Defined conditions for neural commitment and differentiation

Zebrafish chemical screening reveals the impairment of dopaminergic neuronal survival by cardiac glycosides

Parkinson's disease is a neurodegenerative disorder characterized by the prominent degeneration of dopaminergic (DA) neurons among other cell types. Here we report a first chemical screen of over 5,000 compounds in zebrafish, aimed at identifying small molecule modulators of DA neuron development or survival. We find that Neriifolin, a member of the cardiac glycoside family of compounds, impairs survival but not differentiation of both zebrafish and mammalian DA neurons. Cardiac glycosides are inhibitors of Na(+)/K(+) ATPase activity and widely used for treating heart disorders. Our data suggest that Neriifolin impairs DA neuronal survival by targeting the neuronal enriched Na(+)/K(+) ATPase α3 subunit (ATP1A3). Modulation of ionic homeostasis, knockdown of p53, or treatment with antioxidants protects DA neurons from Neriifolin-induced death. These results reveal a previously unknown effect of cardiac glycosides on DA neuronal survival and suggest that it is mediated through ATP1A3 inhibition, oxidative stress, and p53. They also elucidate potential approaches for counteracting the neurotoxicity of this valuable class of medications.

Cell-surface proteomics identifies lineage-specific markers of embryo-derived stem cells

The advent of reprogramming and its impact on stem cell biology has renewed interest in lineage restriction in mammalian embryos, the source of embryonic (ES), epiblast (EpiSC), trophoblast (TS), and extraembryonic endoderm (XEN) stem cell lineages. Isolation of specific cell types during stem cell differentiation and reprogramming, and also directly from embryos, is a major technical challenge because few cell-surface proteins are known that can distinguish each cell type. We provide a large-scale proteomic resource of cell-surface proteins for the four embryo-derived stem cell lines. We validated 27 antibodies against lineage-specific cell-surface markers, which enabled investigation of specific cell populations during ES-EpiSC reprogramming and ES-to-XEN differentiation. Identified markers also allowed prospective isolation and characterization of viable lineage progenitors from blastocysts by flow cytometry. These results provide a comprehensive stem cell proteomic resource and enable new approaches to interrogate the mechanisms that regulate cell fate specification.

Targeted transcriptional activation of silent oct4 pluripotency gene by combining designer TALEs and inhibition of epigenetic modifiers

Specific control of gene activity is a valuable tool to study and engineer cellular functions. Recent studies uncovered the potential of transcription activator-like effector (TALE) proteins that can be tailored to activate user-defined target genes. It remains however unclear whether and how epigenetic modifications interfere with TALE-mediated transcriptional activation. We studied the activity of five designer TALEs (dTALEs) targeting the oct4 pluripotency gene. In vitro assays showed that the five dTALEs that target distinct sites in the oct4 promoter had the expected DNA specificity and comparable affinities to their corresponding DNA targets. In contrast to their similar in vitro properties, transcriptional activation of oct4 by these distinct dTALEs varied up to 25-fold. While dTALEs efficiently upregulated transcription of the active oct4 promoter in embryonic stem cells (ESCs) they failed to activate the silenced oct4 promoter in ESC-derived neural stem cells (NSCs), indicating that as for endogenous transcription factors also dTALE activity is limited by repressive epigenetic mechanisms. We therefore targeted the activity of epigenetic modulators and found that chemical inhibition of histone deacetylases by valproic acid or DNA methyltransferases by 5-aza-2′-deoxycytidine facilitated dTALE-mediated activation of the epigenetically silenced oct4 promoter in NSCs. Notably, demethylation of the oct4 promoter occurred only if chemical inhibitors and dTALEs were applied together but not upon treatment with inhibitors or dTALEs only. These results show that dTALEs in combination with chemical manipulation of epigenetic modifiers facilitate targeted transcriptional activation of epigenetically silenced target genes.

Intergenic Polycomb target sites are dynamically marked by non-coding transcription during lineage commitment

Non-coding (nc) RNAs are involved both in recruitment of vertebrate Polycomb (PcG) proteins to chromatin, and in activation of PcG target genes. Here we investigate dynamic changes in the relationship between ncRNA transcription and recruitment of PcG proteins to chromatin during differentiation. Profiling of purified cell populations from different stages of a defined murine in vitro neural differentiation system shows that over 50% of regulated intergenic non-coding transcripts precisely correspond to PcG target sites. We designate these PcG recruiting elements as Transcribed Intergenic Polycomb (TIP) sites. The relationship between TIP transcription and PcG recruitment switches dynamically during differentiation between different states, in which transcription and PcG recruitment exclude each other, or in which both are present. Reporter assays show that transcribed TIP sites can repress a flanking gene. Knockdown experiments demonstrate that TIP ncRNAs are themselves required for repression of target genes both in cis and in trans. We propose that TIP transcription may ensure coordinated regulation of gene networks via dynamic switching and recruitment of PcG proteins both in cis and in trans during lineage commitment.

Differentiation and functional incorporation of embryonic stem cell-derived GABAergic interneurons in the dentate gyrus of mice with temporal lobe epilepsy

Cell therapies for neurological disorders require an extensive knowledge of disease-associated neuropathology and procedures for generating neurons for transplantation. In many patients with severe acquired temporal lobe epilepsy (TLE), the dentate gyrus exhibits sclerosis and GABAergic interneuron degeneration. Mounting evidence suggests that therapeutic benefits can be obtained by transplanting fetal GABAergic progenitors into the dentate gyrus in rodents with TLE, but the scarcity of human fetal cells limits applicability in patient populations. In contrast, virtually limitless quantities of neural progenitors can be obtained from embryonic stem (ES) cells. ES cell-based therapies for neurological repair in TLE require evidence that the transplanted neurons integrate functionally and replace cell types that degenerate. To address these issues, we transplanted mouse ES cell-derived neural progenitors (ESNPs) with ventral forebrain identities into the hilus of the dentate gyrus of mice with TLE and evaluated graft differentiation, mossy fiber sprouting, cellular morphology, and electrophysiological properties of the transplanted neurons. In addition, we compared electrophysiological properties of the transplanted neurons with endogenous hilar interneurons in mice without TLE. The majority of transplanted ESNPs differentiated into GABAergic interneuron subtypes expressing calcium-binding proteins parvalbumin, calbindin, or calretinin. Global suppression of mossy fiber sprouting was not observed; however, ESNP-derived neurons formed dense axonal arborizations in the inner molecular layer and throughout the hilus. Whole-cell hippocampal slice electrophysiological recordings and morphological analyses of the transplanted neurons identified five basic types; most with strong after-hyperpolarizations and smooth or sparsely spiny dendritic morphologies resembling endogenous hippocampal interneurons. Moreover, intracellular recordings of spontaneous EPSCs indicated that the new cells functionally integrate into epileptic hippocampal circuitry.

Systematic engineering of 3D pluripotent stem cell niches to guide blood development

Pluripotent stem cells (PSC) provide insight into development and may underpin new cell therapies, yet controlling PSC differentiation to generate functional cells remains a significant challenge. In this study we explored the concept that mimicking the local in vivo microenvironment during mesoderm specification could promote the emergence of hematopoietic progenitor cells from embryonic stem cells (ESCs). First, we assessed the expression of early phenotypic markers of mesoderm differentiation (E-cadherin, brachyury (T-GFP), PDGFRα, and Flk1: +/-ETPF) to reveal that E-T+P+F+ cells have the highest capacity for hematopoiesis. Second, we determined how initial aggregate size influences the emergence of mesodermal phenotypes (E-T+P+F+, E-T-P+/-F+, and E-T-P+F-) and discovered that colony forming cell (CFC) output was maximal with ~100 cells per PSC aggregate. Finally, we introduced these 100-cell PSC aggregates into a low oxygen environment (5%; to upregulate endogenous VEGF secretion) and delivered two potent blood-inductive molecules, BMP4 and TPO (bone morphogenetic protein-4 and thrombopoietin), locally from microparticles to obtain a more robust differentiation response than soluble delivery methods alone. Approximately 1.7-fold more CFCs were generated with localized delivery in comparison to exogenous delivery, while combined growth factor use was reduced ~14.2-fold. By systematically engineering the complex and dynamic environmental signals associated with the in vivo blood developmental niche we demonstrate a significant role for inductive endogenous signaling and introduce a tunable platform for enhancing PSC differentiation efficiency to specific lineages.

Mature endothelium and neurons are simultaneously derived from embryonic stem cells by 2D in vitro culture system

The connections existing between vessels and nerves go beyond the structural architecture of vascular and nervous systems to comprise cell fate determination. The analysis of functional/molecular links that interconnect endothelial and neural commitments requires a model in which the two differentiation programs take place at the same time in an artificial controllable environment. To this regard, this work presents an in vitro model to differentiate embryonic stem (ES) cells simultaneously into mature neurons and endothelial cells. Murine ES cells are differentiated within an artificial environment composed of PA6 stromal cells and a serum-free medium. Upon these basal culture conditions ES cells preferentially differentiate into neurons. The addition of basic fibroblast growth factor (FGF2) to the medium allows the simultaneous maturation of neurons and endothelial cells, whereas bone morphogenetic protein (BMP)4 drives endothelial differentiation to the disadvantage of neural commitment. The responsiveness of the system to exogenous cytokines was confirmed by genes expression analysis that revealed a significant up-regulation of endothelial genes in presence of FGF2 and a massive down-regulation of the neural markers in response to BMP4. Furthermore, the role played by single genes in determining endothelial and neural fate can be easily explored by knocking down the expression of the target gene with lentiviruses carrying the corresponding shRNA sequence. The possibility to address the neural and the endothelial fate separately or simultaneously by exogenous stimuli combined with an efficient gene silencing strategy make this model an optimal tool to identify environmental signals and genes pathways involved in both endothelial and neural specification.

Human hypoblast formation is not dependent on FGF signalling

Mouse embryos segregate three different lineages during preimplantation development: trophoblast, epiblast and hypoblast. These differentiation processes are associated with restricted expression of key transcription factors (Cdx2, Oct4, Nanog and Gata6). The mechanisms of segregation have been extensively studied in the mouse, but are not as well characterised in other species. In the human embryo, hypoblast differentiation has not previously been characterised. Here we demonstrate co-exclusive immunolocalisation of Nanog and Gata4 in human blastocysts, implying segregation of epiblast and hypoblast, as in rodent embryos. However, the formation of hypoblast in the human is apparently not dependent upon FGF signalling, in contrast to rodent embryos. Nonetheless, the persistence of Nanog-positive cells in embryos following treatment with FGF inhibitors is suggestive of a transient naïve pluripotent population in the human blastocyst, which may be similar to rodent epiblast and ES cells but is not sustained during conventional human ES cell derivation protocols.

Induction of superficial cortical layer neurons from mouse embryonic stem cells by valproic acid

Within the developing mammalian cortex, neural progenitors first generate deep-layer neurons and subsequently more superficial-layer neurons, in an inside-out manner. It has been reported recently that mouse embryonic stem cells (mESCs) can, to some extent, recapitulate cortical development in vitro, with the sequential appearance of neurogenesis markers resembling that in the developing cortex. However, mESCs can only recapitulate early corticogenesis; superficial-layer neurons, which are normally produced in later developmental periods in vivo, are under-represented. This failure of mESCs to reproduce later corticogenesis in vitro implies the existence of crucial factor(s) that are absent or uninduced in existing culture systems. Here we show that mESCs can give rise to superficial-layer neurons efficiently when treated with valproic acid (VPA), a histone deacetylase inhibitor. VPA treatment increased the production of Cux1-positive superficial-layer neurons, and decreased that of Ctip2-positive deep-layer neurons. These results shed new light on the mechanisms of later corticogenesis.

Derivation and characterization of embryonic stem cells lines derived from transgenic Fischer 344 and Dark Agouti rats

Rat embryonic stem cell (ESC) lines are not widely available, and there are only 2 lines available for distribution. Here, ESC lines were derived and characterized from Fischer 344 (F344) rats that express marker transgenes either β-galactosidase or human placental alkaline phosphatase (AP), nontransgenic F344 rats, and from Dark Agouti (DA) rats. The ESC lines were maintained in an undifferentiated state as characterized by colony morphology, expression of Oct4, Nanog, Sox-2, Cdx2, and Stella, staining for AP, and stage-specific embryonic antigen-1. Pluripotency was demonstrated in vitro by differentiation to embryoid bodies, followed by embryonic monsters. The Cdx2 expression by ESCs was unexpected and was confirmed via reverse transcriptase-polymerase chain reaction, immunocytochemistry. Pluripotency of ESCs was demonstrated in vivo by production of teratoma after an injection into F344 nontransgenic rats, and by an injection of male DA ESCs into F344 or Sprague-Dawley rat blastocysts and the generation of chimeric rats and germline contribution. ESCs from both F344 and DA contributed to chimeric rats, and one DA ESC line was proved to be germline competent. ESC sublines were created by transfection with a plasmid expressing enhanced green fluorescent protein (eGFP) under the control of a beta actin promoter and cytomegalovirus enhancer (pCX-eGFP) or by transfection with a plasmid expressing GFP under the control of a 3.1 kb portion of the rat Oct4 promoter (pN1-Oct4-GFP). In pN1-Oct4-GFP sublines, GFP gene expression and fluorescence were shown to be correlated with endogenous Oct4 gene expression. Therefore, these new ESC lines may be useful for tissue engineering and transplantation studies or for optimizing culture conditions required for self-renewal and differentiation of rat ESCs. While they made chimeric rats, further work is needed to confirm whether the transgenic F344 rat ESCs described here are germline-competent ESCs.

Sequentially acting Sox transcription factors in neural lineage development

Pluripotent embryonic stem (ES) cells can generate all cell types, but how cell lineages are initially specified and maintained during development remains largely unknown. Different classes of Sox transcription factors are expressed during neurogenesis and have been assigned important roles from early lineage specification to neuronal differentiation. Here we characterize the genome-wide binding for Sox2, Sox3, and Sox11, which have vital functions in ES cells, neural precursor cells (NPCs), and maturing neurons, respectively. The data demonstrate that Sox factor binding depends on developmental stage-specific constraints and reveal a remarkable sequential binding of Sox proteins to a common set of neural genes. Interestingly, in ES cells, Sox2 preselects for neural lineage-specific genes destined to be bound and activated by Sox3 in NPCs. In NPCs, Sox3 binds genes that are later bound and activated by Sox11 in differentiating neurons. Genes prebound by Sox proteins are associated with a bivalent chromatin signature, which is resolved into a permissive monovalent state upon binding of activating Sox factors. These data indicate that a single key transcription factor family acts sequentially to coordinate neural gene expression from the early lineage specification in pluripotent cells to later stages of neuronal development.

The evolving biology of small molecules: controlling cell fate and identity

Small molecules have been playing important roles in elucidating basic biology and treatment of a vast number of diseases for nearly a century, making their use in the field of stem cell biology a comparatively recent phenomenon. Nonetheless, the power of biology-oriented chemical design and synthesis, coupled with significant advances in screening technology, has enabled the discovery of a growing number of small molecules that have improved our understanding of stem cell biology and allowed us to manipulate stem cells in unprecedented ways. This review focuses on recent small molecule studies of (i) the key pathways governing stem cell homeostasis, (ii) the pluripotent stem cell niche, (iii) the directed differentiation of stem cells, (iv) the biology of adult stem cells, and (v) somatic cell reprogramming. In a very short period of time, small molecules have defined a perhaps universally attainable naive ground state of pluripotency, and are facilitating the precise, rapid and efficient differentiation of stem cells into somatic cell populations relevant to the clinic. Finally, following the publication of numerous groundbreaking studies at a pace and consistency unusual for a young field, we are closer than ever to completely eliminating the need for genetic modification in reprogramming.

Sox2 and Pax6 maintain the proliferative and developmental potential of gliogenic neural stem cells In vitro

Radial-glia-like neural stem (NS) cells may be derived from neural tissues or via differentiation of pluripotent embryonic stem (ES) cells. However, the mechanisms controlling NS cell propagation and differentiation are not yet fully understood. Here we investigated the roles of Sox2 and Pax6, transcription factors widely expressed in central nervous system (CNS) progenitors, in mouse NS cells. Conditional deletion of either Sox2 or Pax6 in forebrain-derived NS cells reduced their clonogenicity in a gene dosage-dependent manner. Cells heterozygous for either gene displayed moderate proliferative defects, which may relate to human pathologies attributed to SOX2 or PAX6 deficiencies. In the complete absence of Sox2, cells exited the cell cycle with concomitant downregulation of neural progenitor markers Nestin and Blbp. This occurred despite expression of the close relative Sox3. Ablation of Pax6 also caused major proliferative defects. However, a subpopulation of cells was able to expand continuously without Pax6. These Pax6-null cells retained progenitor markers but had altered morphology. They exhibited compromised differentiation into astrocytes and oligodendrocytes, highlighting that the role of Pax6 extends beyond neurogenic competence. Overall these findings indicate that Sox2 and Pax6 are both critical for self-renewal of differentiation-competent radial glia-like NS cells.

BMP4 signaling directs primitive endoderm-derived XEN cells to an extraembryonic visceral endoderm identity

The visceral endoderm (VE) is an epithelial tissue in the early postimplantation mouse embryo that encapsulates the pluripotent epiblast distally and the extraembryonic ectoderm proximally. In addition to facilitating nutrient exchange before the establishment of a circulation, the VE is critical for patterning the epiblast. Since VE is derived from the primitive endoderm (PrE) of the blastocyst, and PrE-derived eXtraembryonic ENdoderm (XEN) cells can be propagated in vitro, XEN cells should provide an important tool for identifying factors that direct VE differentiation. In this study, we demonstrated that BMP4 signaling induces the formation of a polarized epithelium in XEN cells. This morphological transition was reversible, and was associated with the acquisition of a molecular signature comparable to extraembryonic (ex) VE. Resembling exVE which will form the endoderm of the visceral yolk sac, BMP4-treated XEN cells regulated hematopoiesis by stimulating the expansion of primitive erythroid progenitors. We also observed that LIF exerted an antagonistic effect on BMP4-induced XEN cell differentiation, thereby impacting the extrinsic conditions used for the isolation and maintenance of XEN cells in an undifferentiated state. Taken together, our data suggest that XEN cells can be differentiated towards an exVE identity upon BMP4 stimulation and therefore represent a valuable tool for investigating PrE lineage differentiation.

Derivation of rat embryonic stem cells and generation of protease-activated receptor-2 knockout rats

One of the remarkable achievements in knockout (KO) rat production reported during the period 2008-2010 is the derivation of authentic embryonic stem (ES) cells from rat blastocysts using a novel culture medium containing glycogen synthase kinase 3 and mitogen-activated protein kinase kinase inhibitors (2i medium). Here, we report gene-targeting technology via homologous recombination in rat ES cells, demonstrating its use through production of a protease-activated receptor-2 gene (Par-2) KO rat. We began by generating germline-competent ES cells from Dark Agouti rats using 2i medium. These ES cells, which differentiate into cardiomyocytes in vitro, can produce chimeras with high ES cell contribution when injected into blastocysts. We then introduced a targeting vector with a neomycin-resistant gene driven by the CAG promoter to disrupt Par-2. After a 7-day drug selection, 489 neomycin-resistant colonies were obtained. Following screening by polymerase chain reaction (PCR) genotyping and quantitative PCR analysis, we confirmed three homologous recombinant clones, resulting in chimeras that transmitted the Par-2 targeted allele to offspring. Par-2 KO rats showed a loss of Par-2 messenger RNA expression in their stomach cells and a lack of PAR-2 mediated smooth muscle relaxation in the aorta as indicated by pharmacological testing. Compared with mice, rats offer many advantages in biomedical research, including a larger body size; consequently, they are widely used in scientific investigation. Thus, the establishment of a gene-targeting technology using rat ES cells will be a valuable tool in human disease model production and drug discovery.

Pluripotency factors in embryonic stem cells regulate differentiation into germ layers

Cell fate decisions are fundamental for development, but we do not know how transcriptional networks reorganize during the transition from a pluripotent to a differentiated cell state. Here, we asked how mouse embryonic stem cells (ESCs) leave the pluripotent state and choose between germ layer fates. By analyzing the dynamics of the transcriptional circuit that maintains pluripotency, we found that Oct4 and Sox2, proteins that maintain ESC identity, also orchestrate germ layer fate selection. Oct4 suppresses neural ectodermal differentiation and promotes mesendodermal differentiation; Sox2 inhibits mesendodermal differentiation and promotes neural ectodermal differentiation. Differentiation signals continuously and asymmetrically modulate Oct4 and Sox2 protein levels, altering their binding pattern in the genome, and leading to cell fate choice. The same factors that maintain pluripotency thus also integrate external signals and control lineage selection. Our study provides a framework for understanding how complex transcription factor networks control cell fate decisions in progenitor cells.

Microfluidic perfusion for regulating diffusible signaling in stem cells

BACKGROUND

Autocrine & paracrine signaling are widespread both in vivo and in vitro, and are particularly important in embryonic stem cell (ESC) pluripotency and lineage commitment. Although autocrine signaling via fibroblast growth factor-4 (FGF4) is known to be required in mouse ESC (mESC) neuroectodermal specification, the question of whether FGF4 autocrine signaling is sufficient, or whether other soluble ligands are also involved in fate specification, is unknown. The spatially confined and closed-loop nature of diffusible signaling makes its experimental control challenging; current experimental approaches typically require prior knowledge of the factor/receptor in order to modulate the loop. A new approach explored in this work is to leverage transport phenomena at cellular resolution to downregulate overall diffusible signaling through the physical removal of cell-secreted ligands.

METHODOLOGY/PRINCIPAL FINDINGS

We develop a multiplex microfluidic platform to continuously remove cell-secreted (autocrine\paracrine) factors to downregulate diffusible signaling. By comparing cell growth and differentiation in side-by-side chambers with or without added cell-secreted factors, we isolate the effects of diffusible signaling from artifacts such as shear, nutrient depletion, and microsystem effects, and find that cell-secreted growth factor(s) are required during neuroectodermal specification. Then we induce FGF4 signaling in minimal chemically defined medium (N2B27) and inhibit FGF signaling in fully supplemented differentiation medium with cell-secreted factors to determine that the non-FGF cell-secreted factors are required to promote growth of differentiating mESCs.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate for the first time that flow can downregulate autocrine\paracrine signaling and examine sufficiency of extracellular factors. We show that autocrine\paracrine signaling drives neuroectodermal commitment of mESCs through both FGF4-dependent and -independent pathways. Overall, by uncovering autocrine\paracrine processes previously hidden in conventional culture systems, our results establish microfluidic perfusion as a technique to study and manipulate diffusible signaling in cell systems.

Short-term serum-free culture reveals that inhibition of Gsk3β induces the tumor-like growth of mouse embryonic stem cells

Here, we present evidence that the tumor-like growth of mouse embryonic stem cells (mESCs) is suppressed by short-term serum-free culture, which is reversed by pharmacological inhibition of Gsk3β. Mouse ESCs maintained under standard conditions using fetal bovine serum (FBS) were cultured in a uniquely formulated chemically-defined serum-free (CDSF) medium, namely ESF7, for three passages before being subcutaneously transplanted into immunocompromised mice. Surprisingly, the mESCs failed to produce teratomas for up to six months, whereas mESCs maintained under standard conditions generated well-developed teratomas in five weeks. Mouse ESCs cultured under CDSF conditions maintained the expression of Oct3/4, Nanog, Sox2 and SSEA1, and differentiated into germ cells in vivo. In addition, when mESCs were cultured under CDSF conditions supplemented with FBS, or when the cells were cultured under CDSF conditions followed by standard culture conditions, they consistently developed into teratomas. Thus, these results validate that the pluripotency of mESCs was not compromised by CDSF conditions. Mouse ESCs cultured under CDSF conditions proliferated significantly more slowly than mESCs cultured under standard conditions, and were reminiscent of Eras-null mESCs. In fact, their slower proliferation was accompanied by the downregulation of Eras and c-Myc, which regulate the tumor-like growth of mESCs. Remarkably, when mESCs were cultured under CDSF conditions supplemented with a pharmacological inhibitor of Gsk3β, they efficiently proliferated and developed into teratomas without upregulation of Eras and c-Myc, whereas mESCs cultured under standard conditions expressed Eras and c-Myc. Although the role of Gsk3β in the self-renewal of ESCs has been established, it is suggested with these data that Gsk3β governs the tumor-like growth of mESCs by means of a mechanism different from the one to support the pluripotency of ESCs.

Calcineurin-NFAT signaling critically regulates early lineage specification in mouse embryonic stem cells and embryos

Self-renewal and pluripotency are hallmarks of embryonic stem cells (ESCs). However, the signaling pathways that trigger their transition from self-renewal to differentiation remain elusive. Here, we report that calcineurin-NFAT signaling is both necessary and sufficient to switch ESCs from an undifferentiated state to lineage-specific cells and that the inhibition of this pathway can maintain long-term ESC self-renewal independent of leukemia inhibitory factor. Mechanistically, this pathway converges with the Erk1/2 pathway to regulate Src expression and promote the epithelial-mesenchymal transition (EMT), a process required for lineage specification in response to differentiation stimuli. Furthermore, calcineurin-NFAT signaling is activated when the earliest differentiation event occurs in mouse embryos, and its inhibition disrupts extraembryonic lineage development. Collectively, our results demonstrate that the NFAT and Erk1/2 cascades form a signaling switch for early lineage segregation in mouse ESCs and provide significant insights into the regulation of the balance between ESC self-renewal and early lineage specification.

Interplay between FGF2 and BMP controls the self-renewal, dormancy and differentiation of rat neural stem cells

Mouse and human central nervous system progenitor cells can be propagated extensively ex vivo as stem cell lines. For the rat, however, in vitro expansion has proven to be problematic owing to proliferation arrest and differentiation. Here, we analyse the establishment, in adherent culture, of undifferentiated tripotent neural stem (NS) cell lines derived from rat foetal brain and spinal cord. Rat NS cells invariably undergo growth arrest and apparent differentiation after several passages; however, conditioned medium from proliferating cultures can overcome this block, enabling continuous propagation of undifferentiated rat NS cells. We found that dormancy is induced by autocrine production of bone morphogenetic proteins (BMPs). Accordingly, the BMP antagonist noggin can replace conditioned medium to sustain continuous self-renewal. Noggin can also induce dormant cells to re-enter the cell cycle, upon which they reacquire neurogenic potential. We further show that fibroblast growth factor 2 (FGF2) is required to suppress terminal astrocytic differentiation and maintain stem cell potency during dormancy. These findings highlight an extrinsic regulatory network, comprising BMPs, BMP antagonists and FGF2 signals, that governs the proliferation, dormancy and differentiation of rat NS cells and which can be manipulated to enable long-term clonogenic self-renewal.

Regenerative chemical biology: current challenges and future potential

The enthusiasm surrounding the clinical potential of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) is tempered by the fact that key issues regarding their safety, efficacy, and long-term benefits have thus far been suboptimal. Small molecules can potentially relieve these problems at major junctions of stem cell biology and regenerative therapy. In this review we will introduce recent advances in these important areas and the first generation of small molecules used in the regenerative context. Current chemical biology studies will provide the archetype for future interdisciplinary collaborations and improve clinical benefits of cell-based therapies.

mSEL-1L (Suppressor/enhancer Lin12-like) protein levels influence murine neural stem cell self-renewal and lineage commitment

Murine SEL-1L (mSEL-1L) is a key component of the endoplasmic reticulum-associated degradation pathway. It is essential during development as revealed by the multi-organ dysfunction and in uterus lethality occurring in homozygous mSEL-1L-deficient mice. Here we show that mSEL-1L is highly expressed in pluripotent embryonic stem cells and multipotent neural stem cells (NSCs) but silenced in all mature neural derivatives (i.e. astrocytes, oligodendrocytes, and neurons) by mmu-miR-183. NSCs derived from homozygous mSEL-1L-deficient embryos (mSEL-1L(-/-) NSCs) fail to proliferate in vitro, show a drastic reduction of the Notch effector HES-5, and reveal a significant down-modulation of the early neural progenitor markers PAX-6 and OLIG-2, when compared with the wild type (mSEL-1L(+/+) NSCs) counterpart. Furthermore, these cells are almost completely deprived of the neural marker Nestin, display a significant decrease of SOX-2 expression, and rapidly undergo premature astrocytic commitment and apoptosis. The data suggest severe self-renewal defects occurring in these cells probably mediated by misregulation of the Notch signaling. The results reported here denote mSEL-1L as a primitive marker with a possible involvement in the regulation of neural progenitor stemness maintenance and lineage determination.

Systematic chromosomal analysis of cultured mouse neural stem cell lines

The potential use of neural stem cells (NSCs) in basic research, drug testing, and for the development of therapeutic strategies is dependent on their large scale in vitro amplification which, however, introduces considerable risks of genetic instability and transformation. NSCs have been derived from different sources, but the occurrence of chromosomal instability has been monitored only to a limited extent in relationship to the source of derivation, growth procedure, long-term culture, and genetic manipulation. Here we have systematically investigated the effect of these parameters on the chromosomal stability of pure populations of mouse NSCs obtained after neuralization from embryonic stem cells (ESCs) or directly from fetal or adult mouse brain. We found that the procedure of NSCs establishment is not accompanied by genetic instability and chromosomal aberration. On the contrary, we observed that a composite karyotype appears in NSCs above extensive passaging. This phenomenon is more evident in ESC- and adult sub-ventricular zone-derived NSCs and further deteriorates after genetic engineering of the cells. Fetal-derived NSCs showed the greatest euploidy state with negligible clonal structural aberrations, but persistent clonal numerical abnormalities. It was previously published that long-term passaged ESC- and adult sub-ventricular zone-derived NSCs did not show any defects in the cells' proliferative and differentiative capacity nor induced in vivo tumour formation, although we here report on the chromosomal abnormalities of these cells. Although chromosomal aberrations are known to occur less frequently in human cells, studies performed on murine stem cells provide an important complement to understand the biological events occurring in human lines.

The Role of the Leukemia Inhibitory Factor (LIF) - Pathway in Derivation and Maintenance of Murine Pluripotent Stem Cells

Developmental biology, regenerative medicine and cancer biology are more and more interested in understanding the molecular mechanisms controlling pluripotency and self-renewal in stem cells. Pluripotency is maintained by a synergistic interplay between extrinsic stimuli and intrinsic circuitries, which allow sustainment of the undifferentiated and self-renewing state. Nevertheless, even though a lot of efforts have been made in the past years, the precise mechanisms regulating these processes remain unclear. One of the key extrinsic factors is leukemia inhibitory factor (LIF) that is largely used for the cultivation and derivation of mouse embryonic and induced pluripotent stem cells. LIF acts through the LIFR/gp130 receptor and activates STAT3, an important regulator of mouse embryonic stem cell self-renewal. STAT3 is known to inhibit differentiation into both mesoderm and endoderm lineages by preventing the activation of lineage-specific differentiation programs. However, LIF activates also parallel circuitries like the PI3K-pathway and the MEK/ERK-pathway, but its mechanisms of action remain to be better elucidated. This review article aims at summarizing the actual knowledge on the importance of LIF in the maintenance of pluripotency and self-renewal in embryonic and induced pluripotent stem cells.

Sensitivity of dopaminergic neuron differentiation from stem cells to chronic low-dose methylmercury exposure

Perinatal exposure to low doses of methylmercury (MeHg) can cause adult neurological symptoms. Rather than leading to a net cell loss, the toxicant is assumed to alter the differentiation and neuronal functions such as catecholaminergic transmission. We used neuronally differentiating murine embryonic stem cells (mESC) to explore such subtle toxicity. The mixed neuronal cultures that formed within 20 days contained a small subpopulation of tyrosine hydroxylase (TH)-positive neurons with specific dopaminergic functions such as dopamine transport (DAT) activity. The last 6 days of differentiation were associated with the functional maturation of already preformed neuronal precursors. Exposure to MeHg during this period downregulated several neuronal transcripts, without affecting housekeeping genes or causing measurable cell loss. Profiling of mRNAs relevant for neurotransmitter systems showed that dopamine receptors were coordinately downregulated, whereas known counterregulatory systems such as galanin receptor 2 were upregulated. The chronic (6 days) exposure to MeHg, but not shorter incubation periods, attenuated the expression levels of endogenous neurotrophic factors required for the maturation of TH cells. Accordingly, the size of this cell population was diminished, and DAT activity as its signature function was lost. When mixed lineage kinase activity was blocked during MeHg exposure, DAT activity was restored, and the reduction of TH levels was prevented. Thus, transcriptional profiling in differentiating mESC identified a subpopulation of neurons affected by MeHg, and a pharmacological intervention was identified that specifically protected these cells.

Defined culture medium for stem cell differentiation: applicability of serum-free conditions in the mouse embryonic stem cell test

The embryonic stem cell test (EST) is a validated method to assess the developmental toxicity potency of chemicals. It was developed to reduce animal use and allow faster testing for hazard assessment. The cells used in this method are maintained and differentiated in media containing foetal calf serum. This animal product is of considerable variation in quality, and individual batches require extensive testing for their applicability in the EST. Moreover, its production involves a large number of foetuses and possible animal suffering. We demonstrate the serum-free medium and feeder cell-free maintenance of the mouse embryonic stem cell line D3 and investigate the use of specific growth factors for induction of cardiac differentiation. Using a combination of bone morphogenetic protein-2, bone morphogenetic protein-4, activin A and ascorbic acid, embryoid bodies efficiently differentiated into contracting myocardium. Additionally, examining levels of intracellular marker proteins by flow cytometry not only confirmed differentiation into cardiomyocytes, but demonstrated significant differentiation into neuronal cells in the same time frame. Thus, this approach might allow for simultaneous detection of developmental effects on both early mesodermal and neuroectodermal differentiation. The serum-free conditions for maintenance and differentiation of D3 cells described here enhance the transferability and standardisation and hence the performance of the EST.

β-catenin enhances Oct-4 activity and reinforces pluripotency through a TCF-independent mechanism

Understanding the mechanisms regulating pluripotency in embryonic and induced pluripotent stem cells is required to ensure their safe use in clinical applications. Glycogen synthase kinase-3 (GSK-3) has emerged as an important regulator of pluripotency, based primarily on studies with small-molecule GSK-3 inhibitors. Here, we use mouse embryonic stem cells (ESCs) lacking GSK-3 to demonstrate that a single GSK-3 substrate, β-catenin, controls the ability of ESCs to exit the pluripotent state and to differentiate into neurectoderm. Unexpectedly, the effects of β-catenin on pluripotency do not appear to be dependent on TCF-mediated signaling, based on experiments utilizing a β-catenin C-terminal truncation mutant or highly efficient dominant-negative TCF strategies. Alternatively, we find that stabilized β-catenin forms a complex with and enhances the activity of Oct-4, a core component of the transcriptional network regulating pluripotency. Collectively, our data suggest previously underappreciated, divergent TCF-dependent and TCF-independent roles for β-catenin in ESCs.

LIF-independent JAK signalling to chromatin in embryonic stem cells uncovered from an adult stem cell disease

Activating mutations in the tyrosine kinase Janus kinase 2 (JAK2) cause myeloproliferative neoplasms, clonal blood stem cell disorders with a propensity for leukaemic transformation. Leukaemia inhibitory factor (LIF) signalling through the JAK-signal transducer and activator of transcription (STAT) pathway enables self-renewal of embryonic stem (ES) cells. Here we show that mouse ES cells carrying the human JAK2V617F mutation were able to self-renew in chemically defined conditions without cytokines or small-molecule inhibitors, independently of JAK signalling through the STAT3 or phosphatidylinositol-3-OH kinase pathways. Phosphorylation of histone H3 tyrosine 41 (H3Y41) by JAK2 was recently shown to interfere with binding of heterochromatin protein 1α (HP1α). Levels of chromatin-bound HP1α were lower in JAK2V617F ES cells but increased following inhibition of JAK2, coincident with a global reduction in histone H3Y41 phosphorylation. JAK2 inhibition reduced levels of the pluripotency regulator Nanog, with a reduction in H3Y41 phosphorylation and concomitant increase in HP1α levels at the Nanog promoter. Furthermore, Nanog was required for factor independence of JAK2V617F ES cells. Taken together, these results uncover a previously unrecognized role for direct signalling to chromatin by JAK2 as an important mediator of ES cell self-renewal.

A genome-wide screen in EpiSCs identifies Nr5a nuclear receptors as potent inducers of ground state pluripotency

In rodents, the naïve early epiblast undergoes profound morphogenetic, transcriptional and epigenetic changes after implantation. These differences are maintained between blastocyst-derived embryonic stem (ES) cells and egg cylinder-derived epiblast stem cells (EpiSCs). Notably, ES cells robustly colonise chimaeras, whereas EpiSCs show little or no contribution. ES cells self-renew independently of mitogenic growth factors, whereas EpiSCs require fibroblast growth factor. However, EpiSCs retain the core pluripotency factors Oct4 and Sox2 and the developmental barrier dividing them from unrestricted pluripotency can be surmounted by a single reprogramming factor. This provides an opportunity to identify molecules that can reset the naïve state. We undertook a forward genetic screen for effectors of EpiSC reprogramming, employing piggyBac transposition to activate endogenous gene expression at random and selecting for undifferentiated colonies in the absence of growth factor signalling. Three recovered clones harboured integrations that activate the closely related orphan nuclear receptor genes Nr5a1 and Nr5a2. Activity of Nr5a1 and Nr5a2 was confirmed by direct transfection. Reprogrammed colonies were obtained without transgene integration and at 10-fold higher frequency than with other single factors. Converted cells exhibited the diagnostic self-renewal characteristics, gene expression profile and X chromosome activation signature of ground state pluripotency. They efficiently produced adult chimaeras and gave germline transmission. Nr5a receptors regulate Oct4 transcription but this is insufficient for reprogramming. Intriguingly, unlike previously identified reprogramming molecules, Nr5a receptors play no evident role in ES cell self-renewal. This implies a different foundation for their capacity to reset pluripotency and suggests that further factors remain to be identified.

Role of H3K27 methylation in the regulation of lncRNA expression

Once thought to be transcriptional noise, large non-coding RNAs (lncRNAs) have recently been demonstrated to be functional molecules. The cell-type-specific expression patterns of lncRNAs suggest that their transcription may be regulated epigenetically. Using a custom-designed microarray, here we examine the expression profile of lncRNAs in embryonic stem (ES) cells, lineage-restricted neuronal progenitor cells, and terminally differentiated fibroblasts. In addition, we also analyze the relationship between their expression and their promoter H3K4 and H3K27 methylation patterns. We find that numerous lncRNAs in these cell types undergo changes in the levels of expression and promoter H3K4me3 and H3K27me3. Interestingly, lncRNAs that are expressed at lower levels in ES cells exhibit higher levels of H3K27me3 at their promoters. Consistent with this result, knockdown of the H3K27me3 methyltransferase Ezh2 results in derepression of these lncRNAs in ES cells. Thus, our results establish a role for Ezh2-mediated H3K27 methylation in lncRNA silencing in ES cells and reveal that lncRNAs are subject to epigenetic regulation in a similar manner to that of the protein-coding genes.

Coordinated waves of gene expression during neuronal differentiation of embryonic stem cells as basis for novel approaches to developmental neurotoxicity testing

As neuronal differentiation of embryonic stem cells (ESCs) recapitulates embryonic neurogenesis, disturbances of this process may model developmental neurotoxicity (DNT). To identify the relevant steps of in vitro neurodevelopment, we implemented a differentiation protocol yielding neurons with desired electrophysiological properties. Results from focussed transcriptional profiling suggested that detection of non-cytotoxic developmental disturbances triggered by toxicants such as retinoic acid (RA) or cyclopamine was possible. Therefore, a broad transcriptional profile of the 20-day differentiation process was obtained. Cluster analysis of expression kinetics, and bioinformatic identification of overrepresented gene ontologies revealed waves of regulation relevant for DNT testing. We further explored the concept of superimposed waves as descriptor of ordered, but overlapping biological processes. The initial wave of transcripts indicated reorganization of chromatin and epigenetic changes. Then, a transient upregulation of genes involved in the formation and patterning of neuronal precursors followed. Simultaneously, a long wave of ongoing neuronal differentiation started. This was again superseded towards the end of the process by shorter waves of neuronal maturation that yielded information on specification, extracellular matrix formation, disease-associated genes and the generation of glia. Short exposure to lead during the final differentiation phase, disturbed neuronal maturation. Thus, the wave kinetics and the patterns of neuronal specification define the time windows and end points for examination of DNT.

A role for PDGF signaling in expansion of the extra-embryonic endoderm lineage of the mouse blastocyst

The inner cell mass (ICM) of the implanting mammalian blastocyst comprises two lineages: the pluripotent epiblast (EPI) and primitive endoderm (PrE). We have identified platelet-derived growth factor receptor alpha (PDGFRα) as an early marker of the PrE lineage and its derivatives in both mouse embryos and ex vivo paradigms of extra-embryonic endoderm (ExEn). By combining live imaging of embryos and embryo-derived stem cells expressing a histone H2B-GFP fusion reporter under the control of Pdgfra regulatory elements with the analysis of lineage-specific markers, we found that Pdgfra expression coincides with that of GATA6, the earliest expressed transcriptional regulator of the PrE lineage. We show that GATA6 is required for the activation of Pdgfra expression. Using pharmacological inhibition and genetic inactivation we addressed the role of the PDGF pathway in the PrE lineage. Our results demonstrate that PDGF signaling is essential for the establishment, and plays a role in the proliferation, of XEN cells, which are isolated from mouse blastocyst stage embryos and represent the PrE lineage. Implanting Pdgfra mutant blastocysts exhibited a reduced number of PrE cells, an effect that was exacerbated by delaying implantation. Surprisingly, we also noted an increase in the number of EPI cells in implantation-delayed Pdgfra-null mutants. Taken together, our data suggest a role for PDGF signaling in the expansion of the ExEn lineage. Our observations also uncover a possible role for the PrE in regulating the size of the pluripotent EPI compartment.

Three inhibitors of FGF receptor, ERK, and GSK3 establishes germline-competent embryonic stem cells of C57BL/6N mouse strain with high efficiency and stability

C57BL/6 mouse is the most standard strain in mouse genetics. The strain does, however, have several disadvantages; one being the difficulty in establishing embryonic stem (ES) cells. No reliable C57BL/6 ES cell line is widely available for creating mutant mice through gene targeting. It also greatly favors mouse genetics if one can routinely make multiple mutations by stably culturing germline-competent C57BL/6 ES cells or if one can routinely establish ES cells from C57BL/6-derived mutant mice to make multiple mutations. Recently, an ES culture method with three inhibitors (3i: SU5402 for FGFR, PD184352 for ERK, and CHIR99021 for GSK3) has been reported. Here we show that this 3i method is extremely instrumental in establishing and culturing germline-competent ES cells in the C57BL/6N strain.

The ground state of pluripotency

Pluripotency is defined as the capacity of individual cells to initiate all lineages of the mature organism in response to signals from the embryo or cell culture environment. A pluripotent cell has no predetermined programme; it is a blank slate. This is the foundation of mammalian development and of ES (embryonic stem) cell biology. What are the design principles of this naïve cell state? How is pluripotency acquired and maintained? Suppressing activation of ERKs (extracellular-signal-regulated kinases) is critical to establishing and sustaining ES cells. Inhibition of GSK3 (glycogen synthase kinase 3) reinforces this effect. We review the effect of selective kinase inhibitors on pluripotent cells and consider how these effects are mediated. We propose that ES cells represent a ground state, meaning a basal proliferative state that is free of epigenetic restriction and has minimal requirements for extrinsic stimuli. The stability of this state is reflected in the homogeneity of ES cell populations cultured in the presence of small-molecule inhibitors of MEK (mitogen-activated protein kinase/ERK kinase) and GSK3.

Endangered species hold clues to human evolution

We report that 18 conserved, and by extension functional, elements in the human genome are the result of retroposon insertions that are evolving under purifying selection in mammals. We show evidence that 1 of the 18 elements regulates the expression of ASXL3 during development by encoding an alternatively spliced exon that causes nonsense-mediated decay of the transcript. The retroposon that gave rise to these functional elements was quickly inactivated in the mammalian ancestor, and all traces of it have been lost due to neutral decay. However, the tuatara has maintained a near-ancestral version of this retroposon in its extant genome, which allows us to connect the 18 human elements to the evolutionary events that created them. We propose that conservation efforts over more than 100 years may not have only prevented the tuatara from going extinct but could have preserved our ability to understand the evolutionary history of functional elements in the human genome. Through simulations, we argue that species with historically low population sizes are more likely to harbor ancient mobile elements for long periods of time and in near-ancestral states, making these species indispensable in understanding the evolutionary origin of functional elements in the human genome.

NR4A orphan nuclear receptors as mediators of CREB-dependent neuroprotection

Induced expression of neuroprotective genes is essential for maintaining neuronal integrity after stressful insults to the brain. Here we show that NR4A nuclear orphan receptors are induced after excitotoxic and oxidative stress in neurons, up-regulate neuroprotective genes, and increase neuronal survival. Moreover, we show that NR4A proteins are induced by cAMP response element binding protein (CREB) in neurons exposed to stressful insults and that they function as mediators of CREB-induced neuronal survival. Animals with null mutations in three of six NR4A alleles show increased oxidative damage, blunted induction of neuroprotective genes, and increased vulnerability in the hippocampus after treatment with kainic acid. We also demonstrate that NR4A and the transcriptional coactivator PGC-1alpha independently regulate distinct CREB-dependent neuroprotective gene programs. These data identify NR4A nuclear orphan receptors as essential mediators of neuroprotection after exposure to neuropathological stress.

Hes1 regulates embryonic stem cell differentiation by suppressing Notch signaling

Embryonic stem (ES) cells display heterogeneous responses upon induction of differentiation. Recent analysis has shown that Hes1 expression oscillates with a period of about 3–5 h in mouse ES cells and that this oscillating expression contributes to the heterogeneous responses: Hes1-high ES cells are prone to the mesodermal fate, while Hes1-low ES cells are prone to the neural fate. These outcomes of Hes1-high and Hes1-low ES cells are very similar to those of inactivation and activation of Notch signaling, respectively. These results suggest that Hes1 and Notch signaling lead to opposite outcomes in ES cell differentiation, although they work in the same direction in most other cell types. Here, we found that Hes1 acts as an inhibitor but not as an effector of Notch signaling in ES cell differentiation. Our results indicate that sustained Hes1 expression delays the differentiation of ES cells and promotes the preference for the mesodermal rather than the neural fate by suppression of Notch signaling.

Molecular maps of the reorganization of genome-nuclear lamina interactions during differentiation

The three-dimensional organization of chromosomes within the nucleus and its dynamics during differentiation are largely unknown. To visualize this process in molecular detail, we generated high-resolution maps of genome-nuclear lamina interactions during subsequent differentiation of mouse embryonic stem cells via lineage-committed neural precursor cells into terminally differentiated astrocytes. This reveals that a basal chromosome architecture present in embryonic stem cells is cumulatively altered at hundreds of sites during lineage commitment and subsequent terminal differentiation. This remodeling involves both individual transcription units and multigene regions and affects many genes that determine cellular identity. Often, genes that move away from the lamina are concomitantly activated; many others, however, remain inactive yet become unlocked for activation in a next differentiation step. These results suggest that lamina-genome interactions are widely involved in the control of gene expression programs during lineage commitment and terminal differentiation.

Jarid2 is a PRC2 component in embryonic stem cells required for multi-lineage differentiation and recruitment of PRC1 and RNA Polymerase II to developmental regulators

Polycomb Repressor Complexes (PRCs) are important regulators of embryogenesis. In embryonic stem (ES) cells many genes that regulate subsequent stages in development are enriched at their promoters for PRC1, PRC2 and Ser 5-phosphorylated RNA Polymerase II (RNAP), and contain domains of 'bivalent' chromatin (enriched for H3K4me3; histone H3 di- or trimethylated at Lys 4 and H3K27me3; histone H3 trimethylated at Lys 27). Loss of individual PRC components in ES cells can lead to gene de-repression and to unscheduled differentiation. Here we show that Jarid2 is a novel subunit of PRC2 that is required for the co-recruitment of PRC1 and RNAP to genes that regulate development in ES cells. Jarid2-deficient ES cells showed reduced H3K4me2/me3 and H3K27me3 marking and PRC1/PRC2 recruitment, and did not efficiently establish Ser 5-phosporylated RNAP at target genes. ES cells lacking Jarid2, in contrast to previously characterized PRC1 and PRC2 mutants, did not inappropriately express PRC2 target genes. Instead, they show a severely compromised capacity for successful differentiation towards neural or mesodermal fates and failed to correctly initiate lineage-specific gene expression in vitro. Collectively, these data indicate that transcriptional priming of bivalent genes in pluripotent ES cells is Jarid2-dependent, and suggests that priming is critical for subsequent multi-lineage differentiation.

Heparan sulfation-dependent fibroblast growth factor signaling maintains embryonic stem cells primed for differentiation in a heterogeneous state

Embryonic stem (ES) cells continuously decide whether to maintain pluripotency or differentiate. While exogenous leukemia inhibitory factor and BMP4 perpetuate a pluripotent state, less is known about the factors initiating differentiation. We show that heparan sulfate (HS) proteoglycans are critical coreceptors for signals inducing ES cell differentiation. Genetic targeting of NDST1 and NDST2, two enzymes required for N-sulfation of proteoglycans, blocked differentiation. This phenotype was rescued by HS presented in trans or by soluble heparin. NaClO(3) (-), which reduces sulfation of proteoglycans, potently blocked differentiation of wild-type cells. Mechanistically, N-sulfation was identified to be critical for functional autocrine fibroblast growth factor 4 (FGF4) signaling. Microarray analysis identified the pluripotency maintaining transcription factors Nanog, KLF2/4/8, Tbx3, and Tcf3 to be negatively regulated, whereas markers of differentiation such as Gbx2, Dnmt3b, FGF5, and Brachyury were induced by sulfation-dependent FGF receptor (FGFR) signaling. We show that several of these genes are heterogeneously expressed in ES cells, and that targeting of heparan sulfation or FGFR-signaling facilitated a homogenous Nanog/KLF4/Tbx3 positive ES cell state. This finding suggests that the recently discovered heterogeneous state of ES cells is regulated by HS-dependent FGFR signaling. Similarly, culturing blastocysts with NaClO(3) (-) eliminated GATA6-positive primitive endoderm progenitors generating a homogenous Nanog-positive inner cell mass. Functionally, reduction of sulfation robustly improved de novo ES cell derivation efficiency. We conclude that N-sulfated HS is required for FGF4 signaling to maintain ES cells primed for differentiation in a heterogeneous state. Inhibiting this pathway facilitates a more naïve ground state.

FoxP1 promotes midbrain identity in embryonic stem cell-derived dopamine neurons by regulating Pitx3

The robust generation of midbrain dopamine neurons from embryonic stem cells and patient-specific induced pluripotent stem cells is a prospective tool for the development of new drugs and cell based therapies, and investigations into the aetiology of Parkinson's disease. To achieve this, it is crucial to identify the fate-determining regulatory factors that influence dopamine cell fate decision and the underlying molecular machinery. We identified FoxP1 as a novel marker for midbrain dopamine neurons. Enforced expression of FoxP1 in embryonic stem cells actuates the expression of Pitx3, a homeobox protein that is exclusively expressed in midbrain dopaminergic neurons and is required for their differentiation and survival during development and from embryonic stem cells in vitro. We show that FoxP1 can be recruited to the Pitx3 locus in embryonic stem cells and regulate Pitx3 promoter activity in a dual-luciferase assay. This transcriptional regulation of Pitx3 by FoxP1 depends on the presence of two high affinity binding sites in the distal Pitx3 promoter, through which FoxP1 directly binds as demonstrated by chromatin immunoprecipitation and electrophoretic mobility shift assay. Thus, this study demonstrates for the first time a transcription regulatory role for FoxP1 on the Pitx3 gene in mammalian stem cells.

Nodal signaling regulates the bone morphogenic protein pluripotency pathway in mouse embryonic stem cells

Members of the transforming growth factor-beta superfamily play essential roles in both the pluripotency and differentiation of embryonic stem (ES) cells. Although bone morphogenic proteins (BMPs) maintain pluripotency of undifferentiated mouse ES cells, the role of autocrine Nodal signaling is less clear. Pharmacological, molecular, and genetic methods were used to further understand the roles and potential interactions of these pathways. Treatment of undifferentiated ES cells with SB431542, a pharmacological inhibitor of Smad2 signaling, resulted in a rapid reduction of phosphorylated Smad2 and altered the expression of several putative downstream targets. Unexpectedly, inhibition of the Nodal signaling pathway resulted in enhanced BMP signaling, as assessed by Smad1/5 phosphorylation. SB431542-treated cells also demonstrated significant induction of the Id genes, which are known direct targets of BMP signaling and important factors in ES cell pluripotency. Inhibition of BMP signaling decreased the SB431542-mediated phosphorylation of Smad1/5 and induction of Id genes, suggesting that BMP signaling is necessary for some Smad2-mediated activity. Because Smad7, a known inhibitory factor to both Nodal and BMP signaling, was down-regulated following inhibition of Nodal-Smad2 signaling, the contribution of Smad7 to the cross-talk between the transforming growth factor-beta pathways in ES cells was examined. Biochemical manipulation of Smad7 expression, through shRNA knockdown or inducible gene expression, significantly reduced the SB431542-mediated phosphorylation of Smad1/5 and induction of the Id genes. We conclude that autocrine Nodal signaling in undifferentiated mouse ES cells modulates the vital pluripotency pathway of BMP signaling.

An abbreviated protocol for multilineage neural differentiation of murine embryonic stem cells and its perturbation by methyl mercury

Alternative assays are highly desirable to reduce the extensive experimental animal use in developmental toxicity testing. In the present study, we developed an improved test system for assessing neurodevelopmental toxicity using differentiating embryonic stem cells. We advanced previously established methods by merging, modifying and abbreviating the original 20-day protocol into a more efficient 13-day neural differentiation protocol. Using morphological observation, immunocytochemistry, gene expression and flow cytometry, it was shown predominantly multiple lineages of neuroectodermal cells were formed in our protocol and to a lower extent, endodermal and mesodermal differentiated cell types. This abbreviated protocol should lead to an advanced screening method using morphology in combination with selected differentiation markers aimed at predicting neurodevelopmental toxicity. Finally, the assay was shown to express differential sensitivity to a model developmental neurotoxicant, methyl mercury.

Isolation and propagation of enteric neural crest progenitor cells from mouse embryonic stem cells and embryos

Neural crest is a source of diverse cell types, including the peripheral nervous system. The transcription factor Sox10 is expressed throughout early neural crest. We exploited Sox10 reporter and selection markers created by homologous recombination to investigate the generation, maintenance and expansion of neural crest progenitors. Sox10-GFP-positive cells are produced transiently from mouse embryonic stem (ES) cells by treatment with retinoic acid in combination with Fgf8b and the cytokine leukaemia inhibitory factor (Lif). We found that expression of Sox10 can be maintained using noggin, Wnt3a, Lif and endothelin (NWLE). ES cell-derived Sox10-GFP-positive cells cultured in NWLE exhibit molecular markers of neural crest progenitors. They differentiate into peripheral neurons in vitro and are able to colonise the enteric network in organotypic gut cultures. Neural crest cells purified from embryos using the Sox10 reporter also survive in NWLE, but progressively succumb to differentiation. We therefore applied selection to eliminate differentiating cells. Sox10-selected cells could be clonally expanded, cryopreserved, and multiplied for over 50 days in adherent culture. They remained neurogenic in vitro and in foetal gut grafts. Generation of neural crest from mouse ES cells opens a new route to the identification and validation of determination factors. Furthermore, the ability to propagate undifferentiated progenitors creates an opportunity for experimental dissection of the stimuli and molecular circu that govern neural crest lineage progression. Finally, the demonstration of robust enteric neurogenesis provides a system for investigating and modelling cell therapeutic approaches to neurocristopathies such as Hirschsprung's disease.

Epigenetic changes to human umbilical cord blood cells cultured with three proteins indicate partial reprogramming to a pluripotent state

We have previously reported the existence of a subpopulation of cells from human umbilical cord blood capable of differentiating into oligodendrocytes, Schwann cells, bone, muscle, and endothelial cells despite their origins as CD45-positive cells. These stem cells (called FSFl cells) arise only after a period in vitro in medium containing FGF4, SCF, and Flt-3 ligand (FSFl medium) during which they express the pluripotency genes Oct4 and Nanog. The objective of this study was to determine if the novel expression of these pluripotency genes coupled with the newly acquired ability of these cells to differentiate into all three germ layers was the result of epigenetic changes to these cells after reprogramming in FSFl medium. We confirm that CD45-derived FSFl cells express Oct4 protein at levels similar to that observed among undifferentiated embryonic stem cells, during which time acetylated histones H3 and H4 display increased binding at the promoter region of Oct4. Changes to binding of acetylated histones at Oct4 when these cells are in a differentiated state (either prior to FSFl culture or after in vitro differentiation into neural cells) and when they are undifferentiated suggest that this is one way by which these cells acquire their pluripotency. While DNA hypermethylation at this gene region as well as the continued H3 and H4 acetylation at the CD45 promoter region among FSFl cells indicate this is only a partial reprogramming event, this is a significant step toward non-transgene reprogramming of somatic cells.

Lentiviral gene ontology (LeGO) vectors equipped with novel drug-selectable fluorescent proteins: new building blocks for cell marking and multi-gene analysis

Vector-encoded fluorescent proteins (FPs) facilitate unambiguous identification or sorting of gene-modified cells by fluorescence-activated cell sorting (FACS). Exploiting this feature, we have recently developed lentiviral gene ontology (LeGO) vectors (www.LentiGO-Vectors.de) for multi-gene analysis in different target cells. In this study, we extend the LeGO principle by introducing 10 different drug-selectable FPs created by fusing one of the five selection marker (protecting against blasticidin, hygromycin, neomycin, puromycin and zeocin) and one of the five FP genes (Cerulean, eGFP, Venus, dTomato and mCherry). All tested fusion proteins allowed both fluorescence-mediated detection and drug-mediated selection of LeGO-transduced cells. Newly generated codon-optimized hygromycin- and neomycin-resistance genes showed improved expression as compared with their ancestors. New LeGO constructs were produced at titers >10(6) per ml (for non-concentrated supernatants). We show efficient combinatorial marking and selection of various cells, including mesenchymal stem cells, simultaneously transduced with different LeGO constructs. Inclusion of the cytomegalovirus early enhancer/chicken beta-actin promoter into LeGO vectors facilitated robust transgene expression in and selection of neural stem cells and their differentiated progeny. We suppose that the new drug-selectable markers combining advantages of FACS and drug selection are well suited for numerous applications and vector systems. Their inclusion into LeGO vectors opens new possibilities for (stem) cell tracking and functional multi-gene analysis.