Global alignment and local curvature of microtubules in mouse fibroblasts are robust against perturbations of vimentin and actin†

Abstract

The eukaryotic cytoskeleton is an intricate network of three types of mechanically distinct biopolymers – actin filaments, microtubules and intermediate filaments (IFs). These filamentous networks determine essential cellular functions and properties. Among them, microtubules are important for intracellular transport and establishing cell polarity during migration. Despite their intrinsic stiffness, they exhibit characteristic bending and buckling in cells due to nonthermal forces acting on them. Interactions between cytoskeletal filaments have been found but are complex and diverse with respect to their effect on the mechanical behavior of the filaments and the architecture of networks. We systematically study how actin and vimentin IFs influence the network structure and local bending of microtubules by analyzing fluorescence microscopy images of mouse fibroblasts on protein micropatterns. Our automated analysis averages over large amounts of data to mitigate the effect of the considerable natural variance in biological cell data. We find that the radial orientation of microtubules in circular cells is robust and is established independently of vimentin and actin networks. Observing the local curvature of microtubules, we find highly similar average bending of microtubules in the entire cell regardless of the cytoskeletal surrounding. Small systematic differences cannot be attributed directly to vimentin and actin densities. Our results suggest that, on average, microtubules in unpolarized mouse fibroblasts are unexpectedly independent of the rest of the cytoskeleton in their global network structure and their local curvature.