Cell motility : the dynamics of the cortical weave of microfilaments and its relation to microtubules and coated vesicles in fibroblasts and glial cells

Sammanfattning: Actin and myosin, the major components of the microfilament system are found in most - if not all - eukaryotic cells. In muscle they form the basis of the contractile apparatus which generates the rapid, strong and unidirectional movements that characterizes muscle activity. Other cell types have developed their special arrangement of the microfilament system: some form what appears to be rather stable structures, while others undergo considerable reorganizations. Such reorganizations for instance are thought to be fundamental for the dynamic and flexible behavior shown by fibroblasts in vitro. How these reorganizations - which probably involve polymerization, bundling, debundling and depolymerization of actin - are regulated is beginning to be unravelled by the isolation and characterization of various actin-binding proteins.In addition to the various activities exerted by the microfilament system, the microtubules and most likely the intermediate filaments too contribute to non-muscle cell motile phenomena. Studies of the organization of these three fiber systems and their possible relationship are therefore important in order to understand cell moti1ity.This thesis describes the visualization of the peripheral microfilament organization in fibroblasts and glial cells by transmission electron microscopy of negatively- stained whole-cell mounts. Conditions for preparation of the specimen were developed in order to obtain a balanced solubilization and preservation of the cell components. The visualization of the cell ultrastructure was improved by using a mixture of detergent and fixative in combination with sodium si 1icotungstate as negative stain. This made it possible to make observations of the details in the microfilament arrangement in the periphery of spreading and translocating cells as well as of the surface structures induced by the growth-stimulating hormone, platelet-derived growth factor.The microtubules and their relation to the microfilament-based structures in the cell periphery were also visualized by this technique.Some observations concerning the possible involvement of the microfilament system in endocytosis, especially their relation to coated vesicles, are also described.