技术资料

Human pluripotent stem cells (hPSCs) can self-renew or differentiate to diverse cell types,thus providing a platform for basic and clinical applications. However,pluripotent stem cell populations are heterogeneous and functional properties at the single cell level are poorly documented leading to inefficiencies in differentiation and concerns regarding reproducibility and safety. Here,we use non-invasive time-lapse imaging to continuously examine hPSC maintenance and differentiation and to predict cell viability and fate. We document dynamic behaviors and social interactions that prospectively distinguish hPSC survival,self-renewal,and differentiation. Results highlight the molecular role of E-cadherin not only for cell-cell contact but also for clonal propagation of hPSCs. Results indicate that use of continuous time-lapse imaging can distinguish cellular heterogeneity with respect to pluripotency as well as a subset of karyotypic abnormalities whose dynamic properties were monitored. View Publication

Medulloblastoma (MB) is the most common malignant primary pediatric brain tumor and is currently divided into four subtypes based on different genomic alterations,gene expression profiles and response to treatment: WNT,Sonic Hedgehog (SHH),Group 3 and Group 4. This extensive heterogeneity has made it difficult to assess the functional relevance of genes to malignant progression. For example,expression of the transcription factor Orthodenticle homeobox2 (OTX2) is frequently dysregulated in multiple MB variants; however,its role may be subtype specific. We recently demonstrated that neural precursors derived from transformed human embryonic stem cells (trans-hENs),but not their normal counterparts (hENs),resemble Groups 3 and 4 MB in vitro and in vivo. Here,we tested the utility of this model system as a means of dissecting the role of OTX2 in MB using gain- and loss-of-function studies in hENs and trans-hENs,respectively. Parallel experiments with MB cells revealed that OTX2 exerts inhibitory effects on hEN and SHH MB cells by regulating growth,self-renewal and migration in vitro and tumor growth in vivo. This was accompanied by decreased expression of pluripotent genes,such as SOX2,and was supported by overexpression of SOX2 in OTX2+ SHH MB and hENs that resulted in significant rescue of self-renewal and cell migration. By contrast,OTX2 is oncogenic and promotes self-renewal of trans-hENs and Groups 3 and 4 MB independent of pluripotent gene expression. Our results demonstrate a novel role for OTX2 in self-renewal and migration of hENs and MB cells and reveal a cell-context-dependent link between OTX2 and pluripotent genes. Our study underscores the value of human embryonic stem cell derivatives as alternatives to cell lines and heterogeneous patient samples for investigating the contribution of key developmental regulators to MB progression. View Publication

How BMP signaling integrates into and destabilizes the pluripotency circuitry of human pluripotent stem cells (hPSCs) to initiate differentiation into individual germ layers is a long-standing puzzle. Here we report muscle segment homeobox 2 (MSX2),a homeobox transcription factor of msh family,as a direct target gene of BMP signaling and a master mediator of hPSCs' differentiation to mesendoderm. Enforced expression of MSX2 suffices to abolish pluripotency and induce directed mesendoderm differentiation of hPSCs,while MSX2 depletion impairs mesendoderm induction. MSX2 is a direct target gene of the BMP pathway in hPSCs,and can be synergistically activated by Wnt signals via LEF1 during mesendoderm induction. Furthermore,MSX2 destabilizes the pluripotency circuitry through direct binding to the SOX2 promoter and repression of SOX2 transcription,while MSX2 controls mesendoderm lineage commitment by simultaneous suppression of SOX2 and induction of NODAL expression through direct binding and activation of the Nodal promoter. Interestingly,SOX2 can promote the degradation of MSX2 protein,suggesting a mutual antagonism between the two lineage-specifying factors in the control of stem cell fate. Together,our findings reveal crucial new mechanisms of destabilizing pluripotency and directing lineage commitment in hPSCs. View Publication

Rett syndrome (RTT) is a severe neurodevelopmental disorder associated with mutations in either MECP2,CDKL5 or FOXG1. The precise molecular mechanisms that lead to the pathogenesis of RTT have yet to be elucidated. We recently reported that expression of GluD1 (orphan glutamate receptor $\$-1 subunit) is increased in iPSC-derived neurons obtained from patients with mutations in either MECP2 or CDKL5. GluD1 controls synaptic differentiation and shifts the balance between excitatory and inhibitory synapses toward the latter. Thus,an increase in GluD1 might be a critical factor in the etiology of RTT by affecting the excitatory/inhibitory balance in the developing brain. To test this hypothesis,we generated iPSC-derived neurons from FOXG1(+/-) patients. We analyzed mRNA and protein levels of GluD1 together with key markers of excitatory and inhibitory synapses in these iPSC-derived neurons and in Foxg1(+/-) mouse fetal (E11.5) and adult (P70) brains. We found strong correlation between iPSC-derived neurons and fetal mouse brains,where GluD1 and inhibitory synaptic markers (GAD67 and GABA AR-$\$1) were increased,whereas the levels of a number of excitatory synaptic markers (VGLUT1,GluA1,GluN1 and PSD-95) were decreased. In adult mice,GluD1 was decreased along with all GABAergic and glutamatergic markers. Our findings further the understanding of the etiology of RTT by introducing a new pathological event occurring in the brain of FOXG1(+/-) patients during embryonic development and its time-dependent shift toward a general decrease in brain synapses. View Publication

Oncogenic transformation in Ewing sarcoma tumors is driven by the fusion oncogene EWS-FLI1. However,despite the well-established role of EWS-FLI1 in tumor initiation,the development of models of Ewing sarcoma in human cells with defined genetic elements has been challenging. Here,we report a novel approach to model the initiation of Ewing sarcoma tumorigenesis that exploits the developmental and pluripotent potential of human embryonic stem cells. The inducible expression of EWS-FLI1 in embryoid bodies,or collections of differentiating stem cells,generates cells with properties of Ewing sarcoma tumors,including characteristics of transformation. These cell lines exhibit anchorage-independent growth,a lack of contact inhibition and a strong Ewing sarcoma gene expression signature. Furthermore,these cells also demonstrate a requirement for the persistent expression of EWS-FLI1 for cell survival and growth,which is a hallmark of Ewing sarcoma tumors.Oncogene advance online publication,12 October 2015; doi:10.1038/onc.2015.368. View Publication

Replication stress causes DNA damage at fragile sites in the genome. DNA damage at telomeres can initiate breakage-fusion-bridge cycles and chromosome instability,which can result in replicative senescence or tumor formation. Little is known about the extent of replication stress or telomere dysfunction in human embryonic stem cells (hESCs). hESCs are grown in culture with the expectation of being used therapeutically in humans,making it important to minimize the levels of replication stress and telomere dysfunction. Here,the hESC line UCSF4 was cultured in a defined medium with growth factor Activin A,exogenous nucleosides,or DNA polymerase inhibitor aphidicolin. We used quantitative fluorescence in situ hybridization to analyze individual telomeres for dysfunction and observed that it can be increased by aphidicolin or Activin A. In contrast,adding exogenous nucleosides relieved dysfunction,suggesting that telomere dysfunction results from replication stress. Whether these findings can be applied to other hESC lines remains to be determined. However,because the loss of telomeres can lead to chromosome instability and cancer,we conclude that hESCs grown in culture for future therapeutic purposes should be routinely checked for replication stress and telomere dysfunction. View Publication

Fibroblasts from patients with Type I bipolar disorder (BPD) and their unaffected siblings were obtained from an Old Order Amish pedigree with a high incidence of BPD and reprogrammed to induced pluripotent stem cells (iPSCs). Established iPSCs were subsequently differentiated into neuroprogenitors (NPs) and then to neurons. Transcriptomic microarray analysis was conducted on RNA samples from iPSCs,NPs and neurons matured in culture for either 2 weeks (termed early neurons,E) or 4 weeks (termed late neurons,L). Global RNA profiling indicated that BPD and control iPSCs differentiated into NPs and neurons at a similar rate,enabling studies of differentially expressed genes in neurons from controls and BPD cases. Significant disease-associated differences in gene expression were observed only in L neurons. Specifically,328 genes were differentially expressed between BPD and control L neurons including GAD1,glutamate decarboxylase 1 (2.5 fold) and SCN4B,the voltage gated type IV sodium channel beta subunit (-14.6 fold). Quantitative RT-PCR confirmed the up-regulation of GAD1 in BPD compared to control L neurons. Gene Ontology,GeneGo and Ingenuity Pathway Analysis of differentially regulated genes in L neurons suggest that alterations in RNA biosynthesis and metabolism,protein trafficking as well as receptor signaling pathways may play an important role in the pathophysiology of BPD. View Publication

Although we previously reported the development of cell-dense thickened cardiac tissue by repeated transplantation-based vascularization of neonatal rat cardiac cell sheets,the cell sources for human cardiac cells sheets and their functions have not been fully elucidated. In this study,we developed a bioreactor to expand and induce cardiac differentiation of human induced pluripotent stem cells (hiPSCs). Bioreactor culture for 14 days produced around 8×10(7) cells/100 ml vessel and about 80% of cells were positive for cardiac troponin T. After cardiac differentiation,cardiomyocytes were cultured on temperature-responsive culture dishes and showed spontaneous and synchronous beating,even after cell sheets were detached from culture dishes. Furthermore,extracellular action potential propagation was observed between cell sheets when two cardiac cell sheets were partially overlaid. These findings suggest that cardiac cell sheets formed by hiPSC-derived cardiomyocytes might have sufficient properties for the creation of thickened cardiac tissue. View Publication

Immature primary and stem cell-derived cardiomyocytes provide useful models for fundamental studies of heart development and cardiac disease,and offer potentialbackslashrbackslashnfor patient specific drug testing and differentiation protocols aimed at cardiac grafts. To assess their potential for augmenting heart function,and to gain insight into cardiac growth and disease,tissue engineers must quantify the contractile forces of these single cells. Currently,axial contractile forces of isolated adult heart cells can only be measuredbackslashrbackslashnby two-point methods such as carbon fiber techniques,which cannot be applied to neonatal and stem cell-derived heart cells because they are more difficult to handle and lack a persistent shape. Here we present a novel axial technique for measuring the contractile forces of isolated immature cardiomyocytes. We overcome cell manipulation and patterning challenges by using a thermoresponsive sacrificialbackslashrbackslashnsupport layer in conjunction with arrays of widely separated elastomeric microposts. Our approach has the potential to be high-throughput,is functionally analogous to current gold-standard axial force assays for adult heart cells,and prescribes elongated cell shapes without protein patterning. Finally,we calibrate these force posts withbackslashrbackslashnpiezoresistive cantilevers to dramatically reduce measurement error typical for soft polymer-based force assays. We report quantitative measurements of peak contractile forces up to 146 nN with post stiffness standard error (26 nN) far betterbackslashrbackslashnthan that based on geometry and stiffness estimates alone. The addition of sacrificial layers to future 2D and 3D cell culturebackslashrbackslashnplatforms will enable improved cell placement and the complex suspension of cells across 3D constructs. View Publication

Cell Research 23,122 (2013). doi:10.1038/cr.2012.119 View Publication

The Hippo pathway is crucial in organ size control,and its dysregulation contributes to tumorigenesis. However,upstream signals that regulate the mammalian Hippo pathway have remained elusive. Here,we report that the Hippo pathway is regulated by G-protein-coupled receptor (GPCR) signaling. Serum-borne lysophosphatidic acid (LPA) and sphingosine 1-phosphophate (S1P) act through G12/13-coupled receptors to inhibit the Hippo pathway kinases Lats1/2,thereby activating YAP and TAZ transcription coactivators,which are oncoproteins repressed by Lats1/2. YAP and TAZ are involved in LPA-induced gene expression,cell migration,and proliferation. In contrast,stimulation of Gs-coupled receptors by glucagon or epinephrine activates Lats1/2 kinase activity,thereby inhibiting YAP function. Thus,GPCR signaling can either activate or inhibit the Hippo-YAP pathway depending on the coupled G protein. Our study identifies extracellular diffusible signals that modulate the Hippo pathway and also establishes the Hippo-YAP pathway as a critical signaling branch downstream of GPCR. View Publication

Neural progenitor cells (NPCs) derived from human induced pluripotent stem cells (hiPSCs) can be differentiated to neural cells that model neurodegenerative diseases and be used in the screening of potential drugs to ameliorate the disease phenotype. Traditionally,NPCs are produced in 2D cultures,in low yields,using a laborious process that includes generation of embryonic bodies,plating,and colony selections. To simplify the process and generate large numbers of hiPSC-derived NPCs,we introduce a microcarrier (MC) system for the expansion of a hiPSC line and its subsequent differentiation to NPC,using iPS (IMR90) as a model cell line. In the expansion stage,a process of cell propagation in serum-free MC culture was developed first in static culture,which is then scaled up in stirred spinner flasks. A 7.7-fold expansion of iPS (IMR90) and cell yield of 1.3×10�?� cells/mL in 7 days of static MC culture were achieved. These cells maintained expression of OCT 3/4 and TRA-1-60 and possessed a normal karyotype over 10 passages. A higher cell yield of 6.1×10�?� cells/mL and 20-fold hiPSC expansion were attained using stirred spinner flasks (seeded from MC static cultures) and changing the medium-exchange regimen from once to twice a day. In the differentiation stage,NPCs were generated with 78%-85% efficiency from hiPSCs using a simple serum-free differentiation protocol. Finally,the integrated process of cell expansion and differentiation of hiPSCs into NPCs using an MC in spinner flasks yielded 333 NPCs per seeded hiPSC as compared to 53 in the classical 2D tissue culture protocol. Similar results were obtained with the HES-3 human embryonic stem cell line. These NPCs were further differentiated into βIII-tubulin�?� neurons,GFAP�?� astrocytes,and O4�?� oligodendrocytes,showing that cells maintained their multilineage differentiation potential. View Publication