2,940 research outputs found
Dynamics of Cell Shape and Forces on Micropatterned Substrates Predicted by a Cellular Potts Model
Micropatterned substrates are often used to standardize cell experiments and
to quantitatively study the relation between cell shape and function. Moreover,
they are increasingly used in combination with traction force microscopy on
soft elastic substrates. To predict the dynamics and steady states of cell
shape and forces without any a priori knowledge of how the cell will spread on
a given micropattern, here we extend earlier formulations of the
two-dimensional cellular Potts model. The third dimension is treated as an area
reservoir for spreading. To account for local contour reinforcement by
peripheral bundles, we augment the cellular Potts model by elements of the
tension-elasticity model. We first parameterize our model and show that it
accounts for momentum conservation. We then demonstrate that it is in good
agreement with experimental data for shape, spreading dynamics, and traction
force patterns of cells on micropatterned substrates. We finally predict shapes
and forces for micropatterns that have not yet been experimentally studied.Comment: Revtex, 32 pages, 11 PDF figures, to appear in Biophysical Journa
Unifying autocatalytic and zeroth order branching models for growing actin networks
The directed polymerization of actin networks is an essential element of many
biological processes, including cell migration. Different theoretical models
considering the interplay between the underlying processes of polymerization,
capping and branching have resulted in conflicting predictions. One of the main
reasons for this discrepancy is the assumption of a branching reaction that is
either first order (autocatalytic) or zeroth order in the number of existing
filaments. Here we introduce a unifying framework from which the two
established scenarios emerge as limiting cases for low and high filament
number. A smooth transition between the two cases is found at intermediate
conditions. We also derive a threshold for the capping rate, above which
autocatalytic growth is predicted at sufficiently low filament number. Below
the threshold, zeroth order characteristics are predicted to dominate the
dynamics of the network for all accessible filament numbers. Together, this
allows cells to grow stable actin networks over a large range of different
conditions.Comment: revtex, 5 pages, 4 figure
Traction force microscopy on soft elastic substrates: a guide to recent computational advances
The measurement of cellular traction forces on soft elastic substrates has
become a standard tool for many labs working on mechanobiology. Here we review
the basic principles and different variants of this approach. In general, the
extraction of the substrate displacement field from image data and the
reconstruction procedure for the forces are closely linked to each other and
limited by the presence of experimental noise. We discuss different strategies
to reconstruct cellular forces as they follow from the foundations of
elasticity theory, including two- versus three-dimensional, inverse versus
direct and linear versus non-linear approaches. We also discuss how biophysical
models can improve force reconstruction and comment on practical issues like
substrate preparation, image processing and the availability of software for
traction force microscopy.Comment: Revtex, 29 pages, 3 PDF figures, 2 tables. BBA - Molecular Cell
Research, online since 27 May 2015, special issue on mechanobiolog
Effect of adhesion geometry and rigidity on cellular force distributions
The behaviour and fate of tissue cells is controlled by the rigidity and
geometry of their adhesive environment, possibly through forces localized to
sites of adhesion. We introduce a mechanical model that predicts cellular force
distributions for cells adhering to adhesive patterns with different geometries
and rigidities. For continuous adhesion along a closed contour, forces are
predicted to be localized to the corners. For discrete sites of adhesion, the
model predicts the forces to be mainly determined by the lateral pull of the
cell contour. With increasing distance between two neighboring sites of
adhesion, the adhesion force increases because cell shape results in steeper
pulling directions. Softer substrates result in smaller forces. Our predictions
agree well with experimental force patterns measured on pillar assays.Comment: 4 pages, Revtex with 4 figure
Role of anisotropy for protein-protein encounter
Protein-protein interactions comprise both transport and reaction steps.
During the transport step, anisotropy of proteins and their complexes is
important both for hydrodynamic diffusion and accessibility of the binding
site. Using a Brownian dynamics approach and extensive computer simulations, we
quantify the effect of anisotropy on the encounter rate of ellipsoidal
particles covered with spherical encounter patches. We show that the encounter
rate depends on the aspect ratios mainly through steric effects,
while anisotropic diffusion has only a little effect. Calculating analytically
the crossover times from anisotropic to isotropic diffusion in three
dimensions, we find that they are much smaller than typical protein encounter
times, in agreement with our numerical results.Comment: 4 pages, Revtex with 3 figures, to appear as a Rapid Communication in
Physical Review
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