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An excitable signal integrator couples to an idling cytoskeletal oscillator to drive cell migration

Abstract

It is generally believed that cytoskeletal activities drive random cell migration, whereas signal transduction events initiated by receptors regulate the cytoskeleton to guide cells. However, we find that the cytoskeletal network, involving SCAR/WAVE, Arp 2/3 and actin-binding proteins, is capable of generating only rapid oscillations and undulations of the cell boundary. The signal transduction network, comprising multiple pathways that include Ras GTPases, PI(3)K and Rac GTPases, is required to generate the sustained protrusions of migrating cells. The signal transduction network is excitable, exhibiting wave propagation, refractoriness and maximal response to suprathreshold stimuli, even in the absence of the cytoskeleton. We suggest that cell motility results from coupling of ‘pacemaker’ signal transduction and ‘idling motor’ cytoskeletal networks, and various guidance cues that modulate the threshold for triggering signal transduction events are integrated to control the mode and direction of migration.

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Figure 1: Fast oscillations of the cytoskeletal activities revealed by t-stacking.
Figure 2: The slow, excitable signalling network.
Figure 3: Rac activity correlates with the dynamics of the signalling network.
Figure 4: Coupling of signal transduction and cytoskeletal networks in protrusions.
Figure 5: The STEN–CON coupling model and computer simulation.
Figure 6: Predictions of STEN–CON coupling for cell migration.

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Acknowledgements

The authors would like to thank M. Amzel, D. Montell, M. Iijima, T. Inoue and members of the Devreotes and Iglesias laboratories for helpful suggestions, B. Diplas for generating cell centroid tracks, P. Van Haastert for the RBD–GFP construct, R. Insall (The Beatson Institute, UK) for the HSPC300–GFP construct, G. Gerisch (Max Planck Institute for Biochemistry, Germany) for the LimE–RFP construct, and D. Robinson (Johns Hopkins University, USA) for coronin–GFP and the original video of dynacortin-expressing cells. We are grateful to V. Filic and I. Weber (Ruder Boskovic Institute, Croatia) for sharing the PAK(GBD)–YFP biosensor for Rac activity. This work was supported in part by grants from the National Institutes of Health, GM28007 (to P.N.D.), GM34933 (to P.N.D.) and GM71920 (to P.A.I.), and a H. L. Plotnick Fellowship from the Damon Runyon Cancer Research Foundation, DRG2019-09 (to C.H.H.).

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Authors

Contributions

C-H.H. and M.T. performed the experiments. C.S. and P.A.I. carried out computer simulations. All authors analysed the data and wrote the manuscript. P.N.D. supervised the study.

Corresponding author

Correspondence to Peter N. Devreotes.

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The authors declare no competing financial interests.

Integrated supplementary information

Supplementary Figure 1 Cytoskeletal network.

(a) Illustration of the t-stack technique. The frames of a TIRF video (left) are stacked to produce the t-stack (right). The position and orientation of frames t1, t2, and t3 in the t-stack is shown (middle). The immobile red oval generates the red cylinder in the t-stack, while the expansion of the green region over time creates the oblique cone-like appendage. (b-d) T-stacks derived from published TIRF time-lapse videos of a wild-type cell expressing GFP-dynacortin (b) 1, a wild-type cell expressing GFP-Arp3 (c) 2, and a SCAR- cell expressing GFP-WASP (d) 3 showing fast oscillations of cytoskeletal proteins. The red arrowhead indicates a pseudopodium preceding oscillations of dynacortin (green arrowheads). (e) T-stacks from a cell co-expressing HSPC300-GFP and cAR1-RFP. (f-h) T-stacks of LimE expressed in gβ- cells (f), pten- cells (g), and LY294002-treated wild-type cells (h). (i) Cytoskeletal oscillations in cells expressing constitutively active Ras. LimE-RFP in rasC- cells expressing Flag-RasC (left) or Flag-RasCQ62L (right). The videos used for these t-stacks were published earlier4. (j) TIRF image(top) and t-stack (bottom) of a latrunculin-treated cell expressing HSPC300-GFP, showing foci of fluorescence that did not oscillate.

Supplementary Figure 2 Signal transduction network.

(a) TIRF images of a cell co-expressing RBD-GFP and PH-RFP showing coordinated propagation of RBD and PH waves. Video rate was 3 spf (Supplementary Video S3). (b) The temporal profiles of RBD intensity at three spots marked 1, 2, 3 in (a). (c) The progression of contour lines for gray values 10, 20 and 30 along the yellow line in (a) was used to calculate the speed of the wave propagation. In the example, the speed of the wave between 15 sec and 48 sec was 12.8 μm/min by fitting the gray value 20 contour with a least square line. (d-h) Snapshots from TIRF videos of PH-GFP in cells treated with 4 μM latrunculin A (top, Supplementary Movies S4S8) and the corresponding t-stacks (bottom). Panels (e) and (f) are the same cells at different times, (h) is the same cell as the left cell in (d), and (g) is a different cell. To visualize interior activities, a basal level of cellular fluorescence was subtracted from each video before the t-stacks were generated.

Supplementary Figure 3 Signaling and cytoskeletal activities on protrusions.

(a) T-stacks of two cells co-expressing RBD-GFP and LimE-RFP as well as the merged t-stack. The brackets in the cell on the left point to protrusions with high RBD and LimE. The cell on the right has very low level of RBD-GFP expression, but fast LimE oscillations are visible. Note that weak oscillations in the RBD t-stack (left cell) reflect changes in the boundary which delineates cytosolic RBD rather than RBD intensity on the cortex. Video rate was 2 spf. (b) Frames from a TIRF video of cells co-expressing RBD-GFP and LimE-RFP showing the distributions of RBD and LimE in protrusions. (c) Close-up views of a protrusion (yellow boxes in (a)) showing a smoother change of RBD intensity compared with that of LimE. (d) Frames from the TIRF video of a single large protrusion of a cell expressing HSPC300-GFP (Supplementary Movie S10). (e) t-stack of the video in (d). (f) Kymograph across the dashed line in (d). Arrowheads point to pauses in HSPC300 recruitment where cell boundary expansion stalled.

Supplementary Figure 4 Simulation of coupled systems.

(a) The slow excitable system is implemented as an activator (Xs)-inhibitor (Ys) system. (b) Phase plane plot of the slow excitable system. Red and green lines are nullclines for the activator and inhibitor components, respectively. The solid black circle represents the unique, stable equilibrium, found at the intersection of the two nullclines. The blue arrows represent the system evolution at different points in the phase plane. Two different trajectories are denoted by the black lines. The dotted black line represents a sub-threshold perturbation from which the system returns quickly to the equilibrium. The solid black line illustrates a super-threshold perturbation that causes the system to undergo a large excursion before returning to the equilibrium. (c) The Fast oscillatory system is also implemented using an activator (Xf)-inhibitor (Y f) system and also incorporates the influence of stochastic perturbations. (d) Phase plane plot of the fast oscillatory system. Red and green lines are nullclines for the activator and inhibitor components, respectively. In this case the system has three equilibria, at the points where the nullclines intersect. The solid black circles denote two stable equilibria, the open black circle the unique, unstable equilibrium. The blue arrows represent the evolution at different points in the phase plane. Trajectories are denoted by the black lines.

Supplementary Figure 5 Washout of LY294002 reversed the motility to plaA-/piaA- cells.

(a) Trajectories of cell migration. Random migration of cells were recorded and quantified as in Figure 6. For the LY washout experiment, cells were changed to buffer without LY294002, and allowed to settle for 40 min before recording was started. Duration of tracks is 60 min. (b) Quantification of net speed, motility speed, and persistence (mean ± s.d. from n = 4, 3, 3 experiments for plaA-/piaA- with DMSO, plaA-/piaA- with LY294002, and wash off, respectively. The source data is provided in Supplementary Table 3.)

Supplementary Table 1 Parameter values for simulations.
Supplementary Table 2 Statistics source data.

Supplementary information

Supplementary Information

Supplementary Information (PDF 732 kb)

HSPC300-GFP.

Time-lapse TIRF video of a Dictyostelium cell expressing HSPC300-GFP with a rate of 1 spf. The video is shown at 15 frames/s and corresponds to Fig. 1a,b (MOV 1052 kb)

T-stack of HSPC300-GFP.

Rotation of the t-stack along its t(time)-axis. The speed of the rotation is shown at 40 degrees/s. The t-stack was generated from Movie S1and corresponds to Fig. 1b. (MOV 477 kb)

RBD-GFP and PH-RFP.

Time-lapse TIRF video of a Dictyostelium cell expressing RBD-GFP and PH-RFP with a rate of 3 spf. The video is shown at 15 frames/s and corresponds to Supplementary Fig. 2a. (MOV 90 kb)

PH-GFP in latrunculin-treated cell.

Time-lapse TIRF video of latrunculin-treated Dictyostelium cells expressing PH-GFP with a rate of 5 spf. The video is shown at 15 frames/s and corresponds to Supplementary Fig. 2d. (MOV 135 kb)

PH-GFP in latrunculin-treated cell.

Time-lapse TIRF video of latrunculin-treated Dictyostelium cells expressing PH-GFP with a rate of 5 spf. The video is shown at 15 frames/s and corresponds to Supplementary Fig. 2e. (MOV 87 kb)

PH-GFP in latrunculin-treated cell.

Time-lapse TIRF video of latrunculin-treated Dictyostelium cells expressing PH-GFP with a rate of 10 spf. The video is shown at 15 frames/s and corresponds to Supplementary Fig. 2f. (MOV 73 kb)

PH-GFP in latrunculin-treated cell.

Time-lapse TIRF video of a latrunculin-treated Dictyostelium cell expressing PH-GFP with a rate of 10 spf. The video is shown at 15 frames/s and corresponds to Supplementary Fig. 2g. (MOV 69 kb)

PH-GFP in latrunculin-treated cell.

Time-lapse TIRF video of latrunculin-treated Dictyostelium cells expressing PH-GFP with a rate of 10 spf. The video is shown at 15 frames/s and corresponds to Supplementary Fig. 2h. (MOV 56 kb)

RBD-GFP and LimE-RFP in undulations and protrusions.

Time-lapse TIRF video of a Dictyostelium cell co-expressing RBD-GFP and LimE-RFP with a rate of 2 spf. Cytoplasmic fluorescence of RBD-GFP and LimE-RFP was subtracted to highlight areas of increased intensity. Cell boundary (in gray) was derived from the cytoplasmic fluorescence of RBD-GFP. The video is shown at 7 frames/s and corresponds to Fig. 4b. (MOV 259 kb)

HSPC300-GFP in protrusion.

Time-lapse TIRF video of a Dictyostelium cell expressing HSPC300-GFP with a rate of 1 spf. The video is shown at 15 frames/s and corresponds to Supplementary Fig. 4d–f. (MOV 368 kb)

Computer simulation of the STEN-CON coupling model.

Level set simulation of cell movement along with the activities of the slow (Ys, in green) and fast (Yf, in red) systems as well as the merged activities. Cell membrane is driven by the signal of Yf (see Extended Experimental Procedures for simulation details). The video is shown at 20 frames/s. (MOV 1891 kb)

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Huang, CH., Tang, M., Shi, C. et al. An excitable signal integrator couples to an idling cytoskeletal oscillator to drive cell migration. Nat Cell Biol 15, 1307–1316 (2013). https://doi.org/10.1038/ncb2859

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