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Cell movement is a highly complex activity that requires the coordination of the cytoskeletal, membrane and adhesion systems of cells. Protrusion and traction are two subtypes of motility found in a wide variety of cells. Both are characterized by the involvement of actin filaments for force generation. These filaments are organized in arrays and held together by fimbrins inside protrusive structures called filopodia and lamellipodia. The organization of actin differs in many motile cells. Models for protrusion and traction force generation are included.

A study conducted on the movement of actin filaments during cellular motion shows that this process involves myosin II which produces the required energy. Butanedione monoxime (BDM) which inhibits myosin II also temporarily suppresses the postmitotic spreading of Potoroo tridactylis kidney cells. Myosin is present along with actin fibers in the spreading filaments but not in the retraction filaments. Lamellipodia protrusion and Listeria propulsion do not involve myosin.

Microtubules are polar polymers of the protein tubulin. In most cells, the minus ends of microtubules are attached to an organizing center near the cell center, whereas the more peripheral [...], Microtubule polarity arises from the head-to-tail orientation of α-β tubulin heterodimers in the microtubule lattice. The identity of the polypeptide at each end of the microtubule is unknown, but structural models predict that the β-tubulin end contains an exchangeable guanosine triphosphate (GTP) binding site. When GTP-coated fluorescent beads were incubated with microtubules, they bound specifically to plus ends, suggesting that tubulin is oriented in microtubules with β-tubulin toward the plus end.

Time-lapse microscopy and photoactivation of fluorescence helps in the study of the spreading of postmitotic PtK2 cells and the behavior of actin filaments in this system. For spreading in postmitotic cells, the forward movement of actin filaments may be involved in generating force. It may also be responsible for the movement of cells. Most of the actin filaments move forward in spreading edges at the same rate as the edge. With respect to the substrate, actin filaments in retraction fibers do not move.

The role of motor proteins in the chromosome segregation that takes place during cell division is now known in greater detail. The proteins assemble into a structure called the kinetochore, which controls the linking of chromosomes to the mitotic spindle microtubules. The kinetochore allows the CBF3 protein complex to attach the DNA to the microtubules. Moreover, the CBF3 complex includes a minus-end-directed microtubule-based motor protein. These motors probably join microtubules and chromosomes together during mitosis.

Motile cilia and flagella are thin, membrane-covered extensions of certain cells that generate a regular, beating waveform. This ancient motile mechanism powers the swimming of sperm and many small organisms, [...]

This paper concerns the mechanism of mitosis. I briefly review the history of mitosis research, emphasizing the role of microscopic observation. The polymerization and depolymerization of microtubules play central roles in both the assembly of the spindle, and in the way it moves chromosomes. I describe recent advances in understanding the dynamic behavior of individual microtubules, and of microtubules attached to kinetochores. The kinetochore is able to hold on to microtubule ends while allowing them to grow and shrink, reactions that can be studied both in living cells and in the test tube. Experiments in which microtubules in living cells are marked and then followed allow us to relate these individual dynamic processes to the overall mechanism of chromosome movement. I end the review by speculating about biochemical mechanisms for producing force on chromosomes in anaphase, and for balancing chromosomes in the center of the metaphase spindle.

Suggests that actin polymerization provides the driving force for bacterial propulsion. The gram-positive acterium Listeria monocytogenes; Phase-dense `comet tails' made of actin filaments; Investigation of the dynamics of the actin filaments in the comet tails using photoactivation fluorescence; More.

Examines the dynamic behavior of polymerized actin microfilaments in the lamelipodium of locomoting cells using the technique of photoactivation of fluorescence. Caged resoruflin-actin polymerization; Movement of actin filaments; Filament turnover; Implications of filament movement and of rapid turnover.

Extends the analysis of the role of microtubule-based motors in mitosis by examining their function on the kinetochores of isolated chromosomes. Proposes that the kinetochore activity controls the direction of chromosome movements using protein phosphorylation.

Reports the localization of an exchangeable guanosine triphosphate (GTP) binding site in microtubules. Incubation of GTP-coated fluorescent beads with microtubules; Binding at the plus ends; Interpreted structure of microtubule; Implications.