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The inactivation of p53 functions enhances the efficiency and decreases the latency of producing induced pluripotent stem cells (iPSC) in culture. The formation of iPSCs in culture starts with a rapid set of cell divisions followed by an epigenetic reprogramming of the DNA and chromatin. The mechanisms by which the p53 protein inhibits the formation of iPSCs are largely unknown. Using a temperature sensitive mutant of the p53 (Trp53) gene,we examined the impact of the temporal expression of wild type p53 in preventing stem cell induction from somatic cells. We also explored how different p53 mutant alleles affect the reprogramming process. We found that little or no p53 activity favors the entire process of somatic cell reprogramming. Reactivation of p53 at any time point during the reprogramming process not only interrupted the formation of iPSCs,but also induced newly formed stem cells to differentiate. Among p53-regulated genes,p21 (Cdkn1a),but not Puma (Bbc3) played a partial role in iPSCs formation probably by slowing cell division. Activation of p53 functions in iPSCs induced senescence and differentiation in stem cell populations. High rate of birth defects and increases in DNA methylation at the IGF2-H19 loci in female offspring of p53 knockout mice suggested that the absence of p53 may give rise to epigenetic instability in a stochastic fashion. Consistently,selected p53 missense mutations showed differential effects on the stem cell reprogramming efficiency in a c-Myc dependent manner. The absence of p53 activity and functions also contributed to an enhanced efficiency of iPSC production from cancer cells. The production of iPSCs in culture from normal and cancer cells,although different from each other in several ways,both responded to the inhibition of reprogramming by the p53 protein. View Publication

RATIONALE: Molecular imaging has proven to be a vital tool in the characterization of stem cell behavior in vivo. However,the integration of reporter genes has typically relied on random integration,a method that is associated with unwanted insertional mutagenesis and positional effects on transgene expression.backslashnbackslashnOBJECTIVE: To address this barrier,we used genome editing with zinc finger nuclease (ZFN) technology to integrate reporter genes into a safe harbor gene locus (PPP1R12C,also known as AAVS1) in the genome of human embryonic stem cells and human induced pluripotent stem cells for molecular imaging.backslashnbackslashnMETHODS AND RESULTS: We used ZFN technology to integrate a construct containing monomeric red fluorescent protein,firefly luciferase,and herpes simplex virus thymidine kinase reporter genes driven by a constitutive ubiquitin promoter into a safe harbor locus for fluorescence imaging,bioluminescence imaging,and positron emission tomography imaging,respectively. High efficiency of ZFN-mediated targeted integration was achieved in both human embryonic stem cells and induced pluripotent stem cells. ZFN-edited cells maintained both pluripotency and long-term reporter gene expression. Functionally,we successfully tracked the survival of ZFN-edited human embryonic stem cells and their differentiated cardiomyocytes and endothelial cells in murine models,demonstrating the use of ZFN-edited cells for preclinical studies in regenerative medicine.backslashnbackslashnCONCLUSION: Our study demonstrates a novel application of ZFN technology to the targeted genetic engineering of human pluripotent stem cells and their progeny for molecular imaging in vitro and in vivo. View Publication

AIM: The generation and characterization of a human embryonic stem cell (hESC) line stably expressing red fluorescent mCherry protein.backslashnbackslashnMETHODS: Lentiviral transduction of a ubiquitously-expressed human EF-1α promoter driven mCherry transgene was performed in MEL2 hESC. Red fluore-scence was assessed by immunofluorescence and flow cytometry. Pluripotency of stably transduced hESC was determined by immunofluorescent pluripotency marker expression,flow cytometry,teratoma assays and embryoid body-based differentiation followed by reverse transcriptase-polymerase chain reaction. Quantification of cell motility and survival was performed with time lapse microscopy.backslashnbackslashnRESULTS: Constitutively fluorescently-labeled hESCs are useful tools for facile in vitro and in vivo tracking of survival,motility and cell spreading on various surfaces before and after differentiation. Here we describe the generation and characterization of a hESC line (MEL2) stably expressing red fluorescent protein,mCherry. This line was generated by random integration of a fluorescent protein-expressing cassette,driven by the ubiquitously-expressed human EF-1α promoter. Stably transfected MEL2-mCherry hESC were shown to express pluripotency markers in the nucleus (POU5F1/OCT4,NANOG and SOX2) and on the cell surface (SSEA4,TRA1-60 and TG30/CD9) and were shown to maintain a normal karyotype in long-term (for at least 35 passages) culture. MEL2-mCherry hESC further readily differentiated into representative cell types of the three germ layers in embryoid body and teratoma based assays and,importantly,maintained robust mCherry expression throughout differentiation. The cell line was next adapted to single-cell passaging,rendering it compatible with numerous bioengineering applications such as measurement of cell motility and cell spreading on various protein modified surfaces,quantification of cell attachment to nanoparticles and rapid estimation of cell survival.backslashnbackslashnCONCLUSION: The MEL2-mCherry hESC line conforms to the criteria of bona fide pluripotent stem cells and maintains red fluorescence throughout differentiation,making it a useful tool for bioengineering and in vivo tracking experiments. View Publication

De novo DNA methylation is an essential aspect of the epigenetic reprogramming that takes place during early development,yet factors responsible for its instatement at particular genomic loci are poorly defined. Here,we demonstrate that the KRAB-ZFP-mediated recruitment of KAP1 to DNA in embryonic stem cells (ESCs) induces cytosine methylation. This process is preceded by H3K9 trimethylation,and genome-wide analyses reveal that it spreads over short distances from KAP1-binding sites so as to involve nearby CpG islands. In sharp contrast,in differentiated cells,KRAB/KAP1-induced heterochromatin formation does not lead to DNA methylation. Correspondingly,the methylation status of CpG islands in the adult mouse liver correlates with their proximity to KAP1-binding sites in ESCs,not in hepatocytes. Therefore,KRAB-ZFPs and their cofactor KAP1 are in part responsible for the establishment during early embryogenesis of site-specific DNA methylation patterns that are maintained through development View Publication

Neural cells derived from induced pluripotent stem cells (iPSCs) have the potential for autologous cell therapies in treating patients with severe neurological disorders or injury. However,further study of efficacy and safety are needed in large animal preclinical models that have similar neural anatomy and physiology to humans such as the pig. The pig model for pluripotent stem cell therapy has been made possible for the first time with the development of pig iPSCs (piPSCs) capable of in vitro and in vivo differentiation into tissues of all three germ layers. Still,the question remains if piPSCs are capable of undergoing robust neural differentiation using a system similar to those being used with human iPSCs. In this study,we generated a new line of piPSCs from fibroblast cells that expressed pluripotency markers and were capable of embryoid body differentiation into all three germ layers. piPSCs demonstrated robust neural differentiation forming βIII-TUB/MAP2+ neurons,GFAP+ astrocytes,and O4+ oligodendrocytes and demonstrated strong upregulation of neural cell genes representative of all three major neural lineages of the central nervous system. In the presence of motor neuron signaling factors,piPSC-derived neurons showed expression of transcription factors associated with motor neuron differentiation (HB9 and ISLET1). Our findings demonstrate that SSEA4 expression is required for piPSCs to differentiate into neurons,astrocytes,and oligodendrocytes and furthermore develop specific neuronal subtypes. This indicates that the pigs can fill the need for a powerful model to study autologous neural iPSC therapies in a system similar to humans. View Publication

Human pluripotent stem cells (hPSCs) are a promising cell source for tissue engineering and regenerative medicine,especially in the field of neurobiology. Neural differentiation protocols have been developed to differentiate hPSCs into specific neural cells,but these predominantly rely on biochemical cues. Recently,differentiation protocols have incorporated topographical cues to increase the total neuronal yield. However,the means by which these topographical cues improve neuronal yield remains unknown. In this study,we explored the effect of topography on the neural differentiation of hPSC by quantitatively studying the changes in marker expression at a transcript and protein level. We found that 2 ??m gratings increase the rate of neural differentiation,and that an additional culture period of 2 ??m gratings in the absence of neurotrophic signals can improve the neural differentiation of hPSCs. We envisage that this work can be incorporated into future differentiation protocols to decrease the differentiation period as well as the biochemical signals added,thus generating hPSC-derived neural cells in a more cost effective and efficient manner. ?? 2012 Elsevier Ltd. View Publication

MicroRNAs (miRNAs) have emerged as critical regulators of gene expression through translational inhibition and RNA decay and have been implicated in the regulation of cellular differentiation,proliferation,angiogenesis,and apoptosis. In this study,we analyzed global miRNA and mRNA microarrays to predict novel miRNA-mRNA interactions in human embryonic stem cells and induced pluripotent stem cells (iPSCs). In particular,we demonstrate a regulatory feedback loop between the miR-302 cluster and two transcription factors,NR2F2 and OCT4. Our data show high expression of miR-302 and OCT4 in pluripotent cells,while NR2F2 is expressed exclusively in differentiated cells. Target analysis predicts that NR2F2 is a direct target of miR-302,which we experimentally confirm by reporter luciferase assays and real-time polymerase chain reaction. We also demonstrate that NR2F2 directly inhibits the activity of the OCT4 promoter and thus diminishes the positive feedback loop between OCT4 and miR-302. Importantly,higher reprogramming efficiencies were obtained when we reprogrammed human adipose-derived stem cells into iPSCs using four factors (KLF4,C-MYC,OCT4,and SOX2) plus miR-302 (this reprogramming cocktail is hereafter referred to as KMOS3") when compared to using four factors ("KMOS"). Furthermore� View Publication

Aim: Reprogramming of somatic cells utilizing viral free methods provide a remarkable method to generate human induced pluripotent stem cells (hiPSCs) for regenerative medicine. In this study,we evaluate developmental ontogeny of cardiomyocytes following induced differentiation of hiPSCs. Main Methods: Fibroblasts were reprogrammed with episomal vectors to generate hiPSC and were subsequently differentiated to cardiomyocytes. Ontogenic development of cardiomyocytes was studied by real-time PCR. Key findings: Human iPSCs derived from episomal based vectors maintain classical pluripotency markers,generate teratomas and spontaneously differentiate into three germ layers in vitro. Cardiomyogenic induction of these hiPSCs efficiently generated cardiomyocytes. Ontogenic gene expression studies demonstrated that differentiation of cardiomyocytes was initiated by increased expression of mesodermal markers,followed by early cardiac committed markers,structural and ion channel genes. Furthermore,our correlation analysis of gene expression studies with human heart demonstrated that pivotal structural genes like cardiac troponin,actinin,myosin light chain maintained a high correlation with ion channel genes indicating coordinated activation of cardiac transcriptional machinery. Finally,microelectrode recordings show that these cardiomyocytes could respond aptly to pharmacologically active drugs. Cardiomyocytes showed a chronotropic response to isoproterenol,reduced Na+ influx with quinidine,prolongation of beating rate corrected field potential duration (cFPD) with E-4031 and reduced beating frequency and shortened cFPD with verapamil. Significance: Our study shows that viral free hiPSCs efficiently differentiate into cardiomyocytes with cardiac-specific molecular,structural,and functional properties that recapitulate developmental ontogeny of cardiogenesis. These results,coupled with the potential to generate patient-specific hiPSC lines hold great promise for the development of in vitro platform for drug pharmacogenomics; disease modeling and regenerative medicine. textcopyright 2012 Elsevier Inc. All rights reserved. View Publication

Lifelong blood cell production is governed through the poorly understood integration of cell-intrinsic and -extrinsic control of hematopoietic stem cell (HSC) quiescence and activation. MicroRNAs (miRNAs) coordinately regulate multiple targets within signaling networks,making them attractive candidate HSC regulators. We report that miR-126,a miRNA expressed in HSC and early progenitors,plays a pivotal role in restraining cell-cycle progression of HSC in vitro and in vivo. miR-126 knockdown by using lentiviral sponges increased HSC proliferation without inducing exhaustion,resulting in expansion of mouse and human long-term repopulating HSC. Conversely,enforced miR-126 expression impaired cell-cycle entry,leading to progressively reduced hematopoietic contribution. In HSC/early progenitors,miR-126 regulates multiple targets within the PI3K/AKT/GSK3β pathway,attenuating signal transduction in response to extrinsic signals. These data establish that miR-126 sets a threshold for HSC activation and thus governs HSC pool size,demonstrating the importance of miRNA in the control of HSC function. View Publication

Articular cartilage,which is mainly composed of collagen II,enables smooth skeletal movement. Degeneration of collagen II can be caused by various events,such as injury,but degeneration especially increases over the course of normal aging. Unfortunately,the body does not fully repair itself from this type of degeneration,resulting in impaired movement. Microfracture,an articular cartilage repair surgical technique,has been commonly used in the clinic to induce the repair of tissue at damage sites. Mesenchymal stem cells (MSC) have also been used as cell therapy to repair degenerated cartilage. However,the therapeutic outcomes of all these techniques vary in different patients depending on their age,health,lesion size and the extent of damage to the cartilage. The repairing tissues either form fibrocartilage or go into a hypertrophic stage,both of which do not reproduce the equivalent functionality of endogenous hyaline cartilage. One of the reasons for this is inefficient chondrogenesis by endogenous and exogenous MSC. Drugs that promote chondrogenesis could be used to induce self-repair of damaged cartilage as a non-invasive approach alone,or combined with other techniques to greatly assist the therapeutic outcomes. The recent development of human induced pluripotent stem cell (iPSCs),which are able to self-renew and differentiate into multiple cell types,provides a potentially valuable cell resource for drug screening in a more relevant" cell type. Here we report a screening platform using human iPSCs in a multi-well plate format to identify compounds that could promote chondrogenesis." View Publication

Differences in global levels of histone acetylation occur in normal and cancer cells,although the reason why cells regulate these levels has been unclear. Here we demonstrate a role for histone acetylation in regulating intracellular pH (pH(i)). As pH(i) decreases,histones are globally deacetylated by histone deacetylases (HDACs),and the released acetate anions are coexported with protons out of the cell by monocarboxylate transporters (MCTs),preventing further reductions in pH(i). Conversely,global histone acetylation increases as pH(i) rises,such as when resting cells are induced to proliferate. Inhibition of HDACs or MCTs decreases acetate export and lowers pH(i),particularly compromising pH(i) maintenance in acidic environments. Global deacetylation at low pH is reflected at a genomic level by decreased abundance and extensive redistribution of acetylation throughout the genome. Thus,acetylation of chromatin functions as a rheostat to regulate pH(i) with important implications for mechanism of action and therapeutic use of HDAC inhibitors. View Publication

PURPOSE This study aimed to develop a feasible and efficient method for generating embryonic stem cell (ESC)-like induced pluripotent stem (iPS) cells from human Tenon's capsule fibroblasts (HTFs) through the expression of a defined set of transcription factors,which will have significant application value for ophthalmic personalized regenerative medicine. METHODS HTFs were harvested from fresh samples,and reprogramming was induced by the exogenous expression of the four classic transcription factors,OCT-3/4,SOX-2,KLF-4,and C-MYC. The HTF-derived iPS (TiPS) cells were analyzed with phase contrast microscopy,real-time PCR,immunofluorescence,FACS analysis,alkaline phosphatase activity analysis,and a teratoma formation assay. Human ESC colonies were used as the positive control. RESULTS The resulting HTF-derived iPS cell colonies were indistinguishable from human ESC colonies regarding morphology,gene expression levels,pluripotent gene expression,alkaline phosphatase activity,and the ability to generate all three embryonic germ layers. CONCLUSIONS This study presents a simple,efficient,practical procedure for generating patient-tailored iPS cells from HTFs. These cells will serve as a valuable and preferred candidate donor cell population for ophthalmological regenerative medicine. View Publication