Nalae Han | Yonsei University (original) (raw)

Papers by Nalae Han

Research paper thumbnail of Tunable Wettability of Graphene through Nondestructive Hydrogenation and Wettability-Based Patterning for Bioapplications

Nano Letters, Apr 10, 2020

The wettability of graphene has been extensively studied and successfully modified by chemical fu... more The wettability of graphene has been extensively studied and successfully modified by chemical functionalization. Nevertheless, the unavoidable introduction of undesired defects and the absence of systematic and local control over wettability by previous methods have limited the use of graphene in applications. In addition, micro-scale patterning according to wettability has not been attempted. Here, we demonstrate that the wettability of graphene can be systematically controlled and the surface patterned into micro-scale sections based on wettability without creating significant defects, possible by non-destructive hydrogen plasma. Hydrophobic graphene is progressively converted to hydrophilic hydrogenated graphene (H-Gr) that reaches superhydrophilicity. The great contrast in wettability between graphene and H-Gr makes it possible selectively positioning and isolating human-breast-cancer cells on arrays of micro-patterns since strong hydrophilicity facilitates the adsorption of the cells. We believe that our method will provide an essential technique for enabling surface and biological applications requiring micro-scale patterns with different wettability.

Research paper thumbnail of Integrated phase-change memory devices using Bi2Te3 nanowires

Bismuth telluride (Bi 2 Te 3) and its alloys are considered to be the best avaiable materials for... more Bismuth telluride (Bi 2 Te 3) and its alloys are considered to be the best avaiable materials for near room-temperature thermoelectric applications. Moreover, because lowdimensional thermoelectric materials are expected to have a higher figure of merit due to quantum confinement effects, Bi 2 Te 3 nanowires have been studied extensively. However, their memory switching behavior has never been studied in Bi 2 Te 3 nanowires. Here, we report for the first time on reversible memory switching effects in Bi 2 Te 3 nanowires fabricated using anodized aluminum oxide (AAO) membranes. We find that Bi 2 Te 3 nanowires show a reversible crystalline-amorphous phase change induced by temperature or electric field, similar to that reported for chalcogenide materials (Ge-Sb-Te alloys, GST), and we demonstrate that Bi 2 Te 3 nanowires show considerable promise as building blocks for phase change random access memory (PRAM).

Research paper thumbnail of Memristive Switching in Bi1–xSbx Nanowires

ACS Applied Materials & Interfaces, Apr 4, 2016

We investigated the memristive switching behavior in bismuth-antimony alloy (Bi 1-x Sb x) single ... more We investigated the memristive switching behavior in bismuth-antimony alloy (Bi 1-x Sb x) single nanowire devices at 0.1 ≤ x ≤ 0.42. At 0.15 ≤ x ≤ 0.42, most Bi 1-x Sb x single nanowire devices exhibited bipolar resistive switching (RS) behavior with on/off ratios of approximately 10 4 and narrow variations in switching parameters. Moreover, the resistance values in the lowresistance state (LRS) were insensitive to x. On the other hand, at 0.1 ≤ x ≤ 0.15, some Bi 1-x Sb x single nanowire devices showed complementary RS-like behavior, which was ascribed to asymmetric contact properties. Transmission electron microscopy and elemental mapping images of Bi, Sb, and O obtained from the cross-sections of the Bi 1-x Sb x single nanowire devices, which were cut before and after RS, revealed that the mobile species was Sb ions, and the migration of the Sb ions to the nanowire surface brought the switch to LRS. In addition, we demonstrated that two types of synaptic plasticity, namely, short-term plasticity and long-term potentiation could be implemented in Bi 1-x Sb x nanowires by applying a sequence of voltage pulses with different repetition intervals.

Research paper thumbnail of Real-Time Discrimination between Proliferation and Neuronal and Astroglial Differentiation of Human Neural Stem Cells

Scientific Reports, Sep 10, 2014

Neural stem cells (NSCs) are characterized by a capacity for self-renewal, differentiation into m... more Neural stem cells (NSCs) are characterized by a capacity for self-renewal, differentiation into multiple neural lineages, all of which are considered to be promising components for neural regeneration. However, for cell-replacement therapies, it is essential to monitor the process of in vitro NSC differentiation and identify differentiated cell phenotypes. We report a real-time and label-free method that uses a capacitance sensor array to monitor the differentiation of human fetal brain-derived NSCs (hNSCs) and to identify the fates of differentiated cells. When hNSCs were placed under proliferation or differentiation conditions in five media, proliferating and differentiating hNSCs exhibited different frequency and time dependences of capacitance, indicating that the proliferation and differentiation status of hNSCs may be discriminated in real-time using our capacitance sensor. In addition, comparison between real-time capacitance and time-lapse optical images revealed that neuronal and astroglial differentiation of hNSCs may be identified in real-time without cell labeling. H uman neural stem cells (hNSCs), which can give rise to neuronal or glial cells, have received considerable attention for their therapeutic potential to repair neural injury or dysfunction caused by trauma, stroke, and neurodegenerative diseases 1. For cell-replacement therapies, hNSCs could be differentiated into the appropriate neural cell types prior to transplantation, since pre-differentiated cells could be more therapeutically beneficial and undifferentiated hNSCs may remain immature or produce unwanted neural cell types after transplantation into the damaged or diseased brain 2-5. Hence, it is important to monitor the process of in vitro hNSC differentiation and to identify specific differentiated cell fates. The fates of differentiated cells are usually identified via real-time polymerase chain reaction 6 or immunohistochemical methods 7 that involve labeling with nucleic acids or antibodies. However, these methods are invasive and time-consuming. We have therefore developed an alternative approach to monitor the differentiation of hNSCs and to identify the fate potential of differentiated hNSCs in real-time without cell labeling. To monitor the differentiation of stem cells in real-time, electric cell-substrate impedance sensors have been used 8-11 , which measure the alternating current (AC) impedance between a small sensing electrode and a large counter electrode while cells are cultured on the gold-sensing electrode. Cells attach and spread on the surface of the sensing electrode and passively block the current, and thus the electrode impedance is affected by the shape, adhesion, and/or mobility of adherent cells 12,13. However, compared to the electrode impedance, the capacitance (or the dielectric constant) of cells provides more direct information on cellular activities 14-17 ; the fate potential of NSCs was previously reported to be more closely related to cell membrane capacitance than to conductance 18. On this study, we have developed a capacitance sensor to monitor the differentiation of hNSCs. In our capacitance sensor, the cells are placed between the two electrodes rather than on top of the electrodes, and the change in capacitance is measured. Since the cells are placed between two electrodes, optical images of the cells and measurements of real-time capacitance can be obtained simultaneously, enabling a better understanding of hNSC differentiation.

Research paper thumbnail of Real-time monitoring of 3D cell culture using a 3D capacitance biosensor

Biosensors and Bioelectronics, Mar 1, 2016

Three-dimensional (3D) cell cultures have recently received attention because they represent a mo... more Three-dimensional (3D) cell cultures have recently received attention because they represent a more physiologically relevant environment compared to conventional two-dimensional (2D) cell cultures. However, 2D-based imaging techniques or cell sensors are insufficient for real-time monitoring of cellular behavior in 3D cell culture. Here, we report investigations conducted with a 3D capacitance cell sensor consisting of vertically aligned pairs of electrodes. When GFP-expressing human breast cancer cells (GFP-MCF-7) encapsulated in alginate hydrogel were cultured in a 3D cell culture system, cellular activities, such as cell proliferation and apoptosis at different heights, could be monitored non-invasively and in real-time by measuring the change in capacitance with the 3D capacitance sensor. Moreover, we were able to monitor cell migration of human mesenchymal stem cells (hMSCs) with our 3D capacitance sensor.

Research paper thumbnail of Tunable Wettability of Graphene through Nondestructive Hydrogenation and Wettability-Based Patterning for Bioapplications

Nano Letters, 2020

The wettability of graphene has been extensively studied and successfully modified by chemical fu... more The wettability of graphene has been extensively studied and successfully modified by chemical functionalization. Nevertheless, the unavoidable introduction of undesired defects and the absence of systematic and local control over wettability by previous methods have limited the use of graphene in applications. In addition, micro-scale patterning according to wettability has not been attempted. Here, we demonstrate that the wettability of graphene can be systematically controlled and the surface patterned into micro-scale sections based on wettability without creating significant defects, possible by non-destructive hydrogen plasma. Hydrophobic graphene is progressively converted to hydrophilic hydrogenated graphene (H-Gr) that reaches superhydrophilicity. The great contrast in wettability between graphene and H-Gr makes it possible selectively positioning and isolating human-breast-cancer cells on arrays of micro-patterns since strong hydrophilicity facilitates the adsorption of the cells. We believe that our method will provide an essential technique for enabling surface and biological applications requiring micro-scale patterns with different wettability.

Research paper thumbnail of Memristive Switching in Bi1-xSbx Nanowires

ACS applied materials & interfaces, Jan 13, 2016

We investigated the memristive switching behavior in bismuth-antimony alloy (Bi1-xSbx) single nan... more We investigated the memristive switching behavior in bismuth-antimony alloy (Bi1-xSbx) single nanowire devices at 0.1 ≤ x ≤ 0.42. At 0.15 ≤ x ≤ 0.42, most Bi1-xSbx single nanowire devices exhibited bipolar resistive switching (RS) behavior with on/off ratios of approximately 10(4) and narrow variations in switching parameters. Moreover, the resistance values in the low-resistance state (LRS) were insensitive to x. On the other hand, at 0.1 ≤ x ≤ 0.15, some Bi1-xSbx single nanowire devices showed complementary RS-like behavior, which was ascribed to asymmetric contact properties. Transmission electron microscopy and elemental mapping images of Bi, Sb, and O obtained from the cross sections of the Bi1-xSbx single nanowire devices, which were cut before and after RS, revealed that the mobile species was Sb ions, and the migration of the Sb ions to the nanowire surface brought the switch to LRS. In addition, we demonstrated that two types of synaptic plasticity, namely, short-term plast...

Research paper thumbnail of Real-time monitoring of 3D cell culture using a 3D capacitance biosensor

Biosensors & bioelectronics, Jan 6, 2015

Three-dimensional (3D) cell cultures have recently received attention because they represent a mo... more Three-dimensional (3D) cell cultures have recently received attention because they represent a more physiologically relevant environment compared to conventional two-dimensional (2D) cell cultures. However, 2D-based imaging techniques or cell sensors are insufficient for real-time monitoring of cellular behavior in 3D cell culture. Here, we report investigations conducted with a 3D capacitance cell sensor consisting of vertically aligned pairs of electrodes. When GFP-expressing human breast cancer cells (GFP-MCF-7) encapsulated in alginate hydrogel were cultured in a 3D cell culture system, cellular activities, such as cell proliferation and apoptosis at different heights, could be monitored non-invasively and in real-time by measuring the change in capacitance with the 3D capacitance sensor. Moreover, we were able to monitor cell migration of human mesenchymal stem cells (hMSCs) with our 3D capacitance sensor.

Research paper thumbnail of Transcriptional Profiles of Imprinted Genes in Human Embryonic Stem Cells During In vitro Differentiation

International journal of stem cells, 2014

Genomic imprinting is an inheritance phenomenon by which a subset of genes are expressed from one... more Genomic imprinting is an inheritance phenomenon by which a subset of genes are expressed from one allele of two homologous chromosomes in a parent of origin-specific manner. Even though fine-tuned regulation of genomic imprinting process is essential for normal development, no other means are available to study genomic imprinting in human during embryonic development. In relation with this bottleneck, differentiation of human embryonic stem cells (hESCs) into specialized lineages may be considered as an alternative to mimic human development. In this study, hESCs were differentiated into three lineage cell types to analyze temporal and spatial expression of imprinted genes. Of 19 imprinted genes examined, 15 imprinted genes showed similar transcriptional level among two hESC lines and two human induced pluripotent stem cell (hiPSC) lines. Expressional patterns of most imprinted genes were varied in progenitors and fully differentiated cells which were derived from hESCs. Also, no co...

Research paper thumbnail of Real-Time Discrimination between Proliferation and Neuronal and Astroglial Differentiation of Human Neural Stem Cells

Scientific Reports, 2014

Neural stem cells (NSCs) are characterized by a capacity for self-renewal, differentiation into m... more Neural stem cells (NSCs) are characterized by a capacity for self-renewal, differentiation into multiple neural lineages, all of which are considered to be promising components for neural regeneration. However, for cell-replacement therapies, it is essential to monitor the process of in vitro NSC differentiation and identify differentiated cell phenotypes. We report a real-time and label-free method that uses a capacitance sensor array to monitor the differentiation of human fetal brain-derived NSCs (hNSCs) and to identify the fates of differentiated cells. When hNSCs were placed under proliferation or differentiation conditions in five media, proliferating and differentiating hNSCs exhibited different frequency and time dependences of capacitance, indicating that the proliferation and differentiation status of hNSCs may be discriminated in real-time using our capacitance sensor. In addition, comparison between real-time capacitance and time-lapse optical images revealed that neuronal and astroglial differentiation of hNSCs may be identified in real-time without cell labeling. H uman neural stem cells (hNSCs), which can give rise to neuronal or glial cells, have received considerable attention for their therapeutic potential to repair neural injury or dysfunction caused by trauma, stroke, and neurodegenerative diseases 1. For cell-replacement therapies, hNSCs could be differentiated into the appropriate neural cell types prior to transplantation, since pre-differentiated cells could be more therapeutically beneficial and undifferentiated hNSCs may remain immature or produce unwanted neural cell types after transplantation into the damaged or diseased brain 2-5. Hence, it is important to monitor the process of in vitro hNSC differentiation and to identify specific differentiated cell fates. The fates of differentiated cells are usually identified via real-time polymerase chain reaction 6 or immunohistochemical methods 7 that involve labeling with nucleic acids or antibodies. However, these methods are invasive and time-consuming. We have therefore developed an alternative approach to monitor the differentiation of hNSCs and to identify the fate potential of differentiated hNSCs in real-time without cell labeling. To monitor the differentiation of stem cells in real-time, electric cell-substrate impedance sensors have been used 8-11 , which measure the alternating current (AC) impedance between a small sensing electrode and a large counter electrode while cells are cultured on the gold-sensing electrode. Cells attach and spread on the surface of the sensing electrode and passively block the current, and thus the electrode impedance is affected by the shape, adhesion, and/or mobility of adherent cells 12,13. However, compared to the electrode impedance, the capacitance (or the dielectric constant) of cells provides more direct information on cellular activities 14-17 ; the fate potential of NSCs was previously reported to be more closely related to cell membrane capacitance than to conductance 18. On this study, we have developed a capacitance sensor to monitor the differentiation of hNSCs. In our capacitance sensor, the cells are placed between the two electrodes rather than on top of the electrodes, and the change in capacitance is measured. Since the cells are placed between two electrodes, optical images of the cells and measurements of real-time capacitance can be obtained simultaneously, enabling a better understanding of hNSC differentiation.

Research paper thumbnail of DUSP4 Regulates Neuronal Differentiation and Calcium Homeostasis by Modulating ERK1/2 Phosphorylation

Stem cells and development, Jan 14, 2014

Protein tyrosine phosphatases have been recognized as critical components of multiple signaling r... more Protein tyrosine phosphatases have been recognized as critical components of multiple signaling regulators of fundamental cellular processes, including differentiation, cell death, and migration. In this study, we show that dual specificity phosphatase 4 (DUSP4) is crucial for neuronal differentiation and functions in the neurogenesis of embryonic stem cells (ESCs). The endogenous mRNA and protein expression levels of DUSP4 gradually increased during mouse development from ESCs to postnatal stages. Neurite outgrowth and the expression of neuron-specific markers were markedly reduced by genetic ablation of DUSP4 in differentiated neurons, and these effects were rescued by the reintroduction of DUSP4. In addition, DUSP4 knockdown dramatically enhanced extracellular signal-regulated kinase (ERK) activation during neuronal differentiation. Furthermore, the DUSP4-ERK pathway functioned to balance calcium signaling, not only by regulating Ca(2+)/calmodulin-dependent kinase I phosphorylati...

Research paper thumbnail of The reprogramming factor nuclear receptor subfamily 5, group A, member 2 cannot replace octamer-binding transcription factor 4 function in the self-renewal of embryonic stem cells

FEBS Journal, 2013

Although octamer-binding transcription factor 4 (Oct-4) is one of the most intensively studied fa... more Although octamer-binding transcription factor 4 (Oct-4) is one of the most intensively studied factors in mammalian development, no cellular genes capable of replacing Oct-4 function in embryonic stem (ES) cells have been found. Recent data show that nuclear receptor subfamily 5, group A, member 2 (Nr5a2) is able to replace Oct-4 function in the reprogramming process; however, it is unclear whether Nr5a2 can replace Oct-4 function in ES cells. In this study, the ability of Nr5a2 to maintain self-renewal and pluripotency in ES cells was investigated. Nr5a2 localized to the nucleus in ES cells, similarly to Oct-4. However, expression of Nr5a2 failed to rescue the stem cell phenotype or to maintain the self-renewal ability of ES cells. Furthermore, as compared with Oct-4-expressing ES cells, Nr5a2-expressing ES cells showed a reduced number of cells in S-phase, did not expand normally, and did not remain in an undifferentiated state. Ectopic expression of Nr5a2 in ES cells was not able to activate transcription of ES cellspecific genes, and gene expression profiling demonstrated differences between Nr5a2-expressing and Oct-4-expressing ES cells. In addition, Nr5a2-expressing ES cells were not able to form teratomas in nude mice. Taken together, these results strongly suggest that the gene regulation properties of Nr5a2 and Oct-4 and their abilities to confer self-renewal and pluripotency of ES cells differ. The present study provides strong evidence that Nr5a2 cannot replace Oct-4 function in ES cells.

Research paper thumbnail of Combinatorial Activin Receptor-Like Kinase/Smad and Basic Fibroblast Growth Factor Signals Stimulate the Differentiation of Human Embryonic Stem Cells into the Cardiac Lineage

Stem Cells and Development, 2011

The transforming growth factor beta/bone morphogenetic protein-activated Smad signaling pathway p... more The transforming growth factor beta/bone morphogenetic protein-activated Smad signaling pathway plays a complicated role in the maintenance of human embryonic stem cell (hESC) pluripotency and in the cell fate decision of hESCs. Here, we report that sustained inhibition of the transforming growth factor beta type I receptor (also termed activin receptor-like kinase or ALK) using a chemical inhibitor selective for ALK4/5/7 (ALKi) leads to the cardiac differentiation of hESCs under feeder-free and serum-free conditions. Treatment with ALKi reduced Smad2/3 phosphorylation and increased Smad1/5/8 phosphorylation in hESCs, suggesting a requirement for active Smad1/5/8 signaling for cardiac induction in these cells when ALK/Smad2/3 is inhibited. Importantly, active basic fibroblast growth factor (bFGF) signaling was also required for ALKimediated cardiac differentiation of monolayer-cultured hESCs. The FGF receptor inhibitor SU5402 blocked ALKi-mediated cardiac induction in hESCs, whereas bone morphogenetic protein-4 enhanced the ALKiinduced increase in phospho-Smad1/5/8 levels but failed to induce the cardiac differentiation of hESCs and instead promoted trophoblastic differentiation. We also confirmed that ALKi potentially enhanced the cardiac differentiation of human embryoid bodies, as determined by expression of cardiac-specific markers, increased beating areas, and action potential recorded from beating areas. These results demonstrate that an ALKi could be used as a potential cardiac-inducing agent and that the development of culture conditions that provide an appropriate balance between ALK/Smad and bFGF signaling is necessary to direct the fate of hESCs into the cardiac lineage.

Research paper thumbnail of Comparative Proteomic Analysis of Human Somatic Cells, Induced Pluripotent Stem Cells, and Embryonic Stem Cells

Stem Cells and Development, 2012

Induced pluripotent stem cells (iPSCs) are somatic cells that have been reprogrammed to a pluripo... more Induced pluripotent stem cells (iPSCs) are somatic cells that have been reprogrammed to a pluripotent state via introduction of defined transcription factors. iPSCs are a valuable resource for regenerative medicine, but whether iPSCs are identical to embryonic stem cells (ESCs) remains unclear. In this study, we performed comparative proteomic analyses of human somatic cells [human newborn foreskin fibroblasts (hFFs)], human iPSCs (hiPSCs) derived from hFFs, and H9 human ESCs (hESCs). We reprogrammed hFFs to a pluripotent state using 4 core transcription factors: Oct4 (O), Sox2 (S), Klf4 (K), and c-Myc (M). The proteome of hiPSCs induced by 4 core transcription factors was relatively similar to that of hESCs. However, several proteins, including dUTPase, GAPDH, and FUSE binding protein 3, were differentially expressed between hESCs and hiPSCs, implying that hiPSCs are not identical to hESCs at the proteomic level. The proteomes of iPSCs induced by introducing 3, 5, or 6 transcription factors were also analyzed. Our proteomic profiles provide valuable insight into the factors that contribute to the similarities and differences between hESCs and hiPSCs and the mechanisms of reprogramming.

Research paper thumbnail of Unveiling the critical role of REX1 in the regulation of human stem cell pluripotency

Stem Cells, 2013

Reduced expression 1 (REX1) is a widely used pluripotency marker, but little is known about its r... more Reduced expression 1 (REX1) is a widely used pluripotency marker, but little is known about its roles in pluripotency. Here, we show that REX1 is functionally important in the reacquisition and maintenance of pluripotency. REX1-depleted human pluripotent stem cells (hPSCs) lose their self-renewal capacity and full differentiation potential, especially their mesoderm lineage potential. Cyclin B1/B2 expression was found to parallel that of REX1. REX1 positively regulates the transcriptional activity of cyclin B1/B2 through binding to their promoters. REX1 induces the phosphorylation of DRP1 at Ser616 by cyclin B/CDK1, which leads to mitochondrial fission and appears to be important for meeting the high-energy demands of highly glycolytic hPSCs. During reprogramming to pluripotency by defined factors (OCT4, SOX2, KLF4, and c-MYC), the reprogramming kinetics and efficiency are markedly improved by adding REX1 or replacing KLF4 with REX1. These improvements are achieved by lowering repro...

Research paper thumbnail of Prolonged Membrane Depolarization Enhances Midbrain Dopamine Neuron Differentiation via Epigenetic Histone Modifications

Stem Cells, 2011

Understanding midbrain dopamine (DA) neuron differentiation is of importance, because of physiolo... more Understanding midbrain dopamine (DA) neuron differentiation is of importance, because of physiological and clinical implications of this neuronal subtype. We show that prolonged membrane depolarization induced by KCl treatment promotes DA neuron differentiation from neural precursor cells (NPCs) derived from embryonic ventral midbrain (VM). Interestingly, the depolarization-induced increase of DA neuron yields was not abolished by L-type calcium channel blockers, along with no depolarization-mediated change of intracellular calcium level in the VM-derived NPCs (VM-NPCs), suggesting that the depolarization effect is due to a calcium-independent mechanism. Experiments with labeled DA neuron progenitors indicate that membrane depolarization acts at the differentiation fate determination stage and promotes the expression of DA phenotype genes (tyrosine hydroxylase [TH] and DA transporter [DAT]). Recruitment of Nurr1, a transcription factor crucial for midbrain DA neuron development, to ...

Research paper thumbnail of Human histone H3K79 methyltransferase DOT1L protein binds actively transcribing RNA polymerase II to regulate gene expression

Journal of Biological Chemistry, 2013

Authors are urged to introduce these corrections into any reprints they distribute. Secondary (ab... more Authors are urged to introduce these corrections into any reprints they distribute. Secondary (abstract) services are urged to carry notice of these corrections as prominently as they carried the original abstracts.

Research paper thumbnail of Comparative receptor tyrosine kinase profiling identifies a novel role for AXL in human stem cell pluripotency

Human Molecular Genetics, 2013

The extensive molecular characterization of human pluripotent stem cells (hPSCs), human embryonic... more The extensive molecular characterization of human pluripotent stem cells (hPSCs), human embryonic stem cells (hESCs) and human-induced pluripotent stem cells (hiPSCs) is required before they can be applied in the future for personalized medicine and drug discovery. Despite the efforts that have been made with kinome analyses, we still lack in-depth insights into the molecular signatures of receptor tyrosine kinases (RTKs) that are related to pluripotency. Here, we present the first detailed and distinct repertoire of RTK characteristic for hPSC pluripotency by determining both the expression and phosphorylation profiles of RTKs in hESCs and hiPSCs using reverse transcriptase–polymerase chain reaction with degenerate primers that target conserved tyrosine kinase domains and phospho-RTK array, respectively. Among the RTKs tested, the up-regulation of EPHA1, ERBB2, FGFR4 and VEGFR2 and the down-regulation of AXL, EPHA4, PDGFRB and TYRO3 in terms of both their expression and phosphoryla...

Research paper thumbnail of Identification of DNA methylation markers for lineage commitment of in vitro hepatogenesis

Human Molecular Genetics, 2011

Hepatocytes that have differentiated from human embryonic stem cells (hESCs) have great potential... more Hepatocytes that have differentiated from human embryonic stem cells (hESCs) have great potential for the treatment of liver disease as well as for drug testing. Moreover, in vitro hepatogenesis is a powerful model system for studying the molecular mechanisms underlying liver development. DNA methylation is an important epigenetic mechanism that influences differential gene expression during embryonic development. We profiled gene expression and DNA methylation of three cell states of in vitro hepatogenesis-hESC, definitive endoderm and hepatocyte-using microarray analysis. Among 525 state-specific expressed genes, 67 showed significant negative correlation between gene expression and DNA methylation. State-specific expression and methylation of target genes were validated by quantitative reverse transcription-polymerase chain reaction and pyrosequencing, respectively. To elucidate genome-scale methylation changes beyond the promoter, we also performed high-throughput sequencing of methylated DNA captured by the MBD2 protein. We found dynamic methylation changes in intergenic regions of the human genome during differentiation. This study provides valuable methylation markers for the lineage commitment of in vitro hepatogenesis and should help elucidate the molecular mechanisms underlying stem cell differentiation and liver development.

Research paper thumbnail of Expression profiles of miRNAs in human embryonic stem cells during hepatocyte differentiation

Hepatology Research, 2011

Human embryonic stem cells (hESCs) are able to self-renew and differentiate into a variety of c... more Human embryonic stem cells (hESCs) are able to self-renew and differentiate into a variety of cell types. Although miRNAs have emerged as key regulators in the cellular process, a few studies have been reported about behaviors of miRNAs during differentiation of hESCs into a specialized cell type. Here, we demonstrate that different kinds of miRNAs may function in a lineage-specific manner during the differentiation of human embryonic stem cells (hESCs). hESCs were induced to definitive endoderm (DE) cells and further differentiated to hepatocytes. The expression levels of miRNAs were examined in hESCs, DE cells, and hepatocytes by miRNA array using 799 human miRNA probes. Among 387 miRNAs significantly detected, 13 and 56 miRNAs were downregulated and upregulated during transition of hESCs to DE cells, respectively, while 30 and 92 miRNAs were downregulated and upregulated during differentiation of DE cells to hepatocytes, respectively. In particular, 5, 4, and 86 miRNAs were enriched in hESCs, DE cells, and hepatocytes, respectively. Quantitative RT-PCR represented that miR-512-3p, miR-512-5p and miR-520c-3p were enriched in hESCs, miR-9*, miR-205 and miR-375 in hESC-derived DE cells, and miR-10a, miR-122 and miR-21 in hESC-derived hepatocytes. Expression patterns of lineage-specific miRNAs in the liver tissue were similar to those of hESC-derived hepatocytes. The results indicate that different kinds of miRNAs may function in a lineage-specific manner during differentiation of hESCs into a specialized cell type.

Research paper thumbnail of Tunable Wettability of Graphene through Nondestructive Hydrogenation and Wettability-Based Patterning for Bioapplications

Nano Letters, Apr 10, 2020

The wettability of graphene has been extensively studied and successfully modified by chemical fu... more The wettability of graphene has been extensively studied and successfully modified by chemical functionalization. Nevertheless, the unavoidable introduction of undesired defects and the absence of systematic and local control over wettability by previous methods have limited the use of graphene in applications. In addition, micro-scale patterning according to wettability has not been attempted. Here, we demonstrate that the wettability of graphene can be systematically controlled and the surface patterned into micro-scale sections based on wettability without creating significant defects, possible by non-destructive hydrogen plasma. Hydrophobic graphene is progressively converted to hydrophilic hydrogenated graphene (H-Gr) that reaches superhydrophilicity. The great contrast in wettability between graphene and H-Gr makes it possible selectively positioning and isolating human-breast-cancer cells on arrays of micro-patterns since strong hydrophilicity facilitates the adsorption of the cells. We believe that our method will provide an essential technique for enabling surface and biological applications requiring micro-scale patterns with different wettability.

Research paper thumbnail of Integrated phase-change memory devices using Bi2Te3 nanowires

Bismuth telluride (Bi 2 Te 3) and its alloys are considered to be the best avaiable materials for... more Bismuth telluride (Bi 2 Te 3) and its alloys are considered to be the best avaiable materials for near room-temperature thermoelectric applications. Moreover, because lowdimensional thermoelectric materials are expected to have a higher figure of merit due to quantum confinement effects, Bi 2 Te 3 nanowires have been studied extensively. However, their memory switching behavior has never been studied in Bi 2 Te 3 nanowires. Here, we report for the first time on reversible memory switching effects in Bi 2 Te 3 nanowires fabricated using anodized aluminum oxide (AAO) membranes. We find that Bi 2 Te 3 nanowires show a reversible crystalline-amorphous phase change induced by temperature or electric field, similar to that reported for chalcogenide materials (Ge-Sb-Te alloys, GST), and we demonstrate that Bi 2 Te 3 nanowires show considerable promise as building blocks for phase change random access memory (PRAM).

Research paper thumbnail of Memristive Switching in Bi1–xSbx Nanowires

ACS Applied Materials & Interfaces, Apr 4, 2016

We investigated the memristive switching behavior in bismuth-antimony alloy (Bi 1-x Sb x) single ... more We investigated the memristive switching behavior in bismuth-antimony alloy (Bi 1-x Sb x) single nanowire devices at 0.1 ≤ x ≤ 0.42. At 0.15 ≤ x ≤ 0.42, most Bi 1-x Sb x single nanowire devices exhibited bipolar resistive switching (RS) behavior with on/off ratios of approximately 10 4 and narrow variations in switching parameters. Moreover, the resistance values in the lowresistance state (LRS) were insensitive to x. On the other hand, at 0.1 ≤ x ≤ 0.15, some Bi 1-x Sb x single nanowire devices showed complementary RS-like behavior, which was ascribed to asymmetric contact properties. Transmission electron microscopy and elemental mapping images of Bi, Sb, and O obtained from the cross-sections of the Bi 1-x Sb x single nanowire devices, which were cut before and after RS, revealed that the mobile species was Sb ions, and the migration of the Sb ions to the nanowire surface brought the switch to LRS. In addition, we demonstrated that two types of synaptic plasticity, namely, short-term plasticity and long-term potentiation could be implemented in Bi 1-x Sb x nanowires by applying a sequence of voltage pulses with different repetition intervals.

Research paper thumbnail of Real-Time Discrimination between Proliferation and Neuronal and Astroglial Differentiation of Human Neural Stem Cells

Scientific Reports, Sep 10, 2014

Neural stem cells (NSCs) are characterized by a capacity for self-renewal, differentiation into m... more Neural stem cells (NSCs) are characterized by a capacity for self-renewal, differentiation into multiple neural lineages, all of which are considered to be promising components for neural regeneration. However, for cell-replacement therapies, it is essential to monitor the process of in vitro NSC differentiation and identify differentiated cell phenotypes. We report a real-time and label-free method that uses a capacitance sensor array to monitor the differentiation of human fetal brain-derived NSCs (hNSCs) and to identify the fates of differentiated cells. When hNSCs were placed under proliferation or differentiation conditions in five media, proliferating and differentiating hNSCs exhibited different frequency and time dependences of capacitance, indicating that the proliferation and differentiation status of hNSCs may be discriminated in real-time using our capacitance sensor. In addition, comparison between real-time capacitance and time-lapse optical images revealed that neuronal and astroglial differentiation of hNSCs may be identified in real-time without cell labeling. H uman neural stem cells (hNSCs), which can give rise to neuronal or glial cells, have received considerable attention for their therapeutic potential to repair neural injury or dysfunction caused by trauma, stroke, and neurodegenerative diseases 1. For cell-replacement therapies, hNSCs could be differentiated into the appropriate neural cell types prior to transplantation, since pre-differentiated cells could be more therapeutically beneficial and undifferentiated hNSCs may remain immature or produce unwanted neural cell types after transplantation into the damaged or diseased brain 2-5. Hence, it is important to monitor the process of in vitro hNSC differentiation and to identify specific differentiated cell fates. The fates of differentiated cells are usually identified via real-time polymerase chain reaction 6 or immunohistochemical methods 7 that involve labeling with nucleic acids or antibodies. However, these methods are invasive and time-consuming. We have therefore developed an alternative approach to monitor the differentiation of hNSCs and to identify the fate potential of differentiated hNSCs in real-time without cell labeling. To monitor the differentiation of stem cells in real-time, electric cell-substrate impedance sensors have been used 8-11 , which measure the alternating current (AC) impedance between a small sensing electrode and a large counter electrode while cells are cultured on the gold-sensing electrode. Cells attach and spread on the surface of the sensing electrode and passively block the current, and thus the electrode impedance is affected by the shape, adhesion, and/or mobility of adherent cells 12,13. However, compared to the electrode impedance, the capacitance (or the dielectric constant) of cells provides more direct information on cellular activities 14-17 ; the fate potential of NSCs was previously reported to be more closely related to cell membrane capacitance than to conductance 18. On this study, we have developed a capacitance sensor to monitor the differentiation of hNSCs. In our capacitance sensor, the cells are placed between the two electrodes rather than on top of the electrodes, and the change in capacitance is measured. Since the cells are placed between two electrodes, optical images of the cells and measurements of real-time capacitance can be obtained simultaneously, enabling a better understanding of hNSC differentiation.

Research paper thumbnail of Real-time monitoring of 3D cell culture using a 3D capacitance biosensor

Biosensors and Bioelectronics, Mar 1, 2016

Three-dimensional (3D) cell cultures have recently received attention because they represent a mo... more Three-dimensional (3D) cell cultures have recently received attention because they represent a more physiologically relevant environment compared to conventional two-dimensional (2D) cell cultures. However, 2D-based imaging techniques or cell sensors are insufficient for real-time monitoring of cellular behavior in 3D cell culture. Here, we report investigations conducted with a 3D capacitance cell sensor consisting of vertically aligned pairs of electrodes. When GFP-expressing human breast cancer cells (GFP-MCF-7) encapsulated in alginate hydrogel were cultured in a 3D cell culture system, cellular activities, such as cell proliferation and apoptosis at different heights, could be monitored non-invasively and in real-time by measuring the change in capacitance with the 3D capacitance sensor. Moreover, we were able to monitor cell migration of human mesenchymal stem cells (hMSCs) with our 3D capacitance sensor.

Research paper thumbnail of Tunable Wettability of Graphene through Nondestructive Hydrogenation and Wettability-Based Patterning for Bioapplications

Nano Letters, 2020

The wettability of graphene has been extensively studied and successfully modified by chemical fu... more The wettability of graphene has been extensively studied and successfully modified by chemical functionalization. Nevertheless, the unavoidable introduction of undesired defects and the absence of systematic and local control over wettability by previous methods have limited the use of graphene in applications. In addition, micro-scale patterning according to wettability has not been attempted. Here, we demonstrate that the wettability of graphene can be systematically controlled and the surface patterned into micro-scale sections based on wettability without creating significant defects, possible by non-destructive hydrogen plasma. Hydrophobic graphene is progressively converted to hydrophilic hydrogenated graphene (H-Gr) that reaches superhydrophilicity. The great contrast in wettability between graphene and H-Gr makes it possible selectively positioning and isolating human-breast-cancer cells on arrays of micro-patterns since strong hydrophilicity facilitates the adsorption of the cells. We believe that our method will provide an essential technique for enabling surface and biological applications requiring micro-scale patterns with different wettability.

Research paper thumbnail of Memristive Switching in Bi1-xSbx Nanowires

ACS applied materials & interfaces, Jan 13, 2016

We investigated the memristive switching behavior in bismuth-antimony alloy (Bi1-xSbx) single nan... more We investigated the memristive switching behavior in bismuth-antimony alloy (Bi1-xSbx) single nanowire devices at 0.1 ≤ x ≤ 0.42. At 0.15 ≤ x ≤ 0.42, most Bi1-xSbx single nanowire devices exhibited bipolar resistive switching (RS) behavior with on/off ratios of approximately 10(4) and narrow variations in switching parameters. Moreover, the resistance values in the low-resistance state (LRS) were insensitive to x. On the other hand, at 0.1 ≤ x ≤ 0.15, some Bi1-xSbx single nanowire devices showed complementary RS-like behavior, which was ascribed to asymmetric contact properties. Transmission electron microscopy and elemental mapping images of Bi, Sb, and O obtained from the cross sections of the Bi1-xSbx single nanowire devices, which were cut before and after RS, revealed that the mobile species was Sb ions, and the migration of the Sb ions to the nanowire surface brought the switch to LRS. In addition, we demonstrated that two types of synaptic plasticity, namely, short-term plast...

Research paper thumbnail of Real-time monitoring of 3D cell culture using a 3D capacitance biosensor

Biosensors & bioelectronics, Jan 6, 2015

Three-dimensional (3D) cell cultures have recently received attention because they represent a mo... more Three-dimensional (3D) cell cultures have recently received attention because they represent a more physiologically relevant environment compared to conventional two-dimensional (2D) cell cultures. However, 2D-based imaging techniques or cell sensors are insufficient for real-time monitoring of cellular behavior in 3D cell culture. Here, we report investigations conducted with a 3D capacitance cell sensor consisting of vertically aligned pairs of electrodes. When GFP-expressing human breast cancer cells (GFP-MCF-7) encapsulated in alginate hydrogel were cultured in a 3D cell culture system, cellular activities, such as cell proliferation and apoptosis at different heights, could be monitored non-invasively and in real-time by measuring the change in capacitance with the 3D capacitance sensor. Moreover, we were able to monitor cell migration of human mesenchymal stem cells (hMSCs) with our 3D capacitance sensor.

Research paper thumbnail of Transcriptional Profiles of Imprinted Genes in Human Embryonic Stem Cells During In vitro Differentiation

International journal of stem cells, 2014

Genomic imprinting is an inheritance phenomenon by which a subset of genes are expressed from one... more Genomic imprinting is an inheritance phenomenon by which a subset of genes are expressed from one allele of two homologous chromosomes in a parent of origin-specific manner. Even though fine-tuned regulation of genomic imprinting process is essential for normal development, no other means are available to study genomic imprinting in human during embryonic development. In relation with this bottleneck, differentiation of human embryonic stem cells (hESCs) into specialized lineages may be considered as an alternative to mimic human development. In this study, hESCs were differentiated into three lineage cell types to analyze temporal and spatial expression of imprinted genes. Of 19 imprinted genes examined, 15 imprinted genes showed similar transcriptional level among two hESC lines and two human induced pluripotent stem cell (hiPSC) lines. Expressional patterns of most imprinted genes were varied in progenitors and fully differentiated cells which were derived from hESCs. Also, no co...

Research paper thumbnail of Real-Time Discrimination between Proliferation and Neuronal and Astroglial Differentiation of Human Neural Stem Cells

Scientific Reports, 2014

Neural stem cells (NSCs) are characterized by a capacity for self-renewal, differentiation into m... more Neural stem cells (NSCs) are characterized by a capacity for self-renewal, differentiation into multiple neural lineages, all of which are considered to be promising components for neural regeneration. However, for cell-replacement therapies, it is essential to monitor the process of in vitro NSC differentiation and identify differentiated cell phenotypes. We report a real-time and label-free method that uses a capacitance sensor array to monitor the differentiation of human fetal brain-derived NSCs (hNSCs) and to identify the fates of differentiated cells. When hNSCs were placed under proliferation or differentiation conditions in five media, proliferating and differentiating hNSCs exhibited different frequency and time dependences of capacitance, indicating that the proliferation and differentiation status of hNSCs may be discriminated in real-time using our capacitance sensor. In addition, comparison between real-time capacitance and time-lapse optical images revealed that neuronal and astroglial differentiation of hNSCs may be identified in real-time without cell labeling. H uman neural stem cells (hNSCs), which can give rise to neuronal or glial cells, have received considerable attention for their therapeutic potential to repair neural injury or dysfunction caused by trauma, stroke, and neurodegenerative diseases 1. For cell-replacement therapies, hNSCs could be differentiated into the appropriate neural cell types prior to transplantation, since pre-differentiated cells could be more therapeutically beneficial and undifferentiated hNSCs may remain immature or produce unwanted neural cell types after transplantation into the damaged or diseased brain 2-5. Hence, it is important to monitor the process of in vitro hNSC differentiation and to identify specific differentiated cell fates. The fates of differentiated cells are usually identified via real-time polymerase chain reaction 6 or immunohistochemical methods 7 that involve labeling with nucleic acids or antibodies. However, these methods are invasive and time-consuming. We have therefore developed an alternative approach to monitor the differentiation of hNSCs and to identify the fate potential of differentiated hNSCs in real-time without cell labeling. To monitor the differentiation of stem cells in real-time, electric cell-substrate impedance sensors have been used 8-11 , which measure the alternating current (AC) impedance between a small sensing electrode and a large counter electrode while cells are cultured on the gold-sensing electrode. Cells attach and spread on the surface of the sensing electrode and passively block the current, and thus the electrode impedance is affected by the shape, adhesion, and/or mobility of adherent cells 12,13. However, compared to the electrode impedance, the capacitance (or the dielectric constant) of cells provides more direct information on cellular activities 14-17 ; the fate potential of NSCs was previously reported to be more closely related to cell membrane capacitance than to conductance 18. On this study, we have developed a capacitance sensor to monitor the differentiation of hNSCs. In our capacitance sensor, the cells are placed between the two electrodes rather than on top of the electrodes, and the change in capacitance is measured. Since the cells are placed between two electrodes, optical images of the cells and measurements of real-time capacitance can be obtained simultaneously, enabling a better understanding of hNSC differentiation.

Research paper thumbnail of DUSP4 Regulates Neuronal Differentiation and Calcium Homeostasis by Modulating ERK1/2 Phosphorylation

Stem cells and development, Jan 14, 2014

Protein tyrosine phosphatases have been recognized as critical components of multiple signaling r... more Protein tyrosine phosphatases have been recognized as critical components of multiple signaling regulators of fundamental cellular processes, including differentiation, cell death, and migration. In this study, we show that dual specificity phosphatase 4 (DUSP4) is crucial for neuronal differentiation and functions in the neurogenesis of embryonic stem cells (ESCs). The endogenous mRNA and protein expression levels of DUSP4 gradually increased during mouse development from ESCs to postnatal stages. Neurite outgrowth and the expression of neuron-specific markers were markedly reduced by genetic ablation of DUSP4 in differentiated neurons, and these effects were rescued by the reintroduction of DUSP4. In addition, DUSP4 knockdown dramatically enhanced extracellular signal-regulated kinase (ERK) activation during neuronal differentiation. Furthermore, the DUSP4-ERK pathway functioned to balance calcium signaling, not only by regulating Ca(2+)/calmodulin-dependent kinase I phosphorylati...

Research paper thumbnail of The reprogramming factor nuclear receptor subfamily 5, group A, member 2 cannot replace octamer-binding transcription factor 4 function in the self-renewal of embryonic stem cells

FEBS Journal, 2013

Although octamer-binding transcription factor 4 (Oct-4) is one of the most intensively studied fa... more Although octamer-binding transcription factor 4 (Oct-4) is one of the most intensively studied factors in mammalian development, no cellular genes capable of replacing Oct-4 function in embryonic stem (ES) cells have been found. Recent data show that nuclear receptor subfamily 5, group A, member 2 (Nr5a2) is able to replace Oct-4 function in the reprogramming process; however, it is unclear whether Nr5a2 can replace Oct-4 function in ES cells. In this study, the ability of Nr5a2 to maintain self-renewal and pluripotency in ES cells was investigated. Nr5a2 localized to the nucleus in ES cells, similarly to Oct-4. However, expression of Nr5a2 failed to rescue the stem cell phenotype or to maintain the self-renewal ability of ES cells. Furthermore, as compared with Oct-4-expressing ES cells, Nr5a2-expressing ES cells showed a reduced number of cells in S-phase, did not expand normally, and did not remain in an undifferentiated state. Ectopic expression of Nr5a2 in ES cells was not able to activate transcription of ES cellspecific genes, and gene expression profiling demonstrated differences between Nr5a2-expressing and Oct-4-expressing ES cells. In addition, Nr5a2-expressing ES cells were not able to form teratomas in nude mice. Taken together, these results strongly suggest that the gene regulation properties of Nr5a2 and Oct-4 and their abilities to confer self-renewal and pluripotency of ES cells differ. The present study provides strong evidence that Nr5a2 cannot replace Oct-4 function in ES cells.

Research paper thumbnail of Combinatorial Activin Receptor-Like Kinase/Smad and Basic Fibroblast Growth Factor Signals Stimulate the Differentiation of Human Embryonic Stem Cells into the Cardiac Lineage

Stem Cells and Development, 2011

The transforming growth factor beta/bone morphogenetic protein-activated Smad signaling pathway p... more The transforming growth factor beta/bone morphogenetic protein-activated Smad signaling pathway plays a complicated role in the maintenance of human embryonic stem cell (hESC) pluripotency and in the cell fate decision of hESCs. Here, we report that sustained inhibition of the transforming growth factor beta type I receptor (also termed activin receptor-like kinase or ALK) using a chemical inhibitor selective for ALK4/5/7 (ALKi) leads to the cardiac differentiation of hESCs under feeder-free and serum-free conditions. Treatment with ALKi reduced Smad2/3 phosphorylation and increased Smad1/5/8 phosphorylation in hESCs, suggesting a requirement for active Smad1/5/8 signaling for cardiac induction in these cells when ALK/Smad2/3 is inhibited. Importantly, active basic fibroblast growth factor (bFGF) signaling was also required for ALKimediated cardiac differentiation of monolayer-cultured hESCs. The FGF receptor inhibitor SU5402 blocked ALKi-mediated cardiac induction in hESCs, whereas bone morphogenetic protein-4 enhanced the ALKiinduced increase in phospho-Smad1/5/8 levels but failed to induce the cardiac differentiation of hESCs and instead promoted trophoblastic differentiation. We also confirmed that ALKi potentially enhanced the cardiac differentiation of human embryoid bodies, as determined by expression of cardiac-specific markers, increased beating areas, and action potential recorded from beating areas. These results demonstrate that an ALKi could be used as a potential cardiac-inducing agent and that the development of culture conditions that provide an appropriate balance between ALK/Smad and bFGF signaling is necessary to direct the fate of hESCs into the cardiac lineage.

Research paper thumbnail of Comparative Proteomic Analysis of Human Somatic Cells, Induced Pluripotent Stem Cells, and Embryonic Stem Cells

Stem Cells and Development, 2012

Induced pluripotent stem cells (iPSCs) are somatic cells that have been reprogrammed to a pluripo... more Induced pluripotent stem cells (iPSCs) are somatic cells that have been reprogrammed to a pluripotent state via introduction of defined transcription factors. iPSCs are a valuable resource for regenerative medicine, but whether iPSCs are identical to embryonic stem cells (ESCs) remains unclear. In this study, we performed comparative proteomic analyses of human somatic cells [human newborn foreskin fibroblasts (hFFs)], human iPSCs (hiPSCs) derived from hFFs, and H9 human ESCs (hESCs). We reprogrammed hFFs to a pluripotent state using 4 core transcription factors: Oct4 (O), Sox2 (S), Klf4 (K), and c-Myc (M). The proteome of hiPSCs induced by 4 core transcription factors was relatively similar to that of hESCs. However, several proteins, including dUTPase, GAPDH, and FUSE binding protein 3, were differentially expressed between hESCs and hiPSCs, implying that hiPSCs are not identical to hESCs at the proteomic level. The proteomes of iPSCs induced by introducing 3, 5, or 6 transcription factors were also analyzed. Our proteomic profiles provide valuable insight into the factors that contribute to the similarities and differences between hESCs and hiPSCs and the mechanisms of reprogramming.

Research paper thumbnail of Unveiling the critical role of REX1 in the regulation of human stem cell pluripotency

Stem Cells, 2013

Reduced expression 1 (REX1) is a widely used pluripotency marker, but little is known about its r... more Reduced expression 1 (REX1) is a widely used pluripotency marker, but little is known about its roles in pluripotency. Here, we show that REX1 is functionally important in the reacquisition and maintenance of pluripotency. REX1-depleted human pluripotent stem cells (hPSCs) lose their self-renewal capacity and full differentiation potential, especially their mesoderm lineage potential. Cyclin B1/B2 expression was found to parallel that of REX1. REX1 positively regulates the transcriptional activity of cyclin B1/B2 through binding to their promoters. REX1 induces the phosphorylation of DRP1 at Ser616 by cyclin B/CDK1, which leads to mitochondrial fission and appears to be important for meeting the high-energy demands of highly glycolytic hPSCs. During reprogramming to pluripotency by defined factors (OCT4, SOX2, KLF4, and c-MYC), the reprogramming kinetics and efficiency are markedly improved by adding REX1 or replacing KLF4 with REX1. These improvements are achieved by lowering repro...

Research paper thumbnail of Prolonged Membrane Depolarization Enhances Midbrain Dopamine Neuron Differentiation via Epigenetic Histone Modifications

Stem Cells, 2011

Understanding midbrain dopamine (DA) neuron differentiation is of importance, because of physiolo... more Understanding midbrain dopamine (DA) neuron differentiation is of importance, because of physiological and clinical implications of this neuronal subtype. We show that prolonged membrane depolarization induced by KCl treatment promotes DA neuron differentiation from neural precursor cells (NPCs) derived from embryonic ventral midbrain (VM). Interestingly, the depolarization-induced increase of DA neuron yields was not abolished by L-type calcium channel blockers, along with no depolarization-mediated change of intracellular calcium level in the VM-derived NPCs (VM-NPCs), suggesting that the depolarization effect is due to a calcium-independent mechanism. Experiments with labeled DA neuron progenitors indicate that membrane depolarization acts at the differentiation fate determination stage and promotes the expression of DA phenotype genes (tyrosine hydroxylase [TH] and DA transporter [DAT]). Recruitment of Nurr1, a transcription factor crucial for midbrain DA neuron development, to ...

Research paper thumbnail of Human histone H3K79 methyltransferase DOT1L protein binds actively transcribing RNA polymerase II to regulate gene expression

Journal of Biological Chemistry, 2013

Authors are urged to introduce these corrections into any reprints they distribute. Secondary (ab... more Authors are urged to introduce these corrections into any reprints they distribute. Secondary (abstract) services are urged to carry notice of these corrections as prominently as they carried the original abstracts.

Research paper thumbnail of Comparative receptor tyrosine kinase profiling identifies a novel role for AXL in human stem cell pluripotency

Human Molecular Genetics, 2013

The extensive molecular characterization of human pluripotent stem cells (hPSCs), human embryonic... more The extensive molecular characterization of human pluripotent stem cells (hPSCs), human embryonic stem cells (hESCs) and human-induced pluripotent stem cells (hiPSCs) is required before they can be applied in the future for personalized medicine and drug discovery. Despite the efforts that have been made with kinome analyses, we still lack in-depth insights into the molecular signatures of receptor tyrosine kinases (RTKs) that are related to pluripotency. Here, we present the first detailed and distinct repertoire of RTK characteristic for hPSC pluripotency by determining both the expression and phosphorylation profiles of RTKs in hESCs and hiPSCs using reverse transcriptase–polymerase chain reaction with degenerate primers that target conserved tyrosine kinase domains and phospho-RTK array, respectively. Among the RTKs tested, the up-regulation of EPHA1, ERBB2, FGFR4 and VEGFR2 and the down-regulation of AXL, EPHA4, PDGFRB and TYRO3 in terms of both their expression and phosphoryla...

Research paper thumbnail of Identification of DNA methylation markers for lineage commitment of in vitro hepatogenesis

Human Molecular Genetics, 2011

Hepatocytes that have differentiated from human embryonic stem cells (hESCs) have great potential... more Hepatocytes that have differentiated from human embryonic stem cells (hESCs) have great potential for the treatment of liver disease as well as for drug testing. Moreover, in vitro hepatogenesis is a powerful model system for studying the molecular mechanisms underlying liver development. DNA methylation is an important epigenetic mechanism that influences differential gene expression during embryonic development. We profiled gene expression and DNA methylation of three cell states of in vitro hepatogenesis-hESC, definitive endoderm and hepatocyte-using microarray analysis. Among 525 state-specific expressed genes, 67 showed significant negative correlation between gene expression and DNA methylation. State-specific expression and methylation of target genes were validated by quantitative reverse transcription-polymerase chain reaction and pyrosequencing, respectively. To elucidate genome-scale methylation changes beyond the promoter, we also performed high-throughput sequencing of methylated DNA captured by the MBD2 protein. We found dynamic methylation changes in intergenic regions of the human genome during differentiation. This study provides valuable methylation markers for the lineage commitment of in vitro hepatogenesis and should help elucidate the molecular mechanisms underlying stem cell differentiation and liver development.

Research paper thumbnail of Expression profiles of miRNAs in human embryonic stem cells during hepatocyte differentiation

Hepatology Research, 2011

Human embryonic stem cells (hESCs) are able to self-renew and differentiate into a variety of c... more Human embryonic stem cells (hESCs) are able to self-renew and differentiate into a variety of cell types. Although miRNAs have emerged as key regulators in the cellular process, a few studies have been reported about behaviors of miRNAs during differentiation of hESCs into a specialized cell type. Here, we demonstrate that different kinds of miRNAs may function in a lineage-specific manner during the differentiation of human embryonic stem cells (hESCs). hESCs were induced to definitive endoderm (DE) cells and further differentiated to hepatocytes. The expression levels of miRNAs were examined in hESCs, DE cells, and hepatocytes by miRNA array using 799 human miRNA probes. Among 387 miRNAs significantly detected, 13 and 56 miRNAs were downregulated and upregulated during transition of hESCs to DE cells, respectively, while 30 and 92 miRNAs were downregulated and upregulated during differentiation of DE cells to hepatocytes, respectively. In particular, 5, 4, and 86 miRNAs were enriched in hESCs, DE cells, and hepatocytes, respectively. Quantitative RT-PCR represented that miR-512-3p, miR-512-5p and miR-520c-3p were enriched in hESCs, miR-9*, miR-205 and miR-375 in hESC-derived DE cells, and miR-10a, miR-122 and miR-21 in hESC-derived hepatocytes. Expression patterns of lineage-specific miRNAs in the liver tissue were similar to those of hESC-derived hepatocytes. The results indicate that different kinds of miRNAs may function in a lineage-specific manner during differentiation of hESCs into a specialized cell type.