Dynamics of Focal Adhesions

Abstract

Focal adhesions(FA) are the cells machinery to sense the environment and help in migration. They are macromolecular complexes which link the actin to the integrins and are extremely dynamic in nature. The mechanism of FA movement in the cell is unclear. Treadmilling and sliding are the two modes in discussion. Recent experimental results for force velocity relationship in focal adhesions show a biphasic relationship between F-actin speed and traction force.In our study, an FA complex is modelled as a one dimensional array of point masses connected laterally to each other and to the substrate by springs. Binding and unbinding of molecules to the substrate corresponds to sliding and adding/deleting from the ends corresponds to treadmilling in the system. Through gillespie simulations, we sought to understand the mechanism of FA movement by comparing the force velocity curves generated to the experimental data. From our preliminary results, for a one layer model in a small range of forces, we see that there is a range of possible velocities for a given force depending on the ratio of rate constants for treadmilling and sliding mechanisms. Another observation is that on increasing the stiffness of the substrate, the slope of these curves decreases significantly only in the sliding dominated mechanisms.