Quantitation and functional characterization of neural cells derived from ES cells using nestin enhancer-mediated targeting in vitro

Spinal cord organogenesis model reveals role of Flk1+ cells in self-organization of neural progenitor cells into complex spinal cord tissue

A platform for studying spinal cord organogenesis in vivo where embryonic stem cell (ESC)-derived neural progenitor cells (NPC) self-organize into spinal cord-like tissue after transplantation in subarachnoid space of the spinal cord has been described. We advance the applicability of this platform by imaging in vivo the formed graft through T2w magnetic resonance imaging (MRI). Furthermore, we used diffusion tensor imaging (DTI) to verify the stereotypical organization of the graft showing that it mimics the host spinal cord. Within the graft white matter (WM) we identified astrocytes that form glial limitans, myelinating oligodendrocytes, and myelinated axons with paranodes. Within the graft grey matter (GM) we identified cholinergic, glutamatergic, serotonergic and dopaminergic neurons. Furthermore, we demonstrate the presence of ESC-derived complex vasculature that includes the presence of blood brain barrier. In addition to the formation of mature spinal cord tissue, we describe factors that drive this process. Specifically, we identify Flk1⁺ cells as necessary for spinal cord formation, and synaptic connectivity with the host spinal cord and formation of host-graft chimeric vasculature as contributing factors. This model can be used to study spinal cord organogenesis, and as an in vivo drug discovery platform for screening potential therapeutic compounds and their toxicity.

Thermoresponsive hydrogel maintains the mouse embryonic stem cell “naïve” pluripotency phenotype

A chemically defined hydrogel HG21, which allows enzyme-free passaging, is a substitute for gelatin allowing standardised and inexpensive mESC culture.

Genetic approach to track neural cell fate decisions using human embryonic stem cells

With their capability to undergo unlimited self-renewal and to differentiate into all cell types in the body, human embryonic stem cells (hESCs) hold great promise in human cell therapy. However, there are limited tools for easily identifying and isolating live hESC-derived cells. To track hESC-derived neural progenitor cells (NPCs), we applied homologous recombination to knock-in the mCherry gene into the Nestin locus of hESCs. This facilitated the genetic labeling of Nestin positive neural progenitor cells with mCherry. Our reporter system enables the visualization of neural induction from hESCs both in vitro (embryoid bodies) and in vivo (teratomas). This system also permits the identification of different neural subpopulations based on the intensity of our fluorescent reporter. In this context, a high level of mCherry expression showed enrichment for neural progenitors, while lower mCherry corresponded with more committed neural states. Combination of mCherry high expression with cell surface antigen staining enabled further enrichment of hESC-derived NPCs. These mCherry(+) NPCs could be expanded in culture and their differentiation resulted in a down-regulation of mCherry consistent with the loss of Nestin expression. Therefore, we have developed a fluorescent reporter system that can be used to trace neural differentiation events of hESCs.

Lineage-specific purification of neural stem/progenitor cells from differentiated mouse induced pluripotent stem cells

Since induced pluripotent stem (iPS) cells have differentiation potential into all three germ layer-derived tissues, efficient purification of target cells is required in many fields of iPS research. One useful strategy is isolation of desired cells from differentiated iPS cells by lineage-specific expression of a drug-resistance gene, followed by drug selection. With this strategy, we purified neural stem/progenitor cells (NSCs), a good candidate source for regenerative therapy, from differentiated mouse iPS cells. We constructed a bicistronic expression vector simultaneously expressing blasticidin S resistance gene and DsRed under the control of tandem enhancer of a 257-base pair region of nestin second intron, an NSC-specific enhancer. This construct was efficiently inserted into the iPS genome by piggyBac transposon-mediated gene transfer, and the established subclone was differentiated into NSCs in the presence or absence of blasticidin S. Consequently, incubation with blasticidin S led to purification of NSCs from differentiated iPS cells. Our results suggest that a lineage-specific drug selection strategy is useful for purification of NSCs from differentiated iPS cells and that this strategy can be applied for the purification of other cell types.

Generation of human embryonic stem cell reporter lines expressing GFP specifically in neural progenitors

Generation of lineage-specific human embryonic stem cell (hESC) reporter lines will facilitate the real time monitoring of differentiation in live cells and the identification of factors governing these processes. It will also enable researchers to purify specific cell populations from heterogeneous differentiated hESC progeny. Here we report the generation of clonally derived nestin-EGFP reporter hESC lines that express GFP under the control of the neuroepithelial specific nestin 2nd intron enhancer. We show that the nestin-EGFP hESC reporter lines retain the features of undifferentiated hESCs, are able to self-renew in hESC culture conditions and to differentiate into cells of all three germ layers. The nestin-EGFP reporter exhibited high expression in neural progenitor cells upon differentiation, although it is detectable at a low level in the undifferentiated state. Furthermore, the expression of the transgene is exclusively confined to the neural progenitors after differentiation. The specific expression of the transgene is determined by collaborative binding motifs of POU and SOX transcription factors in the nestin enhancer. Deletion of either of the binding elements resulted in a significant reduction of enhancer/promoter activity. Taken together, the nestin-EGFP reporter hESC lines are invaluable not only for the study of the neural differentiation process from hESCs but also for the enrichment of neural progenitor cells from other cell lineages.

Notch exhibits ligand bias and maneuvers stage-specific steering of neural differentiation in embryonic stem cells

Notch dictates multiple developmental events, including stem cell maintenance and differentiation, through intercellular communication. However, its temporal influence during early development and, of particular interest, its regulation of binary fate decision at different stages during neurogenesis are among the least explored. Here, using an embryonic stem cell (ESC) model, we have deciphered Notch ligand preference during ESC commitment to different germ layers and determined the stage-specific temporal effect of Notch during neural differentiation. ESCs during maintenance remain impervious to Notch inhibition. However, Notch activation promotes differentiation even in the presence of leukemia inhibitory factor (LIF), displaying ligand preference-associated lineage discrimination, where Jagged-1 favors neural commitment and Delta-like-4 favors the mesoderm. This differential ligand action involves a combination of Notch receptors influencing specific downstream target gene expression. Though Notch activation during early neural differentiation specifically promotes neural stem cells or early neural progenitors and delays their maturation, its inhibition promotes late neural progenitors and expedites neurogenesis, with a preference for neurons over glia. However, gliogenesis is promoted upon Notch activation only when executed in combination with ciliary neurotrophic factor. Thus, our investigation underscores a multifaceted role of Notch, demonstrating the interdependency of ligand usage and lineage specification and Notch acting as a master switch, displaying stage-specific influence on neurogenesis.

Derivation of homogeneous GABAergic neurons from mouse embryonic stem cells

Embryonic stem cells (ESCs) promise an unlimited source of defined cells for cell transplantation therapy, while protocols for derivation of homogeneous populations of desirable cell types are yet to be developed and/or refined. Gamma aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the central nervous system, and disturbed GABAergic signaling is associated with a host of neurological conditions. We developed a simple ES cell differentiation protocol which led to the production of uniform GABAergic neurons in approximately 2 weeks. The differentiation protocol involved treatment of embryoid bodies (EBs) with high concentrations (10(-5)-10(-)(4) M) of all-trans-retinoic acid (RA) for 3 days. After plating these EBs on attached dishes in neural supportive medium, 93-96% of the cells became GABA-positive neurons in 7-11 days. These cells also expressed immature neuronal markers with voltage-gated delayed rectifier potassium currents, suggesting that they were immature GABAergic neurons. The technology may have implications for modeling and treatment of GABAergic signaling-related diseases and injuries.

Different transcription factors regulate nestin gene expression during P19 cell neural differentiation and central nervous system development

Nestin is a molecular marker for neural progenitor cells. Rat and human nestin genes possess a central nervous system-specific enhancer within their second introns. However, the transcription factors that bind to the nestin enhancer have not been fully elucidated. Here, we show that the second intron of the mouse nestin gene is sufficient to drive reporter gene expression in the developing nervous system. The core sequence of this central nervous system-specific enhancer localizes to the 3' 320-bp region. The cis-elements for Sox and POU family transcription factors and the hormone-responsive element are essential for nestin expression during embryonic carcinoma P19 cell neural differentiation and in the developing chick neural tube. Interestingly, different transcription factors bind to the nestin enhancer at different stages of P19 cell neural differentiation and central nervous system development. Sox2 and SF1 may mediate basal nestin expression in undifferentiated P19EC cells, whereas Sox2, Brn1, and Brn2 bind to the enhancer in P19 neural progenitor cells. Similarly, in vivo, Oct1 binds to the nestin enhancer in embryonic day 8.5 (E8.5) mouse embryos, and Oct1, Brn1, and Brn2 bind to this enhancer in E10.5 and E12.5 mouse embryos. Our studies therefore suggest a temporal coordination of transcription factors in determining nestin gene expression.

Neural induction from ES cells portrays default commitment but instructive maturation

The neural induction has remained a debatable issue pertaining to whether it is a mere default process or it involves precise instructive cues. We have chosen the embryonic stem (ES) cell model to address this issue. In a devised monoculture strategy, the cell-cell interaction availed through optimum cell plating density could define the niche for the attainment of efficient in vitro neurogenesis from the ES cells. The medium plating density was found ideal in generating optimum number of progenitors and also yielded about 80% mature neurons in a serum free culture set up barring any exogenous inducers. We could also demarcate and quantify the neural stem cells/progenitors among the heterogeneous cell population of differentiating ES cells using nestin intron II driven EGFP expression as a tool. The one week post-plating was determined to be the critical time window for optimum neural progenitor generation from ES cells that helped us further in purifying these cells and in demonstrating their proliferation and multipotent differentiation potential. Seeding cells at varying densities, we could decipher an interesting paradoxical scenario that interlinked both commitment and maturation with the initial plating density having a vital influence on neuronal maturation but not specification and the secretory factors were apparently playing a key role during this process. Thus it was comprehended that, the neural specification was a default process independent of exogenous factors and cellular interaction. Conversely, a defined number of cells at the specification stage itself seemed critical to provide an auto-/paracrine means of signaling threshold for the maturation process to materialize.

Signals from embryonic fibroblasts induce adult intestinal epithelial cells to form nestin-positive cells with proliferation and multilineage differentiation capacity in vitro

The intestinal epithelium has one of the greatest regenerative capacities in the body; however, neither stem nor progenitor cells have been successfully cultivated from the intestine. In this study, we applied an "artificial niche" of mouse embryonic fibroblasts to derive multipotent cells from the intestinal epithelium. Cocultivation of adult mouse and human intestinal epithelium with fibroblast feeder cells led to the generation of a novel type of nestin-positive cells (intestinal epithelium-derived nestin-positive cells [INPs]). Transcriptome analyses demonstrated that mouse embryonic fibroblasts expressed relatively high levels of Wnt/bone morphogenetic protein (BMP) transcripts, and the formation of INPs was specifically associated with an increase in Lef1, Wnt4, Wnt5a, and Wnt/BMP-responsive factors, but a decrease of BMP4 transcript abundance. In vitro, INPs showed a high but finite proliferative capacity and readily differentiated into cells expressing neural, pancreatic, and hepatic transcripts and proteins; however, these derivatives did not show functional properties. In vivo, INPs failed to form chimeras following injection into mouse blastocysts but integrated into hippocampal brain slice cultures in situ. We conclude that the use of embryonic fibroblasts seems to reprogram adult intestinal epithelial cells by modulation of Wnt/BMP signaling to a cell type with a more primitive embryonic-like stage of development that has a high degree of flexibility and plasticity.

Second intron of mouse nestin gene directs its expression in pluripotent embryonic carcinoma cells through POU factor binding site

Nestin, an intermediate filament protein, is expressed in the neural stem cells of the developing central nervous system. This tissue-specific expression is driven by the neural stem cell-specific enhancer in the second intron of the nestin gene. In this study, we showed that the mouse nestin gene was expressed in pluripotent embryonic carcinoma (EC) P19 and F9 cells, not in the differentiated cell types. This cell type-specific expression was conferred by the enhancer in the second intron. Mutation of the conserved POU factor-binding site in the enhancer abolished the reporter gene expression in EC cells. Oct4, a Class V POU factor, was found to be coexpressed with nestin in EC cells. Electrophoretic mobility-shift assays and supershift assays showed that a unique protein-DNA complex was formed specifically with nuclear extracts of EC cells, and Oct4 protein was included. Together, these results suggest the functional relevance between the conserved POU factor-binding site and the expression of the nestin gene in pluripotent EC cells.

Fluorescence-activated cell sorting-based purification of embryonic stem cell-derived neural precursors averts tumor formation after transplantation

The differentiation of dopaminergic (DA) neurons from mouse embryonic stem cells (ESCs) can be efficiently induced, making these neurons a potential source for transplantation as a treatment for Parkinson's disease, a condition characterized by the gradual loss of midbrain DA neurons. One of the major persistent obstacles to the successful implementation of therapeutic ESC transplantation is the propensity of ESC-derived grafts to form tumors in vivo. To address this problem, we used fluorescence-activated cell sorting to purify mouse ESC-derived neural precursors expressing the neural precursor marker Sox1. ESC-derived, Sox1+ cells began to express neuronal cell markers and differentiated into DA neurons upon transplantation into mouse brains but did not generate tumors in this site. In contrast, Sox1- cells that expressed ESC markers frequently formed tumors in vivo. These results indicate that Sox1-based cell sorting of neural precursors prevents graft-derived tumor formation after transplantation, providing a promising strategy for cell transplantation therapy of neurodegenerative disorders.

Self-renewal vs. Differentiation of Mouse Embryonic Stem Cells1

Embryonic stem (ES) cells are typically derived from the inner cell mass of the preimplantation blastocyst and can both self-renew and differentiate into all the cells and tissues of the embryo. Because they are pluripotent, ES cells have been used extensively to analyze gene function in development via gene targeting. The embryonic stem cell is also an unsurpassed starting material to begin to understand a critical, largely inaccessible period of development. If their differentiation could be controlled, they would also be an important source of cells for transplantation to replace cells lost through disease or injury or to replace missing hormones or genes. Traditionally, ES cells have been differentiated in suspension culture as embryoid bodies, named because of their similarity to the early postimplantation-staged embryo. Unlike the pristine organization of the early embryo, differentiation in embryoid bodies appears to be largely unpatterned, although multiple cell types form. It has recently been possible to separate the desired cell types from differentiating ES cells in embryoid bodies by using cell-type-restricted promoters driving expression of either antibiotic resistance genes or fluorophores such as EGFP. In combination with growth factor exposure, highly differentiated cell types have successfully been derived from ES cells. Recent technological advances such as RNA interference to knock down gene expression in ES cells are also producing enriched populations of cells and elucidating gene function in early development.

Neural Differentiation from Embryonic Stem Cells: Which Way?

Embryonic stem (ES) cells can in theory produce all cell types of a living organism while renewing themselves with a stable genetic background. These unique features make ES cells a favorable tool for biomedical researches as well as a potential source for therapeutic application. A first step for approaching to ES cells is the directed differentiation to cells of interest, such as the neural cell lineage. Here, we summarize the up and down sides of each category of neural differentiation protocols that have so far been used in mouse and human ES cells, and introduce an efficient and plausible method used in our laboratory for derivation of neuroectodermal cells from human ES cells. This synthesis has led to our suggestions on issues for future design of neural differentiation protocols.

Multilineage differentiation of rhesus monkey embryonic stem cells in three-dimensional culture systems

In the course of normal embryogenesis, embryonic stem (ES) cells differentiate along different lineages in the context of complex three-dimensional (3D) tissue structures. In order to study this phenomenon in vitro under controlled conditions, 3D culture systems are necessary. Here, we studied in vitro differentiation of rhesus monkey ES cells in 3D collagen matrixes (collagen gels and porous collagen sponges). Differentiation of ES cells in these 3D systems was different from that in monolayers. ES cells differentiated in collagen matrixes into neural, epithelial, and endothelial lineages. The abilities of ES cells to form various structures in two chemically similar but topologically different matrixes were different. In particular, in collagen gels ES cells formed gland-like circular structures, whereas in collagen sponges ES cells were scattered through the matrix or formed aggregates. Soluble factors produced by feeder cells or added to the culture medium facilitated ES cell differentiation into particular lineages. Coculture with fibroblasts in collagen gel facilitated ES cell differentiation into cells of a neural lineage expressing nestin, neural cell adhesion molecule, and class III beta-tubulin. In collagen sponges, keratinocytes facilitated ES cell differentiation into cells of an endothelial lineage expressing factor VIII. Exogenous granulocyte-macrophage colony-stimulating factor further enhanced endothelial differentiation. Thus, both soluble factors and the type of extracellular matrix seem to be critical in directing differentiation of ES cells and the formation of tissue-like structures. Three-dimensional culture systems are a valuable tool for studying the mechanisms of these phenomena.

Stable Expression of hrGFP by Mouse Embryonic Stem Cells: Promoter Activity in the Undifferentiated State and During Dopaminergic Neural Differentiation

Three promoters, cellular polypeptide chain elongation factor 1 alpha (EF1), cytomegalovirus (CMV), and Rous sarcoma virus (RSV) were examined for stable transgene expression in mouse embryonic stem (ES) cells and their progeny during dopaminergic neural differentiation. In undifferentiated ES cells the EF1 promoter was highly effective, while CMV had moderate activity. After 3 months in culture, expression of humanized renilla green fluorescent protein (hrGFP) was unchanged for the EF1 promoter and decreased for CMV. At the nestin-positive stage of differentiation, hrGFP and nestin were colocalized in about 20% of cells for EF1, in contrast to 80% of cells for the CMV promoter. In tyrosine hydroxylase (TH)-positive neurons neither the EF1 nor CMV promoter were effective. The RSV promoter was inactive in undifferentiated, nestin-positive, and TH-positive cells. Thus, EF1 and CMV are effective promoters for transgene expression in undifferentiated ES cells and nestin-positive neural precursors.

Oxidative DNA damage in peripheral leukocytes and its association with expression and polymorphisms of hOGG1: A study of adolescents in a high risk region for hepatocellular carcinoma in China

AIM: To study the oxidative DNA damage to adolescents of hepatocellular carcinoma (HCC) families in Guangxi Zhuang Autonomous Region, China.

METHODS: Peripheral leukocytes’ DNA 7,8-dihydro-8-oxoguanine (8-oxoG) and repair enzyme hOGG₁ were quantified by flow-cytometry. hOGG₁-Cys326Ser single nucleotide polymorphism (SNP) was distinguished by polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) assay.

RESULTS: There was a positive correlation between 8-oxoG and repair enzyme hOGG₁ expression (P < 0.001). HCC children (n = 21) in Fusui county had a higher level of hOGG₁ (P < 0.01) and a lower level of 8-oxoG (P < 0.05) than the controls (n = 63) in Nanning city. Children in Nanning exposed to passive-smoking had a higher hOGG₁ expression (P < 0.05) than the non-exposers. 8-oxoG and hOGG₁ were negatively correlated with body mass index, while hOGG₁ was positively correlated with age. There was a peak of 8-oxoG level nearby the 12 year point. Individuals with the hOGG₁ 326Ser allele had a significantly marginal higher concentration of leukocyte 8-oxoG level than hOGG₁ 326Cys allele.

CONCLUSION: This is the first report using flow-cytometry to simultaneously quantify both the DNA oxidative damage and its repairing enzyme hOGG1. The results provide new insights towards a better understanding of the mechanisms of oxidative stress in a population highly susceptible to hepatocarcinogenesis.

Characterization and isolation of promoter-defined nestin-positive cells from the human fetal pancreas

Studies using adult human islets and mouse embryonic stem cells have suggested that the neurepithelial precursor cell marker nestin also identifies and can be used to purify beta-cell precursors. To determine whether nestin can be used to identify beta-cell progenitors in the developing human pancreas, we characterized nestin expression from 12 to 24 gestational weeks, purified nestin+ cells using an enhancer/promoter-driven selection plasmid, and determined whether nestin+ cells can differentiate into beta-cells. Nestin was visualized in the platelet endothelial cell adhesion molecule and alpha smooth muscle actin-positive blood vessels and colocalized with vimentin in the interstitium. Nestin was not observed in pan cytokeratin (pCK)-positive ductal epithelium or insulin cells. Purified nestin+ cells also coexpressed vimentin and lacked pCK immunoreactivity. Purified adult and fetal pancreatic fibroblasts also expressed nestin. The nestin enhancer/promoter used in the selection plasmid was sufficient to drive reporter gene expression, green fluorescent protein, in human fetal pancreatic tissue. Exposure of selected nestin+ cells to nicotinamide, hepatocyte growth factor/scatter factor, betacellulin, activin A, or exendin-4 failed to induce pancreatic and duodenal homeobox gene-1 or insulin message as determined by RT-PCR. Transplantation of nestin+ cells and fetal pancreatic fibroblasts into athymic mice also failed to result in the development of beta-cells, whereas nestin- fetal pancreatic epithelial cells gave rise to functional insulin-secreting beta-cells. We conclude that nestin is not a specific marker of beta-cell precursors in the developing human pancreas.

Defined conditions for neural commitment and differentiation

The efficiency of monolayer differentiation establishes that commitment of ES cells to a neural fate needs neither multicellular aggregation nor extrinsic inducers. The entire process by which pluripotent ES cells acquire neural specification can be visualized and recorded at the level of individual colonies. Furthermore this simple culture system is amenable to cellular and molecular dissection, promising to yield new insights into the mechanism underlying neural determination in mammals and perhaps to deliver the goal of "directed" homogeneous differentiation of ES cells.