Browsing by Author "Nietmann, Peter"

Abstract The implications of the existence of different actins expressed in epithelial cells for network mechanics and dynamics is investigated by microrheology and confocal imaging. γ -actin predominately found in the apical cortex forms stiffer networks compared to β -actin, which is preferentially organized in stress fibers. We attribute this to selective interactions with Mg 2+ -ions interconnecting the filaments’ N-termini. Bundling propensity of the isoforms is different in the presence of Mg 2+ -ions, while crosslinkers such as α -actinin, fascin, and heavy meromyosin alter the mechanical response independent of the isoform. In the presence of myosin, β -actin networks show a large number of small contraction foci, while γ -actin displays larger but fewer foci indicative of a stronger interaction with myosin motors. We infer that subtle changes in the amino acid sequence of actin isoforms lead to alterations of the mechanical properties on the network level with potential implications for specific biological functions.

The cytoskeleton, an intricate network of protein filaments, motor proteins, and cross-linkers, 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.

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.

The hexameric and octameric variants of benzene-fused oligo-BODIPYs emit fluorescence in the near-infrared (NIR). Their potential for biophotonics and imaging is reported.