Impact of Vimentin Intermediate Filaments on 3D Multicellular Collective Behavior

Abstract

Vimentin, a type III intermediate filament, is an understudied component of the cytoskeletal system. However, in recent studies we can see its structural and mechanical properties aid in a cell's survival and migration. It forms a hyperelastic network and works synergistically with actin and microtubule to protect against large deformations. Despite vimentin intermediate filaments critical role in many biological processes, there are limited studies on its role in collective migration in 3D in vitro. To elucidate vimentin’s role in a collective cell cluster, single MCF-7 cells are embedded in a Matrigel-Alginate gel, which then grow into multicellular systems. The MCF-7 cells utilized are vimentin null, chemically inducible to form vimentin networks that interact with the other components of the cytoskeleton. These MCF-7 allow for controlled expression of mature vimentin intermediate filament (VIFs) which then form networks. We study these multicellular clusters over the course of 14 days. We demonstrate that there are key differences in morphology and mechanics, with the presence of vimentin. Our results suggests VIFs create more irregular cell clusters with more visible dynamic interplay with the environment. Uninduced (no VIFs) clusters were overall less dynamic and exhibited spherical morphology and minimal protrusions. Cluster with mature VIFs tended to form more elongated multicellular clusters with increased number of projections into the surrounding gel. In these induced (with VIFs) clusters these projections are shown to be constantly protruding and retracting along with the nuclei continually reorganizing. Our results show that these projections are accompanied with increased protrusive and contractile gel displacements. These results indicate that vimentin network generate an dynamic and functional morphology, along with mechanically perturbing their environment in the early stages of cell cluster collective behavior.