EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2010
Yuya Tanaka
Abstract Communication between the two iron centres in (dithienylethyne)diyl complex 1 can be finely tuned by reversible addition to, ligand replacement at and removal from the C,C moiety in 1 of dicobalt fragments Co2(CO)n(PR3)6,n. Performance analysis reveals that disparate mechanisms are in operation for the two systems. In the case of the dicobalt adducts, indirect communication via the dicobalt steppingstone can be finely tuned by controlling the electronic structure of the dicobalt unit. [source]

Reversible and High-Capacity Nanostructured Electrode Materials for Li-Ion Batteries

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2009
Min Gyu Kim
Abstract Reversible nanostructured electrode materials are at the center of research relating to rechargeable lithium batteries, which require high power, high capacity, and high safety. The higher capacities and higher rate capabilities for the nanostructured electrode materials than for the bulk counterparts can be attributed to the higher surface area, which reduces the overpotential and allows faster reaction kinetics at the electrode surface. These electrochemical enhancements can lead to versatile potential applications of the batteries and can provide breakthroughs for the currently limited power suppliers of mobile electronics. This Feature Article describes recent research advances on nanostructured cathode and anode materials, such as metals, metal oxides, metal phosphides and LiCoO2, LiNi1,xMxO2 with zero-, one-, two-, and three-dimensional morphologies. [source]

Polymeric Nanohairs: Stooped Nanohairs: Geometry-Controllable, Unidirectional, Reversible, and Robust Gecko-like Dry Adhesive (Adv. Mater.

ADVANCED MATERIALS, Issue 22 2009
22/2009)
Kahp Suh, Hong Lee, and co-workers present on p. 2276 a simple, yet robust method for fabricating an array of stooped "nanohairs" by applying a proper choice of materials and post e-beam exposure, even for an aspect ratio of 10. The stooped nanohairs possess the unidirectional feature of frictional adhesion with a remarkably high adhesion force (,11 N cm,2). [source]

Stooped Nanohairs: Geometry-Controllable, Unidirectional, Reversible, and Robust Gecko-like Dry Adhesive

ADVANCED MATERIALS, Issue 22 2009
Tae-il Kim
A simple yet robust method to fabricate an array of stooped nanohairs is presented, with a proper choice of material and post e-beam exposure even for an aspect ratio of 10. The stooped nanohairs have the unidirectional feature of frictional adhesion with a remarkably high adhesion force (,11,N cm,2). [source]

Dual Tuning of the Photonic Band-Gap Structure in Soft Photonic Crystals

ADVANCED MATERIALS, Issue 18 2009
Masaki Honda
A dually tunable photonic crystal composed of thermosensitive gel particles confined in a pH-sensitive inverse-opal gel is reported. The position of the photonic band-gap can be thermally regulated, while its intensity is dramatically changed by pH. Reversible, independent, and extensive switching of the position and intensity of the photonic band-gap could be achieved using independent external stimuli. [source]

Unfolding of the loggerhead sea turtle (Caretta caretta) myoglobin: A 1H-NMR and electronic absorbance study

PROTEIN SCIENCE, Issue 9 2002
Daniela Delli Castelli
Abstract The effect of urea concentration on the backbone solution structure of the cyanide derivative of ferric Caretta caretta myoglobin (at pH 5.4) is reported. By addition of urea, sequential and long-range nuclear Overhauser effects (NOEs) are gradually lost. By using the residual NOE constraints to build the molecular model, a picture of the unfolding pathway was obtained. When the urea concentration is raised to 2.2 M, helices A and B appear largely disordered; helices C, D, and F loose structural constraints at 3.0 M urea. At urea concentration >6 M, the protein appears to be fully unfolded, including the GH hairpin and helix E stabilizing the prosthetic group. Reversible and cooperative denaturation isotherms obtained by following NOE peaks are considerably different from those obtained by monitoring electronic absorption changes. The reversible and cooperative urea-dependent folding-unfolding process of C. caretta myoglobin follows the minimum three-state mechanism N,X,D, where X represents a disordered globin structure (occurring at ,4 M urea) that still binds the heme. [source]

An integrated strategy for identification and relative quantification of site-specific protein phosphorylation using liquid chromatography coupled to MS2/MS3

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2005
Florian Wolschin
Reversible and differential multisite protein phosphorylation is an important mechanism controlling the activity of cellular proteins. Here we describe a robust and highly selective approach for the identification and relative quantification of site-specific phosphorylation events. This integrated strategy has three major parts: visualisation of phosphorylated proteins using fluorescently stained polyacrylamide gels, determination of the phosphorylation site(s) using automatic MS3 triggered by the loss of phosphoric acid, and relative quantification of phosphorylation by integrating MS2 - and MS3 -extracted ion traces using a fast-scanning, linear ion trap mass spectrometer. As a test case, recombinant sucrose-phosphate synthase (SPS) from Arabidopsis thaliana (At5g1110) was used for identification and quantification of site-specific phosphorylation. The identified phosphorylation site of the actively expressed protein coincides with the major regulatory in vivo phosphorylation site in spinach SPS. Site-specific differential in vitro phosphorylation of native protein was demonstrated after incubation of the recombinant protein with cold-adapted plant leaf extracts from A. thaliana, suggesting regulatory phosphorylation events of this key enzyme under stress response. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Reversible and Noncompetitive Inhibition of ,-Tryptase by Protein Surface Binding of Tetravalent Peptide Ligands Identified from a Combinatorial Split,Mix Library,

ANGEWANDTE CHEMIE, Issue 24 2010
Peter
Molekulare Stöpsel: Das On-Bead-Screening einer kombinatorischen Bibliothek von 216 vierarmigen Oligopeptiden lieferte hoch spezifische, nichtkompetitive Inhibitoren der Serinprotease ,-Tryptase mit nanomolarer Affinität. Die Liganden binden sehr wahrscheinlich an die Proteinoberfläche und wirken als molekulare ,Stöpsel", indem sie den Zugang zu den aktiven Zentren blockieren, die sich im Innern einer zentralen Kavität befinden (siehe Bild). [source]

Titelbild: Reversible, nicht metallunterstützte Bindung von Kohlendioxid durch frustrierte Lewis-Paare (Angew. Chem.

ANGEWANDTE CHEMIE, Issue 36 2009
36/2009)
Reversibles Binden von CO2, gelingt mit frustrierten Boran-Phosphan-Lewis-Paaren (FLPs). In der Zuschrift auf S.,6770,ff. beschreiben G. Erker et,al., dass das Treibhausgas CO2 durch P-C- und O-B-Bindungsbildung in Form cyclischer und acyclischer Addukte fixiert wird. Die Reaktion lässt sich unter CO2 -Freisetzung umkehren, indem die Temperatur der Lösung erhöht wird. Nach theoretischen Analysen handelt es sich beim Binden von CO2 durch FLPs um eine synchrone, konzertierte Reaktion. [source]

Reversible, nicht metallunterstützte Bindung von Kohlendioxid durch frustrierte Lewis-Paare,

ANGEWANDTE CHEMIE, Issue 36 2009
Cornelia
Seltene Beispiele für die metallfreie Bindung von Kohlendioxid sind frustrierte Lewis-Paare, bestehend aus sperrigen Phosphan- und Borankomponenten, die CO2 reversibel binden. Der Mechanismus der Bildung der CO2 -Derivate 1 und 2 durch nahezu gleichzeitige P-C- und B-O-Bindungsbildung wurde mithilfe quantenchemischer Rechnungen charakterisiert. [source]

Reversible 100,% Linkage Isomerization in a Single-Crystal to Single-Crystal Transformation: Photocrystallographic Identification of the Metastable [Ni(dppe)(,1 -ONO)Cl] Isomer,

ANGEWANDTE CHEMIE, Issue 31 2009

Mal N, mal O: Raman-spektroskopische und photokristallographische Studien an Einkristallen identifizierten den Komplex [Ni(dppe)(,1 -NO2)Cl] als das erste System, das im Festkörper eine reversible und vollständige Umwandlung in ein metastabiles Isomer, in diesem Fall [Ni(dppe)(,1 -ONO)Cl], eingeht. [source]

Toxic effect of triphenyltin chloride on the alga Spirulina subsalsa

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2002
Guolan Huang
Abstract A previous study on the deleterious effect of triphenyltin chloride (TPTCl) on the alga Spirulina subsalsa reported on four physiological and biochemical indices (or parameters): growth rate, chlorophyll content, phycocyanin content and nitrate reductase activity. In the present study, further research was performed to confirm the findings reported in the previous paper, using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM images show significant changes in the screw-pitch of S. subsalsa, suggesting that TPTCl may damage the inheritance characteristics of S. subsalsa. The TEM images illustrate that the external pectin theca, limiting membrane and inter photosynthetically active lamella in the S. subsalsa cell are those targets that can be easily damaged. Reversible and irreversible cell damage (cell necrosis) are also observed. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Reversible and Efficient Materials-based Actuation by Electrolytic Phase Transformation

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2003
C.G. Cameron
Abstract Electrolytic phase transformation is presented as a means of inducing reversible actuation in devices operating in a wide range of applications and scales. The device exploits the enormous pressure and volume changes that accompany the electrochemical interconversion between liquid and gas phases. With this method, strains beyond 136,000 % and stresses surpassing 200 MPa can be achieved, offering a level of performance many orders of magnitude beyond that of other materials-based strategies. [source]

Reversible 1,4-Cycloaddition of Singlet Oxygen to N-Substituted 2-Pyridones: 1,4-Endoperoxide as a Versatile Chemical Source of Singlet Oxygen.

CHEMINFORM, Issue 19 2005
Masakatsu Matsumoto
No abstract is available for this article. [source]

An Improvement in the Bending Ability of a Hinged Trisaccharide with the Assistance of a Sugar,,Sugar Interaction

CHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2005
Hideya Yuasa Prof.
Abstract Hinged di- and trisaccharides incorporating 2,4-diamino-,- D -xylopyranoside as a hinge unit (Hin) were synthesized. Bridging of the diamino group of Hin by carbonylation or chelation to a metal ion results in a conformational change from 4C1 to 1C4, which in turn causes a bending of the oligosaccharides. In this study, the bending abilities of the hinged oligosaccharides were compared, in terms of the reactivities toward carbonylation and chelation. Di- or trisaccharides containing a 6- O -glycosylated mannopyranoside or galactopyranoside at their reducing ends had bending abilities similar to that of the Hin monosaccharide, probably because there were neither attractive nor repulsive interactions between the reducing and nonreducing ends. However, when Hin was attached at O2 of methyl mannopyranoside (Man,Me), the bending ability was dependent on the nonreducing sugar and the reaction conditions. Typically, a disaccharide,Hin,(1,2)Man,Me,was difficult to bend under all the tested reaction conditions, and the bent population in the presence of ZnII was only 4,%. On the other hand, a trisaccharide,Man,(1,3)Hin,(1,2)Man,Me,was bent immediately after the addition of ZnII or HgII, and the bent population reached 75,%, much larger than those of all the other hinged trisaccharides ever tested (<40,%). This excellent bending ability suggests an attractive interaction between the reducing and nonreducing ends. The extended conformation was recovered by the addition of triethylenetetramine, a metal ion chelator. Reversible, quick, and efficient bending of the hinged trisaccharide was thus achieved. [source]

Tuning of Electronic Properties of Single-Walled Carbon Nanotubes under Homogenous Conditions

CHEMPHYSCHEM, Issue 6 2009
Yutaka Maeda Prof.
Abstract Reversible and non-bonding interaction between SWNTs and ODCB is observed from the analyses of visible near-infrared absorption data and Raman spectroscopies (see spectra). The solvent effect on SWNTs effectively controls the electronic structure of SWNTs under homogeneous conditions. The dispersion of single-walled carbon nanotubes (SWNTs) in o -dichlorobenzene (ODCB) is studied. Reversible and non-bonding interaction between SWNTs and ODCB is observed from the analyses of visible near-infrared (Vis-NIR) absorption data and Raman spectroscopy. This interaction should be one of the important factors for stable dispersion of SWNTs in ODCB. The solvent effect on SWNTs effectively controls the electronic structure of SWNTs under homogeneous conditions. [source]

Generalized treatment of NMR spectra for rapid chemical reactions

CONCEPTS IN MAGNETIC RESONANCE, Issue 4 2007
Matthew D. Christianson
Abstract Application of NMR spectroscopy to fast irreversible reactions (t1/2 < 0.7 s) has been hampered by limitations in instrumentation and general methods for modeling the complicated spectra that result. Analytical descriptions of nuclear spin dynamics during fast reactions, first solved by Ernst and coworkers, are limited to first-order reaction kinetics. We demonstrate that numeric methods enable simulation of NMR spectra for fast reactions having any form of rate law. Simulated stopped-flow NMR spectra are presented for a variety of common kinetic scenarios including reversible and irreversible reactions of first and second-order, multistep reactions, and catalytic transformations. The simulations demonstrate that a wealth of mechanistic information, including reaction rates, rate laws, and the existence of intermediates, is imbedded in a single NMR spectrum. The sensitivity of modern NMR instrumentation along with robust methods for simulating and fitting kinetic parameters of fast reactions make stopped-flow NMR an attractive method for kinetic studies of fast chemical reactions. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 165,183, 2007. [source]

Thalidomide for the treatment of multiple myeloma

CONGENITAL ANOMALIES, Issue 3 2004
Yutaka Hattori
ABSTRACT Although thalidomide was withdrawn in the 1960s after its teratogenic property was recognized, it was subsequently found that this drug possesses immunomodulatory and anti-inflammatory effects. Recent studies have also demonstrated that thalidomide has antineoplastic activity via an antiangiogenic mechanism. Observations in the late 1990s that the microenvironment in the bone marrow plays a role in tumor progression in multiple myeloma provided an impetus to use thalidomide for the treatment of this disease. It is known that thalidomide monotherapy is effective in one-third of refractory cases, and in combination with glucocorticoids and/or antineoplastic drugs, thalidomide provides a response rate of more than 50%. Thus, thalidomide therapy is considered a standard approach for the treatment of relapsed and refractory myeloma. The exact mechanism of the antimyeloma effect of thalidomide is not yet clearly understood. Anti-angiogenic effects, direct activity in tumor cells such as the induction of apoptosis or G1 arrest of the cell cycle, the inhibition of growth factor production, the regulation of interactions between tumor and stromal cells, and the modulation of tumor immunity have been considered as possible mechanisms. In addition to its teratogenicity, the adverse effects of thalidomide have been general symptoms such as somnolence and headache, peripheral neuropathy, constipation, skin rash, and other symptoms. Although these adverse effects are generally reversible and mild, grade 3 and 4 toxicities such as peripheral neuropathy, deep venous thrombosis, neutropenia, and toxic dermal necrosis have occasionally been reported. The application of thalidomide therapy in patients with multiple myeloma is being broadened to include not only cases of refractory myeloma, but also previously untreated cases, as well as for maintenance therapy after hematopoietic stem cell transplantation and for the treatment of other hematological diseases. The safe use of this drug will depend on the establishment of diagnostic and treatment guidelines. In addition, the establishment of a nation-wide regulation system is urgently needed in Japan. [source]

Percutaneous Closure of a Large PDA in a 35-Year-Old Man with Elevated Pulmonary Vascular Resistance

CONGENITAL HEART DISEASE, Issue 2 2008
John S. Hokanson MD
ABSTRACT The presence of a large patent ductus arteriosus (PDA) may result in significant pulmonary hypertension, which may not be reversible. We present the case of a 35-year-old man with pulmonary hypertension who had successful percutaneous closure of a large PDA with an Amplatzer muscular ventricular septal defect occluder and resolution of his pulmonary hypertension. The use of prior balloon test occlusion of the PDA suggested that the procedure would be successful, despite the lack of an immediate fall in the pulmonary artery pressure. [source]

Modulation of antigen expression in B-cell precursor acute lymphoblastic leukemia during induction therapy is partly transient: Evidence for a drug-induced regulatory phenomenon.

CYTOMETRY, Issue 3 2010
Results of the AIEOP-BFM-ALL-FLOW-MRD-Study Group
Abstract Background: Changes of antigen expression on residual blast cells of acute lymphoblastic leukemia (ALL) occur during induction treatment. Many markers used for phenotyping and minimal residual disease (MRD) monitoring are affected. Glucocorticoid (GC)-induced expression modulation has been causally suspected, however, subclone selection may also cause the phenomenon. Methods: We investigated this by following the phenotypic evolution of leukemic cells with flow cytometry from diagnosis to four time points during and after GC containing chemotherapy in the 20 (of 360 consecutive) B-cell precursor patients with ALL who had persistent MRD throughout. Results: The early expression changes of CD10 and CD34 were reversible after stop of GC containing chemotherapy. Modulation of CD20 and CD45 occurred mostly during the GC phase, whereas CD11a also changed later on. Blast cells at diagnosis falling into gates designed according to "shifted" phenotypes from follow-up did not form clusters and were frequently less numerous than later on. Conclusions: Our data support the idea that drug-induced modulation rather than selection causes the phenomenon. The good message for MRD assessment is that modulation is transient in at least two (CD10 and CD34) of the five prominent antigens investigated and reverts to initial aberrant patterns after stop of GC therapy, whereas CD20 expression gains new aberrations exploitable for MRD detection. © 2010 Clinical Cytometry Society [source]

MAP65 in tubulin/colchicine paracrystals of Vigna sinensis root cells: Possible role in the assembly and stabilization of atypical tubulin polymers,

CYTOSKELETON, Issue 3 2010
Emmanuel Panteris
Abstract Members of the MAP65 family, colocalizing with microtubule arrays, have been identified in Vigna sinensis root cells by Western blotting and immunofluorescence. MAP65 proteins were also found in tubulin/colchicine paracrystals, which were formed during colchicine treatment by both immunofluorescence and immunogold microscopy. During recovery from colchicine, MAP65 signal was depleted from disintegrating paracrystals appearing in the reinstating microtubule arrays. MAP65-free perinuclear tubulin/colchicine aggregates were observed in plasmolyzed colchicine-treated cells. Deplasmolysis of the above cells resulted in the formation of MAP65-decorated paracrystals. As confirmed by appropriate biochemical assays with the Phos-tag reagent, MAP65 proteins underwent phosphorylation during plasmolysis, which was reversible by deplasmolysis. According to the effect of the mitogen-activated protein kinase (MAPK) inhibitor UO126, the phosphorylation status of MAP65, as well as its presence in tubulin/colchicine polymers is probably controlled by MAPK-mediated phosphorylation. According to the above, it seems likely that apart from binding to microtubules, MAP65 proteins may act as "tubulin associated proteins" in a broader manner, promoting the polymerization and/or stabilization of atypical polymers such as tubulin/colchicine paracrystals. © 2010 Wiley-Liss, Inc. [source]

Susceptibility of isolated myofibrils to in vitro glutathionylation: Potential relevance to muscle functions,

CYTOSKELETON, Issue 2 2010
Chiara Passarelli
Abstract In this study we investigated the molecular mechanism of glutathionylation on isolated human cardiac myofibrils using several pro-glutathionylating agents. Total glutathionylated proteins appeared significantly enhanced with all the pro-oxidants used. The increase was completely reversed by the addition of a reducing agent, demonstrating that glutathione binding occurs by a disulfide and that the process is reversible. A sensitive target of glutathionylation was ,-actin, showing a different reactivity to the several pro-glutathionylating agents by ELISA. Noteworthy, myosin although highly sensitive to the in vitro glutathionylation does not represent the primary glutathionylation target in isolated myofibrils. Light scattering measurements of the glutathionylated ,-actin showed a slower polymerisation compared to the non-glutathionylated protein and force development was depressed after glutathionylation, when the myofibrils were mounted in a force recording apparatus. Interestingly, confocal laser scanning microscopy of cardiac cryosections indicated, for the first time, the constitutive glutathionylation of ,-cardiac actin in human heart. Due to the critical location of ,-actin in the contractile machinery and to its susceptibility to the oxidative modifications, glutathionylation may represent a mechanism for modulating sarcomere assembly and muscle functionality under patho-physiological conditions in vivo. © 2009 Wiley-Liss, Inc. [source]

Gadolinium, a mechano-sensitive channel blocker, inhibits osmosis-initiated motility of sea- and freshwater fish sperm, but does not affect human or ascidian sperm motility

CYTOSKELETON, Issue 4 2003
Zoltán Krasznai
Abstract Exposure to hypo-osmotic or hyperosmotic environment triggers the initiation of fish sperm motility. In this article, we report that calcium and potassium channel blockers do not influence motility of puffer fish sperm but calmodulin antagonists reversibly decrease it, suggesting that calmodulin,Ca2+ interactions are prerequisite for the initiation of sperm motility in this species. Gadolinium (a stretch activated ion channel blocker) decreased the motility of puffer fish sperm from 92 ± 3% to 6 ± 3% and that of carp sperm from 91 ± 7% to 3.5 ± 4.3% in a dose-dependent manner (10,40 ,M). The effect of gadolinium was reversible, suggesting that stretch activated ion channels participate in the initiation of sperm motility of the two species. Gadolinium inhibits changes in the isoelectric point of certain proteins of puffer fish sperm, which occur when sperm motility is initiated in a hypertonic solution. Anisotropy measurements showed that hypo-osmotic treatment, which initiates carp sperm motility, increased membrane fluidity. When hypo-osmotic treatment was given in the presence of gadolinium, the sperm membrane remained as rigid as in quiescent cells, while motility was blocked. By contrast, gadolinium did not influence the motility parameters of Ciona or human sperm. Based on these lines of evidence, we suggest that conformational changes of mechanosensitive membrane proteins are involved in osmolality-dependent but not osmolality-independent sperm. Cell Motil. Cytoskeleton 55:232,243, 2003. © 2003 Wiley-Liss, Inc. [source]

Treatment of Inflammatory Facial Acne Vulgaris with Intense Pulsed Light and Short Contact of Topical 5-Aminolevulinic Acid: A Pilot Study

DERMATOLOGIC SURGERY, Issue 8 2006
JINDA ROJANAMATIN MD
BACKGROUND Photodynamic therapy (PDT) with topical 5-aminolevulinic acid (ALA) and red light (550,700 nm) has been introduced for effective treatment of facial acne. Untoward side effects are common, however. OBJECTIVE To evaluate the efficacy and safety of the short contact of topical ALA and intense pulsed light (IPL) in treatment of inflammatory facial acne. METHODS Fourteen patients with inflammatory facial acne were treated with IPL on the left side and combination of IPL and topical ALA on the right side at 3- to 4-week intervals for three sessions. Clinical photographs and lesion counts were obtained for evaluation. RESULTS All patients revealed a reduction in number of acne lesions on both sides. On the ALA-pretreated side, lesion counts decreased 87.7% at 12 weeks after the last treatment (p<.01). Meanwhile, lesion counts on the nonpretreated side decreased 66.8% (p<.01). In addition, a number of lesion counts on the ALA-pretreated side decreased. Mild edema and minimal crust developed on the combined-treatment side. CONCLUSION Short contact of topical ALA and IPL or IPL alone showed some beneficial effect in treatment of inflammatory facial acne; however, degree of improvement was better and remained longer with the combined regimen. Side effects were mild and reversible. [source]

Tankyrase is necessary for canonical Wnt signaling during kidney development

DEVELOPMENTAL DYNAMICS, Issue 7 2010
Courtney M. Karner
Abstract Recent studies using small molecule antagonists have revealed that the poly(ADP-ribose) polymerases (PARPs) Tankyrase 1 and 2 are critical regulators of canonical Wnt signaling in some cellular contexts. However, the absence of any activity during zebrafish embryogenesis suggested that the tankyrases may not be general/core components of the Wnt pathway. Here, we show that Tnks1 and 2 are broadly expressed during mouse development and are essential during kidney and lung development. In the kidney, blockage of tankyrase activity phenocopies the effect of blocking production of all Wnt ligands. Tankyrase inhibition can be rescued by activation of ,-catenin demonstrating its specificity for the Wnt pathway. In addition, treatment with tankyrase inhibitors appears to be completely reversible in some cell types. These studies suggest that the tankyrases are core components of the canonical Wnt pathway and their inhibitors should enjoy broad usage as antagonists of Wnt signaling. Developmental Dynamics 239:2014,2023, 2010 © 2010 Wiley-Liss, Inc. [source]

Vascular regression is required for mesenchymal condensation and chondrogenesis in the developing limb

DEVELOPMENTAL DYNAMICS, Issue 3 2001
Melinda Yin
Abstract Vascular regression occurs during limb mesenchymal cell condensation and chondrogenesis, but it is unclear whether it is required for these processes or is a secondary phenomenon without major regulatory roles. To address this issue, beads presoaked with the potent angiogenic factor vascular endothelial growth factor (VEGF) were implanted in the vicinity of the prospective digit 2 in early chick embryo wing buds and the effects on angiogenesis and digit development were determined over time. We found that VEGF treatment caused a marked local increase in blood vessel number and density. Strikingly, this was accompanied by inhibition of digit 2 development as revealed by lack of expression of chondrogenic transcription factor Sox9 and absence of Alcian blue staining. Vascular distribution and skeletal development in adjacent areas remained largely unaffected. Inhibition of digit formation and excess vascularization were both reversible upon further embryonic growth and dissipation of VEGF activity. When supernumerary digits were induced at the anterior limb margin by retinoic acid treatment, their development was also preceded by vascular regression; interestingly, cotreatment with VEGF inhibited supernumerary digit development as well. Direct exposure of limb mesenchymal cells in micromass cultures to VEGF caused no obvious effects on condensation and chondrogenesis, indicating that VEGF effects are not due to direct action on skeletal cells. Our results are the first to provide evidence that vascular regression is required for mesenchymal condensation and chondrogenesis. A model of how patterning mechanisms and vascular regression may intersect and orchestrate limb skeletogenesis is proposed. © 2001 Wiley-Liss, Inc. [source]

Complete reconstruction of the retinal laminar structure from a cultured retinal pigment epithelium is triggered by altered tissue interaction and promoted by overlaid extracellular matrices

DEVELOPMENTAL NEUROBIOLOGY, Issue 14 2009
Fusako Kuriyama
Abstract The retina regenerates from retinal pigment epithelial (RPE) cells by transdifferentiation in the adult newt and Xenopus laevis when it is surgically removed. This was studied under a novel culture condition, and we succeeded, for the first time, in developing a complete retinal laminar structure from a single epithelial sheet of RPE. We cultured a Xenopus RPE monolayer sheet isolated from the choroid on a filter cup with gels overlaid and found that the retinal tissue structure differentiated with all retinal layers present. In the culture, RPE cells isolated themselves from the culture substratum (filter membrane), migrated, and reattached to the overlaid gel, on which they initiated transdifferentiation. This was exactly the same as observed during in vivo retina regeneration of X. laevis. In contrast, when RPE monolayers were cultured similarly without isolation from the choroid, RPE cells proliferated, but remained pigmented instead of transdifferentiating, indicating that alteration in tissue interaction triggers transdifferentiation. We then examined under the conventional tissue culture condition whether altered RPE-choroid interaction induces Pax6 expression. Pax6 was upregulated in RPE cells soon after they were removed from the choroid, and this expression was not dependent of FGF2. FGF2 administration was needed for RPE cells to maintain Pax6 expression. From the present results, in addition to our previous ones, we propose a two-step mechanism of transdifferentiation: the first step is a reversible process and is initiated by the alteration of the cell-extracellular matrix and/or cell,cell interaction followed by Pax6 upregulation. FGF2 plays a key role in driving RPE cells into the second step, during which they differentiate into retinal stem cells. © 2009 Wiley Periodicals, Inc. Develop Neurobiol, 2009 [source]

Gap junctions are involved in cell migration in the early postnatal subventricular zone

DEVELOPMENTAL NEUROBIOLOGY, Issue 11 2009
Mônica Marins
Abstract The massive migration of neuroblasts and young neurons through the anterior extension of the postnatal subventricular zone (SVZ), known as the rostral migratory stream (RMS) is still poorly understood on its molecular basis. In this work, we investigated the involvement of gap junctional communication (GJC) in the robust centrifugal migration from SVZ/RMS explants obtained from early postnatal (P4) rats. Cells were dye-coupled in homocellular and heterocellular pairings and expressed at least two connexins, Cx 43 and 45. Treatment with the uncoupler agent carbenoxolone (CBX, 10,100 ,M) reversibly reduced outgrowth from SVZ explants, while its inactive analog, glycyrhizinic acid (GZA), had no effect. Consistent with a direct effect on cell migration, time-lapse video microscopy show that different pharmacological uncouplers cause an abrupt and reversible arrest of cell movement in explants. Our results indicate that GJC is positively involved in the migration of neuroblasts within the SVZ/RMS. © 2009 Wiley Periodicals, Inc. Develop Neurobiol, 2009 [source]

Is insulin resistance caused by defects in insulin's target cells or by a stressed mind?

DIABETES/METABOLISM: RESEARCH AND REVIEWS, Issue 6 2005
Jonas Burén
Abstract The importance of understanding insulin action is emphasized by the increasing prevalence of insulin resistance in various populations and by the fact that it plays an important pathophysiological role in many common disorders, for example, diabetes, obesity, hypertension and dyslipidemia. The primary factors responsible for the development of insulin resistance are so far unknown, although both genetic and environmental factors are involved. The genetic defects responsible for the common forms of insulin resistance, for example, in type 2 diabetes, are largely unidentified. Some studies from our group as well as by other investigators suggest that cellular insulin resistance is reversible and that it may be secondary to factors in the in vivo environment. These may include insulin-antagonistic action of hormones like catecholamines, glucocorticoids, sex steroids and adipokines as well as dysregulation of autonomic nervous activity and they could contribute to the early development of insulin resistance. Some of these factors can directly impair glucose uptake capacity and this might be due to alterations in key proteins involved in insulin's intracellular signaling pathways. This article briefly summarizes proposed mechanisms behind cellular and whole-body insulin resistance. In particular, we question the role of intrinsic defects in insulin's target cells as primary mechanisms in the development of insulin resistance in type 2 diabetes and we suggest that metabolic and neurohormonal factors instead are the main culprits. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Reversible cognitive deterioration after a single episode of severe hypoglycaemia: a case report

DIABETIC MEDICINE, Issue 12 2004
T. Kubiak
Abstract A case of a male 34-year-old Type 1 diabetic patient who experienced a prolonged severe hypoglycaemic episode is presented. After the hypoglycaemic event, the patient suffered from moderate to severe neuropsychological impairments. On the basis of neuropsychological assessment results, diabetes therapy was modified (less complex insulin regimen, fixed insulin doses and fixed carbohydrate distribution). At a follow-up examination (3 months), presumable complete recovery of cognitive function was observed. This case demonstrates the possible detrimental neuropsychological effects of severe hypoglycaemia, that, in this case, turned out to be reversible. It highlights the clinical implications of impaired cognitive function on self-care and self-management abilities and the usefulness of neuropsychological testing in clinical diabetes care. [source]