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Michael Horn,
Reto Baumann,
Jorge A Pereira,
Páris N M Sidiropoulos,
Christian Somandin,
Hans Welzl,
Claudia Stendel,
Tessa Lühmann,
Carsten Wessig,
Klaus V Toyka, João B Relvas,
Jan Senderek,
Ueli Suter
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ABSTRACT: Studying the function and malfunction of genes and proteins associated with inherited forms of peripheral neuropathies has provided multiple clues to our understanding of myelinated nerves in health and disease. Here, we have generated a mouse model for the peripheral neuropathy Charcot-Marie-Tooth disease type 4H by constitutively disrupting the mouse orthologue of the suspected culprit gene FGD4 that encodes the small RhoGTPase Cdc42-guanine nucleotide exchange factor Frabin. Lack of Frabin/Fgd4 causes dysmyelination in mice in early peripheral nerve development, followed by profound myelin abnormalities and demyelination at later stages. At the age of 60 weeks, this was accompanied by electrophysiological deficits. By crossing mice carrying alleles of Frabin/Fgd4 flanked by loxP sequences with animals expressing Cre recombinase in a cell type-specific manner, we show that Schwann cell-autonomous Frabin/Fgd4 function is essential for proper myelination without detectable primary contributions from neurons. Deletion of Frabin/Fgd4 in Schwann cells of fully myelinated nerve fibres revealed that this protein is not only required for correct nerve development but also for accurate myelin maintenance. Moreover, we established that correct activation of Cdc42 is dependent on Frabin/Fgd4 function in healthy peripheral nerves. Genetic disruption of Cdc42 in Schwann cells of adult myelinated nerves resulted in myelin alterations similar to those observed in Frabin/Fgd4-deficient mice, indicating that Cdc42 and the Frabin/Fgd4-Cdc42 axis are critical for myelin homeostasis. In line with known regulatory roles of Cdc42, we found that Frabin/Fgd4 regulates Schwann cell endocytosis, a process that is increasingly recognized as a relevant mechanism in peripheral nerve pathophysiology. Taken together, our results indicate that regulation of Cdc42 by Frabin/Fgd4 in Schwann cells is critical for the structure and function of the peripheral nervous system. In particular, this regulatory link is continuously required in adult fully myelinated nerve fibres. Thus, mechanisms regulated by Frabin/Fgd4-Cdc42 are promising targets that can help to identify additional regulators of myelin development and homeostasis, which may crucially contribute also to malfunctions in different types of peripheral neuropathies.
Brain 11/2012; · 9.46 Impact Factor
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ABSTRACT: The regulation of adherens junctions (AJs) is critical for multiple events during CNS development, including the formation and maintenance of the neuroepithelium. We have addressed the role of the small GTPase RhoA in the developing mouse nervous system using tissue-specific conditional gene ablation. We show that, in the spinal cord neuroepithelium, RhoA is essential to localize N-cadherin and β-catenin to AJs and maintain apical-basal polarity of neural progenitor cells. Ablation of RhoA caused the loss of AJs and severe abnormalities in the organization of cells within the neuroepithelium, including decreased neuroepithelial cell proliferation and premature cell-cycle exit, reduction of the neural stem cell pool size, and the infiltration of neuroepithelial cells into the lumen of the ventricle. We also show that, in the absence of RhoA, its effector, mammalian diaphanous-related formin1 (mDia1), does not localize to apical AJs in which it likely stabilizes intracellular adhesion by promoting local actin polymerization and microtubule organization. Furthermore, expressing a dominant-negative form of mDia1 in neural stem/progenitor cells results in a similar phenotype compared with that of the RhoA conditional knock-out, namely the loss of AJs and apical polarity. Together, our data show that RhoA signaling is necessary for AJ regulation and for the maintenance of mammalian neuroepithelium organization preventing precocious cell-cycle exit and differentiation.
Journal of Neuroscience 03/2011; 31(13):5120-30. · 7.11 Impact Factor
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ABSTRACT: The thickness of the myelin sheath that insulates axons is fitted for optimal nerve conduction velocity. Here, we show that, in Schwann cells, mammalian disks large homolog 1 (Dlg1) interacts with PTEN (phosphatase and tensin homolog deleted on chromosome 10) to inhibit axonal stimulation of myelination. This mechanism limits myelin sheath thickness and prevents overmyelination in mouse sciatic nerves. Removing this brake results also in myelin outfoldings and demyelination, characteristics of some peripheral neuropathies. Indeed, the Dlg1 brake is no longer functional in a mouse model of Charcot-Marie-Tooth disease. Therefore, negative regulation of myelination appears to be essential for optimization of nerve conduction velocity and myelin maintenance.
Science 06/2010; 328(5984):1415-8. · 31.20 Impact Factor
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ABSTRACT: Diameter, organization, and length of the myelin sheath are important determinants of the nerve conduction velocity, but the basic molecular mechanisms that control these parameters are only partially understood. Cell polarization is an essential feature of differentiated cells, and relies on a set of evolutionarily conserved cell polarity proteins. We investigated the molecular nature of myelin sheath polarization in connection with the functional role of the cell polarity protein pals1 (Protein Associated with Lin Seven 1) during peripheral nerve myelin sheath extension. We found that, in regard to epithelial polarity, the Schwann cell outer abaxonal domain represents a basolateral-like domain, while the inner adaxonal domain and Schmidt-Lanterman incisures form an apical-like domain. Silencing of pals1 in myelinating Schwann cells in vivo resulted in a severe reduction of myelin sheath thickness and length. Except for some infoldings, the structure of compact myelin was not fundamentally affected, but cells produced less myelin turns. In addition, pals1 is required for the normal polarized localization of the vesicular markers sec8 and syntaxin4, and for the distribution of E-cadherin and myelin proteins PMP22 and MAG at the plasma membrane. Our data show that the polarity protein pals1 plays an essential role in the radial and longitudinal extension of the myelin sheath, likely involving a functional role in membrane protein trafficking. We conclude that regulation of epithelial-like polarization is a critical determinant of myelin sheath structure and function.
Journal of Neuroscience 03/2010; 30(11):4120-31. · 7.11 Impact Factor
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ABSTRACT: Reorganization of the actin cytoskeleton is necessary for Schwann cell proliferation, migration and for the morphological changes associated with sorting, ensheathing and myelination of axons. Such reorganization requires regulated severing and depolymerization of actin filaments. Gelsolin is an actin filament severing protein expressed in many cell types including Schwann cells. Using Gelsolin knockout mice, we investigated the role of this protein in the myelination and remyelination of the peripheral nervous system. Our results show that although gelsolin is not necessary for developmental myelination, it is required for timely remyelination of the sciatic nerve following crush injury. Gelsolin is necessary for macrophage motility in culture, and its absence is likely to impair the recruitment of macrophages to the injury site.
Glia 12/2009; 58(6):706-15. · 4.82 Impact Factor
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Jorge A Pereira,
Yves Benninger,
Reto Baumann,
Ana Filipa Gonçalves,
Murat Ozçelik,
Tina Thurnherr,
Nicolas Tricaud,
Dies Meijer,
Reinhard Fässler,
Ueli Suter, João B Relvas
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ABSTRACT: During development, Schwann cells (SCs) interpret different extracellular cues to regulate their migration, proliferation, and the remarkable morphological changes associated with the sorting, ensheathment, and myelination of axons. Although interactions between extracellular matrix proteins and integrins are critical to some of these processes, the downstream signaling pathways they control are still poorly understood. Integrin-linked kinase (ILK) is a focal adhesion protein that associates with multiple binding partners to link integrins to the actin cytoskeleton and is thought to participate in integrin and growth factor-mediated signaling. Using SC-specific gene ablation, we report essential functions for ILK in radial sorting of axon bundles and in remyelination in the peripheral nervous system. Our in vivo and in vitro experiments show that ILK negatively regulates Rho/Rho kinase signaling to promote SC process extension and to initiate radial sorting. ILK also facilitates axon remyelination, likely by promoting the activation of downstream molecules such as AKT/protein kinase B.
The Journal of Cell Biology 05/2009; 185(1):147-61. · 10.26 Impact Factor
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Sebastian Fuchs,
Dominik Herzog,
Grzegorz Sumara,
Stine Büchmann-Møller,
Gianluca Civenni,
Xunwei Wu,
Anna Chrostek-Grashoff,
Ueli Suter,
Romeo Ricci, João B Relvas,
Cord Brakebusch,
Lukas Sommer
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ABSTRACT: The neural crest (NC) generates a variety of neural and non-neural tissues during vertebrate development. Both migratory NC cells and their target structures contain cells with stem cell features. Here we show that these populations of neural crest-derived stem cells (NCSCs) are differentially regulated by small Rho GTPases. Deletion of either Cdc42 or Rac1 in the NC results in size reduction of multiple NC target structures because of increased cell-cycle exit, while NC cells emigrating from the neural tube are not affected. Consistently, Cdc42 or Rac1 inactivation reduces self-renewal and proliferation of later stage, but not early migratory NCSCs. This stage-specific requirement for small Rho GTPases is due to changes in NCSCs that, during development, acquire responsiveness to mitogenic EGF acting upstream of both Cdc42 and Rac1. Thus, our data reveal distinct mechanisms for growth control of NCSCs from different developmental stages.
Cell stem cell 04/2009; 4(3):236-47. · 23.56 Impact Factor
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ABSTRACT: RhoGTPases are molecular switches that integrate extracellular signals to perform diverse cellular responses. This ability relies on the network of proteins regulating RhoGTPases activity and localization, and on the interaction of RhoGTPases with many different cellular effectors. Myelination is an ideal place for RhoGTPases regulation, as it is the result of fine orchestration of many stimuli from at least two cell types. Recent work has revealed that RhoGTPases are required for Schwann cells to sort, ensheath, and myelinate axons. Here, we will review these recent advances showing the critical roles for RhoGTPases in various aspects of Schwann development and myelination, including the recent discovery of their involvement in Charcot-Marie-Tooth disease. Comparison with potential roles of RhoGTPases in central nervous system myelination will be drawn.
Glia 10/2008; 56(14):1508-17. · 4.82 Impact Factor
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ABSTRACT: A thorough knowledge of the cellular and molecular basis of the structure and function of peripheral nerves is of paramount importance not only for a better understanding of the fascinating biology of the peripheral nervous system but also for providing critical insights into the various diseases affecting peripheral nerves as the firm foundation of potential treatments. Genetic approaches in model organisms, in combination with research on hereditary forms of neuropathies, have contributed significantly to our progress in this field. In this review, we will focus on recent advances using these synergistic approaches that led to the identification of small Rho GTPases and their regulators as crucial functional players in proper development and function of myelinated peripheral nerves, with a particular emphasis on the cell biology of Schwann cells in health and disease.
Journal of the Peripheral Nervous System 10/2008; 13(3):188-99. · 2.80 Impact Factor
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Claudia Stendel,
Andreas Roos,
Tine Deconinck,
Jorge Pereira,
Francois Castagner,
Axel Niemann,
Janbernd Kirschner,
Rudolf Korinthenberg,
Uwe-Peter Ketelsen,
Esra Battaloglu, [......],
Peter De Jonghe,
Joachim Weis,
Alexander Krüttgen,
Sabine Rudnik-Schöneborn,
Carsten Bergmann,
Ueli Suter,
Klaus Zerres,
Vincent Timmerman, João B Relvas,
Jan Senderek
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ABSTRACT: GTPases of the Rho subfamily are widely involved in the myelination of the vertebrate nervous system. Rho GTPase activity is temporally and spatially regulated by a set of specific guanine nucleotide exchange factors (GEFs). Here, we report that disruption of frabin/FGD4, a GEF for the Rho GTPase cell-division cycle 42 (Cdc42), causes peripheral nerve demyelination in patients with autosomal recessive Charcot-Marie-Tooth (CMT) neuropathy. These data, together with the ability of frabin to induce Cdc42-mediated cell-shape changes in transfected Schwann cells, suggest that Rho GTPase signaling is essential for proper myelination of the peripheral nervous system.
The American Journal of Human Genetics 08/2007; 81(1):158-64. · 10.60 Impact Factor
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Yves Benninger,
Tina Thurnherr,
Jorge A Pereira,
Sven Krause,
Xunwei Wu,
Anna Chrostek-Grashoff,
Dominik Herzog,
Klaus-Armin Nave,
Robin J M Franklin,
Dies Meijer,
Cord Brakebusch,
Ueli Suter, João B Relvas
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ABSTRACT: During peripheral nervous system (PNS) myelination, Schwann cells must interpret extracellular cues to sense their environment and regulate their intrinsic developmental program accordingly. The pathways and mechanisms involved in this process are only partially understood. We use tissue-specific conditional gene targeting to show that members of the Rho GTPases, cdc42 and rac1, have different and essential roles in axon sorting by Schwann cells. Our results indicate that although cdc42 is required for normal Schwann cell proliferation, rac1 regulates Schwann cell process extension and stabilization, allowing efficient radial sorting of axon bundles.
The Journal of Cell Biology 07/2007; 177(6):1051-61. · 10.26 Impact Factor
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ABSTRACT: The formation of myelin sheaths in the CNS is the result of a complex series of events involving oligodendrocyte progenitor cell (OPC) proliferation, directed migration, and the morphological changes associated with axon ensheathment and myelination. To examine the role of Rho GTPases in oligodendrocyte biology, we have used a conditional tissue-specific gene-targeting approach. Ablation of Cdc42 in cells of the oligodendrocyte lineage did not affect OPC proliferation, directed migration, or in vitro differentiation, but it led to the formation of a unique and stage-specific myelination phenotype. This was characterized by the extraordinary enlargement of the inner tongue of the oligodendrocyte process and concomitant formation of a myelin outfolding as a result of abnormal accumulation of cytoplasm in this region. Ablation of Rac1 also resulted in the abnormal accumulation of cytoplasm in the inner tongue of the oligodendrocyte process, and we provide genetic evidence that rac1 synergizes with cdc42 in a gene dosage-dependent way to regulate myelination.
Journal of Neuroscience 11/2006; 26(40):10110-9. · 7.11 Impact Factor
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ABSTRACT: Previous reports, including transplantation experiments using dominant-negative inhibition of beta1-integrin signaling in oligodendrocyte progenitor cells, suggested that beta1-integrin signaling is required for myelination. Here, we test this hypothesis using conditional ablation of the beta1-integrin gene in oligodendroglial cells during the development of the CNS. This approach allowed us to study oligodendroglial beta1-integrin signaling in the physiological environment of the CNS, circumventing the potential drawbacks of a dominant-negative approach. We found that beta1-integrin signaling has a much more limited role than previously expected. Although it was involved in stage-specific oligodendrocyte cell survival, beta1-integrin signaling was not required for axon ensheathment and myelination per se. We also found that, in the spinal cord, remyelination occurred normally in the absence of beta1-integrin. We conclude that, although beta1-integrin may still contribute to other aspects of oligodendrocyte biology, it is not essential for myelination and remyelination in the CNS.
Journal of Neuroscience 08/2006; 26(29):7665-73. · 7.11 Impact Factor
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ABSTRACT: Neural stem cells give rise to undifferentiated nestin-positive progenitors that undergo extensive cell division before differentiating into neuronal and glial cells. The precise control of this process is likely to be, at least in part, controlled by instructive cues originating from the extracellular environment. Some of these cues are interpreted by the integrin family of extracellular matrix receptors. Using neurosphere cell cultures as a model system, we show that beta1-integrin signalling plays a crucial role in the regulation of progenitor cell proliferation, survival and migration. Following conditional genetic ablation of the beta1-integrin allele, and consequent loss of beta1-integrin cell surface protein, mutant nestin-positive progenitor cells proliferate less and die in higher numbers than their wild-type counterparts. Mutant progenitor cell migration on different ECM substrates is also impaired. These effects can be partially compensated by the addition of exogenous growth factors. Thus, beta1-integrin signalling and growth factor signalling tightly interact to control the number and migratory capacity of nestin-positive progenitor cells.
Journal of Cell Science 07/2005; 118(Pt 12):2589-99. · 6.11 Impact Factor
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ABSTRACT: To examine the role of the extracellular matrix in regulating astrocyte behavior we previously characterized αv integrin expression on postnatal astrocytes in vitro and found that they express αvβ5 and αvβ8. Here we show that differentiation of immature cells into astrocytes is accompanied by developmental regulation of αv integrins, downregulation of αvβ1 and αvβ8, and upregulation of αvβ5. In addition, using two previously described astrocyte cell lines, we found that the neurite-permissive A7 cell line expressed high levels of αvβ1 in addition to αvβ5 and αvβ8, while the neurite-inhibitory Neu7 cell line expressed only αvβ5. To examine integrin function we generated clones of the Neu7 cell line expressing αvβ1 or αvβ3 in addition to αvβ5. This showed that the parent Neu7 cells migrated more slowly than the A7 cells on fibronectin and vitronectin, but that Neu7 cells expressing αvβ1 or αvβ3 integrins showed enhanced migration on fibronectin and vitronectin, respectively. These results show that αv integrin expression is regulated during astrocyte development and confirm an instructive role in cell migration for αvβ1 in embryonic cells and αvβ3 in astroglial tumors.
Molecular and Cellular Neuroscience.
