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. 2019 Jul 22;50(2):197–211.e5. doi: 10.1016/j.devcel.2019.05.027

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© 2019 The Author(s)

This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

PMC Copyright notice

Forces Generated by the Apoptotic Myosin Cable Are Transmitted to the Apical Surface and the Nucleus

(A–D) Laser ablation of apico-basal myosin cable (A and B) and control lateral cut in nonapoptotic cells (C and D). In kymographs, red and green double arrows indicate the distance between two dots before and after cut respectively. Cuts were performed at the level of the apico-basal myosin cable (A) or at control lateral site (C). The timing of laser cut is indicated by the purple line.

(B and D) Stills extracted from movies showing sagittal views of the epithelium before (red) and after (green) laser cut at the level of the apico-basal myosin cable (B) or at a control lateral site (D). The myosin cable and the localization of the cut are shown by red and purple brackets respectively. Apico-basal recoil is observed in 13 out of 14 cases following cable cut (B) and 3 out of 17 following control lateral cut (D).

(E) Curves of the average apico-basal recoil +/− SEM over time (cable cut n = 14; control cut n = 17).

(F) Box plot representation of the apical surface release following apico-basal ablation in the indicated contexts. It corresponds to the variation in the angle made by the apical surface 25 s after ablation, compared to 1 s prior ablation (cable cut n = 15; control cut n = 17). Wilcoxon test: p value < 0.0002 (^∗∗∗).

(G and H) Stills extracted from a movie showing apoptotic nucleus behavior upon laser ablation of apico-basal myosin cable. (G) The DBS-S apoptosensor (cyan on the left panel) labels the nucleus in dying cells (arrow) and is enriched in the apical membrane in nonapoptotic cells. Myosin is shown in red and the apico-basal cable is highlighted by the white bracket. (H) Merge of DBS-S signal before (red) and after (green) myosin cable cut and associated schematization. Site of ablation is indicated by purple brackets. Individual images are shown in black and white on the left. The apoptotic nucleus moves basally after ablation in 9 cases out of 16, leading to an average basal displacement of 0.6 +/− 0.14 μm.

(I) Stills extracted from a movie showing nuclear envelope dynamics (red) of a dying cell (green) before (left) and during (right) the apoptotic nucleus upward movement associated with the force-generation stage. A close-up view of the apoptotic nuclear envelope is shown in black and schematized. Note that the apoptotic nucleus is apically deformed during the force-generation stage (arrowheads, n = 12/12). Asterisks identify the center of the nucleus, highlighting the upward nuclear movement (black arrow).

(J) Normalized index of nuclear envelope apical deformation before and during the force-generation stage represented as box plots (see STAR Methods; apoptotic nuclei, n = 12; nonapoptotic nuclei, n = 35). AU: arbitrary unit. Wilcoxon statistical test was used for the comparison of nuclei before and during force transmission; apoptotic nuclei (p value < 0.0005 for ^∗∗∗) and nonapoptotic nuclei (n.s., nonsignificant). Mann Whitney was used for comparison of apoptotic nuclei versus nonapoptotic nuclei before force transmission (n.s.).