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  • 1. Bembenek, Joshua N.
    et al.
    Meshik, Xenia
    Tsarouhas, Vasilios
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Meeting report - Cellular dynamics: membrane-cytoskeleton interface2017In: Journal of Cell Science, ISSN 0021-9533, E-ISSN 1477-9137, Vol. 130, no 17, p. 2775-2779Article in journal (Refereed)
    Abstract [en]

    The first ever 'Cellular Dynamics' meeting on the membrane-cytoskeleton interface took place in Southbridge, MA on May 21-24, 2017 and was co-organized by Michael Way, Elizabeth Chen, Margaret Gardel and Jennifer Lippincott-Schwarz. Investigators from around the world studying a broad range of related topics shared their insights into the function and regulation of the cytoskeleton and membrane compartments. This provided great opportunities to learn about key questions in various cellular processes, from the basic organization and operation of the cell to higher-order interactions in adhesion, migration, metastasis, division and immune cell interactions in different model organisms. This unique and diverse mix of research interests created a stimulating and educational meeting that will hopefully continue to be a successful meeting for years to come.

  • 2.
    Jayaram, Satish Arcot
    et al.
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Senti, Kirsten-André
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Tiklová, Katarina
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Tsarouhas, Vasilios
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Hemphälä, Johanna
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Samakovlis, Christos
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    COPI Vesicle Transport Is a Common Requirement for Tube Expansion in Drosophila2008In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 09 AprArticle in journal (Refereed)
    Abstract [en]

    Background Tube expansion defects like stenoses and atresias cause devastating human diseases. Luminal expansion during organogenesis begins to be elucidated in several systems but we still lack a mechanistic view of the process in many organs. The Drosophila tracheal respiratory system provides an amenable model to study tube size regulation. In the trachea, COPII anterograde transport of luminal proteins is required for extracellular matrix assembly and the concurrent tube expansion.

    Principal Findings We identified and analyzed Drosophila COPI retrograde transport mutants with narrow tracheal tubes. γCOP mutants fail to efficiently secrete luminal components and assemble the luminal chitinous matrix during tracheal tube expansion. Likewise, tube extension is defective in salivary glands, where it also coincides with a failure in the luminal deposition and assembly of a distinct, transient intraluminal matrix. Drosophila γCOP colocalizes with cis-Golgi markers and in γCOP mutant embryos the ER and Golgi structures are severely disrupted. Analysis of γCOP and Sar1 double mutants suggests that bidirectional ER-Golgi traffic maintains the ER and Golgi compartments and is required for secretion and assembly of luminal matrixes during tube expansion.

    Conclusions/Significance Our results demonstrate the function of COPI components in organ morphogenesis and highlight the common role of apical secretion and assembly of transient organotypic matrices in tube expansion. Intraluminal matrices have been detected in the notochord of ascidians and zebrafish COPI mutants show defects in notochord expansion. Thus, the programmed deposition and growth of distinct luminal molds may provide distending forces during tube expansion in diverse organs.

  • 3. Ronnberg-Wastljung, Ann-Christin
    et al.
    Samils, Berit
    Tsarouhas, Vasilios
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Gullberg, Urban
    Resistance to Melampsora larici-epitea leaf rust in Salix: analyses of quantitative trait loci2008In: Journal of Applied Genetics, ISSN 1234-1983, E-ISSN 2190-3883, Vol. 49, no 4, p. 321-331Article in journal (Refereed)
    Abstract [en]

    Quantitative resistance of Salix to Melampsora larici--epitea leaf rust was studied in 2 Salix mapping populations. One population was a backcross between a S, schwerinii x S. viminalis hybrid and S. viminalis, and the other was all F-2 population between S. viminalis and S. dasyclados. A leaf disc bioassay was used to study the components of quantitative resistance (latent period, uredinia number, and uredinia size) to 3 isolates of the leaf rust. The analysis of quantitative trait loci (QTLs) revealed 9 genomic regions in the backcross population and 7 genomic regions in the F-2 population that were important for rust resistance, with QTLs explaining 8-26% of the phenotypic variation. An important genomic region was identified for the backcross population in linkage group 2, where QTLs were identified for all resistance components for 2 of the rust isolates. Four of the QTLs had overlapping mapping intervals, demonstrating a common genetic background for latent period, uredinia diameter, and uredinia number. QTLs specific to some rust isolates and to some resistance components were also found, indicating a combination of common and specific mechanisms involved in the various resistance components. Breeding implications in relation to these findings are discussed.

  • 4. Skouloudaki, Kassiani
    et al.
    Christodoulou, Ioannis
    Khalili, Dilan
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Tsarouhas, Vaeos
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Samakovlis, Christos
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. University of Giessen, Germany..
    Tomancak, Pavel
    Knust, Elisabeth
    Papadopoulos, Dimitrios K.
    Yorkie controls tube length and apical barrier integrity during airway development2019In: Journal of Cell Biology, ISSN 0021-9525, E-ISSN 1540-8140, Vol. 218, no 8, p. 2762-2781Article in journal (Refereed)
    Abstract [en]

    Epithelial organ size and shape depend on cell shape changes, cell-matrix communication, and apical membrane growth. The Drosophila melanogaster embryonic tracheal network is an excellent model to study these processes. Here, we show that the transcriptional coactivator of the Hippo pathway, Yorkie (YAP/TAZ in vertebrates), plays distinct roles in the developing Drosophila airways. Yorkie exerts a cytoplasmic function by binding Drosophila Twinstar, the orthologue of the vertebrate actin-severing protein Cofilin, to regulate F-actin levels and apical cell membrane size, which are required for proper tracheal tube elongation. Second, Yorkie controls water tightness of tracheal tubes by transcriptional regulation of the d-aminolevulinate synthase gene (Alas). We conclude that Yorkie has a dual role in tracheal development to ensure proper tracheal growth and functionality.

  • 5.
    Tiklova, Katarina
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Tsarouhas, Vasilios
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Samakovlis, Christos
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Control of Airway Tube Diameter and Integrity by Secreted Chitin-Binding Proteins in Drosophila2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 6, p. e67415-Article in journal (Refereed)
    Abstract [en]

    The transporting function of many branched tubular networks like our lungs and circulatory system depend on the sizes and shapes of their branches. Understanding the mechanisms of tube size control during organ development may offer new insights into a variety of human pathologies associated with stenoses or cystic dilations in tubular organs. Here, we present the first secreted luminal proteins involved in tube diametric expansion in the Drosophila airways. obst-A and gasp are conserved among insect species and encode secreted proteins with chitin binding domains. We show that the widely used tracheal marker 2A12, recognizes the Gasp protein. Analysis of obst-A and gasp single mutants and obst-A; gasp double mutant shows that both genes are primarily required for airway tube dilation. Similarly, Obst-A and Gasp control epidermal cuticle integrity and larval growth. The assembly of the apical chitinous matrix of the airway tubes is defective in gasp and obst-A mutants. The defects become exaggerated in double mutants indicating that the genes have partially redundant functions in chitin structure modification. The phenotypes in luminal chitin assembly in the airway tubes are accompanied by a corresponding reduction in tube diameter in the mutants. Conversely, overexpression of Obst-A and Gasp causes irregular tube expansion and interferes with tube maturation. Our results suggest that the luminal levels of matrix binding proteins determine the extent of diametric growth. We propose that Obst-A and Gasp organize luminal matrix assembly, which in turn controls the apical shapes of adjacent cells during tube diameter expansion.

  • 6. Tran, Martin
    et al.
    Tsarouhas, Vasilios
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Kegel, Andreas
    Early development of Drosophila embryos requires Smc5/6 function during oogenesis2016In: Biology Open, ISSN 2046-6390, Vol. 5, no 7, p. 928-941Article in journal (Refereed)
    Abstract [en]

    Mutations in structural maintenance of chromosomes (Smc) proteins are frequently associated with chromosomal abnormalities commonly observed in developmental disorders. However, the role of Smc proteins in development still remains elusive. To investigate Smc5/6 function during early embryogenesis we examined smc5 and smc6 mutants of the fruit fly Drosophila melanogaster using a combination of reverse genetics and microscopy approaches. Smc5/6 exhibited a maternally contributed function in maintaining chromosome stability during early embryo development, which manifested as female subfertility in its absence. Loss of Smc5/6 caused an arrest and a considerable delay in embryo development accompanied by fragmented nuclei and increased anaphase-bridge formation, respectively. Surprisingly, early embryonic arrest was attributable to the absence of Smc5/6 during oogenesis, which resulted in insufficient repair of pre-meiotic and meiotic DNA double-strand breaks. Thus, our findings contribute to the understanding of Smc proteins in higher eukaryotic development by highlighting a maternal function in chromosome maintenance and a link between oogenesis and early embryogenesis.

  • 7.
    Tsarouhas, Vasilios
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Liu, Dan
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Tsikala, Georgia
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Fedoseienko, Alina
    Zinn, Kai
    Matsuda, Ryo
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Billadeau, Daniel D.
    Samakovlis, Christos
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab). Justus Liebig University of Giessen, Germany.
    WASH phosphorylation balances endosomal versus cortical actin network integrities during epithelial morphogenesis2019In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 2193Article in journal (Refereed)
    Abstract [en]

    Filamentous actin (F-actin) networks facilitate key processes like cell shape control, division, polarization and motility. The dynamic coordination of F-actin networks and its impact on cellular activities are poorly understood. We report an antagonistic relationship between endosomal F-actin assembly and cortical actin bundle integrity during Drosophila airway maturation. Double mutants lacking receptor tyrosine phosphatases (PTP) Ptp10D and Ptp4E, clear luminal proteins and disassemble apical actin bundles prematurely. These defects are counterbalanced by reduction of endosomal trafficking and by mutations affecting the tyrosine kinase Btk29A, and the actin nucleation factor WASH. Btk29A forms protein complexes with Ptp10D and WASH, and Btk29A phosphorylates WASH. This phosphorylation activates endosomal WASH function in flies and mice. In contrast, a phospho-mimetic WASH variant induces endosomal actin accumulation, premature luminal endocytosis and cortical F-actin disassembly. We conclude that PTPs and Btk29A regulate WASH activity to balance the endosomal and cortical F-actin networks during epithelial tube maturation.

  • 8.
    Tsarouhas, Vasilios
    et al.
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Senti, Kirsten-André
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Jayaram, Satish Arcot
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Tiklová, Katarina
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Hemphälä, Johanna
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Adler, Jeremy
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Samakovlis, Christos
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Sequential Pulses of Apical Epithelial Secretion and Endocytosis Drive Airway Maturation in Drosophila2007In: Developmental Cell, ISSN 1534-5807, E-ISSN 1878-1551, Vol. 13, no 2, p. 214-225Article in journal (Refereed)
    Abstract [en]

    The development of air-filled respiratory organs is crucial for survival at birth. We used a combination of live imaging and genetic analysis to dissect respiratory organ maturation in the embryonic Drosophila trachea. We found that tracheal tube maturation entails three precise epithelial transitions. Initially, a secretion burst deposits proteins into the lumen. Solid luminal material is then rapidly cleared from the tubes, and shortly thereafter liquid is removed. To elucidate the cellular mechanisms behind these transitions, we identified gas-filling-deficient mutants showing narrow or protein-clogged tubes. These mutations either disrupt endoplasmatic reticulum-to-Golgi vesicle transport or endocytosis. First, Sar1 is required for protein secretion, luminal matrix assembly, and diametric tube expansion. Subsequently, a sharp pulse of Rab5-dependent endocytic activity rapidly internalizes and clears luminal contents. The coordination of luminal matrix secretion and endocytosis may be a general mechanism in tubular organ morphogenesis and maturation.

  • 9.
    Tsarouhas, Vasilios
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Yao, Liqun
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Samakovlis, Christos
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Src kinases and ERK activate distinct responses to Stitcher receptor tyrosine kinase signaling during wound healing in Drosophila2014In: Journal of Cell Science, ISSN 0021-9533, E-ISSN 1477-9137, Vol. 127, no 8, p. 1829-1839Article in journal (Refereed)
    Abstract [en]

    Metazoans have evolved efficient mechanisms for epidermal repair and survival following injury. Several cellular responses and key signaling molecules that are involved in wound healing have been identified in Drosophila, but the coordination of cytoskeletal rearrangements and the activation of gene expression during barrier repair are poorly understood. The Ret-like receptor tyrosine kinase (RTK) Stitcher (Stit, also known as Cad96Ca) regulates both re-epithelialization and transcriptional activation by Grainy head (Grh) to induce restoration of the extracellular barrier. Here, we describe the immediate downstream effectors of Stit signaling in vivo. Drk (Downstream of receptor kinase) and Src family tyrosine kinases bind to the same docking site in the Stit intracellular domain. Drk is required for the full activation of transcriptional responses but is dispensable for re-epithelialization. By contrast, Src family kinases (SFKs) control both the assembly of a contractile actin ring at the wound periphery and Grh-dependent activation of barrier-repair genes. Our analysis identifies distinct pathways mediating injury responses and reveals an RTK-dependent activation mode for Src kinases and their central functions during epidermal wound healing in vivo.

  • 10.
    Wang, Shenqiu
    et al.
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Jayaram, Arcot Jayaram
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Hemphälä, Johanna
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Senti, Kirsten-André
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Tsarouhas, Vasilis
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Jin, Haining
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Samakovlis, Christos
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Septate-Junction-Dependent Luminal Deposition  of Chitin Deacetylases Restricts  Tube Elongation in the Drosophila Trachea2006In: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 16, no 2, p. 180-185Article in journal (Refereed)
    Abstract [en]

    The function of tubular epithelial organs like the kidney and lung is critically dependent on the length and diameter of their constituting branches. Genetic analysis of tube size control during Drosophila tracheal development has revealed that epithelial septate junction (SJ) components and the dynamic chitinous luminal matrix coordinate tube growth. However, the underlying molecular mechanisms controlling tube expansion so far remained elusive. Here, we present the analysis of two luminal chitin binding proteins with predicted polysaccharide deacetylase activities (ChLDs). ChLDs are required to assemble the cable-like extracellular matrix (ECM) and restrict tracheal tube elongation. Overexpression of native, but not of mutated, ChLD versions also interferes with the structural integrity of the intraluminal ECM and causes aberrant tube elongation. Whereas ChLD mutants have normal SJ structure and function, the luminal deposition of the ChLD requires intact cellular SJs. This identifies a new molecular function for SJs in the apical secretion of ChLD and positions ChLD downstream of the SJs in tube length control. The deposition of the chitin luminal matrix first promotes and coordinates radial tube expansion. We propose that the subsequent structural modification of chitin by chitin binding deacetylases selectively instructs the termination of tube elongation to the underlying epithelium.

  • 11.
    Wang, Shenqiu
    et al.
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Tsarouhas, Vasilis
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Xylourgidis, Nikos
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Sabri, Nafiseh
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Tiklová, Katarína
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Nautiyal, Naumi
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Gallio, Marco
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Samakovlis, Christos
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    The tyrosine kinase Stitcher activates Grainy head and epidermal woundhealing in Drosophila.2009In: Nature Cell Biology, ISSN 1465-7392, E-ISSN 1476-4679, Vol. 11, no 7, p. 890-895Article in journal (Refereed)
    Abstract [en]

    Epidermal injury initiates a cascade of inflammation, epithelial remodelling and integument repair at wound sites. The regeneration of the extracellular barrier and damaged tissue repair rely on the precise orchestration of epithelial responses triggered by the injury1, 2. Grainy head (Grh) transcription factors induce gene expression to crosslink the extracellular barrier in wounded flies and mice3, 4. However, the activation mechanisms and functions of Grh factors in re-epithelialization remain unknown. Here we identify stitcher (stit), a new Grh target in Drosophila melanogaster. stit encodes a Ret-family receptor tyrosine kinase required for efficient epidermal wound healing. Live imaging analysis reveals that Stit promotes actin cable assembly during wound re-epithelialization. Stit activation also induces extracellular signal-regulated kinase (ERK) phosphorylation along with the Grh-dependent expression of stit and barrier repair genes at the wound sites. The transcriptional stimulation of stit on injury triggers a positive feedback loop increasing the magnitude of epithelial responses. Thus, Stit activation upon wounding coordinates cytoskeletal rearrangements and the level of Grh-mediated transcriptional wound responses.

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