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Keith E Mostov - One of the best experts on this subject based on the ideXlab platform.

  • involvement of rhoa rock i and myosin ii in inverted orientation of Epithelial Polarity
    EMBO Reports, 2008
    Co-Authors: Annette M Shewan, Paul Brakeman, Dennis J Eastburn, Anirban Datta, David M Bryant, Qiwen Fan, William A Weiss, Mirjam M P Zegers, Keith E Mostov
    Abstract:

    In multicellular Epithelial tissues, the orientation of Polarity of each cell must be coordinated. Previously, we reported that for Madin–Darby canine kidney cells in three-dimensional collagen gel culture, blockade of β1-integrin by the AIIB2 antibody or expression of dominant-negative Rac1N17 led to an inversion of Polarity, such that the apical surfaces of the cells were misorientated towards the extracellular matrix. Here, we show that this process results from the activation of RhoA. Knockdown of RhoA by short hairpin RNA reverses the inverted orientation of Polarity, resulting in normal cysts. Inhibition of RhoA downstream effectors, Rho kinase (ROCK I) and myosin II, has similar effects. We conclude that the RhoA–ROCK I–myosin II pathway controls the inversion of orientation of Epithelial Polarity caused by AIIB2 or Rac1N17. These results might be relevant to the hyperactivation of RhoA and disruption of normal Polarity frequently observed in human Epithelial cancers.

  • involvement of rhoa rock i and myosin ii in inverted orientation of Epithelial Polarity
    EMBO Reports, 2008
    Co-Authors: Annette M Shewan, Paul Brakeman, Dennis J Eastburn, Anirban Datta, David M Bryant, Qiwen Fan, William A Weiss, Mirjam M P Zegers, Keith E Mostov
    Abstract:

    In multicellular Epithelial tissues, the orientation of Polarity of each cell must be coordinated. Previously, we reported that for Madin-Darby canine kidney cells in three-dimensional collagen gel culture, blockade of beta1-integrin by the AIIB2 antibody or expression of dominant-negative Rac1N17 led to an inversion of Polarity, such that the apical surfaces of the cells were misorientated towards the extracellular matrix. Here, we show that this process results from the activation of RhoA. Knockdown of RhoA by short hairpin RNA reverses the inverted orientation of Polarity, resulting in normal cysts. Inhibition of RhoA downstream effectors, Rho kinase (ROCK I) and myosin II, has similar effects. We conclude that the RhoA-ROCK I-myosin II pathway controls the inversion of orientation of Epithelial Polarity caused by AIIB2 or Rac1N17. These results might be relevant to the hyperactivation of RhoA and disruption of normal Polarity frequently observed in human Epithelial cancers.

  • regulation of cell Polarity during Epithelial morphogenesis
    Current Opinion in Cell Biology, 2008
    Co-Authors: Fernando Martinbelmonte, Keith E Mostov
    Abstract:

    Epithelial cells have an apical surface facing a lumen or outside of the organism, and a basolateral surface facing other cells and extracellular matrix. The identity of the apical surface is determined by phosphatidylinositol 4,5-bisphosphate, while phosphatidylinositol 3,4,5-trisphophosphate determines the identity of the basolateral surface. The Par3/Par6/atypical protein kinase C complex, as well as the Crumbs and Scribble complexes, controls Epithelial Polarity. Par4 and AMP kinase regulate Polarity during conditions of energy depletion. Lumens are formed in hollow cysts and tubules by fusions of apical vesicles, such as the vacuolar apical compartment, with the plasma membrane. The Polarity of individual cells is oriented and coordinated with other cells by interactions with the extracellular matrix.

  • liver progenitor cells develop cholangiocyte type Epithelial Polarity in three dimensional culture
    Molecular Biology of the Cell, 2007
    Co-Authors: Naoki Tanimizu, Atsushi Miyajima, Keith E Mostov
    Abstract:

    Cholangiocytes are cellular components of the bile duct system of the liver, which originate from hepatoblasts during embryonic liver development. Although several transcription factors and signaling molecules have been implicated in bile duct development, its molecular mechanism has not been studied in detail. Here, we applied a three-dimensional (3D) culture technique to a liver progenitor cell line, HPPL, to establish an in vitro culture system in which HPPL acquire differentiated cholangiocyte characteristics. When HPPL were grown in a gel containing Matrigel, which contains extracellular matrix components of basement membrane, HPPL developed apicobasal Polarity and formed cysts, which had luminal space inside. In the cysts, F-actin bundles and atypical protein kinase C were at the apical membrane, E-cadherin was localized at the lateral membrane, and beta-catenin and integrin alpha6 were located at the basolateral membrane. HPPL in cysts expressed cholangiocyte markers, including cytokeratin 19, integrin beta4, and aquaporin-1, but not a hepatocyte marker, albumin. Furthermore, HPPL transported rhodamine 123, a substrate for multidrug resistance gene products, from the basal side to the central lumen. These data indicate that HPPL develop cholangiocyte-type Epithelial Polarity in 3D culture. Phosphatidylinositol 3-kinase signaling was essential for proliferation and survival of HPPL in culture, whereas laminin-1 was a crucial component of Matrigel for inducing Epithelial polarization of HPPL. Because HPPL cysts display structural and functional similarities with bile ducts, the 3D culture of HPPL recapitulates in vivo cholangiocyte differentiation and is useful to study the molecular mechanism of bile duct development in vitro.

  • β1 integrin orients Epithelial Polarity via rac1 and laminin
    Molecular Biology of the Cell, 2004
    Co-Authors: Anirban Datta, Keith E Mostov, Lucy Erin Obrien, Pascale Leroy, Grace Z Mak, Tzuushuh Jou, Karl S Matlin, Mirjam M Zegers
    Abstract:

    Epithelial cells polarize and orient Polarity in response to cell-cell and cell-matrix adhesion. Although there has been much recent progress in understanding the general polarizing machinery of epithelia, it is largely unclear how this machinery is controlled by the extracellular environment. To explore the signals from cell-matrix interactions that control orientation of cell Polarity, we have used three-dimensional culture systems in which Madin-Darby canine kidney (MDCK) cells form polarized, lumen-containing structures. We show that interaction of collagen I with apical β1-integrins after collagen overlay of a polarized MDCK monolayer induces activation of Rac1, which is required for collagen overlay-induced tubulocyst formation. Cysts, comprised of a monolayer enclosing a central lumen, form after embedding single cells in collagen. In those cultures, addition of a β1-integrin function-blocking antibody to the collagen matrix gives rise to cysts that have defects in the organization of laminin into the basement membrane and have inverted Polarity. Normal Polarity is restored by either expression of activated Rac1, or the inclusion of excess laminin-1 (LN-1). Together, our results suggest a signaling pathway in which the activation of β1-integrins orients the apical pole of polarized cysts via a mechanism that requires Rac1 activation and laminin organization into the basement membrane.

Daniel St Johnston - One of the best experts on this subject based on the ideXlab platform.

  • an alternative mode of Epithelial Polarity in the drosophila midgut
    bioRxiv, 2018
    Co-Authors: Jia Chen, Aram-christopher Sayadian, Nick Lowe, Holly E Lovegrove, Daniel St Johnston
    Abstract:

    Apical-basal Polarity is essential for the formation and function of Epithelial tissues, whereas loss of Polarity is a hallmark of tumours. Studies in Drosophila have identified conserved Polarity factors that define the apical (Crumbs, Stardust, Par-6, aPKC), junctional (Baz/Par-3) and basolateral (Scribbled, Discs large, Lgl) domains of Epithelial cells1. Because these conserved factors mark equivalent domains in diverse vertebrate and invertebrate Epithelial types, it is generally assumed that this system organises Polarity in all epithelia. Here we show that this is not the case, as none of these canonical factors are required for the polarisation of the endodermal epithelium of the Drosophila adult midgut. Furthermore, unlike other Drosophila epithelia, the midgut forms occluding junctions above adherens junctions, as in vertebrates, and requires the integrin adhesion complex for Polarity. Thus, Drosophila contains two types of epithelia that polarise by different mechanisms. Since knock-outs of canonical Polarity factors often have little effect on the Polarity of vertebrate epithelia, this diversity of Polarity mechanisms is likely to be conserved in other animals.

  • An alternative mode of Epithelial Polarity in the Drosophila midgut.
    Public Library of Science (PLoS), 2018
    Co-Authors: Jia Chen, Aram-christopher Sayadian, Nick Lowe, Holly E Lovegrove, Daniel St Johnston
    Abstract:

    Apical-basal Polarity is essential for the formation and function of Epithelial tissues, whereas loss of Polarity is a hallmark of tumours. Studies in Drosophila have identified conserved Polarity factors that define the apical (Crumbs, Stardust, Par-6, atypical protein kinase C [aPKC]), junctional (Bazooka [Baz]/Par-3), and basolateral (Scribbled [Scrib], Discs large [Dlg], Lethal [2] giant larvae [Lgl]) domains of Epithelial cells. Because these conserved factors mark equivalent domains in diverse types of vertebrate and invertebrate epithelia, it is generally assumed that this system underlies Polarity in all epithelia. Here, we show that this is not the case, as none of these canonical factors are required for the polarisation of the endodermal epithelium of the Drosophila adult midgut. Furthermore, like vertebrate epithelia but not other Drosophila epithelia, the midgut epithelium forms occluding junctions above adherens junctions (AJs) and requires the integrin adhesion complex for Polarity. Thus, Drosophila contains two types of epithelia that polarise by fundamentally different mechanisms. This diversity of Epithelial types may reflect their different developmental origins, junctional arrangement, or whether they polarise in an apical-basal direction or vice versa. Since knock-outs of canonical Polarity factors in vertebrates often have little or no effect on Epithelial Polarity and the Drosophila midgut shares several common features with vertebrate epithelia, this diversity of Polarity mechanisms is likely to be conserved in other animals

  • Epithelial Polarity and spindle orientation intersecting pathways
    Philosophical Transactions of the Royal Society B, 2013
    Co-Authors: Daniel T Bergstralh, Timm Haack, Daniel St Johnston
    Abstract:

    During asymmetric stem cell divisions, the mitotic spindle must be correctly oriented and positioned with respect to the axis of cell Polarity to ensure that cell fate determinants are appropriately segregated into only one daughter cell. By contrast, Epithelial cells divide symmetrically and orient their mitotic spindles perpendicular to the main apical–basal Polarity axis, so that both daughter cells remain within the epithelium. Work in the past 20 years has defined a core ternary complex consisting of Pins, Mud and Gαi that participates in spindle orientation in both asymmetric and symmetric divisions. As additional factors that interact with this complex continue to be identified, a theme has emerged: there is substantial overlap between the mechanisms that orient the spindle and those that establish and maintain apical–basal Polarity in Epithelial cells. In this review, we examine several factors implicated in both processes, namely Canoe, Bazooka, aPKC and Discs large, and consider the implications of this work on how the spindle is oriented during Epithelial cell divisions.

  • Epithelial Polarity and morphogenesis
    Current Opinion in Cell Biology, 2011
    Co-Authors: Daniel St Johnston, Benedicte Sanson
    Abstract:

    The adult form of a multicellular organism is shaped by a series of morphogenetic processes that organise the body into tissues and organs. Most of these events involve the deformation of sheets of Epithelial cells that are highly polarised along their apical-basal axes and attached to each other by lateral junctions. Here we discuss the role played by modifications in the apical-basal Polarity system in driving morphogenesis, with an emphasis on well-characterised events during Drosophila development. Changing the activity of Polarity factors can alter the relative sizes of the apical, lateral and basal domains. This can drive transitions between cuboidal, columnar and squamous Epithelial morphologies, to increase or decrease the surface area of an Epithelial sheet. These changes can also cause Epithelial cells to become wedge-shaped, which can drive tissue bending and invagination. In addition, it has recently emerged that the activity of apical-basal Polarity factors can also be modulated in a planar polarised manner. By affecting the contractility of the actomyosin cytoskeleton and the stability of adherens junctions, changes within the plane of the epithelium can cause cell rearrangements that contribute to convergence and extension movements, boundary formation and cell alignment.

  • dystroglycan and perlecan provide a basal cue required for Epithelial Polarity during energetic stress
    Developmental Cell, 2009
    Co-Authors: Vincent Mirouse, Christina P Christoforou, Cornelia Fritsch, Daniel St Johnston, Robert P Ray
    Abstract:

    Dystroglycan localizes to the basal domain of Epithelial cells and has been reported to play a role in apical-basal Polarity. Here, we show that Dystroglycan null mutant follicle cells have normal apical-basal Polarity, but lose the planar Polarity of their basal actin stress fibers, a phenotype it shares with Dystrophin mutants. However, unlike Dystrophin mutants, mutants in Dystroglycan or in its extracellular matrix ligand Perlecan lose Polarity under energetic stress. The maintenance of Epithelial Polarity under energetic stress requires the activation of Myosin II by the cellular energy sensor AMPK. Starved Dystroglycan or Perlecan null cells activate AMPK normally, but do not activate Myosin II. Thus, Perlecan signaling through Dystroglycan may determine where Myosin II can be activated by AMPK, thereby providing the basal Polarity cue for the low-energy Epithelial Polarity pathway. Since Dystroglycan is often downregulated in tumors, loss of this pathway may play a role in cancer progression.

P Obrist - One of the best experts on this subject based on the ideXlab platform.

Ulrich Tepass - One of the best experts on this subject based on the ideXlab platform.

  • myosin ii promotes the anisotropic loss of the apical domain during drosophila neuroblast ingression
    Journal of Cell Biology, 2017
    Co-Authors: Sergio Simoes, Youjin Oh, Michael F Z Wang, Rodrigo Fernandezgonzalez, Ulrich Tepass
    Abstract:

    Epithelial–mesenchymal transitions play key roles in development and cancer and entail the loss of Epithelial Polarity and cell adhesion. In this study, we use quantitative live imaging of ingressing neuroblasts (NBs) in Drosophila melanogaster embryos to assess apical domain loss and junctional disassembly. Ingression is independent of the Snail family of transcriptional repressors and down-regulation of Drosophila E-cadherin (DEcad) transcription. Instead, the posttranscriptionally regulated decrease in DEcad coincides with the reduction of cell contact length and depends on tension anisotropy between NBs and their neighbors. A major driver of apical constriction and junctional disassembly are periodic pulses of junctional and medial myosin II that result in progressively stronger cortical contractions during ingression. Effective contractions require the molecular coupling between myosin and junctions and apical relaxation of neighboring cells. Moreover, planar polarization of myosin leads to the loss of anterior–posterior junctions before the loss of dorsal–ventral junctions. We conclude that planar-polarized dynamic actomyosin networks drive apical constriction and the anisotropic loss of cell contacts during NB ingression.

  • novel insights into Epithelial Polarity proteins in drosophila
    Trends in Cell Biology, 2011
    Co-Authors: Patrick Laprise, Ulrich Tepass
    Abstract:

    Apical–basal Polarity is a basic organizing principle of Epithelial cells. Consequently, defects in Polarity are associated with numerous human pathologies, including many forms of cancer. Recent work in Drosophila has identified novel roles for, or has greatly enhanced our understanding of, functional modules within the Epithelial Polarity network. A series of recent papers have highlighted the key function of the scaffolding protein Bazooka/Par3 as an early Polarity landmark, and its crucial role in dynamic segregation of the apical membrane from the adherens junction. Moreover, novel Polarity modules have recently been discovered; the Yurt/Coracle group supports the basolateral membrane during a defined time window of development, while a second module, including the kinases LKB1 and AMP-activated protein kinase, is required for Polarity when Epithelial cells experience metabolic stress. These new findings emphasize unforeseen complexities in the regulation of Epithelial Polarity, and raise new questions about the mechanisms of Epithelial tissue organization and function.

  • Epithelial Polarity proteins regulate drosophila tracheal tube size in parallel to the luminal matrix pathway
    Current Biology, 2010
    Co-Authors: Patrick Laprise, Sarah M Paul, Greg J Beitel, Jim Boulanger, Renee M Robbins, Ulrich Tepass
    Abstract:

    Summary Regulation of Epithelial tube size is critical for organ function. However, the mechanisms of tube size control remain poorly understood. In the Drosophila trachea, tube dimensions are regulated by a luminal extracellular matrix (ECM) [1–4]. ECM organization requires apical (luminal) secretion of the protein Vermiform (Verm), which depends on the basolateral septate junction (SJ) [5, 6]. Here, we show that apical and basolateral Epithelial Polarity proteins interact to control tracheal tube size independently of the Verm pathway. Mutations in yurt ( yrt ) and scribble ( scrib ), which encode SJ-associated Polarity proteins [7, 8], cause an expansion of tracheal tubes but do not disrupt Verm secretion. Reducing activity of the apical Polarity protein Crumbs (Crb) suppresses the length defects in yrt but not scrib mutants, suggesting that Yrt acts by negatively regulating Crb. Conversely, Crb overexpression increases tracheal tube dimensions. Reducing crb dosage also rescues tracheal size defects caused by mutations in coracle ( cora ), which encodes an SJ-associated Polarity protein [8, 9]. In addition, crb mutations suppress cora length defects without restoring Verm secretion. Together, these data indicate that Yrt, Cora, Crb, and Scrib operate independently of the Verm pathway. Our data support a model in which Cora and Yrt act through Crb to regulate Epithelial tube size.

  • yurt coracle neurexin iv and the na k atpase form a novel group of Epithelial Polarity proteins
    Nature, 2009
    Co-Authors: Patrick Laprise, Kimberly Lau, Kathryn P Harris, Nancy F Silvagagliardi, Sarah M Paul, Slobodan Beronja, Greg J Beitel, Jane C Mcglade, Ulrich Tepass
    Abstract:

    The integrity of polarized epithelia is critical for development and human health. Many questions remain concerning the full complement and the function of the proteins that regulate cell Polarity. Here we report that the Drosophila FERM proteins Yurt (Yrt) and Coracle (Cora) and the membrane proteins Neurexin IV (Nrx-IV) and Na(+),K(+)-ATPase are a new group of functionally cooperating Epithelial Polarity proteins. This 'Yrt/Cora group' promotes basolateral membrane stability and shows negative regulatory interactions with the apical determinant Crumbs (Crb). Genetic analyses indicate that Nrx-IV and Na(+),K(+)-ATPase act together with Cora in one pathway, whereas Yrt acts in a second redundant pathway. Moreover, we show that the Yrt/Cora group is essential for Epithelial Polarity during organogenesis but not when Epithelial Polarity is first established or during terminal differentiation. This property of Yrt/Cora group proteins explains the recovery of Polarity in embryos lacking the function of the Lethal giant larvae (Lgl) group of basolateral Polarity proteins. We also find that the mammalian Yrt orthologue EPB41L5 (also known as YMO1 and Limulus) is required for lateral membrane formation, indicating a conserved function of Yrt proteins in Epithelial Polarity.

  • the ferm protein yurt is a negative regulatory component of the crumbs complex that controls Epithelial Polarity and apical membrane size
    Developmental Cell, 2006
    Co-Authors: Patrick Laprise, Nancy F Silvagagliardi, Slobodan Beronja, Jane C Mcglade, Milena Pellikka, Abbie M Jensen, Ulrich Tepass
    Abstract:

    The Crumbs (Crb) complex is a key regulator of Epithelial cell architecture where it promotes apical membrane formation. Here, we show that binding of the FERM protein Yurt to the cytoplasmic domain of Crb is part of a negative-feedback loop that regulates Crb activity. Yurt is predominantly a basolateral protein but is recruited by Crb to apical membranes late during Epithelial development. Loss of Yurt causes an expansion of the apical membrane in embryonic epithelia and photoreceptor cells similar to Crb overexpression and in contrast to loss of Crb. Analysis of yurt crb double mutants suggests that these genes function in one pathway and that yurt negatively regulates crb. We also show that the mammalian Yurt orthologs YMO1 and EHM2 bind to mammalian Crb proteins. We propose that Yurt is part of an evolutionary conserved negative-feedback mechanism that restricts Crb complex activity in promoting apical membrane formation.

Vincent Mirouse - One of the best experts on this subject based on the ideXlab platform.

  • tissue specific function of patj in regulating the crumbs complex and Epithelial Polarity
    Journal of Cell Science, 2012
    Co-Authors: Clothilde Penalva, Vincent Mirouse
    Abstract:

    Patj is described as a core component of the Crumbs complex. Along with the other components, Crumbs and Stardust, Patj has been proposed as essential for Epithelial Polarity. However, no proper in vivo genetic analysis of Patj function has been performed in any organism. We have generated the first null mutants for Drosophila Patj. These mutants are lethal. However, Patj is not required in all epithelia where the Crumbs complex is essential. Patj is dispensable for ectoderm Polarity and embryonic development, whereas more severe defects are observed in the adult follicular epithelium, including mislocalisation of the Crumbs complex from the apical domain, as well as morphogenetic defects. These defects are similar to those observed with crumbs and stardust mutants, although weaker and less frequent. Also, gain-of-function of Crumbs and Patj mutation genetically suppress each other in follicular cells. We also show that the first PDZ domain of Patj associated with the Stardust-binding domain are sufficient to fully rescue both Drosophila viability and Crumbs localisation. We propose that the only crucial function of Patj hinges on the ability of its first two domains to positively regulate the Crumbs complex, defining a new developmental level of regulation of its dynamics.

  • dystroglycan and perlecan provide a basal cue required for Epithelial Polarity during energetic stress
    Developmental Cell, 2009
    Co-Authors: Vincent Mirouse, Christina P Christoforou, Cornelia Fritsch, Daniel St Johnston, Robert P Ray
    Abstract:

    Dystroglycan localizes to the basal domain of Epithelial cells and has been reported to play a role in apical-basal Polarity. Here, we show that Dystroglycan null mutant follicle cells have normal apical-basal Polarity, but lose the planar Polarity of their basal actin stress fibers, a phenotype it shares with Dystrophin mutants. However, unlike Dystrophin mutants, mutants in Dystroglycan or in its extracellular matrix ligand Perlecan lose Polarity under energetic stress. The maintenance of Epithelial Polarity under energetic stress requires the activation of Myosin II by the cellular energy sensor AMPK. Starved Dystroglycan or Perlecan null cells activate AMPK normally, but do not activate Myosin II. Thus, Perlecan signaling through Dystroglycan may determine where Myosin II can be activated by AMPK, thereby providing the basal Polarity cue for the low-energy Epithelial Polarity pathway. Since Dystroglycan is often downregulated in tumors, loss of this pathway may play a role in cancer progression.

  • lkb1 and ampk maintain Epithelial cell Polarity under energetic stress
    Journal of Cell Biology, 2007
    Co-Authors: Vincent Mirouse, Daniel St Johnston, Lance Swick, Nevzat Kazgan, Jay E Brenman
    Abstract:

    LKB1 is mutated in both familial and spontaneous tumors, and acts as a master kinase that activates the PAR-1 Polarity kinase and the adenosine 5′monophosphate–activated kinase (AMPK). This has led to the hypothesis that LKB1 acts as a tumor suppressor because it is required to maintain cell Polarity and growth control through PAR-1 and AMPK, respectively. However, the genetic analysis of LKB1–AMPK signaling in vertebrates has been complicated by the existence of multiple redundant AMPK subunits. We describe the identification of mutations in the single Drosophila melanogaster AMPK catalytic subunit AMPKα. Surprisingly, ampkα mutant Epithelial cells lose their Polarity and overproliferate under energetic stress. LKB1 is required in vivo for AMPK activation, and lkb1 mutations cause similar energetic stress–dependent phenotypes to ampkα mutations. Furthermore, lkb1 phenotypes are rescued by a phosphomimetic version of AMPKα. Thus, LKB1 signals through AMPK to coordinate Epithelial Polarity and proliferation with cellular energy status, and this might underlie the tumor suppressor function of LKB1.