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      Forceful closure: cytoskeletal networks in embryonic wound repair

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          Abstract

          Embryonic tissues heal wounds rapidly and without scarring, in a process conserved across species and driven by collective cell movements. The mechanisms of coordinated cell movement during embryonic wound closure also drive tissue development and cancer metastasis; therefore, embryonic wound repair has received considerable attention as a model of collective cell migration. During wound closure, a supracellular actomyosin cable at the wound edge coordinates cells, while actin-based protrusions contribute to cell crawling and seamless wound healing. Other cytoskeletal networks are reorganized during wound repair: microtubules extend into protrusions and along cell–cell boundaries as cells stretch into damaged regions, septins accumulate at the wound margin, and intermediate filaments become polarized in the cells adjacent to the wound. Thus, diverse cytoskeletal networks work in concert to maintain tissue structure, while also driving and organizing cell movements to promote rapid repair. Understanding the signals that coordinate the dynamics of different cytoskeletal networks, and how adhesions between cells or with the extracellular matrix integrate forces across cells, will be important to elucidate the mechanisms of efficient embryonic wound healing and may have far-reaching implications for developmental and cancer cell biology.

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          Most cited references35

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          Rho GTPases Control Polarity, Protrusion, and Adhesion during Cell Movement

          Cell movement is essential during embryogenesis to establish tissue patterns and to drive morphogenetic pathways and in the adult for tissue repair and to direct cells to sites of infection. Animal cells move by crawling and the driving force is derived primarily from the coordinated assembly and disassembly of actin filaments. The small GTPases, Rho, Rac, and Cdc42, regulate the organization of actin filaments and we have analyzed their contributions to the movement of primary embryo fibroblasts in an in vitro wound healing assay. Rac is essential for the protrusion of lamellipodia and for forward movement. Cdc42 is required to maintain cell polarity, which includes the localization of lamellipodial activity to the leading edge and the reorientation of the Golgi apparatus in the direction of movement. Rho is required to maintain cell adhesion during movement, but stress fibers and focal adhesions are not required. Finally, Ras regulates focal adhesion and stress fiber turnover and this is essential for cell movement. We conclude that the signal transduction pathways controlled by the four small GTPases, Rho, Rac, Cdc42, and Ras, cooperate to promote cell movement.
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            Multiple Forces Contribute to Cell Sheet Morphogenesis for Dorsal Closure in Drosophila

            The molecular and cellular bases of cell shape change and movement during morphogenesis and wound healing are of intense interest and are only beginning to be understood. Here, we investigate the forces responsible for morphogenesis during dorsal closure with three approaches. First, we use real-time and time-lapsed laser confocal microscopy to follow actin dynamics and document cell shape changes and tissue movements in living, unperturbed embryos. We label cells with a ubiquitously expressed transgene that encodes GFP fused to an autonomously folding actin binding fragment from fly moesin. Second, we use a biomechanical approach to examine the distribution of stiffness/tension during dorsal closure by following the response of the various tissues to cutting by an ultraviolet laser. We tested our previous model (Young, P.E., A.M. Richman, A.S. Ketchum, and D.P. Kiehart. 1993. Genes Dev. 7:29–41) that the leading edge of the lateral epidermis is a contractile purse-string that provides force for dorsal closure. We show that this structure is under tension and behaves as a supracellular purse-string, however, we provide evidence that it alone cannot account for the forces responsible for dorsal closure. In addition, we show that there is isotropic stiffness/tension in the amnioserosa and anisotropic stiffness/tension in the lateral epidermis. Tension in the amnioserosa may contribute force for dorsal closure, but tension in the lateral epidermis opposes it. Third, we examine the role of various tissues in dorsal closure by repeated ablation of cells in the amnioserosa and the leading edge of the lateral epidermis. Our data provide strong evidence that both tissues appear to contribute to normal dorsal closure in living embryos, but surprisingly, neither is absolutely required for dorsal closure. Finally, we establish that the Drosophila epidermis rapidly and reproducibly heals from both mechanical and ultraviolet laser wounds, even those delivered repeatedly. During healing, actin is rapidly recruited to the margins of the wound and a newly formed, supracellular purse-string contracts during wound healing. This result establishes the Drosophila embryo as an excellent system for the investigation of wound healing. Moreover, our observations demonstrate that wound healing in this insect epidermal system parallel wound healing in vertebrate tissues in situ and vertebrate cells in culture (for review see Kiehart, D.P. 1999. Curr. Biol. 9:R602–R605).
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              Actin cables and epidermal movement in embryonic wound healing.

              Skin wounds in embryos heal rapidly and perfectly. Even though the epidermis appears to be stretched taut over the surface of a structure such as a growing limb bud, its response to wounding is to close over the lesion, rather than to gape more widely. In adult wounds, the epidermis seems to migrate by means of lamellipodia, crawling over the exposed connective tissue. But in embryonic wounds we do not see lamellipodia. The epidermis at the edge of the wound looks smooth, as though under a circumferential tension. Here we show that a cable of filamentous actin appears to run continuously around most of the wound margin. It is confined to the single row of basal cells at the free edge of the epidermis. We suggest that the actin cable acts as a contractile 'purse string' to close up the embryonic wound.
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                Author and article information

                Contributors
                Role: Monitoring Editor
                Journal
                Mol Biol Cell
                Mol. Biol. Cell
                molbiolcell
                mbc
                mboc
                Molecular Biology of the Cell
                The American Society for Cell Biology
                1059-1524
                1939-4586
                01 June 2019
                : 30
                : 12
                : 1353-1358
                Affiliations
                [a ]Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON M5S 3G9, Canada
                [b ]Ted Rogers Centre for Heart Research, University of Toronto, Toronto, ON M5G 1M1, Canada
                [c ]Department of Cell and Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada
                [d ]Developmental and Stem Cell Biology Program, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada
                University of Wisconsin
                Author notes
                *Address correspondence to: Rodrigo Fernandez-Gonzalez ( rodrigo.fernandez.gonzalez@ 123456utoronto.ca ).
                Article
                E18-04-0248
                10.1091/mbc.E18-04-0248
                6724689
                31145669
                ceed50e2-f652-4382-bc7e-6751a991081b
                © 2019 Rothenberg and Fernandez-Gonzalez. “ASCB®,” “The American Society for Cell Biology®,” and “Molecular Biology of the Cell®” are registered trademarks of The American Society for Cell Biology.

                This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License.

                History
                : 11 February 2019
                : 26 March 2019
                : 02 April 2019
                Categories
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                Molecular biology
                Molecular biology

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