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      Elucidating the Sources of β-Catenin Dynamics in Human Neural Progenitor Cells

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          Abstract

          Human neural progenitor cells (hNPCs) form a new prospect for replacement therapies in the context of neurodegenerative diseases. The Wnt/ -catenin signaling pathway is known to be involved in the differentiation process of hNPCs. RVM cells form a common cell model of hNPCs for in vitro investigation. Previous observations in RVM cells raise the question of whether observed kinetics of the Wnt/ -catenin pathway in later differentiation phases are subject to self-induced signaling. However, a concern when investigating RVM cells is that experimental results are possibly biased by the asynchrony of cells w.r.t. the cell cycle.

          In this paper, we present, based on experimental data, a computational modeling study on the Wnt/ -catenin signaling pathway in RVM cell populations asynchronously distributed w.r.t. to their cell cycle phases. Therefore, we derive a stochastic model of the pathway in single cells from the reference model in literature and extend it by means of cell populations and cell cycle asynchrony. Based on this, we show that the impact of the cell cycle asynchrony on wet-lab results that average over cell populations is negligible. We then further extend our model and the thus-obtained simulation results provide additional evidence that self-induced Wnt signaling occurs in RVM cells. We further report on significant stochastic effects that directly result from model parameters provided in literature and contradict experimental observations.

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          Most cited references34

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          It's a noisy business! Genetic regulation at the nanomolar scale.

          Many molecules that control genetic regulatory circuits act at extremely low intracellular concentrations. Resultant fluctuations (noise) in reaction rates cause large random variation in rates of development, morphology and the instantaneous concentration of each molecular species in each cell. To achieve regulatory reliability in spite of this noise, cells use redundancy in genes as well as redundancy and extensive feedback in regulatory pathways. However, some regulatory mechanisms exploit this noise to randomize outcomes where variability is advantageous.
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            Head inducer Dickkopf-1 is a ligand for Wnt coreceptor LRP6.

            Dickkopf-1 (Dkk-1) is a head inducer secreted from the vertebrate head organizer and induces anterior development by antagonizing Wnt signaling. Although several families of secreted antagonists have been shown to inhibit Wnt signal transduction by binding to Wnt, the molecular mechanism of Dkk-1 action is unknown. The Wnt family of secreted growth factors initiates signaling via the Frizzled (Fz) receptor and its candidate coreceptor, LDL receptor-related protein 6 (LRP6), presumably through Fz-LRP6 complex formation induced by Wnt. The significance of the Fz-LRP6 complex in signal transduction remains to be established. We report that Dkk-1 is a high-affinity ligand for LRP6 and inhibits Wnt signaling by preventing Fz-LRP6 complex formation induced by Wnt. Dkk-1 binds neither Wnt nor Fz, nor does it affect Wnt-Fz interaction. Dkk-1 function in head induction and Wnt signaling inhibition strictly correlates with its ability to bind LRP6 and to disrupt the Fz-LRP6 association. LRP6 function and Dkk-1 inhibition appear to be specific for the Wnt/Fz beta-catenin pathway. Our results demonstrate that Dkk-1 is an LRP6 ligand and inhibits Wnt signaling by blocking Wnt-induced Fz-LRP6 complex formation. Our findings thus reveal a novel mechanism for Wnt signal modulation. LRP6 is a Wnt coreceptor that appears to specify Wnt/Fz signaling to the beta-catenin pathway, and Dkk-1, distinct from Wnt binding antagonists, may be a specific inhibitor for Wnt/beta-catenin signaling. Our findings suggest that Wnt-Fz-LRP6 complex formation, but not Wnt-Fz interaction, triggers Wnt/beta-catenin signaling.
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              Biphasic role for Wnt/beta-catenin signaling in cardiac specification in zebrafish and embryonic stem cells.

              Understanding pathways controlling cardiac development may offer insights that are useful for stem cell-based cardiac repair. Developmental studies indicate that the Wnt/beta-catenin pathway negatively regulates cardiac differentiation, whereas studies with pluripotent embryonal carcinoma cells suggest that this pathway promotes cardiogenesis. This apparent contradiction led us to hypothesize that Wnt/beta-catenin signaling acts biphasically, either promoting or inhibiting cardiogenesis depending on timing. We used inducible promoters to activate or repress Wnt/beta-catenin signaling in zebrafish embryos at different times of development. We found that Wnt/beta-catenin signaling before gastrulation promotes cardiac differentiation, whereas signaling during gastrulation inhibits heart formation. Early treatment of differentiating mouse embryonic stem (ES) cells with Wnt-3A stimulates mesoderm induction, activates a feedback loop that subsequently represses the Wnt pathway, and increases cardiac differentiation. Conversely, late activation of beta-catenin signaling reduces cardiac differentiation in ES cells. Finally, constitutive overexpression of the beta-catenin-independent ligand Wnt-11 increases cardiogenesis in differentiating mouse ES cells. Thus, Wnt/beta-catenin signaling promotes cardiac differentiation at early developmental stages and inhibits it later. Control of this pathway may promote derivation of cardiomyocytes for basic research and cell therapy applications.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2012
                20 August 2012
                : 7
                : 8
                : e42792
                Affiliations
                [1 ]Modelling and Simulation Group, Institute of Computer Science, University of Rostock, Rostock, Germany
                [2 ]BioComputing Group, Lifl & Iri, University of Lille 1, Lille, France
                [3 ]Albrecht-Kossel-Institute for Neuroregeneration (AKos), Center for Mental Health, University of Rostock, Rostock, Germany
                Northwestern University Feinberg School of Medicine, United States of America
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: OM MJ AU. Performed the experiments: OM MJ SL. Analyzed the data: OM MJ AR AU. Contributed reagents/materials/analysis tools: OM MJ SL. Wrote the paper: OM MJ AU.

                Article
                PONE-D-11-09973
                10.1371/journal.pone.0042792
                3431164
                22952611
                d45443c1-0bc7-4c26-ac5e-bc417f5612ba
                Copyright @ 2012

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 6 June 2011
                : 11 July 2012
                Page count
                Pages: 12
                Funding
                This work has been supported as part of the research training group dIEM oSiRiS (The integrative development of modeling and simulation methods for regenerative systems) and the research project dIER MoSiS (Discrete event multi-level modeling and simulation for systems biology), both financed by the German foundation for research. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology
                Computational Biology
                Computational Neuroscience
                Signaling Networks
                Systems Biology
                Molecular Cell Biology
                Cellular Types
                Stem Cells
                Neural Stem Cells
                Signal Transduction
                Signaling Cascades
                WNT Signaling Cascade
                Signaling in Cellular Processes
                Beta-Catenin Signaling
                Signaling Pathways
                Catenin Signal Transduction
                Neuroscience
                Computational Neuroscience
                Computer Science
                Computer Modeling

                Uncategorized
                Uncategorized

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