scholarly journals Reconstitution of contractile actomyosin rings in vesicles

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Thomas Litschel ◽  
Charlotte F. Kelley ◽  
Danielle Holz ◽  
Maral Adeli Koudehi ◽  
Sven K. Vogel ◽  
...  
Keyword(s):  
Large Scale ◽  
Actin Polymerization ◽  
Living Cells ◽  
Actin Ring ◽  
Actin Networks ◽  
Mechanical Transformation ◽  
Myosin Motors ◽  
Spherical Vesicles ◽  
Theoretical Considerations ◽  
Encapsulation Methods

AbstractOne of the grand challenges of bottom-up synthetic biology is the development of minimal machineries for cell division. The mechanical transformation of large-scale compartments, such as Giant Unilamellar Vesicles (GUVs), requires the geometry-specific coordination of active elements, several orders of magnitude larger than the molecular scale. Of all cytoskeletal structures, large-scale actomyosin rings appear to be the most promising cellular elements to accomplish this task. Here, we have adopted advanced encapsulation methods to study bundled actin filaments in GUVs and compare our results with theoretical modeling. By changing few key parameters, actin polymerization can be differentiated to resemble various types of networks in living cells. Importantly, we find membrane binding to be crucial for the robust condensation into a single actin ring in spherical vesicles, as predicted by theoretical considerations. Upon force generation by ATP-driven myosin motors, these ring-like actin structures contract and locally constrict the vesicle, forming furrow-like deformations. On the other hand, cortex-like actin networks are shown to induce and stabilize deformations from spherical shapes.

scholarly journals Reconstitution of contractile actomyosin rings in vesicles

2020 ◽  
Author(s):  
Thomas Litschel ◽  
Charlotte F. Kelley ◽  
Danielle Holz ◽  
Maral Adeli Koudehi ◽  
Sven Kenjiro Vogel ◽  
...  
Keyword(s):  
Large Scale ◽  
Actin Polymerization ◽  
Living Cells ◽  
Actin Ring ◽  
Actin Networks ◽  
Mechanical Transformation ◽  
Myosin Motors ◽  
Spherical Vesicles ◽  
Theoretical Considerations ◽  
Encapsulation Methods

AbstractOne of the grand challenges of bottom-up synthetic biology is the development of minimal machineries for cell division. The mechanical transformation of large-scale compartments, such as Giant Unilamellar Vesicles (GUVs), requires the geometry-specific coordination of active elements, several orders of magnitude larger than the molecular scale. Of all cytoskeletal structures, large-scale actomyosin rings appear to be the most promising cellular elements to accomplish this task. Here, we have adopted advanced encapsulation methods to study bundled actin filaments in GUVs and compare our results with theoretical modeling. By changing few key parameters, actin polymerization can be differentiated to resemble various types of networks in living cells. Importantly, we find membrane binding to be crucial for the robust condensation into a single actin ring in spherical vesicles, as predicted by theoretical considerations. Upon force generation by ATP-driven myosin motors, these ring-like actin structures contract and locally constrict the vesicle, forming furrow-like deformations. On the other hand, cortex-like actin networks are shown to induce and stabilize deformations from spherical shapes.

scholarly journals Contribution of Filopodia to Cell Migration: A Mechanical Link between Protrusion and Contraction

2010 ◽  
Vol 2010 ◽  
pp. 1-13 ◽  
Author(s):  
Fei Xue ◽  
Deanna M. Janzen ◽  
David A. Knecht
Keyword(s):  
Cell Migration ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Temporal Distribution ◽  
Leading Edge ◽  
Distal Portion ◽  
Actin Binding ◽  
Actin Networks ◽  
Motile Cells ◽  
A Cell

Numerous F-actin containing structures are involved in regulating protrusion of membrane at the leading edge of motile cells. We have investigated the structure and dynamics of filopodia as they relate to events at the leading edge and the function of the trailing actin networks. We have found that although filopodia contain parallel bundles of actin, they contain a surprisingly nonuniform spatial and temporal distribution of actin binding proteins. Along the length of the actin filaments in a single filopodium, the most distal portion contains primarily T-plastin, while the proximal portion is primarily bound byα-actinin and coronin. Some filopodia are stationary, but lateral filopodia move with respect to the leading edge. They appear to form a mechanical link between the actin polymerization network at the front of the cell and the myosin motor activity in the cell body. The direction of lateral filopodial movement is associated with the direction of cell migration. When lateral filopodia initiate from and move toward only one side of a cell, the cell will turn opposite to the direction of filopodial flow. Therefore, this filopodia-myosin II system allows actin polymerization driven protrusion forces and myosin II mediated contractile force to be mechanically coordinated.

Modelling sarcoplasmic reticulum calcium ATPase and its regulation in cardiac myocytes

2009 ◽  
Vol 367 (1896) ◽  
pp. 2181-2202 ◽  
Author(s):  
Jussi T. Koivumäki ◽  
Jouni Takalo ◽  
Topi Korhonen ◽  
Pasi Tavi ◽  
Matti Weckström
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Large Scale ◽  
Cardiac Myocyte ◽  
Model Complexity ◽  
Transport Mechanisms ◽  
Physiological Properties ◽  
Theoretical Considerations ◽  
Sarcoplasmic Reticulum Calcium ◽  
Modelling Approach

When developing large-scale mathematical models of physiology, some reduction in complexity is necessarily required to maintain computational efficiency. A prime example of such an intricate cell is the cardiac myocyte. For the predictive power of the cardiomyocyte models, it is vital to accurately describe the calcium transport mechanisms, since they essentially link the electrical activation to contractility. The removal of calcium from the cytoplasm takes place mainly by the Na + /Ca 2+ exchanger, and the sarcoplasmic reticulum Ca 2+ ATPase (SERCA). In the present study, we review the properties of SERCA, its frequency-dependent and β -adrenergic regulation, and the approaches of mathematical modelling that have been used to investigate its function. Furthermore, we present novel theoretical considerations that might prove useful for the elucidation of the role of SERCA in cardiac function, achieving a reduction in model complexity, but at the same time retaining the central aspects of its function. Our results indicate that to faithfully predict the physiological properties of SERCA, we should take into account the calcium-buffering effect and reversible function of the pump. This ‘uncomplicated’ modelling approach could be useful to other similar transport mechanisms as well.

scholarly journals Actin-ring segment switching drives nonadhesive gap closure

2020 ◽  
Vol 117 (52) ◽  
pp. 33263-33271
Author(s):  
Qiong Wei ◽  
Xuechen Shi ◽  
Tiankai Zhao ◽  
Pingqiang Cai ◽  
Tianwu Chen ◽  
...  
Keyword(s):  
Large Scale ◽  
Traction Force ◽  
Collective Cell Migration ◽  
Actin Ring ◽  
Purse String ◽  
Actin Cable ◽  
Gap Closure ◽  
Actin Fiber ◽  
Ring Segment ◽  
Cable Segment

Gap closure to eliminate physical discontinuities and restore tissue integrity is a fundamental process in normal development and repair of damaged tissues and organs. Here, we demonstrate a nonadhesive gap closure model in which collective cell migration, large-scale actin-network fusion, and purse-string contraction orchestrate to restore the gap. Proliferative pressure drives migrating cells to attach onto the gap front at which a pluricellular actin ring is already assembled. An actin-ring segment switching process then occurs by fusion of actin fibers from the newly attached cells into the actin cable and defusion from the previously lined cells, thereby narrowing the gap. Such actin-cable segment switching occurs favorably at high curvature edges of the gap, yielding size-dependent gap closure. Cellular force microscopies evidence that a persistent rise in the radial component of inward traction force signifies successful actin-cable segment switching. A kinetic model that integrates cell proliferation, actin fiber fusion, and purse-string contraction is formulated to quantitatively account for the gap-closure dynamics. Our data reveal a previously unexplored mechanism in which cells exploit multifaceted strategies in a highly cooperative manner to close nonadhesive gaps.

scholarly journals Elasticity of dense actin networks produces nanonewton protrusive forces

2021 ◽  
Author(s):  
Marion Jasnin ◽  
Jordan Hervy ◽  
Stéphanie Balor ◽  
Anais Bouissou ◽  
Amsha Proag ◽  
...  
Keyword(s):  
Actin Filaments ◽  
Actin Polymerization ◽  
Electron Tomography ◽  
Force Production ◽  
Basal Membrane ◽  
Theoretical Modelling ◽  
Elastic Behavior ◽  
Integrative Approach ◽  
Cellular Functions ◽  
Actin Networks

AbstractActin filaments assemble into force-generating systems involved in diverse cellular functions, including cell motility, adhesion, contractility and division. It remains unclear how networks of actin filaments, which individually generate piconewton forces, can produce forces reaching tens of nanonewtons. Here we use in situ cryo-electron tomography to unveil how the nanoscale architecture of macrophage podosomes enables basal membrane protrusion. We show that the sum of the actin polymerization forces at the membrane is not sufficient to explain podosome protrusive forces. Quantitative analysis of podosome organization demonstrates that the core is composed of a dense network of bent actin filaments storing elastic energy. Theoretical modelling of the network as a spring-loaded elastic material reveals that it exerts forces of up to tens of nanonewtons, similar to those evaluated experimentally. Thus, taking into account not only the interface with the membrane but also the bulk of the network, is crucial to understand force generation by actin machineries. Our integrative approach sheds light on the elastic behavior of dense actin networks and opens new avenues to understand force production inside cells.

scholarly journals Active multistage coarsening of actin networks driven by myosin motors

2011 ◽  
Vol 108 (23) ◽  
pp. 9408-9413 ◽  
Author(s):  
M. Soares e Silva ◽  
M. Depken ◽  
B. Stuhrmann ◽  
M. Korsten ◽  
F. C. MacKintosh ◽  
...  
Keyword(s):  
Actin Networks ◽  
Myosin Motors

An Overview of Multilingual Learners' Literacy Needs for the 21st Century

2020 ◽  
pp. 1-21
Author(s):  
MaryAnn Christison ◽  
Denise E. Murray
Keyword(s):  
Critical Literacy ◽  
21St Century ◽  
Large Scale ◽  
Literacy Skills ◽  
Human Migration ◽  
Multimodal Literacy ◽  
Common Definition ◽  
Societal Changes ◽  
Definition Of ◽  
Theoretical Considerations

The most common definition of literacy is the ability to read and write. However, for teachers working with multilingual learners, the development of literacy skills is much more complex than this simple definition would suggest. Notions of literacy in the 21st century have evolved in response to a number of societal changes, such as globalization, large-scale human migration, and advances in digital technologies. This chapter considers how these societal changes have influenced conceptions and practices of literacy. It provides a brief overview of some important theoretical considerations that inform understandings of literacy development for multilingual learners, including critical literacy, multiliteracies, multimodal literacy, and translanguaging, and explores current conceptions of literacy to help second and foreign language (SFL) teachers better understand how to meet the literacy needs of multilingual learners in the 21st century, offering practical suggestions for teaching from a multiliteracies perspective.

scholarly journals A continuum model for the growth of dendritic actin networks

2020 ◽  
Vol 476 (2241) ◽  
pp. 20200464
Author(s):  
Rohan Abeyaratne ◽  
Prashant K. Purohit
Keyword(s):  
Cell Biology ◽  
Continuum Model ◽  
Intracellular Transport ◽  
Actin Polymerization ◽  
Growth Cones ◽  
Complex Interplay ◽  
Actin Networks ◽  
Chemical Models ◽  
Growing Networks ◽  
Filament Networks

Polymerization of dendritic actin networks underlies important mechanical processes in cell biology such as the protrusion of lamellipodia, propulsion of growth cones in dendrites of neurons, intracellular transport of organelles and pathogens, among others. The forces required for these mechanical functions have been deduced from mechano-chemical models of actin polymerization; most models are focused on single growing filaments, and only a few address polymerization of filament networks through simulations. Here, we propose a continuum model of surface growth and filament nucleation to describe polymerization of dendritic actin networks. The model describes growth and elasticity in terms of macroscopic stresses, strains and filament density rather than focusing on individual filaments. The microscopic processes underlying polymerization are subsumed into kinetic laws characterizing the change of filament density and the propagation of growing surfaces. This continuum model can predict the evolution of actin networks in disparate experiments. A key conclusion of the analysis is that existing laws relating force to polymerization speed of single filaments cannot predict the response of growing networks. Therefore, a new kinetic law, consistent with the dissipation inequality, is proposed to capture the evolution of dendritic actin networks under different loading conditions. This model may be extended to other settings involving a more complex interplay between mechanical stresses and polymerization kinetics, such as the growth of networks of microtubules, collagen filaments, intermediate filaments and carbon nanotubes.

Fabricating large-scale three-dimensional constructs with living cells by processing with syringe needles

2019 ◽  
Vol 107 (4) ◽  
pp. 904-909
Author(s):  
Jun-Ichi Sasaki ◽  
Chihiro Katata ◽  
Gabriela L Abe ◽  
Takuya Matsumoto ◽  
Satoshi Imazato
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Living Cells

scholarly journals Relational Resources As A Source Of Regional Competitive Advantage. Illustrated By The Examples Of The Lodzkie Voivodship And The Novosibirsk Oblast

2015 ◽  
Vol 18 (3) ◽  
pp. 115-137
Author(s):  
Wawrzyniec Rudolf ◽  
Almira Yusupova
Keyword(s):  
Large Scale ◽  
Institutional Environment ◽  
Innovation Policy ◽  
Development Cooperation ◽  
Novosibirsk Oblast ◽  
Socioeconomic System ◽  
Relational Resources ◽  
Theoretical Considerations ◽  
Desk Research

The paper aims to show relational resources as an increasingly significant factor in the competitiveness of territories. The authors argue that regions trying to increase their competitive position should undertake actions to facilitate the creation of a knowledge base and an institutional environment. This elaboration relies on the resource-based theory, used especially for analyzing relations between an organization and its environment. The paper presents theoretical considerations based on the desk research methodology and worldwide literature. Descriptive characterizations of two cases complete the presentations. The paper presents examples of two regions from different socio - economic systems, illustrating the role of relational resources in their development policy. These regions are the Lodz Voivodeship in Poland and the Novosibirsk Oblast of the Russian Federation. In their home countries, both of them had a strong economic position before the 1980's, and in the time of today’s recession are considered as regions with a slightly above-average potential for growth and good prospects for the development of their economy. Their current competitive positions in the investment market, in comparison with other regions in their countries, are also presented. The paper presents evidence that activities aimed at supporting relational resources (innovation policy, cluster development, cooperation between authorities and regional stakeholders) are conducted on a large scale. It also shows the importance given to relational resources in the developmental strategies of both regions. However, determinants resulting from the socioeconomic system and regional qualifications in the area of development management provide different opportunities to use these resources in practice.

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