A model for filament buckling at finite temperatures is presented. Starting from the classical worm-like chain model under constant compression, we use a mean-field approach for filament inextensibility to find the complete partition function. We find that there is a simple interpolation formula that describes the free energy of chains or filaments as a function of end-to-end separation, which ...

Actin-based thin filament arrays constitute a fundamental core component of muscle sarcomeres. We have used formation of the Drosophila indirect flight musculature for studying the assembly and maturation of thin-filament arrays in a skeletal muscle model system. Employing GFP-tagged actin monomer incorporation, we identify several distinct phases in the dynamic construction of thin-filament ar...

We study the dynamics of filaments formed when certain materials undergo the isotropic-smectic A phase transition. The basis of this work is a solidification model derived from first principles, taking into account elastic, hydrodynamic and thermodynamic effects. The permeation process, which is solely responsible for the growth of the filament, is analyzed in detail. Various characteristics of...

A possible propulsion mechanism at low Reynolds number is the rotation of a flexible filament, tilted with respect to its rotation axis. Using a simple linear model, we establish the non linear torque-force relations for two torque-driven actuation modes. When the rotation of the filament is induced by two perpendicular transverse oscillating torques, the propulsive force increases monotonicall...

We review the use of thin filament-reconstituted muscle fibers in the study of muscle physiology. Thin filament extraction and reconstitution protocol is a powerful technique to study the role of each component of the thin filament. It is also useful for studying the properties of genetically modified molecules such as actin and tropomyosin. We also review the combination of this protocol with ...

We introduce a novel algorithm for actin filament segmentation in a 2D TIRFM image sequence. We treat the 2D time-lapse sequence as a 3D image volume and propose an over-grown active surface model to segment the body of a filament on all slices simultaneously. In order to locate the two ends of the filament on the over-grown surface, a novel 2D spatiotemporal domain is created based on the resu...

We have used two actin-binding proteins of the intestinal brush border, TW 260/240 and villin, to examine the effects of filament cross-linking and filament length on myosin-actin interactions. TW 260/240 is a nonerythroid spectrin that is a potent cross-linker of actin filaments. In the presence of this cross-linker we observed a concentration-dependent enhancement of skeletal muscle actomyosi...

Actin polymerization powers the directed motility of eukaryotic cells. Sustained motility requires rapid filament turnover and subunit recycling. The essential regulatory protein cofilin accelerates network remodeling by severing actin filaments and increasing the concentration of ends available for elongation and subunit exchange. Although cofilin effects on actin filament assembly dynamics ha...

Polarized total internal reflection fluorescence microscopy (polTIRFM) can be used to detect the spatial orientation and rotational dynamics of single molecules. polTIRFM determines the three-dimensional angular orientation and the extent of wobble of a fluorescent probe bound to the macromolecule of interest. This protocol describes the twirling filament assay, so named because actin sometimes...

The bacterial flagellar apparatus, which involves ∼40 different proteins, has been a model system for understanding motility and chemotaxis. The bacterial flagellar filament, largely composed of a single protein, flagellin, has been a model for understanding protein assembly. This system has no homology to the eukaryotic flagellum, in which the filament alone, composed of a microtubule-based ax...