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Keratocytes pull with similar forces on their dorsal and ventral surfaces.

Galbraith CG, Sheetz MP - J. Cell Biol. (1999)

Bottom Line: Borisy. 1997.Cell Biol. 139:397-415).Similar forces were generated on both the ventral (0.2 nN/microm(2)) and the dorsal (0.4 nN/microm(2)) surfaces of the lamella, suggesting that dorsal matrix contacts are as effectively linked to the force-generating cytoskeleton as ventral contacts.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.

ABSTRACT
As cells move forward, they pull rearward against extracellular matrices (ECMs), exerting traction forces. However, no rearward forces have been seen in the fish keratocyte. To address this discrepancy, we have measured the propulsive forces generated by the keratocyte lamella on both the ventral and the dorsal surfaces. On the ventral surface, a micromachined device revealed that traction forces were small and rearward directed under the lamella, changed direction in front of the nucleus, and became larger under the cell body. On the dorsal surface of the lamella, an optical gradient trap measured rearward forces generated against fibronectin-coated beads. The retrograde force exerted by the cell on the bead increased in the thickened region of the lamella where myosin condensation has been observed (Svitkina, T.M., A.B. Verkhovsky, K.M. McQuade, and G. G. Borisy. 1997. J. Cell Biol. 139:397-415). Similar forces were generated on both the ventral (0.2 nN/microm(2)) and the dorsal (0.4 nN/microm(2)) surfaces of the lamella, suggesting that dorsal matrix contacts are as effectively linked to the force-generating cytoskeleton as ventral contacts. The correlation between the level of traction force and the density of myosin suggests a model for keratocyte movement in which myosin condensation in the perinuclear region generates rearward forces in the lamella and forward forces in the cell rear.

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Beads that escape the force of a laser trap are more likely to be recaptured before they reach the thickened region of the lamella. A 50-mW laser trap was used to place and hold a 1-μm bead coated with FNIII 7–10 on the lamella. The bead was more likely to escape the trap if it was initially placed on the cell edge (t = 2.4 s). The same power trap could easily recapture the bead in the thin region of the lamella, as indicated by the sharp change in bead position (t = 10.3 s). However, the bead could not be recaptured if it reached the thickened region of the lamella (t = 29.9 s) or the nucleus.
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Figure 8: Beads that escape the force of a laser trap are more likely to be recaptured before they reach the thickened region of the lamella. A 50-mW laser trap was used to place and hold a 1-μm bead coated with FNIII 7–10 on the lamella. The bead was more likely to escape the trap if it was initially placed on the cell edge (t = 2.4 s). The same power trap could easily recapture the bead in the thin region of the lamella, as indicated by the sharp change in bead position (t = 10.3 s). However, the bead could not be recaptured if it reached the thickened region of the lamella (t = 29.9 s) or the nucleus.

Mentions: We asked whether the regional differences in binding of FN-coated beads (Fig. 6) correlated with differences in the traction forces exerted by the leading edge, compared with other regions of the lamella. To measure the strength of cytoskeletal attachment and force generation against the bead, we tested for reinforcement of the fibronectin beads (Choquet et al. 1997). A laser trap was used to place and hold FN-coated beads near the leading edge of the cell. When placed on the cell at this location, the beads frequently escaped the restraining force of the trap (Fig. 8t = 9 s). We then tried to recapture the beads into the center of the trap to determine if the force exerted on the bead by the cytoskeleton was less than or greater than that exerted by the trap. If the strength of the force exerted on the bead by the cytoskeleton was greater than the force exerted by the trap, then we could not recapture the bead, and the linkage between the bead and the cytoskeleton was considered to be reinforced. This response frequently (∼80%) occurred when FN-coated beads were placed on 3T3 fibroblasts (Choquet et al. 1997); however, as shown by the rapid displacement of the bead when the trap was turned on (Fig. 8t = 10.3 s), beads could easily be recaptured near the edge of the keratocyte lamella (100%, n = 10). Further into the lamella, at the region where it thickens, beads frequently (67%, n = 12) could not be recaptured (Fig. 8t = 29.2 s), and beads could also not be recaptured in the perinuclear region (Fig. 8t = 40.9 s). Control experiments in which beads were continuously recaptured in the front of the lamella indicate that this phenomenon is a function of location, not a function of the number of times that a recapture is attempted. Thus, there appears to be a positional reinforcement of the linkage between the bead and the cytoskeleton as the bead travels into the lamella.


Keratocytes pull with similar forces on their dorsal and ventral surfaces.

Galbraith CG, Sheetz MP - J. Cell Biol. (1999)

Beads that escape the force of a laser trap are more likely to be recaptured before they reach the thickened region of the lamella. A 50-mW laser trap was used to place and hold a 1-μm bead coated with FNIII 7–10 on the lamella. The bead was more likely to escape the trap if it was initially placed on the cell edge (t = 2.4 s). The same power trap could easily recapture the bead in the thin region of the lamella, as indicated by the sharp change in bead position (t = 10.3 s). However, the bead could not be recaptured if it reached the thickened region of the lamella (t = 29.9 s) or the nucleus.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2168090&req=5

Figure 8: Beads that escape the force of a laser trap are more likely to be recaptured before they reach the thickened region of the lamella. A 50-mW laser trap was used to place and hold a 1-μm bead coated with FNIII 7–10 on the lamella. The bead was more likely to escape the trap if it was initially placed on the cell edge (t = 2.4 s). The same power trap could easily recapture the bead in the thin region of the lamella, as indicated by the sharp change in bead position (t = 10.3 s). However, the bead could not be recaptured if it reached the thickened region of the lamella (t = 29.9 s) or the nucleus.
Mentions: We asked whether the regional differences in binding of FN-coated beads (Fig. 6) correlated with differences in the traction forces exerted by the leading edge, compared with other regions of the lamella. To measure the strength of cytoskeletal attachment and force generation against the bead, we tested for reinforcement of the fibronectin beads (Choquet et al. 1997). A laser trap was used to place and hold FN-coated beads near the leading edge of the cell. When placed on the cell at this location, the beads frequently escaped the restraining force of the trap (Fig. 8t = 9 s). We then tried to recapture the beads into the center of the trap to determine if the force exerted on the bead by the cytoskeleton was less than or greater than that exerted by the trap. If the strength of the force exerted on the bead by the cytoskeleton was greater than the force exerted by the trap, then we could not recapture the bead, and the linkage between the bead and the cytoskeleton was considered to be reinforced. This response frequently (∼80%) occurred when FN-coated beads were placed on 3T3 fibroblasts (Choquet et al. 1997); however, as shown by the rapid displacement of the bead when the trap was turned on (Fig. 8t = 10.3 s), beads could easily be recaptured near the edge of the keratocyte lamella (100%, n = 10). Further into the lamella, at the region where it thickens, beads frequently (67%, n = 12) could not be recaptured (Fig. 8t = 29.2 s), and beads could also not be recaptured in the perinuclear region (Fig. 8t = 40.9 s). Control experiments in which beads were continuously recaptured in the front of the lamella indicate that this phenomenon is a function of location, not a function of the number of times that a recapture is attempted. Thus, there appears to be a positional reinforcement of the linkage between the bead and the cytoskeleton as the bead travels into the lamella.

Bottom Line: Borisy. 1997.Cell Biol. 139:397-415).Similar forces were generated on both the ventral (0.2 nN/microm(2)) and the dorsal (0.4 nN/microm(2)) surfaces of the lamella, suggesting that dorsal matrix contacts are as effectively linked to the force-generating cytoskeleton as ventral contacts.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.

ABSTRACT
As cells move forward, they pull rearward against extracellular matrices (ECMs), exerting traction forces. However, no rearward forces have been seen in the fish keratocyte. To address this discrepancy, we have measured the propulsive forces generated by the keratocyte lamella on both the ventral and the dorsal surfaces. On the ventral surface, a micromachined device revealed that traction forces were small and rearward directed under the lamella, changed direction in front of the nucleus, and became larger under the cell body. On the dorsal surface of the lamella, an optical gradient trap measured rearward forces generated against fibronectin-coated beads. The retrograde force exerted by the cell on the bead increased in the thickened region of the lamella where myosin condensation has been observed (Svitkina, T.M., A.B. Verkhovsky, K.M. McQuade, and G. G. Borisy. 1997. J. Cell Biol. 139:397-415). Similar forces were generated on both the ventral (0.2 nN/microm(2)) and the dorsal (0.4 nN/microm(2)) surfaces of the lamella, suggesting that dorsal matrix contacts are as effectively linked to the force-generating cytoskeleton as ventral contacts. The correlation between the level of traction force and the density of myosin suggests a model for keratocyte movement in which myosin condensation in the perinuclear region generates rearward forces in the lamella and forward forces in the cell rear.

Show MeSH
Related in: MedlinePlus