scholarly journals Topological defects in the nematic order of actin fibers as organization centers of Hydra morphogenesis

2020 ◽  
Author(s):  
Yonit Maroudas-Sacks ◽  
Liora Garion ◽  
Lital Shani-Zerbib ◽  
Anton Livshits ◽  
Erez Braun ◽  
...  
Keyword(s):  
Functional Outcomes ◽  
Topological Defects ◽  
Coarse Grained ◽  
Orientation Field ◽  
Biochemical Processes ◽  
Nematic Order ◽  
Mechanical Signaling ◽  
Defect Sites ◽  
Functional Patterns ◽  
Effective Description

Animal morphogenesis arises from the complex interplay between multiple mechanical and biochemical processes with mutual feedback. Developing an effective, coarse-grained description of morphogenesis is essential for understanding how these processes are coordinated across scales to form robust, functional outcomes. Here we show that the nematic order of the supra-cellular actin fibers in regenerating Hydra defines a slowly-varying field, whose dynamics provide an effective description of the morphogenesis process. We show that topological defects in this field, which are long-lived yet display rich dynamics, act as organization centers with morphological features developing at defect sites. These observations suggest that the nematic orientation field can be considered a “mechanical morphogen” whose dynamics, in conjugation with various biochemical and mechanical signaling processes, result in the robust emergence of functional patterns during morphogenesis.

Mechanical Patterning in Animal Morphogenesis

2021 ◽  
Vol 37 (1) ◽  
Author(s):  
Yonit Maroudas-Sacks ◽  
Kinneret Keren
Keyword(s):  
Pattern Formation ◽  
Large Scale ◽  
Coarse Grained ◽  
Annual Review ◽  
Publication Date ◽  
Biochemical Processes ◽  
Substantial Progress ◽  
Biological Pattern Formation ◽  
Effective Theories ◽  
Biochemical Signals

Morphogenesis is one of the most remarkable examples of biological pattern formation. Despite substantial progress in the field, we still do not understand the organizational principles responsible for the robust convergence of the morphogenesis process across scales to form viable organisms under variable conditions. Achieving large-scale coordination requires feedback between mechanical and biochemical processes, spanning all levels of organization and relating the emerging patterns with the mechanisms driving their formation. In this review, we highlight the role of mechanics in the patterning process, emphasizing the active and synergistic manner in which mechanical processes participate in developmental patterning rather than merely following a program set by biochemical signals. We discuss the value of applying a coarse-grained approach toward understanding this complex interplay, which considers the large-scale dynamics and feedback as well as complementing the reductionist approach focused on molecular detail. A central challenge in this approach is identifying relevant coarse-grained variables and developing effective theories that can serve as a basis for an integrated framework for understanding this remarkable pattern-formation process. Expected final online publication date for the Annual Review of Cell and Developmental Biology, Volume 37 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

scholarly journals Axial-Compressive Behavior, Including Kink-Band Formation and Propagation, of Singlep-Phenylene Terephthalamide (PPTA) Fibers

2013 ◽  
Vol 2013 ◽  
pp. 1-15 ◽  
Author(s):  
M. Grujicic ◽  
S. Ramaswami ◽  
J. S. Snipes ◽  
R. Yavari ◽  
C.-F. Yen ◽  
...  
Keyword(s):  
Detrimental Effect ◽  
Mechanical Response ◽  
Topological Defects ◽  
Kink Band ◽  
Coarse Grained ◽  
Computational Investigation ◽  
Band Formation ◽  
Longitudinal Tensile Strength ◽  
Kink Bands

The mechanical response ofp-phenylene terephthalamide (PPTA) single fibers when subjected to uniaxial compression is investigated computationally using coarse-grained molecular statics/dynamics methods. In order to construct the coarse-grained PPTA model (specifically, in order to define the nature of the coarse-grained particles/beads and to parameterize various components of the bead/bead force-field functions), the results of an all-atom molecular-level computational investigation are used. In addition, the microstructure/topology of the fiber core, consisting of a number of coaxial crystalline fibrils, is taken into account. Also, following our prior work, various PPTA crystallographic/topological defects are introduced into the model (at concentrations consistent with the prototypical PPTA synthesis/processing conditions). The analysis carried out clearly revealed (a) formation of the kink bands during axial compression; (b) the role of defects in promoting the formation of kink bands; (c) the stimulating effects of some defects on the fiber-fibrillation process; and (d) the detrimental effect of the prior compression, associated with fiber fibrillation, on the residual longitudinal-tensile strength of the PPTA fibers.

scholarly journals A Bidimensional Gay-Berne Calamitic Fluid: Structure and Phase Behavior in Bulk and Strongly Confined Systems

2021 ◽  
Vol 8 ◽  
Author(s):  
A. Calderón-Alcaraz ◽  
J. Munguía-Valadez ◽  
S. I. Hernández ◽  
A. Ramírez-Hernández ◽  
E. J. Sambriski ◽  
...  
Keyword(s):  
Order Parameter ◽  
Nematic Phase ◽  
Orientational Order ◽  
Topological Defects ◽  
Md Simulations ◽  
Structural Behavior ◽  
Nematic Order ◽  
Lower Temperature ◽  
Geometry Characteristic ◽  
Strong Confinement

A bidimensional (2D) thermotropic liquid crystal (LC) is investigated with Molecular Dynamics (MD) simulations. The Gay-Berne mesogen with parameterization GB(3, 5, 2, 1) is used to model a calamitic system. Spatial orientation of the LC samples is probed with the nematic order parameter: a sharp isotropic-smectic (I-Sm) transition is observed at lower pressures. At higher pressures, the I-Sm transition involves an intermediate nematic phase. Topology of the orthobaric phase diagram for the 2D case differs from the 3D case in two important respects: 1) the nematic region appears at lower temperatures and slightly lower densities, and 2) the critical point occurs at lower temperature and slightly higher density. The 2D calamitic model is used to probe the structural behavior of LC samples under strong confinement when either planar or homeotropic anchoring prevails. Samples subjected to circular, square, and triangular boundaries are gradually cooled to study how orientational order emerges. Depending on anchoring mode and confining geometry, characteristic topological defects emerge. Textures in these systems are similar to those observed in experiments and simulations of lyotropic LCs.

scholarly journals Topological defects in the nematic order of actin fibres as organization centres of Hydra morphogenesis

2020 ◽  
Author(s):  
Yonit Maroudas-Sacks ◽  
Liora Garion ◽  
Lital Shani-Zerbib ◽  
Anton Livshits ◽  
Erez Braun ◽  
...  
Keyword(s):  
Topological Defects ◽  
Nematic Order

scholarly journals Scaling properties of ageing orientation fluctuations in stripe phases

2017 ◽  
Vol 7 (4) ◽  
pp. 20160146 ◽  
Author(s):  
Christian Riesch ◽  
Günter Radons ◽  
Robert Magerle
Keyword(s):  
Phase Field Model ◽  
Topological Defects ◽  
Elastic Model ◽  
Coulomb Interactions ◽  
Orientation Field ◽  
Scaling Properties ◽  
Linear Elastic ◽  
Equilibrium Dynamics ◽  
Modulated Phase ◽  
Coarsening Dynamics

We investigate the non-equilibrium dynamics of an ordered stripe-forming system free of topological defects. In particular, we study the ageing and the coarsening of orientation fluctuations parallel and perpendicular to the stripes via computer simulations based on a minimal phase-field model (model B with Coulomb interactions). Under the influence of noise, the stripe orientation field develops fluctuations parallel to the stripes, with the dominant modulation length λ* ∥ increasing with time t as λ* ∥ ∼ t 1/4 and the correlation length perpendicular to the stripes ξ ⊥ θ increasing as ξ ⊥ θ ∼ t 1/2 . We explain these anisotropic coarsening dynamics with an analytic theory based on the linear elastic model for stripe displacements first introduced by Landau and Peierls. We thus obtain the scaling forms and the scaling exponents characterizing the correlation functions and the structure factor of the stripe orientation field. Our results reveal how the coarsening of orientation fluctuations prevents a periodically modulated phase free of topological defects from reaching equilibrium.

scholarly journals Topological defects in two-dimensional orientation-field models for grain growth

2017 ◽  
Vol 96 (5) ◽  
Author(s):  
Bálint Korbuly ◽  
Mathis Plapp ◽  
Hervé Henry ◽  
James A. Warren ◽  
László Gránásy ◽  
...  
Keyword(s):  
Grain Growth ◽  
Topological Defects ◽  
Two Dimensional ◽  
Orientation Field

scholarly journals Crisscross multilayering of cell sheets

2021 ◽  
Author(s):  
Trinish Sarkar ◽  
Victor Yashunsky ◽  
Louis Brézin ◽  
Carles Blanch Mercader ◽  
Thibault Aryaksama ◽  
...  
Keyword(s):  
Present Article ◽  
Opposite Direction ◽  
Topological Defects ◽  
Apical Surface ◽  
Cell Sheets ◽  
Nematic Order ◽  
Apical Side ◽  
Cell Layers ◽  
Topmost Layer

Simple hydrostatic skeletons such as the Hydra's consist of two stacked layers of cells perpendicularly oriented. Although this crisscross architecture can be recapitulated in vitro, little is known on the formation of such multilayers starting from a monolayer. In the present article, we show that bilayering of myoblasts results from the organization and activity of the cells originally in the monolayer which can be described as a contractile active nematic. As expected, most of the +1/2 topological defects that are associated with this nematic order self-propel. However, a subpopulation of these defects remains immobile. Perpendicular bilayering occurs exclusively at these motionless defects. Indeed, cells located at the head of these defects converge toward the (immobile) core and accumulate there until they start migrating on top of the tail of the first layer while the tail cells migrate in the opposite direction under the head cells. Since the cells keep their initial orientations, the two stacked layers end up perpendicularly oriented. This concerted process leading to a bilayer is dependent on the apical secretion of Extra Cellular Matrix (ECM) by the cells. Indeed, we evidence the presence of ECM between the cell layers and at the apical surface of the topmost layer. ECM molecules are oriented in the direction of the cells that produce them, which may guide the migration of the subsequent cell layers on their apical side.

scholarly journals Geoquímica das Rochas Máficas Toleíticas da Suíte Pós-Colisional Paulo Lopes, Neoproterozóico do Sul do Brasil

2005 ◽  
Vol 32 (2) ◽  
pp. 69 ◽  
Author(s):  
LUANA MOREIRA FLORISBAL ◽  
LAURO NARDI ◽  
MARIA DE FÁTIMA BITENCOURT ◽  
LEANDRO MENEZES BETIOLLO
Keyword(s):  
Coarse Grained ◽  
Main Body ◽  
Chronological Order ◽  
Orientation Field ◽  
Rapid Crystallization ◽  
Magmatic Rocks ◽  
Microgranular Enclaves ◽  
Mafic Microgranular Enclaves ◽  
Basic Rocks

The Paulo Lopes Suite (SPL), composed of the Paulo Lopes Granite (GPL), Garopaba Granitoids (GG) and Silveira Gabbro (GS), is an association of contemporaneous acid and basic rocks, comprising monzo and syenogranites associated to basic dikes, with abundant mafic microgranular enclaves, interpreted as co-mingling products. The contacts between the granitoids and the basic rocks are evidences of coeval and interactive magmas. The Silveira Gabbro occurs in the study area as a main body and several narrow dikes of NNE orientation. Field relations define a chronological order of magmatic events, where the GPL is the first magmatic pulse and, while steel partially crystallized, was intruded by mingled magmas, represented by the GG and the GS. The basic components are medium-grained, equigranular rocks, with subophitic and ophitic textures. The centre of the main body contains medium- to coarse-grained, equigranular rocks, where agglomerates of early-formed clinopyroxene and plagioclase crystals are found. In the chilled margins, they are microporphyritc rocks of aphanitic groundmass, indicative of rapid crystallization. The Silveira Gabbro rocks are composed of labradorite-andesine, orthopyroxene, augite, pigeonite, olivine (occasionally serpentinized), Fe-hornblende and magnesian hornblende, red biotite, magnetite, ilmenite, apatite, and baddeleyite. The composition is tholeiitic, similar to the high-Ti-P basalts of the Serra Geral Formation. Their high contents of K, Rb, Sr and Ba, as well as negative anomalies of Nb and Ta in multielemental diagrams are similar to the ones observed in magmatic rocks from mature arcs or post-collisional environments. The Neoproterozoic basic rocks may be discriminated from the ones belonging to the Cretaceous Serra Geral Formation by their higher contents of alcalis, Cs, U, Th, and by their fractionated REEpatterns, expressed in the La/LuN ratio. The associated granitoids are structural and compositionally compatible with the ones found in post collisional settings, which indicates that the SPL magmatism developed in such environment.

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