Microfilaments cell locomotion

The Locomotion of Amoeba The Locomotion of Fibroblastic Cell Types The Locomotion of Leukocytes The Behavior of Locomoting Cells The Role of the Cytoskeleton in Cell Locomotion The Microtubule-Based Cytoskeleton The Intermediate Filament-Based Cytoskeleton The Microfilament-Based Cytoskeleton The Organization of Microfilaments in Cells Microfilament Dynamics and Cell Locomotion Sites of Lamellar Protrusion May Be Determined by the Nucleation of Actin Polymerization... 

Both microfilaments and microtubules undergo carefully regulated disassembly to and reassembly from their component molecules chiefly actin and tubulin respectively. They influence cell shape. Microfilament roles include cell locomotion, cell adhesion, cell division and endocytosis. The structural status of microfilaments may be modulated by over 30 different proteins some of which, e.g. ankyrin, spectrin... 

Theriot, J.A., Mitchison, T.J. (1991). Actin microfilament dynamics in locomoting cells. Nature, 352, 126-131. 

The cytoskeleton is the collective name for all structural filaments in the cell. The cytoskeletal filaments are involved in establishing cell shape, and providing mechanical strength, locomotion, intracellular transport of organelles and chromosome separation in mitosis and meiosis. The cytoskeleton is made up of three kinds of protein filaments actin filaments (also called microfilaments), intermediate filaments and microtubules. 

The cytoskeletons of other eukaryotic cells typically include both microtubules and microfilaments, which consist of long, chainlike oligomers of the proteins tubulin and actin, respectively. Bundles of microfilaments often lie just underneath the plasma membrane (fig. 17.22). They participate in processes that require changes in the shape of the cell, such as locomotion and phagocytosis. In some cells, cytoskeletal microfilaments appear to be linked indirectly through the plasma membrane to peripheral proteins on the outer surface of the cell (fig. 17.23). Among the cell surface proteins connected to this network is fibronectin, a glycoprotein believed to play a role in cell-cell interactions. The lateral diffusion of fibronectin is at least 5,000 times slower than that of freely diffusible membrane proteins. 

Microfilaments, which are small (5-7 nm in diameter) fibers composed of the protein actin, perform their functions by interacting with certain cross-linking proteins. Important roles of microfilaments include involvement in cytoplasmic streaming (a process that is most easily observed in plant cells in which cytoplasmic currents rapidly displace organelles such as chloroplasts) and ameboid movement (a type of locomotion created by the formation of temporary cytoplasmic protrusions). 

Figure 4a. The illustration depicts a spread fibroblast on a layer of adsorbed protein the arrows represent forces generated by the microfilaments of the cell as an action-reaction pair. These forces are involved in the process of spreading as well as locomotion of the cells on the substrate.

---