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Self-organization and mechanics of actomyosin networks attached to artificial and cellular plasma membranes

Subject Area Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
Term from 2019 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 427751228
 
Final Report Year 2024

Final Report Abstract

The cortex of animal cells is a thin, highly dynamically crosslinked actin network directly connected to the plasma membrane. Although it is known that this network is key to the cell's morphogenesis and mechanics, there is still limited understanding of how the plasma membrane influences the organization and behavior of the cortex network and subsequently, how these dynamics impact the cell's mechanical properties and functionality. In this project, we developed physiologically inspired minimal actin cortices to explore these gaps in knowledge. We discovered that the membrane composition influences the amount of the membrane-bound protein ezrin that serves as a linker between membrane and F-actin and as a result, the architecture of the membrane-bound actin network. In particular, lipid species found in the inner leaflet of the mammalian plasma membrane orchestrate the F-actin architecture and the collective dynamics in conjunction with myosin II motors. To compare with an in vivolike situation, we further investigated and manipulated natural cell membrane fragments, maintaining their cortices, to understand the importance of different components in the mesoscopic organization of this dynamic network. We created apical and basal membrane fragments from living cells that spanned micrometer-sized pores and subjected them to sharp-tip indentation. We developed a theoretical model to describe the indentation and relaxation responses of these pore-spanning membranes, capturing the viscoelastic properties of the cortices and relating them to the parameters of intact cells. We investigated the role of cytosolic actin isoforms in cortex mechanics by employing both bottom-up approaches and indentation experiments on MDCK II mutants with a specific isoform knocked out. We found that γ-actin stiffens the cortex compared to β-actin, which is inclined to form clusters rather than networks.

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