Correlation of Actin Dynamics with Cell Motility and with Expression of Cofilin
The control of cell locomotion and shape change are important mechanisms of many mammalian cells. In the cell cytoplasm, monomeric actin polymerizes to form filaments. During steady crawling of cells, this polymerization extends the plasma membrane, while depolymerization causes membrane withdrawal. Parameters in cell motility, then, can be determined by tracing the lifetime, diffusion, and length of actin filaments. To determine how the actin cycle is controlled, these parameters have been measured and the results resolved with known activities of the actin binding protein cofilin. BAECs (bovine aortic endothelial cells) in mechanically wounded monolayers separate into zones with distinct motility and morphology, thus providing a model for examining the role of actin in determining these characteristics. Photoactivation of fluorescence (p AF), fluorescence recovery after photobleaching (FRAP), and Coomassie experiments revealed that filament turnover and the fraction polymerized correlate with cell motility in mono layers (McGrath, 1998). Here, biochemical assays were used to investigate the mechanisms controlling the transformation from non-motile confluent cells to motile subconfluent cells. Preliminary results indicate a decrease in polymerized actin and an increase in the percentage of cofilin associated with actin filaments correlates with this transition. However, the greater number of filaments present in subconfluent cells indicate a number of other possible factors in this transition. Severing and nucleation are suggested as possible mechanisms involved in the increase in short filaments. The association of short filaments and of cofilin in the cell could provide key evidence of the importance of both of these factors in regulation of cell motility.
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