Biology subjects

Schepers, A. V.

Publications and source records attributed to Schepers, A. V..

5 recordsLinked to original sources

bioRxiv2025

The keratin cortex stabilizes cells at high strains

The eukaryotic cytoskeleton consists of three filament types: actin filaments, microtubules and intermediate filaments (IFs). IF proteins are expressed in a cell-type specific manner, and keratins are found in epithelial cells. In certain cell types, keratin forms a layer close to the membrane which may be referred to as an "IF-cortex". It is hypothesized that this IF-cortex arranges with radial bundles in a "rim-and-spokes" structure in epithelia. Based on this hypothesis, IFs and actin filaments might add complementary mechanical properties to the cortex. It was previously shown that single IFs in vitro remain undamaged at high strains and display a non-linear stretching behavior. We now ask the question of whether this unique force-extension behavior of single IFs is also relevant in the context of a filament network within a cell. We show that keratin-deficient (KO) MDCK II cells readily form 2D cell layers and 3D cysts and withstand high equibiaxial strains. High-resolution imaging using STED microscopy reveals altered actin cortex structures in KO cells, presumably in response to the missing keratin. We investigate the influence of the equibiaxial strain on the viscoelastic properties of wild-type (WT) and KO cells using atomic force microscopy. We find that the KO cells exhibit a higher pre-stress than the WT cells, likely due to the change of the cortical structure. Interestingly, both the pre-stress and the fluidity of the KO cells are altered already at intermediate strains, whereas the WT cells show a response only at high strain. Similarly, the KO cysts are stretched more easily at low strains than the WT cysts during injection experiments. The compressibility modulus is analyzed in a spatially resolved manner and we find this modulus to be increased at the cell rim, compared to the inside region, due to the geometry of the cell layer. Our results indicate that KO cells compensate for the missing keratin, but are nevertheless very sensitive to external strain, whereas the intricate interplay between the actin and keratin cortices in WT cells preserves the mechanical state and cell stability.

biophysics↗

bioRxiv2021

Multiscale mechanics and temporal evolution of vimentin intermediate filament networks

The cytoskeleton, an intricate network of protein filaments, motor proteins, and crosslinkers, largely determines the mechanical properties of cells. Among the three filamentous components, F-actin, microtubules, and intermediate filaments (IFs), the IF network is by far the most extensible and resilient to stress. We present a multiscale approach to disentangle the three main contributions to vimentin IF network mechanics - single filament mechanics, filament length, and interactions between filaments - including their temporal evolution. Combining particle tracking, quadruple optical trapping and computational modeling, we derive quantitative information on the strength and kinetics of filament interactions. Specifically, we find that hydrophobic contributions to network mechanics enter mostly via filament elongation kinetics, whereas electrostatics have a direct influence on filament-filament interactions. These results indicate that cells might need to explicitly suppress attractive interactions to re-organize the extremely stable cellular vimentin network.

biophysics↗

bioRxiv2020

Vimentin Intermediate Filaments Stabilize Dynamic Microtubules by Direct Interactions

The cytoskeleton determines cell mechanics and lies at the heart of important cellular functions. Growing evidence suggests that the manifold tasks of the cytoskeleton rely on the interactions between its filamentous components - actin filaments, intermediate filaments and microtubules. However, the nature of these interactions and their impact on cytoskeletal dynamics are largely unknown. Here, we show in a reconstituted in vitro system that vimentin intermediate filaments stabilize microtubules against depolymerization and support microtubule rescue. To understand these stabilizing effects, we directly measured the interaction forces between individual microtubules and vimentin filaments. Combined with numerical simulations, our observations provide detailed insight into the physical nature of the interactions and how they affect microtubule dynamics. Thus, we describe an additional, direct mechanism for cells to establish the fundamental cross-talk of cytoskeletal components alongside linker proteins. Moreover, we suggest a novel strategy to estimate the binding energy of tubulin dimers within the microtubule lattice.

biophysics↗

bioRxiv2019

Tuning intermediate filament mechanics by indirect and direct charge variations

The cytoskeleton is formed by three types of filamentous proteins - microtubules, actin filaments, and intermediate filaments (IFs) - and enables cells to withstand external and internal forces. Vimentin is the most abundant IF protein in humans and assembles into 10 nm diameter filaments with remarkable mechanical properties, such as high extensibility and stability. It is, however, unclear to which extent these properties are influenced by the electrostatic environment. Here, we study the mechanical properties of single vimentin filaments by employing optical trapping combined with microfluidics. Force-strain curves, recorded at varying ion concentrations and pH values, reveal that the mechanical properties of single vimentin IFs are influenced by pH and ion concentration. By combination with Monte Carlo simulations, we relate these altered mechanics to electrostatic interactions of subunits within the filaments. We thus suggest possible mechanisms that allow cells to locally tune their stiffness without remodeling the entire cytoskeleton.

biophysics↗

bioRxiv2019

Lateral Subunit Coupling Determines Intermediate Filament Mechanics

The cytoskeleton is a composite network of three types of protein filaments, among which in-termediate filaments (IFs) are the most extensible ones. Two very important IFs are keratin and vimentin, which have similar molecular architectures, but different mechanical behaviors. Here we compare the mechanical response of single keratin and vimentin filaments using optical tweezers. We show that the mechanics of vimentin strongly depends on the ionic strength of the buffer and that its force-strain curve suggests a high degree of cooperativity between subunits. Indeed, a computational model indicates that in contrast to keratin, vimentin is characterized by strong lateral subunit coupling of its charged monomers during unfolding of -helices. We conclude that cells can tune their mechanics by differential use of keratin versus vimentin.

biophysics↗