Limits...
Fluctuations of intracellular forces during cell protrusion.

Ji L, Lim J, Danuser G - Nat. Cell Biol. (2008)

Bottom Line: Surprisingly, the maxima in adhesion and boundary forces lag behind maximal edge advancement by about 40 s.Maximal F-actin assembly was observed about 20 s after maximal edge advancement.On the basis of these findings, we propose that protrusion events are limited by membrane tension and that the characteristic duration of a protrusion cycle is determined by the efficiency in reinforcing F-actin assembly and adhesion formation as tension increases.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.

ABSTRACT
We present a model to estimate intracellular force variations from live-cell images of actin filament (F-actin) flow during protrusion-retraction cycles of epithelial cells in a wound healing response. To establish a mechanistic relationship between force development and cytoskelal dynamics, force fluctuations were correlated with fluctuations in F-actin turnover, flow and F-actin-vinculin coupling. Our analyses suggest that force transmission at focal adhesions requires binding of vinculin to F-actin and integrin (indirectly), which is modulated at the vinculin-integrin but not the vinculin-F-actin interface. Force transmission at focal adhesions is colocalized in space and synchronized in time with transient increases in the boundary force at the cell edge. Surprisingly, the maxima in adhesion and boundary forces lag behind maximal edge advancement by about 40 s. Maximal F-actin assembly was observed about 20 s after maximal edge advancement. On the basis of these findings, we propose that protrusion events are limited by membrane tension and that the characteristic duration of a protrusion cycle is determined by the efficiency in reinforcing F-actin assembly and adhesion formation as tension increases.

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Predicted adhesion force transients near the leading edge are synchronized in time and co-localized in space with predicted boundary force transients. (a) Definition of edge-tracking probing windows (see Video 3). Per window and time-point averaged boundary and adhesion force transients are calculated. (b) Construction of activity maps of predicted adhesion (left) and boundary forces (right). For one time-point, predicted force magnitudes are collected in all probing windows along the cell edge and copied into one column of the activity map (see example of probing window #19 mapped into the first column). The procedure is repeated for the entire time-lapse sequence to reveal the spatiotemporal organization of force development. Arrows: concurrent dropping of adhesion and boundary forces at the time-points adhesion begin to slide (cf. Fig. 3b). (c) Cross-correlation of adhesion and boundary force activity maps. Scale bar in a: 10 μm.
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Figure 4: Predicted adhesion force transients near the leading edge are synchronized in time and co-localized in space with predicted boundary force transients. (a) Definition of edge-tracking probing windows (see Video 3). Per window and time-point averaged boundary and adhesion force transients are calculated. (b) Construction of activity maps of predicted adhesion (left) and boundary forces (right). For one time-point, predicted force magnitudes are collected in all probing windows along the cell edge and copied into one column of the activity map (see example of probing window #19 mapped into the first column). The procedure is repeated for the entire time-lapse sequence to reveal the spatiotemporal organization of force development. Arrows: concurrent dropping of adhesion and boundary forces at the time-points adhesion begin to slide (cf. Fig. 3b). (c) Cross-correlation of adhesion and boundary force activity maps. Scale bar in a: 10 μm.

Mentions: Efficient cell protrusion requires a balance of propulsive forces at the leading edge and adhesion forces behind the protruding sector. To investigate the coordination of propulsive and adhesive forces, we performed a spatiotemporal correlation analysis of boundary and adhesion force transients along the leading edge. Predicted force magnitudes were averaged in probing windows that moved with the cell edge (Fig. 4a; Video 3) and were copied column-by-column into a color-coded matrix (blue - weak forces; red - strong forces) referred to as activity maps (Fig. 4b). Activity maps of adhesion and boundary forces show similar spatiotemporal organizations. Both forces drop in bottom and top sectors at 4 min and 10 min, respectively (arrows). These events coincide with the onset of FA sliding (arrows in Fig. 3b).


Fluctuations of intracellular forces during cell protrusion.

Ji L, Lim J, Danuser G - Nat. Cell Biol. (2008)

Predicted adhesion force transients near the leading edge are synchronized in time and co-localized in space with predicted boundary force transients. (a) Definition of edge-tracking probing windows (see Video 3). Per window and time-point averaged boundary and adhesion force transients are calculated. (b) Construction of activity maps of predicted adhesion (left) and boundary forces (right). For one time-point, predicted force magnitudes are collected in all probing windows along the cell edge and copied into one column of the activity map (see example of probing window #19 mapped into the first column). The procedure is repeated for the entire time-lapse sequence to reveal the spatiotemporal organization of force development. Arrows: concurrent dropping of adhesion and boundary forces at the time-points adhesion begin to slide (cf. Fig. 3b). (c) Cross-correlation of adhesion and boundary force activity maps. Scale bar in a: 10 μm.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2597050&req=5

Figure 4: Predicted adhesion force transients near the leading edge are synchronized in time and co-localized in space with predicted boundary force transients. (a) Definition of edge-tracking probing windows (see Video 3). Per window and time-point averaged boundary and adhesion force transients are calculated. (b) Construction of activity maps of predicted adhesion (left) and boundary forces (right). For one time-point, predicted force magnitudes are collected in all probing windows along the cell edge and copied into one column of the activity map (see example of probing window #19 mapped into the first column). The procedure is repeated for the entire time-lapse sequence to reveal the spatiotemporal organization of force development. Arrows: concurrent dropping of adhesion and boundary forces at the time-points adhesion begin to slide (cf. Fig. 3b). (c) Cross-correlation of adhesion and boundary force activity maps. Scale bar in a: 10 μm.
Mentions: Efficient cell protrusion requires a balance of propulsive forces at the leading edge and adhesion forces behind the protruding sector. To investigate the coordination of propulsive and adhesive forces, we performed a spatiotemporal correlation analysis of boundary and adhesion force transients along the leading edge. Predicted force magnitudes were averaged in probing windows that moved with the cell edge (Fig. 4a; Video 3) and were copied column-by-column into a color-coded matrix (blue - weak forces; red - strong forces) referred to as activity maps (Fig. 4b). Activity maps of adhesion and boundary forces show similar spatiotemporal organizations. Both forces drop in bottom and top sectors at 4 min and 10 min, respectively (arrows). These events coincide with the onset of FA sliding (arrows in Fig. 3b).

Bottom Line: Surprisingly, the maxima in adhesion and boundary forces lag behind maximal edge advancement by about 40 s.Maximal F-actin assembly was observed about 20 s after maximal edge advancement.On the basis of these findings, we propose that protrusion events are limited by membrane tension and that the characteristic duration of a protrusion cycle is determined by the efficiency in reinforcing F-actin assembly and adhesion formation as tension increases.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.

ABSTRACT
We present a model to estimate intracellular force variations from live-cell images of actin filament (F-actin) flow during protrusion-retraction cycles of epithelial cells in a wound healing response. To establish a mechanistic relationship between force development and cytoskelal dynamics, force fluctuations were correlated with fluctuations in F-actin turnover, flow and F-actin-vinculin coupling. Our analyses suggest that force transmission at focal adhesions requires binding of vinculin to F-actin and integrin (indirectly), which is modulated at the vinculin-integrin but not the vinculin-F-actin interface. Force transmission at focal adhesions is colocalized in space and synchronized in time with transient increases in the boundary force at the cell edge. Surprisingly, the maxima in adhesion and boundary forces lag behind maximal edge advancement by about 40 s. Maximal F-actin assembly was observed about 20 s after maximal edge advancement. On the basis of these findings, we propose that protrusion events are limited by membrane tension and that the characteristic duration of a protrusion cycle is determined by the efficiency in reinforcing F-actin assembly and adhesion formation as tension increases.

Show MeSH
Related in: MedlinePlus