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Here we describe a protocol to generate a co-culture consisting of 2 different neuronal populations. Induced pluripotent stem cells (iPSCs) are reprogrammed from human fibroblasts using episomal vectors. Colonies of iPSCs can be observed 30 days after initiation of fibroblast reprogramming. Pluripotent colonies are manually picked and grown in neural induction medium to permit differentiation into neural progenitor cells (NPCs). iPSCs rapidly convert into neuroepithelial cells within 1 week and retain the capability to self-renew when maintained at a high culture density. Primary mouse NPCs are differentiated into astrocytes by exposure to a serum-containing medium for 7 days and form a monolayer upon which embryonic day 18 (E18) rat cortical neurons (transfected with channelrhodopsin-2 (ChR2)) are added. Human NPCs tagged with the fluorescent protein,tandem dimer Tomato (tdTomato),are then seeded onto the astrocyte/cortical neuron culture the following day and allowed to differentiate for 28 to 35 days. We demonstrate that this system forms synaptic connections between iPSC-derived neurons and cortical neurons,evident from an increase in the frequency of synaptic currents upon photostimulation of the cortical neurons. This co-culture system provides a novel platform for evaluating the ability of iPSC-derived neurons to create synaptic connections with other neuronal populations. View Publication

Huntington's disease (HD) is a fatal neurodegenerative disease,caused by expansion of polyglutamine repeats in the Huntingtin gene,with longer expansions leading to earlier ages of onset. The HD iPSC Consortium has recently reported a new in vitro model of HD based on the generation of induced pluripotent stem cells (iPSCs) from HD patients and controls. The current study has furthered the disease in a dish model of HD by generating new non-integrating HD and control iPSC lines. Both HD and control iPSC lines can be efficiently differentiated into neurons/glia; however,the HD-derived cells maintained a significantly greater number of nestin-expressing neural progenitor cells compared with control cells. This cell population showed enhanced vulnerability to brain-derived neurotrophic factor (BDNF) withdrawal in the juvenile-onset HD (JHD) lines,which appeared to be CAG repeat-dependent and mediated by the loss of signaling from the TrkB receptor. It was postulated that this increased death following BDNF withdrawal may be due to glutamate toxicity,as the N-methyl-d-aspartate (NMDA) receptor subunit NR2B was up-regulated in the cultures. Indeed,blocking glutamate signaling,not just through the NMDA but also mGlu and AMPA/Kainate receptors,completely reversed the cell death phenotype. This study suggests that the pathogenesis of JHD may involve in part a population of 'persistent' neural progenitors that are selectively vulnerable to BDNF withdrawal. Similar results were seen in adult hippocampal-derived neural progenitors isolated from the BACHD model mouse. Together,these results provide important insight into HD mechanisms at early developmental time points,which may suggest novel approaches to HD therapeutics. View Publication

BACKGROUND: Long noncoding RNAs (lncRNAs) have emerged as critical epigenetic regulators with important functions in development and disease. Here,we sought to identify and functionally characterize novel lncRNAs critical for vertebrate development. METHODS AND RESULTS: By relying on human pluripotent stem cell differentiation models,we investigated lncRNAs differentially regulated at key steps during human cardiovascular development with a special focus on vascular endothelial cells. RNA sequencing led to the generation of large data sets that serve as a gene expression roadmap highlighting gene expression changes during human pluripotent cell differentiation. Stage-specific analyses led to the identification of 3 previously uncharacterized lncRNAs,TERMINATOR,ALIEN,and PUNISHER,specifically expressed in undifferentiated pluripotent stem cells,cardiovascular progenitors,and differentiated endothelial cells,respectively. Functional characterization,including localization studies,dynamic expression analyses,epigenetic modification monitoring,and knockdown experiments in lower vertebrates,as well as murine embryos and human cells,confirmed a critical role for each lncRNA specific for each analyzed developmental stage. CONCLUSIONS: We have identified and functionally characterized 3 novel lncRNAs involved in vertebrate and human cardiovascular development,and we provide a comprehensive transcriptomic roadmap that sheds new light on the molecular mechanisms underlying human embryonic development,mesodermal commitment,and cardiovascular specification. View Publication

Loss of pluripotency is a gradual event whose initiating factors are largely unknown. Here we report the earliest metabolic changes induced during the first hours of differentiation. High-resolution NMR identified 44 metabolites and a distinct metabolic transition occurring during early differentiation. Metabolic and transcriptional analyses showed that pluripotent cells produced acetyl-CoA through glycolysis and rapidly lost this function during differentiation. Importantly,modulation of glycolysis blocked histone deacetylation and differentiation in human and mouse embryonic stem cells. Acetate,a precursor of acetyl-CoA,delayed differentiation and blocked early histone deacetylation in a dose-dependent manner. Inhibitors upstream of acetyl-CoA caused differentiation of pluripotent cells,while those downstream delayed differentiation. Our results show a metabolic switch causing a loss of histone acetylation and pluripotent state during the first hours of differentiation. Our data highlight the important role metabolism plays in pluripotency and suggest that a glycolytic switch controlling histone acetylation can release stem cells from pluripotency. View Publication

Recent studies have suggested that REX1 (reduced expression 1) plays an important role in pluripotency,proliferation,and differentiation. However,the molecular mechanisms involved in REX1-dependent regulation of diverse cellular processes remain unclear. To elucidate the regulatory functions of REX1 in human embryonic stem cells (hESCs),comparative proteomic analysis was performed on REX1 RNAi specifically silenced hESCs. Analysis of the proteome via nano-LC-MS/MS identified 140 differentially expressed proteins (DEPs) displaying a textgreater2-fold difference in expression level between control and REX1 knockdown (KD) hESCs,which were then compared with transcriptome data and validated by quantitative real-time RT-PCR and Western blotting. These DEPs were analyzed by GO,pathway,and functional clustering analyses to determine the molecular functions of the proteins and pathways regulated by REX1. The REX1 KD-mediated DEPs mapped to major biological processes involved in the regulation of ribosome-mediated translation and mitochondrial function. Functional network analysis revealed a highly interconnected network among these DEPs and indicated that these interconnected proteins are predominantly involved in translation and the regulation of mitochondrial organization. These findings regarding REX1-mediated regulatory network have revealed the contributions of REX1 to maintaining the status of hESCs and have improved our understanding of the molecular events that underlie the fundamental properties of hESCs. View Publication

Current protocols for human pluripotent stem cell (hPSC) expansion require feeder cells or matrices from animal sources that have been the major obstacle to obtain clinical grade hPSCs due to safety issues,difficulty in quality control,and high expense. Thus,feeder-free,chemically defined synthetic platforms have been developed,but are mostly confined to typical polystyrene culture plates. Here,we report a chemically defined,material-independent,bio-inspired surface coating allowing for feeder-free expansion and maintenance of self-renewal and pluripotency of hPSCs on various polymer substrates and devices. Polydopamine (pDA)-mediated immobilization of vitronectin (VN) peptides results in surface functionalization of VN-dimer/pDA conjugates. The engineered surfaces facilitate adhesion,proliferation,and colony formation of hPSCs via enhanced focal adhesion,cell-cell interaction,and biophysical signals,providing a chemically defined,xeno-free culture system for clonal expansion and long-term maintenance of hPSCs. This surface engineering enables the application of clinically-relevant hPSCs to a variety of biomedical systems such as tissue-engineering scaffolds and medical devices. View Publication

Heterogeneity in human pluripotent stem cell (PSC) fates is partially caused by mechanical asymmetry arising from spatial polarization of cell-cell and cell-matrix adhesions. Independent studies have shown that integrin and E-cadherin adhesions promote opposing differentiation and pluripotent fates respectively although their crosstalk mechanism in modulating cell fate heterogeneity remains unknown. Here,we demonstrated that spatial polarization of integrin and E-cadherin adhesions in a human PSC colony compete to recruit Rho-ROCK activated myosin II to different localities to pattern pluripotent-differentiation decisions,resulting in spatially heterogeneous colonies. Cell micropatterning was used to modulate the spatial polarization of cell adhesions,which enabled us to prospectively determine localization patterns of activated myosin II and mesoendoderm differentiation. Direct inhibition of Rho-ROCK-myosin II activation phenocopied E-cadherin rather than integrin inhibition to form uniformly differentiated colonies. This indicated that E-cadherin was the primary gatekeeper to differentiation progression. This insight allows for biomaterials to be tailored for human PSC maintenance or differentiation with minimal heterogeneity. View Publication

The development of xeno-free,chemically defined stem cell culture systems has been a primary focus in the field of regenerative medicine to enhance the clinical application of pluripotent stem cells (PSCs). In this regard,various electrospun substrates with diverse physiochemical properties were synthesized utilizing various polymer precursors and surface treatments. Human induced pluripotent stem cells (IPSCs) cultured on these substrates were characterized by their gene and protein expression to determine the effects of the substrate physiochemical properties on the cells' self-renewal,i.e.,proliferation and the maintenance of pluripotency. The results showed that surface chemistry significantly affected cell colony formation via governing the colony edge propagation. More importantly,when surface chemistry of the substrates was uniformly controlled by collagen conjugation,the stiffness of substrate was inversely related to the sphericity,a degree of three dimensionality in colony morphology. The differences in sphericity subsequently affected spontaneous differentiation of IPSCs during a long-term culture,implicating that the colony morphology is a deciding factor in the lineage commitment of PSCs. Overall,we show that the capability of controlling IPSC colony morphology by electrospun substrates provides a means to modulate IPSC self-renewal. View Publication

Bipolar disorder (BD) is a common neuropsychiatric disorder characterized by chronic recurrent episodes of depression and mania. Despite evidence for high heritability of BD,little is known about its underlying pathophysiology. To develop new tools for investigating the molecular and cellular basis of BD,we applied a family-based paradigm to derive and characterize a set of 12 induced pluripotent stem cell (iPSC) lines from a quartet consisting of two BD-affected brothers and their two unaffected parents. Initially,no significant phenotypic differences were observed between iPSCs derived from the different family members. However,upon directed neural differentiation,we observed that CXCR4 (CXC chemokine receptor-4) expressing central nervous system (CNS) neural progenitor cells (NPCs) from both BD patients compared with their unaffected parents exhibited multiple phenotypic differences at the level of neurogenesis and expression of genes critical for neuroplasticity,including WNT pathway components and ion channel subunits. Treatment of the CXCR4(+) NPCs with a pharmacological inhibitor of glycogen synthase kinase 3,a known regulator of WNT signaling,was found to rescue a progenitor proliferation deficit in the BD patient NPCs. Taken together,these studies provide new cellular tools for dissecting the pathophysiology of BD and evidence for dysregulation of key pathways involved in neurodevelopment and neuroplasticity. Future generation of additional iPSCs following a family-based paradigm for modeling complex neuropsychiatric disorders in conjunction with in-depth phenotyping holds promise for providing insights into the pathophysiological substrates of BD and is likely to inform the development of targeted therapeutics for its treatment and ideally prevention. View Publication

The RNA-guided nuclease Cas9 can be reengineered as a programmable transcription factor. However,modest levels of gene activation have limited potential applications. We describe an improved transcriptional regulator obtained through the rational design of a tripartite activator,VP64-p65-Rta (VPR),fused to nuclease-null Cas9. We demonstrate its utility in activating endogenous coding and noncoding genes,targeting several genes simultaneously and stimulating neuronal differentiation of human induced pluripotent stem cells (iPSCs). View Publication

Human embryonic stem cells hold great promise for future biomedical applications such as disease modeling and regenerative medicine. However,these cells are notoriously difficult to culture and are refractory to common means of genetic manipulation,thereby limiting their range of applications. In this protocol,we present an easy and robust method of gene repression in human embryonic stem cells using lipofection of small interfering RNA (siRNA). View Publication

The self-renewal and differentiation capacities of human pluripotent stem cells (hPSCs) make them a promising source of material for cell transplantation therapy,drug development,and studies of cellular differentiation and development. However,the large numbers of cells necessary for many of these applications require extensive expansion of hPSC cultures,a process that has been associated with genetic and epigenetic alterations. We have performed a combinatorial study on both hESCs and hiPSCs to compare the effects of enzymatic vs. mechanical passaging,and feeder-free vs. mouse embryonic fibroblast feeder substrate,on the genetic and epigenetic stability and the phenotypic characteristics of hPSCs. In extensive experiments involving over 100 continuous passages,we observed that both enzymatic passaging and feeder-free culture were associated with genetic instability,higher rates of cell proliferation,and persistence of OCT4/POU5F1-positive cells in teratomas,with enzymatic passaging having the stronger effect. In all combinations of culture conditions except for mechanical passaging on feeder layers,we noted recurrent deletions in the genomic region containing the tumor suppressor gene TP53,which was associated with decreased mRNA expression of TP53,as well as alterations in the expression of several downstream genes consistent with a decrease in the activity of the TP53 pathway. Among the hESC cultures,we also observed culture-associated variations in global gene expression and DNA methylation. The effects of enzymatic passaging and feeder-free conditions were also observed in hiPSC cultures. Our results highlight the need for careful assessment of the effects of culture conditions on cells intended for clinical therapies. View Publication