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      Neural crest stem cell maintenance by combinatorial Wnt and BMP signaling

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          Abstract

          Canonical Wnt signaling instructively promotes sensory neurogenesis in early neural crest stem cells (eNCSCs) (Lee, H.Y., M. Kléber, L. Hari, V. Brault, U. Suter, M.M. Taketo, R. Kemler, and L. Sommer. 2004. Science. 303:1020–1023). However, during normal development Wnt signaling induces a sensory fate only in a subpopulation of eNCSCs while other cells maintain their stem cell features, despite the presence of Wnt activity. Hence, factors counteracting Wnt signaling must exist. Here, we show that bone morphogenic protein (BMP) signaling antagonizes the sensory fate-inducing activity of Wnt/β-catenin. Intriguingly, Wnt and BMP act synergistically to suppress differentiation and to maintain NCSC marker expression and multipotency. Similar to NCSCs in vivo, NCSCs maintained in culture alter their responsiveness to instructive growth factors with time. Thus, stem cell development is regulated by combinatorial growth factor activities that interact with changing cell-intrinsic cues.

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          Most cited references38

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          Convergence of Wnt, beta-catenin, and cadherin pathways.

          W Nelson (2004)
          The specification and proper arrangements of new cell types during tissue differentiation require the coordinated regulation of gene expression and precise interactions between neighboring cells. Of the many growth factors involved in these events, Wnts are particularly interesting regulators, because a key component of their signaling pathway, beta-catenin, also functions as a component of the cadherin complex, which controls cell-cell adhesion and influences cell migration. Here, we assemble evidence of possible interrelations between Wnt and other growth factor signaling, beta-catenin functions, and cadherin-mediated adhesion.
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            Multiple roles for activated LEF/TCF transcription complexes during hair follicle development and differentiation.

            LEF/TCF DNA-binding proteins act in concert with activated beta -catenin, the product of Wnt signaling, to transactivate downstream target genes. To probe the role of activated LEF/TCF transcription factor complexes in hair follicle morphogenesis and differentiation, we engineered mice harboring TOPGAL, a beta -galactosidase gene under the control of a LEF/TCF and beta -catenin inducible promoter. In mice, TOPGAL expression was directly stimulated by a stabilized form of beta -catenin, but was also dependent upon LEF1/TCF3 in skin. During embryogenesis, TOPGAL activation occurred transiently in a subset of LEF1-positive cells of pluripotent ectoderm and underlying mesenchyme. Downgrowth of initiated follicles proceeded in the absence of detectable TOPGAL expression, even though LEF1 was still expressed. While proliferative matrix cells expressed the highest levels of Lef1 mRNAs, LEF1 concentrated in the precursor cells to the hair shaft, where TOPGAL expression was co-induced with hair-specific keratin genes containing LEF/TCF-binding motifs. LEF1 and TOPGAL expression ceased during catagen and telogen, but reappeared at the start of the postnatal hair cycle, concomitant with precortex formation. In contrast to hair shaft precursor cells, postnatal outer root sheath expressed TCF3, but not TOPGAL. TCF3 was also expressed in the putative follicle stem cells, and while TOPGAL was generally silent in this compartment, it was stimulated at the start of the hair cycle in a fashion that appeared to be dependent upon stabilization of beta -catenin. Taken together, our findings demonstrate that LEF1/TCF3 is necessary but not sufficient for TOPGAL activation, revealing the existence of positive and negative regulators of these factors in the skin. Furthermore, our findings unveil the importance of activated LEF/TCF complexes at distinct times in hair development and cycling when changes in cell fate and differentiation commitments take place.
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              The Wnt/beta-catenin pathway directs neuronal differentiation of cortical neural precursor cells.

              Neural precursor cells (NPCs) have the ability to self-renew and to give rise to neuronal and glial lineages. The fate decision of NPCs between proliferation and differentiation determines the number of differentiated cells and the size of each region of the brain. However, the signals that regulate the timing of neuronal differentiation remain unclear. Here, we show that Wnt signaling inhibits the self-renewal capacity of mouse cortical NPCs, and instructively promotes their neuronal differentiation. Overexpression of Wnt7a or of a stabilized form of beta-catenin in mouse cortical NPC cultures induced neuronal differentiation even in the presence of Fgf2, a self-renewal-promoting factor in this system. Moreover, blockade of Wnt signaling led to inhibition of neuronal differentiation of cortical NPCs in vitro and in the developing mouse neocortex. Furthermore, the beta-catenin/TCF complex appears to directly regulate the promoter of neurogenin 1, a gene implicated in cortical neuronal differentiation. Importantly, stabilized beta-catenin did not induce neuronal differentiation of cortical NPCs at earlier developmental stages, consistent with previous reports indicating self-renewal-promoting functions of Wnts in early NPCs. These findings may reveal broader and stage-specific physiological roles of Wnt signaling during neural development.
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                Author and article information

                Journal
                J Cell Biol
                The Journal of Cell Biology
                The Rockefeller University Press
                0021-9525
                1540-8140
                25 April 2005
                : 169
                : 2
                : 309-320
                Affiliations
                [1 ]Institute of Cell Biology, Department of Biology, Swiss Federal Institute of Technology, ETH-Hönggerberg, CH-8093 Zurich, Switzerland
                [2 ]Department of Genetics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
                [3 ]Research Laboratory for Calcium Metabolism, University Hospital Balgrist, University of Zurich, CH-8008 Zurich, Switzerland
                Author notes

                Correspondence to Lukas Sommer: sommer@ 123456cell.biol.ethz.ch

                Article
                200411095
                10.1083/jcb.200411095
                2171862
                15837799
                3b88feed-7798-4cdb-ad35-07f30f4ba38f
                Copyright © 2005, The Rockefeller University Press
                History
                : 16 November 2004
                : 7 March 2005
                Categories
                Research Articles
                Article

                Cell biology
                Cell biology

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