Drosophila embryos close epithelial wounds using a combination of cellular protrusions and an actomyosin purse string
ABSTRACT The repair of injured tissue must occur rapidly to prevent microbial invasion and maintain tissue integrity. Epithelial tissues in particular, which serve as a barrier against the external environment, must repair efficiently in order to restore their primary function. Here we analyze the effect of different parameters on the epithelial wound repair process in the late stage Drosophila embryo using in vivo wound assays, expression of cytoskeleton and membrane markers, and mutant analysis. We define four distinct phases in the repair process-expansion, coalescence, contraction, and closure-and describe the molecular dynamics of each phase. Specifically, we find that myosin, E-cadherin, Echinoid, the plasma membrane, microtubules, and the Cdc42 small GTPase respond dynamically during wound repair, and demonstrate that perturbations of each of these components result in specific impairments to the wound healing process. Our results show that embryonic epithelial wound repair is mediated by two simultaneously acting mechanisms: crawling driven by cellular protrusions and actomyosin ring contraction along the leading edge of the wound.
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ABSTRACT: Actin microridges form labyrinth like patterns on superficial epithelial cells across animal species. This highly organized assembly has been implicated in mucus retention and in the mechanical structure of mucosal surfaces, however the mechanisms that regulate actin microridges remain largely unknown. Here we characterize the composition and dynamics of actin microridges on the surface of zebrafish larvae using live imaging. Microridges contain phospho-tyrosine, cortactin and VASP, but not focal adhesion kinase. Time-lapse imaging reveals dynamic changes in the length and branching of microridges in intact animals. Transient perturbation of the microridge pattern occurs before cell division with rapid re-assembly during and after cytokinesis. Microridge assembly is maintained with constitutive activation of Rho or inhibition of myosin II activity. However, expression of dominant negative RhoA or Rac alters microridge organization, with an increase in distance between microridges. Latrunculin A treatment and photoconversion experiments suggest that the F-actin filaments are actively treadmilling in microridges. Accordingly, inhibition of Arp2/3 or PI3K signaling impairs microridge structure and length. Taken together, actin microridges in zebrafish represent a tractable in vivo model to probe pattern formation and dissect Arp2/3-mediated actin dynamics in vivo.PLoS ONE 01/2015; 10(1):e0115639. DOI:10.1371/journal.pone.0115639 · 3.53 Impact Factor
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ABSTRACT: The arrival of multicellularity in evolution facilitated cell-cell signaling in conjunction with adhesion. As the ectodomains of cadherins interact with each other directly in trans (as well as in cis), spanning the plasma membrane and associating with multiple other entities, cadherins enable the transduction of "outside-in" or "inside-out" signals. We focus this review on signals that originate from the larger family of cadherins that are inwardly directed to the nucleus, and thus have roles in gene control or nuclear structure-function. The nature of cadherin complexes varies considerably depending on the type of cadherin and its context, and we will address some of these variables for classical cadherins versus other family members. Substantial but still fragmentary progress has been made in understanding the signaling mediators used by varied cadherin complexes to coordinate the state of cell-cell adhesion with gene expression. Evidence that cadherin intracellular binding partners also localize to the nucleus is a major point of interest. In some models, catenins show reduced binding to cadherin cytoplasmic tails favoring their engagement in gene control. When bound, cadherins may serve as stoichiometric competitors of nuclear signals. Cadherins also directly or indirectly affect numerous signaling pathways (e.g., Wnt, receptor tyrosine kinase, Hippo, NFκB, and JAK/STAT), enabling cell-cell contacts to touch upon multiple biological outcomes in embryonic development and tissue homeostasis. © 2015 Elsevier Inc. All rights reserved.Current Topics in Developmental Biology 01/2015; 112:129-96. DOI:10.1016/bs.ctdb.2014.11.018 · 4.21 Impact Factor
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ABSTRACT: Drosophila immune cells, the hemocyte, undergo four stereotypical developmental migrations to populate the embryo where they provide immune reconnoitering, as well as a number of non-immune related functions necessary for proper embryogenesis. Here, we describe a role for Rho1 in one of these developmental migrations in which posteriorly located hemocytes migrate toward the head. This migration requires the interaction of Rho1 with its downstream effector Wash, a Wiskott Aldrich Syndrome family protein. Both Wash knockdown and a Rho1 transgene harboring a mutation that prevents Wash binding exhibits the same developmental migratory defect as Rho1 knockdown. Wash activates the Arp2/3 complex whose activity is needed for this migration, whereas members of the WASH Regulatory Complex (SWIP, Strumpellin, and CCDC53) are not. Our results suggest a WASH complex-independent signaling pathway to regulate the cytoskeleton during a subset of hemocyte developmental migrations. © 2015 by The American Society for Cell Biology.Molecular Biology of the Cell 03/2015; 26(9). DOI:10.1091/mbc.E14-08-1266 · 4.55 Impact Factor