Nanoscale Organization of the Actomyosin Cortex During the Cell Cycle

Cell shape regulation is key to a number of fundamental biological processes, including cell migration and division. In animal cells, cell morphology is controlled primarily by the cortex, a thin actomyosin network underlying the plasma membrane. The cortex determines global physical properties of the cell, such as tension. Previous studies have shown that spatial and temporal changes in cortical tension drive shape changes during the cell cycle, such as mitotic rounding and cytokinetic furrow ingression. However, the changes in cortical structure and composition driving changes in cortical tension remain unclear. We are investigating this question using a combination of cell biology experiments, quantitative imaging and modeling. As the cortex dimensions are below the resolution limit of conventional light microscopy, we have developed a dual-color localization method to investigate the spatial organization of the cortex. This method is based on estimating the relative localization of cortex components with respect to one another by labeling them with chromatically different fluorophores. Using our method, we quantified cortex thickness and compared the localization of key actin binding proteins in interphase and mitosis. We showed that cortex thickness decreases in mitosis, indicating a reorganization of the cortical network. Using targeted siRNA knockdowns, we identified key regulators of cortex thickness. Interestingly, proteins controlling cortex thickness also affect cortical tension, measured using atomic force microscopy. Agent based simulations of the cortex shed light on how network spatial organization controls cortex tension. Our systematic analysis will help uncover the mechanisms by which cortical structure and organization regulate cortical mechanics, thereby driving cellular morphogenesis.