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Notch1-Dll4 signalling and mechanical force regulate leader cell formation during collective cell migration.

Riahi R, Sun J, Wang S, Long M, Zhang DD, Wong PK - Nat Commun (2015)

Bottom Line: However, the factors driving the leader cell formation as well as the mechanisms regulating leader cell density during the migration process remain to be determined.Furthermore, mechanical stress inhibits Dll4 expression and leader cell formation in the monolayer.Collectively, our findings suggest that a reduction of mechanical force near the boundary promotes Notch1-Dll4 signalling to dynamically regulate the density of leader cells during collective cell migration.

View Article: PubMed Central - PubMed

Affiliation: Department of Aerospace and Mechanical Engineering, The University of Arizona, Tucson, Arizona 85721-0119, USA.

ABSTRACT
At the onset of collective cell migration, a subset of cells within an initially homogenous population acquires a distinct 'leader' phenotype with characteristic morphology and motility. However, the factors driving the leader cell formation as well as the mechanisms regulating leader cell density during the migration process remain to be determined. Here we use single-cell gene expression analysis and computational modelling to show that the leader cell identity is dynamically regulated by Dll4 signalling through both Notch1 and cellular stress in a migrating epithelium. Time-lapse microscopy reveals that Dll4 is induced in leader cells after the creation of the cell-free region and leader cells are regulated via Notch1-Dll4 lateral inhibition. Furthermore, mechanical stress inhibits Dll4 expression and leader cell formation in the monolayer. Collectively, our findings suggest that a reduction of mechanical force near the boundary promotes Notch1-Dll4 signalling to dynamically regulate the density of leader cells during collective cell migration.

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Migration speed correlates with leader cell density(a-b) Bright-field images illustrating the leading edges with Y-27632, DAPT, Jagged-1, and control. Yellow lines indicate the leading edges. Data are expressed as mean ± s.e.m. (n=3, * P < 0.05, *** P < 0.001; unpaired Student's t-test). (c-d) Displacement and collective migration speed of cells at different leader cell densities under the treatment of DAPT and Jagged-1. Data are expressed as mean ± s.e.m. (n=3). Scale bar, 100 μm.
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Figure 7: Migration speed correlates with leader cell density(a-b) Bright-field images illustrating the leading edges with Y-27632, DAPT, Jagged-1, and control. Yellow lines indicate the leading edges. Data are expressed as mean ± s.e.m. (n=3, * P < 0.05, *** P < 0.001; unpaired Student's t-test). (c-d) Displacement and collective migration speed of cells at different leader cell densities under the treatment of DAPT and Jagged-1. Data are expressed as mean ± s.e.m. (n=3). Scale bar, 100 μm.

Mentions: To shed light on the function of leader cells, the migration speed of the leading edge was analyzed after the disruption of the leader cells (Fig. 6c). Remarkably, the speed of the leading edge was reduced dramatically after cell ablation. Nevertheless, the speed gradually increased and reached the control level after 10-12 hours. Notably, the time required to regain the initial speed correlated with the time scale of Dll4 expression. In addition, the existence of ablated leader cells could reduce the speed of the leading edge. We therefore performed control experiments to selectively ablate non-leader (random) cells at the boundary (Fig. 6c). The migration speed of cells with random cell disruption was significantly higher than those with leader cell disruption in the first 6 hours. After the formation of new leader cells, the migrating speeds were similar between random and leader cell disruption. To further study the relationship between leader cell density and the migration speed, we applied DAPT and Jagged-1 to modulate the number of leader cells at the leading edge (Fig. 7a-b). We measured the migration speed of cells treated with DAPT or Jagged-1 (Fig. 7c-d). Results showed that the migration speed correlated with the density of the leader cells. In particular, DAPT treatment increased the leader cell density and the migration speed. The leader cell density and the migration speed both decreased in Jagged-1 treated cells.


Notch1-Dll4 signalling and mechanical force regulate leader cell formation during collective cell migration.

Riahi R, Sun J, Wang S, Long M, Zhang DD, Wong PK - Nat Commun (2015)

Migration speed correlates with leader cell density(a-b) Bright-field images illustrating the leading edges with Y-27632, DAPT, Jagged-1, and control. Yellow lines indicate the leading edges. Data are expressed as mean ± s.e.m. (n=3, * P < 0.05, *** P < 0.001; unpaired Student's t-test). (c-d) Displacement and collective migration speed of cells at different leader cell densities under the treatment of DAPT and Jagged-1. Data are expressed as mean ± s.e.m. (n=3). Scale bar, 100 μm.
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Figure 7: Migration speed correlates with leader cell density(a-b) Bright-field images illustrating the leading edges with Y-27632, DAPT, Jagged-1, and control. Yellow lines indicate the leading edges. Data are expressed as mean ± s.e.m. (n=3, * P < 0.05, *** P < 0.001; unpaired Student's t-test). (c-d) Displacement and collective migration speed of cells at different leader cell densities under the treatment of DAPT and Jagged-1. Data are expressed as mean ± s.e.m. (n=3). Scale bar, 100 μm.
Mentions: To shed light on the function of leader cells, the migration speed of the leading edge was analyzed after the disruption of the leader cells (Fig. 6c). Remarkably, the speed of the leading edge was reduced dramatically after cell ablation. Nevertheless, the speed gradually increased and reached the control level after 10-12 hours. Notably, the time required to regain the initial speed correlated with the time scale of Dll4 expression. In addition, the existence of ablated leader cells could reduce the speed of the leading edge. We therefore performed control experiments to selectively ablate non-leader (random) cells at the boundary (Fig. 6c). The migration speed of cells with random cell disruption was significantly higher than those with leader cell disruption in the first 6 hours. After the formation of new leader cells, the migrating speeds were similar between random and leader cell disruption. To further study the relationship between leader cell density and the migration speed, we applied DAPT and Jagged-1 to modulate the number of leader cells at the leading edge (Fig. 7a-b). We measured the migration speed of cells treated with DAPT or Jagged-1 (Fig. 7c-d). Results showed that the migration speed correlated with the density of the leader cells. In particular, DAPT treatment increased the leader cell density and the migration speed. The leader cell density and the migration speed both decreased in Jagged-1 treated cells.

Bottom Line: However, the factors driving the leader cell formation as well as the mechanisms regulating leader cell density during the migration process remain to be determined.Furthermore, mechanical stress inhibits Dll4 expression and leader cell formation in the monolayer.Collectively, our findings suggest that a reduction of mechanical force near the boundary promotes Notch1-Dll4 signalling to dynamically regulate the density of leader cells during collective cell migration.

View Article: PubMed Central - PubMed

Affiliation: Department of Aerospace and Mechanical Engineering, The University of Arizona, Tucson, Arizona 85721-0119, USA.

ABSTRACT
At the onset of collective cell migration, a subset of cells within an initially homogenous population acquires a distinct 'leader' phenotype with characteristic morphology and motility. However, the factors driving the leader cell formation as well as the mechanisms regulating leader cell density during the migration process remain to be determined. Here we use single-cell gene expression analysis and computational modelling to show that the leader cell identity is dynamically regulated by Dll4 signalling through both Notch1 and cellular stress in a migrating epithelium. Time-lapse microscopy reveals that Dll4 is induced in leader cells after the creation of the cell-free region and leader cells are regulated via Notch1-Dll4 lateral inhibition. Furthermore, mechanical stress inhibits Dll4 expression and leader cell formation in the monolayer. Collectively, our findings suggest that a reduction of mechanical force near the boundary promotes Notch1-Dll4 signalling to dynamically regulate the density of leader cells during collective cell migration.

Show MeSH