scholarly journals Negative tension controls stability and structure of intermediate filament networks

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Ehud Haimov ◽  
Michael Urbakh ◽  
Michael M. Kozlov
Keyword(s):  
Global Minimum ◽  
Unique Feature ◽  
Energy State ◽  
Live Cells ◽  
Two Dimensional ◽  
Network Stability ◽  
Symmetric State ◽  
Elastic Resistance ◽  
Filament Networks ◽  
Keratin Intermediate Filaments

AbstractNetworks, whose junctions are free to move along the edges, such as two-dimensional soap froths and membrane tubular networks of endoplasmic reticulum are intrinsically unstable. This instability is a result of a positive tension applied to the network elements. A paradigm of networks exhibiting stable polygonal configurations in spite of the junction mobility, are networks formed by bundles of Keratin Intermediate Filaments (KIFs) in live cells. A unique feature of KIF networks is a, hypothetically, negative tension generated in the network bundles due to an exchange of material between the network and an effective reservoir of unbundled filaments. Here we analyze the structure and stability of two-dimensional networks with mobile three-way junctions subject to negative tension. First, we analytically examine a simplified case of hexagonal networks with symmetric junctions and demonstrate that, indeed, a negative tension is mandatory for the network stability. Another factor contributing to the network stability is the junction elastic resistance to deviations from the symmetric state. We derive an equation for the optimal density of such networks resulting from an interplay between the tension and the junction energy. We describe a configurational degeneration of the optimal energy state of the network. Further, we analyze by numerical simulations the energy of randomly generated networks with, generally, asymmetric junctions, and demonstrate that the global minimum of the network energy corresponds to the irregular configurations.

scholarly journals Deformation of the Fermi surface of a spinless two-dimensional electron gas in presence of an anisotropic Coulomb interaction potential

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Orion Ciftja
Keyword(s):  
Fermi Surface ◽  
Coulomb Interaction ◽  
Interaction Potential ◽  
Fermi Liquid ◽  
Energy State ◽  
Electron Gas ◽  
Two Dimensional ◽  
Dimensional Electron ◽  
Two Dimensional Electron Gas ◽  
Dimensional Electron Gas

AbstractWe consider the stability of the circular Fermi surface of a two-dimensional electron gas system against an elliptical deformation induced by an anisotropic Coulomb interaction potential. We use the jellium approximation for the neutralizing background and treat the electrons as fully spin-polarized (spinless) particles with a constant isotropic (effective) mass. The anisotropic Coulomb interaction potential considered in this work is inspired from studies of two-dimensional electron gas systems in the quantum Hall regime. We use a Hartree–Fock procedure to obtain analytical results for two special Fermi liquid quantum electronic phases. The first one corresponds to a system with circular Fermi surface while the second one corresponds to a liquid anisotropic phase with a specific elliptical deformation of the Fermi surface that gives rise to the lowest possible potential energy of the system. The results obtained suggest that, for the most general situations, neither of these two Fermi liquid phases represent the lowest energy state of the system within the framework of the family of states considered in this work. The lowest energy phase is one with an optimal elliptical deformation whose specific value is determined by a complex interplay of many factors including the density of the system.

Spatiotemporal dynamics of actin concentration during cytokinesis and locomotion in Dictyostelium

1998 ◽  
Vol 111 (15) ◽  
pp. 2097-2108 ◽  
Author(s):  
S. Yumura ◽  
Y. Fukui
Keyword(s):  
Relative Concentration ◽  
Leading Edge ◽  
Live Cells ◽  
Cell Behavior ◽  
Cleavage Furrow ◽  
Two Dimensional ◽  
Dynamic Changes ◽  
Temporal Regulation ◽  
Ph Dependent ◽  
Actin Concentration

To study the spatial and temporal regulation of the actin cytoskeleton, we have analyzed the actin concentration dynamics in live Dictyostelium. The relative actin concentration was analyzed with respect to cell behavior by fluorescence morphometry. We electroporated rhodamine-actin into Dictyostelium cells and acquired images with 200–300 millisecond temporal and approximately 250 nm spatial resolutions. To convert fluorescence intensity into actin concentration, the observation was made on nearly two-dimensional cells, and the actin signal was ratioed over a volume marker (FITC-BSA or GFP). Since the emission of FITC and GFP is pH-dependent, we first measured the cytoplasmic pH in live cells and determined that the pHi in pseudopods is same as that of general cytoplasm. During cytokinesis, the relative concentration of actin in the cleavage furrow was significantly higher than in the general cytoplasm. In migrating cells, actin was recruited surprisingly rapidly, particularly in the pseudopod. We found that the region of high actin concentration moves relative to the leading edge when a pseudopod projects or retracts. When the pseudopod retracts, the actin density dissipates within 5 seconds. We have also found that actin accumulates in developing pseudopods in an oscillatory manner, and this timing coordinates with advancement of the centroid. This is the first study to reveal the dynamic changes in relative concentration of actin in live cells and to quantitatively correlate these changes with the locomotive behavior of the amoeba.

scholarly journals HOW POLITICAL PARTIES ADJUST TO FIXED VOTER OPINIONS

2005 ◽  
Vol 16 (10) ◽  
pp. 1587-1595
Author(s):  
KRZYSZTOF KUŁAKOWSKI
Keyword(s):  
Political Parties ◽  
Spatial Model ◽  
Two Dimensional ◽  
Symmetric State ◽  
Gaussian Peak ◽  
Political Issues ◽  
Spatial Model Of Voting

We propose a new version of the spatial model of voting. Platforms of five parties were allowed to evolve in a two-dimensional landscape of political issues so as to get maximal numbers of voters. For a Gaussian landscape the evolution leads to a spatially symmetric state, where the platform centers form a pentagon around the Gaussian peak. For a bimodal landscape the platforms located at different peaks get different numbers of voters.

scholarly journals MICAL2 acts through Arp3B isoform-specific Arp2/3 complexes to destabilize branched actin networks

2020 ◽  
Author(s):  
Chiara Galloni ◽  
Davide Carra ◽  
Jasmine V. G. Abella ◽  
Svend Kjær ◽  
Pavithra Singaravelu ◽  
...  
Keyword(s):  
Functional Properties ◽  
Actin Filament ◽  
Actin Assembly ◽  
Actin Network ◽  
Network Stability ◽  
Actin Networks ◽  
Cellular Processes ◽  
Actin Turnover ◽  
Filament Networks

AbstractThe Arp2/3 complex (Arp2, Arp3 and ARPC1-5) is essential to generate branched actin filament networks for many cellular processes. Human Arp3, ARPC1 and ARPC5 exist as two isoforms but the functional properties of Arp2/3 iso-complexes is largely unexplored. Here we show that Arp3B, but not Arp3 is subject to regulation by the methionine monooxygenase MICAL2, which is recruited to branched actin networks by coronin-1C. Although Arp3 and Arp3B iso-complexes promote actin assembly equally efficiently in vitro, they have different cellular properties. Arp3B turns over significantly faster than Arp3 within the network and upon its depletion actin turnover decreases. Substitution of Arp3B Met293 by Thr, the corresponding residue in Arp3 increases actin network stability, and conversely, replacing Arp3 Thr293 with Gln to mimic Met oxidation promotes network disassembly. Thus, MICAL2 regulates a subset of Arp2/3 complexes to control branched actin network disassembly.

Monoclonal antibody to a 43 000 Mr surface protein of a human leukaemia cell line (THP-1) crossreacts with the fibroblast intermediate filament protein vimentin

1985 ◽  
Vol 73 (1) ◽  
pp. 87-103
Author(s):  
H. Herrmann ◽  
W. Aberer ◽  
O. Majdic ◽  
G. Schuler ◽  
G. Wiche
Keyword(s):  
Cell Line ◽  
Intermediate Filaments ◽  
Immunofluorescence Microscopy ◽  
Live Cells ◽  
Intermediate Filament Protein ◽  
Two Dimensional ◽  
Leukaemia Cell ◽  
Drug Induced ◽  
Leukaemia Cell Line ◽  
Cultured Fibroblasts

Monoclonal antibodies were produced against surface antigens of live cells from a human acute monocytic leukaemia cell line (THP-1). One clone, VIC-C2, when assayed by immunofluorescence microscopy, brightly stained the surface of THP-1 cells and the cytoplasm of Langerhans cells, fibroblasts and melanocytes in sections of human skin. The immunoreactive cytoplasmic structures were filamentous and resembled intermediate filaments. By double immunofluorescence microscopy using VIC-C2 and polyclonal antibodies to vimentin, the VIC-C2 antigen was shown to be located on intermediate filaments of cultured fibroblasts and to follow these filaments during various drug-induced rearrangements. As demonstrated by immunoprecipitation, antibody gel overlay and immunoblotting of two-dimensional polyacrylamide gels, VIC-C2 recognized two different antigens in extracts of THP-1 cells: one of Mr = 43 000 and pI = 7, the other of Mr = 57 000. In extracts from various cultured fibroblast cells only the 57 000 Mr antigen was detected. This 57 000 Mr protein was identified as vimentin by immunoblotting of rat glioma C6 cytoskeletons on two-dimensional gels. When vimentin was digested with chymotrypsin, only fragments containing parts of both helical rod pieces and the connecting non-helical spacer-region were strongly antigenic, whereas the helical rods alone were only weakly crossreactive. Moreover, immunoprecipitation revealed that VIC-C2 preferentially reacted with native compared to denatured vimentin.

scholarly journals Two-Dimensional Quantum Hall Effect and Zero Energy State in Few-Layer ZrTe5

Nano Letters ◽  
2021 ◽  
Author(s):  
Fangdong Tang ◽  
Peipei Wang ◽  
Mingquan He ◽  
Masahiko Isobe ◽  
Genda Gu ◽  
...  
Keyword(s):  
Hall Effect ◽  
Quantum Hall Effect ◽  
Energy State ◽  
Quantum Hall ◽  
Two Dimensional ◽  
Zero Energy

scholarly journals Multidisciplinary constraints within a two-dimensional aerodynamic optimization method

2021 ◽  
Author(s):  
Maureen Kolla
Keyword(s):  
Global Minimum ◽  
Optimization Method ◽  
Curvature Function ◽  
Maximum Point ◽  
Two Dimensional ◽  
Aerodynamic Optimization ◽  
Minimum Thickness ◽  
Airfoil Surface ◽  
High Lift ◽  
Additional Constraints

This research demonstrates the importance of including multi-disciplinary constraints within a two-dimensional aerodynamic optimization method. These constraints increase the methods flexibility and versatility by providing the aerodynamic designer with the latitude to expand the design envelope. The additional constraints include a global minimum thickness, a maximum point thickness, an area, two curvature functions and a stowability constraint. The global minimum thickness constraint is used to prevent airfoil surface crossovers. The maximum point thickness and area constraint address airfoil structural requirements. The curvature function constraints deal with the airfoils manufacturability. Finally, the stowability constraints combines flap trajectory, including the flap mechanics, together with the final airfoil shape, to ensure high-lift stowability

scholarly journals Properties of the Free-Standing Two-Dimensional Copper Monolayer

2016 ◽  
Vol 2016 ◽  
pp. 1-6 ◽  
Author(s):  
Li-Ming Yang ◽  
Thomas Frauenheim ◽  
Eric Ganz
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Valence Electron ◽  
Global Minimum ◽  
Electron Gas ◽  
Two Dimensional ◽  
Free Standing ◽  
Functional Theory ◽  
Hexagonal Close Packed ◽  
Dynamics Simulations

We use density functional theory to study a free-standing 2D copper monolayer. We find that the Cu monolayer is stable in 15 ps ab initio molecular dynamics simulations up to 1200 K. Due to the smaller number of bonds per atom in the 2D layer compared to the 3D bulk, we observe a significantly enhanced energy per bond (0.92 versus 0.58 eV/bond). This is similar to the increase in bond strength going from 3D diamond to 2D graphene. We predict various properties of this material, including band structure and density of states. The free-standing 2D Cu monolayer is hexagonal close packed and is the global minimum structure. One valence electron from each atom is delocalized and is donated into a 2D nearly free electron gas.

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