Calcium transients induce spatially coordinated increases in traction force during the movement of fish keratocytes

Abstract

The coordination of protrusion with retraction is essential for continuous cell movement. In fish keratocytes the activation of stretch-activated calcium channels, and the resulting increase in intracellular calcium, trigger release of the rear cell margin when forward movement is impeded. Although it is likely that retraction involves a calcium-dependent increase in cytoskeletal contractility, it is not known how the timing, magnitude and localization of contractile forces are organized during retraction. We have addressed this question using a new gelatin traction force assay in combination with calcium imaging to determine what changes in cytoskeletal force production accompany calcium-induced retraction. We find that individual calcium transients are followed within seconds by a rapid increase in traction stress that is maintained, or increases in a stepwise manner, until retraction occurs. Increases in traction stress are accompanied by a distinct sequence of changes in the spatial distribution of large traction stresses. Regions of increased traction stress enlarge at the lateral cell margins and expand forward along the cell margin. In particular, rearward facing propulsive' tractions at the leading edge of the cell, which are normally very low, increase several fold. Following retraction, a precipitous drop in traction stress is observed. Such distinct variations in traction stress are not observed in cells when calcium transients are absent. These results suggest a mechanism by which global increases in intracellular calcium can locally regulate contractile force production, in order to maintain a rapid highly directed mode of movement.

TRPC1 channels regulate directionality of migrating cells

“…In general, the coordination of traction forces along the axis of movement is regulated by Ca 2+ influx through Ca 2+ channels. Traction forces are maintained via adhesion contacts until retraction occurs [9]. This is in line with observations made in fibroblasts.…”

“…It has been shown that mechanosensitive Ca 2+ channels are involved in the coordination of the protrusion of the lamellipodium with the retraction of the rear part of migrating cells [8,9]. But so far, the molecular identity of such channels is not known.…”

“…Moreover, [Ca 2+ ] i gradients have been shown to be important in determining cellular polarity and thereby directionality [16,20,36]. Ca 2+ transients can be evoked by the action of Ca 2+ -permeable stretch-activated channels which appear to be gated by membrane stretch that, in migrating cells, could be provoked by the protruding lamellipodium or directly by tension generated by actomyosin forces at sites of adhesion to the matrix [9,17]. Local increases in traction force during the movement of fish keratocytes [8,9,24] and fibroblasts [28] have been connected to such Ca 2+ transients.…”

“…Ca 2+ transients can be evoked by the action of Ca 2+ -permeable stretch-activated channels which appear to be gated by membrane stretch that, in migrating cells, could be provoked by the protruding lamellipodium or directly by tension generated by actomyosin forces at sites of adhesion to the matrix [9,17]. Local increases in traction force during the movement of fish keratocytes [8,9,24] and fibroblasts [28] have been connected to such Ca 2+ transients. The nonspecific blocker of stretch-activated cation channels gadolinium was used to block Ca 2+ transients and impaired migration in these studies.…”

Dynamic determinations: patterning the cell behaviours that close the amphibian blastopore

“…Finally, tensile forces transmitted to neighbouring cells by mediolateral traction may activate stretch-activated calcium channels ( Jaffe 2007), and result in the propagation of contraction, development of traction force (Doyle et al 2004) and the further development of mediolaterally oriented tension. The waves of calcium transients and associated contraction waves are propagated across the IMZ explants (Wallingford et al 2001), and although they do not appear to be temporally or spatially correlated with the directions of MIB progression, or the axes of intercalation under the culture conditions in which they were observed, they may reflect a phenomenon used locally, with different timing and spatial parameters, in vivo.…”