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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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Displacement of FN-coated beads within the laser trap determines the force exerted by the dorsal surface of keratocytes. A 50-mW laser trap was used to place and hold a 1 μm bead coated with FNIII 7–10 on the lamella of a keratocyte. The cell displaces the bead with a force of 158 pN (t = 7.7 s) before it exerts enough force to escape the trap. Once the bead escapes the trap, it travels rearward at approximately the same velocity as the cell travels forward.
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Figure 7: Displacement of FN-coated beads within the laser trap determines the force exerted by the dorsal surface of keratocytes. A 50-mW laser trap was used to place and hold a 1 μm bead coated with FNIII 7–10 on the lamella of a keratocyte. The cell displaces the bead with a force of 158 pN (t = 7.7 s) before it exerts enough force to escape the trap. Once the bead escapes the trap, it travels rearward at approximately the same velocity as the cell travels forward.

Mentions: To quantify dorsal traction forces, a 1-μm diam FN-coated bead was placed on the cell surface and constrained within an optical gradient laser trap. An example of a typical experiment is shown in Fig. 7. As the cell pulled on the bead that was constrained by the laser trap, the bead displaced from the center of the trap (Fig. 7t = 7.7 s), but it did not escape from the trap. From the displacement of the bead within the trap and the stiffness of the trap, we were able to calculate that the cell exerted a force on the bead of 158 pN, or 0.4 ± 0.3 nN/μm2 (n = 7, ± SD). Eventually (Fig. 7t > 12 s), the cell exerted enough force on the bead to pull the bead from the trap. Once the bead escaped the trap, it traveled rearward with approximately the same velocity as the forward traveling cell, until it reached the nuclear region when the bead stopped moving. Moreover, this velocity is equivalent to the rate of retrograde flow of the actin cytoskeleton (data not shown).


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

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

Displacement of FN-coated beads within the laser trap determines the force exerted by the dorsal surface of keratocytes. A 50-mW laser trap was used to place and hold a 1 μm bead coated with FNIII 7–10 on the lamella of a keratocyte. The cell displaces the bead with a force of 158 pN (t = 7.7 s) before it exerts enough force to escape the trap. Once the bead escapes the trap, it travels rearward at approximately the same velocity as the cell travels forward.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2168090&req=5

Figure 7: Displacement of FN-coated beads within the laser trap determines the force exerted by the dorsal surface of keratocytes. A 50-mW laser trap was used to place and hold a 1 μm bead coated with FNIII 7–10 on the lamella of a keratocyte. The cell displaces the bead with a force of 158 pN (t = 7.7 s) before it exerts enough force to escape the trap. Once the bead escapes the trap, it travels rearward at approximately the same velocity as the cell travels forward.
Mentions: To quantify dorsal traction forces, a 1-μm diam FN-coated bead was placed on the cell surface and constrained within an optical gradient laser trap. An example of a typical experiment is shown in Fig. 7. As the cell pulled on the bead that was constrained by the laser trap, the bead displaced from the center of the trap (Fig. 7t = 7.7 s), but it did not escape from the trap. From the displacement of the bead within the trap and the stiffness of the trap, we were able to calculate that the cell exerted a force on the bead of 158 pN, or 0.4 ± 0.3 nN/μm2 (n = 7, ± SD). Eventually (Fig. 7t > 12 s), the cell exerted enough force on the bead to pull the bead from the trap. Once the bead escaped the trap, it traveled rearward with approximately the same velocity as the forward traveling cell, until it reached the nuclear region when the bead stopped moving. Moreover, this velocity is equivalent to the rate of retrograde flow of the actin cytoskeleton (data not shown).

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