| Detergent extracted cells in tissue culture often maintain their insoluble intern scaffolding called cytoskeleton. As the name implies, the function of cytoskeleton is structural, and is essential for providing complex and dynamic organization of the cytoplasm. This thesis focuses on the mechanical properties of the cytoskeleton, with an emphasis towards a characterization of their intrinsic physical properties that underlie their cellular roles. I examined the mechanical properties of cytoskeleton as they occur in cells using the thermal fluctuation of endogenous organelles, as well as in reconstituted suspensions using mechanical rheometry.; The complex pattern and dynamics of cytoskeletal networks are evident from the thermal fluctuations of spherical organelles in cytoplasm. The mechanical properties of the cytoplasm are highly heterogeneous, but the elasticity generally correlates with F-actin distribution. F-actin disrupting agents act quickly to soften the elasticity. Yet, a network of purified F-actin does not provide sufficient rigidity. Thus, the cells must utilize accessory proteins for structural scaffolding.; Keratins, the epithelial specific cytoskeletal proteins, form an extensive network in the cytoplasm that maintains the integrity of the epithelial tissues. Unlike F-actin, very few binding proteins for keratin filaments are known. This deficiency seems to be compensated by the ability of keratin filaments to self-organize into bundled array. Using a strain-controlled rheometer, we analyzed and compared keratin filaments existing in simple and complex epithelial tissues. When the interfacial elasticity is minimized by the addition of phospholipids, the mechanical properties of various keratin filaments correlate with the structural features observed using microscopic techniques. The bundling of filaments induced by a minimal change in buffer condition increases the elasticity to the cellular level. The mechanical properties of cytoskeletal elements measured in cells and reconstituted samples reveal the complexity of cytoskeletal networks and organization that are required for their functions. |
