The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Kiyotoshi Sekiguchi - One of the best experts on this subject based on the ideXlab platform.
-
laminin isoforms in human embryonic stem cells synthesis receptor usage and growth support
Journal of Cellular and Molecular Medicine, 2009Co-Authors: Sanna Vuoristo, Kiyotoshi Sekiguchi, Ismo Virtanen, Minna Takkunen, Jaan Palgi, Yamato Kikkawa, Patricia Rousselle, Timo Tuuri, Timo OtonkoskiAbstract:To reveal the functional intrinsic niche of human embryonic stem cells (hESC) we examined the production of basement membrane (BM) proteins and the presence of their receptors in feeder-free cell culture conditions. In addition, we investigated binding of hESCs to purified human BM proteins and identified the receptors mediating these contacts. Also, we tested whether purified human laminin (Lm) isoforms have a role in hESC self-renewal and growth in short-term cultures. The results show that hESCs synthesize Lm α1 and Lm α5 chains together with Lm β1 and γ1 chains suggesting the production of Lms-111 and -511 into the culture medium and deposits on cells. hESCs contain functionally important integrin (Int) subunits, Int β1, α3, α6, α5, β5 and αV, as well as the Lm α5 receptor, Lutheran (Lu) glycoprotein and its truncated form, basal cell adhesion molecule (B-CAM). In cell adhesion experiments, Int β1 was crucial for adhesion to most of the purified human BM proteins. Lu/B-CAM mediated adhesion to Lm-511 together with Int α3β1, and was essential for the adhesion of hESCs to embryonic feeder cells. Adhesion to Lm-411 was mediated by Int α6β1. Lm-511 supported hESC growth in defined medium equally well as Matrigel. These results provide consequential information of the biological role of BM in hESCs, warranting further investigation of BM biology of human pluripotent stem cells.
-
recombinant human laminin isoforms can support the undifferentiated growth of human embryonic stem cells
Biochemical and Biophysical Research Communications, 2008Co-Authors: Takamichi Miyazaki, Kiyotoshi Sekiguchi, Maria Hayashi, Noriko Sanzen, Sugiko Futaki, Kouichi Hasegawa, Miwa Kawasaki, Eihachiro Kawase, Norio Nakatsuji, Hirofumi SuemoriAbstract:Human embryonic stem cells (hESCs) are thought to be a promising cell source for cell transplantation therapy. For such a clinical application, the hESCs should be manipulated using appropriate and qualified materials. In this study, we examined the efficacy of recombinant human laminin (rhLM) isoforms on the undifferentiated growth of hESCs. We first determined the major integrins expressed on the hESCs to reveal the preference of the hESCs for rhLMs, and found that the hESCs mainly expressed integrin α6β1, which binds predominantly to laminin-111, -332 and -511/-521. When the hESCs were seeded onto rhLMs, the cells indeed adhered markedly to rhLM-332, and to rhLM-511 and rhLM-111 to a lesser extent. The hESCs proliferated on these three rhLMs for several passages while preserving their pluripotency. These results show that rhLM-111, -332, and -511 are good substrates to expand undifferentiated hESCs due to their high affinity to integrin α6β1 expressed on hESCs.
-
laminin 511 is an epithelial message promoting dermal papilla development and function during early hair morphogenesis
Genes & Development, 2008Co-Authors: Jing Gao, Kiyotoshi Sekiguchi, Hiroyuki Ido, Mindy C Deroue, Chihhsi Che, Michael Nguye, Ngo T Nguye, Kenji Harada, Uce A Morga, Jeffery H MineAbstract:Hair morphogenesis takes place through reciprocal epithelial and mesenchymal signaling; however, the mechanisms controlling signal exchange are poorly understood. Laminins are extracellular proteins that play critical roles in adhesion and signaling. Here we demonstrate the mechanism of how laminin-511 controls hair morphogenesis. Dermal papilla (DP) from laminin-511 mutants showed developmental defects by E16.5, including a failure to maintain expression of the key morphogen noggin. This maintenance was critical as exogenous introduction of noggin or sonic hedgehog (Shh) produced downstream from noggin was sufficient to restore hair follicle development in lama5−/− (laminin-511-null) skin. Hair development required the β1 integrin binding but not the heparin binding domain of laminin-511. Previous studies demonstrated that Shh signaling requires primary cilia, microtubule-based signaling organelles. Laminin-511 mutant DP showed decreased length and structure of primary cilia in vitro and in vivo. Laminin-511, but not laminin-111, restored primary cilia formation in lama5−/− mesenchyme and triggered noggin expression in an Shh- and PDGF-dependent manner. Inhibition of laminin-511 receptor β1 integrin disrupted DP primary cilia formation as well as hair development. These studies show that epithelial-derived laminin-511 is a critical early signal that directs ciliary function and DP maintenance as a requirement for hair follicle downgrowth.
-
ligand binding specificities of laminin binding integrins a comprehensive survey of laminin integrin interactions using recombinant α3β1 α6β1 α7β1 and α6β4 integrins
Matrix Biology, 2006Co-Authors: Ryoko Nishiuchi, Junichi Takagi, Maria Hayashi, Hiroyuki Ido, Yoshiko Yagi, Noriko Sanzen, Tsutomu Tsuji, Masashi Yamada, Kiyotoshi SekiguchiAbstract:Abstract The interactions of cells with basement membranes are primarily mediated via the engagement of laminins by a group of integrin family proteins, including integrins α3β1, α6β1, α7β1 and α6β4. To explore the ligand-binding specificities of these laminin-binding integrins, we produced these integrins, including two α7β1 splice variants (α7X1β1 and α7X2β1), as soluble recombinant proteins and determined their binding specificities and affinities toward a panel of purified laminin isoforms containing distinct α chains. Among the five laminin-binding integrins investigated, α3β1 and α6β4 exhibited a clear specificity for laminin-332 (α3β3γ2) and laminin-511 (α5β1γ1)/521 (α5β2γ1), while integrin α6β1 showed a broad specificity, binding to all laminin isoforms with a preference for laminin-111 (α1β1γ1), laminin-332 and laminin-511/521. The two α7β1 variants were distinct from α3β1, α6β1 and α6β4 in that they did not bind to laminin-332. α7X1β1 bound to all laminins, except laminin-332, with a preference for laminin-211 (α2β1γ1)/221 (α2β2γ1) and laminin-511/521, while α7X2β1 bound preferentially to laminin-111 and laminin-211/221. Laminin-511/521 was the most preferred ligand for all the laminin-binding integrins, except for α7X2β1, whereas laminin-411 was the poorest ligand, capable of binding to α6β1 and α7X1β1 with only modest binding affinities. These comprehensive analyses of the interactions between laminin-binding integrins and a panel of laminins clearly demonstrate that the isoforms of both integrins and laminins differ in their binding specificities and affinities, and provide a molecular basis for better understanding of the adhesive interactions of cells with basement membranes of defined laminin compositions.
M Hopkinson - One of the best experts on this subject based on the ideXlab platform.
-
nitrogen incorporation into strained in ga as n thin films grown on 100 511 411 311 and 111 gaas substrates studied by photoreflectance spectroscopy and high resolution x ray diffraction
Journal of Applied Physics, 2006Co-Authors: J Ibanez, R Kudrawiec, J Misiewicz, M Schmidbauer, M Henini, M HopkinsonAbstract:We have used photoreflectance (PR) and high-resolution x-ray diffraction (HRXRD) measurements to assess the composition of InxGa1−xAs1−yNy thin films (x∼20%, y∼3%) grown by molecular beam epitaxy on GaAs substrates with different surface orientations. The aim of our work is to investigate the effect of substrate orientation on the incorporation of N and In into the films. Whereas in principle the composition of the InxGa1−xAs1−yNy films cannot be characterized by HRXRD alone because lattice spacings depend on both x and y, we show that a combined analysis of the PR and HRXRD data allows us to determine the sample composition. Our data analysis suggests that the incorporation of N in (In, Ga)(As, N) exhibits some dependence on substrate orientation, although not as strong as previously observed in Ga(As, N). We determine shear deformation potentials for our samples that are sizably different than those obtained by linearly interpolating from the values of the pure binary compounds, which has already been o...
Thomas Bligaard - One of the best experts on this subject based on the ideXlab platform.
-
intrinsic selectivity and structure sensitivity of rhodium catalysts for c2 oxygenate production
Journal of the American Chemical Society, 2016Co-Authors: Nuoya Yang, Thomas Bligaard, Felix Studt, Andrew J Medford, Xinyan Liu, Stacey F Bent, Jens K NorskovAbstract:Synthesis gas (CO + H2) conversion is a promising route to converting coal, natural gas, or biomass into synthetic liquid fuels. Rhodium has long been studied as it is the only elemental catalyst that has demonstrated selectivity to ethanol and other C2+ oxygenates. However, the fundamentals of syngas conversion over rhodium are still debated. In this work a microkinetic model is developed for conversion of CO and H2 into methane, ethanol, and acetaldehyde on the Rh (211) and (111) surfaces, chosen to describe steps and close-packed facets on catalyst particles. The model is based on DFT calculations using the BEEF-vdW functional. The mean-field kinetic model includes lateral adsorbate–adsorbate interactions, and the BEEF-vdW error estimation ensemble is used to propagate error from the DFT calculations to the predicted rates. The model shows the Rh(211) surface to be ∼6 orders of magnitude more active than the Rh(111) surface, but highly selective toward methane, while the Rh(111) surface is intrinsicall...
-
on the structure sensitivity of direct no decomposition over low index transition metal facets
Topics in Catalysis, 2014Co-Authors: Hanne Falsig, Juan Shen, Tuhin Suvra Khan, Wei Guo, Glenn Jones, Soren Dahl, Thomas BligaardAbstract:We present a study of the dissociative chemisorption of NO, O2, and N2 over close-packed, stepped, kinked, and open (fcc {111}, {211}, {311}, {532}, {100}, and {110}) transition metal facets using density functional theory (DFT). The offset of the Bronsted–Evans–Polanyi (BEP) relations suggest that the {111} surface is the least reactive, and that the {110} surface is the most reactive. This observation is verified by establishing volcano-relations based on mean-field microkinetic models for each facet, showing that the maximum rate over {110} is 4 orders of magnitude larger than the maximum {111} rate. The ordering of the maximum activity over the facets is: {110} > {100} ~ {532} > {311} ~ {211} > {111}, which is in general agreement with the offset in the BEP relations. We show that the top-point location and shape of the volcano relations are approximately independent of facet. This observation lends credibility to the approach of analyzing trends in catalytic reactivity over a single low-index facet, and assuming the experimentally observed activity trends are qualitatively well-described by such a single-facet analysis. Our study suggests that a key element for generally obtaining quantitative agreement between theory and experiments is for the simulations to address in detail the propensities of the various types of active sites. Finally, we show that the ordering of NO decomposition rates among metals and facets is essentially unaltered when using BEP- and scaling relations in the microkinetics instead of explicit DFT calculations for each elementary reaction step, and that using a “universal” BEP relation introduces no significant additional qualitative error in trend prediction.
Shiv Pillai - One of the best experts on this subject based on the ideXlab platform.
-
disease severity linked to increase in autoantibody diversity in igg4 related disease
Arthritis & Rheumatism, 2020Co-Authors: Hang Liu, Cory A Perugino, Musie Ghebremichael, Zachary S Wallace, Sydney B Montesi, John H Stone, Shiv PillaiAbstract:Objective Four autoantigens have been described recently in IgG4-related disease (IgG4-RD): prohibitin, annexin A11, laminin 511-E8, and galectin-3. However, no external validation has been performed, and the possibility that some individuals break tolerance to more than 1 autoantigen has not been explored. We undertook this study to evaluate the relative frequencies of antibody responses against these autoantigens in order to explore the role of adaptive immune response in IgG4-RD. Methods Autoantibody responses against prohibitin, annexin A11, and laminin 511-E8 were measured among a clinically diverse cohort of IgG4-RD patients (n = 100) using enzyme-linked immunosorbent assays. Autoantibody responses were correlated with disease severity and organ distribution. Results The frequencies of IgG4 autoantibody responses against prohibitin (10%), annexin A11 (12%), and laminin 511-E8 (7%) were not significantly different from those of controls. A portion of the cohort (n = 86) had been analyzed previously at our center for anti-galectin-3 antibody responses, with 25 patients (29%) having IgG4 anti-galectin-3 antibodies. Of these 86 patients, 32 (37%) had IgG4 antibodies to ≥1 of the 4 autoantigens and 12 (14%) showed reactivity with ≥2 of the tested antigens. The subset of patients with ≥2 autoantibodies had higher total levels of IgG1, IgG2, IgG4, and C-reactive protein, were more commonly hypocomplementemic, and were more likely to have visceral organ involvement. Conclusion Antibodies against prohibitin, annexin A11, and laminin 511-E8 were found in only a small portion of patients with IgG4-RD. A subset of IgG4-RD patients, however, had IgG4 antibodies against ≥2 autoantigens. These patients presented with robust IgG subclass elevations, complement consumption, and visceral organ involvement. This broader break in immunologic tolerance in IgG4-RD was associated with more severe disease.
Nagahiro Hoshi - One of the best experts on this subject based on the ideXlab platform.
-
structural effects of electrochemical oxidation of formic acid on single crystal electrodes of palladium
Journal of Physical Chemistry B, 2006Co-Authors: Nagahiro Hoshi, Kaori Kida, Masashi Nakamura, Miou Nakada, Kazuhito OsadaAbstract:Structural effects on the rates of formic acid oxidation have been studied on Pd(111), Pd(100), Pd(110), and Pd(S)-[n(100)×(111)] (n = 2−9) electrodes in 0.1 M HClO4 containing 0.1 M formic acid with use of voltammetry. On the low index planes of Pd, the maximum current density of formic acid oxidation (jP) increases in the positive scan as follows: Pd(110) < Pd(111) < Pd(100). This order differs from that on the low index planes of Pt: Pt(111) < Pt(100) < Pt(110). Pd(S)-[n(100)×(111)] electrodes with terrace atomic rows n ≥ 3 have almost the same jP as Pd(100), except Pd(911) n = 5. The value of jP on Pd(911) n = 5 is 20% higher than those of the other surfaces. Pd(311) n = 2, of which the first layer is composed of only step atoms, has the lowest jP in the Pd(S)-[n(100)×(111)] series. The adsorption geometry of the reaction intermediate (formate ion) is optimized by using density functional theory.
-
selective formation of c2 compounds from electrochemical reduction of co2 at a series of copper single crystal electrodes
Journal of Physical Chemistry B, 2002Co-Authors: Yoshio Hori, Ichiro Takahashi, And Osamu Koga, Nagahiro HoshiAbstract:Electrochemical reduction of CO2 was studied using single-crystal electrodes, Cu(111), Cu(100), Cu(S)-[n(100) × (111)], and Cu(S)-[n(100) × (110)] at a constant current density 5 mA cm-2 in 0.1 M KHCO3 aqueous solution. Copper single crystals were prepared from 99.999% copper metal in graphite crucibles by the Bridgeman method. The crystal orientation was determined by the X-ray back reflection method. The Cu(111) electrode yields mainly CH4 from CO2, and the Cu(100) favorably gives C2H4. Introduction of (111) steps to Cu(100) basal plane, leading to Cu(S)-[n(100) × (111)] orientations, significantly promoted C2H4 formation and suppressed CH4 formation. The selectivity ratio C2H4/CH4 on Cu(711) (n = 4) amounted to 14, 2 orders of magnitude higher than that on Cu(111).
