numbers of regulatory variants genome-wide using minimally invasive skin biopsies from a large number of human subjects.

Derivation and characterization of human embryonic germ cells: serum-free culture and differentiation potential

This study examined the effects of a chemically defined culture medium supplement, knock-out serum replacement (KSR), on the growth and differentiation of human embryonic germ cells (hEgc) and found that the efficiency of the initial establishment of hEGC lines in KSR medium was significantly higher than in fetal calf serum (FCS) medium. The percentage of undifferentiated hEGC colonies growing in KSR medium was significantly higher than in FCS-based medium (P < 0.05). The hEGC colonies showed typical mouse embryonic germ cell-like morphology. They showed normal and stable diploid karyotype and expressed alkaline phosphatase (AP), stage-specific embryonic antigens (SSEA) and other specific markers of pluripotent cells. In addition, hEGC could form simple and cystic embryoid bodies (EB) that consisted of various cell types including neural, epithelial and rhythmically beating cardiac cells, even sperm-like and oocyte-like cells. Tumour-like outgrowths were formed in nude mice and found to contain a variety of cell types, including uterine epithelium, adipocytes, squamous tissue and skin structures. In conclusion, an appropriate serum-free culture system has been developed for the establishment of hEGC lines. This may provide an in-vitro model to study differentiation and can be used as a potential source of therapy for infertility and regenerative medicine.

Microfluidic platform for controlling the differentiation of embryoid bodies

Embryonic stem (ES) cells are pluripotent cells, which can differentiate into any cell type. This cell type has often been implicated as an eminent source of renewable cells for tissue regeneration and cellular replacement therapies. Studies on manipulation of the various differentiation pathways have been at the forefront of research. There are many ways in which ES cells can be differentiated. One of the most common techniques is to initiate the development of embryoid bodies (EBs) by in vitro aggregation of ES cells. Thereafter, EBs can be induced to undergo differentiation into various cell lineages. In this article, we present a microfluidic platform using biocompatible materials, which is suitable for culturing EBs. The platform is based on a Y-channel device with two inlets for two different culturing media. An EB is located across both streams. Using the laminar characteristics at low Reynolds number and high Peclet numbers, we have induced cell differentiation on half of the EB while maintaining the other half in un-induced stages. The results prove the potential of using microfluidic technology for manipulation of EBs and ES cells in tissue engineering.

Moderate strength (0.23-0.28 T) static magnetic fields (SMF) modulate signaling and differentiation in human embryonic cells

Background

Compelling evidence exists that magnetic fields modulate living systems. To date, however, rigorous studies have focused on identifying the molecular-level biosensor (e.g., radical ion pairs or membranes) or on the behavior of whole animals leaving a gap in understanding how molecular effects are translated into tissue-wide and organism-level responses. This study begins to bridge this gulf by investigating static magnetic fields (SMF) through global mRNA profiling in human embryonic cells coupled with software analysis to identify the affected signaling pathways.

Results

Software analysis of gene expression in cells exposed to 0.23–0.28 T SMF showed that nine signaling networks responded to SMF; of these, detailed biochemical validation was performed for the network linked to the inflammatory cytokine IL-6. We found the short-term (<24 h) activation of IL-6 involved the coordinate up-regulation of toll-like receptor-4 (TLR4) with complementary changes to NEU3 and ST3GAL5 that reduced ganglioside GM3 in a manner that augmented the activation of TLR4 and IL-6. Loss of GM3 also provided a plausible mechanism for the attenuation of cellular responses to SMF that occurred over longer exposure periods. Finally, SMF-mediated responses were manifest at the cellular level as morphological changes and biochemical markers indicative of pre-oligodendrocyte differentiation.

Conclusion

This study provides a framework describing how magnetic exposure is transduced from a plausible molecular biosensor (lipid membranes) to cell-level responses that include differentiation toward neural lineages. In addition, SMF provided a stimulus that uncovered new relationships – that exist even in the absence of magnetic fields – between gangliosides, the time-dependent regulation of IL-6 signaling by these glycosphingolipids, and the fate of embryonic cells.

Isolation and characterization of pluripotent human spermatogonial stem cell-derived cells

Several reports have documented the derivation of pluripotent cells (multipotent germline stem cells) from spermatogonial stem cells obtained from the adult mouse testis. These spermatogonia-derived stem cells express embryonic stem cell markers and differentiate to the three primary germ layers, as well as the germline. Data indicate that derivation may involve reprogramming of endogenous spermatogonia in culture. Here, we report the derivation of human multipotent germline stem cells (hMGSCs) from a testis biopsy. The cells express distinct markers of pluripotency, form embryoid bodies that contain derivatives of all three germ layers, maintain a normal XY karyotype, are hypomethylated at the H19 locus, and express high levels of telomerase. Teratoma assays indicate the presence of human cells 8 weeks post-transplantation but limited teratoma formation. Thus, these data suggest the potential to derive pluripotent cells from human testis biopsies but indicate a need for novel strategies to optimize hMGSC culture conditions and reprogramming.

Physical transfer of membrane and cytoplasmic components as a general mechanism of cell-cell communication

Recent evidence from different research areas has revealed a novel mechanism of cell-cell communication by spontaneous intercellular transfer of cellular components (ICT). Here we studied this phenomenon by co-culturing different cells that contain distinct levels of proteins or markers for the plasma membrane or cytoplasm. We found that a variety of transmembrane proteins are transferable between multiple cell types. Membrane lipids also show a high efficiency of intercellular transfer. Size-dependent cytoplasmic transfer allows exchange of cytoplasmic macromolecules up to 40 kDa between somatic cells, and up to 2000 kDa between uncommitted human precursor cells and human umbilical vein endothelial cells. Protein transfer, lipid transfer and cytoplasmic component transfer can occur simultaneously and all require direct cell-cell contact. Analyses of the properties of ICT, together with a close examination of cell-cell interactions, suggest that the spontaneous ICT of different cellular components might have a common underlying process: transient local membrane fusions formed when neighboring cells undergo close cell-cell contact.

Important precautions when deriving patient-specific neural elements from pluripotent cells

Multipotent human neural stem cells (hNSC) have traditionally been isolated directly from the central nervous system (CNS). To date, as a therapeutic tool in the treatment of neurologic disorders, the most promising results have been obtained using hNSC isolated directly from the human fetal neuroectoderm. The propagation ability of such tissue-derived hNSC is often limited, however, making it difficult to establish a large-scale culture. Following engraftment, these hNSC often show low efficiency in generating the desired neuronal cells necessary for reconstruction of the damaged host milieu and, as a result, have failed to give satisfactory results in clinical trials so far. Alternatively, human embryonic stem cells (hESC) offer a pluripotent reservoir for in vitro derivation of a rich spectrum of well-characterized neural-lineage committed stem/progenitor/precursor cells that can, theoretically, be picked at precisely their safest and most efficacious state of plasticity to meet a given clinical challenge. However, the need for 'foreign' biologic additives and multilineage differentiation inclination may make direct use of such cell-derived hNSC in patients problematic. The hNSC, when derived from pluripotent cells under protocols presently employed in the field, tend to display not only a low efficiency in neuronal differentiation, but also an inclination for phenotypic heterogeneity and instability and, hence, increased risk of tumorigenesis following engraftment. For hNSC derived in vitro to be used safely in therapeutic paradigms, it requires conversion of human pluripotent cells uniformly to cells that are restricted to the neural lineage in need of repair. Developing strategies for direct induction of human pluripotent cells exclusively into neural-committed progenies at a broad range of developmental stages will allow a large supply of optimal therapeutic hNSC tailor-made for safe and effective treatment of particular neurologic diseases and injuries in patients.

Skeletal myogenesis by human primordial germ cell-derived progenitors

We have isolated and cultured human primordial germ cells (PGCs) from early embryos. The PGCs expressed embryonic germ (EG) cell-specific surface markers, including Oct4 and Nanos. We derived a cell population from these PGCs that we termed embryoid body-derived (EBD) cells. EBD cells can be extensively expanded in vitro for more than 50 passages and express lineage markers from all three primary germ layers. The myogenic potential of the EBD cells was examined both in vitro and in vivo.In vitro, the EBD cells can be induced to form multinucleated myotubes, which express late skeletal muscle-specific markers, including MHC and dystrophin, when exposed to human galectin-1. In vivo, the EBD cells gave rise to all the myogenic lineages, including the skeletal muscle stem cells known as satellite cells. Strikingly, these cells were able to partially restore degenerated muscles in the SCID/mdx mouse, an animal model of the Duchenne's muscular dystrophy. These results indicate the EBD cells may be a promising source of myogenic stem cells for cell-based therapies for muscle degenerative disorders.

Differential expression of epigenetic modulators during human embryonic stem cell differentiation

Although the progression of aging and the diseases associated with it are extensively studied, little is known about the initiation of the aging process. Telomerase is down-regulated early in embryonic differentiation, thereby contributing to telomeric attrition and aging. The mechanisms underlying this inhibition remain elusive, but epigenetic studies in differentiating human embryonic stem (hES) cells could give clues about how and when DNA methylation and histone deacetylation work together to contribute to the inactivation of hTERT, the catalytic subunit of telomerase, at the onset of the aging process. We have confirmed the differentiation status of cultured hES colonies with morphological assessment and immunohistochemical stainings for pluripotent stem cells. In hES cells with varying degrees of differentiation, we have shown a stronger association between hES differentiation and expression of the epigenetic regulators DNMT3A and DNMT3B than between genetic modulators of differentiation such as c-MYC. We also propose a new model system for analyses of stem cell regions, which are differentially down-regulating the expression of hTERT and the actions of epigenetic modulators such as the DNMTs and histone methyltransferases.

Gene expression analysis of RNA purified from embryonic stem cells and embryoid body-derived cells using a high-throughput microarray platform

In this unit, starting with purified RNA, experimental protocols for performing microarray expression analysis of embryonic stem cell lines compared to their corresponding differentiated embryocidal bodies are described. Methods for data analysis are suggested, with the goal of determining which genes are differentially expressed between the preparations. As an example, the use of the Affymetrix microarray expression platform is described, but alternative experimental options for analysis of RNA transcript levels are also summarized. This unit suggests quality control metrics, summarizes the critical parameters necessary for obtaining reproducible experimental results, and outlines quantitative PCR methods for validating microarray results.

Generation of pluripotent stem cells from adult human testis

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

Generation of humanized animal livers using embryoid body-derived stem cell transplant

OBJECTIVE

Animal organs engineered to be chimeric for human cells could contribute significantly to the field of transplantation, including studies of human-specific diseases such as hepatitis-C, as treatment for in-born errors of metabolism, and for development of a renewable source of transplantable organs via modified xenotransplantation. We sought to use human embryoid body-derived stem cells (EBDs) to populate livers in animals for applications in transplant surgery.

METHODS

SCID mice and rats underwent liver injury with carbon tetrachloride exposure or partial hepatectomy. Animals received intrasplenic injection of fluorescently labeled human stem cells. Spleen and liver were assessed at 2, 7, 15, and 30 days after transplant for the presence of EBDs and markers of human hepatocyte differentiation.

RESULTS

EBDs migrate to and engraft in animal liver after splenic injection under conditions of hepatic injury. EBDs are detectable at 2 days and are in abundance at 1 week after transplant. EBDs persist in rodent liver long term (>1 month), and once engrafted differentiate into functional human hepatocytes as assessed by production of human alpha-feto-protein (AFP) and human albumin.

CONCLUSIONS

We developed a novel animal model in which hepatic injury and stem cell transplantation lead to the generation of humanized animal organs. We are currently using our model to study recurrent hepatitis-C after liver transplantation, and as an alternative to whole organ transplantation for treatment of in-born errors of metabolism.

A new tool for probing of cell-cell communication: human embryonic germ cells inducing apoptosis of SKOV3 ovarian cancer cells on a microfluidic chip

A microfluidic device with unidirectional perfusion has been developed to observe the effect of human embryonic germ (hEG) cells on SKOV3 cells. The hEG and SKOV3 cells were seeded in the inlet and the outlet reservoirs separately, and co-cultured for 2 days. The medium was perfused unidirectionally from the inlet to the outlet. The growth inhibition of SKOV3 cells was monitored online and the apoptosis signals in SKOV3 culture area decreased along the flow of the medium. In conclusion, microfluidic chip is a potentially useful tool to investigate the effect of stem cells on cancer cells with intuitionistic cell-based screens.

Chondrogenic differentiation of human embryonic germ cell derived cells in hydrogels

Human embryonic germ (hEG) cells have the potential to self-renew over long periods of time and differentiate into various lineages. Cells derived from embryoid bodies of hEG cells express a broad spectrum of gene markers and have been induced towards cells of ecto-dermal and recently endo-dermal and mesenchymal lineages. LVEC cells express a number of surface marker proteins characteristic of mesenchymal stem cells (MSCs), indicating the potential of these cells to differentiate into mesenchymal tissues. Here we demonstrate the homogenous differentiation of LVEC cells into hyaline cartilage. Three dimensional tissue formation is achieved by encapsulating cells in synthetic hydrogels followed by incubation in chondrocyte-conditioned culture medium. Homogenous hyaline cartilage was produced, even after 63 population doublings (13 passages). The high proliferative capacity of these cells without teratoma formation, homogenous differentiation, and three-dimensional cartilage tissue formation suggests the significant potential of LVEC cells for cartilage tissue engineering applications.

Stem cells in amniotic fluid as new tools to study human genetic diseases

In future, the characterization and isolation of different human stem cells will allow the detailed molecular investigation of cell differentiation processes and the establishment of new therapeutic concepts for a wide variety of diseases. Since the first successful isolation and cultivation of human embryonic stem cells about 10 years ago, their usage for research and therapy has been constrained by complex ethical consideration as well as by the risk of malignant development of undifferentiated embryonic stem cells after transplantation into the patient's body. Adult stem cells are ethically acceptable and harbor a low risk of tumor development. However, their differentiation potential and their proliferative capacity are limited. About 4 years ago, the discovery of amniotic fluid stem cells, expressing Oct-4, a specific marker of pluripotent stem cells, and harboring a high proliferative capacity and multilineage differentiation potential, initiated a new and promising stem cell research field. In between, amniotic fluid stem cells have been demonstrated to harbor the potential to differentiate into cells of all three embryonic germlayers. These stem cells do not form tumors in vivo and do not raise the ethical concerns associated with human embryonic stem cells. Further investigations will reveal whether amniotic fluid stem cells really represent an intermediate cell type with advantages over both, adult stem cells and embryonic stem cells. The approach to generate clonal amniotic fluid stem cell lines as new tools to investigate molecular and cell biological consequences of human natural occurring disease causing mutations is discussed.