scholarly journals Cdc42 regulates junctional actin but not cell polarization in the Caenorhabditis elegans epidermis

2017 ◽  
Vol 216 (11) ◽  
pp. 3729-3744 ◽  
Author(s):  
Yuliya Zilberman ◽  
Joshua Abrams ◽  
Dorian C. Anderson ◽  
Jeremy Nance
Keyword(s):  
Caenorhabditis Elegans ◽  
Epidermal Cell ◽  
Cell Shape ◽  
Time Lapse ◽  
Cell Polarization ◽  
Epithelial Morphogenesis ◽  
Actin Organization ◽  
Protein Levels ◽  
Guanosine Triphosphatase ◽  
Shape Changes

During morphogenesis, adherens junctions (AJs) remodel to allow changes in cell shape and position while preserving adhesion. Here, we examine the function of Rho guanosine triphosphatase CDC-42 in AJ formation and regulation during Caenorhabditis elegans embryo elongation, a process driven by asymmetric epidermal cell shape changes. cdc-42 mutant embryos arrest during elongation with epidermal ruptures. Unexpectedly, we find using time-lapse fluorescence imaging that cdc-42 is not required for epidermal cell polarization or junction assembly, but rather is needed for proper junctional actin regulation during elongation. We show that the RhoGAP PAC-1/ARHGAP21 inhibits CDC-42 activity at AJs, and loss of PAC-1 or the interacting linker protein PICC-1/CCDC85A-C blocks elongation in embryos with compromised AJ function. pac-1 embryos exhibit dynamic accumulations of junctional F-actin and an increase in AJ protein levels. Our findings identify a previously unrecognized molecular mechanism for inhibiting junctional CDC-42 to control actin organization and AJ protein levels during epithelial morphogenesis.

scholarly journals A Genetic Screen for Temperature-sensitive Morphogenesis-defective Caenorhabditis elegans Mutants

2020 ◽  
Author(s):  
Molly Christine Jud ◽  
Josh Lowry ◽  
Thalia Padilla ◽  
Erin Clifford ◽  
Yuqi Yang ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Epidermal Cell ◽  
Cell Shape ◽  
The Body ◽  
Forward Genetics ◽  
Temperature Sensitive ◽  
Embryonic Lethal ◽  
Embryonic Morphogenesis ◽  
Cell Shape Changes ◽  
Shape Changes

ABSTRACTMorphogenesis involves coordinated cell migrations and cell shape changes that generate tissues and organs, and organize the body plan. Cell adhesion and the cytoskeleton are important for executing morphogenesis, but their regulation remains poorly understood. As genes required for embryonic morphogenesis may have earlier roles in development, temperature-sensitive embryonic-lethal mutations are useful tools for investigating this process. From a collection of ∼200 such Caenorhabditis elegans mutants, we have identified 17 that have highly penetrant embryonic morphogenesis defects after upshifts from the permissive to the restrictive temperature, just prior to the cell shape changes that mediate elongation of the ovoid embryo into a vermiform larva. Using whole genome sequencing, we identified the causal mutations in seven affected genes. These include three genes that have roles in producing the extracellular matrix, which is known to affect the morphogenesis of epithelial tissues in multicellular organisms. The rib-1 and rib-2 genes encode glycosyltransferases, and the emb-9 gene encodes a collagen subunit. We also used live imaging to characterize epidermal cell shape dynamics in one mutant, or1219ts, and observed cell elongation defects during dorsal intercalation and ventral enclosure that may be responsible for the body elongation defects. These results indicate that our screen has identified factors that influence morphogenesis and provides a platform for advancing our understanding of this fundamental biological process.SUMMARYWe performed a systematic, forward genetics screen for temperature-sensitive embryonic-lethal (TS-EL) Caenorhabditis elegans mutants that are specifically defective in embryonic morphogenesis. By taking advantage of temperature-upshifts, we identified several essential genes influencing morphogenesis. We also demonstrated that one mutant has defects in epidermal cell shape changes that likely account for the failure in morphogenesis. The TS-EL mutants we identified will be useful tools for advancing our understanding of the gene networks controlling cell shape changes and movements during morphogenesis.

A dominant inhibitory version of the small GTP-binding protein Rac disrupts cytoskeletal structures and inhibits developmental cell shape changes in Drosophila

Development ◽  
1995 ◽  
Vol 121 (3) ◽  
pp. 903-914 ◽  
Author(s):  
N. Harden ◽  
H.Y. Loh ◽  
W. Chia ◽  
L. Lim
Keyword(s):  
Epidermal Cell ◽  
Cell Shape ◽  
Shape Change ◽  
Yeast Cells ◽  
Cell Shape Change ◽  
Gtp Binding ◽  
Wide Range ◽  
Cell Shape Changes ◽  
Germband Retraction ◽  
Shape Changes

The Rho subfamily of Ras-related small GTP-binding proteins is involved in regulation of the cytoskeleton. The cytoskeletal changes induced by two members of this subfamily, Rho and Rac, in response to growth factor stimulation, have dramatic effects on cell morphology. We are interested in using Drosophila as a system for studying how such effects participate in development. We have identified two Drosophila genes, DRacA and DRacB, encoding proteins with homology to mammalian Rac1 and Rac2. We have made transgenic flies bearing dominant inhibitory (N17DRacA), and wild-type versions of the DRacA cDNA under control of an Hsp70 promoter. Expression of the N17DRacA transgene during embryonic development causes a high frequency of defects in dorsal closure which are due to disruption of cell shape changes in the lateral epidermis. Embryonic expression of N17DRacA also affects germband retraction and head involution. The epidermal cell shape defects caused by expression of N17DRacA are accompanied by disruption of a localized accumulation of actin and myosin thought to be driving epidermal cell shape change. Thus the Rho subfamily may be generating localized changes in the cytoskeleton during Drosophila development in a similar fashion to that seen in mammalian and yeast cells. The Rho subfamily is likely to be participating in a wide range of developmental processes in Drosophila through its regulation of the cytoskeleton.

scholarly journals Shear stress–induced endothelial cell polarization is mediated by Rho and Rac but not Cdc42 or PI 3-kinases

2003 ◽  
Vol 161 (2) ◽  
pp. 429-439 ◽  
Author(s):  
Beata Wojciak-Stothard ◽  
Anne J. Ridley
Keyword(s):  
Shear Stress ◽  
Cell Shape ◽  
Rho Kinase ◽  
Cell Movement ◽  
Cell Polarization ◽  
Migration Speed ◽  
Rhoa Activity ◽  
Endothelial Response ◽  
And Migration ◽  
Shape Changes

Shear stress induces endothelial polarization and migration in the direction of flow accompanied by extensive remodeling of the actin cytoskeleton. The GTPases RhoA, Rac1, and Cdc42 are known to regulate cell shape changes through effects on the cytoskeleton and cell adhesion. We show here that all three GTPases become rapidly activated by shear stress, and that each is important for different aspects of the endothelial response. RhoA was activated within 5 min after stimulation with shear stress and led to cell rounding via Rho-kinase. Subsequently, the cells respread and elongated within the direction of shear stress as RhoA activity returned to baseline and Rac1 and Cdc42 reached peak activation. Cell elongation required Rac1 and Cdc42 but not phosphatidylinositide 3-kinases. Cdc42 and PI3Ks were not required to establish shear stress–induced polarity although they contributed to optimal migration speed. Instead, Rho and Rac1 regulated directionality of cell movement. Inhibition of Rho or Rho-kinase did not affect the cell speed but significantly increased cell displacement. Our results show that endothelial cells reorient in response to shear stress by a two-step process involving Rho-induced depolarization, followed by Rho/Rac-mediated polarization and migration in the direction of flow.

scholarly journals Actin polymerization or myosin contraction: two ways to build up cortical tension for symmetry breaking

2013 ◽  
Vol 368 (1629) ◽  
pp. 20130005 ◽  
Author(s):  
Kevin Carvalho ◽  
Joël Lemière ◽  
Fahima Faqir ◽  
John Manzi ◽  
Laurent Blanchoin ◽  
...  
Keyword(s):  
Symmetry Breaking ◽  
Self Assembly ◽  
Actin Filaments ◽  
Cell Shape ◽  
Actin Polymerization ◽  
Cell Polarization ◽  
Critical Tension ◽  
Cell Shape Changes ◽  
Myosin Motors ◽  
Shape Changes

Cells use complex biochemical pathways to drive shape changes for polarization and movement. One of these pathways is the self-assembly of actin filaments and myosin motors that together produce the forces and tensions that drive cell shape changes. Whereas the role of actin and myosin motors in cell polarization is clear, the exact mechanism of how the cortex, a thin shell of actin that is underneath the plasma membrane, can drive cell shape changes is still an open question. Here, we address this issue using biomimetic systems: the actin cortex is reconstituted on liposome membranes, in an ‘outside geometry’. The actin shell is either grown from an activator of actin polymerization immobilized at the membrane by a biotin–streptavidin link, or built by simple adsorption of biotinylated actin filaments to the membrane, in the presence or absence of myosin motors. We show that tension in the actin network can be induced either by active actin polymerization on the membrane via the Arp2/3 complex or by myosin II filament pulling activity. Symmetry breaking and spontaneous polarization occur above a critical tension that opens up a crack in the actin shell. We show that this critical tension is reached by growing branched networks, nucleated by the Arp2/3 complex, in a concentration window of capping protein that limits actin filament growth and by a sufficient number of motors that pull on actin filaments. Our study provides the groundwork to understanding the physical mechanisms at work during polarization prior to cell shape modifications.

scholarly journals Cell volume changes contribute to epithelial morphogenesis in zebrafish Kupffer’s vesicle

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Agnik Dasgupta ◽  
Matthias Merkel ◽  
Madeline J Clark ◽  
Andrew E Jacob ◽  
Jonathan Edward Dawson ◽  
...  
Keyword(s):  
Cell Volume ◽  
Cell Shape ◽  
Single Cells ◽  
Ion Flux ◽  
Epithelial Morphogenesis ◽  
Volume Changes ◽  
Kupffer’S Vesicle ◽  
Kupffer's Vesicle ◽  
Cell Shape Changes ◽  
Shape Changes

How epithelial cell behaviors are coordinately regulated to sculpt tissue architecture is a fundamental question in biology. Kupffer’s vesicle (KV), a transient organ with a fluid-filled lumen, provides a simple system to investigate the interplay between intrinsic cellular mechanisms and external forces during epithelial morphogenesis. Using 3-dimensional (3D) analyses of single cells we identify asymmetric cell volume changes along the anteroposterior axis of KV that coincide with asymmetric cell shape changes. Blocking ion flux prevents these cell volume changes and cell shape changes. Vertex simulations suggest cell shape changes do not depend on lumen expansion. Consistent with this prediction, asymmetric changes in KV cell volume and shape occur normally when KV lumen growth fails due to leaky cell adhesions. These results indicate ion flux mediates cell volume changes that contribute to asymmetric cell shape changes in KV, and that these changes in epithelial morphology are separable from lumen-generated forces.

scholarly journals Keeping the Vimentin Network under Control: Cell–Matrix Adhesion–associated Plectin 1f Affects Cell Shape and Polarity of Fibroblasts

2010 ◽  
Vol 21 (19) ◽  
pp. 3362-3375 ◽  
Author(s):  
Gerald Burgstaller ◽  
Martin Gregor ◽  
Lilli Winter ◽  
Gerhard Wiche
Keyword(s):  
Cell Shape ◽  
Network Formation ◽  
De Novo ◽  
Control Cell ◽  
Focal Adhesions ◽  
Time Lapse ◽  
Cell Polarization ◽  
Dependent Manner ◽  
Cell Matrix ◽  
Contractile Stress

Focal adhesions (FAs) located at the ends of actin/myosin-containing contractile stress fibers form tight connections between fibroblasts and their underlying extracellular matrix. We show here that mature FAs and their derivative fibronectin fibril-aligned fibrillar adhesions (FbAs) serve as docking sites for vimentin intermediate filaments (IFs) in a plectin isoform 1f (P1f)-dependent manner. Time-lapse video microscopy revealed that FA-associated P1f captures mobile vimentin filament precursors, which then serve as seeds for de novo IF network formation via end-to-end fusion with other mobile precursors. As a consequence of IF association, the turnover of FAs is reduced. P1f-mediated IF network formation at FbAs creates a resilient cage-like core structure that encases and positions the nucleus while being stably connected to the exterior of the cell. We show that the formation of this structure affects cell shape with consequences for cell polarization.

scholarly journals DRhoGEF2 regulates actin organization and contractility in the Drosophila blastoderm embryo

2005 ◽  
Vol 168 (4) ◽  
pp. 575-585 ◽  
Author(s):  
Mojgan Padash Barmchi ◽  
Stephen Rogers ◽  
Udo Häcker
Keyword(s):  
Cell Shape ◽  
Cell Formation ◽  
Small Gtpases ◽  
Actin Organization ◽  
Actomyosin Contractility ◽  
Pole Cell ◽  
Rho Family ◽  
Cytoskeletal Function ◽  
Actin Rings ◽  
Shape Changes

Morphogenesis of the Drosophila melanogaster embryo is associated with a dynamic reorganization of the actin cytoskeleton that is mediated by small GTPases of the Rho family. Often, Rho1 controls different aspects of cytoskeletal function in parallel, requiring a complex level of regulation. We show that the guanine triphosphate (GTP) exchange factor DRhoGEF2 is apically localized in epithelial cells throughout embryogenesis. We demonstrate that DRhoGEF2, which has previously been shown to regulate cell shape changes during gastrulation, recruits Rho1 to actin rings and regulates actin distribution and actomyosin contractility during nuclear divisions, pole cell formation, and cellularization of syncytial blastoderm embryos. We propose that DRhoGEF2 activity coordinates contractile actomyosin forces throughout morphogenesis in Drosophila by regulating the association of myosin with actin to form contractile cables. Our results support the hypothesis that specific aspects of Rho1 function are regulated by specific GTP exchange factors.

scholarly journals Cellular structure image classification with small targeted training samples

2019 ◽  
Author(s):  
Dali Wang ◽  
Zheng Lu ◽  
Yichi Xu ◽  
Zi Wang ◽  
Chengcheng Li ◽  
...  
Keyword(s):  
Deep Learning ◽  
Image Classification ◽  
Cell Shape ◽  
Time Lapse ◽  
Training Dataset ◽  
Generative Adversarial Networks ◽  
Training Samples ◽  
Cell Shapes ◽  
Cell Shape Changes ◽  
Shape Changes

AbstractMotivationCell shapes provide crucial biology information on complex tissues. Different cell types often have distinct cell shapes, and collective shape changes usually indicate morphogenetic events and mechanisms. The identification and detection of collective cell shape changes in an extensive collection of 3D time-lapse images of complex tissues is an important step in assaying such mechanisms but is a tedious and time-consuming task. Machine learning provides new opportunities to automatically detect cell shape changes. However, it is challenging to generate sufficient training samples for pattern identification through deep learning because of a limited amount of images and annotations.ResultWe present a deep learning approach with minimal well-annotated training samples and apply it to identify multicellular rosettes from 3D live images of the Caenorhabditis elegans embryo with fluorescently labelled cell membranes. Our strategy is to combine two approaches, namely, feature transfer and generative adversarial networks (GANs), to boost image classification with small training samples. Specifically, we use a GAN framework and conduct an unsupervised training to capture the general characteristics of cell membrane images with 11,250 unlabelled images. We then transfer the structure of the GAN discriminator into a new Alex-style neural network for further learning with several dozen labelled samples. Our experiments showed that with 10-15 well-labelled rosette images and 30-40 randomly selected non-rosette images our approach can identify rosettes with over 80% accuracy and capture over 90% of the model accuracy achieved with a training dataset that is five times larger. We also established a public benchmark dataset for rosette detection. This GAN-based transfer approach can be applied to study other cellular structures with minimal training [email protected], [email protected]

scholarly journals Asymmetric cell volume changes regulate epithelial morphogenesis in zebrafish Kupffer’s vesicle

2017 ◽  
Author(s):  
Agnik Dasgupta ◽  
Matthias Merkel ◽  
Andrew E. Jacob ◽  
Jonathan Dawson ◽  
M. Lisa Manning ◽  
...  
Keyword(s):  
Cell Volume ◽  
Cell Shape ◽  
Single Cells ◽  
Ion Flux ◽  
Epithelial Morphogenesis ◽  
Volume Changes ◽  
Kupffer’S Vesicle ◽  
Kupffer's Vesicle ◽  
Cell Shape Changes ◽  
Shape Changes

ABSTRACTHow epithelial cell behaviors are coordinately regulated to sculpt tissue architecture is a fundamental question in biology. Kupffer's vesicle (KV), a transient organ with a fluid - filled lumen, provides a simple system to investigate the interplay between intrinsic cellular mechanisms and external forces during epithelial morphogenesis. Using 3 - dimensional (3D) analyses of single cells we identify asymmetric cell volume changes along the anteroposterior axis of KV that coincide with asymmetric cell shape changes. Blocking ion flux prevents these cell volume changes and cell shape changes. Vertex simulations suggest cell shape changes do not depend on lumen expansion. Consistent with this prediction, asymmetric changes in KV cell volume and shape occur normally when KV lumen growth fails due to leaky cell adhesions. These results indicate ion flux mediates asymmetric cell volume changes that contribute to asymmetric cell shape changes in KV, and that these changes in epithelial morphology are separable from lumen - generated forces.

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