Cord Brakebusch

Publications of Cord Brakebusch

• A Radial Glia-Specific Role of RhoA in Double Cortex Formation.

  Authors: Silvia Cappello, Christian R J Böhringer, Matteo Bergami, Karl-Klaus Conzelmann, Alexander Ghanem, Giulio Srubek Tomassy, Paola Arlotta, Marco Mainardi, Manuela Allegra, Matteo Caleo, Jolanda van Hengel, Cord Brakebusch, Magdalena Götz

  Neuron. 03/2012; 73(5):911-24.

  The positioning of neurons in the cerebral cortex is of crucial importance for its function as highlighted by the severe consequences of migrational disorders in patients. Here we show that geneticThe positioning of neurons in the cerebral cortex is of crucial importance for its function as highlighted by the severe consequences of migrational disorders in patients. Here we show that genetic deletion of the small GTPase RhoA in the developing cerebral cortex results in two migrational disorders: subcortical band heterotopia (SBH), a heterotopic cortex underlying the normotopic cortex, and cobblestone lissencephaly, in which neurons protrude beyond layer I at the pial surface of the brain. Surprisingly, RhoA(-/-) neurons migrated normally when transplanted into wild-type cerebral cortex, whereas the converse was not the case. Alterations in the radial glia scaffold are demonstrated to cause these migrational defects through destabilization of both the actin and the microtubules cytoskeleton. These data not only demonstrate that RhoA is largely dispensable for migration in neurons but also showed that defects in radial glial cells, rather than neurons, can be sufficient to produce SBH.

• A function for Rac1 in the terminal differentiation and pigmentation of hair.

  Authors: Kristina Behrendt, Jennifer Klatte, Ruth Pofahl, Wilhelm Bloch, Neil Smyth, Michael Tscharntke, Thomas Krieg, Ralf Paus, Carien Niessen, Catherin Niemann, Cord Brakebusch, Ingo Haase

  Journal of cell science. 01/2012;

  The small GTPase Rac1 is ubiquitiously expressed in proliferating and differentiating layers of the epidermis and hair follicles. Previously, Rac1 was shown to regulate stem cell behaviour in theseThe small GTPase Rac1 is ubiquitiously expressed in proliferating and differentiating layers of the epidermis and hair follicles. Previously, Rac1 was shown to regulate stem cell behaviour in these compartments. We have asked whether Rac1 has, in addition, a specific, stem cell independent function in the regulation of terminal hair follicle differentiation. To address this we have expressed a constitutively active mutant of Rac1, L61Rac1, only in the basal epidermal layer and outer root sheath of mice with epidermis specific deletion of endogenous Rac1, which show severe hair loss. The resulting Rescue mice exhibited a hair coat throughout their lives. Therefore, expression of Rac1 activity in the keratin 14 positive compartment of the skin is sufficient for the formation of hair follicles and hair at normal quantity. The quality of hair formed in Rescue mice was, however, not normal. Rescue mice showed a grey, dull hair coat, whereas that of wild type and L61Rac1 transgenic mice was black and shiny. Hair analysis in Rescue mice revealed altered structures of the hair shaft and the cuticle and disturbed organization of medulla cells and pigment distribution. Disorganization of medulla cells correlates with the absence of cortical, keratin filled spikes that normally protrude from the cortex into the medulla. The desmosomal cadherin Dsc2, which normally decorates these protrusions, was found to be reduced or absent in the hair of Rescue mice. Our study demonstrates regulatory functions for Rac1 in hair structure formation and -pigmentation and thereby identifies, for the first time, a role for Rac1 in terminal differentiation.

• Rho GTPase knockout induction in primary keratinocytes from adult mice.

  Authors: Esben Pedersen, Astrid Basse, Tine Lefever, Karine Peyrollier, Cord Brakebusch

  Methods in molecular biology (Clifton, N.J.). 01/2012; 827:157-66.

  Primary keratinocytes are an important tool to investigate the molecular mechanism underlying the skin phenotype of mice with null mutations in Rho GTPase genes. If the RhoA gene deletion isPrimary keratinocytes are an important tool to investigate the molecular mechanism underlying the skin phenotype of mice with null mutations in Rho GTPase genes. If the RhoA gene deletion is conditional, the knockout can be induced in vitro by transfection with cre-IRES-GFP and sorting for GFP positive cells by flow cytometry. Such in vitro knockout will allow determining the cell autonomous functions of the Rho GTPase, independent of any in vivo interactions. Using the same method, also other expression vectors or knockdown constructs can be introduced into primary mouse keratinocytes.

• Megakaryocyte-specific RhoA deficiency causes macrothrombocytopenia and defective platelet activation in hemostasis and thrombosis.

  Authors: Irina Pleines, Ina Hagedorn, Shuchi Gupta, Frauke May, Lidija Chakarova, Jolanda van Hengel, Stefan Offermanns, Georg Krohne, Christoph Kleinschnitz, Cord Brakebusch, Bernhard Nieswandt

  Blood. 11/2011; 119(4):1054-63.

  Vascular injury initiates rapid platelet activation that is critical for hemostasis, but it also may cause thrombotic diseases, such as myocardial infarction or ischemic stroke. Reorganizations ofVascular injury initiates rapid platelet activation that is critical for hemostasis, but it also may cause thrombotic diseases, such as myocardial infarction or ischemic stroke. Reorganizations of the platelet cytoskeleton are crucial for platelet shape change and secretion and are thought to involve activation of the small GTPase RhoA. In this study, we analyzed the in vitro and in vivo consequences of megakaryocyte- and platelet-specific RhoA gene deletion in mice. We found a pronounced macrothrombocytopenia in RhoA-deficient mice, with platelet counts of approximately half that of wild-type controls. The mutant cells displayed an altered shape but only a moderately reduced life span. Shape change of RhoA-deficient platelets in response to G(13)-coupled agonists was abolished, and it was impaired in response to G(q) stimulation. Similarly, RhoA was required for efficient secretion of α and dense granules downstream of G(13) and G(q). Furthermore, RhoA was essential for integrin-mediated clot retraction but not for actomyosin rearrangements and spreading of activated platelets on fibrinogen. In vivo, RhoA deficiency resulted in markedly prolonged tail bleeding times but also significant protection in different models of arterial thrombosis and in a model of ischemic stroke. Together, these results establish RhoA as an important regulator of platelet function in thrombosis and hemostasis.

• Genetic deletion of cdc42 reveals a crucial role for astrocyte recruitment to the injury site in vitro and in vivo.

  Authors: Stefanie Robel, Sophia Bardehle, Alexandra Lepier, Cord Brakebusch, Magdalena Götz

  The Journal of neuroscience : the official journal of the Society for Neuroscience. 08/2011; 31(35):12471-82.

  It is generally suggested that astrocytes play important restorative functions after brain injury, yet little is known regarding their recruitment to sites of injury, despite numerous in vitroIt is generally suggested that astrocytes play important restorative functions after brain injury, yet little is known regarding their recruitment to sites of injury, despite numerous in vitro experiments investigating astrocyte polarity. Here, we genetically manipulated one of the proposed key signals, the small RhoGTPase Cdc42, selectively in mouse astrocytes in vitro and in vivo. We used an in vitro scratch assay as a minimal wounding model and found that astrocytes lacking Cdc42 (Cdc42Δ) were still able to form protrusions, although in a nonoriented way. Consequently, they failed to migrate in a directed manner toward the scratch. When animals were injured in vivo through a stab wound, Cdc42Δ astrocytes developed protrusions properly oriented toward the lesion, but the number of astrocytes recruited to the lesion site was significantly reduced. Surprisingly, however, lesions in Cdc42Δ animals, harboring fewer astrocytes contained significantly higher numbers of microglial cells than controls. These data suggest that impaired recruitment of astrocytes to sites of injury has a profound and unexpected effect on microglia recruitment.

• Cdc42 controls vascular network assembly through protein kinase Cι during embryonic vasculogenesis.

  Authors: Yanmei Qi, Jie Liu, Xunwei Wu, Cord Brakebusch, Michael Leitges, Yaling Han, Siobhan A Corbett, Stephen F Lowry, Alan M Graham, Shaohua Li

  Arteriosclerosis, thrombosis, and vascular biology. 06/2011; 31(8):1861-70.

  The goal of this study was to determine the role of Cdc42 in embryonic vasculogenesis and the underlying mechanisms. By using genetically modified mouse embryonic stem (ES) cells, we demonstrate thatThe goal of this study was to determine the role of Cdc42 in embryonic vasculogenesis and the underlying mechanisms. By using genetically modified mouse embryonic stem (ES) cells, we demonstrate that ablation of the Rho GTPase Cdc42 blocks vascular network assembly during embryoid body (EB) vasculogenesis without affecting endothelial lineage differentiation. Reexpression of Cdc42 in mutant EBs rescues the mutant phenotype, establishing an essential role for Cdc42 in vasculogenesis. Chimeric analysis revealed that the vascular phenotype is caused by inactivation of Cdc42 in endothelial cells rather than surrounding cells. Endothelial cells isolated from Cdc42-null EBs are defective in directional migration and network assembly. In addition, activation of atypical protein kinase Cι (PKCι) is abolished in Cdc42-null endothelial cells, and PKCι ablation phenocopies the vascular abnormalities of the Cdc42-null EBs. Moreover, the inhibitory phosphorylation of glycogen synthase kinase-3β (GSK-3β) at Ser9 depends on Cdc42 and PKCι, and expression of kinase-dead GSK-3β in Cdc42-null EBs promotes the formation of linear endothelial segments without branches. These results suggest that PKCι and GSK-3β are downstream effectors of Cdc42 during vascular morphogenesis. Cdc42 controls vascular network assembly but not endothelial lineage differentiation by activating PKCι during embryonic vasculogenesis.

• The small GTPase RhoA is required to maintain spinal cord neuroepithelium organization and the neural stem cell pool.

  Authors: Dominik Herzog, Pirmin Loetscher, Jolanda van Hengel, Sebastian Knüsel, Cord Brakebusch, Verdon Taylor, Ueli Suter, João B Relvas

  The Journal of neuroscience : the official journal of the Society for Neuroscience. 03/2011; 31(13):5120-30.

  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 theThe 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.

• Rhoh deficiency reduces peripheral T-cell function and attenuates allogenic transplant rejection.

  Authors: Stefan Porubsky, Shijun Wang, Eva Kiss, Stefan Dehmel, Mahnaz Bonrouhi, Tatjana Dorn, Bruno Luckow, Cord Brakebusch, Hermann-Josef Gröne

  European journal of immunology. 01/2011; 41(1):76-88.

  Rhoh is a hematopoietic system-specific GTPase. Rhoh-deficient T cells have been shown to have a defect in TCR signaling manifested during their thymic development. Our aims were to investigate theRhoh is a hematopoietic system-specific GTPase. Rhoh-deficient T cells have been shown to have a defect in TCR signaling manifested during their thymic development. Our aims were to investigate the phenotype of peripheral Rhoh-deficient T cells and to explore in vivo the potential benefit of Rhoh deficiency in a clinically relevant situation, in which T-cell inhibition is desirable. In murine allogenic kidney transplantation, Rhoh deficiency caused a significant 75% reduction of acute and chronic transplant rejection accompanied by 75% lower alloantigen-specific antibody levels and significantly better graft function. This effect was independent of the lower T-cell numbers in Rhoh-deficient recipients, because injection of equal numbers of Rhoh-deficient or control T cells into kidney transplanted mice with SCID led again to a significant 60% reduction of rejection. Mixed lymphocyte reaction revealed that the weaker alloreactivity was associated with a 85% lower cytotoxicity and a 50-80% lower cytokine release in Rhoh-deficient T cells without an influence on the secretion itself. Antigen uptake and presentation in DC were unaffected by Rhoh deficiency. These findings stress the importance of Rhoh for the function of peripheral T cells.

• RhoA is dispensable for skin development, but crucial for contraction and directed migration of keratinocytes.

  Authors: Ben Jackson, Karine Peyrollier, Esben Pedersen, Astrid Basse, Richard Karlsson, Zhipeng Wang, Tine Lefever, Alexandra M Ochsenbein, Gudula Schmidt, Klaus Aktories, Alanna Stanley, Fabio Quondamatteo, Markus Ladwein, Klemens Rottner, Jolanda van Hengel, Cord Brakebusch

  Molecular biology of the cell. 01/2011; 22(5):593-605.

  RhoA is a small guanosine-5'-triphosphatase (GTPase) suggested to be essential for cytokinesis, stress fiber formation, and epithelial cell-cell contacts. In skin, loss of RhoA was suggested toRhoA is a small guanosine-5'-triphosphatase (GTPase) suggested to be essential for cytokinesis, stress fiber formation, and epithelial cell-cell contacts. In skin, loss of RhoA was suggested to underlie pemphigus skin blistering. To analyze RhoA function in vivo, we generated mice with a keratinocyte-restricted deletion of the RhoA gene. Despite a severe reduction of cofilin and myosin light chain (MLC) phosphorylation, these mice showed normal skin development. Primary RhoA-null keratinocytes, however, displayed an increased percentage of multinucleated cells, defective maturation of cell-cell contacts. Furthermore we observed increased cell spreading due to impaired RhoA-ROCK (Rho-associated protein kinase)-MLC phosphatase-MLC-mediated cell contraction, independent of Rac1. Rho-inhibiting toxins further increased multinucleation of RhoA-null cells but had no significant effect on spreading, suggesting that RhoB and RhoC have partially overlapping functions with RhoA. Loss of RhoA decreased directed cell migration in vitro caused by reduced migration speed and directional persistence. These defects were not related to the decreased cell contraction and were independent of ROCK, as ROCK inhibition by Y27632 increased directed migration of both control and RhoA-null keratinocytes. Our data indicate a crucial role for RhoA and contraction in regulating cell spreading and a contraction-independent function of RhoA in keratinocyte migration. In addition, our data show that RhoA is dispensable for skin development.

• The rho GTPase Rac1 is required for proliferation and survival of progenitors in the developing forebrain.

  Authors: Dino P Leone, Karpagam Srinivasan, Cord Brakebusch, Susan K McConnell

  Developmental neurobiology. 08/2010; 70(9):659-78.

  Progenitor cells in the ventricular zone (VZ) and subventricular zone (SVZ) of the developing forebrain give rise to neurons and glial cells, and are characterized by distinct morphologies andProgenitor cells in the ventricular zone (VZ) and subventricular zone (SVZ) of the developing forebrain give rise to neurons and glial cells, and are characterized by distinct morphologies and proliferative behaviors. The mechanisms that distinguish VZ and SVZ progenitors are not well understood, although the homeodomain transcription factor Cux2 and Cyclin D2, a core component of the cell cycle machinery, are specifically involved in controlling SVZ cell proliferation. Rho GTPases have been implicated in regulating the proliferation, differentiation, and migration of many cell types, and one family member, Cdc42, affects the polarity and proliferation of radial glial cells in the VZ. Here, we show that another family member, Rac1, is required for the normal proliferation and differentiation of SVZ progenitors and for survival of both VZ and SVZ progenitors. A forebrain-specific loss of Rac1 leads to an SVZ-specific reduction in proliferation, a concomitant increase in cell cycle exit, and premature differentiation. In Rac1 mutants, the SVZ and VZ can no longer be delineated, but rather fuse to become a single compact zone of intermingled cells. Cyclin D2 expression, which is normally expressed by both VZ and SVZ progenitors, is reduced in Rac1 mutants, suggesting that the mutant cells differentiate precociously. Rac1-deficient mice can still generate SVZ-derived upper layer neurons, indicating that Rac1 is not required for the acquisition of upper layer neuronal fates, but instead is needed for the normal regulation of proliferation by progenitor cells in the SVZ.

• Rac1 regulates neuronal polarization through the WAVE complex.

  Authors: Sabina Tahirovic, Farida Hellal, Dorothee Neukirchen, Robert Hindges, Boyan K Garvalov, Kevin C Flynn, Theresia E Stradal, Anna Chrostek-Grashoff, Cord Brakebusch, Frank Bradke

  The Journal of neuroscience : the official journal of the Society for Neuroscience. 05/2010; 30(20):6930-43.

  Neuronal migration and axon growth, key events during neuronal development, require distinct changes in the cytoskeleton. Although many molecular regulators of polarity have been identified andNeuronal migration and axon growth, key events during neuronal development, require distinct changes in the cytoskeleton. Although many molecular regulators of polarity have been identified and characterized, relatively little is known about their physiological role in this process. To study the physiological function of Rac1 in neuronal development, we have generated a conditional knock-out mouse, in which Rac1 is ablated in the whole brain. Rac1-deficient cerebellar granule neurons, which do not express other Rac isoforms, showed impaired neuronal migration and axon formation both in vivo and in vitro. In addition, Rac1 ablation disrupts lamellipodia formation in growth cones. The analysis of Rac1 effectors revealed the absence of the Wiskott-Aldrich syndrome protein (WASP) family verprolin-homologous protein (WAVE) complex from the plasma membrane of knock-out growth cones. Loss of WAVE function inhibited axon growth, whereas overexpression of a membrane-tethered WAVE mutant partially rescued axon growth in Rac1-knock-out neurons. In addition, pharmacological inhibition of the WAVE complex effector Arp2/3 also reduced axon growth. We propose that Rac1 recruits the WAVE complex to the plasma membrane to enable actin remodeling necessary for axon growth.

• Rac1 is essential for basement membrane-dependent epiblast survival.

  Authors: Xiaowen He, Jie Liu, Yanmei Qi, Cord Brakebusch, Anna Chrostek-Grashoff, David Edgar, Peter D Yurchenco, Siobhan A Corbett, Stephen F Lowry, Alan M Graham, Yaling Han, Shaohua Li

  Molecular and cellular biology. 05/2010; 30(14):3569-81.

  During murine peri-implantation development, the egg cylinder forms from a solid cell mass by the apoptotic removal of inner cells that do not contact the basement membrane (BM) and the selectiveDuring murine peri-implantation development, the egg cylinder forms from a solid cell mass by the apoptotic removal of inner cells that do not contact the basement membrane (BM) and the selective survival of the epiblast epithelium, which does. The signaling pathways that mediate this fundamental biological process are largely unknown. Here we demonstrate that Rac1 ablation in embryonic stem cell-derived embryoid bodies (EBs) leads to massive apoptosis of epiblast cells in contact with the BM. Expression of wild-type Rac1 in the mutant EBs rescues the BM-contacting epiblast, while expression of a constitutively active Rac1 additionally blocks the apoptosis of inner cells and cavitation, indicating that the spatially regulated activation of Rac1 is required for epithelial cyst formation. We further show that Rac1 is activated through integrin-mediated recruitment of the Crk-DOCK180 complex and mediates BM-dependent epiblast survival through activating the phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway. Our results reveal a signaling cascade triggered by cell-BM interactions essential for epithelial morphogenesis.

• Multiple alterations of platelet functions dominated by increased secretion in mice lacking Cdc42 in platelets.

  Authors: Irina Pleines, Anita Eckly, Margitta Elvers, Ina Hagedorn, Sandra Eliautou, Markus Bender, Xunwei Wu, Francois Lanza, Christian Gachet, Cord Brakebusch, Bernhard Nieswandt

  Blood. 02/2010; 115(16):3364-73.

  Platelet activation at sites of vascular injury is crucial for hemostasis, but it may also cause myocardial infarction or stroke. Cytoskeletal reorganization is essential for platelet activation andPlatelet activation at sites of vascular injury is crucial for hemostasis, but it may also cause myocardial infarction or stroke. Cytoskeletal reorganization is essential for platelet activation and secretion. The small GTPase Cdc42 has been implicated as an important mediator of filopodia formation and exocytosis in various cell types, but its exact function in platelets is not established. Here, we show that the megakaryocyte/platelet-specific loss of Cdc42 leads to mild thrombocytopenia and a small increase in platelet size in mice. Unexpectedly, Cdc42-deficient platelets were able to form normally shaped filopodia and spread fully on fibrinogen upon activation, whereas filopodia formation upon selective induction of GPIb signaling was reduced compared with wild-type platelets. Furthermore, Cdc42-deficient platelets showed enhanced secretion of alpha granules, a higher adenosine diphosphate (ADP)/adenosine triphosphate (ATP) content, increased aggregation at low agonist concentrations, and enhanced aggregate formation on collagen under flow. In vivo, lack of Cdc42 resulted in faster occlusion of ferric chloride-injured arterioles. The life span of Cdc42-deficient platelets was markedly reduced, suggesting increased clearing of the cells under physiologic conditions. These data point to novel multiple functions of Cdc42 in the regulation of platelet activation, granule organization, degranulation, and a specific role in GPIb signaling.

• N-WASP is a novel regulator of hair-follicle cycling that controls antiproliferative TGF{beta} pathways.

  Authors: Tine Lefever, Esben Pedersen, Astrid Basse, Ralf Paus, Fabio Quondamatteo, Alanna C Stanley, Lutz Langbein, Xunwei Wu, Jürgen Wehland, Silvia Lommel, Cord Brakebusch

  Journal of cell science. 01/2010; 123(Pt 1):128-40.

  N-WASP is a cytoplasmic molecule mediating Arp2/3 nucleated actin polymerization. Mice with a keratinocyte-specific deletion of the gene encoding N-WASP showed normal interfollicular epidermis, butN-WASP is a cytoplasmic molecule mediating Arp2/3 nucleated actin polymerization. Mice with a keratinocyte-specific deletion of the gene encoding N-WASP showed normal interfollicular epidermis, but delayed hair-follicle morphogenesis and abnormal hair-follicle cycling, associated with cyclic alopecia and prolonged catagen and telogen phases. The delayed anagen onset correlated with an increased expression of the cell-cycle inhibitor p21CIP, and increased activity of the TGFbeta pathway, a known inducer of p21CIP expression. Primary N-WASP-null keratinocytes showed reduced growth compared with control cells and enhanced expression of the gene encoding the cell-cycle inhibitor p15INK4B, a TGFbeta target gene. Inhibition of TGFbeta signaling blocked overexpression of p15INK4B and restored proliferation of N-WASP-deficient keratinocytes in vitro. However, induction of N-WASP gene deletion in vitro did not result in obvious changes in TGFbeta signaling or growth of keratinocytes, indicating that the in vivo environment is required for the phenotype development. These data identify the actin nucleation regulator N-WASP as a novel element of hair-cycle control that modulates the antiproliferative and pro-apoptotic TGFbeta pathway in keratinocytes in vivo and in vitro.

• A central role for the small GTPase Rac1 in hippocampal plasticity and spatial learning and memory.

  Authors: Ursula Haditsch, Dino P Leone, Mélissa Farinelli, Anna Chrostek-Grashoff, Cord Brakebusch, Isabelle M Mansuy, Susan K McConnell, Theo D Palmer

  Molecular and cellular neurosciences. 05/2009;

  Rac1 is a member of the Rho family of small GTPases that are important for structural aspects of the mature neuronal synapse including basal spine density and shape, activity-dependent spineRac1 is a member of the Rho family of small GTPases that are important for structural aspects of the mature neuronal synapse including basal spine density and shape, activity-dependent spine enlargement, and AMPA receptor clustering in vitro. Here we demonstrate that selective elimination of Rac1 in excitatory neurons in the forebrain in vivo not only affects spine structure, but also impairs synaptic plasticity in the hippocampus with consequent defects in hippocampus-dependent spatial learning. Furthermore, Rac1 mutants display deficits in working/episodic-like memory in the delayed matching-to-place (DMP) task suggesting that Rac1 is a central regulator of rapid encoding of novel spatial information in vivo.

• Rho GTPase function in tumorigenesis.

  Authors: R Karlsson, E D Pedersen, Z Wang, Cord Brakebusch

  Biochimica et biophysica acta. 04/2009;

  Malignant tumor cells display uncontrolled proliferation, loss of epithelial cell polarity, altered interactions with neighboring cells and the surrounding extracellular matrix, and enhancedMalignant tumor cells display uncontrolled proliferation, loss of epithelial cell polarity, altered interactions with neighboring cells and the surrounding extracellular matrix, and enhanced migratory properties. Proteins of the Rho GTPase family regulate all these processes in cell culture and, for that reason, Rho GTPases, their regulators, and their effectors have been suggested to control tumor formation and progression in humans. However, while the tumor-relevant functions of Rho GTPases are very well documented in vitro, we are only now beginning to assess their contribution to cancer in human patients and in animal models. This review will give a very brief overview of Rho GTPase function in general and then focus on in vivo evidence for a role of Rho GTPases in malignant tumors, both in human patients and in genetically modified mice.

• Stage-specific control of neural crest stem cell proliferation by the small rho GTPases Cdc42 and Rac1.

  Authors: 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

  Cell stem cell. 04/2009; 4(3):236-47.

  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.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.

• Cdc42-dependent leading edge coordination is essential for interstitial dendritic cell migration.

  Authors: Tim Lammermann, Jorg Renkawitz, Xunwei Wu, Karin Hirsch, Cord Brakebusch, Michael Sixt

  Blood. 03/2009;

  Mature dendritic cells (DCs) moving from the skin to the lymph node are a prototypic example of rapidly migrating amoeboid leukocytes. Interstitial DC migration is directionally guided by chemokines,Mature dendritic cells (DCs) moving from the skin to the lymph node are a prototypic example of rapidly migrating amoeboid leukocytes. Interstitial DC migration is directionally guided by chemokines, but independent of specific adhesive interactions with the tissue as well as pericellular proteolysis. Instead, the protrusive flow of the actin cytoskeleton directly drives a basal mode of locomotion that is occasionally supported by actomyosin contractions at the trailing edge to propel the cell's rigid nucleus. We here delete the small GTPase Cdc42 in DCs and find that actin flow and actomyosin contraction are still initiated in response to chemotactic cues. Accordingly, the cells are able to polarize and form protrusions. However, in the absence of Cdc42 the protrusions are temporally and spatially dysregulated which leads to impaired leading edge coordination. While this defect still allows the cells to move on two-dimensional surfaces, their in vivo motility is completely abrogated. We show that this difference is entirely caused by the geometrical complexity of the environment as multiple competing protrusions lead to instantaneous entanglement within three-dimensional extracellular matrix scaffolds. This demonstrates that the decisive factor for migrating DCs is not specific interaction with the extracellular environment, but adequate coordination of cytoskeletal flow.

• {beta}1 integrins differentially control extravasation of inflammatory cell subsets into the CNS during autoimmunity.

  Authors: Martina Bauer, Cord Brakebusch, Caroline Coisne, Michael Sixt, Hartmut Wekerle, Britta Engelhardt, Reinhard Fässler

  Proceedings of the National Academy of Sciences of the United States of America. 02/2009;

  Inhibiting the alpha(4) subunit of the integrin heterodimers alpha(4)beta(1) and alpha(4)beta(7) with the monoclonal antibody natalizumab is an effective treatment for multiple sclerosis (MS).Inhibiting the alpha(4) subunit of the integrin heterodimers alpha(4)beta(1) and alpha(4)beta(7) with the monoclonal antibody natalizumab is an effective treatment for multiple sclerosis (MS). However, the pharmacological action of natalizumab is not understood conclusively. Previous studies suggested that natalizumab inhibits activation, proliferation, or extravasation of inflammatory cells. To specify which mechanisms, cell types, and alpha(4) heterodimers are affected by the antibody treatment, we studied MS-like experimental autoimmune encephalomyelitis (EAE) in mice lacking the beta(1)-integrin gene either in all hematopoietic cells or selectively in T lymphocytes. Our results show that T cells critically rely on beta(1) integrins to accumulate in the central nervous system (CNS) during EAE, whereas CNS infiltration of beta(1)-deficient myeloid cells remains unaffected, suggesting that T cells are the main target of anti-alpha(4)-antibody blockade. We demonstrate that beta(1)-integrin expression on encephalitogenic T cells is critical for EAE development, and we therefore exclude alpha(4)beta(7) as a target integrin of the antibody treatment. T cells lacking beta(1) integrin are unable to firmly adhere to CNS endothelium in vivo, whereas their priming and expansion remain unaffected. Collectively, these results suggest that the primary action of natalizumab is interference with T cell extravasation via inhibition of alpha(4)beta(1) integrins.

• Beta1 integrin-mediated adhesion signalling is essential for epidermal progenitor cell expansion.

  Authors: Aleksandra Piwko-Czuchra, Heidi Koegel, Hannelore Meyer, Martina Bauer, Sabine Werner, Cord Brakebusch, Reinhard Fässler

  PLoS ONE. 02/2009; 4(5):e5488.

  BACKGROUND: There is a major discrepancy between the in vitro and in vivo results regarding the role of beta1 integrins in the maintenance of epidermal stem/progenitor cells. Studies of mice withBACKGROUND: There is a major discrepancy between the in vitro and in vivo results regarding the role of beta1 integrins in the maintenance of epidermal stem/progenitor cells. Studies of mice with skin-specific ablation of beta1 integrins suggested that epidermis can form and be maintained in their absence, while in vitro data have shown a fundamental role for these adhesion receptors in stem/progenitor cell expansion and differentiation. METHODOLOGY/PRINCIPAL FINDINGS: To elucidate this discrepancy we generated hypomorphic mice expressing reduced beta1 integrin levels on keratinocytes that developed similar, but less severe defects than mice with beta1-deficient keratinocytes. Surprisingly we found that upon aging these abnormalities attenuated due to a rapid expansion of cells, which escaped or compensated for the down-regulation of beta1 integrin expression. A similar phenomenon was observed in aged mice with a complete, skin-specific ablation of the beta1 integrin gene, where cells that escaped Cre-mediated recombination repopulated the mutant skin in a very short time period. The expansion of beta1 integrin expressing keratinocytes was even further accelerated in situations of increased keratinocyte proliferation such as wound healing. CONCLUSIONS/SIGNIFICANCE: These data demonstrate that expression of beta1 integrins is critically important for the expansion of epidermal progenitor cells to maintain epidermal homeostasis.