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Ivanov AI, Naydenov NG. Dynamics and regulation of epithelial adherens junctions: recent discoveries and controversies. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 303:27-99. [PMID: 23445808 DOI: 10.1016/b978-0-12-407697-6.00002-7] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Adherens junctions (AJs) are evolutionarily conserved plasma-membrane structures that mediate cell-cell adhesions in multicellular organisms. They are organized by several types of adhesive integral membrane proteins, most notably cadherins and nectins that are clustered and stabilized by a number of cytoplasmic scaffolds. AJs are key regulators of tissue architecture and dynamics via control of cell proliferation, polarity, shape, motility, and survival. They are absolutely critical for normal tissue morphogenesis and their disruption results in pathological abnormalities in different tissues. Although the field of adherens-junction research dramatically progressed in recent years, a number of important questions remain controversial and poorly understood. This review outlines basic principles that regulate organization of AJs in mammalian epithelia and discusses recent advances and standing controversies in the field. A special attention is paid to the regulation of AJs by vesicle trafficking and the intracellular cytoskeleton as well as roles and mechanisms of adherens-junction disruption during tumor progression and tissue inflammation.
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Affiliation(s)
- Andrei I Ivanov
- Department of Human and Molecular Genetics, Virginia Institute of Molecular Medicine, Virginia Commonwealth University School of Medicine, Richmond, VA 23298, USA.
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Eom DS, Amarnath S, Agarwala S. Apicobasal polarity and neural tube closure. Dev Growth Differ 2012; 55:164-72. [PMID: 23277919 DOI: 10.1111/dgd.12030] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Revised: 11/10/2012] [Accepted: 11/12/2012] [Indexed: 01/30/2023]
Abstract
During development, a flat neural plate rolls up and closes to form a neural tube. This process, called neural tube closure, is complex and requires morphogenetic events to occur along multiple axes of the neural plate. Recent studies suggest that cell and tissue polarity play a major role in neural tube morphogenesis. While the planar cell polarity pathway is known to be involved in this process, a role for the apicobasal polarity pathway has only recently begun to be elucidated. These studies show that bone morphogenetic proteins can regulate the apicobasal polarity pathway in the neural plate in a cell cycle dependent manner. This dynamically modulates apical junctions in the neural plate, resulting in cell and tissue shape changes that help bend, shape and close the neural tube.
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Affiliation(s)
- Dae Seok Eom
- Institute for Cell and Molecular Biology, University of Texas at Austin, TX 78712, USA
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53
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Eom DS, Amarnath S, Fogel JL, Agarwala S. Bone morphogenetic proteins regulate hinge point formation during neural tube closure by dynamic modulation of apicobasal polarity. ACTA ACUST UNITED AC 2012; 94:804-16. [PMID: 22865775 DOI: 10.1002/bdra.23052] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Revised: 05/23/2012] [Accepted: 06/07/2012] [Indexed: 01/23/2023]
Abstract
BACKGROUND A critical event in neural tube closure is the formation of median hinge points (MHPs) and dorsolateral hinge points (DLHPs). Together, they buckle the ventral midline and elevate and juxtapose the neural folds for proper neural tube closure. Dynamic cell behaviors occur at hinge points (HPs), but their molecular regulation is largely unexplored. Bone morphogenetic proteins (BMPs) have been implicated in a variety of neural tube closure defects, although the underlying mechanisms are poorly understood. METHODS In this study, we used in vivo electroporations, high-resolution microscopy, and biochemical analyses to explore the role of BMP signaling in chick midbrain neural tube closure. RESULTS We identified a cell-cycle-dependent BMP gradient in the midbrain neural plate, which results in low-level BMP activity at the MHP. We show that although BMP signaling does not have a role in midbrain cell-fate specification, its attenuation is necessary and sufficient for MHP formation and midbrain closure. BMP blockade induces MHP formation by regulating apical constriction and basal nuclear migration. Furthermore, BMP signaling is critically important for maintaining epithelial organization by biochemically interacting with apicobasal polarity proteins (e.g., PAR3). As a result, prolonged BMP blockade disrupts apical junctions, desegregating the apical (PAR3(+), ZO1(+)) and basolateral (LGL(+)) compartments. Direct apical LGL-GFP misexpression in turn is sufficient to induce ectopic HPs. CONCLUSIONS BMPs have a critical role in maintaining epithelial organization, a role that is conserved across species and tissue types. Its cell-cycle-dependent modulation in the neural plate dynamically regulates apicobasal polarity and helps to bend, shape, and close the neural tube.
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Affiliation(s)
- Dae Seok Eom
- Institute for Cell and Molecular Biology, University of Texas, Austin, TX 78712, USA
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Thumberger T, Hagenlocher C, Tisler M, Beyer T, Tietze N, Schweickert A, Feistel K, Blum M. Ciliary and non-ciliary expression and function of PACRG during vertebrate development. Cilia 2012; 1:13. [PMID: 23351225 PMCID: PMC3555705 DOI: 10.1186/2046-2530-1-13] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Accepted: 05/30/2012] [Indexed: 01/07/2023] Open
Abstract
Background Park2-co-regulated gene (PACRG) is evolutionarily highly conserved from green algae to mammals. In Chlamydomonas and trypanosomes, the PACRG protein associates with flagella. Loss of PACRG results in shortened or absent flagella. In mouse the PACRG protein is required for spermatogenesis. The purpose of the present study was to analyze (1) the expression patterns of PACRG during vertebrate embryogenesis, and (2) whether the PACRG protein was required for left-right (LR) axis specification through cilia-driven leftward flow in Xenopus laevis. Methods PACRG cDNAs were cloned and expression was analyzed during early embryonic development of Xenopus, mouse, rabbit and zebrafish. Antisense morpholino oligonucleotide (MO) mediated gene knockdown was applied in Xenopus to investigate LR development at the level of tissue morphology, leftward flow and asymmetric marker gene expression, using timelapse videography, scanning electron microscopy (SEM) and whole-mount in situ hybridization. Results were statistically evaluated using Wilcoxon paired and χ2 tests. Results PACRG mRNA expression was found in cells and tissues harboring cilia throughout the vertebrates. Highly localized expression was also detected in the brain. During early development, PACRG was specifically localized to epithelia where leftward flow arises, that is, the gastrocoel roof plate (GRP) in Xenopus, the posterior notochord (PNC) in mammals and Kupffer’s vesicle (KV) in zebrafish. Besides its association with ciliary axonemes, subcellular localization of PACRG protein was found around the nucleus and in a spotty pattern in the cytoplasm. A green fluorescent protein (GFP) fusion construct preferentially labeled cilia, rendering PACRG a versatile marker for live imaging. Loss-of-function in the frog resulted dose dependently in LR, neural tube closure and gastrulation defects, representing ciliary and non-ciliary functions of PACRG. Conclusions The PACRG protein is a novel essential factor of cilia in Xenopus.
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Affiliation(s)
- Thomas Thumberger
- Institute of Zoology, Working group Embryology, University of Hohenheim, Garbenstraße 30, Stuttgart, 70593, Germany.
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Suzuki M, Morita H, Ueno N. Molecular mechanisms of cell shape changes that contribute to vertebrate neural tube closure. Dev Growth Differ 2012; 54:266-76. [DOI: 10.1111/j.1440-169x.2012.01346.x] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
| | - Hitoshi Morita
- Division of Morphogenesis; Department of Developmental Biology; National Institute for Basic Biology; Nishigonaka 38, Myodaiji; Okazaki; 444-8585; Aichi; Japan
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Regulation of epithelial polarity by the E3 ubiquitin ligase Neuralized and the Bearded inhibitors in Drosophila. Nat Cell Biol 2012; 14:467-76. [PMID: 22504274 DOI: 10.1038/ncb2481] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Accepted: 03/14/2012] [Indexed: 12/17/2022]
Abstract
Understanding how epithelial polarity is established and regulated during tissue morphogenesis is a major issue. Here, we identify a regulatory mechanism important for mesoderm invagination, germ-band extension and transepithelial migration in the Drosophila melanogaster embryo. This mechanism involves the inhibition of the conserved E3 ubiquitin ligase Neuralized by proteins of the Bearded family. First, Bearded mutant embryos exhibited a loss of epithelial polarity associated with an early loss of the apical domain. Bearded regulated epithelial polarity by antagonizing neuralized. Second, repression of Bearded gene expression by Snail was required for the Snail-dependent disassembly of adherens junctions in the mesoderm. Third, neuralized was strictly required to promote the downregulation of the apical domain in the midgut epithelium and to facilitate the transepithelial migration of primordial germ cells across this epithelium. This function of Neuralized was independent of its known role in Notch signalling. Thus, Neuralized has two distinct functions in epithelial cell polarity and Notch signalling.
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Morita H, Kajiura-Kobayashi H, Takagi C, Yamamoto TS, Nonaka S, Ueno N. Cell movements of the deep layer of non-neural ectoderm underlie complete neural tube closure in Xenopus. Development 2012; 139:1417-26. [PMID: 22378637 DOI: 10.1242/dev.073239] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In developing vertebrates, the neural tube forms from a sheet of neural ectoderm by complex cell movements and morphogenesis. Convergent extension movements and the apical constriction along with apical-basal elongation of cells in the neural ectoderm are thought to be essential for the neural tube closure (NTC) process. In addition, it is known that non-neural ectoderm also plays a crucial role in this process, as the neural tube fails to close in the absence of this tissue in chick and axolotl. However, the cellular and molecular mechanisms by which it functions in NTC are as yet unclear. We demonstrate here that the non-neural superficial epithelium moves in the direction of tensile forces applied along the dorsal-ventral axis during NTC. We found that this force is partly attributable to the deep layer of non-neural ectoderm cells, which moved collectively towards the dorsal midline along with the superficial layer. Moreover, inhibition of this movement by deleting integrin β1 function resulted in incomplete NTC. Furthermore, we demonstrated that other proposed mechanisms, such as oriented cell division, cell rearrangement and cell-shape changes have no or only minor roles in the non-neural movement. This study is the first to demonstrate dorsally oriented deep-cell migration in non-neural ectoderm, and suggests that a global reorganization of embryo tissues is involved in NTC.
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Affiliation(s)
- Hitoshi Morita
- Division of Morphogenesis, National Institute for Basic Biology, Nishigonaka 38, Myodaiji, Okazaki, Aichi, Japan
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58
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Active reinforcement of externally imposed folding in amphibians embryonic tissues. Mech Dev 2012; 129:51-60. [PMID: 22342666 DOI: 10.1016/j.mod.2012.02.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2011] [Revised: 01/31/2012] [Accepted: 02/02/2012] [Indexed: 11/20/2022]
Abstract
Although the folding of epithelial layers is one of the most common morphogenetic events, the underlying mechanisms of this process are still poorly understood. We aimed to determine whether an artificial bending of an embryonic cell sheet, which normally remains flat, is reinforced and stabilized by intrinsic cell transformations. We observed both reinforcement and stabilization in double explants of blastocoel roof tissue from Xenopus early gastrula embryos. The reinforcement of artificial bending occurred over the course of a few hours and was driven by the gradual apical constriction and radial elongation of previously compressed cells situated at the bending arch of the concave layer of explant. Apical constriction was associated with actomyosin contraction and endocytosis-mediated engulfing of the apical cell membranes. Cooperative apical constrictions of the concave layer of cells produced a tensile force that extended over the entire surface of the explant and correlated with apical contraction of the concave side cells. In the explants taken from the anterior regions of the embryo, this reinforcement was more stable and the bending better expressed than in those taken from suprablastoporal areas. The morphogenetic role of cell responses to the bending force is discussed.
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Roh-Johnson M, Shemer G, Higgins CD, McClellan JH, Werts AD, Tulu US, Gao L, Betzig E, Kiehart DP, Goldstein B. Triggering a cell shape change by exploiting preexisting actomyosin contractions. Science 2012; 335:1232-5. [PMID: 22323741 DOI: 10.1126/science.1217869] [Citation(s) in RCA: 195] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Apical constriction changes cell shapes, driving critical morphogenetic events, including gastrulation in diverse organisms and neural tube closure in vertebrates. Apical constriction is thought to be triggered by contraction of apical actomyosin networks. We found that apical actomyosin contractions began before cell shape changes in both Caenorhabitis elegans and Drosophila. In C. elegans, actomyosin networks were initially dynamic, contracting and generating cortical tension without substantial shrinking of apical surfaces. Apical cell-cell contact zones and actomyosin only later moved increasingly in concert, with no detectable change in actomyosin dynamics or cortical tension. Thus, apical constriction appears to be triggered not by a change in cortical tension, but by dynamic linking of apical cell-cell contact zones to an already contractile apical cortex.
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Affiliation(s)
- Minna Roh-Johnson
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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Lee JY. Uncorking gastrulation: the morphogenetic movement of bottle cells. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2011; 1:286-93. [PMID: 23801442 DOI: 10.1002/wdev.19] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Bottle cell-driven blastopore lip formation externally marks the initiation of gastrulation in amphibian embryos. The blastopore groove is formed when bottle cells undergo apical constriction and transform from cuboidal to flask-shaped. Apical constriction is sufficient to cause invagination and is a highly conserved mechanism for sheet bending and folding during morphogenesis; therefore, studying apical constriction in Xenopus bottle cells could provide valuable insight into this fundamental shape change. Initially described over a century ago, the dramatic shape change that occurs in bottle cells has long captured the imaginations of embryologists. However, only recently have investigators begun to examine the cellular and molecular mechanisms underlying bottle cell apical constriction. Bottle cell apical constriction is driven by actomyosin contractility as well as by endocytosis of the apical membrane. The Nodal signaling pathway, Wnt5a, and Lgl1 are all required for bottle cell formation, but how they induce subcellular changes resulting in apical constriction remains to be elucidated. Xenopus bottle cells now represent an excellent vertebrate system for the dissection of how molecular inputs can drive cellular outputs, specifically the cell shape change of apical constriction.
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Affiliation(s)
- Jen-Yi Lee
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA, USA.
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Eom DS, Amarnath S, Fogel JL, Agarwala S. Bone morphogenetic proteins regulate neural tube closure by interacting with the apicobasal polarity pathway. Development 2011; 138:3179-88. [PMID: 21750029 DOI: 10.1242/dev.058602] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
During neural tube closure, specialized regions called hinge points (HPs) display dynamic and polarized cell behaviors necessary for converting the neural plate into a neural tube. The molecular bases of such cell behaviors (e.g. apical constriction, basal nuclear migration) are poorly understood. We have identified a two-dimensional canonical BMP activity gradient in the chick neural plate that results in low and temporally pulsed BMP activity at the ventral midline/median hinge point (MHP). Using in vivo manipulations, high-resolution imaging and biochemical analyses, we show that BMP attenuation is necessary and sufficient for MHP formation. Conversely, BMP overexpression abolishes MHP formation and prevents neural tube closure. We provide evidence that BMP modulation directs neural tube closure via the regulation of apicobasal polarity. First, BMP blockade produces partially polarized neural cells, which retain contact with the apical and basal surfaces but where basolateral proteins (LGL) become apically localized and apical junctional proteins (PAR3, ZO1) become targeted to endosomes. Second, direct LGL misexpression induces ectopic HPs identical to those produced by noggin or dominant-negative BMPR1A. Third, BMP-dependent biochemical interactions occur between the PAR3-PAR6-aPKC polarity complex and phosphorylated SMAD5 at apical junctions. Finally, partially polarized cells normally occur at the MHP, their frequencies inversely correlated with the BMP activity gradient in the neural plate. We propose that spatiotemporal modulation of the two-dimensional BMP gradient transiently alters cell polarity in targeted neuronal cells. This ensures that the neural plate is flexible enough to be focally bent and shaped into a neural tube, while retaining overall epithelial integrity.
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Affiliation(s)
- Dae Seok Eom
- Institute for Cell and Molecular Biology, University of Texas at Austin, TX 78712, USA
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Mateus AM, Gorfinkiel N, Schamberg S, Martinez Arias A. Endocytic and recycling endosomes modulate cell shape changes and tissue behaviour during morphogenesis in Drosophila. PLoS One 2011; 6:e18729. [PMID: 21533196 PMCID: PMC3077405 DOI: 10.1371/journal.pone.0018729] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2010] [Accepted: 03/10/2011] [Indexed: 12/27/2022] Open
Abstract
During development tissue deformations are essential for the generation of organs and to provide the final form of an organism. These deformations rely on the coordination of individual cell behaviours which have their origin in the modulation of subcellular activities. Here we explore the role endocytosis and recycling on tissue deformations that occur during dorsal closure of the Drosophila embryo. During this process the AS contracts and the epidermis elongates in a coordinated fashion, leading to the closure of a discontinuity in the dorsal epidermis of the Drosophila embryo. We used dominant negative forms of Rab5 and Rab11 to monitor the impact on tissue morphogenesis of altering endocytosis and recycling at the level of single cells. We found different requirements for endocytosis (Rab5) and recycling (Rab11) in dorsal closure, furthermore we found that the two processes are differentially used in the two tissues. Endocytosis is required in the AS to remove membrane during apical constriction, but is not essential in the epidermis. Recycling is required in the AS at early stages and in the epidermis for cell elongation, suggesting a role in membrane addition during these processes. We propose that the modulation of the balance between endocytosis and recycling can regulate cellular morphology and tissue deformations during morphogenesis.
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Affiliation(s)
- Ana Margarida Mateus
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
- Gulbenkian PhD Programme in Biomedicine, Oeiras, Portugal
- * E-mail: (AMM); (AMA)
| | - Nicole Gorfinkiel
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
| | - Sabine Schamberg
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
| | - Alfonso Martinez Arias
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
- * E-mail: (AMM); (AMA)
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von Dassow M, Strother JA, Davidson LA. Surprisingly simple mechanical behavior of a complex embryonic tissue. PLoS One 2010; 5:e15359. [PMID: 21203396 PMCID: PMC3011006 DOI: 10.1371/journal.pone.0015359] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Accepted: 11/15/2010] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Previous studies suggest that mechanical feedback could coordinate morphogenetic events in embryos. Furthermore, embryonic tissues have complex structure and composition and undergo large deformations during morphogenesis. Hence we expect highly non-linear and loading-rate dependent tissue mechanical properties in embryos. METHODOLOGY/PRINCIPAL FINDINGS We used micro-aspiration to test whether a simple linear viscoelastic model was sufficient to describe the mechanical behavior of gastrula stage Xenopus laevis embryonic tissue in vivo. We tested whether these embryonic tissues change their mechanical properties in response to mechanical stimuli but found no evidence of changes in the viscoelastic properties of the tissue in response to stress or stress application rate. We used this model to test hypotheses about the pattern of force generation during electrically induced tissue contractions. The dependence of contractions on suction pressure was most consistent with apical tension, and was inconsistent with isotropic contraction. Finally, stiffer clutches generated stronger contractions, suggesting that force generation and stiffness may be coupled in the embryo. CONCLUSIONS/SIGNIFICANCE The mechanical behavior of a complex, active embryonic tissue can be surprisingly well described by a simple linear viscoelastic model with power law creep compliance, even at high deformations. We found no evidence of mechanical feedback in this system. Together these results show that very simple mechanical models can be useful in describing embryo mechanics.
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Affiliation(s)
- Michelangelo von Dassow
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
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Kremnyov SV. Changes in the shape of epithelial embryonic cells of the spur-toed frog upon deformation of the cell layer. Biophysics (Nagoya-shi) 2010. [DOI: 10.1134/s0006350910060187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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