Measurement of the Persistence Length of Cytoskeletal Filaments using Curvature Distributions

Abstract

Cytoskeletal filaments such as microtubules and actin filaments play important roles in the mechanical integrity of cells and the ability of cells to respond to their environment. Measuring the mechanical properties of cytoskeletal structures is crucial for gaining insight into intracellular mechanical stresses and their role in regulating cellular processes. One of the ways to characterize these mechanical properties is by measuring their persistence length, the average length over which filaments stay straight. There are several approaches in the literature for measuring filament deformations, including Fourier analysis of images obtained using fluorescence microscopy. Here, we show how curvature distributions can be used as an alternative tool to quantify bio-filament deformations, and investigate how the apparent stiffness of filaments depends on the resolution and noise of the imaging system. We present analytical calculations of the scaling curvature distributions as a function of filament discretization, and test our predictions by comparing Monte Carlo simulations to results from existing techniques. We also apply our approach to microtubules and actin filaments obtained from in vitro gliding assay experiments with high densities of non-functional motors, and calculate the persistence length of these filaments. The presented curvature analysis is significantly more accurate compared to existing approaches for small data sets, and can be readily applied to both in vitro or in vivo filament data through the use of an ImageJ plugin we provide.1 not peer-reviewed)

Controlling the Rigidity of Kinesin-Propelled Microtubules in an In Vitro Gliding Assay Using the Deep-Sea Osmolyte Trimethylamine N-Oxide

“…The outcome, shown in Figure a, clearly reveals that the persistence length of MTs gradually decreased upon increasing the concentration of TMAO in the in vitro gliding assay. The persistence length of MTs was 285 ± 47 μm (fit value ± standard deviation) in the absence of TMAO, which agrees to that previously reported in the literature. , At the highest concentration of TMAO employed in this study (1.5 M), the persistence length of MTs decreased to 37 ± 4 μm. Based on the above results, it is evident that the rigidity of the MTs, propelled by kinesins in an in vitro gliding assay, can be modulated by tuning the concentration of TMAO in the gliding assay.…”

PCP and Septins govern the polarized organization of the actin cytoskeleton during convergent extension

“…Because our recent work with deep cell-cell junctions during CE has revealed a key role for very local, subcellular mechanical heterogeneity 31,47,48 , we looked for similar heterogeneities conferred by the actin node and cable system during CE. To this end, we examined persistence length (Lp) of actin filaments, a basic mechanical property that reflects bending stiffness of a polymer, and this metric can be assayed simply from image data 49,50 . By segmenting LifeAct-GFP labeled actin from TIRF movies using SOAX software 51 , we calculated the Lp 49 .…”

Connecting conformational stiffness of the protein with energy landscape by a single experiment

“…This is also relevant to the nucleic acid, which exhibits very weak dependence to the ionic strength 20 . Indeed, the mechanosensing polyprotein like microtubules and actin have relatively higher persistence length (L p ) and thus show higher bending rigidity that allows them to form crosslinking structures 105,106 in cell cortex and protrusion. Moreover, due to extended topology they are constantly exposed to the varying ionic environments that change unfolding pattern of their domains during interaction with other proteins that further can decode unprecedented physical viewpoints of cell division and structure maintenance.…”