Toward Magnetic Control of Cell Polarity

Abstract

Cell polarity is involved in many aspects of cell and developmental biology. It is of fundamental importance for processes as diverse as cell motility, division, or differentiation. Cell polarization manifests itself through complex signaling and transport mechanisms by which molecules are asymmetrically localized within the cell. Whereas usual genetic and biochemical approaches are adapted to identify the elements in a transduction pathway which are necessary for the emergence of a cell polarity, they are not sufficient to know if the sole localized activity of a given effector is sufficient for the cell to acquire a polarity or to determine the kinetics of polarity formation. To address these important issues, we present a novel approach based on functionalized magnetic nanoparticles which are used to induce a localized signaling event of polarization. By doing so, we are able to monitor the cellular dynamic response to a local perturbation while preserving the complexity of the interaction feedbacks needed for the emergence of a global polarity. In our experiments, fluorescent magnetic nanoparticles (100-500 nm in size) are coated with purified constitutively active Cdc42 proteins, a key regulator of cell polarity. Once injected in the cytoplasm of live cells, these nanoparticles are manipulated using a customized magnetic setup able to exert forces on the order of 1-100 pN. We monitor at the single cell level the dynamics of nanoparticles and analyze the role of diverse factors (cytoskeleton, ER, substrate rigidity) on their intracellular mobility. Finally, we measure in different cell lines (Hela, 3T3) the effect of the local signalization on downstream effectors such as actin dynamics.