Figure 1.
Morphological changes in mitosis coincide with an increase in local tensile forces.(A) Temporal color-coded overlay of an MDCK cell monolayer expressing GFP–α-catenin, with mitotic entry of a cell indicated by an asterisk (Video 1). (B) Quantification of cell perimeter of MDCK cells in interphase and following entry into mitosis. Quantified data were pooled from three independent experiments (n = 55). Gray bars show the mean cell perimeter with SD. ****, P < 0.0001; Wilcoxon matched-pairs signed-rank test. (C) Analysis of cellular (tensile) strain in an MDCK monolayer (A) as cells enter mitosis and undergo mitotic rounding over a period of 20 min. Cellular (tensile) strain is defined as the maximum relative increase in distance between two opposing cell edges (Δ length/initial length). The mitotic cell, which only undergoes compressive strain, is shown in black. The directionality of the maximum (tensile) strain is indicated by white arrows. (D) Analysis of the relative changes in junction length (Δ length/initial length) in an MDCK monolayer (A) as cells enter mitosis and undergo mitotic rounding over a period of 20 min. (E) Quantification of relative junction length (Δ junction length/initial junction length) in epithelial layers during progression from interphase to completion of mitotic rounding. Each dot represents the average change of length of all junctions neighboring either a mitotic cell (blue) or an interphase cell during the same time interval (dark blue; n = 29). Gray bars show the mean levels of change in length with SD. ****, P < 0.0001; Mann–Whitney. (F) Schematic illustration (left) of recoil analyses following nanoscissor laser ablation of the actin cortex at cell–cell contacts neighboring either interphase (dark blue) or mitotic (blue) cells. The representative example (right, Video 2) shows recoil of the cell–cell contact neighboring a mitotic cell (inset) over time. Note that nanoscissor ablation of the mitotic cell–cell junctions itself was not feasible, as mitotic cells immediately collapse following ablation (Fig. S1 C), which is likely explained by high osmotic pressure in mitotic cells (Stewart et al., 2011). (G) Quantification of the recoil of cell–cell contacts neighboring interphase (dark blue; n = 24) or mitotic (blue; n = 22) cells following laser ablation, defined as the absolute increase in distance between the two vertices of the ablated cell–cell contact (indicated by arrowheads in F). Dots represent the mean amount of recoil with SD, with lines showing the best-fit single exponential curve. Data were pooled from two independent experiments. Note that the differences in recoil between junctions neighboring mitotic and interphase cells were comparable when determined by the relative increase in distance between vertices (Fig. S1 B), indicating that changes in recoil in cell–cell contacts neighboring mitotic cells are not caused by differences in junctional length (E). (H) Initial recoil velocities for laser cuts of cell–cell contacts neighboring mitotic (n = 22) or interphase cells (n = 24). Bars show the average initial recoil velocities with SD. Data were pooled from two independent experiments. ****, P < 0.0001; unpaired t test. All scale bars, 10 µm or 2 µm (inset, F). E-cad, E-cadherin.

Morphological changes in mitosis coincide with an increase in local tensile forces. (A) Temporal color-coded overlay of an MDCK cell monolayer expressing GFP–α-catenin, with mitotic entry of a cell indicated by an asterisk (Video 1). (B) Quantification of cell perimeter of MDCK cells in interphase and following entry into mitosis. Quantified data were pooled from three independent experiments (n = 55). Gray bars show the mean cell perimeter with SD. ****, P < 0.0001; Wilcoxon matched-pairs signed-rank test. (C) Analysis of cellular (tensile) strain in an MDCK monolayer (A) as cells enter mitosis and undergo mitotic rounding over a period of 20 min. Cellular (tensile) strain is defined as the maximum relative increase in distance between two opposing cell edges (Δ length/initial length). The mitotic cell, which only undergoes compressive strain, is shown in black. The directionality of the maximum (tensile) strain is indicated by white arrows. (D) Analysis of the relative changes in junction length (Δ length/initial length) in an MDCK monolayer (A) as cells enter mitosis and undergo mitotic rounding over a period of 20 min. (E) Quantification of relative junction length (Δ junction length/initial junction length) in epithelial layers during progression from interphase to completion of mitotic rounding. Each dot represents the average change of length of all junctions neighboring either a mitotic cell (blue) or an interphase cell during the same time interval (dark blue; n = 29). Gray bars show the mean levels of change in length with SD. ****, P < 0.0001; Mann–Whitney. (F) Schematic illustration (left) of recoil analyses following nanoscissor laser ablation of the actin cortex at cell–cell contacts neighboring either interphase (dark blue) or mitotic (blue) cells. The representative example (right, Video 2) shows recoil of the cell–cell contact neighboring a mitotic cell (inset) over time. Note that nanoscissor ablation of the mitotic cell–cell junctions itself was not feasible, as mitotic cells immediately collapse following ablation (Fig. S1 C), which is likely explained by high osmotic pressure in mitotic cells (Stewart et al., 2011). (G) Quantification of the recoil of cell–cell contacts neighboring interphase (dark blue; n = 24) or mitotic (blue; n = 22) cells following laser ablation, defined as the absolute increase in distance between the two vertices of the ablated cell–cell contact (indicated by arrowheads in F). Dots represent the mean amount of recoil with SD, with lines showing the best-fit single exponential curve. Data were pooled from two independent experiments. Note that the differences in recoil between junctions neighboring mitotic and interphase cells were comparable when determined by the relative increase in distance between vertices (Fig. S1 B), indicating that changes in recoil in cell–cell contacts neighboring mitotic cells are not caused by differences in junctional length (E). (H) Initial recoil velocities for laser cuts of cell–cell contacts neighboring mitotic (n = 22) or interphase cells (n = 24). Bars show the average initial recoil velocities with SD. Data were pooled from two independent experiments. ****, P < 0.0001; unpaired t test. All scale bars, 10 µm or 2 µm (inset, F). E-cad, E-cadherin.

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